The effect of methamphetamine on social interaction of adult male rats.

The effect of psychostimulants on social behavior still remains unclear. Therefore the aim of the present study was to assess the effect of low doses of methamphetamine (MA) on social interaction (SI) in adult male rats. Rats were tested in three environmental conditions: (1) dimly lit, familiar environment, (2) dimly lit, unfamiliar environment and (3) intensely lit, unfamiliar environment considered to be low, middle and high stress, respectively. In each condition different set of animals was used. Rats were always divided into five groups. Control (without injection), saline (with 1 ml/kg saline injection) and three MA groups (doses: 0.5, 1 and 1.5mg/kg). Injections were applied 30 min prior to testing. Always a pair of unfamiliar rats of the same treatment group was tested. Their behavior was video recorded for 5 min in an open field. Times spent by SI (following, climbing, genital investigation, etc.) and non-social behavior (locomotion, rearing) were analyzed using a two-way ANOVA (drug treatment x stress condition). Our data demonstrate that all doses of MA, reduced SI. In addition, the unfamiliarity of the arena increased exploratory behavior (locomotion and rearing) in all treatment groups, while the SI was affected by the environmental condition only in controls or saline-treated rats, but not in MA-treated groups. In conclusion, our data demonstrate that MA administration impairs SI in dose- and stress condition-specific manner, however, some of our results may be due to increase locomotion and rearing induced by MA. Copyright (c) 2010 Elsevier B.V. All rights reserved.