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 adrenale...