Eating-associated VMN-dopamine levels of rats: comparison of oral and intragastric feeding.

Eating is associated with persistently low dopamine (DA) concentration in the ventromedial hypothalamic nucleus (VMN), postulated to influence postprandial satiety. Whether pregastric factors contribute to eating-associated low VMN-DA was examined. VMN-DA levels were continuously measured in awake rats, food-deprived for 24 h, and either subsequently allowed to eat solid chow freely available for 20 min, an oral liquid diet, or an isovolemic isocaloric liquid diet infused intragastrically to bypass the oropharynx. Eating either solid chow or a liquid diet was associated with an immediate decrease in VMN-DA concentration. The lower VMN-DA concentration lasted longer after solid chow was consumed than following consumption of the liquid diet. When the oropharynx was bypassed no significant change in VMN-DA concentration was observed either during or after the liquid diet was infused. Results suggest that pregastric oropharyngeal factors contribute to eating-associated low VMN-DA concentration.