Opposite effects of oxytocin and vasopressin on avoidance behaviour and hippocampal theta rhythm in the rat

Intracerebroventricular administration of oxytocin and argmine-8-vasopressin (AVP) immediately after a single learning trial resulted in opposite effects on retention of passive avoidance behaviour. Passive avoidance behaviour was attenuated by oxytocin and facilitated by AVP in a dosedependent manner. Reverse effects were found after neutralizing the centrally circulating oxytocin and vasopressin by intraventricular injection of specific antiserum to these peptides. Administration of oxytocin into a lateral ventricle resulted in a decrease of the peak frequency of hippocampal theta rhythm generated during paradoxical sleep episodes. Conversely, oxytocin antiserum increased the incidence of higher frequencies in the theta rhythm. Peripheral administration of oxytocin mimicked the effect of AVP on extinction of pole-jumping avoidance behaviour. Resistance to extinction rather than facilitation of extinction was observed when higher doses of oxytocin were given. Passive avoidance behaviour appeared to be either facilitated or attenuated after subcutaneous oxytocin administration. It is concluded that centrally released oxytocin may be a naturally occurring amnesic neuropeptide.