Stimulant-like effects of magnesium on aggression in mice.

The effects of magnesium excesses resulting from daily injections of magnesium chloride (MgCl2) were examined on offensive behavior in a resident-intruder situation. Male mice tested 5 min post-injection of 15 mg/kg or 30 mg/kg exhibited a significantly greater number of attacks and threats than saline controls; while in mice injected with 125 mg/kg threat and attack behaviors were decreased. No tolerance developed to this decrease which persisted throughout the 15 day injection period. Tolerance to the aggression enhancing effects developed in the 30 mg/kg group which returned to normal by Day 4 and in the 15 mg/kg group which returned to normal by Day 15. Two weeks following the last injection, all groups performed equally. When mice were tested prior to daily injections on Days 4, 8, and 15 in a second experiment, there were no MgCl2 dose differences in threat or attack behavior, thus there was no cumulative effect of MgCl2 on behavior. These data and our previous data showing that MgCl2 deficiencies reduce offensive aggression suggest an inverted U-shape function to magnesium's influence on behavior. Since aggression has been linked to the neurotransmitters dopamine, norepinephrine, and serotonin, and magnesium has been shown to be an important cofactor in the activity of these neurotransmitters, it is possible that the effects seen here are related to changes in one or more of these systems.