Modulation of hypothalamic galanin gene expression by estrogen in peripubertal rats

Hypothalamic galanin gene expression was investigated during reproductive maturation in peripubertal rats. Rat galanin-like immunoreactivity (rGAL-LI) increased in the median eminence and anterior pituitary during the extended first estrous and diestrous phases relative to anestrous phase female or male rats. In the neurointermediate lobe, rGAL-LI was elevated in first diestrous phase compared to anestrous phase females or males. In a second study, hypothalamic tissue was divided into quadrants for analysis of rat galanin (rGAL) mRNA by Northern blot hybridization. Two days after the injection of pregnant mare's serum gonadotropin (PMSG), rGAL mRNA increased approximately twofold in the paraventricular area and preoptic area quadrants. No effects of PMSG on galanin gene expression were found in medial basal or supraoptic hypothalamic quadrants. Because PMSG acts through the stimulation of ovarian estrogen secretion, these studies conclude that galanin gene expression in dorsal hypothalamic nuclei is under the stimulatory influence of estrogen and suggest that galanin may be a mediator of central ovarian steroid feedback.