Other substances may be intermediaries in the signal transduction pathway between leptin and GnRH release. Neurons containing products of the proopiomelanocortin (POMC) gene (e.g., (3-endorphin, adrenocorticotropic hormone) make direct synaptic contacts with GnRH-containing neurons, and are found in the Arc, a region of high expression of Ob-R mRNA. Using double-label in situ hybridization, we have demonstrated a high coincidence of expression of both POMC and Ob-R mRNAs in the Arc of both rats and monkeys (Fig. 2B), while Hakims-son et al. have shown colocalization of Ob-R and adrenocorticotropic hormone immunoreactivity in the Arc of the rat. antibiotics levaquin
Does this coexpression reflect an actual ability of leptin to modify POMC signaling in the brain? We tested this hypothesis by comparing levels of POMC mRNA in wild-type and ob/ob mice. POMC gene expression in untreated ob/ob mice was approximately 50-70% of that found in wild-type animals throughout the Arc and retro-chiasmatic area, whereas leptin-treated ob/ob mice showed POMC mRNA expression restored to levels of wild-type mice. Regulation of POMC gene expression by leptin in ob/ob mice has been confirmed by others, who have also documented a reduction of POMC mRNA in fasted rats and mice, which are presumably hypoleptinemic.