Drug induced facilitation of avoidance learning in isolated weanling rats

Abstract

A significantly delayed rate of acquisition of conditioned avoidance responding (CAR) was found in CF male isolated weanling rats, in contrast to littermates reared in groups. No post-training differences in catecholamines of brain, heart and adrenals or MAO activity of brain and liver homogenates were observed between isolated and aggregated weanling rats. Pretreatment of isolated weanlings with 6-hydroxydopamine, 50 mg/kg s.c. given on alternate days from birth to Day 14 resulted in significantly lowered CAR performance with respect to untreated controls. Apomorphine and methylphenidate, 1 mg/kg i.p., and imipramine and nitroxazepine, 5 mg/kg i.p., given daily for 4 days produced significantly enhanced facilitation of avoidance learning in isolated weanling rats. Apomorphine had a short lasting effect whereas in the case of all the other drugs, improved CAR performance persisted in the post-drug period. Haloperidol, 100 µg/kg s.c., inhibited the CAR on drug days, but performance improved after drug discontinuation. The results support involvement of dopaminergic mechanisms in conditioned avoidance responding behaviour in weanling rats.