Corticosterone and immune cytokine characterization following environmental manipulation in female WKY rats

This study investigated the effects of environmental manipulation on female Wistar Kyoto (WKY), an animal model of depression, and female Wistar rats. It explored the function of the hypothalamic-pituitary-adrenal axis (HPA) and immune system, as they have both been implicated in the pathophysiology of depression. A further goal was to characterize the immune cytokine concentrations of female WKY rats as this has, to our knowledge, never been documented. Animals were assigned to enriched, standard, or impoverished housing for four consecutive weeks. Following this, serum was collected at baseline and post-stress periods to measure the concentration of corticosterone, TNF-α, IL-1β, and IL-10. WKY animals had significantly higher corticosterone levels at the post-stress time-point than their Wistar counterparts. WKY females in isolation tended to have the lowest corticosterone levels which may indicate that they prefer a solitary environment, a symptom of depression. We observed a significant decrease in TNF-α after enrichment in the Wistar strain. A similar decrease in TNF-α was found in the WKY strain, but there was no difference between environmental conditions. There was a significant increase in pre- to post-stress IL-10 level in both Wistar and WKY animals. WKY females had a significantly lower level of IL-1β as compared to the Wistar animals at both pre- and post-stress time points. Given this strain difference, it is likely that the WKY rats had a dysregulated HPA axis which further influenced their circulating cytokine levels. Further studies are needed to examine how this pattern of findings plays a role in the pathophysiology of depression.