Effect of intranigral administration of 6-hydroxydopamine and 5,7-dihydroxytryptamine on rat brain tryptamine

Earlier experiments have shown that unilateral electrolytic lesions of the substantia nigra result in significant reductions in the rate of accumulation of rat striatal tryptamine. For elucidation of the type of neuronal degeneration that is associated with tryptamine depletion, the effects of intranigral injections of 6-hydroxydopamine or 5,7-dihydroxytryptamine, which would affect, respectively, dopamine- or indoleamine-containing neurons, have been assessed. Nigral 6-hydroxydopamine lesions resulted in an ipsilateral reduction in the rate of accumulation of striatal tryptamine, but no changes were observed after nigral injections of 5,7-dihydroxytryptamine. The present results suggest that decreases in the pargyline-induced accumulation of striatal tryptamine may be associated with lesions of the nigral dopamine-containing cell bodies. Alternatively, there may exist specific tryptamine-containing neurons that are damaged by 6-hydroxytryptamine and unaffected by 5,7-dihydroxytryptamine.