Postconditioning effects of magnesium on cocaine conditioned place preference in mice

Magnesium chloride (MgCl2) has recently been shown to have stimulant-like properties. Because stimulants are known to induce conditioned place preference (CPP), the CPP procedure was used to test the hypothesis that cocaine and MgCl2 share similar stimulus properties. This would be shown if cocaine-induced CPP could be enhanced in a postconditioning preference test by MgCl2 and other stimulants. Mice were conditioned with 5.0 mg/kg cocaine to the nonpreferred end of a three-compartment straight shuttle box. All groups showed significant shifts in preference from the preconditioning test to the postconditioning test. There were no changes in place preference over test days in mice that were injected only with saline and therefore not conditioned. When animals were given acute injections of either saline, 5.0 mg/kg cocaine, 1.0 mg/kg amphetamine, 30 mg/kg MgCl2, 10 mg/kg pentobarbital, or 0.25 mg/kg haloperidol following conditioning with cocaine, amphetamine and MgCl2 elevated the conditioned cocaine effect, and pentobarbital and haloperidol decreased the conditioned cocaine effect compared to saline. In addition, there was a dose-dependent influence of MgCl2, with 30 mg/kg producing the maximum effect on the conditioned cocaine effect.