On the transmitter function of 5‐hydroxytryptamine at excitatory and inhibitory monosynaptic junctions

Abstract
1. Two symmetrical giant neurones located in the cerebral ganglion of Aplysia californica contain 4-6 p-mole 5-hydroxytryptamine (5-HT) and are able to synthesize it (Weinreich, McCaman, McCaman & Vaughn, 1973; Eisenstadt, Goldman, Kandel, Koike, Koester & Schwartz, 1973). Stimulation of each of these neurones evokes excitatory and inhibitory potentials in various cells of the ipsilateral buccal ganglion. In nine buccal neurones it evokes excitatory potentials, in other three, `classical' inhibitory potentials and in one neurone an `atypical' inhibitory potential.