Soma potential of an interneurone controls transmitter release in a monosynaptic pathway in Aplysia

Abstract

IN the molluscan nervous system, action potentials and synaptic potentials invade the soma so that its potential reflects intrinsically and extrinsically initiated electrical activity¹. However, its functions related to the electrical activity of the neurone are unknown. Recently, it was shown that the soma potentials of arthropod interneurones controlled transmitter release on to motoneurones^2,3. In Aplysia, soma potentials of some interneurones have been observed to have an effect on the size of post synaptic potentials (p.s.ps) in the cell with which they synapse; the possibility that p.s.ps were affected by changes in temporal properties of the spike induced by the soma potential⁴ or electronic coupling between cells⁹ was not excluded. We investigated this observation and report here that soma potentials of one interneurone regulate the release of transmitter, possibly by a direct effect on its terminals. Release can be sustained beyond the normal time course of the p.s.p. by prolonged depolarisation of the soma.