Atropine sulfate impairs selective parameters of performance in the Morris water maze

Twelve rats were trained to learn the location of a spatially fixed platform hidden in a Morris water maze. Asymptotic performance was achieved over six training days (10 trials/day). Then retention of the spatial task was assessed 30 min after treatment with 5, 25, 50, 75, or 100 mg/kg, ip, atropine sulfate or the equivalent volume of saline. There was a significant drug effect on escape latency, swim distance, swim speed and swim path measures of spatial performance. There was no significant drug effect on heading error; atropinized animals initially headed toward the escape platform over the first 12 cm of their swim path. However, treatment with atropine sulfate significantly disrupted the usual, direct swim path used to reach the hidden escape platform. Atropinized animals frequently swam a spiraled or looping pattern to locate the platform. We suggest that cholinergic blockade may significantly disrupt the processing of visual cues which rats use in place navigation tasks.