Neurohypophysial peptides and the hippocampus. II. Excitation of rat hippocampal neurones by oxytocin and vasopressin applied in vitro.

Neurohypophysial peptides were applied by superfusion to rat hippocampal slices. The peptides, arginine vasopressin, lysine vasopressin, arginine vasotocin and oxytocin, increased the activity of 88% of spontaneously active cells in the CA1 region and induced firing in many neurones that were not spontaneously active. The peptide sensitive cells appeared to be pyramidal cells rather than interneurones. The four peptides were found to be of roughly equivalent potency, producing a reversible, dose-dependent response in the range 10(-9) to 10(-6)M. Most of the cells were tested with more than one peptide and were always found to respond either to all or to none of them. The analogue [7-glycine]oxytocin and the deamino, dicarba derivatives of oxytocin and vasopressin were about as active as the parent compounds, but the oxytocin fragment prolyl-leucyl-glycinamide had no effect, and desglycinamide vasopressin was extremely weak. Responses to the peptides could be blocked by "specific" antagonists. The results suggest that all of the peptides are acting upon a single class of receptor.