Figure 6.

Granule cell excitability may contribute to the late reduction in DDI. (A) Drawing of the recording configuration. Consecutive 500 ms duration current injections from −20 to +150 pA were delivered into GCs, with 10 pA increments and 5 s inter-injection intervals. (B) Sample traces of the minimum current injection to evoke action potentials (APs) in GCs with age, showing the injected current and the latency to the first spike. (C) The minimum current to evoke APs does not change significantly with age (ANOVA p = 0.50). (D) The latency to the first AP increases with age. The current above threshold is plotted vs. time between the onset of the current step and the first spike for ages P5, P15, and P30 (N-way ANOVA, contribution of age p = 3.4e⁻⁷). Curves are fitted to a single exponential. Asterisks indicate time points for which the P30 values are significantly different from P5 and P15 (Tukey’s p < 0.05). (E) Input resistance does not change significantly with age (ANOVA p = 0.48). (F) Resting potentials become significantly more negative with age (ANOVA p = 0.05, pairwise Tukey’s p < 0.05 indicated by asterisk). N = 6 for P5; N = 25 for P15; N = 12 for P30 for (D–F), N = 3 for P5; N = 16 for P15; N = 10 for P30 for (C).