a calcium dependent model of synaptic plasticity (cadp) describe various induction protocols
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A Calcium dependent model of synaptic plasticity (CaDp) Describe various induction protocols. Can a single model, based on a limited set of assumptions, account for the various induction protocols? - PowerPoint PPT PresentationTRANSCRIPT
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A Calcium dependent model of synaptic plasticity (CaDp)
Describe various induction protocols
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Can a single model, based on a limited set of assumptions, account for the various induction protocols?
Approach: Find a minimal set of assumptions that can qualitatively account for the various forms of induction.
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Assumption 1: The calcium control hypothesis.
The idea that calcium levels control the sign and magnitude of synaptic plasticity has been around for a while (Lisman, 1989; Bear et. al., 1987; Artola et. al. 1990)
ΔΔWW
LTDCa
LTPθd θp
I. A Unified theory of NMDA Receptor-Dependent synaptic plasticity
)]([ ii Ca
dt
dW
ΩΩ function function
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)( )]([)]([ iiii WCaCa
dt
dW
Where and
*This equation can be derived from a lower level biophysical formulation. (Castellani et. al. 2001, Shouval et. al. 2002)
The calcium control hypothesis, is a generalization of this equation.
0.2 0.4 0.6 0.8 10
0.25
0.5
0.75
1
Ca ( M)
d p
0.2 0.4 0.6 0.8 10
0.2
0.4
0.6
0.8
1
Ca ( M)
sec -1
the rate function is: has the form
*
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Assumption 2: NMDA receptors are the primary source of calcium influx to spines during synaptic plasticity (Sabatini et. al 2002).
• Voltage dependence of NMDAR (Jahr and Stevens, 1990)
Standard assumptions
Fra
ctio
n o
fop
en N
MD
AR
ICa
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• Ligand binding kinetics – sum of two exponentials with different time constants (Carmignoto and Vicini, 1992)
• Calcium Dynamics- first order ODE
CaiCa
i ICadt
Cad ][
1][
msCa 5020
NR2A+NR2B
0.7
0.5
0.0
In these examples
NMDA receptor kinetics- sum of two exponents
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Pairing Induced Plasticity Voltage clamping postsynaptic neuron while stimulating presynapticaly at 1 Hz.
Examples LTP/LTD curve
WW
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Bi and Poo, 1998
prepost ttt
Spike time dependent plasticity (STDP)
STDP Curve
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prepost ttt
For the calcium control hypothesis to account for STDP it is necessary that:
• For (post-pre) the calcium influx is
higher than at baseline ( )
• For ( pre-post) the calcium influx is
higher than at ( )
0t
0t0t
pd Ca ][
pCa ][
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Axon: output
Action potentials
| || | || |
| | |
| | || | |
Neuron – cell body
Dendrite: input
Synapse
Back propagating action potentials
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Assume a narrow spike (Width 3ms)
Problems:• No difference between baseline and post-pre
• Only a small elevation in Ca for pre-post
Back spike – assume width 3ms
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Assumption 3:The Back Spike has a slow component (long tail).
narrow spike (3ms)
spike with long tail (width 25 ms)
An example of a BPAP recorded by C. Colbert from a hippocampal dendrite (slice, from 180 gm Sprague Dawley rat at 31o C , 150µM from soma)
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Back Spike with long tail (tail width 25ms)
Problems solved •Ca level in post-pre larger than at baseline.
• Larger elevation of Ca in pre-post condition.
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BPAP with wide tail
(ms)
Similar results: Karmarkar and Bunomano, 2002; Abarbanel et. al. 2003;Kitijima and Hara, 2000
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Nishiyama et. al. Nature, 2000 Bi and Poo J. Neurosci. 1998
Wittenberg and Wang, J. Neurosci 2006 Froemke and Dan, Nature 2006
Does the second LTD Window exist?Does the second LTD Window exist?