Figure 7.

Repeated stress decreases the firing rate of lateral nucleus (LAT) interneurons. (a) GABAergic interneurons of the LAT can be putatively identified based on their narrow action potentials (top) compared with projection neurons (bottom; gray: overlay of 10 traces; black: average of traces). (b) The frequency distribution of neurons (percent of total) was plotted by action potential half-widths. The data distribution was better fit with two second-order polynomial curves than one, indicative of two populations of LAT neurons. A cutoff of 0.225 ms action potential half-width with ±0.015 ms buffer was used to separate the populations. Neurons with a half-width <0.205 ms were classified as putative interneurons. (c) Repeated stress decreased the firing rate of putative LAT interneurons in adolescent rats (*p<0.05, Holm–Sidak's multiple comparisons test after significance in two-way analysis of variance (ANOVA) but not in adult rats (p<0.05, Holm–Sidak's multiple comparisons test after significance in two-way ANOVA). (d) The firing rate was plotted by half-width for each putative interneuron. If a different population of neurons were sampled in control (those with a higher firing rate) and stress groups (those with a lower firing rate), a correlation would be expected between firing rate and half-width. There was no significant correlation (R²=0.038, p=0.243).