AMPA receptor phosphorylation and recognition memory: learning-related, time-dependent changes in the chick brain following filial imprinting

There is strong evidence that a restricted part of the chick forebrain, the intermediate medial mesopallium (IMM), stores information acquired through the learning process of visual imprinting. We have previously demonstrated that at 1 h but not 24 h after imprinting training, a learning-specific increase in the amount of membrane Thr286-autophosphorylated alpha-calcium/calmodulin-dependent protein kinase II (alpha CaMKII), and in the proportion of total alpha CaMKII that is phosphorylated, occurs in the IMM but not in a control brain region, the posterior pole of the nidopallium (PPN). alpha CaMKII directly phosphorylates Ser831 in the GluA1 subunit of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor. In the present study we have inquired whether the learning-related increase in alpha CaMKII autophosphorylation is followed by changes in the Ser831 phosphorylation of GluA1 (P-GluA1) and in the total amount of this subunit (T-GluA1). Trained chicks together with untrained control chicks were killed either 1 or 24 h after training. Tissue was removed from the IMM together with tissue from the PPN as a control. Amounts of P-GluA1 and T-GluA1 were measured. In the left IMM of the 1 h group the P-GluA1/T-GluA1 ratio increased in a learning-specific way. No learning-related changes were observed in other brain regions at 1 h or in any region 24 h after training. The results indicate that a time- and regionally-dependent, learning-specific increase in GluA1 phosphorylation occurs early in recognition memory formation.