Immunohistochemical Changes in Orexigenic and Anorexigenic Neuropeptides in the Rat Hypothalamus after Capsaicin Administration

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Capsaicin has effects on the adiposity by increasing energy and lipid metabolism, and decreases appetite and fat intake. In the present study, we investigated changes in food intake and body weight after capsaicin treatment. We also observed changes in orexigenic and anorexigenic neuropeptides-agouti-related peptide (AgRP), α-melanocyte-stimulating hormone (α-MSH), adrenocorticotropic hormone (ACTH) and orexin-immunoreactivities in the rat hypothalamus after capsaicin administration. Only one day after capsaicin treatment, the mean food intake was significantly decreased. There was no significant difference in the mean body weight between vehicle- and capsaicin-treated groups. In addition, after capsaicin treatment, numbers of AgRP- and orexin-immunoreactive (⁺) cells were significantly decreased in the arcuate nucleus (ARC) and lateral hypothalamic area, respectively. In contrast, the number of α-MSH⁺ and ACTH⁺ cells in the ARC of the capsaicin-treated rats was higher than in the vehicle-treated rats. These results indicate that capsaicin reduces food intake, not body weight, transiently, and decreases AgRP and orexin immunoreactivities, whereas it increases α-MSH and ACTH immunoreactivities in rat hypothalamic nuclei.