Programmed self-administration of potentially addictive drugs in young rats and its effects on learning.

Abstract

Young Norwegian rats of both sexes were trained in a conditioned avoidance (CAR) or a maze-learning paradigm, under the chronic influence of nine potentially addictive drugs, administered in drinking water in a step-up dosage schedule. Growth of these rats was variably impeded by all drugs except ethanol and meprobamate (MPB). Compared to the water controls, acquisition of CAR was accelerated by amphetamine (AMP) and medazepam (MZP), significantly delayed by morphine and pentobarbitone (PNB), and marginally affected by ethanol, phenobarbitone (PHB), flurazepam (FZP), nitrazepam (NZP) and MPB. Except for AMP, PHB and MPB, performance generally improved upon withdrawal of the drugs. Extinction of the acquired CAR was achieved in all but two groups during drug-treatment but not in the drug-free state; the AMP- and the morphine-rats showed no extinction of CAR in either state. In the Y-maze experiment, the rate of maze-learning was generally impeded by all drugs relative to that of the water controls. Ethanol-, FZP-, MZP- and morphine-treated rats again exhibited significant impairment upon withdrawal of the drugs; whereas, the AMP-, MPB- and PNB-treated rats improved in maze-performance during withdrawal. These results are discussed in the light of the development of tolerance and dependence to and relevant neurological actions of the drugs concerned.