Influence of magnesium pemoline upon acquired DRL performance.

Summary.-5 rats, previously trained to a criterion on drl, were tested, in 3 replications, with injections of tragacanth on 2 days and of magnesium pemoline on 1 day. Magnesium pemoline significantly impaired drl performance, but there were no significant changes within each session nor as a function of replications. Plotnikoff (1966a, 1966b) has recently presented evidence that magnesium pemoline, a CNS stimulant, enhanced avoidance conditioning and memory. However, a number of investigators (Beach & Kimble, 1967; Frey & Polidora, 1967; Powell, Martin, & Kamano, 1967) suggest that the enhancement is a function of performance rather than learning. In general, it has been sug~esred thar the drug facilitated avoidance conditioning by decreasing "freezing" behavior and Increasing general activity. Filby and Frank (1968) have suggested that these drug effects would not necessarily facilitate performance in a drl situation (differential reinforcement of low rate) bur would improve performance if the central associative processes were affected by the drug. However, they report thar high dosage levels of magnesium pemoline impaired the acquisition of drl performance. The present study investigated the effects of magnesium pemoline upon performance of an already acquired drl response. Ss were five naive male racs approximately 90 days old at the beginning of the experiment. The rats were housed in individual cages throughout the study. The apparatus consisted of rwo conventional operant boxes, each placed in a sound deadened chamber equipped with a circulating fan and white noise which served as an auditory mask. Standard relay equipment was used to program all reinforcement contingencies. The reinforcers were 45-mg. Noyes pellets, and were given under a drl 15-sec. schedule. Ss' responses and reinforcements were recorded on counters. Each S was maintained at 80% of its ad lib. weight throughout the experiment, Ss were habituated to the operant box and then were shaped and run for 100 continuous reinforcements. In all subsequent sessions Ss were placed on a drl 15-sec. for a 50-min. session. Each S was run to a criterion of obtaining reinforcement on at least 50% of its responses on three consecutive days. To adapr Ss to the injection procedure, following the third criterion session, each S was injected I.P. with 0.3% tragacanth (2 cc/kg) 30 min. prior to the rest session. All Ss then received three replications of the following rreaunent: on the first two days Ss were injected I.P. with tragacanth 30 min. before each session; and on the third day they were injected I.P. with 20 mg/kg of magnesium pemoline' (10 rng/cc suspended in 0.3% tragacanth) 30 min. before the 50-min. test session. The proportion of responses reinforced was computed for each of the five 10-min. intervals in each daily test session. The data from the second tragacanth day and the magnesium pemoline day of each replication were used to compute an analysis of variance with drug conditions, intervals, and days as factors. The data from the first tragacanth day of each replication were not included in this analysis as they might have been contami'The magnesium pemoline used in this study was supplied by Dr. H. G. Schoepke of Abbott Laboratories. The work was conducted according to the APA statement of "Guiding principles for humane care and treaunent of animals," December 15, 1962.