Dopamine receptor subtype agonists and feeding behavior

Stimulation or blockade of various dopamine receptor subtypes is associated with reduced feeding, For example, D-2 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 D-1 receptor agonists, and these compounds can interact synergistically with D-2 receptor agonists to potentiate reductions in feeding, Using microstructural analysis to compare D-1 and D-2 agonist effects, specific differences emerge in their modes of action, D-1 agonists reduce the duration of feeding, primarily by decreasing the frequency of feeding bouts, whereas D-2 agonists reduce the local rate of eating, However, since D-1 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 D-1 agonists are more likely than D-2 agonists to act on central mechanisms regulating food intake, Moreover, only D-1 agonists are effective in suppressing sucrose sham-feeding suggesting that D-1 receptor stimulation may promote satiety. Nevertheless, many questions remain, For example, antagonist studies have implicated 5-HT receptor stimulation in the anorectic effects of D-1 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 D-3, D-4 and D-5 receptors in feeding.