Role of dopamine D1 and D2 receptors in the nucleus accumbens in jaw movements of rats: a critical role of the shell.

Given the differences in the dopamine neurotransmission between the shell and the core of the nucleus accumbens, as well as the differential involvement of these two domains in oral behaviour of rats, it was decided to determine whether or not dopamine D1 and/or dopamine D2 receptors differentially direct oral behaviour in these two domains in rats. Intra-accumbens injections of the dopamine D1 receptor agonist (+/-)-6-chloro-7,8-dihydroxy-3-allyl-1-phenyl-2,3,4,5-tetrahydro-1H-3- benzazepine (SKF 82958: 5 micrograms/0.2 microliters), the dopamine D2 receptor agonist quinpirole (10 micrograms/0.2 microliters) and their combination were used to assess the role of these accumbens domains in jaw movements of rats. The present study shows that the combined administration of SKF 82958 and quinpirole into the shell, but not the core, of the nucleus accumbens produced a highly significant increase in jaw movements, when doses which per se were nearly ineffective, were injected. This effect was fully inhibited by prior administration of either the dopamine D1 receptor antagonist R-(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine (SCH 23390: 0.5 microgram/0.2 micrograms) or the dopamine D2 receptor antagonist (-)-sulpiride (25 ng/0.5 microliter) into the same region. It is concluded that dopamine D1 and D2 receptors in the shell, but not the core, of the nucleus accumbens are involved in jaw movements of the rat, providing the first piece of evidence that dopamine D1 and D2 receptors in the shell of the nucleus accumbens mediate a particular behaviour.