This experiment tested the effect of risperidone on the sympathetic and thermogenic effects induced by orexin A. The firing rates of sympathetic nerves to interscapular brown adipose tissue (IBAT), along with IBAT and colon temperatures and heart rate were monitored in urethane-anesthetized male Sprague-Dawley rats before an injection of orexin A (1.5 nmol) into the lateral cerebral ventricle and over a period of 2 hours after the injection. The same variables were monitored in rats with an intraperitoneal administration of risperidone (50 mg/kg bw), injected 30 min before the orexin administration. The results show that orexin A increases the sympathetic firing rate, IBAT, colonic temperatures and heart rate. This increase is enhanced by the injection of risperidone. These findings suggest that risperidone elevates the responses due to orexin, probably through an involvement of serotoninergic and dopaminergic pathways, which are affected by risperidone. Furthermore, we suggested the name "hyperthermine A" as additional denomination of "orexin A" by considering the strong influence of this neuropeptide on body temperature.

Department of Experimental Medicine Section of Human Physiology 2nd University of Naples via Costantinopoli 16 80138 Naples Italy

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