[Effects of puromycin on the retention of instrumental training in mice]

Positional choices and visual discrimination in non-delayed appetitive discrimination tasks in mice

Mice were submitted to visual discrimination learning using a large choice compartment positioned in front of two adjacent runways, black and white, one of which was baited. Rate of acquisition, expressed by the mean number of sessions to criterion did not differ between the initial task and two reversals. However, the number of correct choices before criterion was significantly lower on both reversals compared to original learning. Position habit rates did not vary significantly between acquisitions, and they were negatively correlated with visual discrimination rates in the three learning phases. This observation, and the fact that on each phase, position habits were largely absent on initial sessions and only developed gradually, suggest that position habits may occur when animals do not grasp the solution to the visual task.

Aversive effects and retention impairment induced by acetoxycycloheximide in an instrumental task

AXM, when subcutaneously injected during the first 3 min following the acquisition of a nondiscriminative instrumental learning task, induced an aversion for the food reinforcement which had been associated with the training situation and with the pharmacological treatment. The high number of nonreinforced responses preceding the first reinforced response(RR) that animals performed when tested 6 days after AXM treatment, was not due to forgetting of the lever significance, but to this aversion. Animals treated with AXM showed low levels of lever pressing response and long latencies for their first RR; this deficit did not seem only to be due to food reinforcement aversion; it disappeared, as well as food aversion, when food reinforcement which had been associated with the learning situation and to treatment, was added to the daily feeding regimen during treatment-test interval. It has been shown, moreover, that more than 90 percent of cerebral protein synthesis was inhibited during the 5 hr following subcutaneous AXM injection. These findings are interpreted as an indication that AXM does not affect memory consolidation of a non discriminative instrumental learning.