Serotonergic basis of reward in median raphé of the rat.

Rats were trained to self-stimulate simultaneously in the ventromedian tegmentum (VMT) and the median raphe (MR) by pressing two independent bars. Bar-pressing rates for VMT self-stimulation (SS) were increased following methamphetamine and decreased following alpha-methyl-para-tyrosine while no appreciable effects were observed on SS in the MR. On the other hand, MR SS was specifically decreased following para-chlorophenylalanine. The above results taken together support the hypothesis that SS in the MR is due to the stimulation of serotonergic neuronal elements.