TI - Biochemical Studies of AMPA Receptors . AB - To explore the possible mechanism for the enhanced AMPA receptor -mediated responses , biochemical experiments were conducted . The increased AMPA receptor -mediated synaptic responses may reflect the altered expression or PHOSphorylation of AMPA receptors in neurabin KO mice [20] . To test the possibilities , we studied the expression of main AMPA receptor subunits , GluR1 and GluR2&3 in the hippocampus ( Fig 4E ) . We found that there is no difference in the expression of total GluR1 between wild-type ( n = 4 mice ) and neurabin KO mice ( n = 4 mice , P gt 005 , paired t-test ; Fig 4E and G ) . Moreover , no difference was found for total GluR2&3 expression between two groups ( n = 4 mice for each group , P gt 005 , paired t-test ; Fig 4E and G ) . phosphorylaTION and dePHOSphorylation of GluR1 play a critical role for AMPA receptor insertion and internalization [9] , [12] , thereby affecting AMPA receptor -mediated synaptic responses . We therefore studied the PHOSphorylation of GluR1 at two main sites , Ser845 (PKA site) and Ser831 (CaMKII/PKC site) (Fig 4F) . Surprisingly , we found that PHOSphorylation of PKA site was decreased in neurabin KO mice to 36.0+-9.0 % of the levels in wild-type mice ( n = 4 mice , P lt 001 , paired t-test ; Fig 4F and G ) . However , PHOSphorylation of GluR1 at CaMKII/PKC site was not altered in neurabin KO mice ( n = 4 mice , P gt 005 , paired t-test ; Fig 4F and G ) . Therefore , deletion of neurabin regulates GluR1 PHOSphorylation in a site -specific manner .