Dose-dependent facilitation or supression of rat fighting by methamphetamine, phenobarbital, or imipramine.

Abstract

To clarify the effects of different doses of methamphetamine HCl, Na phenobarbital, and imipramine HCl on aggressive behavior, the drugs were administered to pairs of rats trained to regularly fight on an electric shock grid. Fighting time and motor activity were measured during the shock sessions. Each drug was given to a different group of rats, in the following doses (mg/kg i.p.): methamphetamine HCl 0, 0.25, 0.50, 1, 2, and 4; Na phenobarbital 0, 5, 10, 20, 40, and 80; imipramine HCl 0, 2.5, 5, 10, and 20. At lower doses methamphetamine and phenobarbital both stimulated fighting behavior, and at higher doses both reduced it. Motor activity rose above control with lower doses of both of these drugs; it fell markedly with higher doses of phenobarbital, while remaining elevated at higher doses of methamphetamine. Imipramine reduced fighting time at higher doses. The results show that, depending upon the dose, the “stimulant”, methamphetamine, and the “sedative”, phenobarbital, can both increase or decrease aggressive behaviors. Together with previous animal studies, these findings fit with clinical observations that amphetamines and barbiturates can increase aggressive behavior, and suggest that dose may be important in that increase.