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ManyAsianplantstoutedtobeusefulinthetreatment of psychological disorders have beenidentifiedtopossesspsychoactivityproperties.Apsychoactiveplantisonethathasphytochemicalcompound(s) that affect the central nervoussystem, producing changes in mental activityand/or behaviour (1). These herbal remediesmay produce changes in mood and behaviouras well as decrease epileptic attacks. Currently,a fourth of the world’s pharmaceutical drugscontain phytochemicals directly extractedfrom higher plants, or their derivates (2). Theelectrophysiologicalpropertiesof4plants,namelyCentella asiatica (pegaga) and its compound(asiaticacid), Zizyphus mauritiana (bidara)anditscrudeextracts,Myristica fragrans(Malaysiannutmeg)anditsextracts,andMitragyna speciosa Korth (ketum)and its crudeextracts, havebeenstudiedtolookattheirinvivoandinvitroeffects. AsiaticacidfromtheMalaysianC. asiatica,at0.125µg,wasshowntoinhibitacetylcholinesteraseenzyme.Asiaticacidalsoproducedadepressanteffect to the synaptic activity in extracellularrecording experiments. The major effects ofasiatic acid were the dose- and time-dependentincreasesintheintensityanddurationofgamma-
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aminobutyric acid (GABA)A blocker–mediatedinhibitioncomparedwithGABABblocker,whichshowednoresponse.Thisdepressanteffectwasnotreversibleaftera30-minutewashoutoftheasiaticacid in the recording chamberwhen exposed toknownGABAantagonistbicuculineorphaclofen.These findings were consistent with asiatic acidactingselectivelyontheGABABreceptor,whichismetabotropic,andnotontheGABAAreceptor.TheimpairmentofexcitatorysynaptictransmissionattheSchaffercollateral–CA1synapsebyasiaticacidindicatedthatthiseffectwascausedbyitsdirectorindirectactiononGABAergicreceptors.Asiaticacid’s interactionwith specific GABAB receptorsleads to the receptors’ opening that effected theoutflow of potassium ions from the neuronalcell and, subsequently, the hyperpolarisationof the neuronal cell, resulting in the decreasedexcitatory post-synaptic potential (EPSP)withintime.Thehalfmaximal inhibitoryconcentration(IC50)ofasiaticacidderivedfromC. asiaticawas14μM(3). From the dose-dependent inhibitory effectsof asiatic acid, the concentration responsecurrent were fitted, and further examination ofthe inhibitory effect of asiatic acid on the field
Abstract Therehavebeennumerousnon-scientificreportsonthebehaviouraleffectsofAsianplantsinhumanswhoconsumedtheseplantswhollyorpartthereof.Knowledgepassedfromgenerationtogenerationinformsusofplantsthatincreaseeffortandstamina,suchasduringpaddyplantingaftertheingestionofMitragyna speciosaKorth(ketum)asateasupplement.Centella asiaticaandMyristica fragransareusedasherbstoimprovememoryandtotreatepilepsy,respectively.Zizyphus mauritianaisusedtotreatheadacheandburnpain,actsasanantitussive,andreducesrigormortisimmediately after death. These plants,whichhave been identified to exhibit analgaesic,muscle-relaxing,andnootropiceffects,maycontainimportantbio-compoundsformedicinalchemistryandpharmaceutical research inMalaysia. The electrophysiology properties of these plants and theireffectsonepilepsy,behaviour,andpainwillleadMalaysiatofuturenewdrugdiscoveries.
Keywords: behaviour, electrophysiology, GABA, long-term potentiation, medicinal chemistry, neurosciences, plants
Interesting Asian Plants: Their Compounds and Effects on Electrophysiology and Behaviour
Jafri Malin AbdullAh
Malaysian Journal of Medical Sciences,Universiti Sains Malaysia Press, Universiti Sains Malaysia Health Campus, 16150 Kubang Kerian, Kelantan, Malaysia
Submitted: 1May2011Accepted: 15Aug2011
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EPSPs (fEPSPs) evoked in the CA1 subregionwas performed. Asiatic acid decreased fEPSPsin a dose-dependent manner, with an IC50 ofapproximately14μM(3). Theeffectsofasiaticacidonactiveandpassivebehaviour indicated that it could contribute tobetterperformancesinlearningandmemoryviaan inhibitory GABAergic effect through GABABreceptor(4). TheessentialoilofM. fragranswastestedinXenopus oocytes thatwere injectedwithGABAAreceptorcomprisingof2α1,2β2,andγ2ssubunitsbyusingautomatedfastperfusionsystemduring2-microelectrode voltage-clamp measurement(5). At 1.0% essential oil and 5 uM GABA, thepercentageofcurrentstimulationwasmorethan100%.TwocompoundsfromM. fragrans,X1000a
andX1000b,alsoexhibitedasignificantincreaseincurrentflowat100uM(Figure1aand1b)(6).Thesefindingsshowedthatthecompoundsactedat the GABAA receptor as positive modulatorsor agonists. The compounds also showedinteresting antiepileptic effects, as observed inthe improvement of the number and the typeof seizures in rats monitored with intracranialimplantsusingvideowirelesstelemetrymethods(Figures2and3)(6). Another similar experiment usingZ. mauritania did not show the potentialto generate GABA current even for a smallpercentage(Figure1c).ThemechanismofactionofZ. mauritaniainpainreductionwasunlikelyviatheGABApathway,dissimilartotheM. fragransexperimentalfindings(6).
Figure1:RepresentativecurrenttracesrecordedfromoocyteexpressingGABAAreceptorscomposedofα1,β2andγ2subunitsat100μMconcentrationsofX1000aandX1000b. The figure shows the difference of the GABA current stimulation5μMGABAandinthepresenceof(a)100μMX1000a,(b)100μMX1000b,or(c)1%Z. mauritiana rootcrudeextract.
Figure 2: Antiepileptic effects of X1000a(50 mg/kg) on GAERS rat incomparison with diazepam(positive control) and normalsaline(negativecontrol).
Figure 3: Antiepileptic effects of X1000b(50 mg/kg) on GAERS rat incomparison with diazepam(positive control) and saline as(negativecontrol).
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Our experiments with the standardisedcrudeextractsofM. speciosa Korthdemonstratedthat,intherathippocampalslices,superfusionofextracts brought about a long-lasting reductionofneurotransmissionatthesynapsesconnectingthe Schaffer collateral–commissural fibres withCAl hippocampal pyramidal cells. NormalisedfEPSP responses from groups treated with0.0001%, 0.001%, 0.005%, and 0.01% extractsshowed irreversible decreases of the fEPSPamplitudeforapproximately40minutes.Inorderto determine the recovery from the inhibitoryeffectexertedbyM. speciosa,thepeakamplitudewas measured during 20-minute washout. Thedrug-induced inhibition of the peak amplitudewasirreversibleduringthisperiod(7). The M. speciosa crude extract showedinhibitory and excitatory effects concurrently.This trend is because many compounds arepresent in the crude extract, all of which havevarious effects (8); specific compounds eliciting
the observed effects could not be differentiated.From the trend, we can also postulate that theresponseshowedcontinuouslydecreasingpatterndue to the irreversible action of the compoundsavailable. The two highest concentrations ofM. speciosa(0.05%and0.1%)showedconsistentlydecreasing patterns from the beginning of theexperiment,especiallyat0.1%inwhichadrasticdecreasewasobserved.Thehighconcentrationofbiocompoundsisbelievedtohavecontributedtothisirreversibleeffect. The highest dose of M. speciosa Korthstandardised methanol extract was necessaryfor the learningacquisitionstudyusingSpragueDawley rats. However, when administeredacutely (singledose),noconsolidationoccurred,whichleadstothefailureofinformationretrieval(memory impairment) in both inhibitoryavoidancetasks(one-waypassiveavoidanceandtwo-wayactiveavoidancetests)withoutanyacutepathologicaleffectstothebrain(Figure4)(9).
Figure 4: Long-termpotentiation(LTP)experimentindicatingstablebaselineresponseswererecordedinhippocampalareaCA1ofslicesfrombothgroupsfor20min.LTP-inducinghighfrequencystimulation(HFS)consistedofonetrainofHFS(100pulsesat100Hz).Perfusionwithvehicle(0.1%dimethylsulfoxide,DMSO)resultedinrapidandlong-lastingpotentiation.Thegrouptreatedwith0.008%M. speciosa Korthstandardisedmethanolextractdissolvedin0.1%DMSOshowedinhibitionoftheinducedlong-termpotentiation,ashort-termpotentiation.Theinitialslopeofthefieldexcitatorypost-synapticpotential(fEPSP)hasbeennormalisedtotheaveragebaselinevalueduringtheperfusion.Thepointsrepresentmeans,andtheerrorbarsrepresentSEM(n=6,respectively).
NormalisedfEPSPslope
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Across the concentration of M. speciosa Korth standardised methanol extract testedin this experiment, the fEPSPs appeared todecrease over time; this effect was irreversible.The IC50 of 0.008% extract showed short-term potentiation (STP) response in ratCA1 hippocampus neurons. The induction ofSTPresultedinlessCa2+influxintopost-synapticcellandtriggeredlowerthresholdcomparedwiththe long-termpotentiation.STP isdependent toN-methyl-D-aspartatereceptor,whichisrequiredinlearningtheprocess. The multitude of electrophysiologicalfindings from standardised crude extracts oridentified plant compounds will eventually helpthe pharmaceutical industries of Malaysia todecide, after screening, which plants and theircompounds are the future drug candidates thatcan act on the central and peripheral nervoussystems.
Acknowledgements
IwouldliketoacknowledgethecontributionsofProfessorDrGerhardRammesoftheMaxPlanckInstitute of Psychiatry and the Department ofAnaesthesiology,TechnicalUniversity,KlinikumRechts der Isar, Munich, Germany; ProfessorDr Stefann Hering of the Institute ofPharmacology and Toxicology, University ofVienna, Austria; Hans Reiner Polder of NPIElectronic GmbH, Tamm, Germany; and theDeutscher Akademischer Austausch Dienst–Universiti Sains Malaysia ElectrophysiologySummer School 2009 headed by ProfessorDr Michael Horner of the Georg-AugustUniversity, Gottingen. The electrophysiologyexperiments and animal behaviour and epilepsystudiesweredone inpartundermysupervisionof these Master students in Neurosciences,Universiti Sains Malaysia: Harizal Senikon M. speciosa Korth, Nasir Mat Noor onC. asiatica, Ahmad Tarmizi Che Has onZ. mauritiana as well as on M. fragrans, andpost-doctoral fellow Dr M Rafiqul Islam, whoworked on the effects of these compounds onepileptic rat models. I also would like to thankmy other investigators Professor Dr SharifMahsufiMansoroftheCentreforDrugResearch,Universiti Sains Malaysia; Associate ProfessorDr Hasnah Osman of the School of ChemicalSciences, Universiti Sains Malaysia; andDrHabsahMohamadof the Institute ofMarineBiotechnology, Universiti Malaysia Terengganu,whohadequalcontributionstothisresearch.
Correspondence
ProfessorDrJafriMalinAbdullahFASc (Malaysia), MD (Universiti Sains Malaysia),PhD (University of Ghent), FRCS (Ed), FACS (USA),FAAN(USA),DSCNeurosurgery(Belgium)Editor-in-ChiefMedicalJournalofMedicalSciencesUniversitiSainsMalaysiaPressUniversitiSainsMalaysiaHealthCampus16150KubangKerianKelantan,MalaysiaTel:+609-7676972Fax:+609-7672359Email:[email protected]
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