Effects of cholinergic drugs on scopolamine-induced memory impairment in rhesus monkeys.

Rhesus monkeys were trained to perform matching-to-sample responses in which monkeys had to choose one of two stimuli that had the same color as the previously presented sample. Half of a daily session consisted of simultaneous trials where the sample was present during the trial, and the other half consisted of delayed trials, where the sample had been presented at the start of the trial but was withheld at the time of choosing. With vehicle control, the percentage of correct responses (CR%) in both trials exceeded 85%. Scopolamine (4-32 micrograms/kg, SC) selectively decreased the CR% for delayed trials in five out of eight animals, suggesting impairment of short-term memory. Physostigmine (2-16 micrograms/kg, SC), arecoline (16-128 micrograms/kg, SC) and nicotine (4-32 micrograms/kg, SC) attenuated the scopolamine-induced impairment of CR% in delayed trials with concurrent administration with scopolamine. Methamphetamine (16-64 micrograms/kg, SC) did not show such effects. These results suggested that scopolamine-induced memory impairment could be recovered by cholinergic agonists.