Dopaminergic modulation of ACTH-induced grooming

ACTH-(1-24)-induced grooming was studied after administration of the peptide into the substantia nigra or intracerebroventricularly (i.c.v.). The modulation of dopamine receptors in neostriatum (with haloperidol and apomorphine) and nucleus accumbens (with 3,4-dihydroxyphenylamino-2-imidazoline hydrochloride; DPI and ergometrine) was investigated. In the nucleus accumbens, the modulatory effects of ergometrine and DPI on ACTH-(1-24)-induced grooming were based on their affinity for dopamine receptors and not on their affinity for adrenoceptors. Intrastriatal application of dopaminergic agents inhibited i.c.v. ACTH-(1-24)-induced excessive grooming, whereas the grooming score was enhanced if ACTH-(1-24) was administered into the substantia nigra. The finding of differential effects of dopaminergic agents on ACTH-induced excessive grooming depending on the route of administration indicate that i.c.v. ACTH-induced excessive grooming is not mediated solely through the substantia nigra. The increase in grooming behavior seen after the intrastriatal administration of dopaminergic agents - when ACTH was injected into the substantia nigra - suggests the involvement of the striato-nigral GABAergic pathway. Local injections of ACTH-(1-24) into the periaqueductal gray also induced excessive grooming. Since a second injection of ACTH-(1-24) into the periaqueductal gray did not lead to a grooming response, irrespective of where the first injection of ACTH-(1-24) was given (i.c.v. into the nigra or via the periaqueductal gray) it is suggested that this structure seems to play a primary role in the induction of excessive grooming. Therefore the modulatory effects of the dopaminergic influence on ACTH-(1-24)-induced grooming may be exerted via the striato-nigro-collicular pathway.