Evidence that muscarinic receptors are involved in nicotine-facilitated spatial memory

A delayed nonmatching-to-position task (DNMPT) in a water maze (nine trials per day, 10 days) was used to investigate the role of muscarinic acetylcholinergic receptor (mAChR) in nicotine-facilitated spatial memory in Wistar rats. The index of spatial memory was determined by the number of correct choices made in choice swim (CS) and the time taken to complete the swim in the correct CS. Diazepam (6 mg kg(-1) ip, daily) significantly impaired choice accuracy and increased the swim time for correct CS. In contrast, when nicotine (2 mg kg(-1) sc, twice daily) and diazepam were administered simultaneously in the last three sessions of training, the choice accuracies of CS were similar to controls and significantly higher than in the diazepam group. However, the swim times for correct CS were longer in the nicotine+diazepam group than in controls. Atropine (30 mg kg(-1) ip, daily) significantly decreased the choice accuracies of CS. The choice accuracies of CS swim times for correct CS in the atropine group did not differ significantly from those in the nicotine+atropine group, in which nicotine (2 mg kg(-1) sc, twice daily) and atropine were given simultaneously. These results show that nicotine improves memory performance when the functions of mAChRs are normal; when the mAChRs are blocked, nicotine does not enhance spatial memory. Therefore, mAChRs are involved in the spatial memory-enhancing effect of nicotine.