Do alpha-2 adrenoceptors modify coping strategies in rats?

Previous research has shown that resident rats treated with alpha(2) adrenoceptor blockers display a modified appressive response towards intruding animals. In the present study we report data on the behavioral changes induced by alpha(2) adrenoceptor blockers in intruder animals. In experiments 1 and 2 intruders smaller in body weight than the residents were treated with 0.0, 0.5, and 1.0 mg/kg CH-38083 and idazoxan, respectively; in experiment 3 weight matched intruders were injected with 1 mg/kg CH-38083 or idazoxan. The treatment of smaller intruders did not change the behavior of residents. In contrast, weight-matched intruders injected with alpha(2) adrenoceptor blockers elicited increased aggression in residents. Social behaviors, exploration and offensive aggression showed insignificant variation in intruders. Defensive behaviors, in contrast, showed major changes: in experiments and 2 a dose-dependent decrease in immobility and a dose-dependent increase in defensive upright was noticed. In experiment 3, high scores of defensive upright were apparent, precluding detection of drug-induced changes. However, when the last 5 min of the encounter were analysed separately, results similar to the first two experiments were observed. Significant negative correlations were found between immobility and defensive upright scores. The results suggest that alpha(2) adrenoceptor blockers induce a shift from a passive (immobility) towards a more active (defensive upright) coping style. These and previous data show that alpha(2) adrenoceptor blockers, other than yohimbine, seem to exert a behavior-activating effect in rats.