OXYTOCIN INHIBITS NONPHASICALLY FIRING SUPRAOPTIC AND PARAVENTRICULARNEURONS IN THE VIRGIN FEMALE RAT

Nonphasically firing activities were recorded from neurons in the supr aoptic (s.o.) and paraventricular (p.v.) nucleus of the virgin female, male, and ovariectomized rat hypothalamic slice preparations. Followi ng bath application of oxytocin (OXT), less than 1.0 X 10(-8) M, 24 (7 5%) of 32 virgin female s.o. neurons showed inhibitory responses and o nly one neuron showed excitatory response. In contrast to virgin femal e, five (63%) of eight male s.o. neurons were excited by OXT applicati on. The same tendency was shown in the p.v. neurons. Among six s.o. ne urons obtained from ovariectomized virgin rats, five neurons increased their firing rate to the application of OXT. After blocking synaptic transmission, the inhibitory responses of virgin s.o. neurons and the excitatory responses of ovariectomized virgin s.o. neurons to applicat ion of OXT were still observed with equal configulations. These findin gs suggest that the responses of nonphasic neurons to OXT may not due to synaptic drives.