CZAAWE Resource Article

Brain opioid receptors in relation to stereotypies, inactivity, and housing in sows
Publication Type 
Journal Article
Year of publication 
1996
Publication/Journal 
Physiology & Behavior
ISBN 
0031-9384
Abstract 
When animals encounter difficult conditions, endogenous opioids are often released and may help in coping with the difficulties. In sows, prolonged confinement results in behavior abnormalities: high levels of stereotypies or excessive inactivity and unresponsiveness. The possibilities of causal links between endogenous opioids and these behavioral indicators of poor welfare have been raised. Mu receptor density was found to be greater in tethered sows than in group-housed sows and to be positively correlated with time spent inactive. There were negative correlations between both mu and kappa receptor densities and stereotypy duration. Kappa agonists are associated with aversion, and there are complex links between endorphin levels, dynorphin levels, and dopamine action. These results provide the first demonstration of a relationship between abnormal behavior in pigs and opioid receptor density, and help to clarify the links between behavioral responses and opioid action.