FIG. 4.
Intrinsic excitability of layer V pyramidal neurons in the mPFC is minimally altered after rTBI. (A) Representative traces from layer V pyramidal neurons showing the membrane potential response to current injection (−250, −150, −50, 200 pA). Analysis of the passive membrane properties showed no significant difference between sham and rTBI groups for the resting membrane potential (B, F(11,12) = 2.00, p = 0.81; h2 = 0.003; two-tailed t test) or input resistance (C, F(12,11) = 1.96, p = 0.87; h2 = 0.001; two-tailed t test). The sum of the sag, and rebound response, indicative of the amount of IH current, was not altered (D, F(11,12) = 6.57, p = 0.14; h2 = 0.15; two-tailed t test with Welch's correction). A non-significant trend for a reduction in action potential (AP) half width was noted in the rTBI group (E, F(11,12) = 1.74, p = 0.07; h2 = 0.14; two-tailed t test); however, the AP threshold (F, F(12,11) = 1.75, p = 0.89; h2 = 0.001; two-tailed t test) and AP amplitude (G, F(11,12) = 1.60, p = 0.42; h2 = 0.03; two-tailed t test) were similar between groups. There was a trend for a decreased initial instantaneous frequency of firing with rTBI, which was not significant with repeated measures two-way ANOVA testing (H, F(1,23) = 2.86, p = 0.10; h2 = 0.02 for rTBI treatment effect, repeated measures two-way ANOVA). The slope of the relationship between current injection and AP frequency response (I, F(12,11) = 1.53, p = 0.39; h2 = 0.03; two-tailed t test) was not different. However, a reduction in the adaptation of the AP interval over time was identified in the rTBI group compared with the sham group (J, Mann-Whitney U = 37, *p < 0.05 two-tailed). All data are mean ± SEM. (n = 4 animals/group with 3–4 cells per animal). ANOVA, analysis of variance; mPFC, medical prefrontal cortex; rTBI, repetitive traumatic brain injury; SEM, standard error of the mean. Color image is available online at www.liebertpub.com/neu