AJP - Regulatory, Integrative and Comparative Physiology, Vol 271, Issue 4 825-R831, Copyright © 1996 by American Physiological Society

ARTICLES

Photoperiod-dependent correlation between light-induced SCN c-fos expression and resetting of circadian phase

Z. Travnickova, A. Sumova, R. Peters, W. J. Schwartz and H. Illnerova
Institute of Physiology, Academy of Sciences of the Czech Republic, Prague 4, Czech Republic.

In rodents, brief light pulses that shift the phase of the circadian locomotor rhythm also increase c-fos gene expression in the suprachiasmatic nucleus (SCN), site of an endogenous clock that regulates such rhythmicity. Because the magnitude of photic phase shifts varies when light pulses are applied at different time points over the course of the subjective night, we examined the degree of SCN c-fos gene expression after single 30-min light pulses were delivered at time points that spanned the early and late subjective night in rats maintained in either short (8:16-h light-dark cycle) or long (16:8-h light-dark cycle) photoperiods. The light-induced level of c-fos mRNA and the number of cells expressing immunoreactive c-Fos protein were measured in the SCN by in situ hybridization and immunohistochemistry, respectively, and compared with the magnitude of the corresponding phase shifts of the circadian rhythm of pineal N-acetyltransferase (NAT) activity. We found a robust correlation between c-fos photoinduction and NAT phase shifts, but this relationship was dependent on photoperiod. The degree of c-fos gene expression was strongly correlated with the magnitude of NAT phase advances and delays under the short photoperiod and with phase advances under the long photoperiod, but not with phase delays under the long photoperiod. The data suggest that c-fos gene expression in the SCN may be involved in the photic resetting of the pineal NAT rhythm. Under the long photoperiod, however, the magnitude of phase delays may be limited by the functional state of the circadian pacemaking system.

This article has been cited by other articles:

				A. Sumova and H. Illnerova Spontaneous c-Fos rhythm in the rat suprachiasmatic nucleus: location and effect of photoperiod Am J Physiol Regulatory Integrative Comp Physiol, December 1, 2000; 279(6): R2262 - R2269. [Abstract] [Full Text] [PDF]

				M. Jác, A. Sumova, and H. Illnerova c-Fos rhythm in subdivisions of the rat suprachiasmatic nucleus under artificial and natural photoperiods Am J Physiol Regulatory Integrative Comp Physiol, December 1, 2000; 279(6): R2270 - R2276. [Abstract] [Full Text] [PDF]

				A. Sumova and H. Illnerova Photic resetting of intrinsic rhythmicity of the rat suprachiasmatic nucleus under various photoperiods Am J Physiol Regulatory Integrative Comp Physiol, March 1, 1998; 274(3): R857 - R863. [Abstract] [Full Text] [PDF]