Circadian and photic-induced expression of Fos protein in the suprachiasmatic nucleus of the rabbit

Abstract

Even though the rabbit has been widely used for circadian studies, very little information is available in this species about the morphology and physiology of the suprachiasmatic nucleus (SCN). The aim of the present study was to characterize expression of the Fos protein by immunocytochemistry in the rabbit's SCN under two conditions: light – dark (L/D, 12:12 h, lights on at 7:00 a.m.) every four hours, starting at ZT01 (08:00 h geographical time) and constant darkness (D/D), starting at CT03. We also analyzed the induction of Fos in the SCN in response to a light pulse (850 lux/30 min) at CT03, CT11, CT15 and CT19 in D/D conditions. In L/D there was a clear Fos induction by light at ZT01 and ZT05 (p < 0.01) in comparison to the other time points. In D/D we found an endogenous rhythm of Fos that peaked at CT07 (p < 0.01). Light pulses induced a strong Fos immunoreactivity only during the subjective night at CT15 and CT19, in the ventrolateral region of the SCN (p < 0.05), in contrast to the maximum expression of Fos during L/D and D/D, where only a sparse distribution in the nucleus was found. In conclusion, we found a daily and a circadian rhythm of Fos and a photic induction at times that produce phase-shifts in other species.

Keywords:

• Circadian rhythms
• Rabbit
• immunocytochemistry
• Fos
• suprachiasmatic nucleus

Acknowledgements

This work was supported by grants from CONACYT, Refs. 34652-N, J000-0686/2003; (to M.C.), 33034 (to R.A.-R.) and 160300 (to R.T.), and a NIH/Fogarty, Grant # R01 TW006636-01 (to M.C.). We gratefully acknowledge Biol. Mercedes Acosta for their invaluable help maintaining and caring for the rabbit colony.