In vivo microdialysis evidence that midazolam facilitates propofol-inducedreduction in rat accumbal dopamine release

The aim of this study was to determine whether propofol reduces extracellul ar concentrations of dopamine in the rat nucleus accumbens and, if so, whet her this effect is potentiated by midazolam. Propofol and midazolam wire ad ministered intravenously, via the external jugular vein, to freely-moving r ats. The extracellular concentrations of dopamine in the nucleus accumbens were measured consecutively every 25 min by using in vivo brain microdialys is with electrochemical detection. Propofol(2.5, 5.0 and 10.0 mg/kg) decrea sed the accumbal dopamine concentrations in a dose-dependent manner. The la rgest dose (10.0 mg/kg) decreased dopamine concentration by a maximum of 34 % (P < 0.01) at its peak effect. The smallest dose of propofol (2.5 mg/kg) did not affect dopamine concentrations when given alone, but decreased conc entrations by 23% (P < 0.05) when combined with a dose of midazolam (0.075 mg/kg) having only a minimal effect on dopamine concentrations. The present study demonstrates that propofol dose-dependently reduces dopamine release in rat nucleus accumbens, and that the effect is facilitated by midazolam; a similar interaction is also seen clinically, on preoperative anxiety and on anaesthesia.