Evidence for dopamine D-1 receptor-mediated facilitatory and inhibitory effects on feeding behaviour in rats

Early studies on dopamine agonists and feeding behaviour showed that apomorphine, administered either centrally or systemically, reduced food intake. While this anorectic effect was later analysed in some detail, it was also recognized that, under some circumstances, apomorphine could increase food consumption. Once the distinction between dopamine D-1 and D-2 receptors had been drawn, and receptor-specific agonists and antagonists had become available, the way was clear to investigate the potential roles of D-1 and D-2 receptor subtypes in relation to ingestional behaviour. This paper reviews evidence which indicates, first of all, that D-1 receptor agonists reduce food intake relatively specifically and that the effect cannot be attributed to the induction of intrusive mouth movements or to general behavioural changes (e.g. increased arousal or sedation). We show that dopamine D-1 agonists reduce sucrose sham-feeding in the gastric-fistulated rat. Secondly, however, we provide initial evidence that D-1 agonist activity can have a facilitatory effect on feeding behaviour. More specifically, the D-1 agonist, SKF 38393, increased the response to a highly palatable food in a food-preference test. This result is compared with published reports that injections of either D-amphetamine or morphine into the nucleus accumbens increases feeding behaviour. We speculate that D-1 receptors in the nucleus accumbens may be involved in the mediation of preference for more palatable foods.