A single exposure to immobilization causes long-lasting pituitary-adrenal and behavioral sensitization to mild stressors.
We have previously reported that a single exposure to immobilization (IMO) in rats causes a long-term desensitization of the hypothalamic-pituitary-adrenal (HPA) response to the same (homotypic) stressor. Since there are reports showing that a single exposure to other stressors causes sensitization of the HPA response to heterotypic stressors and increases anxiety-like behavior, we studied in the present work the long-term effects of IMO on behavioral and HPA response to mild superimposed stressors. In Experiments 1 and 2, adult male Sprague-Dawley rats were subjected to 2 h of IMO and then exposed for 5 min to the elevated plus-maze (EPM) at 1, 3 or 7 days after IMO. Blood samples were taken at 15 min after initial exposure to the EPM. Increases in anxiety-like behavior and HPA responsiveness to the EPM were found at all times post-IMO. Changes in the resting levels of HPA hormones did not explain the enhanced HPA responsiveness to the EPM (Experiment 3). In Experiments 4 and 5, we studied the effects of a single exposure to a shorter session of IMO (1 h) on behavioral and HPA responses to a brief and mild session of foot-shocks done 10 days after IMO. Neither previous IMO nor exposure to shocks in control rats modified behavior in the EPM. However, a brief session of shocks in previously IMO-exposed rats dramatically increased anxiety in the EPM. HPA and freezing responses to shocks were similar in control and previous IMO groups. Therefore, a single exposure to IMO appears to induce long-lasting HPA and behavioral sensitization to mild superimposed stressors, although the two responses are likely to be at least partially independent. Long-term effects of IMO on the susceptibility to stress-induced endocrine and emotional disturbances may be relevant to the characterization of animal models of post-traumatic stress.
Belda
Xavier
X
Institut de Neurociències, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Spain.
Fuentes
Silvia
S
Nadal
Roser
R
Armario
Antonio
A
D000222:Adaptation, Physiological / Q000502:physiology; D000324:Adrenocorticotropic Hormone / Q000097:blood; D000818:Animals; D001522:Behavior, Animal / Q000502:physiology; D003345:Corticosterone / Q000097:blood; D046352:Freezing Reaction, Cataleptic / Q000502:physiology; D007030:Hypothalamo-Hypophyseal System / Q000503:physiopathology*; D008297:Male; D018782:Maze Learning / Q000502:physiology; D010913:Pituitary-Adrenal System / Q000503:physiopathology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012149:Restraint, Physical / Q000502:physiology*; D013313:Stress Disorders, Post-Traumatic / Q000473:pathology / Q000503:physiopathology*; D013312:Stress, Physiological / Q000502:physiology*; D013315:Stress, Psychological / Q000503:physiopathology*; D013997:Time Factors
D000324:Adrenocorticotropic Hormone; D003345:Corticosterone