Comparison of tetrahydroaminoacridine and physostigmine on scopolamine-induced free swim behavior in the rat.

The effect of acetylcholinesterase inhibitors on free swim behavior in rats pretreated with scopolamine (0.32 mg/kg, IP) was examined. Long-Evans rats received a single 5-min testing trial in a 1.5 m black swimming pool, and swim distance in three concentric annulus corridors (peripheral, middle, and inner) and the number of body-turn transitions (greater than 45 degrees) were measured. Physostigmine (1.0 mg/kg, IP) increased swim distance in the middle and inner annulus corridors, compared to tetrahydroaminoacridine (2.0 mg/kg and 10 mg/kg, IP) and scopolamine alone (control) (Ps less than 0.01), and increased body-turn transitions, compared to all the other groups (Ps less than 0.05), but had no significant effect on peripheral annulus corridor swim distance, total swim distance, or swim speed. The results suggest that physostigmine produces uniquely different free swim patterns from tetrahydroaminoacridine following cholinergic blockade. These findings have implications for investigations attempting to restore spatial learning and navigation (e.g., Morris water maze) using acetylcholinesterase inhibitors following experimentally-induced cholinergic losses.