CHOLINERGIC FUNCTIONS FOR BRAIN PLASTICITY DURING BIRD SONG LEARNING

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A young male zebra finch learns its song during a sensitive period. The sensory motor phase of song learning is closely correlated to development of a song control nucleus, RA,which receives inputs from two other song control nuclei. We previously found that acetylcholine (ACh) content and the enzyme activity of choline acetyltransferase (ChAT) increase transiently in the RA during a sensitive period of song learning, when RA synapses for two inputs are highly plastic. For this purpose, we have investigated whether muscarinic agonist carbachol would affect phosphoinositide (PI) metabolism in the RA.The male zebra finch at 30 days, 50 days after hatching and adults were used. Carbachol-stimulated PI turnover was examined by measuring the accumulation of [3H]-inositol phosphates from [3H]-inositol labeled synaptoneurosomes of RA,in the presence of lithium. Carbachol increased PI turnover significantly. Carbachol-stimulated PI turnover reached a maximum at 50 days after hatching, and decreased to adult level. These results suggest that ACh affects synaptic plasticity of zebra finch RA during song learning, because PI turnover activate protein kinase C responsible for the phosphorylation of some phosphoproteins, which play a important role in synaptic plasticity.