The inhibitory GABAergic influence on striatal serotonergic neurons depends upon the habenulo-raphe pathways.

Bilateral lesion of the habenular nuclei by electrocoagulation or by local ibotenate injection antagonized the ability of the GABA agonist agents progabide and depamide (given systemically) or of GABA (applied locally into the dorsal raphé) to diminish 5-HTP accumulation in the rat striatum. Similarly, cessation of impulse flow in the habenulo-raphé tract prevented the reduction of striatal serotonin synthesis caused by systemic administration of the GABA agonist drugs. These data suggest that the GABAergic inhibition of striatal serotonergic transmission exerted in the dorsal raphé depends upon the habenulo-raphé pathways.