Magnesium-induced conditioned place preference in mice.

A conditioned place preference procedure was used in mice to test the hypothesis that magnesium possesses reinforcing properties. Mice were conditioned to the nonpreferred end of a three-compartment straight shuttle box with MgCl2 injections alternating with saline injections on the preferred end. Dose of MgCl2 was varied (0, 15, 30, 125 mg/kg) as well as number of conditioning trials (8 or 16). On the day after the first postconditioning test, animals were given acute injections of 5 mg/kg cocaine, or other test drug, to determine if the conditioned effect on behavior would be potentiated, maintained or blocked by these test drugs. Results demonstrated that 15 mg/kg MgCl2 induced the greatest amount of conditioning and that increasing the number of MgCl2/place pairings did not enhance the amount of conditioning, but rather, it decreased it. Amphetamine potentiated MgCl2-induced place preference; cocaine and pentobarbital maintained it; and haloperidol blocked it. These data indicate that MgCl2 has some primary reinforcing properties in mice and that MgCl2 shares stimulus properties with other stimulants and reinforcing substances.