MILLAR, A.G.; ZUCKER, R.S.; CHARLTON, M.P.; ATWOOD, H.L.; University of Toronto; University of California, Berkeley; University of Toronto; University of Toronto: Cellular Mechanisms of Synaptic Differentiation in Crustacean Motor Neurons

We are examining mechanisms governing transmitter release efficacy at two vastly different crustacean motor neurons. Phasic nerve terminals release 100-1000 fold transmitter per action potential than tonic nerve terminals, although they share the same postsynaptic muscle cells. We hypothesized that the transmitter release mechanism of phasic neurons possesses a greater sensitivity to calcium, and thus produces a greater amount of tranmsitter release. We tested this using photoactivation of “caged calcium” while recording transmitter release from individual boutons. We found that phasic terminals exhibit a lower calcium threshold at which release begins to occur, and release transmitter at a higher rate for a given calcium concentration. These preliminary results support our hypothesis that transmitter release of phasic neurons is more sensitive to calcium entry than that of tonic neurons.