OBJECTIVETo investigate the developmental profiles on surface expression and co-localization of NMDA receptor clusters and AMPA receptor clusters on dendrite in cultured hippocampal neurons of rats.

METHODSGreen fluorescent protein tagged GluR2 subunit (GFP-GluR2) and FLAG tagged NR2B subunit (FLAG-NR2B) were transfected into cultured hippocampal neurons at 5 days in vitro (DIV5). FLAG-NR2B containing NMDA receptor clusters and GFP-GluR2 containing AMPA receptor clusters expressed on membrane surface were then labeled in living neurons using anti FLAG mAb/Cy3-conjugated anti-mouse antibody and anti-GFP pAb/Alex488-conjugated anti-rabbit antibody.

RESULTThe numbers of receptor cluster per 100 microm dendrite in the neurons at DIV7 and DIV19 were 39.7+/-5.0 and 64.7+/-6.1 (P<0.01) for NR2B-NMDAR, 59.1+/-3.3 and 99.7+/-6.4 (P<0.01) for GluR2-AMPAR, and 29.9+/-4.5 and 37.5+/-2.5(P<0.05) for the co-localized, respectively. At DIV7 and DIV19, 75.4% and 57.9% NR2B-NMDAR clusters were co-localized with GluR2-AMPAR; and 50.6% and 37.6% GluR2-AMPAR clusters were co-localized with NR2B-NMDAR, respectively.

CONCLUSIONThe density of NR2B-NMDAR containing and GluR2-AMPAR containing receptor clusters increases during development of hippocampal neurons in culture. Although the co-localized clusters are increased as well in an unit length of dendrite, the extent to which the two receptor clusters are co-localized decreases. These data imply a possible change in the partnership of AMPA receptor subtype and NMDA receptor subtype at newly formed synapses during development.