Daily rhythm and regulation of clock gene expression in the rat pineal gland

Per1, Per3, Cry2, and Cry1 clock genes are expressed in the rat pineal gland, with their transcription increasing during the night.

• The expression of Per1 and Cry2 genes maintains a 24-hour rhythm, even in constant darkness, though this rhythm is dampened.
• Nocturnal increases in Per1 and Cry2 expression are eliminated by light exposure or injection of a beta-adrenergic antagonist.
• Daytime expression of Per1 and Cry2 is stimulated by a beta-adrenergic agonist injection.
• Per3 and Cry1 exhibit daily rhythm patterns that are not influenced by adrenergic ligands and are significantly dampened or absent in constant darkness.
• The regulation of Per1 and Cry2 by norepinephrine resembles the regulation of the melatonin rhythm-generating enzyme, while Per3 and Cry1 may involve different regulatory mechanisms.

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