NMDA receptor antagonist-induced dopamine release in the ventral pallidum does not correlate with motor activation

The ventral pallidum is the output structure of the nucleus accumbens in th e ventral corticostriato-thalamocortical loop. Information processing in th is loop is critically involved in motor behavior and reinforcement. The ven tral pallidum receives a direct dopaminergic input from the ventral tegment al area, but also glutamatergic input from cortical and limbic areas. It ha s been assumed that dopamine release in the VP is indeed modulated by gluta mate. The present study investigated the effects of NMDA receptor blockade on motor behavior and dopamine release in the ventral pallidum. In a first experiment, rats were implanted with microdialysis probes in the ventral pa llidum and were systemically injected or locally perfused via the microdial ysis probe with dizocilpine (0.32 mg/kg, 10 and 100 mu M, respectively). Ef fects on dopamine and on locomotion were simultaneously monitored. In a sec ond experiment, ventral pallidum was lesioned by quinolinic acid and the ef fects of systemic dizocilpine (0.08 and 0.16 mg/kg) on locomotion and stere otyped sniffing behavior were determined. It was found that systemic and lo cal dizocilpine administration increased dopamine release in the ventral pa llidum to a similar extent whereas only systemic treatment was accompanied by locomotor stimulation. Lesion of the ventral pallidum did not affect loc omotion and stereotyped sniffing behavior induced by systemic dizocilpine t reatment. Thus, DA release in the ventral pallidum that is elevated by bloc kade of NMDA receptors is not relevant for activation of motor behavior. (C ) 2000 Elsevier Science B.V. All rights reserved.