NMDA, KAINATE, AND AMPA DEPOLARIZE NONDOPAMINE NEURONS IN THE RAT VENTRAL TEGMENTUM

The possible existence of N-methyl-o-aspartate (NMDA) and non-NMDA rec eptors on electrophysiologically identified nondopamine neurones in th e ventral tegmental area (VTA) was tested in rat midbrain slice prepar ations. NMDA, kainate (KA), and AM PA (alpha-amino-3-hydroxy-5-methyl- 4-isoxazole propionic acid) depolarized the membrane potential of nond opamine neurons in a dose-dependent manner. The NMDA effect was blocke d by the selective NMDA receptor antagonist, CGS 19755 (cis-4-phosphon omethyl-2-piperidine carboxylate), but not by the non-NMDA receptor an tagonist, NBQX ihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline]. In c ontrast, the effects of KA and AMPA were antagonized by NBQX, but not by CGS 19755. The rank order potency of the three agonists was AMPA > KA > NMDA, with thresholds of 0.1, 0.3, and 3 mu M, respectively. Thes e results provide clear electrophysiological evidence that nondopamine neurons in the ventral tegmental area possess both NMDA and non-NMDA receptors.