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First published online January 25, 2005
Journal of Experimental Biology 208, 497-504 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01424

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Circadian rhythms of behavioral cone sensitivity and long wavelength opsin mRNA expression: a correlation study in zebrafish

Ping Li^1,3, Shelby Temple², Yan Gao^1,3, Theordore J. Haimberger², Craig W. Hawryshyn² and Lei Li^1,3,*

¹ Department of Physiology, University of Kentucky College of Medicine, Lexington, KY 40536 USA
² Department of Biology, University of Victoria, British Columbia, V8W3N5 Canada
³ Department of Biological Sciences, University of Notre Dame, Notre Dame, IN 46556 USA

^* Author for correspondence (e-mail: li.78{at}nd.edu)

Accepted 1 December 2004

Using a behavioral assay based on visually mediated escape responses, we measured long-wavelength-sensitive red cone (LC) sensitivities in zebrafish. In a 24 h period, the zebrafish were least sensitive to red light in the early morning and most sensitive in the late afternoon. To investigate if the fluctuation of behavioral cone sensitivity correlates with opsin gene expression, we measured LC opsin mRNA expression at different times in the day and night under different lighting conditions. Under a normal light–dark cycle, the expression of LC opsin mRNA determined by real-time RT–PCR was low in the early morning and high in the late afternoon, similar to the fluctuation of behavioral cone sensitivity. This rhythm of LC opsin mRNA expression, however, dampened out gradually in constant conditions. After 24 h of constant light (LL), the expression of LC opsin mRNA dropped to levels similar to those determined in the early morning in control animals. By contrast, when the zebrafish were kept in constant dark (DD), the expression of LC opsin mRNA increased, to levels about 30-fold higher than the expression in the early morning in control animals. This day–night fluctuation in LC opsin mRNA expression was correlated to changes in opsin density in the outer segment of cone photoreceptor cells. Microspectrophotometry (MSP) measurements found significant differences in red cone outer segment optical density with a rhythm following the behavioral sensitivity. Furthermore, dopamine modulated the circadian rhythms in expression of LC opsin mRNA. Administration of dopamine increased LC opsin mRNA expression, but only in the early morning.

Key words: circadian rhythm, opsin mRNA expression, behavioral visual sensitivity, zebrafish

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