No evidence for extraocular photoreceptors in the circadian system of the Syrian hamster

Shin Yamazaki, Maki Goto, Michael Menaker

Research output: Contribution to journalArticlepeer-review

83 Scopus citations


Campbell and Murphy reported recently that 3 h of bright light (13,000 lux) exposure to the area behind the knee caused phase shifts of the circadian rhythms of both body temperature and saliva melatonin in humans. The authors tested the hypothesis that extraocular photoreception is also involved in the circadian system of the Syrian hamster. Hamsters were bilaterally enucleated (eyes removed), and their backs were shaved. Hamsters with stable free-running rhythms in constant darkness were exposed to direct sunlight for 1 or 3 hours during their subjective night. Intact (control) animals showed phase shifts as expected, but the locomotor activity of enucleated animals was unaffected by the exposure to sunlight. The authors also measured the pineal melatonin content after exposure to sunlight. Pineal melatonin content in intact animals declined markedly as expected, but no decline was observed in the enucleated hamsters. The authors conclude that extraocular phototransduction is not capable of shifting the phase of the hamster's locomotor activity rhythm or of suppressing pineal melatonin synthesis.

Original languageEnglish (US)
Pages (from-to)197-201
Number of pages5
JournalJournal of Biological Rhythms
Issue number3
StatePublished - Jun 1999


  • Circadian photoreceptor
  • Circadian rhythm
  • Extraocular photoreceptor
  • Jet lag
  • Melatonin
  • Pineal
  • Syrian hamster

ASJC Scopus subject areas

  • Physiology
  • Physiology (medical)


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