In rats, destroying a brain area called the PVN makes them eat more and become obese. Giving them ghrelin (a hunger hormone) makes them eat even more, while giving CRH (a stress hormone) cuts their eating, especially in the PVN‑damaged rats. Melanotan‑II, a synthetic peptide often used for skin tanning, normally reduces food intake, but it stops working in rats with PVN damage, suggesting its appetite‑suppressing effect depends on that brain region.

Bilateral lesions of the hypothalamic paraventricular nuclei (PVN) induce hyperphagia and obesity, and ghrelin stimulates appetite in rodents and humans. Conversely, corticotrophin-releasing hormone (CRH) and melanotan-II (MT-II, a synthetic structural homologue of alpha-melanocyte-stimulating hormone, alphaMSH) inhibit feeding behavior. The purpose of the present study was to determine whether these peptides are involved in the hyperphagia and obesity induced by PVN lesions. After bilateral electrolytic lesions of the PVN, rats were given ghrelin intraperitoneally (i. p.), or intracerebroventricular (i. c. v.) infusion of CRH or MT-II. We measured the cumulative food intake (FI) for 4 h after ghrelin injection in rats fed AD LIB, and the changes in FI at 15 min, 30 min, 1 h, and 2 h after infusion of CRH and MT-II in rats fasted for 24 h. Ghrelin significantly increased cumulative FI, with maximal response 3 h and 4 h after injection, and at these times, the FI of PVN-lesioned rats was greater than that of sham-operated rats. CRH significantly decreased FI in all experimental animals, but at 1 h, there was a more powerful inhibitory effect on FI in the PVN-lesioned group than in the sham-operated group. MT-II decreased FI in sham-operated, but not in PVN-lesioned rats. Thus, ghrelin and CRH showed more potent orexigenic and anorectic effects in PVN-lesioned rats, respectively, but MT-II lost its inhibitory action on feeding behavior. These results suggest that the hyperphagia and obesity induced by PVN lesions may be related to an increased orexigenic action of ghrelin due to the destruction of endogenous CRH and alphaMSH receptors.