100:2348-2360, 2008. First published Jul 16, 2008;  doi:10.1152/jn.90396.2008 J Neurophysioland L. S. Krimer N. V. Povysheva, A. V. Zaitsev, D. C. Rotaru, G. Gonzalez-Burgos, D. A. Lewis

You might find this additional information useful...

76 articles, 36 of which you can access free at: This article cites http://jn.physiology.org/cgi/content/full/100/4/2348#BIBL

including high-resolution figures, can be found at: Updated information and services http://jn.physiology.org/cgi/content/full/100/4/2348

can be found at: Journal of Neurophysiologyabout Additional material and information http://www.the-aps.org/publications/jn

This information is current as of October 15, 2008 .  

http://www.the-aps.org/.American Physiological Society. ISSN: 0022-3077, ESSN: 1522-1598. Visit our website at (monthly) by the American Physiological Society, 9650 Rockville Pike, Bethesda MD 20814-3991. Copyright © 2005 by the

publishes original articles on the function of the nervous system. It is published 12 times a yearJournal of Neurophysiology

on October 15, 2008

jn.physiology.orgD

ownloaded from

Parvalbumin-Positive Basket Interneurons in Monkey and RatPrefrontal Cortex

N. V. Povysheva,1 A. V. Zaitsev,1 D. C. Rotaru,1 G. Gonzalez-Burgos,1 D. A. Lewis,1,2 and L. S. Krimer1

Departments of 1Psychiatry and 2Neuroscience, University of Pittsburgh, Pittsburgh, Pennsylvania

Submitted 24 March 2008; accepted in final form 14 July 2008

Povysheva NV, Zaitsev AV, Rotaru DC, Gonzalez-Burgos G,Lewis DA, Krimer LS. Parvalbumin-positive basket interneurons inmonkey and rat prefrontal cortex. J Neurophysiol 100: 2348–2360,2008. First published July 16, 2008; doi:10.1152/jn.90396.2008. Dif-ferences in the developmental origin and relative proportions ofbiochemically distinct classes of cortical neurons have been foundbetween rodents and primates. In addition, species differences in theproperties of certain cell types, such as neurogliaform cells, have alsobeen reported. Consequently, in this study we compared the anatom-ical and physiological properties of parvalbumin (PV)-positive basketinterneurons in the prefrontal cortex of macaque monkeys and rats.The somal size, total dendritic length, and horizontal and verticalspans of the axonal arbor were similar in monkeys and rats. Physio-logically, PV basket cells could be identified as fast-spiking interneu-rons in both species, based on their short spike and high-frequencyfiring without adaptation. However, important interspecies differencesin the intrinsic physiological properties were found. In monkeys,basket cells had a higher input resistance and a lower firing threshold,and they generated more spikes at near-threshold current intensitiesthan those in rats. Thus monkey basket cells appeared to be moreexcitable. In addition, rat basket cells consistently fired the first spikewith a substantial delay and generated spike trains interrupted byquiescent periods more often than monkey basket cells. The frequencyof miniature excitatory postsynaptic potentials in basket cells wasconsiderably higher in rats than that in monkeys. These differencesbetween rats and monkeys in the electrophysiological properties ofPV-positive basket cells may contribute to the differential patterns ofneuronal activation observed in rats and monkeys performing work-ing-memory tasks.

I N T R O D U C T I O N

The existence of a microcircuit template that is conservedacross different species and different neocortical regions hasbeen widely discussed (Douglas and Martin 2004; Nelson et al.2006; Silberberg et al. 2002). The idea of a canonical corticalcircuit, however, has been challenged by recent evidence ofinterspecies differences in the inhibitory component of neocor-tical circuitry. For example, interneurons constitute a consid-erably larger proportion of cortical neurons in primates (25–34%) than that in rodents (15–25%) (Beaulieu 1993; DeFelipeet al. 2002; Gabbott and Bacon 1996; Gabbot et al. 1997;Gonchar and Burkhalter 1997; Meinecke and Peters 1987). Inaddition, the proportions of chemically defined subpopulationsof neocortical interneurons might differ between rodents andprimates. Thus cells immunoreactive for the Ca-binding pro-tein parvalbumin (PV) seem to predominate in rodent neocor-tex, but constitute a much smaller proportion of interneurons in

primates (Conde et al. 1994; Desgent et al. 2005; Gabbott andBacon 1996; Gabbott et al. 1997; Glezer et al. 1998; Goncharand Burkhalter 1997; Kubota et al. 1994), although whetherthese differences represent species differences in specific sub-types of interneurons or differences only in relative levels ofCa-binding protein expression must yet be determined. Fur-thermore, the frequency of colocalization of neurochemicalmarkers in the same cell is lower in monkeys than that inrodents (Conde et al. 1994; Kawaguchi and Kubota 1997; Xuet al. 2006; Zaitsev et al. 2005), although a relatively smalloverlap of neurochemical markers was reported in rat visualcortex (Gonchar and Burkhalter 1997). Moreover, interneuronsin primates and rodents might differ in their anatomical site oforigin. In rodents, most neocortical �-aminobutyric acid (GABA)cells originate in the subcortical ganglionic eminence of thetelencephalon (Butt et al. 2005; Xu et al. 2004), whereas inhumans, as well as in nonhuman primates, GABAergic neuro-nal progenitors were found not only in the ganglionic emi-nence, but also in the cortical subventricular zone (Letinic et al.2002; Petanjek et al. 2008). Electrophysiological differencesbetween interneurons of monkey and rat prefrontal cortex(PFC) were first suggested (Krimer et al. 2005) and thenexplicitly shown for neurogliaform (NGF) cells (Povyshevaet al. 2007). NGF cells in monkey PFC appear to be moreexcitable than those in rat PFC because they have higher inputresistance (Rin), lower firing threshold, and higher firing fre-quency. Monkey NGF cells fired without a pronounced delayat threshold and thus do not seem to have the “late spiking”phenotype described for rat NGF cells (Kawaguchi 1995).

PV-positive cells in both monkey and rat PFC have beenidentified morphologically as basket or chandelier cells (Condeet al. 1994; Gabbot et al. 1997). These interneurons innervatethe soma and proximal dendrites or the axon initial segment ofpyramidal cells, respectively (Somogyi et al. 1998). Physio-logically, in both species PV-positive cells are characterized bybrief action potentials (APs) and lack of spike adaptation,characteristic features of the “fast-spiking (FS) phenotype”and, vice versa, cells identified as fast-spiking usually expressPV (Kawaguchi and Kubota 1997; Toledo-Rodriguez et al.2004; Zaitsev et al. 2005).

In single-unit recordings in vivo in the PFC, FS units play animportant role in working-memory (WM) function in monkeysince they are spatially tuned during visual WM tasks (Rao1999). In addition, they contribute to sharpening the tuning ofpyramidal cells during WM in modeling studies (Tanaka 1999;Wang et al. 2004) and GABAA-receptor blockade in the PFC

Address for reprint requests and other correspondence: N. V. Povysheva,University of Pittsburgh School of Arts and Sciences, Department of Neuro-science, Langley A210, Pittsburgh, PA 15260 (E-mail: nvp1@pitt.edu).

The costs of publication of this article were defrayed in part by the paymentof page charges. The article must therefore be hereby marked “advertisement”in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

J Neurophysiol 100: 2348–2360, 2008.First published July 16, 2008; doi:10.1152/jn.90396.2008.

2348 0022-3077/08 $8.00 Copyright © 2008 The American Physiological Society www.jn.org

on October 15, 2008

jn.physiology.orgD

ownloaded from

produces an expansion of the receptive fields of FS units (Raoet al. 2000). Importantly, the firing frequency of FS units,putative FS interneurons, in monkey PFC during the delayperiod of oculomotor delayed response task is 40–60 Hz(Wilson et al. 1994), which is considerably higher than that inprefrontal FS units of rats performing a figure-eight mazedelayed spatial alternation task (�12 Hz; Jung et al. 1998). Thedifferences in the spiking behavior of putative FS interneuronsbetween monkey and rat PFC might be related to the differ-ences in their intrinsic membrane properties.

Our recent physiological studies of interneurons in monkeyand rat PFC (Krimer et al. 2005; Povysheva et al. 2006)suggested that PV-positive basket cells in primates might differfrom those in rats. However, a definitive interspecies compar-ison was not possible in those studies because of significantdifferences in the developmental stages of rats (prepubertal)and monkeys (young adults) that were studied. Here, wedirectly compared morphological and physiological propertiesof PV-positive basket cells in adult monkey and adult rat PFC.We report that monkey basket cells are more excitable and alsofire a first spike with less delay than that in rat basket cells. Inmonkeys, these cells have fewer quiescent periods at near-suprathreshold current intensities and, accordingly, generatemore spikes at a near-threshold current level. Finally, thefrequency of miniature excitatory postsynaptic potentials(mEPSPs) is considerably higher in rat than that in monkeybasket cells and positively correlates with the rheobase current,indicating a possible important association between membraneand synaptic properties in basket cells. These differences insubthreshold and suprathreshold membrane properties of PV-positive basket cells in rats and monkeys could serve as a basisfor the different patterns of activation of FS units reportedpreviously in animals performing WM tasks (Constantinidisand Goldman-Rakic 2002; Jung et al. 1998; Wilson et al.1984).

M E T H O D S

Brain slices were obtained from adult (56–135 days, 350–550 g;n � 20) male Wistar rats and adult (3.5–6.0 kg; 4–5 yr old; n � 15)male long-tailed macaque monkeys (Macaca fascicularis). Slicesfrom the same monkeys were also used in the other studies (Krimeret al. 2005; Povysheva et al. 2006; Zaitsev et al. 2005). All animalswere treated in accordance with the guidelines outlined in the NationalInstitutes of Health Guide for the Care and Use of LaboratoryAnimals and approved by the University of Pittsburgh InstitutionalAnimal Care and Use Committee. Rats were deeply anesthetized withhalothane and decapitated. The brain was quickly removed andimmersed in ice-cold preoxygenated artificial cerebrospinal fluid(ACSF). Tissue block containing the prelimbic cortex in rats (Paxinosand Watson 1998) was excised for slicing. The protocol used to obtaintissue blocks from monkey PFC was previously described (Gonzalez-Burgos et al. 2000). Coronal slices (350 �m thick) were cut with avibratome (Model VT1000S, Leica, Nussloch, Germany). Slices wereincubated at 37°C for 0.5–1 h and further stored at room temperatureuntil transfer to a recording chamber perfused with ACSF at 31–32°C.The recording temperatures were identical for both species. Throughall steps of the experiments, ACSF of the following composition wasused (in mM): 126 NaCl, 2.5 KCl, 1.25 NaH2PO4, 1 MgSO4, 2 CaCl2,24 NaHCO3, and 10–20 dextrose. ACSF was perfused with 95%O2-5% CO2 gas mixture.

Electrophysiological recordings

Whole cell voltage recordings were made from layer 2/3 neuronsvisualized by infrared differential interference contrast videomicros-copy using a Zeiss Axioskop 2 FS microscope, equipped with a �40water-immersion objective and a Dage-MTI NC-70 video camera(Dage-MTI Television, Michigan City, IN). Interneurons were iden-tified based on their round or oval cell body and lack of apicaldendrite. Pyramidal cells were recognized by their apical dendritesand triangular somata. Patch electrodes were filled with an internalsolution containing (in mM): 114 K-gluconate, 6 KCl, 10 HEPES, 4ATP-Mg, and 0.3 GTP; pH was adjusted to 7.25 with KOH. Biocytin(0.5%; Molecular Probes, Eugene, OR) was added to the solution forlater morphological identification of the recorded neurons. Electrodeshad 5- to 12-M� open-tip resistance. Voltages were amplified with anIE-210 electrometer (Warner Instruments, Hamden, CT) or a Multi-Clamp 700A amplifier (Axon Instruments, Union City, CA) operatingin bridge-balance mode. Signals were filtered at 5 or 4 kHz in theIE-210 and the MultiClamp, respectively, and acquired at a samplingrate of 20 kHz using a 16-bit-resolution Power 1401 interface andSignal software (CED, Cambridge, UK). Access resistance and ca-pacitance were compensated on-line. Access resistance typically was15–30 M� and remained relatively stable during experiments (�30%increase) for the cells included in the analysis. Membrane potentialwas not corrected for the liquid junction potential. During some of theexperiments, gabazine (4.5–6 �M; Sigma, St. Louis, MO) was addedto the bath to block GABAA receptors. D-2-Amino-5-phospho-pen-tanoic acid (APV, 50 �M; Sigma) and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 20 �M; Sigma) were included in the bath to blockN-methyl-D-aspartate (NMDA) and �-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, respectively. �-Dendro-toxin (�-DTX, 150–200 nM; Alomone Labs, Jerusalem, Israel) wasused to block Kv1 channels and 4-(N-ethyl-N-phenylamino-1,2-di-methyl-6-methylamino)pyrimidinium chloride (ZD7288, 20 �M;Alomone Labs) was used to block Ih channels.

Miniature EPSPs were recorded at a membrane potential of about �75mV in both rat and monkey PFC neurons. Tetrodotoxin (TTX, 0.5–1�M; Alomone Labs) and bicuculline methiodide (BMI, 10–20 �M;Sigma) were added to the bath to block APs and GABAA-mediatedinhibitory postsynaptic potentials, respectively.

Electrophysiological data analysis

To characterize the membrane properties of neurons, hyper- anddepolarizing current steps were applied for 500 ms in 5- to 10-pAincrements at 0.5 Hz. Input resistance (Rin) was measured from theslope of a linear regression fit to the voltage–current relation in ahyperpolarizing range. The membrane time constant was determinedby single-exponential fitting to the on-phase of the average voltageresponses to the initial (5–15 pA) hyperpolarizing current steps, whichpresumably are less affected by voltage-dependent membrane con-ductances. All AP measures were taken from the first AP of the firstevoked sweep that reached the spike threshold (level of voltagedeflection exceeding 10 mV/1 ms). Peak amplitude of the AP wasmeasured from the AP threshold. The spike rise time was measured asthe time taken to rise from 10 to 90% of the peak amplitude. The spikedecay time was measured as the time taken to decay from 10 to 90%of the amplitude between peak and spike threshold. Duration of theAP was measured at its half-amplitude. Depolarizing sag was esti-mated as the difference between the most negative membrane poten-tial during a 500-ms hyperpolarizing current step and the membranepotential at the end of the step as the percentage relative to the voltagedeflection from the resting membrane potential (RMP) at the end ofthe step. Hump was estimated at the depolarizing current step thatpreceded spiking as the difference between the most positive mem-brane potential and the membrane potential at the end of the step asthe percentage relative to the voltage deflection from the RMP at the

2349PV BASKET CELLS IN MONKEY AND RAT PFC

J Neurophysiol • VOL 100 • OCTOBER 2008 • www.jn.org

on October 15, 2008

jn.physiology.orgD

ownloaded from

end of the step. Adaptation ratio (AR) coefficient was used to describespike frequency adaptation in spike trains. First, the ratio between thefirst and the last interspike interval (ISI) was calculated for eachstimulation current intensity. Then, the AR coefficient was estimatedfrom the linear regression of AR versus current at 60 pA abovethreshold. The coefficient of variation (CV) of ISIs was measuredwithin the last 350 ms of the response to depolarizing current pulsesat the level of 20 pA above spike threshold.

Basket cells were identified as FS based on the results of thepreviously performed cluster analysis, ANOVA, and Fisher leastsignificant difference post hoc test (Krimer et al. 2005). The param-eters with the most discriminative values, action potential duration(APD; average value 0.37 � 0.09), and AR (average value 0.82 �0.21) were used as criteria for FS interneurons: APD � 1.5SDs as thehigh limit and AR coefficient �SD as the low limit. Accordingly, onlybasket cells with the spike half-duration �0.51 ms and AR coefficient0.61 were included in the analysis. The aforementioned criteriacorrespond to those previously used in the neocortex of young rats(Kawaguchi 1995) and adult rats (Thomson et al. 1996).

Miniature events were analyzed using MiniAnalysis (Synaptosoft,Decatur, GA). Peak events were first detected automatically using anamplitude threshold of twofold the average root mean square noise,which was about 0.3 mV for mEPSPs. After automatic analysis,events were rechecked by visual inspection of the traces and wereaccepted for analysis if they had a monophasic rising phase anddecayed to baseline in an exponential manner. Approximately 100–300 events in each cell were included in the analysis. Amplitudes ofminiature responses were determined from baseline to peak. The timeconstants of single-exponential fits were used to describe the decaytime. The rise time was estimated as the time necessary to risebetween 10 and 90% of the peak response.

Morphological data analysis

To identify cell morphology after the electrophysiological experi-ments, neurons were filled with biocytin (0.5%) added to the internalsolution. After recordings, slices were immersed in 4% paraformal-dehyde in 0.1 M phosphate-buffered saline (PBS) and then were keptin storing solution (33% glycerol, 33% ethylene glycol, in 0.1 M PBS)at �80°C. PV immunoreactivity (and calretinin and/or calbindin insome cells) in a sample of FS interneurons from monkey (n � 21) andrat (n � 14) PFC was detected by an indirect immunofluorescencetechnique as previously described (Zaitsev et al. 2005). Briefly, sliceswere incubated for 24–48 h at 4°C in blocking serum (10% normalgoat serum; 2% bovine serum albumin; 0.4% Triton X-100 in phos-phate buffer [PB]) containing streptavidin-Alexa Fluor 633 conjugate(dilution 1:500; Invitrogen). After this, cells were confocally recon-structed for morphological identification. Next, slices were seriallyresectioned at 40–50 �m and then incubated in a mixture of antibod-ies against two of the three calcium-binding proteins: PV (1:2,000;Sigma or Swant, Bellinzona, Switzerland), calretinin (1:2,000; Swantor Chemicon, Temecula, CA), or calbindin (1:2,000; Swant) and,subsequently, in a mixture of the two secondary antibodies (AlexaFluor 594 conjugated goat anti-mouse IgG, 1:500 and Alexa Fluor 488conjugated goat anti-rabbit IgG, 1:500, Molecular Probes) diluted inthe blocking serum. This procedure yielded differential fluorescentcovisualization of Alexa Fluor 633-biocytin-filled interneurons andAlexa Fluor 488- and 594-labeled calcium-binding proteins. Rinsedsections were kept in a storing solution until they were analyzed usingan Olympus FluoviewTM 500 confocal laser scanning microscope(Olympus America, Melville, NY). After that, the sections weretreated with 1% H2O2 for 2–3 h at room temperature, rinsed, andincubated with the avidin-biotin-peroxidase complex (1:100; VectorLaboratories, Burlingame, CA) in PB for 4 h. Sections were rinsed,stained with Ni-3,3-diaminobenzidine (DAB), mounted on gelatin-coated glass slides, dehydrated, and coverslipped. Slices from someexperiments were processed for biocytin only.

Cells were morphologically identified as basket cells based on theconfocal reconstructions or/and development of biocytin. Some cellswere three-dimensionally reconstructed and their dendritic trees werequantitatively described using the Neurolucida neuron tracing systemwith NeuroExplorer software (MBF Bioscience, Williston, VT). Thehorizontal and vertical axonal spans were measured in the cellsdeveloped for biocytin as the mean distance between the three mostdistal axonal endings on each side of the soma of individual interneu-rons.

Statistical analysis

Two-tailed t-tests were used for group comparisons in most cases.Pearson correlation coefficient was used to measure the relationbetween mEPSP frequency and the rheobase current. Statistical sig-nificance of between-group differences for CV of ISIs and number ofspikes measured at different depolarizing current steps was evaluatedusing repeated-measures ANOVA and Fisher’s post hoc test.

Unless otherwise noted values are presented as means � SD.Statistical tests were performed using Excel (Microsoft, Redmond,WA) or Statistica 6.1 (Statsoft, Tulsa, OK).

Twenty of 39 basket cells and 23 of 27 pyramidal cells frommonkey dorsolateral PFC were reported in our previous publications(Krimer et al. 2005; Povysheva et al. 2006; Zaitsev et al. 2005).

R E S U L T S

Morphological properties of monkey and rat basket cells

Interneurons from monkey and rat PFC were classified as“basket” based on previously described morphological features(Jones and Hendry 1984; Kawaguchi 1995; Lund and Lewis1993). Because PV-positive basket cells are known to be FS inthe neocortex of different species, only neurons with basketcell morphology and FS electrophysiological properties (basedon short spike duration and firing without significant adapta-tion; see METHODS) were included in this study. Basket cellsomata had a round or slightly vertical oval shape and werelocated in layers 2/3. The cells possessed smooth and multi-polar dendrites (Fig. 1, A and C). The axon of the cellsoriginated from the cell body or one of the primary dendrites.Axons spread either in all directions or predominantly hori-zontally, rarely extending into layer I or layer V. Therefore thebasket cell axonal tree occupied a significant volume, but stillwas mainly located within layers 2/3, the same cortical layersas the soma.

Since basket cells are known to have a great range of theiraxonal horizontal dimension, and are often viewed as a mor-phologically heterogeneous group of cells (see e.g. Lund andLewis 1993), we evaluated the spatial distribution of theiraxonal trees in monkeys and rats. We found that the averageaxonal vertical and horizontal spans were comparable in bothspecies (Table 1). Distributions of horizontal span did notsignificantly differ between species (Kolmogorov–Smirnovtest, P 0.1; Fig. 1B), indicating that basket cells frommonkeys and rats were equally represented by smaller andlarger cells.

Additional quantitative analysis was performed on the cellswith fully reconstructed on the transmitted light microscope.Monkey basket cells had somata that were comparable withthose from rats (Table 1). The number of primary dendrites andthe total dendritic length did not differ between species (Table1, Fig. 1C). Dendrites of both monkey and rat basket cellsbranched up to the fifth-order and had very similar branching

2350 POVYSHEVA ET AL.

J Neurophysiol • VOL 100 • OCTOBER 2008 • www.jn.org

on October 15, 2008

jn.physiology.orgD

ownloaded from

Monkey

Rat

A C

B

Monkey

Rat

D

E

Biocytin PV Merge

F

400 600 800 1000 12000

5

10

15

20

25

% o

f cel

ls

Horizontal span, mm

Monkey Rat

0 50 100 150 200 250 3000

100

200

300

400

Den

driti

c le

ngth

(µm

)

Distance from soma (µm)

Monkey Rat

0.2 0.3 0.4 0.5 0.60.6

0.7

0.8

0.9

1.0

1.1

1.2

AR c

oeffi

cient

Spike duration, ms

Monkey Rat Monkey PV-positive Rat PV-positive

FIG. 1. Morphological and neurochemical features of monkey and rat basket cells. A: representative examples of monkey and rat basket cells (axons areindicated in red; dendrites are indicated in black; scale bar 100 �m). B: distributions of horizontal axonal span values are comparable in monkeys (n � 26) andrats (n � 19). C: morphological varieties of dendritic trees of basket cells (scale bar 100 �m). D: Sholl analysis of dendritic arbors from monkey (n � 10) andrat (n � 12) basket cells. Average dendritic length is plotted against the distance from the soma. Error bars represent SE. E: parvalbumin (PV)-immunoreactivityin rat basket cell. F: graphs of adaptation ratio (AR) coefficient against spike duration revealed that 2 populations of fast-spiking (FS) basket cells from monkeysand rats (those that were shown to be PV-positive and those that did not go through immunohistochemical analysis) totally overlap in the distributions.

2351PV BASKET CELLS IN MONKEY AND RAT PFC

J Neurophysiol • VOL 100 • OCTOBER 2008 • www.jn.org

on October 15, 2008

jn.physiology.orgD

ownloaded from

patterns. Sholl analysis did not reveal any significant differ-ences in dendritic distribution between monkey and rat basketcells (Fig. 1D). The only features that differed between specieswere axonal length and number of axonal nodes, both of whichwere greater in rat than in monkey basket cells (Table 1).

PV immunoreactivity was identified in a subset of FS basketinterneurons from monkey (14 of 21; 67%) and rat (11 of 14;78%) PFC (Fig. 1E). Reasons for the absence of PV-labeling insome cells could be 1) washout of low-weight molecules, suchas PV, from the cytosol during the whole cell recording(Baimbridge et al. 1992), or 2) a general reduction in immu-noreactivity in brain slices used in physiological experiments.None of the monkey cells (n � 9) that were also tested forcalretinin and/or calbindin was immunoreactive for these pro-teins.

Comparison of the membrane properties of FS basket inter-neurons containing PV and those that did not undergo immu-nohistochemistry revealed that the membrane properties ofPV-positive interneurons and the rest of the basket cells weresimilar in both species; the scatterplot of adaptation ratio (AR)coefficient versus spike duration (Fig. 1F) shows substantialoverlap of PV-positive and other basket cells with FS pheno-type. Based on these results, we pooled data from PV-positivebasket cells and all other FS basket cells.

Subthreshold membrane properties of basket cells in adultrat and monkey

Although the RMP of basket cells was comparable in bothspecies (Table 2), most of the other subthreshold membraneproperties appeared to be different. Input resistance was sig-nificantly larger in basket cells from monkey than from rat(Table 2, Fig. 2, A and B), indicating their greater excitability.Hyperpolarizing current steps of the same strength generatedlarger voltage responses in basket cells from monkey than fromrats. Accordingly, current–voltage (I–V) curves obtained fromthe subthreshold responses to hyperpolarizing and depolarizingcurrent pulses from monkey cells were much steeper than thosefrom rat (Fig. 2B). The time constant was also longer inmonkey basket cells (Table 2).

Spontaneous synaptic activity in vivo can directly affect acell’s input resistance (Steriade et al. 2001) and therefore could

potentially influence the observed differences between monkeyand rat PFC basket cells. To assess the direct effects ofspontaneous synaptic activity in our brain slice conditions, werecorded the responses to subthreshold hyperpolarizing currentpulses after blocking excitatory and inhibitory synaptic trans-mission with gabazine (4.5–6 �M), CNQX (20 �M), and APV(50 �M). Blockade of spontaneous synaptic activity did notresult in a significant change of input resistance in any of thespecies (rat: P � 0.79, n � 8; monkey: P � 0.75, n � 4, pairedcomparison) (Fig. 2C). We therefore conclude that the differ-ence in the input resistance observed between the two speciescan be attributed to the intrinsic membrane properties, but notto the shunting associated with the presence of synaptic con-ductances.

Although the I–V plot revealed time-independent inwardrectification in both monkey and rat basket cells (Fig. 2, A andB), the majority of monkey basket cells exhibited time-depen-dent changes of responses to the hyperpolarizing currentpulses. This characteristic depolarizing sag was estimated to be19 � 9% with a stimulation current of �50 pA (n � 32) inmonkey basket cells. The majority (69%) of monkey basketcells exhibited sag that was �15%. At the same level ofstimulation current, and also with the increase of the stimula-tion current up to �100 pA (Fig. 2D), we failed to observe anydepolarizing sag in rat basket cells. Depolarizing sag in mon-key basket cells was blocked by bath application of Ih channelblocker (Fig. 2E). When subthreshold depolarizing currentsteps were applied, monkey basket cells generated voltageresponses with an initial hump followed by a hyperpolarizingsag (Fig. 2A). We estimated the hump to be 29 � 10% (n � 31)on the subthreshold sweeps preceding generation of AP inmonkey basket cells. The hump was not observed in rat basketcells.

Firing properties of basket cells in adult monkey and rat

SINGLE SPIKE PROPERTIES. Single spikes of monkey and ratbasket cells were comparable in some parameters, includingspike amplitude and afterhyperpolarization (AHP) amplitude

TABLE 2. Intrinsic subthreshold and firing physiologicalproperties of basket cells in monkeys and rats

PropertyMonkey(n � 39)

Rat(n � 31)

Resting membrane potential, mV �68 � 8 �67 � 6Spike threshold, mV �41 � 5*** �34 � 3Spike threshold, pA 74 � 50*** 132 � 69Spike amplitude, mV 55 � 11 52 � 7Spike half-duration, ms 0.34 � 0.06* 0.38 � 0.08Spike 10–90% rise time, ms 0.15 � 0.03*** 0.21 � 0.04Spike 10–90% fall time, ms 0.23 � 0.06 0.25 � 0.03First spike latency, ms 71 � 69*** 220 � 159Afterhyperpolarization amplitude, mV 23 � 8 24 � 5Adaptation ratio coefficient 0.90 � 0.13 0.85 � 0.12Number of spikes (20 pA above

threshold) 16 � 5** 11 � 5CV of interspike intervals (20 pA

above threshold) 5.1 � 2.2*** 27 � 26Input resistance, M� 251 � 130* 182 � 83Time constant, ms 9.5 � 2.8* 7.7 � 3.8

Values are means � SD. Significantly different between the two species:*P � 0.05; **P � 0.01; ***P � 0.001.

TABLE 1. Morphometric analysis of basket cells from monkeysand rats

Parameter Measured Monkeys (n � 11) Rats (n � 14)

Soma area, �m2 92 � 25 94 � 19Number of primary

dendrites 6.8 � 2.1 6.1 � 1.8Total dendritic

length, �m 2,000 � 970 2,268 � 936Number of dendritic

nodes 12 � 5 14 � 5Axonal horizontal

span, �m 810 � 394 (n � 26) 750 � 531 (n � 19)Axonal vertical

span, �m 576 � 173 (n � 26) 553 � 92 (n � 19)Axonal length, �m 21,912 � 4,033 (n � 4) 34,655 � 5,190 (n � 3)Number of axonal

nodes 161 � 36 (n � 4) 359 � 83 (n � 3)

Values are means � SD.

2352 POVYSHEVA ET AL.

J Neurophysiol • VOL 100 • OCTOBER 2008 • www.jn.org

on October 15, 2008

jn.physiology.orgD

ownloaded from

(Table 2, Fig. 3A). However, interspecies differences in othersingle-spike parameters were observed. Monkey basket neu-rons had a shorter spike duration than that in rats. A differencebetween species was observed in spike rise time but not indecay time, indicating different activation properties or densityof Na� channels in the two species.

The majority of basket cells from rat PFC demonstrated thedelayed firing pattern with near-threshold current intensities(Table 2, Fig. 3A). This delay of the first spike progressivelyshortened with the subsequently stronger current stimulation.At the same time, monkey basket cells generated a first spikewith a considerably shorter delay at all ranges of stimulatingcurrent (Figs. 3A and 4A).

Action potential threshold was considerably lower in basketcells from monkeys than that from rats (Table 2, Fig. 3B),which could be associated with the higher Rin in monkeybasket cells (Prescott et al. 2006; Segev and London 1999), aswell as with the other mechanisms and, again, could beindicative of greater excitability of monkey basket cells.

Notably, the first spike that we used for the measurements ofthe voltage threshold was significantly more delayed in rat thanin monkey basket cells. Delayed first spike is known to beassociated with the activation of low-threshold K� channels(Banks et al. 1996) that can also affect spike threshold and thusinfluence the observed interspecies difference. Would the dif-ference between the species persist for the APs occurring withequal and much shorter latency, which would also be physio-logically more meaningful? To address this issue we measuredthe threshold of the APs that were generated with a latency ofabout 8 ms, which is similar to the EPSP spike latency reportedfor the FS interneurons (Fricker and Miles 2000; Maccaferriand Dingledine 2002). Voltage threshold of the spikes occur-ring with a latency of about 8 ms was still more negative inmonkey than in rat basket cells (Fig. 3, C and D).

A more delayed first spike in rat basket cells can have ahigher AP threshold due either to inactivation of Na� currentsor to activation of low-threshold K� currents. We evaluated thesecond of these possibilities by the application of the Kv1

A

DB

-150 -100 -50 0 50 100 150 200

-30

-20

-10

0

10

20

30

mV

pA

RatMonkey

E

C

-100

-75

-50

-25

0

25

50

75

100

% R

in c

hang

e

Monkey Rat

10 mV

150 ms

+ synaptic blockers100 pA

100 ms

10 mV

Monkey Rat

10 mV

100 pA100 ms

+ ZD7288

cell 1

cell 2

cell 315 mV

150 ms100 pA

cell 1

cell 2

Monkey Rat

FIG. 2. Subthreshold membrane properties of basket cells in monkey and rat. A: voltage responses to the hyperpolarizing and depolarizing current steps(representative examples from monkey and rat). Note the depolarizing sag on hyperpolarizing responses and the hump on depolarizing responses in monkeybasket cells (arrows). B: current–voltage plots for traces shown in A. C: synaptic blockers (CNQX, 20 �M; APV, 50 �M; gabazine, 4.5–6 �M) did not produceany significant changes in input resistance in both monkey and rat basket cells. D: different examples of depolarizing sags (arrows) and rebound depolarizations(arrowheads) in monkey basket cells. Traces from rat basket cells lack both depolarizing sag and rebound depolarization. E: ZD7288 (20 �M) eliminateddepolarizing sag in monkey basket cells (n � 4).

2353PV BASKET CELLS IN MONKEY AND RAT PFC

J Neurophysiol • VOL 100 • OCTOBER 2008 • www.jn.org

on October 15, 2008

jn.physiology.orgD

ownloaded from

channel blocker �-dendrotoxin (�-DTX). �-DTX decreasedthe first-spike latency by 47% (137 � 86 and 72 � 44 ms, P �0.05, n � 5, paired comparison) in rat basket cells, but it didnot significantly affect the latency in monkey basket cells.Also, we found that after blocking Kv1 channels, the thresholdof first spikes became more negative in rat (by 16%: �33 �3.5 mV before and �39.5 � 2.5 mV after, n � 5, P � 0.01),as well as in monkey basket cells (by 13%: �41.5 � 5 and �47 �5 mV accordingly, n � 4, P � 0.05; Fig. 3E). Similar effectsof �-DTX on the spike threshold in the two species mightindicate that the Kv1 current that contributes to the longerfirst-spike delay in rat basket cells does not seem to beresponsible for the observed interspecies difference in APthreshold.

FIRING PATTERN PROPERTIES. Both rat and monkey basket cellsfired without, or with very little, adaptation. Representativeexamples of the nonadapting firing pattern in monkey and ratbasket cells are shown in Fig. 4A. With the highest intensitiesof stimulation current, the temporal structure of firing wassimilar in monkey and rat basket cells, but rat cells exhibitedquiescent periods at near-threshold levels of stimulating cur-rent (Fig. 4A), which made their firing more irregular. Thisirregularity was evaluated by the CV of ISIs, which wassignificantly higher in rat basket cells (n � 23) than that inmonkey (n � 28) at near-threshold levels of stimulating cur-rents (0–60 pA above threshold) according to the ANOVA test(F � 32.5; P � 0.001) and Fisher post hoc test (Fig. 4B). Thesame type of analysis was performed exclusively for the

A

C

B

E

20 mV100 ms

Monkey Rat

15 mV

5 ms

Monkey

Rat

15 mV

20 ms

D -50

-40

-30

-20

Monkey Rat

AP th

resh

old,

mV

p<0.001

p<0.01

1st spike Spike at 8 ms latency

15 mV

10 ms

RMP -70 mV RMP -69 mV

AP threshold

AP threshold

Rat

α-DTX Monkey

20 mV

100 ms

FIG. 3. Properties of the first evoked spike in monkey and rat basket cells. A: first suprathreshold response to the depolarizing current was significantly delayedin rat, but not in monkey basket cells. B: spike threshold was considerably lower in monkey basket cells than that in rat (APs are truncated). C: spikes evokedby rectangular current pulses with the latency of 8 ms still had more negative threshold in monkey (n � 15) basket cells than that in rat (n � 14). D: threshold of the1st spikes and 8-ms-latency spikes is lower in monkeys than that in rats. Error bars represent SE. E: �-dendrotoxin (�-DTX) decreased spike threshold for the1st spikes evoked in monkey (n � 4) and rat basket cells (n � 5).

2354 POVYSHEVA ET AL.

J Neurophysiol • VOL 100 • OCTOBER 2008 • www.jn.org

on October 15, 2008

jn.physiology.orgD

ownloaded from

population of PV-positive basket cells in both species. Simi-larly to the combined populations of basket cells, PV-positivebasket cells in rat (n � 9) have a more irregular firing patternthan that from monkey (F � 16.3; P � 0.001, n � 10). Posthoc Fisher test revealed differences at the levels of stimulatingcurrent of 10–30 and 50 pA (data not shown).

To further compare the excitability of monkey and rat basketcells, we looked at the number of spikes produced in these cellsby different stimulating currents. Relative to rats, monkeybasket cells generated more spikes at levels of 10–100 pAabove firing threshold according to the ANOVA test (F �

4.15; P � 0.05, n � 20) and post hoc Fisher test (Fig. 4C,Table 2). Fewer spikes were associated with the irregular firingin rat basket cells interrupted by quiescent periods. Quiescentperiods and irregularity of firing were eliminated after theblockade of Kv1 channels by �-DTX (Fig. 4D).

Miniature EPSPs of monkey and rat basket cells

Although we showed that blockade of spontaneous synapticactivity did not produce immediate changes in membraneproperties (Fig. 2C), it is known that decreasing the levels of

20 mV

-64 mV-67 mV

200 ms

200 pA

Monkey RatA

B

C

20 mV

150 ms

+ α-DendrotoxinD

0 10 20 30 40 50 60

5

10

15

20

25

30

35

40

CV IS

I

Current above threshold, pA

Monkey Rat* *

**

* **

0 20 40 60 80 1000

10

20

30

40

50

Num

ber o

f spi

kes

Current above threshold, pA

Monkey Rat

*

**

*

*

**

*

**

FIG. 4. Firing pattern in basket cells from monkeys and rats. A: firing patterns produced by monkey and rat basket cells in response to the current steps ofdifferent intensities. Note that the firing pattern in rats was characterized by the presence of quiescent periods. B: plot of coefficient of variation of interspikeintervals (CV ISIs) vs. current intensity demonstrates more variability in ISIs in rat basket cells (n � 28) than that in monkey basket cells (n � 31). The differencewas more substantial for the responses evoked by the near-threshold current intensities. Error bars represent SE. Asterisks indicate P � 0.05. C: number of spikesevoked in monkeys (n � 20) was considerably larger than that in rats (n � 18) for the near-threshold current intensities. Error bars represent SE. Asterisks indicateP � 0.05. D: application of �-DTX (150–200 nM) eliminated quiescent periods in rat firing pattern (n � 5).

2355PV BASKET CELLS IN MONKEY AND RAT PFC

J Neurophysiol • VOL 100 • OCTOBER 2008 • www.jn.org

on October 15, 2008

jn.physiology.orgD

ownloaded from

excitatory synaptic input in a long-term fashion can increasethe firing response elicited by current injection, reflectinginvolvement of homeostatic mechanisms (Desai et al. 1999;Turrigiano and Nelson 2000). Differential properties of excit-atory responses in the two species, if revealed, could providepotential explanatory mechanisms for the observed interspeciesdifferences in membrane properties. Thus we analyzed theproperties of excitatory postsynaptic inputs received by inter-neurons, which were shown to be cell-type specific (Cossartet al. 2006).

To characterize the excitatory inputs to FS basket cells, werecorded mEPSPs, which provide a measure of number andstrength of excitatory inputs onto an individual neuron. Asshown on the representative sweeps (Fig. 5A) and on the bargraph (Fig. 5B), the frequency of mEPSPs was considerablyhigher in rat than that in monkey basket cells. At the same time,the average mEPSP amplitude was 0.92 � 0.24 mV in monkeybasket cells (n � 6) and 0.95 � 0.19 mV in rat basket cells(n � 16). Cumulative histograms of mEPSP amplitude showedthat the amplitude distribution in monkey basket cells was

A

0.0

0.2

0.4

0.6

0.8

1.0

0 1 2 3 4

mEPSPs amplitude, mV

Cum

ulat

ive

fract

ion

C0.0

0.5

1.0

1.5

2.0

2.5

3.0m

EPSP

s fre

quen

cy, H

z Monkey Rat

Monkey pyramidal cells

Rat pyramidal cells

F

E

2 mV

100 ms

2 mV100 ms

Monkey basket cells

Rat basket cells

D

0 50 100 150 200 250 300

0

10

20

30

40

50

mEP

SPs

frequ

ency

, Hz

Spike threshold, pA

R = 0.63p<0.01

0

5

10

15

20

25

30

mEP

SPs

frequ

ency

, Hz

Monkey RatB

p<0.01

20 mV

100 ms

- 67 mV - 64 mV

Monkey Rat

10 mV

20 ms

G

FIG. 5. Miniature excitatory postsynaptic potentials (mEPSPs) in monkey and rat basket cells. A: series of mEPSPs recorded from monkey and rat basket cells.B: mEPSPs were more frequent in rats (n � 16) than in monkeys (n � 6). Error bars represent SE. C: cumulative frequency distribution histograms of mEPSPamplitudes were similar in monkey (n � 6) and rat basket cells (n � 16). D: frequency of mEPSPs positively correlated with the spike threshold (pA) in rat basketcells (n � 16). E: series of mEPSPs recorded from monkey and rat pyramidal cells. F: mEPSP frequencies were similar in rat (n � 11) and in monkey (n �7) pyramidal cells. Error bars represent SE. G: membrane properties of pyramidal cells were comparable in both species.

2356 POVYSHEVA ET AL.

J Neurophysiol • VOL 100 • OCTOBER 2008 • www.jn.org

on October 15, 2008

jn.physiology.orgD

ownloaded from

similar to that from rat basket cells (Fig. 5C). The kinetics ofevents was also comparable in the two species (rise times:monkey 1.9 � 0.2 ms; rat: 1.8 � 0.2 ms), although weobserved a tendency toward a longer decay time in monkeyEPSPs (12.9 � 5 ms) than that in rats (11.5 � 3 ms), which canbe associated with their longer membrane time constant.

To address the potential mechanism that connects membraneproperties and an excitatory drive expressed as a frequency ofquantal synaptic inputs, we estimated the correlation betweenmEPSP frequency and spike threshold in rat basket cells. Asignificant positive correlation between these two parameterswas found (Fig. 5D), providing evidence for the potentiallong-term association of synaptic inputs and membrane prop-erties.

To exclude the possibility that differences in mEPSP fre-quencies can be caused by varying qualities of slices, we alsoestimated mEPSP frequencies in monkey and rat pyramidalcells. In contrast to basket cells, mEPSP frequency of pyrami-dal cells was comparable in monkey and rat PFC (Fig. 5, E andF). These results suggest that the differences in mEPSP fre-quency reported here are cell-type and species specific.

Interestingly, unlike in FS basket cells, physiological mem-brane properties of pyramidal cells were very similar in mon-key (n � 27) and rat (n � 21) (Fig. 5G). Specifically, they didnot show any significant difference in input resistance, spikethreshold, firing frequency, or first-spike latency.

D I S C U S S I O N

The results of this study revealed important differencesbetween monkeys and rats in the intrinsic physiological char-acteristics of PFC basket cells. In contrast to rat basket cells,monkey basket cells were more excitable, as indicated by theirlower spike threshold, higher input resistance and the numberof spikes they could generate at near-threshold current inten-sities. Furthermore, basket cells in monkeys produced a less-delayed first spike at near-threshold currents than that in rats.On the contrary, the morphological characteristics of basketcells were very similar in both species. Our findings suggestthat interspecies differences in FS basket cells can be detectedat the level of intrinsic cellular properties and provide someinsights into the different spiking behavior of FS units duringworking-memory tasks in monkey and rat (Constantinidis andGoldman-Rakic 2002; Jung et al. 1998;Wilson et al. 1994).

Differential membrane properties of basket cells frommonkey and rat

A number of physiological properties of basket cells werehighly comparable across species. The similarities includedsingle spike properties such as spike amplitude, spike decaytime, and the AHP amplitude, as well as firing pattern proper-ties, such as high firing frequency and lack of frequencyadaptation. Still, some critical electrophysiological propertiesdiffered significantly between monkey and rat basket cells.

Monkey basket cells were more excitable than those in rats,displaying higher input resistance, lower threshold of AP, andhigher firing frequency. Excitability in general and input resis-tance in particular are shown to be defined by the density of K�

currents, which are mostly leak currents but also inwardrectifiers (Gorelova et al. 2002; Nichols and Lopatin 1997;

Rudy 1988). We showed that AP threshold was more negativein monkey basket cells than that in rat because spikes occurredat different latencies. More negative spike thresholds can beassociated with the differential expression of voltage-gatedchannels that are open at the near-threshold level of membranepotential and can be responsible for the shunting of Na�

currents (the only mechanism of an ideal isopotential struc-ture). Thus association between Kv1 channels and excitabilitywas previously demonstrated (Glazebrook et al. 2002; Guanet al. 2006). In this study, we showed that Kv1 channel blockerdecreased AP threshold in both monkey and rat basket cells.Properties of the inward Na� and low-threshold T-type Ca2�

currents could also contribute to the observed differences infiring threshold (Yang et al. 1996). Ih currents are also shownto contribute to neuronal excitability (Pape 1996; Robinson andSigelbaum 2003). Aponte et al. (2006) demonstrated theirpresence in FS interneurons in the hippocampus of rats. In ourstudy we showed the presence of Ih currents in monkey FSinterneurons, although we could not resolve the differences inexpression between the two species. Dissimilarities in APthreshold could also be connected with the differences in inputresistance between the species (Prescott et al. 2006; Segev andLondon 1999); higher input resistance in monkey basket cellscan produce more negative AP threshold. The role of thepassive membrane properties in the sculpting of the spikethreshold was shown in modeling studies that demonstratedthat the electrotonic structure of the cable affects voltage, aswell as current, spike threshold (Segev and London 1999).Recently, Prescott et al. (2006) showed that changes in inputresistance (or membrane conductance) produced by shuntingcould influence voltage spike threshold in a phase-plane modeland also in dynamic-clamp experiments in real CA1 pyramidalneurons. The possible mechanism suggested by the authors isthat with a larger outward leak current (in high conductancestates), AP generation requires a greater activation of thesodium current.

Also, we demonstrated that the first spikes in monkey basketcells were less delayed than in rat basket cells. Mainly, theygenerated the first spike shortly after stimulation onset. Moredelayed first spikes in rat basket cells could be associated withthe low-threshold outward K� current (Banks et al. 1996).

Unlike firing in monkey basket cells, the firing pattern in ratPFC basket cells was often interrupted by quiescent periodswith the near-threshold current intensities, so the firing patternappeared irregular or “stuttering” (Markram et al. 2004): withstronger current intensities, the irregular firing pattern becametypical fast-spiking nonadapting. This feature of FS basketcells was previously reported in rat neocortex (Descalzo et al.2005; Kawaguchi 1995). The irregular firing of rat basket cellsresulted in fewer spikes at the near-threshold current levels.Mechanisms producing irregular firing in rat basket cells couldinvolve activation of the low-threshold Kv1 channels since weshowed that application of Kv1 channel blocker eliminatedquiescent periods in their firing pattern (Fig. 4D). The sameeffect was also demonstrated in other studies on rat neocortexwhen �-DTX blocked “stuttering” in interneurons (Toledo-Rodriguez et al. 2004).

The connectivity pattern of the dendritic tree can determinethe firing properties of neurons (Mainen and Sejnowski 1996;van Ooyen et al. 2002). Quantitative morphological analysis ofbasket cells from monkeys and rats undertaken in our study did

2357PV BASKET CELLS IN MONKEY AND RAT PFC

J Neurophysiol • VOL 100 • OCTOBER 2008 • www.jn.org

on October 15, 2008

jn.physiology.orgD

ownloaded from

not reveal any significant interspecies differences and thuscould not provide an explanatory mechanism for the observeddifferences in physiological membrane properties between thespecies.

The firing activity of neurons is largely driven by theproperties of their synaptic inputs (Fuchs et al. 2001; Pouilleand Scanziani 2004; Traub et al. 1993). First, spontaneoussynaptic activity can directly affect input resistance, as waspreviously shown through in vivo studies (Steriade et al. 2001),and therefore can influence the observed difference betweenmonkey and rat basket cells. This influence can be executed asa direct shunt of applied current. To test this possibility, wemeasured input resistance of basket cells before and afterapplication of synaptic blockers. No significant difference wasfound in either species (Fig. 2C). However, it should be notedhere, that the concentration of gabazine used in this study ismost probably not enough to block tonic GABA current, whichcan also influence input resistance (Semyanov et al. 2003; Stelland Mody 2002).

Reflected in spontaneous activity excitatory inputs receivedby neurons are also known to produce long-term homeostaticchanges in ion channels and thus in membrane properties ofneurons, as was previously demonstrated (Desai et al. 1999;Pratt and Aizenman 2007; Turrigiano and Nelson 2000). In thisstudy, we found that the frequency of mEPSPs is much lowerin monkey than that in rat basket cells. The higher frequency ofmEPSPs in rat basket cells can indicate more abundant exci-tatory synapses impinging onto rat basket cells than onto thosein monkeys. Two studies using electron microscopy reportedon the number of asymmetric synapses in different types ofinterneurons. Although they used different methodologies, thusnot allowing for direct comparison between species, indirectlythe studies suggest that the density of excitatory synapses islower in monkey than that in rat basket cells (Gulyas et al.1999; Melchitzky and Lewis 2003). Given the positive corre-lation between the spike threshold and mEPSP frequency, thisfinding might represent a homeostatic mechanism by whichneurons with more abundant excitatory inputs reduce theirexcitability to normalize the effects of greater synaptic driveand thereby maintain a constant functional output (Hansel et al.2001; Marder and Goaillard 2006;Turrigiano and Nelson2000). Importantly, because the properties of dendrites did notdiffer between the FS basket cells recorded from monkey andrat PFC (Table 1, Fig. 1), it is unlikely that the differences inmEPSP frequency are due to a less well preserved FS basketcell dendritic tree in slices of monkey PFC.

Notably, the frequency, amplitude, and kinetics of miniatureevents were comparable in pyramidal cells from both monkeysand rats. Interestingly, physiological membrane properties ofpyramidal cells in the hippocampus were also very similar inboth monkeys and rats (Altemus et al. 2005).

Contribution to species differences in PFC functioning

PV-positive basket cells appear to be responsible for gener-ation of gamma-oscillations in the hippocampus, since inter-neurons providing perisomatic inhibition were found to firewith gamma-frequency discharge rate and to be strongly phaselocked to the different rhythms of network oscillations(Buzsaki and Draguhn 2004; Hajos et al. 2004; Tukker et al.2007). Irregularity in firing of rat basket cells (due to the

presence of quiescent periods in their firing pattern), as well asdelayed firing, can contribute to the differences in shaping ofneuronal oscillations in the two species (Buzsaki and Draguhn2004).

The different physiological properties of basket FS interneu-rons from monkey and rat PFC may further inform our under-standing of the nature of the functional differences betweenprimate and rodent PFC during the performance of WM tasks(Brown and Bowman 2002; Preuss 1995; Uylings et al. 2003).Although “memory cells” that are active during the delayperiod of working-memory tasks are described in both monkeyand rat PFC, their spiking behavior is different in the twospecies—both excitatory and inhibitory “memory cells” fire atconsiderably lower frequencies in rats (Constantinidis andGoldman-Rakic 2002; Jung et al. 1998;Wilson et al. 1994).

In conclusion, the results of this study help clarify thetranslation of data from rodents to primates and is critical forstudies focused on understanding the pathophysiologicalmechanisms of mental illnesses, such as schizophrenia, that areassociated with dysfunction of PFC interneurons (Lewis et al.2005).

A C K N O W L E D G M E N T S

We thank O. A. Krimer and J. Kosakowski for excellent technical assistance.Present addresses: N. V. Povysheva, University of Pittsburgh, Department

of Neuroscience, Pittsburgh, PA 15260; A. V. Zaitsev, Trinity College,Department of Physiology, Dublin, Ireland.

G R A N T S

This work was supported by National Institute of Mental Health GrantsR01MH-067963 and R01MH-051234. The content is solely the responsibilityof the authors and does not necessarily represent the official views of theNational Institute of Mental Health or the National Institutes of Health.

R E F E R E N C E S

Altemus KL, Lavenex P, Ishizuka N, Amaral DG. Morphological charac-teristics and electrophysiological properties of CA1 pyramidal neurons inmacaque monkeys. Neuroscience 136: 741–756, 2005.

Aponte Y, Lien CC, Reisinger E, Jonas P. Hyperpolarization-activatedcation channels in fast-spiking interneurons of rat hippocampus. J Physiol574: 229–243, 2006.

Baimbridge KG, Celio MR, Rogers JH. Calcium-binding proteins in thenervous system. Trends Neurosci 15: 303–308, 1992.

Banks MI, Haberly LB, Jackson MB. Layer-specific properties of thetransient K current (IA) in piriform cortex. J Neurosci 16: 3862–3876, 1996.

Beaulieu C. Numerical data on neocortical neurons in adult rat, with specialreference to the GABA population. Brain Res 609: 284–292, 1993.

Brown VJ, Bowman EM. Rodent models of prefrontal cortical function.Trends Neurosci 25: 340–343, 2002.

Butt SJ, Fuccillo M, Nery S, Noctor S, Kriegstein A, Corbin JG, Fishell G.The temporal and spatial origins of cortical interneurons predict theirphysiological subtype. Neuron 48: 591–604, 2005.

Buzsaki G, Draguhn A. Neuronal oscillations in cortical networks. Science304: 1926–1929, 2004.

Conde F, Lund JS, Jacobowitz DM, Baimbridge KG, Lewis DA. Localcircuit neurons immunoreactive for calretinin, calbindin D-28k or parval-bumin in monkey prefrontal cortex: distribution and morphology. J CompNeurol 341: 95–116, 1994.

Constantinidis C, Goldman-Rakic PS. Correlated discharges among putativepyramidal neurons and interneurons in the primate prefrontal cortex. J Neu-rophysiol 88: 3487–3497, 2002.

Cossart R, Petanjek Z, Dumitriu D, Hirsch JC, Ben-Ari Y, Esclapez M,Bernard C. Interneurons targeting similar layers receive synaptic inputswith similar kinetics. Hippocampus 16: 408–420, 2006.

DeFelipe J, Alonso-Nanclares L, Arellano JI. Microstructure of the neocor-tex: comparative aspects. J Neurocytol 31: 299–316, 2002.

Desai NS, Rutherford LC, Turrigiano GG. Plasticity in the intrinsic excit-ability of cortical pyramidal neurons. Nat Neurosci 2: 515–520, 1999.

2358 POVYSHEVA ET AL.

J Neurophysiol • VOL 100 • OCTOBER 2008 • www.jn.org

on October 15, 2008

jn.physiology.orgD

ownloaded from

Descalzo VF, Nowak LG, Brumberg JC, McCormick DA, Sanchez-VivesMV. Slow adaptation in fast-spiking neurons of visual cortex. J Neuro-physiol 93: 1111–1118, 2005.

Desgent S, Boire D, Ptito M. Distribution of calcium binding proteins invisual and auditory cortices of hamsters. Exp Brain Res 163: 159–172, 2005.

Douglas RJ, Martin KA. Neuronal circuits of the neocortex. Annu RevNeurosci 27: 419–451, 2004.

Freund TF, Buzsaki G. Interneurons of the hippocampus. Hippocampus 6:347–470, 1996.

Fricker D, Miles R. EPSP amplification and the precision of spike timing inhippocampal neurons. Neuron 28: 559–569, 2000.

Fuchs EC, Doheny H, Faulkner H, Caputi A, Traub RD, Bibbig A, KopellN, Whittington MA, Monyer H. Genetically altered AMPA-type glutamatereceptor kinetics in interneurons disrupt long-range synchrony of gammaoscillation. Proc Natl Acad Sci USA 98: 3571–3576, 2001.

Gabbott PL, Bacon SJ. Local circuit neurons in the medial prefrontal cortex(areas 24a,b,c, 25 and 32) in the monkey: II. Quantitative areal and laminardistributions. J Comp Neurol 364: 609–636, 1996.

Gabbott PL, Dickie BG, Vaid RR, Headlam AJ, Bacon SJ. Local-circuitneurones in the medial prefrontal cortex (areas 25, 32 and 24b) in the rat:morphology and quantitative distribution. J Comp Neurol 377: 465–499,1997.

Glazebrook PA, Ramirez AN, Schild JH, Shieh CC, Doan T, Wible BA,Kunze DL. Potassium channels Kv1.1, Kv1.2 and Kv1.6 influence excit-ability of rat visceral sensory neurons. J Physiol 541: 467–482, 2002.

Glezer II, Hof PR, Morgane PJ. Comparative analysis of calcium-bindingprotein-immunoreactive neuronal populations in the auditory and visualsystems of the bottlenose dolphin (Tursiops truncatus) and the macaquemonkey (Macaca fascicularis). J Chem Neuroanat 15: 203–237, 1998.

Gonchar Y, Burkhalter A. Three distinct families of GABAergic neurons inrat visual cortex. Cereb Cortex 7: 347–358, 1997.

Gonzalez-Burgos G, Barrionuevo G, Lewis DA. Horizontal synaptic con-nections in monkey prefrontal cortex: an in vitro electrophysiological study.Cereb Cortex 10: 82–92, 2000.

Gorelova N, Seamans JK, Yang CR. Mechanisms of dopamine activation offast-spiking interneurons that exert inhibition in rat prefrontal cortex. J Neu-rophysiol 88: 3150–3166, 2002.

Guan D, Lee JC, Tkatch T, Surmeier DJ, Armstrong WE, Foehring RC.Expression and biophysical properties of Kv1 channels in supragranularneocortical pyramidal neurones. J Physiol 571: 371–389, 2006.

Gulyas AI, Megias M, Emri Z, Freund TF. Total number and ratio ofexcitatory and inhibitory synapses converging onto single interneurons ofdifferent types in the CA1 area of the rat hippocampus. J Neurosci 19:10082–10097, 1999.

Hajos N, Palhalmi J, Mann EO, Nemeth B, Paulsen O, Freund TF. Spiketiming of distinct types of GABAergic interneuron during hippocampalgamma oscillations in vitro. J Neurosci 24: 9127–9137, 2004.

Hansel C, Linden DJ, D’Angelo E. Beyond parallel fiber LTD: the diversityof synaptic and non-synaptic plasticity in the cerebellum. Nat Neurosci 4:467–475, 2001.

Jones EG, Hendry SHC. Basket cells. In: Cerebral Cortex, edited by PetersA, Jones E. New York: Plenum Press, 1984, p. 309–335.

Jung MW, Qin Y, McNaughton BL, Barnes CA. Firing characteristics ofdeep layer neurons in prefrontal cortex in rats performing spatial workingmemory tasks. Cereb Cortex 8: 437–450, 1998.

Kawaguchi Y. Physiological subgroups of nonpyramidal cells with specificmorphological characteristics in layer II/III of rat frontal cortex. J Neurosci15: 2638–2655, 1995.

Kawaguchi Y, Kubota Y. GABAergic cell subtypes and their synapticconnections in rat frontal cortex. Cereb Cortex 7: 476–486, 1997.

Krimer LS, Zaitsev AV, Czanner G, Kroner S, Gonzalez-Burgos G,Povysheva NV, Iyengar S, Barrionuevo G, Lewis DA. Cluster analysis-based physiological classification and morphological properties of inhibitoryneurons in layers 2–3 of monkey dorsolateral prefrontal cortex. J Neuro-physiol 94: 3009–3022, 2005.

Kubota Y, Hattori R, Yui Y. Three distinct subpopulations of GABAergicneurons in rat frontal agranular cortex. Brain Res 649: 159–173, 1994.

Letinic K, Zoncu R, Rakic P. Origin of GABAergic neurons in the humanneocortex. Nature 417: 645–649, 2002.

Lewis DA, Hashimoto T, Volk DW. Cortical inhibitory neurons and schizo-phrenia. Nat Rev Neurosci 6: 312–324, 2005.

Lund JS, Lewis DA. Local circuit neurons of developing and mature macaqueprefrontal cortex: Golgi and immunocytochemical characteristics. J CompNeurol 328: 282–312, 1993.

Maccaferri G, Dingledine R. Control of feedforward dendritic inhibition byNMDA receptor-dependent spike timing in hippocampal interneurons.J Neurosci 22: 5462–5472, 2002.

Mainen ZF, Sejnowski TJ. Influence of dendritic structure on firing pattern inmodel neocortical neurons. Nature 382: 363–366, 1996.

Marder E, Goaillard JM. Variability, compensation and homeostasis inneuron and network function. Nat Rev Neurosci 7: 563–574, 2006.

Markram H, Toledo-Rodriguez M, Wang Y, Gupta A, Silberberg G, WuC. Interneurons of the neocortical inhibitory system. Nat Rev Neurosci 5:793–807, 2004.

Meinecke DL, Peters A. GABA immunoreactive neurons in rat visual cortex.J Comp Neurol 261: 388–404, 1987.

Melchitzky DS, Lewis DA. Pyramidal neuron local axon terminals in monkeyprefrontal cortex: differential targeting of subclasses of GABA neurons.Cereb Cortex 13: 452–460, 2003.

Nelson SB, Sugino K, Hempel CM. The problem of neuronal cell types: aphysiological genomics approach. Trends Neurosci: 29: 339–345, 2006.

Nichols CG, Lopatin AN. Inward rectifier potassium channels. Annu RevPhysiol 59: 171–191, 1997.

Pape HC. Queer current and pacemaker: the hyperpolarization-activatedcation current in neurons. Annu Rev Physiol 58: 299–327, 1996.

Paxinos G, Watson C. The Rat Brain in Stereotaxic Coordinates (4th ed.).New York: Academic Press, 1998.

Petanjek Z, Berger B, Esclapez M. Origins of cortical GABAergic neuronsin the cynomolgus monkey. Cereb Cortex (May 13, 2008) doi:10.1093/cercor/bhn078.

Pouille F, Scanziani M. Routing of spike series by dynamic circuits in thehippocampus. Nature 429: 717–723, 2004.

Povysheva NV, Gonzalez-Burgos G, Zaitsev AV, Kroner S, BarrionuevoG, Lewis DA, Krimer LS. Properties of excitatory synaptic responses infast-spiking interneurons and pyramidal cells from monkey and rat prefron-tal cortex. Cereb Cortex 16: 541–552, 2006.

Povysheva NV, Zaitsev AV, Kroner S, Krimer OA, Rotaru DC, Gonzalez-Burgos G, Lewis DA, Krimer LS. Electrophysiological differences be-tween neurogliaform cells from monkey and rat prefrontal cortex. J Neuro-physiol 97: 1030–1039, 2007.

Pratt KG, Aizenman CD. Homeostatic regulation of intrinsic excitability andsynaptic transmission in a developing visual circuit. J Neurosci 27: 8268–8277, 2007.

Prescott SA, Ratte S, De Koninck Y, Sejnowski TJ. Nonlinear interactionbetween shunting and adaptation controls a switch between integration andcoincidence detection in pyramidal neurons. J Neurosci 26: 9084–9097,2006.

Preuss TM. Do rats have prefrontal cortex? The Rose–Woolsey–Akert Pro-gram reconsidered. J Cogn Neurosci 7: 1–24, 1995.

Rao SG, Williams GV, Goldman-Rakic PS. Isodirectional tuning of adjacentinterneurons and pyramidal cells during working memory: evidence formicrocolumnar organization in PFC. J Neurophysiol 81: 1903–1916, 1999.

Rao SG, Williams GV, Goldman-Rakic PS. Destruction and creation ofspatial tuning by disinhibition: GABA(A) blockade of prefrontal corticalneurons engaged by working memory. J Neurosci 20: 485–494, 2000.

Robinson RB, Siegelbaum SA. Hyperpolarization-activated cation currents:from molecules to physiological function. Annu Rev Physiol 65: 453–480,2003.

Rudy B. Diversity and ubiquity of K channels. Neuroscience 25: 729–749,1988.

Segev I, London M. A theoretical view of passive and active dendrites. In:Dendrites, edited by Stuart G, Spruston N, Hausser M. New York: OxfordUniv. Press, 1999, p. 205–230.

Semyanov A, Walker MC, Kullmann DM. GABA uptake regulates corticalexcitability via cell type-specific tonic inhibition. Nat Neurosci 6: 484–490,2003.

Silberberg G, Gupta A, Markram H. Stereotypy in neocortical microcir-cuits. Trends Neurosci 25: 227–230, 2002.

Somogyi P, Tamas G, Lujan R, Buhl EH. Salient features of synapticorganisation in the cerebral cortex. Brain Res Brain Res Rev 26: 113–135,1998.

Stell BM, Mody I. Receptors with different affinities mediate phasic and tonicGABA(A) conductances in hippocampal neurons. J Neurosci 22: RC223,2002.

Steriade M, Timofeev I, Grenier F. Natural waking and sleep states: a viewfrom inside neocortical neurons. J Neurophysiol 85: 1969–1985, 2001.

Tanaka S. Architecture and dynamics of the primate prefrontal cortical circuitfor spatial working memory. Neural Networks 12: 1007–1020, 1999.

2359PV BASKET CELLS IN MONKEY AND RAT PFC

J Neurophysiol • VOL 100 • OCTOBER 2008 • www.jn.org

on October 15, 2008

jn.physiology.orgD

ownloaded from

Thomson AM, West DC, Hahn J, Deuchars J. Single axon IPSPs elicited inpyramidal cells by three classes of interneurones in slices of rat neocortex.J Physiol 496: 81–102, 1996.

Toledo-Rodriguez M, Blumenfeld B, Wu C, Luo J, Attali B, Goodman P,Markram H. Correlation maps allow neuronal electrical properties to bepredicted from single-cell gene expression profiles in rat neocortex. CerebCortex 14: 1310–1327, 2004.

Traub RD, Miles R, Jefferys JG. Synaptic and intrinsic conductances shapepicrotoxin-induced synchronized after-discharges in the guinea-pig hip-pocampal slice. J Physiol 461: 525–547, 1993.

Tukker JJ, Fuentealba P, Hartwich K, Somogyi P, Klausberger T. Celltype-specific tuning of hippocampal interneuron firing during gamma oscil-lations in vivo. J Neurosci 27: 8184–8189, 2007.

Turrigiano GG, Nelson SB. Hebb and homeostasis in neuronal plasticity.Curr Opin Neurobiol 10: 358–364, 2000.

Uylings HB, Groenewegen HJ, Kolb B. Do rats have a prefrontal cortex?Behav Brain Res 146: 3–17, 2003.

van Ooyen A, Duijnhouwer J, Remme MW, van Pelt J. The effect of dendritictopology on firing patterns in model neurons. Network 13: 311–325, 2002.

Wang XJ, Tegner J, Constantinidis C, Goldman-Rakic PS. Division oflabor among distinct subtypes of inhibitory neurons in a cortical microcircuitof working memory. Proc Natl Acad Sci USA 101: 1368–1373, 2004.

Wilson FA, O’Scalaidhe SP, Goldman-Rakic PS. Functional synergismbetween putative gamma-aminobutyrate-containing neurons and pyrami-dal neurons in prefrontal cortex. Proc Natl Acad Sci USA 91: 4009 –4013, 1994.

Xu Q, Cobos I, De La Cruz E, Rubenstein JL, Anderson SA. Origins ofcortical interneuron subtypes. J Neurosci 24: 2612–2622, 2004.

Xu X, Roby KD, Callaway EM. Mouse cortical inhibitory neuron type thatcoexpresses somatostatin and calretinin. J Comp Neurol 499: 144–160,2006.

Yang CR, Seamans JK, Gorelova N. Electrophysiological and morphologicalproperties of layers V–VI principal pyramidal cells in rat prefrontal cortexin vitro. J Neurosci 16: 1904–1921, 1996.

Zaitsev AV, Gonzalez-Burgos G, Povysheva NV, Kroner S, Lewis DA,Krimer LS. Localization of calcium-binding proteins in physiologically andmorphologically characterized interneurons of monkey dorsolateral prefron-tal cortex. Cereb Cortex 15: 1178–1186, 2005.

2360 POVYSHEVA ET AL.

J Neurophysiol • VOL 100 • OCTOBER 2008 • www.jn.org

on October 15, 2008

jn.physiology.orgD

ownloaded from