Different effect of oxytocin on membrane potential of supraoptic oxytocin neurons in virgin female and male rats in vitro.

The effects of oxytocin on membrane potential were investigated in the supraoptic nucleus (SON) neurons of rats using whole-cell patch-clamp technique. SON neurons were electrophysiologically identified as oxytocin (OT) or vasopressin (VP) neurons. Application of OT (1 x 10[-7] M) hyperpolarized membrane potentials of OT neurons in virgin female rats but depolarized membrane potentials of putative OT neurons in male rats. The membrane conductance of SON neurons were increased by treatment of OT in both sexes, suggesting that OT increased the opening of channels on SON neurons. The reversal potential of OT neurons in virgin female rats and putative OT neurons in male rats under OT effective conditions were -66 +/- 1 mV (n = 4) and -46 +/- 2 mV (n = 5), respectively. These data suggest that OT released within the SON suppresses the activity of OT neurons in virgin female rats while it excites putative OT neurons in male rats.