Estrogen excites oxytocinergic, but not vasopressinergic cells in the paraventricular nucleus of female rat hypothalamus.

Extracellular antidromic potentials were recorded from the paraventricular nucleus of the ovariectomized female rat hypothalamus following electrical stimulation of the neurohypophysis. Effects of estrogen-treatment were investigated after classifying the antidromically identified cells into tonically-firing, phasically-firing, or silent groups according to their patterns of spontaneous discharge. Estrogen significantly decreased the antidromic activation threshold and shortened the refractory period as well as the antidromic spike latency in the tonic-firing cells. We suggest that estrogen selectively and directly excited the tonically-firing, presumably oxytocinergic cells.