Characterization of excitatory amino acid modulation of dopamine release in the prefrontal cortex of conscious rats

The effect of various classes of excitatory amino acid agonists on the release of dopamine in the medial prefrontal cortex (PFC) of awake rats was examined using intracerebral microdialysis. Local infusion of 20 μM α- amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA), through the microdialysis probe, produced a significant increase of more than twofold in extracellular levels of dopamine. Application of 100 μM AMPA increased these levels nearly 15 fold. The AMPA/kainate receptor antagonist 6-cyano-7- nitroquinoxaline-2,3-di-one (CNQX) (50 μM) blocked the increase in dopamine release produced by 20 μM AMPA. Local infusion of kainate at concentrations of 5 and 20 μM increased dopamine release by nearly 150 and 500%, respectively. Local application of CNQX (50 μM) before 20 μM kainate significantly attenuated the stimulatory effect of kainate on dopamine levels. In contrast to AMPA and kainate, infusion of N-methyl-D-aspartate (NMDA) at 20 or 100 μM did not increase dopamine release. In fact, a trend toward a decrease in dopamine release was evident after 100 μM NMDA. The present study indicates that the in vivo release of dopamine in the PFC is facilitated by AMPA and kainate receptors. This modulation is more profound than that previously reported in the basal ganglia. The lack of an excitatory effect of NMDA is in agreement with recent reports that the NMDA receptor may inhibit indirectly dopaminergic neurotransmission in the PFC.