EFFECTS OF ADRENALECTOMY AND SUBSEQUENT CORTICOSTERONE REPLACEMENT ONRAT SLEEP STATE AND EEG POWER SPECTRA

Individual effects of corticotropin-releasing hormone (CRH) and glucoc orticoids on sleep have been difficult to discern due to the feedback effects each hormone exerts on the other. In addition, it is not known whether hypothalamic-pituitary-adrenal axis hormones alter sleep home ostasis or circadian influences on sleep propensity. We therefore anal yzed sleep architecture and electroencephalographic (EEG) power in fre ely moving rats before and after removal of corticosterone (thus eleva ting endogenous CRH) by surgical adrenalectomy. Adrenalectomy reduced the amplitude of the diurnal rhythms of maximal and average sleep bout lengths (P < 0.004). After adrenalectomy, power from 1 to 4 Hz decrea sed (P < 0.042), whereas power from 9 to 12 Hz increased in the power spectra of the EEG; recording (P = 0.001). Administration of physiolog ical corticosterone replacement reversed some of these effects. Suprap hysiological corticosterone replacement in adrenalectomized rats reduc ed the amount of non-rapid-eye-movement sleep in the 24-h cycle (P = 0 .001). During each endocrine condition, rats were sleep deprived for 6 h. Endocrine status did not alter the subsequent homeostatic response to sleep deprivation. Thus ADX and supraphysiological corticosteroid replacement each altered sleep architecture without a demonstrable eff ect on sleep homeostasis.