Fluoxetine alters mu opiod receptor expression in obese Zucker rat hypothalamus

The aim of the present work was to study the potential involvement of hypothalamic opiod system in the anorectic machanism of fluoxetine in obese Zucker rats, assessing the effects of chronic fluoxetine treatment on mu opiod receptor immunostaining in several hypothalamic regions. Male obese Zucker (fa/fa) rats were administered with fluoxetine (10 mg/kg; i.p.) daily for two weeks. The control group was given 0.9% NaCl solution. Regional hypothalamic immunostaining for mu opiod receptor was carried out. Fluoxetine administration increased the numbers of neural cells positively immunostained for mu opiod receptor in the hypothalamic, paraventricular, arcuate, ventromedial and suprachiasmatic nuclei, as well as the medial preoptic and lateral hypothalamic areas, without changed in dorsomedial, supraoptic and periventricular nuclei, and the lateral preoptic area. These results suggest the involvement of hypothalamic opiod system in fluoxetine-induced anorexia in obese Zucker rats. Increased regional hypothalamic density of neural cells expressing mu opiod receptors after fluoxetine treatment could be a compensatory mechanism against a possible reduction in opiodergic tone.