RF-amide Related Peptide-3 (RFRP-3) Neurons do not Mediate Leptin Actions (#42)
Leptin, an adipose-derived anorectic hormone, has several hypothalamic actions including a permissive regulation of fertility. Leptin sends information to the hypothalamic gonadotrophin-realasing hormone (GnRH) neuronal system regarding the body’s metabolic status. Our lab has shown that leptin does not directly act on GnRH neurons (Endocrinology 150:2805), and the indirect mechanisms by which leptin acts upon GnRH remain unclear. When the hypothalamic leptin receptor is stimulated, signal transducer and activator of transcription-3 (STAT-3) is phosphorylated mainly in the regions of the arcuate nucleus, ventral premamillary nucleus, medial preoptic area, and to a lesser extent the dorsal medial hypothalamus (DMH). RFRP-3 neurons are located in the DMH, and have been proven to directly act on GnRH neurons to inhibit reproduction. We tested whether leptin could indirectly act via RFRP-3 neurons to regulate GnRH activity. To examine this, we used two approaches. First, the presence of leptin-induced STAT-3 in RFRP-3 neurons was examined in female and male wild type C57BL/6J mice. Mice were given an acute leptin challenge (1 mg/kg) two hours prior to perfusion, followed by dual label immunohistochemistry for RFRP-3 and pSTAT-3. Results showed that although being present and in close proximity in the DMH, there was no colocalization between RFRP-3 neurons and pSTAT-3. Lastly, qPCR was used to compare RFRP mRNA levels between leptin-deficient ob/ob mice and wild type mice of both sexes. There was no significant difference between the levels of RFRP mRNA in wild type versus ob/ob males and females. Collectively, these results show that although it is able to act in the same region, leptin does not act on RFRP-3 neurons to modulate fertility.