Prevention of stereotypy in laboratory mice: effects on stress physiology and behaviour.

According to the coping hypothesis, the adaptive significance of stereotypies in barren housing conditions may lie in their potency to attenuate the deleterious consequences of chronic stress. Present evidence from experimental studies is ambiguous. When Zur:ICR mice were selectively prevented from stereotypic wire gnawing at the cage lid, the previous amount of stereotyped behaviour after a short-term decrease in activity was compensated by variable active behaviour on the cage floor. This change in behaviour was associated with a short-term elevation of serum corticosterone concentrations 24 h after stereotypy prevention. However, 3 days later corticosterone levels were back at pretreatment base levels. Both behavioural and physiological short-term effects were caused by the impact of prevention on behavioural organization. They disappeared as soon as new habits were established, even though they were not stereotyped. In contrast to the predictions of the coping hypothesis, prevention of stereotypy had no significant effects on chronic measures of both the sympathetic-adrenal-medullary system and the hypothalamus-pituitary-adrenal system. Thus, there is no evidence that stereotypic wire gnawing reduces chronic stress in Zur:ICR mice. This implies that coping with stress is not a general aspect of cage-induced stereotypic behaviour.