Contrasting effects of neurohypophysial peptides on pyramidal and non-pyramidal neurones in the rat hippocampus

Oxytocin and vasopressin increased the rate of firing of a class of presumed non-pyramidal neurones located in the CA1 area of rat hippocampal slices. This excitatory effect persisted in conditions of synaptic uncoupling. In contrast, pyramidal neurones were either unaffected by neurohypophysial peptides or showed one or several of the following effects: (a) a decrease in firing rate in cells which were spontaneously active; (b) a slight membrane hyperpolarization; and (c) an increase in the rate of occurrence os spontaneous inhibitory postsynaptic potentials. We therefore propose that oxytocin and vasopressin excite directly a class of non-pyramidal inhibitory interneurones, whereas their observed effect on pyramidal neurones is indirect and inhibitory.