Absence of pineal-independent mediation of seasonal differences in suprachiasmatic nucleus AVP and VIP mRNA expression in Siberian hamsters

David A. Freeman, Jana M. Herron, Marilyn J. Duncan

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


Assessment of seasonal variations in expression of brain neuropeptide mRNA is complicated by concurrent circadian variations. Because entrainment of suprachiasmatic nucleus (SCN) based rhythms differs in long versus short day lengths, valid seasonal comparisons must be made at equivalent circadian phases. We used a novel experimental design which permitted sampling at identical circadian phases of animals exhibiting opposite seasonal reproductive responses to the same intermediate day length. This allowed us to test whether seasonal changes in arginine vasopressin (AVP) and vasoactive intestinal peptide (VIP) mRNA expression in the SCN occur in the absence of the pineal gland. Juvenile Siberian hamsters were gestated and maintained postnatally in either a long photoperiod (16 h light/day) or short photoperiod (10 h light/day). At the time of weaning (18 days of age), the hamsters were pinealectomized and either transferred to a new photoperiod (10-, 16- or 14-h light/day) or left in the original photoperiod. Hamsters from 10L had substantially smaller and lighter testes than those from 16L. If photoperiodic modulation of AVP and VIP mRNA expression occurs in the absence of the pineal, then transfer of pinealectomized hamsters from a longer (16L) or shorter (10L) photoperiod to an intermediate photoperiod (14L) should result in a differential response with respect to SCN AVP and VIP mRNA expression but not testis size. When sampled at an identical circadian phase (3 h after lights on) in 14L there was no difference in the expression of AVP or VIP mRNA in the SCN between animals previously housed in long versus short day lengths. In contrast to a previous study that did not carefully control for circadian phase, the present findings suggest that seasonal photoperiodic control of SCN neuropeptide mRNA expression depends upon the pineal gland. In addition, the present findings demonstrate a significant, negative correlation between AVP mRNA expression in the SCN and the length of the daily active phase (alpha).

Original languageEnglish
Pages (from-to)33-38
Number of pages6
JournalMolecular Brain Research
Issue number1-2
StatePublished - May 30 2002

Bibliographical note

Funding Information:
This research was supported by National Institutes of Health grants MH-11655 and MH-61171 and AG-13418. We thank Irving Zucker for helpful comments on the manuscript.


  • Circadian rhythm
  • Melatonin
  • Photoperiodism

ASJC Scopus subject areas

  • Molecular Biology
  • Cellular and Molecular Neuroscience


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