Sex-dependent effects of environmental enrichment on mood-related behaviors, central and peripheral BDNF, and adrenal catecholamine enzymes in mice.

Housing conditions, particularly environmental enrichment (EE), can influence experimental outcomes and welfare. While EE is generally regarded as beneficial, a male bias exists in research supporting this. This study investigated whether sex differences exist in levels of BDNF in the brain and peripheral tissues in environmentally enriched mice. Expression of the catecholamine biosynthetic enzymes of the adrenal glands, key to the sympathoadrenal medullary system and stress response, was also investigated. We showed that female mice exposed to EE exhibited increased anxiety-like behaviors. EE in male mice did not induce anxiety-like behavior, and it was associated with increased hippocampal and pituitary BDNF expression, suggestive of enhanced neurotrophic support. In the adrenal gland, the levels of adrenal catecholamine biosynthetic enzymes, specifically total tyrosine hydroxylase and PNMT levels, were increased in females, but not in males. In conclusion, EE may serve as a mild stressor in female mice. In male mice, EE may have induced neurotrophic support of the hippocampus since hippocampal BDNF levels were increased with minimal changes to adrenal catecholamine synthetic enzymes. This study highlights the importance of considering sex as a biological variable in translational neuroscientific research.