The effect of ovariectomy on the responsiveness of preoptic-septal neurons to microelectrophoresed estrogen.

Extracellular potentials were recorded from medical preoptic-septal (MPOA-S) neurons in 2-week and 3--4 month ovariectomized rats, and the effects of microelectrophoresed 17beta-estradiol hemisuccinate (17betaE2S), acetylcholine (Ach), cortisol hemisuccinate (CS) and glutamate (Glut) were studied. 17betaE2S failed to produce changes in the firing rate of the majority of MPOA-S neurons tested, but Ach excited 48% of these neurons. MPOA-S neurons showed very little response to either Glut or CS. Previous findings from this laboratory have demonstrated that MPOA-S neurons recorded in 4-day cyclic female rats will respond to 17betaE2S. Therefore, the present results suggest that the ovarian steroids are necessary for maintaining this electrical sensitivity. Also, the involvement of a specific membrane or cytoplasmic receptor is discussed.