Butorphanol (BT), a mixed κ- and μ-opioid receptor agonist, induces vigorous food intake in rats. Peripheral injection of BT seems to increase food intake more effectively than intracerebroventricular administration. To further elucidate the nature of BT's influence on consummatory behavior, we examined which feeding-related brain areas exhibit increased c-Fos immunoreactivity (IR) following subcutaneous injection of 4 mg/kg body weight BT, a dose known to induce a maximal orexigenic response. We also evaluated whether direct administration of BT into the forebrain regions activated by peripheral BT injection affects food intake. Peripheral BT administration induced c-Fos-IR in the hypothalamic paraventricular nucleus (PVN), central nucleus of the amygdala (CeA), and nucleus of the solitary tract (NTS). However, 0.1-30 μg BT infused into the CeA, failed to increase food intake 1, 2, and 4 h after injection. Only the highest dose of BT (30 μg) injected into the PVN increased feeding. These results suggest that the PVN, CeA, and NTS mediate the effects of peripherally-injected BT. The PVN or CeA are probably not the main target sites of immediate BT action.
Bibliographical noteFunding Information:
This research was supported by the General Research Funds of the Department of Veterans Affairs, NIDA DA-03999 and P30-DK-50456. The authors thank Dr James Pomonis for his technical assistance.
Copyright 2007 Elsevier B.V., All rights reserved.
- Food intake
- Nucleus of the solitary tract
- Paraventricular nucleus
- c-fos immunoreactivity