BRAIN OPIOID RECEPTORS IN RELATION TO STEREOTYPIES, INACTIVITY, AND HOUSING IN SOWS

When animals encounter difficult conditions, endogenous opioids are of ten released and may help in coping with the difficulties. In sows, pr olonged confinement results in behavior abnormalities: high levels of stereotypies or excessive inactivity and unresponsiveness. The possibi lities 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 stereot ypy duration. Kappa agonists are associated with aversion, and there a re complex links between endorphin levels, dynorphin levels, and dopam ine action. These results provide the first demonstration of a relatio nship between abnormal behavior in pigs and opioid receptor density, a nd help to clarify the links between behavioral responses and opioid a ction.