Melatonin induces gene-specific effects on rhythmic mRNA expression in the pars tuberalis of the Siberian hamster (Phodopus sungorus)

Gabriela Christina Wagner, Jonathan D. Johnston, Benjamin B. Tournier, Francis J. P. Ebling, David G. Hazlerigg

Research output: Contribution to journalArticle

30 Citations (Scopus)

Abstract

In mammals, circadian and photoperiodic information is encoded in the pineal melatonin signal. The pars tuberalis (PT) of the pituitary is a melatonin target tissue, which transduces photoperiodic changes and drives seasonal changes in prolactin secretion from distal lactotroph cells. Measurement of photoperiodic time in the PT is believed to occur through melatonin dependent changes in clock gene expression, although it is unclear whether the PT should be considered a melatonin sensitive peripheral oscillator. We tested this hypothesis in the Siberian hamster (Phodopus sungorus) firstly by investigating the effects of melatonin injection, and secondly by determining whether temporal variation in gene expression within the PT persists in the absence of a rhythmic melatonin signal. Hamsters preconditioned to long days were treated with melatonin during the late light phase, to advance the timing of the nocturnal melatonin peak, or placed in constant light for one 24 h cycle, thereby suppressing endogenous melatonin secretion. Gene expression in the PT was measured by in situ hybridization. We show that melatonin rapidly induces cry1 mRNA expression without the need for a prolonged melatonin-free interval, acutely inhibits mt1 expression, advances the timing of peak rev-erb alpha expression and modulates per1 expression. With the exception of cry1, these genes continue to show temporal changes in expression over a first cycle in the absence of a melatonin signal. Our data are consistent with the hypothesis that the hamster PT contains a damped endogenous circadian oscillator, which requires a rhythmic melatonin signal for long-term synchronization.

Original languageEnglish
Pages (from-to)485-490
Number of pages6
JournalEuropean Journal of Neuroscience
Volume25
Issue number2
DOIs
Publication statusPublished - Jan 2007

Keywords

  • clock genes
  • melatonin
  • pars tuberalis
  • photoperiod
  • decoding photoperiodic time
  • suprachiasmatic nucleus
  • prolactin secretion
  • photic regulation
  • circadian clock
  • pituitary-gland
  • Syrian-hamsters
  • binding changes
  • seasonal time
  • receptors

Cite this

Melatonin induces gene-specific effects on rhythmic mRNA expression in the pars tuberalis of the Siberian hamster (Phodopus sungorus). / Wagner, Gabriela Christina; Johnston, Jonathan D.; Tournier, Benjamin B.; Ebling, Francis J. P.; Hazlerigg, David G.

In: European Journal of Neuroscience, Vol. 25, No. 2, 01.2007, p. 485-490.

Research output: Contribution to journalArticle

Wagner, Gabriela Christina ; Johnston, Jonathan D. ; Tournier, Benjamin B. ; Ebling, Francis J. P. ; Hazlerigg, David G. / Melatonin induces gene-specific effects on rhythmic mRNA expression in the pars tuberalis of the Siberian hamster (Phodopus sungorus). In: European Journal of Neuroscience. 2007 ; Vol. 25, No. 2. pp. 485-490.
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AB - In mammals, circadian and photoperiodic information is encoded in the pineal melatonin signal. The pars tuberalis (PT) of the pituitary is a melatonin target tissue, which transduces photoperiodic changes and drives seasonal changes in prolactin secretion from distal lactotroph cells. Measurement of photoperiodic time in the PT is believed to occur through melatonin dependent changes in clock gene expression, although it is unclear whether the PT should be considered a melatonin sensitive peripheral oscillator. We tested this hypothesis in the Siberian hamster (Phodopus sungorus) firstly by investigating the effects of melatonin injection, and secondly by determining whether temporal variation in gene expression within the PT persists in the absence of a rhythmic melatonin signal. Hamsters preconditioned to long days were treated with melatonin during the late light phase, to advance the timing of the nocturnal melatonin peak, or placed in constant light for one 24 h cycle, thereby suppressing endogenous melatonin secretion. Gene expression in the PT was measured by in situ hybridization. We show that melatonin rapidly induces cry1 mRNA expression without the need for a prolonged melatonin-free interval, acutely inhibits mt1 expression, advances the timing of peak rev-erb alpha expression and modulates per1 expression. With the exception of cry1, these genes continue to show temporal changes in expression over a first cycle in the absence of a melatonin signal. Our data are consistent with the hypothesis that the hamster PT contains a damped endogenous circadian oscillator, which requires a rhythmic melatonin signal for long-term synchronization.

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