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 micro-structural 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.