Model-based prediction of maximum pool size in the ribbon synapse

Authors

Caitlyn M. Parmelee, University of Nebraska-Lincoln
Matthew Van Hook, University of Nebraska Medical Center
Wallace B. Thoreson, University of Nebraska Medical Center
Carina Curto, The Pennsylvania State University

Date of this Version

2015

Citation

Parmelee et al. BMC Neuroscience 2015, 16(Suppl 1):P41

Comments

© 2015 Parmelee et al. This is an Open Access article distributed under the terms of the Creative Commons Attribution License

Abstract

The synaptic ribbon is a specialized structure in photoreceptor neurons that tethers vesicles prior to release (Figure 1A). When a cell is stimulated, vesicles are released from the ribbon and later replenished from the population of mobile vesicles in the synaptic terminal. A train of depolarizing pulses causes the ribbon to alternate between periods of release (lasting Δt = 25 ms) and replenishment (lasting T = 50ms), which occur on estimated timescales of τ_r = 5 ms (for release) and τ_a = 815ms (for replenishment). After the first few pulses, the system approaches a limit cycle, and the amount of vesicles released on each pulse converges to a limiting value, R (Figure 1B). This can be used to determine the maximum available pool size on the ribbon, A. The standard method for estimating A is to measure the rate of replenishment in the limit, and then back-extrapolate from the cumulative release plot to obtain the available pool size at the start of the pulse train [1]. When comparing pulse trains of different strengths, this method yields substantially different values for A, a somewhat paradoxical result. Back-extrapolation assumes, however, that the replenishment rate is constant, even though it is thought to be proportional to the available space on the ribbon [2].