VASOPRESSIN EFFECTS ON HIPPOCAMPAL SLICES OF RATS AFTER CONDITIONING

Vasopressin effects were compared in hippocampal slices of control and conditioned rats. Continuous presentation both of paired and unpaired conditioned and unconditioned stimuli induced an increase in sensitiv ity of hippocampal neurons to vasopressin. This effect consisted in a complex biphasic reaction (excitatory-inhibitory modulation of populat ion spike amplitude) to peptide application similar to the reaction of the control slices to the increased peptide concentration. The excita tory increased with the number of stimuli presentations and did not de pend on the factor of learning. The inhibitory phase increased to a gr eater extent with the number of paired stimulations. It is suggested t hat the enhancement of depression by vasopressin in the trained animal s in comparison with the active control most probably results from int racellular Ca2+ accumulation during conditioning.