Interactions between serotonergic and dopaminergic systems in rat brain demonstrated by small unilateral lesions of the raphe nuclei.

Unilateral lesions in the dorsal raphe (DR) resulted in decreased concentrations of 5-hydroxytryptamine and 5-hydroxyindoleacetic acid and increases in homovanillic acid and 3,4-dihydroxyphenylacetic acid in the ipsilateral substantia nigra (SN). Unilateral lesions in the median raphe (MR) caused similar biochemical changes in the corpus striatim (CS). Apomorphine and amphetamine caused turning behaviour in the lesiond animals which was ipsiversive after DR lesions but contraversive after MR damage. The animals turned in the opposite direction to that induced by these drugs after treatment with 5-methoxy-N,N-dimethyltryptamine and in the same direction after treatment with phenelzine plus L-tryptophan. All the drug-induced turning behaviour was blocked by haloperidol. The turning induced by 5-methoxy-N,N-dimethyltryptamine and in the same direction after treatment with phenelzine plus L-tryptophan. All the drug-induced turning behaviour was blocked by haloperidol. The turning induced by 5-methoxy-N,N-dimethyltryptamine was blocked by methysergide. This work suggested that the DR and MR nuclei send projections differentially to SN and CS respectively. These projections may exert a tonically active inhibition of dopamine metabolism in their respective terminal areas.