Circadian expression of tryptophan hydroxylase mRNA in the chicken retina

Nelson W. Chong, Vincent M. Cassone, Marianne Bernard, David C. Klein, P. Michael Iuvone

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52 Scopus citations


Many aspects of retinal physiology are controlled by a circadian clock located within the eye. This clock controls the rhythmic synthesis of melatonin, which results in elevated levels during the night and low levels during the day. The rate-limiting enzyme in melatonin biosynthesis in retina appears to be tryptophan hydroxylase (TPH)[G.M. Cahill and J.C. Besharse, Circadian regulation of melatonin in the retina of Xenopus laevis: Limitation by serotonin availability, J. Neurochem. 54 (1990) 716-719]. In this report, we found that TPH mRNA is strongly expressed in the photoreceptor layer and the vitread portion of the inner nuclear layer; the message is also expressed, but to a lesser extent, in the ganglion cell layer. The abundance of retinal TPH mRNA exhibits a circadian rhythm which persists in constant light or constant darkness. The phase of the rhythm can be reversed by reversing the light:dark cycle. In parallel experiments we found a similar pattern of expression in the chicken pineal gland. However, whereas a pulse of light at midnight suppressed retinal TPH mRNA by 25%, it did not alter pineal TPH mRNA, suggesting that there are tissue-specific differences in photic regulation of TPH mRNA. In retinas treated with kainic acid to destroy serotonin-containing amacrine and bipolar cells, a high amplitude rhythm of TPH mRNA was observed indicating that melatonin-synthesizing photoreceptors are the primary source of the rhythmic message. These observations provide the first evidence that chick retinal TPH mRNA is under control of a circadian clock. Copyright (C) 1998 Elsevier Science B.V.

Original languageEnglish
Pages (from-to)243-250
Number of pages8
JournalMolecular Brain Research
Issue number1-2
StatePublished - Oct 30 1998

Bibliographical note

Funding Information:
The authors wish to thank Leo Goe and Rashidul Haque (Emory University School of Medicine) for excellent technical assistance. This research was supported in part by NIH grant EY04864.


  • Circadian clock
  • Melatonin
  • Photoreceptor cells
  • Pineal gland
  • Retina
  • Tryptophan hydroxylase

ASJC Scopus subject areas

  • Molecular Biology
  • Cellular and Molecular Neuroscience


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