Acquisition of conditioned avoidance response in rats under the influence of addicting drugs.

Abstract

Four groups of white rats, aged 8–12 weeks, were treated with morphine, d-lysergic acid diethylamide, dl-amphetamine and ethanol, respectively, while being trained in a conditioned avoidance response (CAR) schedule. Morphine caused deterioration in the acquisition of CAR, as manifested by significant increases in the number of training sessions required for 100% correct CAR and in the reaction time (RT), when compared to those of a control group. The RT decreased after withdrawal of morphine and was associated with a revival of the conditioned emotional responses (CER). LSD and ethanol insignificantly retarded the acquisition of CAR, while withdrawal of LSD caused significant increases in the RT, error and CER. Amphetamine facilitated the acquisition rate associated with increased CER; during withdrawal, the CER was negligible whereas the error increased significantly. In another series of rats, tolerance was seen to morphine and, to a less extent, to ethanol and amphetamine after 8–12 days of continued treatment; whereas the withdrawal effects lasted for 3–4 days only. These effects of the addicting drugs on conditioned learning are discussed in the light of their influence on the emotional responses of the animals and the degree of development of drug-dependence.