ΠDevelopment/Plasticity/Repair Phenotypes of Hippocampal and Hypothalamic Progenitors

Calcium entry into nerve terminals is generally considered one of the most reliable aspects of synaptic transmission, although the probability of transmitter release at excitatory synapses often is low. Because high concentrations of calcium are required for release, free calcium must be high at active zones. However, the small size of most active zones has made it difficult to assess calcium levels at subactive zone resolution. This week, Wachman et al., taking advantage of the large size of frog neuromuscular junction (NMJ) active zones, took 1 msec snapshots of calcium influx across the active zone. Blocking some of the N-type calcium channels with -conotoxin reduced the number but not the intensity of calcium transients detected by Calcium Green-1. The authors conclude that only very few or perhaps even single calcium channels mediate calcium entry at the 30 or so release sites within an active zone, and that calcium channels at this synapse have a low probability of opening. It seems that, at least for the NMJ, you can make a highly reliable synapse if you use enough unreliable components.