Differential effects of acute cold and footshock on the sleep of rats

Several studies have shown that 1 h of immobilisation stress during the rat 's active period results in rebound of paradoxical (PS) and slow wave sleep (SWS). Since the effects of stress on behaviour and physiological paramete rs vary according to the stimulus, the present study sought to examine the activation of the hypothalamic-pituitary-adrenal (HPA) axis and the sleep p attern of rats submitted to 1 h of footshock, immobilisation or cold, or 18 h of PS deprivation (PSD). Stress sessions began between 0900 and 0930 h. Immediately after the end of the stress session, or at the corresponding ti me for controls, animals were blood sampled for determination of ACTH and c orticosterone (CORT) plasma levels. In Experiment 2, animals were implanted with electrodes for basal and post-stress polysomnographic recording (6 h long). The results showed that all stressors produced an activation of the HPA axis; however, footshock induced the largest ACTH levers, whereas cold resulted in the highest CORT levels. In regard to the sleep data, immobilis ation and PSD led to a rebound of SWS (+16.87% and +9.37%, respectively) an d PS (+42.45% and +55.25%, respectively). Immobilisation, however, induced an increased number of PS episodes, whereas PSD resulted in longer PS episo des. Cold stress produced an exclusive rebound of SWS (+ 14.23%) and footsh ock promoted sustained alertness during the animal's resting period ( + 47. 18%). These results indicate that different stimuli altered the sleep patte rn in a distinct manner; and these alterations might be related to the stat e of the HPA axis activation. (C) 2000 Published by Elsevier Science B.V. A ll rights reserved.