Sex Differences in the Daily Rhythm of Vasoactive Intestinal Polypeptide But Not Arginine Vasopressin Messenger Ribonucleic Acid in the Suprachiasmatic Nuclei¹

Sep 29, 1998Endocrinology

Sex differences in daily patterns of a blood vessel-regulating molecule but not a water balance molecule in the brain’s body clock center

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Abstract

VIP messenger RNA levels in the SCN of female rats exhibit rhythmic expression with peak levels during the light phase.

Female rats showed rhythmic expression of VIP mRNA, peaking in the light phase and reaching a low during the dark phase.
This rhythmic pattern was approximately 12 hours out of phase compared to the expression observed in male rats.
AVP mRNA levels in the SCN were consistent across both sexes and were unaffected by estradiol.
The sex-specific pattern of VIP mRNA expression does not rely on estradiol levels.

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The timing of the preovulatory surge of LH in female rodents is tightly coupled to the environmental light/dark cycle. This coupling is mediated by the circadian pacemaker located in the suprachiasmatic nuclei (SCN). Studies indicate that vasoactive intestinal polypeptide (VIP) and arginine vasopressin (AVP), which are synthesized in the SCN, transmit circadian information from the SCN to GnRH neurons, thereby regulating the timing of the LH surge. However, to date, the rhythmic expression of these two peptides in the SCN has only been examined in males. The pattern of VIP expression in males is difficult to reconcile with its role in the LH surge. The purpose of the present study was to assess the rhythm of VIP messenger RNA (mRNA) levels in the SCN of female rats under several endocrine conditions. We compared this rhythm to that in males and to AVP mRNA rhythms in all experimental groups. In all groups of females, VIP mRNA levels were rhythmic, with peak expression occurring during the light phase and a nadir occurring during the dark phase. The rhythm was approximately 12 h out of phase compared with that in males. The rhythmic expression of AVP mRNA in the SCN was virtually identical in all groups of animals. Based on these results, we conclude that 1) the rhythm of VIP seen in the SCN of females during the day may serve as a facilitory signal from the SCN to GnRH neurons; 2) the sex-specific pattern of VIP mRNA does not depend on estradiol; and 3) AVP gene expression within the SCN is not sexually differentiated or altered by estradiol.

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Sex Differences in the Daily Rhythm of Vasoactive Intestinal Polypeptide But Not Arginine Vasopressin Messenger Ribonucleic Acid in the Suprachiasmatic Nuclei¹

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