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Workshop: David Sterratt, Chair: Douglas Armstrong

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Synaptically-evoked action potentials and synaptic democracy

What
  • ANC Workshop Talk
When Oct 09, 2012
from 11:00 AM to 12:00 PM
Where IF 4.31/4.33
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This talk, which is a repeat of the one on 3rd July at which very few people were present, will describe joint work with Martine Groen, Rhiannon Meredith and Arjen van Ooyen.

CA1 pyramidal neurons receive hundreds of synaptic inputs at different distances from the soma. Distance-dependent synaptic scaling assists distal and proximal synapses to influence the somatic membrane equally, a phenomenon called ‘‘synaptic democracy’’. How this is established is unclear. The backpropagating action potential (BAP) is hypothesised to provide distance-dependent information to synapses, allowing synaptic strengths to scale accordingly. Experimental measurements show that a BAP evoked by current injection at the soma causes calcium currents in the apical shaft whose amplitudes decay with distance from the soma.
However, in vivo action potentials are not induced by somatic current injection but by synaptic inputs along the dendrites, which creates a different excitable state of the dendrites. We used a compartmental model to measure BAP-induced voltage and calcium signals in spines after Schaffer collateral synapse stimulation. This shows that peak calcium concentration is correlated with soma-synapse distance under a number of suprathreshold stimulation regimes and for a number of dendritic morphologies. Peak calcium levels also predicted the attenuation of the EPSP across the dendritic tree. Furthermore, we show that peak calcium can be used to set up a synaptic democracy in a homeostatic manner, whereby synapses regulate their synaptic strength on the basis of the difference between peak calcium and a uniform target value. We conclude that information derived from synaptically-generated BAPs could indicate synapse location and could subsequently be utilised to implement a synaptic democracy.