Phase relation between episodic fluctuations of spontaneous locomotor activity and plasma corticosterone in rats with suprachiasmatic nuclei lesions.

Phase relation between plasma corticosterone and locomotor activity rhythms was analyzed in individual rats with selective lesions of suprachiasmatic nuclei (SCN). SCN in Wistar male rats were selectively coagulated electrically and the extent of SCN destruction was examined histologically. Spontaneous locomotor activity was monitored on an Animex and blood samples were simultaneously taken from the cut end of the tail vein or through a catheter which had been implanted into the right jugular vein. Plasma corticosterone was determined by a competitive protein binding assay. After the SCN lesion, both locomotor activity and plasma corticosterone lost a circadian rhythmicity and decomposed into ultradian components. Both least squares and periodogram analyses of the ultradian components of locomotor activity revealed the presence of a burst component of about 1-2 h duration. In addition, episodic fluctuations of plasma corticosterone were closely correlated with those of locomotor activity (r = 0.755, p less than 0.001). The findings suggest the existence of a phase-locking mechanism between ultradian components of both functions in the absence of SCN function.