QUINPIROLE AND D-AMPHETAMINE ADMINISTRATION POSTTRAINING ENHANCES MEMORY ON SPATIAL AND CUED DISCRIMINATIONS IN A WATER MAZE
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Two behavioral testing procedures, a spatial discrimination and a cued discrimination, were used in a water maze to assess memory enhancement following posttraining administration of d-amphetamine, an indirect catecholamine agonist, and quinpirole, a dopaminergic D2 receptor agonist. Rats received an eight-trial (30-sec intertriai interval) training session on a single-platform spatial or cued discrimination in a water maze. In the spatial task, a submerged escape platform was located in the same quadrant of the maze on all trials. In the cued task, a visible escape platform was located in a different quadrant of the maze on each trial. Following Trial 8 in both tasks, the rats received a posttraining subcutaneous injection of d-amphetamine (1.0 mg/kg), quinpirole (LY 171555; 2.0 mg/kg), or saline. On a retention test session 24 h later, latency to mount the escape platform was used as a measure of memory. In both tasks, the retention test escape latencies of the animals given d-amphetamine or quinpirole were lower than those of the saline-injected controls. In both tasks, injections of (d-amphetamine and quinpirole did not affect retention when administered 2 h posttraining, indicating a time-dependent effect of the posttraining treatments on retention. Control experiments indicated that the effects of d-amphetamine on retention were not due to enhancement of memory of a search strategy common to both tasks. Rather, the effects of the drug on retention were due to an influence on memory for the type of discrimination learned (i.e., spatial or cued). The findings indicate that both spatial and cued discriminations in a water maze are sensitive to posttraining memory enhancement, and they suggest a neuromodulatory role for dopaminergic systems in both tasks. 1994, Psychonomic Society, Inc.. All rights reserved.