Mechanism of the re-entrainment of the circadian rhythm in the rat pineal N-acetyltransferase activity to an eight-hour advance of the light-dark cycle: phase-jump is involved

Abstract

During the re-entrainment of the rat pineal N-acetyltransferase (NAT) rhythm to an 8-h advance of a light-dark (LD) cycle accomplished by shortening of one dark period, the advanced light period phase-delayed the evening NAT rise and phase-advanced the morning decline. The phase-relationship between the rise and the decline became so compressed that after the second and the third light period the NAT rhythm was not expressed even in constant darkness and reappeared only within another cycle at the time of the original night. Only after the fourthdvanced light period, the NAT rhythm phase-jumped into the advanced night.