Cholinergic receptor blockade produces impairments in a sensorimotor subsystem for place navigation in the rat: evidence from sensory, motor, and acquisition tests in a swimming pool

Abstract

Studies have shown that central cholinergic receptor blockade biases the behavior of rats so that they make less use of the sensorimotor behaviors that are normally used to orient to the relational properties of distal cues and that they simultaneously become more reliant on proximal cues. In Experiment 1, control rats and rats treated with atropine sulfate or atropine methyl nitrate (50 mg/kg) were trained to escape to a visible platform from different starting points in a swimming pool. All groups learned the task by concomitantly developing position responses, by orienting according to room cues, and by orienting to the platform, but probe trials showed that the atropine-sulfate group made more use of the platform as a local cue and made less use of distal cues than did the other groups. The atropine-sulfate group also made fewer searches during acquisition, made fewer searches when the platform was removed on probe trials, and were less responsive to novel cues placed above and around the pool. Swim speed, as estimated by the distance swum on probe trials, was also greater in atropine-sulfate-treated rats. The postulate that rats treated with atropine sulfate preferentially guide swimming by using position responses and local cues was tested in Experiment 2 by comparing their performance with that of control rats in a place task in which a target platform was hidden (no local cues present) and in a similar place task in which the target platform was visible, as was a second incorrect platform that sank when climbed upon (two competing local cues present). Although both tasks were acquired by the control and drugged rats, the two-platform task, as predicted, was comparatively more difficult for the atropine-treated rats. These results suggest that one effect of central cholinergic blockade is to impair the use of a sensorimotor subsystem used for place navigation.