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Abstract
Stressed animals produce glucocorticoids (GCs) that act to liberate energy for use to escape a stressors negative effects. Long-term exposure to stress exerts inhibitory influences on reproductive behavior and physiology through the actions of GCs. A potential mechanism by which chronic stress may directly inhibit reproduction involves gonadotropin inhibitory hormone (GnIH), an inhibitory neuropeptide responsive to acute stress. We tested the influences of chronic stress on GnIH expression in the hypothalamus of white leghorns (Gallus gallus). Hens were administered corticosterone or exposed to social stress for 10 days. We predicted chronic stress would result in higher levels of GnIH. Both treatments decreased reproductive output and significantly reduced egg mass. Neither treatment altered hypothalamic GnIH expression. Animals have personalities that correlate with the degree of stress responsiveness. White laying hens are reactive, flighty, and exhibit large hormonal and behavioral responses to stress while brown laying hens are proactive, exploratory, and exhibit low hormonal and behavioral responses to acute stress. We examined how hens with different personality types may react differently to chronic stress, and whether these strains also exhibit differences in immunity. Chronic stress was applied with an unpredictable feeding schedule for 14 days. We predicted that white hens would show greater stress reactions with higher corticosterone, heat shock protein expression, and H:L ratios. Strains did not differ in plasma corticosterone responses, brown hens were more reactive in one response (H/L ratios) while white hens were more reactive in another (HSP expression). We predicted reactive hens would show more dampened immune responses than proactive hens. We assessed immune function by comparing febrile responses, food consumption, and reproductive output after an injection of lipopolysaccharide (LPS) or saline, inflammatory responses to phytohaemagluttinin (PHA), innate phagocytic activity in whole blood, and antibody responses to an injection of Sheep Red Blood Cells (SRBCs). White hens had significantly greater swelling of the toe web in response to PHA injection than brown hens, and also showed a greater inhibition of feeding and reproductive output in response to LPS. There were no differences in phagocytic activity or antibody titers between the strains.