Leptin attenuates D₂ receptor-mediated inhibition of putative ventral tegmental area dopaminergic neurons

Obesity causes hyperleptinemia. We have previously shown that D₂ receptor-mediated inhibition of ventral tegmental area (VTA) dopaminergic neurons is attenuated in diet-induced mice with obesity. Consequently, we hypothesized that high concentrations of serum leptin during obesity might modulate D₂ receptor-mediated effects on VTA dopaminergic neurons. To investigate our hypothesis, we examined leptin effects on D₂ receptor-mediated inhibition of putative VTA dopaminergic neurons from lean mice using electrophysiological techniques. Leptin (100 nmol/L) directly inhibited spontaneous firing in 71% of putative VTA dopaminergic neurons (leptin-responsive), whereas the remaining 29% of neurons were leptin-nonresponsive. In 41% of leptin-responsive neurons, leptin attenuated the reduced firing rate produced by quinpirole (100 nmol/L), whereas the remaining 59% of neurons exhibited no effect of leptin. In leptin-nonresponsive neurons, no significant leptin-induced effect was observed on reduced firing rate produced by quinpirole. In leptin-responsive neurons with positive leptin-induced attenuation of quinpirole effects, leptin-induced attenuation persisted for >20 min, whereas no such persistent attenuation was observed in other types of neurons. In conclusion, leptin attenuates D₂ receptor-mediated inhibition in a subpopulation of putative VTA dopaminergic neurons. We suggest that leptin directly decreases, and indirectly increases, excitability of VTA dopaminergic neurons. In turn, this may contribute to a change in feeding behavior through the mesolimbic dopaminergic system during the development of obesity.