Influence of the ovarian cycle and estradiol on binge eating evoked in female rats by food restriction followed by frustration stress.

Eating disorders show marked gender differences (Klump et al 2008 Psych Med 38:1749-57) and several epidemiologic studies suggest that binge eating episodes are more common in females than in males. To further investigate the mechanisms underlying this sex difference, we used an animal model first described by Cifani et al (2009 Psychopharm 204:113-125), in which binge-eating is evoked in female rats by 3 cycles of food restriction followed by frustration stress (15 min exposure to the sight of the palatable food). We aimed to determine whether binge eating behavior (1) varies across the estrus cycle and (2) is influenced by estradiol (E2) in ovariectomized (OVX) rats. Finally, using immunocytochemistry, we quantified the activation of extracellular signal regulated kinase (ERK) signaling pathway in OVX rats treated with E2 or oil, in basolateral (BLA) and the central (CeA) amygdala, paraventricular nucleus of hypothalamus (PVN) and arcuate nucleus (ARC). Restricted and stressed rats in estrus and OVX rats treated with E2 did not show binge eating behavior in comparison to the control non-restricted and non-stressed rats. The lack of binge eating behavior in estrous rats was accompanied by a significant decrease in ERK phosphorylation in ARC, PVN and in the CeA, but not in BLA, in comparison to non-estrous rats and to non-restricted and non-stressed animals. Our findings show that binge eating does not occur during the estrous phase. Because this was recapitulated in OVX rats treated with E2, they suggest that the inhibitory effect of E2 on eating is partly responsible for the lack of bingeing. These results are consistent with reports in women with bulimia nervosa (Edler et al 2007 Psych Med, 37:131-141) and extend our previous findings and increase the validity of our model, that can be used in translational studies of the mechanism of binge eating behavior.