The effect of pirenzepine on spatial learning in the Morris Water Maze.

The effects of the selective M1-muscarinic antagonist, pirenzepine, were studied on the Morris Water Maze, a test of spatial learning in the rat. Pirenzepine (0, 10 or 30 micrograms) was administered into lateral ventricle during acquisition of this task. Although 30 micrograms of pirenzepine impaired acquisition of the spatial aspects of the task, treated animals still appeared to be able to acquire a taxon strategy. A low dose of pirenzepine (10 micrograms) produced a slight deficit but this was only visible in a "spatial probe" trial. Although these results are consistent with the belief that muscarinic M1-receptors are involved in spatial learning, it cannot be excluded that the effects recorded were mediated by muscarinic M2-receptors, due to the low selectivity of pirenzepine.