Effects of caffeine on aggressive behavior and avoidance learning of rats with isolation syndrome.

Caffeine at a dose of 40 mg/kg i.p. administered 60 min before testing for aggressive mouse-killing behavior in Wistar rats with isolation syndrome inhibited mouse-killing response in 48 per cent of the aggressive rats. When injected 60 min before two-way active avoidance training caffeine improved learning in grouped rats, did not facilitate it in isolated non-aggressive rats and significantly improved avoidance behavior in isolated aggressive rats. The antiaggressive effect of caffeine is most probably due to its inhibitory action on phosphodiesterase and the resulting increase of brain cAMP, to the provoked increase of brain 5-HT and to its binding to brain benzodiazepine receptors. The positive effect of caffeine on avoidance learning of isolated aggressive rats is likely due to its indirect stimulant action on the brain dopaminergic system.