Hippocampal gene expression changes underlying stress sensitization and recovery

Abstract

Chronic and acute stressors have been linked to changes in hippocampal function and anxiety-like behaviors. Both produce changes in gene expression, but the extent to which these changes endure beyond the end of stress remains poorly understood. As an essential first step to characterize abnormal patterns of gene expression after stress, this study demonstrates how chronic restraint stress (CRS) modulates gene expression in response to a novel stressor in the hippocampus of wild type mice and the extent to which these changes last beyond the end of CRS. Male C57/bl6 mice were subjected to 1) a forced swim test (FST), 2) Corticosterone (Cort) or vehicle injections, 3) CRS for 21 days and then a FST, or 4) allowed to recover 21 days after CRS and subjected to FST. Hippocampal mRNA was extracted and used to generate cDNA libraries for microarray hybridization. Naïve acute stressors (FST and vehicle injection) altered similar sets of genes, but Cort treatment produced a profile that was distinct from both FST and vehicle. Exposure to a novel stress after CRS activated substantially more and different genes than naïve exposure. Most genes increased by CRS were decreased after recovery, but many remained altered and did not return to baseline. Pathway analysis identified significant clusters of differentially expressed genes across conditions, most notably the NfKB pathway. Quantitative RT-PCR validated changes from the microarrays in known stress-induced genes and confirmed alterations in the NfKb pathway genes, Ikbα, RelA and Nfkb1. FST increased anxiety-like behavior in both the naïve and recovery from CRS conditions, but not in mice 24hrs subsequent to their CRS exposure. These findings suggest the effects of naïve stress are distinct from Cort elevation and that a history of stress exposure can permanently alter gene expression patterns in the hippocampus and the behavioral response to a novel stressor. These findings establish a baseline profile of normal recovery and adaptation to stress. Importantly, they will serve as a conceptual basis to facilitate the future study of the cellular and regional basis of gene expression changes as well as genetic risk factors and adverse early life experiences that lead to impaired recovery from stress such as occurs in mood and anxiety disorders.

Hippocampal gene expression induced by cold swim stress depends on sex and handling

“…However, we demonstrate here that the rapid changes in gene expression in response to stress are not mediated by corticosterone. Our results are in agreement with a recent microarray analysis showing that Fos, Per1 and Sgk1 are increased by acute swim stress in the male mouse hippocampus, but that these changes are not detected after acute corticosterone injections (Gray et al, 2013). In support of a corticosterone-independent process, stress was found to increase Fos expression also after adrenalectomy (Melia et al, 1994).…”

“…Our data confirm previous reports showing that Per1 can be rapidly regulated by acute stressors in several brain regions (Gray et al, 2013;Yamamoto et al, 2005) and even in peripheral tissues (Yamamoto et al, 2005). However, we are the first to show that Per1 expression is extremely sensitive to a very short period of handling in males.…”

“…The rapid activation of Sgk1 in response to acute stress could thus be important for the effects of stress on memory performance, as it is well-known that acute stress can enhance memory acquisition (Sandi et al, 1997). Our data confirm a previous report that acute swim stress induces Sgk1 expression in the hippocampus (Gray et al, 2013). We demonstrate that Sgk1 expression is regulated similarly in males and females, and is insensitive to the effects of handling.…”

“…It is known that corticosterone has widespread effects on gene regulation, both with rapid as well as with delayed onset after stress (Gray et al, 2013;Groeneweg et al, 2012). We thus tested whether an acute injection of corticosterone could mimic the effects of stress on gene expression.…”

“…Female rodents show a stronger increase in ACTH and corticosteroid levels than males in response to acute stressors Bale, 2010, 2008;Handa et al, 1994), and regulation of corticosteroid receptors in response to acute stress is different in male and female rats (Karandrea et al, 2002). Corticosterone, which acts as a potent regulator of gene expression in the CNS (Datson et al, 2011;Gray et al, 2013), is therefore a likely candidate to mediate some of the sex differences in stress-induced gene expression. Another key regulator of gene expression following stress is corticotropin-releasing hormone (Crh) (Joëls and Baram, 2009).…”