Striatal regulation of morphine-induced hyperphagia: an anatomical mapping study.

Both systemic and intracranial administration of morphine can result in spontaneous feeding in non-deprived rats. The present investigation was conducted to examine the involvement of the striatum in this phenomenon. Morphine sulfate (0, 0.5, 1.0, 5.0, 10.0, and 20.0 micrograms/0.5 microliters) was microinjected into five discrete striatal subregions in non-deprived rats: the nucleus accumbens, the ventromedial striatum, the ventrolateral striatum, the anterior dorsal striatum, and the posterior dorsal striatum. Feeding, drinking, locomotion, rearing, and food intake were measured over 4 h after infusion. Results indicate that the striatum is a heterogeneous structure with regard to the regulation of opiate-induced feeding behavior and locomotor activity. Morphine infusion into anteroventromedial regions including the nucleus accumbens resulted in a marked hyperphagia that was generally delayed in onset; much smaller increases or no change in feeding occurred after administration into more dorsal, lateral and posterior areas. It is hypothesized that there may exist within the striatum an anatomical gradient that is most sensitive to opiate-induced feeding within the anteroventromedial sector. Since this area has extensive connections with other brain sites sensitive to opiate-induced feeding, it may be a critical part of an opiatergic feeding system within the brain. In addition, a possible role for the anteroventromedial striatum in compulsive feeding and bulimia is discussed.