Mouse social stress induces increased fear conditioning, helplessness and fatigue to physical challenge together with markers of altered immune and dopamine function

Abstract

In neuropsychiatry, animal studies demonstrating causal effects of environmental manipulations relevant to human aetiology on behaviours relevant to human psychopathologies are valuable. Such valid models can improve understanding of aetio-pathophysiology and preclinical discovery and development of new treatments. In depression, specific uncontrollable stressful life events are major aetiological factors, and subsequent generalized increases in fearfulness, helplessness and fatigue are core symptoms or features. Here we exposed adult male C57BL/6 mice to 15-day psychosocial stress with loss of social control but minimal physical wounding. One cohort was assessed in a 3-day test paradigm of motor activity, fear conditioning and 2-way avoid-escape behaviour on days 16-18, and a second cohort was assessed in a treadmill fatigue paradigm on days 19 and 29, followed by the 3-day paradigm on days 30-32. All tests used a physical aversive stimulus, namely mild, brief electroshocks. Socially stressed mice displayed decreased motor activity, increased fear acquisition, decreased 2-way avoid-escape responding (increased helplessness) and increased fatigue. They also displayed increased plasma TNF and spleen hypertrophy, and adrenal hypertrophy without hyper-corticoidism. In a third cohort, psychosocial stress effects on brain gene expression were assessed using next generation sequencing. Gene expression was altered in pathways of inflammation and G-protein coupled receptors in prefrontal cortex and amygdala; in the latter, expression of genes important in dopamine function were de-regulated including down-regulated Drd2, Adora2a and Darpp-32. This model can be applied to identify targets for treating psychopathologies such as helplessness or fatigue, and to screen compounds/biologics developed to act at these targets. AbstractIn neuropsychiatric research, animal studies that demonstrate causal effects of environmental manipulations relevant to human aetiological factors on emotional and cognitive behaviours relevant to human psychopathologies are valuable. Such valid animal models can be useful for improved understanding of aetio-pathophysiology and preclinical discovery and development of new treatments. In depression, specific uncontrollable stressful life events are major aetiological factors, and subsequent generalized increases in fearfulness, helplessness and fatigue are core psychopathology symptoms or features. In the present study we exposed adult male C57BL/6 mice to an environmental manipulation of 15-day psychosocial stress with loss of social control but with minimal physical wounding. One cohort of stressed and control mice was assessed in a novel 3-day test paradigm of motor activity, fear conditioning and 2-way avoid-escape behaviour on days 16-18, and a second cohort was assessed in a treadmill fatigue paradigm on days 19 and 29, followed by the 3-day paradigm on days 30-32. All tests used a physical aversive stimulus, namely mild, brief electroshocks. The socially stressed mice displayed dec...

Mouse chronic social stress increases blood and brain kynurenine pathway activity and fear behaviour: Both effects are reversed by inhibition of indoleamine 2,3-dioxygenase

“…Chronic social defeat (CSD) was conducted using a refined protocol as described elsewhere (Azzinnari et al, 2014). Briefly, a C57BL/6 (CSD) mouse was housed singly in the home cage of a CD-1 mouse separated by a transparent, perforated divider.…”

“…The CSD mouse was placed 8 with the CD-1 mouse for either a cumulative total of 60 sec physical attack or 10 min maximum. To avoid bite wounds, essential for the study of psychosocial stress-induced immune-inflammation, the lower incisors of CD-1 mice were trimmed every third day across CSD (Azzinnari et al, 2014). Each day for 15 days, the CSD x CD-1 mouse pairings were rotated so that CSD mice were confronted daily with a novel CD-1 mouse.…”

“…In Expt A and B, frozen brains were placed in a stainless steel mouse brain matrix (Plastics One, model MMCS-1) and cut coronally into 1 mm sections (Azzinnari et al, 2014). Using a brain punch (Ø=1 mm, Stoelting Europe, model 57397) and a mouse brain atlas (Franklin and Paxinos, 2008) the following regions were microdissected: amygdala (1 biopsy/hemisphere) at bregma -1.0 to -2.0 mm, ventral hippocampus (vHIPP, 3 biopsies/hemisphere) at bregma -3.0 to -4.0 mm, medial prefrontal cortex (mPFC, 1 biopsy/hemisphere) at bregma 2.0 to 1.0 mm, dorsal striatum (DS, 2 biopsies/hemisphere) at bregma 0.0 to -1.0 mm, and dorsal raphe nucleus (DRN, 1 medial biopsy) at -4.0 to -5.0 mm.…”

“…A saline 13 perfusion step was not included in the brain collection protocol: a pilot study in naive and LPS-treated mice demonstrated comparable tryptophan metabolite levels in brain tissue collected with and without saline perfusion; expression levels of haemoglobin genes (e.g. , also expressed by brain cells (Biagioli et al, 2009)) obtained in brain tissues collected without saline perfusion were markedly lower (<0.02 %) than those measured in blood monocytes (Azzinnari et al, 2014); unpublished data).…”

“…Social disruption stress induces increased blood levels of proinflammatory cytokines and inflammatory monocytes, splenomegaly, increased monocyte trafficking to the brain, microglia activation in amygdala, hippocampus and prefrontal cortex, and hyper-anxiety (Hanke et al, 2012;Wohleb et al, 2011;Wohleb et al, 2013). Chronic exposure to social stress by an aggressive strain (chronic social defeat, CSD) induces increased blood levels of pro-inflammatory cytokines (TNF-, IL-6) and splenomegaly (Azzinnari et al, 2014;Savignac et al, 2011), and CSD mice exhibit increased social avoidance ( (Krishnan et al, 2007), see above), decreased active avoidance of footshock US (Azzinnari et al, 2014), and excessive CS fear expression (Yu et al, 2011).…”