Adrenal Steroids and the Maintenance of a Circadian Distribution of Paradoxical Sleep in Rats

Abstract

From continuous electroencephalographic (EEG) recordings with electrodes permanently implanted in the brain, the 24-hr circadian distribution of paradoxical sleep (PS) was determined in unanesthetized rats shifted to a 1-hr lighting cycle (30 min light–30 min dark), and the influences of gonadal and adrenal steroids were studied. Under these conditions neither estrogen (5 μg estradiol benzoate/day, sc) nor progesterone (40–500 μg/day) affected the total amount of PS, its tendency to occur predominantly during the dark half of the hourly light cycle, or its diurnal distribution over the 24-hr day in 6 ovariectomized rats. Adrenalectomy abolished the circadian rhythm of PS distribution. In adrenalectomized rats the administration of cortisol (1 mg/100 g/day, sc, late afternoon) re-established a circadian rhythm but it was almost completely out of phase with the original rhythm. Neither the total 24-hr daily amount of PS nor its predilection for the dark half of the hourly light cycle was altered by adrenalectomy or cortisol treatment. No sex differences in the effects of adrenalectomy or cortisol treatment were observed in the 5 males and 5 ovariectomized females studied. (Endocrinology89: 507, 1971)