Individual differences in the speed of recovery of the hypothalamic-pituitary-adrenal (HPA) axis response to immobilization in wooden boards (IMO) were studied in two experiments using a normal population of two months old male outbred Sprague-Dawley rats. In a first experiment, rats were subjected to 2 h IMO and were sampled, together with a group of control rats, at various times by the tail-nick procedure. Rats were divided into three groups depending on plasma corticosterone levels observed 2 h after termination of exposure to IMO: fast recovery (FR), intermediate recovery (IR) and slow recovery (SR). When the samples obtained at different times were classified in function of the three groups obtained at 2 h post-stress, no differences among groups were observed just after IMO. However, in the morning on the day after stress, all IMO rats showed higher plasma corticosterone levels than controls, but SR rats showed higher levels than FR rats, whereas IR rats were in between. Neither ambulatory activity in the open-field nor behaviour in the plus-maze was related to the HPA responsiveness to IMO. In a second experiment, there were no between-groups differences in ACTH and corticosterone levels obtained just after IMO. However, at 2 h, post-stress ACTH levels followed the same pattern as corticosterone. These data indicate that individual differences in the speed of recovery of the HPA axis after exposure to a severe stressor are not related either to individual differences in fear/anxiety or to the HPA response during exposure to the stressor. These individual differences in the capability to terminate the activation of the HPA axis after stress might be related to individual differences in the predisposition to develop stress-induced pathology. © 2001 Elsevier Science Ltd.
- Hypothalamus-pituitary-adrenal axis
- Individual differences
- Post-stress recovery