Involvement of the nucleus accumbens in oral behaviour in the freely moving rat

The role of the nucleus accumbens in oral behaviour was examined by intra-accumbens injections of a single dose of a selective dopamine D1 receptor agonist (SKF 38393: 5 micrograms/side), a selective dopamine D2 receptor agonist (quinpirole: 10 micrograms/side), and their combination in freely moving rats. Principal factor analysis revealed four factors to be involved in the scored behaviours, two of which concerned oral behaviour: a chew factor, comprising the behaviours chew, tongue protrusion, yawn and lick, and a groom factor, with high factor loadings of tremor and groom. The two remaining factors were the circle factor comprising circle, walk and rear, and the sniff factor comprising sniff, yawn and rear. Two-way ANOVA (independent variable D1 with H2O and SKF 38393 level; independent variable D2 with H2O and quinpirole level) of the factor scores revealed that SKF 38393 and quinpirole had similar or opposite effects which were additive or antagonistic, depending on which behaviour was studied. This study demonstrates that (a) the nucleus accumbens plays a major role in the oral behaviour of freely moving rats, and (b) an integrated study of all oral behavioural elements is necessary to describe the effects of drugs on oral behaviour.