Dopamine receptor subtype agonists and feeding behavior.

Stimulation or blockade of various dopamine receptor subtypes is associated with reduced feeding. For example, D2 receptor agonists suppress feeding in food-deprived and free-feeding rats, and in rats given access to a highly palatable diet. Similarly, reduced food intake is associated with the actions of diverse D1 receptor agonists, and these compounds can interact synergistically with D2 receptor agonists to potentiate reductions in feeding. Using microstructural analysis to compare D1 and D2 agonist effects, specific differences emerge in their modes of action. D1 agonists reduce the duration of feeding, primarily by decreasing the frequency of feeding bouts, whereas D2 agonists reduce the local rate of eating. However, since D1 agonists uniquely reduce feeding in the absence of other behavioral impairments and are less disruptive of the pattern of feeding behavior, it has been suggested that D1 agonists are more likely than D2 agonists to act on central mechanisms regulating food intake. Moreover, only D1 agonists are effective in suppressing sucrose sham-feeding, suggesting that D1 receptor stimulation may promote satiety. Nevertheless, many questions remain. For example, antagonist studies have implicated 5-HT receptor stimulation in the anorectic effects of D1 agonists, suggesting that further pharmacological and behavioral analyses of receptor-subtype agonist effects are required. Above all, recent developments in the classification of dopamine receptor subtypes reveal the need for new studies examining the involvement of D3, D4 and D5 receptors in feeding.