Figure 6.

mEPSCs showed varied contribution from NMDA-R and AMPA-R. A, Examples of mEPSCs recorded in the one E14 neuron in the presence of 1 μm tetrodotoxin. The addition of 100 μm APV helped confirm the existence of predominantly AMPA-only mEPSCs, NMDA-only mEPSCs, or those with mixed contribution from AMPA-R and NMDA-R (“Mixed”). Right, Portions of the recording on the left on an expanded time scale, highlighting the apparent effect of APV. B, From the same neuron in A, overlaid mEPSCs classified as AMPA only, NMDA only, or mixed. C, Average frequency of mEPSCs shows a fivefold increase during development (p = 0.02, ANOVA), consistent with an increase in the number of release sites or release probability. D, The average peak amplitude of mEPSCs showed only a modest (less than twofold) but significant increase during development (p = 0.0002, ANOVA). E, The average amplitude of NMDA-R component (excluding AMPA only events) decreased significantly between E14 and E15 (p = 0.005, ANOVA), consistent with the removal of NMDA-R from postsynaptic sites. F, The relative fraction of all events in the three categories and linear fits. During development, the relative fraction of AMPA-only or mixed events changed significantly (p = 0.0002, ANOVA), whereas NMDA-only mEPSCs remained rare (p > 0.05, ANOVA).