Effects of chronic food restriction on mu and kappa opioid binding in rat forebrain: a quantitative autoradiographic study.

It was previously observed that chronic food restriction lowers the threshold for lateral hypothalamic self-stimulation in a manner that is reversible by mu- and kappa-selective opioid antagonists. The present quantitative autoradiographic study was designed to investigate whether chronic food restriction alters regional mu and kappa opioid binding in brain. [3H]DAGO (mu) and mu/delta blocked [3H]BMZ (kappa) binding were analyzed in 34 brain regions from the medial prefrontal cortex to posterior hypothalamus. Significant reductions in mu binding were observed in caudal portions of the medial and lateral habenula, and the basolateral and basomedial nuclei of the amygdala. kappa binding was similarly reduced in medial habenula. Large increases in kappa binding were observed in the bed nucleus of the stria terminalis, ventral pallidum, and medial preoptic area. The possible involvement of these changes in the sensitization of reward by food restriction is discussed.