Conditioned place preference and locomotor activation produced by injection of psychostimulants into ventral pallidum

Abstract

The ventral pallidum (VP) is often viewed as an output structure of the nucleus accumbens septi (NAS). However, VP, like NAS, receives a dopaminergic input from the ventral tegmental area. These experiments investigated some behavioral effects of microinjection into VP of drugs which enhance dopaminergic transmission. Injection of 25 μg dopamine or 5–10 μg amphetamine into VP produced hypermotility. In contrast, injection of 12.5–50 μg cocaine initially suppressed, then increased, activity. Injection of 100 μg cocaine only produced hypomotility in the 1-h period examined. The hypomotility following cocaine seemed to be a local anesthetic effect, because it was mimicked by 50–200 μg procaine. Procaine did not, however, produce subsequent hypermotility. Conditioned place preference (CPP) was produced by 10 μg amphetamine and 50 μg cocaine but not 100 μg procaine. We conclude that injection of cocaine into VP, unlike similar injections into NAS, produces CPP. These results support the idea of an involvement of dopamine in VP in reward and locomotor activation, independent of dopamine in NAS. The use of intracerebral injections of cocaine is complicated, however, by an apparent local anesthetic effect of the drug.