FIG. 1.

The functional expression of synaptic NR2A/NR2B increases over development in the mouse visual cortex. A: postsynaptic density fractions, enriched for synaptic proteins, show the relative expression of NR2A and NR2B at 4 developmental time points. Samples were obtained by pooling together visual cortices from 3 to 10 brains (see methods). B: N-methyl-d-aspartate receptor (NMDAR) subunit expression normalized to P8 values. NR2A expression increases dramatically over development, whereas there is only a modest developmental increase in NR2B expression. Note that some error bars are obscured by the overlying symbol. C: shortening of NMDAR current durations over development reflects an increase in the relative level of NR2A expression. Using whole cell voltage-clamp recordings, NMDAR currents were isolated at 3 age groups from L2/3 pyramidal cells following extracellular L4 stimulation. Cells were held at +40 mV in the presence of 6,7-dinitroquinoxaline-2,3-dione (DNQX; see methods). ○, averages of individual cells; •, the age group's average ± SE. A double-exponential fit of the deactivation current revealed a decrease in τ_w, corresponding to faster current kinetics over development. Stimulation artifacts were blanked in this and all subsequent figures for clarity.