TI - Biochemical Studies of NMDA Receptors . AB - We further examined the expression of different subunits of NMDA receptors , NR1 , NR2A and NR2B in hippocampus of wild-type and neurabin KO mice . We found that there is no difference in the expression of NR1 ( n = 4 mice , P gt 005 , paired t-test ) , NR2A ( n = 4 mice , P gt 005 , paired t-test ) or NR2B ( n = 4 mice , P gt 005 , paired t-test ) between wild-type and neurabin KO mice ( Fig 3C ) . Moreover , we studied the expression of NMDA receptor scaffolding protein , PSD95 in neurabin KO mice . We found that PSD95 expression is not altered in neurabin KO mice ( n = 4 mice , P gt 005 , paired t-test , Fig 3C ) . phosphorylaTION of NMDA receptor is critical for the receptor activity and PP1 , a neurabin-binding protein , is known to regulate protein PHOSphorylation [14] , [32] . Therefore , we wanted to know whether PHOSphorylation of NMDA receptor was altered or not in neurabin KO mice . We compared the PHOSphorylation of all three NMDA receptor subunits at serine sites in wild-type mice to those in neurabin KO mice . No significant change was found for the PHOSphorylation of NMDA receptor subunits ( Fig 3D ; n = 4 mice , P gt 005 , paired t-test ) . Taken together , these results indicate the function of NMDA receptor is intact in neurabin KO mice .