The influence of magnesium on morphine-induced stimulation of the reward system.

The present study was designed to assess the influence of magnesium (Mg) as MgCl(2) (10 or 40 mg/kg b.wt/day i.p.) and of its interaction with morphine on the reward system (RS) in Wistar rats. For this purpose, we evaluated conditioning place preference on a 12 day experiment schedule. Our data show that MgCl(2) (10 mg/kg b.wt/day) has moderate but significant effects on stimulating RS (increasing the time spent in associated conditioned compartment) (327.75 +/- 11 s in the Mg (10 mg/kg b.wt) group vs 295.2 +/- 8 s in the control (saline) group, p < 0.05) but not at higher Mg doses (40 mg/kg b.wt/day). We tested the influence of MgCl(2) (10 mg/kg b.wt./day i.p.) upon naloxone (2 mg/kg b.wt/ i.p.)-induced place aversion. Administrated alone, naloxone has an aversive effect on place preference. MgCl(2) (10 mg/kg b.wt/day i.p.) has a significantly decreased aversive effect of naloxone (280.7 +/- 37 s in naloxone + MgCl(2) (10 mg/kg b.wt) group vs 189 +/- 21 s in naloxone group, p < 0.05). MgCl(2) at both tested doses, added to morphine (3 mg/kg b.wt/day i.p), decreased the acquisition of morphine-induced place preference (262.2 +/- 17 s) in morphine + MgCl(2) (40 mg/kg b.wt) group vs 462.15 +/- 28 s in morphine group, p < 0.05). MgCl(2), 10 mg/kg b.wt/day i.p. decreased both morphine-induced place preference and naloxone-induced place aversion.