Ventral tegmental injections of morphine but not U-50,488H enhance feeding in food-deprived rats.

Food-deprived rats received microinjections of the preferential mu opiate morphine or the selective kappa opiate U-50,488H (0.1, 1 and 10 nmol) into the ventral tegmental area (VTA). Meals were divided into discrete segments so that repeated measures of the speed of eating and the latency to initiate eating could be obtained. Morphine produced a dose-dependent increase in the speed of eating. Injections of saline or U-50,488H into the VTA or injections of morphine dorsal to the VTA were ineffective. Neither morphine nor U-50,488H had a significant effect on the latency to initiate feeding. These data suggest that mu but not kappa opioid receptors in the VTA are involved in the regulation of feeding in food-deprived rats.