Effects of Ovarian Hormones on Internal Circadian Organization in Rats1

The estrous cycle stage affects the phase of per1-luc expression in the SCN and peripheral tissues, with steroid hormone depletion altering the timing system.

• The estrous cycle has modest effects on the mean phase and distribution of clock gene expression in the SCN.
• Peak clock gene expression occurs mainly at night, regardless of the estrous cycle stage, but is eliminated by ovariectomy (OVX).
• Ovarian steroid treatment does not significantly affect clock gene expression in SCN tissue explants.
• Estrous cycle stage influences the phase relationship between some peripheral clocks and the light-dark cycle.
• Steroid hormone depletion due to OVX may be linked to irregular internal circadian organization, potentially impacting behavioral and physiological changes during menopause.

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