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TRANSCRIPT
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Modeling Synaptic Ca2+ Dynamics in
Hippocampal Dendritic Spines
Pablo d’Alcantara, PhD
Department of NeurophysiologyNational Institute for Medical Research
Columbus, 26 January 2004 London, United Kingdom
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• Introduction of Hippocampus and Plasticity
• Methods and Results
• Modeling Ca2+ Dynamics
• Discussion
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• Introduction of Hippocampus and Plasticity
• Methods and Results
• Modeling Ca2+ Dynamics
• Discussion
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The Hippocampus
• Implication in Memory
• Change of [Ca2+] in dendritic spines induces synaptic plasticity
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Selective plasticity induction in CA1
by specific patterns of Ca2+ elevation
via flash photolysis of caged Ca2+
Yang et al., J. Neurophysiol., 1999
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Model describing the regulation of
synaptic plasticity by postsynaptic
Ca2+
d’Alcantara et al., Eur. J. Neurosci. 2003
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While the mechanisms induced by [Ca2+]
changes are being elucidated, how the Ca2+
dynamics is governed remains mysterious.
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• Introduction of Hippocampus and Plasticity
• Methods and Results
• Modeling Ca2+ Dynamics
• Discussion
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10 µm
1 µm
Confocal Laser Scanning Microscopy of
CA1 Hippocampal Dendritic Spines in
rat organotypic slices
Line Scan
x
y
t
y
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Dendritic Ca2+
transient triggered
by
Backpropagating
Action PotentialBAP
AP
t
y
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Confocal fluorescence imaging allows us to measure
properties of Ca2+ channels and Ca2+ buffering:
Ca2+ Saturation of Dye Measure of [Ca2+](Maravall et al., Biophys. J. 2000)
Optical Fluctuation Analysis Measure of VSCC N and po
(Sabatini and Svoboda, Nature 2000)
Experiments with Different [Dye] Ca2+ Buffer Capacity(Neher and Augustine, J. Physiol. 1992)
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Saturation of the
intracellular Ca2+
indicator by
membrane
depolarisation
Patch Clamp
Depolarisation
Dye Saturation
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Calculation of
[Ca2+] with
Normalised Fluorescence
[Ca2+]
[Ca2+] = 215nM - 3.7M [Ca2+]0 = 81 ± 2 nM
[Ca2+] = Kd . (F - Fmin) / (Fmax - F)
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Analysis of Ca2+ channels in spines by
Optical Fluctuation Analysis
50 x
Single Spine BAP-induced Fluorescence
Mean BAP-induced Fluorescence
Variance on BAP-induced Fluorescence
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CVF,[Ca] CVopen
N . po = (1- po) / CV2F,[Ca]
and
Failure Probability P(0) = (1- po)N
System of 2 Equations with N and po
Calculation of N and po from the
optical fluctuation analysis with
Coefficients of Variation of [Ca2+] and
Nopen
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Experiments with Different Dye
Concentration:15 M OGB1
= 20 ms
30 M OGB1
= 36 ms
Calculation of Dye
Buffering Capacity D:
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Measurement of Ca2+ Buffer Capacity E
Fit with equation of
in function of E and
D:
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• Introduction of Hippocampus and Plasticity
• Methods and Results
• Modeling Ca2+ Dynamics
• Discussion
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IVSCC = iVSCC . N . po . (Vm - ECa2+)
JPump = ( [Ca2+]0 - [Ca2+] ) / Ca2+
[Ca2+] + [Buffer]free [Buffer]Bound
Behaviour of Ca2+ current, Ca2+ pump
and Ca2+ buffering
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[Buffer] = 100 M
Kd Buffer =0.5 M
[Ca2+]0 = 60 nM
[Ca2+]ext = 2 mM
Spine Volume = 0.1 fl
(Ca2+)0 = 20 ms
iVSCC = 15 pS
N = 12
po = 60%
Parameters used during modeling
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According to our
data and
previously
published data,
simulation of
Ca2+ transients
predicts a huge
concentration
increase
Simulation of [Ca2+] during a BAP
Simulation a BAP
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• Introduction of Hippocampus and Plasticity
• Methods and Results
• Modeling Ca2+ Dynamics
• Discussion
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Additional Ca2+ buffering could
explain lower [Ca2+] increases
Simulation of [Ca2+] during a BAP with 10x more buffer
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Simulation of Ca2+ dynamics in a spine
with spatiotemporal diffusion shows a
high local increase of [Ca2+]
Max (M)
Min (M)
Sharp et al., 1993Simulation made in Virtual Cell
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In this work we’ve shown how to measure
[Ca2+], NVSCC, po,VSCC and E to build a
physiology-based model of Ca2+ dynamics
in dendritic spines.
We find that additional Ca2+ buffer and
spatiotemporal diffusion of Ca2+ can
explain experimental observations.
Conclusions
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NIMR, London• Dr. Donald Dixon (Experimentalist) • Dr. Reza Zamani (Experimentalist)
• Thomas Stackhouse (Technician)
Acknowledgeme
ntsDalhousie University, Halifax• Prof. Alan Fine (Supervisor)
NRCAM, Connecticut• Prof. Leslie Loew (Virtual Cell) • Dr. Jim Schaff (Virtual Cell)
• Dr. Boris Slepchenko (Virtual Cell)
Emory University, Atlanta• Prof. George Hentschel (Modeling)