Behavioural and neurochemical effects of cholinergic and dopaminergic agonists administered into the accumbal core and shell in rats

The first goal of this study was to investigate whether turning behaviour e licited by unilateral injections of the cholinergic agonist carbachol into the shell of the nucleus accumbens differs from that elicited by similar in jections into: the core of this nucleus, and to compare the behavioural eff ects with the known effects of such injections of the mixture of the dopami ne D-1 and D-2 receptor agonists SKF 38393 (5 mu g) and quinpirole (10 mu g ). The second goal was to investigate whether these injections of carbachol produce neurochemical alterations in the ventrolateral striatum that diffe r from similar injections of the mixture of the dopamine D-1 and D-2 recept or agonists into these brain regions. Injections of carbachol into the shel l produced predominantly (a) contralateral circling marked by normal steppi ng and running in wide circles during the initial 50 min and (b) postural a symmetry during the following 75 min; similar injections into the core prod uced (a) contralateral pivoting, namely pathological head-to-tail turning m arked by abnormal hindlimb stepping during the initial 50 min and (b) postu ral asymmetry during the next 75 min. The postural asymmetry seen after the carbachol injections was closely associated with the drug-induced increase in the dopamine release measured by microdialysis in the ipsilateral stria tum. Injections of the mixture of dopamine agonists into the shell, but not core, also produced pivoting. These shell injections increased the dopamin e release in the ipsilateral striatum, and decreased it in the contralatera l striatum. The relative increase in the ipsilateral striatum was closely a ssociated with the drug-induced pivoting. The data show that stimulation of cholinergic and dopaminergic receptors in the shell and core elicit effect s that vary according to the subregion of the nucleus accumbens. It is conc luded that the accumbens-specific, cholinergic effects are mediated via sub strates that differ from those involved in the shell-specific, dopaminergic effects. (C) 1999 Elsevier Science Ltd. All rights reserved.