Dopamine denervation of frontal cortex or nucleus accumbens does not affect ACTH-induced grooming behaviour

Studies with dopamine (DA) receptor antagonists have implicated brain DA systems in the increased grooming behaviour elicited by intracerebroventricular (i.c.v.) administration of ACTH or exposure to a novel environment. To evaluate the potential contributions of DA terminals innervating frontal cortex and nucleus accumbens, stereotaxically guided injections of 6-hydroxydopamine (6-OHDA) were made into these regions of rat brain following peripheral administration of desmethylimipramine and pargyline. Despite an 88% mean reduction of DA, and 68% mean reduction of noradrenaline in frontal cortex, the amount of grooming behaviour observed either in a novel cage, or after i.c.v. injection of ACTH1-24 was not detectably altered. The lesions also did not affect locomotor activity measured during the scoring of grooming, in an open field, in photocell cages, or in a running wheel, even in the animals most severely depleted of DA. Following nucleus accumbens 6-OHDA infusions, depletions of DA as great as 99% were obtained. Animals with accumbens depletions greater than 90% showed the expected attenuation of amphetamine-stimulated locomotor activity. Nevertheless, they exhibited normal grooming scores in a novel cage, and in response to i.c.v. ACTH1-24. It is concluded that dopaminergic terminals in nucleus accumbens and probably those in frontal cortex are not necessary for the expression of novelty- or ACTH-induced grooming.