Selective involvement of dopamine in the nucleus accumbens in the feeding response elicited by muscimol injection in the nucleus raphe dorsalis of sated rats.

Muscimol injection (100 ng) in the nucleus raphe dorsalis (NRD) caused intense eating in non-food-deprived rats. At a dose (10 micrograms) blocking dopamine mediated responses (examined by increased locomotion or stereotypy caused by systemically injected d-amphetamine), fluphenazine injected in the n. accumbens, but not in the striatum, significantly reduced the eating response elicited by muscimol in the NRD while food intake of deprived rats was not significantly modified by fluphenazine injected in either area. Fluphenazine (20 micrograms) in the striatum reduced eating in both conditions, but the animals showed marked sedation which obviously interfered with the feeding response. Dopamine release and synthesis, measured respectively by 3-methoxytyramine and accumulation of dihydroxyphenylalanine after aromatic amino acid decarboxylase inhibition, were significantly reduced in the n. accumbens, but not in the striatum, of muscimol treated animals. The metabolism of serotonin was reduced in both areas of muscimol treated rats. It is suggested that changes in dopamine receptor sensitivity, together with changes in serotonin function, might be involved in the feeding response caused by muscimol injection in the NRD.