Expression of RFamide-related peptide in the dorsomedial nucleus of hypothalamus during the estrous cycle of rats

Introduction: RFamide-related peptide (RFRP) is believed to act as an inhibitor of gonadotropin releasing hormone (GnRH) secretion. The aim of the present study was to compare the expression pattern of RFRP neurons in the dorsomedial nucleus of hypothalamus (DMH) at different phases of the rat estrous cycle. Methods: The phases of the estrous cycle were determined in 16 adult female Sprague-Dawley rats using vaginal smears. The rats were divided into five groups: proestrus phase (n=4), early estrus phase (n=3), estrus phase (n=3), metestrus phase (n=3) and diestrus phase (n=3). After transcardial perfusion, their brains were removed and fixed. Diencephalon of each rat brain was sectioned, and DMH-containing sections were stained using an immunohistochemical method. The number of RFRP positive neurons in DMH was counted microscopically. Results: Almost all of the neurons expressing RFRP in the DMH were bipolar. Mean and standard error of the number of RFRP neurons during diestrus (45.8±12.6) and estrus phases (44.7±3.6) were greater (P<0.05) than early estrus (18.8±0.8) and proestrus phases (16.2±2.0). Conclusion: Results confirm a regulatory role for RFRP in DMH in the control of rat estrous cycle.