Captivity alters neuroendocrine regulators of stress and reproduction in the hypothalamus in response to acute stress

Abstract

Wild animals are brought into captivity for many reasons. However, unlike laboratory-bred animals, wild caught animals often respond to the dramatic shift in their environment with physiological changes in the stress and reproductive pathways. Using wild-caught male and female house sparrows (Passer domesticus) we examined how time in captivity affects the expression of reproductive and stress-associated genes in the brain, specifically, the hypothalamus. We quantified relative mRNA expression of a neurohormone involved in the stress response (corticotropin releasing hormone [CRH]), a hypothalamic inhibitor of reproduction (gonadotropin inhibitory hormone [GnIH]), and the glucocorticoid receptor (GR), which is important in terminating the stress response. To understand potential shifts at the cellular level, we also examined the presence of hypothalamic GnIH (GnIH-ir) using immunohistochemistry. We hypothesized that expression of these genes and the abundance of cells immunoreactive for GnIH would change in response to time in captivity as compared to free-living individuals. We found that GR mRNA expression and GnIH-ir cell abundance increased after 24 and 45 days in captivity, as compared to wild-caught birds. At 66 days in captivity, GR expression and GnIH cell abundance did not differ from wild-caught birds, suggesting birds had acclimated to captivity. Evaluation of CRH and GnIH mRNA expression yielded similar trends, though they were not statistically significant. In addition, although neuroendocrine factors appeared to acclimate to captivity, a previous study indicated that corticosterone release and immune responses of these same birds did not acclimate to captivity, suggesting that neuroendocrine endpoints may adapt more rapidly to captivity than downstream physiological measures. These data expand our understanding of the physiological shifts occurring when wild animals are brought into captivity.

Keywords: Adrenocorticotropin hormone (ACTH); Chronic stress; Corticosterone; Corticotropin releasing hormone (CRH); Glucocorticoid receptors (GR); Gonadotropin Inhibiting Hormone (GnIH); House sparrow (Passer domesticus); Negative feedback.