Functional Convergence of Neurons Generated in the Developing and Adult Hippocampus
Figure 3
Short-Term Plasticity of Entorhinal Glutamatergic Afferents
(A) Average EPSCs recorded at VHold = −80 mV (downward deflections) and +50 mV (upward deflections) from pup and adult DGCs (n = 8 to 11) upon stimulation of MPP or LPP. Dashed line indicates zero level. Arrowheads denote time points for quantification of AMPA (open triangles) and NMDA (filled triangles) currents shown in (B). Criteria for AMPA/NMDA quantification are detailed in the Materials and Methods section. Scale bars indicate 20 ms, 100 pA.
(B) AMPA/NMDA ratio from pup and adult DGCs (n = 9 to 13) in response to MPP or LPP stimulation. Two-way ANOVA revealed a significant effect of MPP versus LPP (p = 0.006), but no significant effect of pup versus adult (p = 0.63).
(C) Averages of EPSCs in response to paired-pulse stimulation of the MPP or LPP delivered at increasing interpulse intervals (20, 50, 100, and 500 ms). Traces are averages of 7–14 cells aligned and normalized to the first EPSC. Stimulation artifacts and late decay phases of the second EPSC were removed for clarity. Scale bar indicates 100 ms.
(D) Paired-pulse ratio as a function of interpulse interval for the experiments shown in (C). Two-way ANOVAs revealed a significant effect of interpulse interval for MPP (dashed lines, p < 0.0001) and LPP (solid lines, p < 0.0001), but no significant effect of pup (green lines, solid circles) versus adult (red lines, open circles) for either MPP (p = 0.073) or LPP (p = 0.72) stimulation (n = 9 to 14)
(E) Example of EPSCs from a pup (green) and an adult DGC (red) in response to MPP stimulation (ten pulses, 50 Hz) Traces are normalized to the first EPSC amplitude. Scale bar indicates 40 ms.
(F) Relative EPSC amplitudes measured in response to 50-Hz stimulation evoked as shown in (E). No difference was found between pup and adult responses (two-way ANOVA, p = 0.49, n = 10 pups [solid circles], n = 4 adults [open circles]). All recordings were carried out in the presence of 20-μm BMI. Neurons were approximately 18 wk old (pup) and approximately 13 wk old (adult). All plots depict mean ± SEM.