Eating-related increase in dopamine concentration in the LHA with oronasal stimulation.

Previously, we showed that eating was associated with an increase in lateral hypothalamic area dopamine (LHA-DA) release, which returns to previous level when eating stops. We therefore hypothesize that LHA-DA release may be primarily contributed to by oronasal stimulation. To test our hypothesis, microdialysis was used to compare LHA-DA release during oral and intragastric feeding. A gastrostomy tube was inserted in 12 rats. After recovery from surgery, in vivo microdialysis was performed. Six rats were allowed to drink a liquid diet, whereas in another six rats the same liquid diet was infused at paired doses (volume = 4.8 +/- 0.6 ml; time = 5-10 min) through the gastrostomy tube into the stomach. Oral feeding increased baseline LHA-DA from 10.6 +/- 0.2 to 14.0 +/- 0.8 pg/10 microliters dialysate (P < 0.01) within 20 min. No significant change in measured LHA-DA occurred during intragastric feeding [baseline: 10.5 +/- 0.3 pg/10 microliters; postintragastric: 10.2 +/- 0.3 pg/10 microliters (P < 0.01 vs. oral feeding)], indicating that LHA-DA release occurs with oronasal stimulation.