Social stress differentially regulates neuroendocrine responses in laying hens: I. Genetic basis of dopamine responses under three different social conditions.

Effects of genetic-environmental interactions on plasma dopamine (DA) concentrations were studied in White Leghorn chickens selected for both high (HGPS) or low (LGPS) group productivity and survivability resulting from cannibalism and flightiness. Plasma DA levels were measured from chickens in three social treatments: single-, two-, or ten-hen cages. The two-hen treatment consisted of paired chickens from three genetic lines: HGPS, LGPS and a commercial strain, Dekalb XL (DXL). In HGPS/DXL and LGPS/DXL pairs, the DXL hen was used as a standardized genetic competitor. The ten-hen treatment contained only hens from the same line, which is similar to the original selection condition. After 7 weeks housing in the social environments, LGPS hens in the ten-hen treatment had greater plasma DA concentrations than HGPS hens (P<0.05). Compared to levels in the ten-hen treatment from the same line, plasma DA concentrations in both HGPS and LGPS hens were significantly lower in the two-hen treatment (average mean, 0.09 vs. 0.15 ng/ml and 0.22 vs. 0.44 ng/ml, P<0.05, respectively), but significantly higher in the single-hen treatment (average mean, 0.44 vs. 0.15 ng/ml and 1.78 vs. 0.44 ng/ml, P<0.05 and P<0.01, respectively). In the single-hen treatment, LGPS hens had greater plasma DA levels than HGPS hens (P<0.05). The results provide evidence of genetically related differences in the regulation of chickens' plasma DA concentrations in response to social stress. These differences may magnify the behavioral and physiological differences observed in the lines under basal and challenged conditions. These results suggest that these chicken lines may provide a new model for investigating effects of DA on the control of behavioral, neural and endocrine responses to stress.