Facilitation, Biophysical Models

Facilitation is a temporary increase in postsynaptic response to a presynaptic action potential or depolarization induced by a preceding presynaptic depolarization. It is distinguished from longer-term components of activity-dependent synaptic enhancement by its low activation threshold (a pair of action potentials is often sufficient, hence the term paired-pulse facilitation) and short persistence time: facilitated response decays back to initial amplitude within less than a second after the stimulus train. Facilitation is very common in central and peripheral synapses of both vertebrate and invertebrate nervous systems; it is readily observed under conditions of low initial vesicle release probability, but is often occluded by synaptic depression when the initial vesicle release probability is sufficiently high. Biophysical models of facilitation go beyond a simple phenomenological description and often combine a model for presynaptic Ca2+ dynamics with a model of Ca2+ binding to exocytosis sites that trigger vesicle fusion. Detailed Description