Controllable and Uncontrollable Stress Differentially Impact Fear Conditioned Alterations in Sleep and Neuroimmune Signaling in Mice

Abstract

Stress induces neuroinflammation and disrupts sleep, which together can promote a number of stress-related disorders. Fear memories associated with stress can resurface and reproduce symptoms. Our previous studies have demonstrated sleep outcomes can be modified by stressor controllability following stress and fear memory recall. However, it is unknown how stressor controllability alters neuroinflammatory signaling and its association with sleep following fear memory recall. Mice were implanted with telemetry transmitters and experienced escapable or inescapable footshock and then were re-exposed to the shuttlebox context one week later. Gene expression was assessed with Nanostring^® panels using RNA extracted from the basolateral amygdala and hippocampus. Freezing and temperature were examined as behavioral measures of fear. Increased sleep after escapable stress was associated with a down-regulation in neuro-inflammatory and neuro-degenerative related genes, while decreased sleep after inescapable stress was associated with an up-regulation in these genes. Behavioral measures of fear were virtually identical. Sleep and neuroimmune responses appear to be integrated during fear conditioning and reproduced by fear memory recall. The established roles of disrupted sleep and neuroinflammation in stress-related disorders indicate that these differences may serve as informative indices of how fear memory can lead to psychopathology.

Keywords: extinction learning; fear memory; neuroinflammation; sleep; stressor controllability.

Figure 1

Rapid Eye Movement Sleep is Reduced After Inescapable but not Escapable Stress. Total REM ± SEM duration plotted following Baseline (Base), shock training days (ST 1 and ST 2), and context re-exposure (CTX) during the (A) first 2 h, (B) light period (8 h), (C) dark period (12 h) and (D) total 20 h. Significant differences in ES vs. IS: * p < 0.05, ** p < 0.01.

Figure 2

Non-Rapid Eye Movement Sleep is Increased After Escapable Stress. Total NREM ± SEM duration plotted following Baseline (Base), shock training days (ST 1 and ST 2) and context re-exposure (CTX) during the (A) first 2 h, (B) light period (8 h), (C) dark period (12 h) and (D) total 20 h. Significant differences in ES vs. IS: * p < 0.05.

Figure 3

Freezing Behavior and Stress-Induced Hyperthermia Does Not Differ Between Escapable and Inescapable Stress. (A) Percent time freezing ± SEM plotted in 10 min blocks (B1-3) for the total 30 min timeframe during each shock training day (ST 1 and ST 2) and context re-exposure (CTX). Average core body temperature ± SEM plotted in 15 min intervals for a total of 2 h (B) at baseline, (C) after shock training day 1 (ST 1), (D) after shock training day 2 (ST 2) and (E) after context re-exposure (CTX).

Figure 4

Escapable Stress Decreases the Expression of Pro-inflammatory Immune Genes. Volcano plot displaying each gene expression levels in HPC compared to home cage (HC) control following CTX for (A) escapable stress (ES) and (B) inescapable stress (IS) groups. Statistically significant genes fall above the horizontal line, and highly differentially expressed genes fall to either side of the zero on the x-axis. The most relevant genes are labelled in the plot.

Figure 5

Escapable Stress Increases the Expression of Neuroprotective Genes. Volcano plot displaying each gene expression levels in BLA compared to home cage (HC) control following CTX for (A) escapable stress (ES) and (B) inescapable stress (IS) groups. Statistically significant genes fall above the horizontal line, and highly differentially expressed genes fall to either side of the zero on the x-axis. The most relevant genes are labeled in the plot.

Figure 6

Stressor Controllability Differentially Influences Pathways Involved in Brain Homeostasis. Heatmaps displaying the directed global significance scores of overlayed differential gene expression data for sets of genes grouped by biological function relative to HC in (A) HPC and (B) BLA, respectively. Directed global significance statistics measure the extent to which a gene set’s genes are up- or down-regulated with the variable. Red denotes gene sets whose genes exhibit extensive over-expression with the covariate, green denotes gene sets with extensive under-expression.