Transient increase in forebrain muscarinic cholinergic receptor binding following passive avoidance learning in the young chick

The concentration of the muscarinic cholinergic receptor in two regions of the chick brain was measured by atropine-sensitive binding of the ligand [ 3H]quinuclidinyl benzilate at varying times after training 1–2 day old chicks on a one-trial passive avoidance task. Thirty min after training, there was a 21% increase ( P < 0.001) in [ 3H]quinuclidinyl benzilate binding/mg protein in the chick fore brain, though not the optic lobes. The elevation was not significant at 10 min after training and had disappeared in 3 h. The elevation could not be induced merely by making the birds taste the aversive stimulus, methylanthranilate, whilst agents which disrupted acquisition and memory, ouabain and cyclo heximide, also abolished the training-induced rise in [ 3H]quinuclidinyl benzilate binding activity. We suggest that increased [ 3H]quinuclidinyl benzilate binding in the chick forebrain is a correlate of the early phases of memory fixation.