ANTICHOLINERGIC EFFECTS ON ACQUISITION OF PLACE LEARNING IN THE MORRIS WATER TASK - SPATIAL-MAPPING DEFICIT OR INABILITY TO INHIBIT NONPLACE STRATEGIES

The role of central cholinergic blockage in spatial learning was exami ned by testing atropine sulfate-treated (50 mg/kg) rats and saline-inj ected controls in the Morris water task using training procedures desi gned to promote the use of a spatial search strategy. First, constrain ts used in early trials deterred thigmotaxis. Second, an originally ov ersized hidden platform that nearly occupied the entire pool was effec tively ''shrunk'' into the southwest quadrant of the pool by substitut ing smaller platforms over trials, a procedure intended to focus atten tion on the hidden platform in relation to extramaze cues. Task acquis ition did not differ between groups, and on the probe trial both group s increased distance and latency and swam preferentially in the previo usly correct quadrant. Impairments caused by atropine sulfate may be t he result of deficits in ability to inhibit nonefficient escape strate gies.