Physical but not emotional stress induces a delay in behavioural coping responses in rats

Physical stress (PS) and emotional stress (ES) have opposite long-term effects on open field behaviour. PS consisted of a repeated mild foot shock treatment, which the ES animals witnessed. PS caused a long-term decrease in locomotor activity and exploration behaviours and increased immobility. ES induced an increase in locomotor activity. These changes in open field behaviour could be the result of several factors such as increased anxiety, a shift in coping strategy or simply a change in locomotor activity. To investigate the effect of the PS and ES treatment on these separate factors, the following behavioural tests were performed: defensive withdrawal, shock prod bury, large open field and social interaction. PS animals initially showed immobility in the shock prod bury test and the large open field, while the differences measured over the entire test period were small or not present. PS did not induce differences in the defensive withdrawal and the social interaction tests. ES and control animals did not differ significantly in any of the tests. The effects of PS in the shock prod bury test in particular can be interpreted as an indication of a passive coping style. However, PS animals showed the same behaviour as controls, but started displaying the behaviour after the initial immobility response. It is concluded that neither PS nor ES affects the coping style and anxiety level of the rats. PS induces a delay in behavioural responding and ES induces locomotor activation per se. It seems that the shock prod bury test is most suitable to distinguish between exploration and coping style.