Specific disruption of spatial behaviour in rats by central muscarinic receptor blockade

Three groups of rats were required to locate a single water bottle from an octagonal array of eight otherwise empty bottles. For one group (place navigation) the goal bottle remained in the same place from trial to trial; for a second group (cue navigation) the position of the goal bottle was cued by a black card over the nozzle; for the third group the goal bottle was uncued and moved randomly from trial to trial. Place and cue groups improved more than controls on all measures of performance. Scopolamine (0.2 mg/kg) substantially impaired performance in the place group, but had no effect on either of the other groups; the peripherally acting anticholinergic drug meth-scopolamine (0.2 mg/kg) had no effect in any group. In a second experiment, using food rewards, scopolamine caused a dose-dependent impairment of place navigation at doses from 0.025 to 0.4 mg/kg; 0.4 mg/kg also impaired cue navigation, but at this dose behaviour was visibly abnormal. In both experiments, scopolamine primarily affected speed of performance rather than accuracy. Olfactory cues were shown not to contribute to performance in either group. The results implicate central cholinergic transmission in the processing of visuo-spatial information.