Implication of amygdaloid muscarinic cholinergic mechanisms in passive avoidance learning in the developing rat

Young rats, 12–20 days of age, received bilateral microinjections of atropine sulfate (1, 5 and 20 μg) into the basolateral part of the amygdala, and were trained to learn a cool-draft-stimulus passive avoidance task 17 min later. Twelve-day rats did not perform differently from their controls. In contrast, rats 13–20 days of age exhibited significant age- and dose-related acquisition deficits. Sensitivity to atropine was high until day 17, and decreased progressively thereafter. These results demonstrate that muscarinic cholinergic synaptic elements located in the basolateral part of the amygdala are involved in passive avoidance learning in the young rat and begin to function on postnatal day 13. They also suggest that the number of functioning muscarinic receptor sites increase reliably after day 17.