Effects of Hindbrain Infusion of an Estrogen Receptor Antagonist on Estrogenic Modulation of Eating Behavior

Estradiol (E₂) inhibits eating behavior in females via activating estrogen receptors (ERs) within the brain. Activation of hindbrain ERαs has been shown to be sufficient to inhibit eating behavioral pattern. To investigate the involvement of hindbrain ERαs in estrogenic control of eating behavior, intracerebroventricular infusion (4th i.c.v.) of an estrogen receptor antagonist, ICI 182780 (ICI), was performed in ovariectmized female rats. Significantly lower daily food intake was observed in rats after estradiol benzoate (EB) injections. The effect of EB on food intake was significantly compromised by 4th i.c.v. infusions of both 4 and 8 nM ICI solutions. The results suggest that hindbrain infusions of ICI can significantly attenuate the inhibitory effect of E₂ on food intake. Importantly, 4th i.c.v. infusions during 12 days exerted no effect per se on eating. Further, there was no difference in the number of ERα immunopositive neurons in the selected hypothalamic nuclei and nucl. tractus solitarius. We conclude that the 4th i.c.v. infusions with ICI attenuated the exogenous estrogenic effect on food intake in ovariectomized rats, and the hindbrain is an important site pro viding estrogenic control of food intake.

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