CHOLINERGIC EFFECTS ON SPATIAL EXPLORATION AND ITS MEMORY

In their first swim in an unfamiliar circular swimming pool, control r ats showed declines in average swimming speed and in the time spent in the perimeter of the pool. Both declines were antagonized by the musc arinic antagonist scopolamine, but not by methylscopolamine, a muscari nic antagonist that crosses the blood - brain barrier only poorly, ind icating that these declines depend upon central cholinergic activity. In the first minute of a second swim 3 days later, control rats spent a much longer time in the central region of the pool than in the first minute of the first swim. This modification of behaviour by previous experience suggests that a long-term memory of the first swim was form ed. Scopolamine, but not methylscopolamine, administered before the fi rst swim attenuated this modification of behaviour. Pilocarpine, admin istered shortly after scopolamine before the first swim, significantly normalized all the scopolamine-induced changes, whereas oxotremorine and arecoline normalized only habituation of perimeter preference; ago nists administered alone decreased swimming speed and perimeter prefer ence without affecting their rates of decline. The results suggest tha t in this test, different cholinergic mechanisms are involved in habit uation of swimming speed and habituation of perimeter preference.