Joint effects of medial septal lesions and amylobarbitone injections on resistance to extinction in the rat

32 male rats, of which half had sustained small electrolytic lesions in the medial septal area and half had received sham operations, were trained on continuous reinforcement to run an alley for water reward and then given four days of extinction testing. Half of both the lesioned and sham-operated groups were given sodium amylobarbitone on Days 1 and 2 of extinction and the other half on Days 3 and 4, saline being administered on non-drug days. The drug, unusually, decreased resistance to extinction. This effect was probably due to the subjects having taken part in a previous experiment in which they had received, without drugs, training and extinction under the same conditions as in this experiment. In the goal section of the alley, the drug effect was greater in lesioned than shamoperated rats. The lesions retarded extinction, and this effect was reduced by the drug. A model for the neural loci at which amylobarbitone acts to affect resistance to extinction, based on these and other results, is proposed.