Figure 2.

The AMPA:NMDA ratio at ON synapses increases with postnatal maturation of ETCs and PGCs and with maturation of adult-born GFP+ neurons. A, Calculating an AMPA:NMDA ratio from ON-evoked inputs in a PGC. At −70 mV, in the presence of gabazine to block GABA_A receptors, magnesium blockade of NMDA receptors means that the recorded current is AMPA dominated. An estimate of AMPA amplitude (amp1) was therefore taken as the peak of this response. At +40 mV, however, magnesium block is removed from NMDA receptors, revealing a mixed AMPA+NMDA response. Because AMPA responses are fast, as illustrated by the gray trace showing the AMPA-only trace after l-APV application (50 μm), an estimate of NMDA amplitude (amp2) could be taken from this combined response at 50 ms after stimulation. The AMPA:NMDA (A:N) ratio was then simply calculated as amp1/amp2. B, Representative traces showing A:N ratios at different stages of maturation in ETCs, PGCs, and adult-generated GFP+ neurons. Bottom traces show responses at −70 mV; top traces show responses at +40 mV. Traces for each cell are normalized by amp1, and the A:N ratio is displayed at the bottom right of each example, showing the clear increase in A:N ratio as maturation proceeds in all three cell types. C, Significant positive correlations between maturation stage and A:N ratio for all three cell types. r and p report results of a nonparametric rank correlation on each dataset. A, Adult. D, Group comparisons show increasing A:N ratios with maturation in all three cell types. In this and in subsequent figures, data plotted are mean ± SEM, and values within bars show sample sizes (n). *p < 0.05; **p < 0.01. W1, Postnatal week 1; W4, postnatal week 4; 7–14, 45, and 90 refer to GFP+ cell groupings based on dpi; GFP− refers to control PGCs in adult tissue.