|Cheng, Heng Wei|
Submitted to: Behavioural Brain Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/9/2006
Publication Date: 11/26/2006
Citation: Dennis, R.L., Muir, W.M., Cheng, H. 2006. Effects of raclopride on aggression and stress in diversely selected chicken lines. Behavioural Brain Research. 175(1):104. Interpretive Summary: Social stress, aggression, and cannibalism are of increasing concern to animal production and welfare as well as human psychology and pharmacology. The current study was designed to investigate the effect of environmental-genetic interactions on the functions of dopaminergic system in regulation of bird aggression, with an emphasis on the role of the D2 in controlling birds displaying distinct stress coping capability and propensity for cannibalism. Our results demonstrate that selection of chickens for high and low group productivity and survivability altered the neural mechanisms regulating aggression and stress through the dopamine system. Our findings support the potential for using behavioral and physiological indicators, such as dopamine and epinephrine, to selectively breed animals with superior stress coping ability and reduced aggression for production to improve the well-being of the birds and increase profitability to the producer. Additionally, we have shown that chickens diversely selected for phenotypes indicative of differential aggressiveness and stress coping capability provide an excellent animal model for aggression research investigating the underlying neuronal mechanisms and genetic environmental interactions effecting aggressiveness. The observed differences in aggressiveness following dopamine manipulation implies that phenotypes indicative of superior stress coping ability can be used as indicators for lower aggressive individuals. The selection program and the physiological indicators, such as dopamine, can be adopted or used by scientists and the breeder industry in developing new chicken strains with greater adaptation to the production system, with an emphasis on improving animal well-being and maintaining economic efficiency.
Technical Abstract: Lines of White Leghorn chickens were diversely selected for high (HGPS) and low (LGPS) group productivity and survivability. Selection resulted in two distinct genetic lines characterized by differential cannibalism, flightiness and immunocompetence, resulting in difference in behaviour and coping with social stress. HGPS birds have a superior stress coping strategy when compared with LGPS birds or birds of Dekalb XL (DXL), a commercial strain. Line differences in stress response and behavior could be due to selection-induced difference in expression of the dopaminergic system. The D2 receptor, being an integral part of the dopaminergic system, was hypothesized to be a key contributory agent. This hypothesis was tested by injecting either a D2 antagonist (raclopride) or saline in group housed birds and examining stress coping ability. Specifically, at 65 wk of age, birds of the same strain were housed in replicated pairs; the dominant bird was treated with either raclopride or saline injections for ten consecutive days. Results showed that dominant birds of both strains showed a reduced frequency of aggressive pecks on subordinates (P<0.05; n=15) following raclopride injection. In contrast, the subordinates paired with the raclopride injected birds increased in pecking frequency (P<0.05). Two days after stopping injections, LGPS and DXL birds returned to pre-injection levels of aggressive threats (P>0.05; n=5), while HGPS birds maintained depressed frequency of threats (P<0.05). In addition, strain differences in aggressive responsiveness coincided with increased epinephrine levels in raclopride treated LGPS birds (P<0.05) relative to control LGPS birds, but not by HGPS and DXL birds (P>0.05). Our findings suggest a functional linkage between the genetic basis of stress coping ability and the dopamine system regulating aggressive responsiveness. The data further indicate that the sympathetic-adreno-medullary axis is directly involved in regulating both stress coping strategy and aggressiveness.