Brain stimulation-induced feeding alters regional opioid receptor binding in the rat: an in vivo autoradiographic study.

Although opioid antagonists block feeding behavior in a variety of animal models, the number and identity of CNS regions in which the inferred endogenous opioid activity mediates feeding have yet to be established. Furthermore, it is not yet clear whether the opioid activity that sustains feeding is a concomitant of the appetitive motivational state or the consummatory response. In an effort to address these issues, an in vivo autoradiographic method was used to visualize CNS regional changes in opioid release during appetitively motivating electrical stimulation in the lateral hypothalamus (ESLH) and during consummatory behavior elicited by such stimulation. Regional decreases in [3H]diprenorphine [(3H]Dpr) binding, suggesting increased release of an endogenous opioid peptide, were observed in the medial prefrontal cortex, medial septum, gustatory cortex, zona incerta, mediodorsal thalamus, and hippocampus of rats receiving ESLH. Decreased binding in the latter 4 structures did not appear when animals were allowed to eat during ESLH, suggesting that the inferred opioid release is associated with appetitive behaviors elicited by ESLH which are suppressed when food is available and consummatory behavior predominates. When animals were allowed to eat during ESLH, [3H]Dpr binding in anterior cingulate cortex decreased substantially, suggesting that feeding behavior specifically triggers opioid release in this region. ESLH and feeding were found to increase [3H]Dpr binding in a number of CNS regions. Alternative explanations for increased binding, including inhibition of tonic opioid release, changes in cerebral blood flow, and opioid receptor up-regulation are discussed.