Mediation of passive avoidance learning by nicotinic hippocampo-entorhinal components in young rats.

Young rats, 11, 16, and 20 days of age, received bilateral injections of three antinicotinic agents into the posteroventral hippocampo-subiculo-entorhinal area, and were trained to learn a cool-draft-stimulus, passive-avoidance task shortly after (17 min). Gallamine triethiodide had no action at low doses and provoked convulsions at higher concentrations. Pempidine tartrate produced age- and dose-dependent impairments of the passive avoidance, and was much more effective in younger groups (11 and 16 days) than at 20 days. alpha-bungarotoxin also induced dose-dependent deficits. These results, together with the mecamylamine-induced deficits already reported, suggest that nicotinic cholinergic synapses located in the posteroventral part of the hippocampal complex play a role in passive-avoidance learning in the young rat as soon as this type of conditioning is possible, but become relatively less important at older ages, when muscarinic mechanisms also become involved.