Abstract
The effects of the anxiogenic beta-carboline FG 7142 (N-methyl-beta-carboline-3-carboxylate) on motor activity and dopamine release in nucleus accumbens and striatum were measured in the rat. Changes in extracellular homovanillic acid (HVA) concentration, monitored by computer-controlled linear sweep voltammetry with carbon-paste electrodes, were used as an index of changes in dopamine release. An intraperitoneal injection of FG 7142 was followed by an inhibition of the nocturnal rise in motor activity and in dopamine release in nucleus accumbens, but not striatum. Two days after the drug injection, dopamine release in nucleus accumbens returned to control level and then increased on days 3-6 after the injection; there was no delayed change in motor activity or in striatal dopamine release. In parallel experiments using ex vivo changes in the ratio of 3,4-dihydroxyphenylacetic acid (DOPAC) to dopamine as an index of changes in dopamine turnover, a similar early depression and delayed increase of dopamine turnover in nucleus accumbens, with no change in striatum, was found after an intraperitoneal injection of FG 7142. Regression analysis of motor activity versus dopamine release showed a decrease in correlation between these 2 parameters for nucleus accumbens but not striatum after FG 7142 injection. These results suggest that the inverse benzodiazepine receptor agonist FG 7142 has a biphasic effect on dopamine release from mesolimbic neurons and support the hypothesis that dopamine release in nucleus accumbens and striatum has a modulatory effect on the control of motor activity but does not play a determining role in the regulation of movement.