Social deprivation stress is a triggering factor for the emergence of anxiety- and depression-like behaviours and leads to reduced brain BDNF levels in C57BL/6J mice

Stress is a main risk factor that can trigger psychiatric disorders, including anxiety and major depression. Neurotrophins, such as Brain-Derived Neurotrophic Factor (BDNF), have been identified as neuroendocrine effectors involved in the response to stress and in the neurobehavioural changes associated with depression. Aim of this paper was to study the relationship between neuroendocrine activation (circulating corticosterone and brain BDNF levels) and a wide array of depression- and anxiety-like behaviours (anhedonia, behavioural despair, generalised and social anxiety) resulting from exposure to chronic stress. To this end, 3-month-old C57BL/6J male mice were exposed to either chronic disruption of the social structure (SS), to a stable social structure (SG) or to social deprivation (SD), a condition lacking social stimuli. Results show that, despite not developing anhedonia (decreased preference for a sucrose solution), SD mice were characterised by increased emotionality and hypothalamic-pituitary-adrenal axis reactivity in addition to reduced BDNF levels. By contrast, SG and SS mice showed increased anhedonia accompanied by no alterations in the behavioural and neuroendocrine profile. The results here reported indicate that mice exposed to different social housing conditions use different behavioural strategies to cope with external challenges. In addition they suggest that social deprivation might represent a stressful condition triggering the emergence of both anxiety- and depression-like behaviours and clearly indicate BDNF as a main neurobiological variable mediating these responses.