Sex differences of the impact of transportation on the stress response and brain neurochemistry associated with affective state

Why this research is being done

microscopic view of chicken pituitary gland When birds are exposed to a stressor and are unable to maintain homeostasis, the hypothalamic pituitary adrenal (HPA) axis is up regulated to respond to stress. The HPA is a hormonal pathway from hypothalamus to adrenal glands that results in the release of glucocorticoids (GC). Our study’s objective was to measure several peripheral and central physiological parameters to assess response to transportation. This included responses to stress such as circulating corticosterone and blood heterophil to lymphocyte ratio (HLR), and central CRH and NPY gene expression, and measures of affective state by assessing 5-HT and DA turnover and TPH1, TPH2, and TH gene expression. We hypothesized that transportation could elicit a negative affective state as indicated by multiple biological factors.

Results

Blood was collected for serum corticosterone and blood smear analyses. Brains were hemisected and each half was dissected into three brain areas: caudal mesencephalon (CM), rostral mesencephalon (RM), and diencephalon (DI). Mass spectrometry was run on the right half of the brain, and gene expression of TPH1, TPH2, TH, CRH, and NPY were measured on the left half of brain using qRT-PCR. Serum corticosterone levels were increased in crated hens and in transported hens and drakes when compared to control. HLR is increased in crated hens and transported hens and drakes compared to control. No differences in serotonin turnover were observed in drakes but increased in hens within the CM and RM from control to crate and crate to transport. There were no differences in DA turnover or in gene expression for all brain areas for drakes and CM and RM for hens. Within the DI, hens showed a decrease in TPH1 for transport compared to crate. Overall, transportation elicits an acutely stressful event that increases corticosterone and HLR in a sex dependent manner where hens appear to be more reactive to the stressor than drakes. Our data supports that when assessing a stress response, care must be given to the sex of the bird and to the relative timepoint of sampling compared to the perceived onset of the stressor.

 

Fraley transporting ducks
Conclusions
  1. Transportation can be an acutely stressful event where corticosterone, HLR, and 5-HT activity are altered in a sex dependent manner.
  2. It is important to consider collection time after onset of stressor and the sex of subjects to accurately assess a stress response.
  3. 5-HT and DA activity should continue to be utilized as a repeatable indicator of affective state to broaden our understanding of how an animal’s mental state is affected by environmental changes.
Future Directions:

1. Determine how transportation stress affects the physiology and brain neurochemisty of birds at different ages: ducklings, prepubertal, young adult, and geriatric
2. To determine what neural factors can be measured that are specifically associated with a positive affective state.

Contact information

Gregory S. Fraley gfraley@purdue.edu | Purdue ANSC Directory