Role of cholinergic neurotransmission in the amygdala on performances of passive avoidance learning in mice.

To clarify the role of cholinergic neurons in the amygdala on learning and memory, scopolamine was injected topically into the bilateral amygdala of mice, and the ability to perform two types of passive avoidance tasks (step-through and step-down) was investigated. On the first day mice performed the learning trial and on the second day their retention was tested. Scopolamine (0.5 or 1 microgram/site) was injected bilaterally into the amygdala 30 min before or immediately after the learning trial or 30 min before the testing trial. Scopolamine impaired the performance ability of the mice dose-dependently only when it was injected 30 min before the learning trial. The results coincided well with the effect of scopolamine injected intraperitoneally. Taken together, these results suggest that the site of action for scopolamine to cause anterograde amnesia is the amygdala, and that cholinergic neurons projecting to the amygdala play an important role in memory acquisition in the two passive avoidance tasks.