Developmental tightening of cerebellar cortical synaptic influx-release coupling
04.02.2015
Baur D, Bornschein G, Althof D, Watanabe M, Kulik A, Eilers J, Schmidt H
J Neurosci. 2015;35(5):1858 –1871
Tight coupling between Ca2+ chanels and the sensor for vesicular transmitter release at the presynaptic active zone (AZ) is crucial for high-fidelity transmission. It has been hypothesized that a switch from a loosely coupled to a tightly coupled transmission is a common step in the maturation of CNS synapses. We addressed this hypothesis at a small cortical synapse: parallel fiber-Purkinje cell synapse. EGTA effected release stronger at immature than at mature synapses, while BAPTA was similarly effective in both groups. Analysis of paired-pulse ratios and quantification of release probability (pr) revealed increased facilitation at immature synapses accompained by reduced pr. Cav2.1 channel immunoreactivity was scattered over immature boutons but confined to AZs at mature boutons. Presynaptic Ca2+ signals were quantified with two-photon microscopy and found to be similar between maturation stages. Models indicate looser and less homogenous coupling at immature terminals compared with mature ones. These results demonstrate functionally relevant developmental tightening of influx-release coupling at a single AZ cortical synapse and corroborate developmental tightening of coupling as a prevalent phenomenon in the mammalian brain.
