Objective: The aim of this work was to study the potential involvement of neuropeptide Y (NPY) and orexins in the anorexigenic mechanism of fluoxetine in obese Zucker rats, assessing the effects of chronic fluoxetine treatment on NPY and orexin immunostaining in several hypothalamic regions.
Research methods and procedures: Male obese Zucker (fa/fa) rats were administered fluoxetine (10 mg/kg intraperitoneally) daily for 2 weeks. The control group was administered 0.9% NaCl solution. Carcass composition was assessed using the official methods of the Association of Official Analytical Chemists. To test the potential thermogenic effect of fluoxetine administration, total body oxygen consumption was measured daily for 60 minutes before fluoxetine or saline injection and for 30 minutes after drug or saline injection. Hypothalamic arcuate and paraventricular nuclei, and the lateral hypothalamic area were immunostained for NPY, orexin A, and orexin B. Commercial kits were used for serum determinations.
Results: Chronic fluoxetine administration in obese Zucker rats generated a reduction in body weight gain, food intake, adipocyte size, fat mass, and body protein. A decrease in NPY immunostaining in the paraventricular nucleus, without changes in the arcuate, was observed. However, no changes were observed in the number of neural cells immunostained for orexin A or orexin B in the lateral hypothalamic area.
Discussion: Due to the hyperphagic effect of NPY in the paraventricular nucleus, these results suggest that NPY, but not orexins, could be involved in the anorexigenic effect of fluoxetine in obese Zucker rats.