Intracranial estradiol in ovariectomized guinea pigs: effects on ingestive behaviors and body weight.

The present study was undertaken to evaluate the effects of intracranial estradiol stimulation on food intake (FI), water intake (WI), and body weight (BWt) of ovariectomized guinea pigs (GPs). Thirty-five GPs were implanted with bilateral guide cannulae aimed at either the ventromedial hypothalamus, paraventricular nucleus (PVN), or preoptic area and then were stimulated unilaterally with cholesterol and estradiol 17-beta, yielding a total of 70 stimulation sites. Across all GPs, estradiol implants significantly reduced FI, WI and BWt relative to implants of cholesterol. The possibility that the behavioral changes observed were due to the peripheral rather than central effects of the implants was evaluated by comparing the results of stimulations which produced vaginal membrane rupture (VMR) to the results of cases without VMR. There were no significant differences between these groups on any of the dependent variables studied, indicating that peripheral estradiol sufficient to induce VMR was neither necessary nor sufficient to account for the behavioral changes. Histological analysis revealed that implants in the ventromedial-arcuate region (VM/ARC) and PVN significantly lowered FI and BWt, with the effects being greatest in the PVN. Placements in other areas, on the average, did not significantly suppress FI or BWt. The effect of central estradiol on WI was more diffuse. No significant effect of implant location was found for the estrogenic suppression of drinking. These findings are the first demonstration that estradiol applied to particular brain areas can lower FI, WI, and BWt of ovariectomized GPs.(ABSTRACT TRUNCATED AT 250 WORDS)