The Effects of Ovariectomy on the Responsiveness of Preoptic-Septal Neurons to Microelectrophoresed Estrogen

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Abstract
Extracellular potentials were recorded from medial preoptic-septal (MPOA-S) neurons in 2-week and 3–4 month ovariectomized rats, and the effects of microelectrophoresed l7β-estradiol hemisuccinate (17βE2S), acetylcholine (Ach), cortisol hemisuccinate (CS) and glutamate (Glut) were studied. 17βE2S 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 17βE2S. 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.