The effects of extrinsic stress on somatic markers and behavior are dependent on animal housing conditions

Properties of the environment play an important role in animal wellbeing and may modulate the effects of external threats. Whereas stressors can affect emotion and impair cognition, environmental enrichment may prevent the occurrence of such negative sequelae. Animals exposed to semi-natural group-housing experience a complex environment; whereas environmental enrichment might protect against stressors, a social and environmental enrichment (SEE) could entail aggressive inter-male encounters with additive stress effects. In the present study, we investigated the effects of exposure to external stressors, footshocks and forced swimming, on adrenal- and bodyweight as well as on behavior in rats housed under SEE or standard, non-enriched environment (NEE), conditions. We found that SEE reduced the anxiogenic effects of stress. Moreover, SEE improved the performance of an operant task and prevented the increase in impulsive behavior produced by external stressors on NEE animals. Whereas these findings are indicative of stress-buffering effects of SEE, adrenal weights were increased while total body weights were decreased in SEE rats, suggesting that SEE may simultaneously exacerbate physiological measurements of stress. Finally, in the SEE, total aggressive behaviors and body wounds were paradoxically reduced in animals that received external stressors in comparison to non-stressed controls. The consequences of the external stressors applied here are not uniform, varying according to the housing condition and the outcome considered.