Estrogen Reduces Cholecystokinin-Induced c-Fos Expression in the Rat Brain

Recent reports have shown that estradiol increases the hypophagic effect of exogenous cholecystokinin-octapeptide (CCK). CCK is known to increase the expression of Fos, a marker of neuronal activation, in specific medullary and hypothalamic nuclei. The present experiment tested the hypothesis that as estradiol enhances the behavioral effects of CCK, there is a parallel amplification of CCK-induced Fos expression. Instead, estradiol pretreatment reduced the level of CCK-induced Fos expression in the nucleus of the solitary tract (NTS) and in the medial parvocellular region of the hypothalamic paraventricular nucleus (PVN). The number of Fos-containing cells in the supraoptic nucleus and other regions of the PVN were not affected by estradiol pretreatment. The results are consistent with the hypothesis that the NTS and/or the PVN may mediate the estrogen-induced increased sensitivity to peripheral inhibitory signals in the control of food intake.