Interaction Between Galanin-Like Peptide (GALP) and Estradiol in the Control of Reproduction and Energy Homeostasis in Female Rats

Galanin-like peptide (GALP) is a known hypothalamic mediator between energy states and reproduction. It has been suggested that sex differences may exist in the actions of GALP and these may be due to GALP-estradiol interactions. The purpose of these studies was to examine GALP’s effect on food intake and body weight, metabolic rate and body temperature, sex behaviors, leutinizing hormone (LH) and growth hormone (GH) secretion. We also examined GALP and estrogen receptor co-localization and GALP-induced fos activation in estrogen receptor-immunoreactive neurons of the hypothalamus. To accomplish these purposes, we ovariectomized adult female rats and implanted cannulas in the lateral ventricles that were then used for intracerebroventricular (ICV) injections. Each animal received estradiol (EB) replacement therapy in two groups: EB or no EB (Blank). We found that there were significant estradiol-dependant effects of GALP on food intake (p\u3c0.05), hormone secretions (p\u3c0.000) and body temperature (p\u3c0.05), but not on other measures. As has been shown in male rats, GALP stimulates food intake over the first 30 min after ICV injection in estradiol-treated rats but not Blank rats. ICV GALP significantly (p \u3c 0.01) decreased plasma LH levels in Blank rats, but significantly (p \u3c 0.05) increased LH in EB rats. Histological analyses revealed that there are significantly (p \u3c 0.05) fewer GALP-ir cell bodies in the arcuate (Arc) nucleus of EB rats compared to Blank rats. Furthermore, we found that ERα- and GALP-immunoreactivity are not co-localized in the hypothalamus. Finally, we demonstrate that GALP-induced fos-immunoreactivity is significantly (p \u3c 0.05) increased in the mPOA and Arc, but decreased in the VMN. These findings suggest that there is a GALP-estradiol interaction in the hypothalamic targets of female rats and that estradiol apparently regulates GALP neurons indirectly. These data have important implications for sex differences in GALP’s actions