Fig. 2.

Acute stressor exposure increases anxiety-like behavior and alters LC neuronal membrane properties one week later. The experimental timeline is shown in A. Animals underwent a surgical procedure to inject a red fluorescent retrograde tracer into mPFC or CeA. Seven days later, they underwent stressor exposure (n = 10) or control conditions (n = 9). One week later, anxiety-like behavior was assessed in the OFT. Rats were then sacrificed for whole-cell recordings of retrogradely labeled LC neurons. Stressor-exposed rats spent significantly less time in the center of the OFT (B). Time freezing was square root transformed to satisfy requirements for parametric statistical testing and found to significantly increase in response to stress (C; shown as median with interquartile range). Mean heat maps for behavior in the EPM are shown in D. LC→CeA neurons from stressed animals (n = 14 cells from 6 rats) were significantly more depolarized than LC→CeA neurons from control animals (n = 9 cells from 5 rats), while and LC→mPFC neurons from stressed rats (n = 12 cells from 4 rats) wre significantly more depolarized than LC→mPFC neurons from control animals (n = 9 cells from 4 rats). LC→mPFC neurons from control rats were also significantly more depolarized than LC→CeA neurons in control animals (E). Action potential threshold was also significantly more depolarized in LC→mPFC cells from stressed animals than in LC→CeA cells in both control and stressed animals (F). Activation gap, or the voltage required to reach threshold from rest, was significantly increased in LC→mPFC cells by stressor exposure. It was also significantly higher in LC→mPFC neurons from stressed animals than in LC→CeA neurons from either control or stressed animals (G). Afterhyperpolarization was significantly increased in LC→mPFC neurons by stressor exposure, and was significantly larger in LC→CeA cells from stressed animals than in LC→mPFC cells from control animals (H). Spontaneous firing rates were square root transformed to meet requirements for parametric statistical testing. Stress significantly increased the spontaneous firing rate of LC→CeA neurons, but decreased it in LC→mPFC projection cells (I; shown as median with interquartile range). Input resistance was significantly decreased by stressor exposure in the LC→mPFC cells, and was significantly greater in LC→CeA cells than LC→mPFC cells within the stress group (J). Stressor exposure and terminal field both significantly affected neuronal responsiveness to all levels of current injection (K). A summary of significant post hoc tests for results in (K) is shown in Table 1. Representative traces of spontaneous and evoked firing in response to 300 pA current injection are shown in L and M, respectively. *: p < 0.05. †: p < 0.05 after square root transformation. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)