Gender-specific effects of social housing in rats after chronic mild stress exposure

Stress plays an important role in the development of affective disorders. Women show a higher prevalence for these disorders than men. The course of a depression is thought to be positively influenced by social support. The authors have used a chronic mild stress model in which rats received footshocks daily for 3 weeks. Since rats are social animals we hypothesized that "social support" might reduce the adverse effects of chronic stress. To test this hypothesis, male and female rats were housed individually or socially in unisex groups of four rats. An open field test was repeated four times during the 3 weeks of treatment. Neuronal activation in the paraventricular nucleus of the hypothalamus (PVN) and dorsal raphe nucleus (DRN) in response to stress was measured the last day with c-fos. Chronic stress exposure increased locomotor activity in the open field, especially during the first minute. This was most pronounced in the individually housed females. In females, social housing prevented the stress-induced increase of locomotor activity, while in males social housing had no effect. Fos immunoreactive (FOS-ir) in the PVN was increased in all stress-exposed groups, except for the socially housed females due to a higher FOS-ir in controls. Individually housed males and socially housed females showed increased FOS-ir in the DRN and the increase was almost significant in socially housed males.

These results show that social housing can enhance coping with stress in female rats, whereas in male rats group housing did not have a positive influence on stress-sensitivity.