The activation of mesoprefrontal dopamine neurons by FG 7142 is absent in rats treated chronically with diazepam

Administration of methyl-beta-carboline-3-carboxamide (FG 7142, 15 mg/kg i.p.) to rats has previously been shown to cause a selective increase in the levels of 3,4-dihydroxy-phenylacetic acid (DOPAC) in the prefrontal cortex and ventral tegmental area (VTA) via an interaction with benzodiazepine receptors. On withdrawal 3 days following chronic treatment with diazepam for 21 days, FG 7142 no longer increased DOPAC levels in either the prefrontal cortex or the VTA. Chronic diazepam treatment alone was ineffective in altering dopamine metabolism in the eight brain regions examined. The present findings indicate that chronic diazepam treatment may cause changes at the level of GABA/benzodiazepine receptor macromolecular complex, which is normally functionally integrated with the mesoprefrontal dopaminergic neurons, so that FG 7142 can no longer exert its intrinsic actions.