Target-specific glutamatergic regulation of dopamine neurons in the ventral tegmental area

Dopamine (DA) neurons in the ventral tegmental area (VTA) are thought to play a critical role in affective, motivational, and cognitive functioning. There are fundamental target-specific differences in the functional characteristics of subsets of these neurons. For example, DA afferents to the prefrontal cortex (PFC) have a higher firing and transmitter turnover rate and are more responsive to some pharmacological and environmental stimuli than DA projections to the nucleus accumbens (NAc). These functional differences may be attributed in part to differences in tonic regulation by glutamate. The present study provides evidence for this mechanism: in freely moving animals, blockade of basal glutamatergic activity in the VTA by the selective alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)/kainate antagonist LY293558 produced an increase in DA release in the NAc while significantly decreasing DA release in the PFC. These data support an AMPA receptor-mediated tonic inhibitory regulation of mesoaccumbens neurons and a tonic excitatory regulation of mesoprefrontal DA neurons. This differential regulation may result in target-specific effects on the basal output of DA neurons and on the regulatory influence of voltage-gated NMDA receptors in response to phasic activation by behaviorally relevant stimuli.