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

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Abstract
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, passiveavoidance task shortly after (17 min). Gallamine triethiodide had no action at low doses and provoked convulsions at higher concentrations. Pempidine tartrate produced ageq and dose‐dependent impairments of the passive avoidance, and was much more effective in younger groups (11 and 16 days) than at 20 days. α‐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.