Abstract
The seasonal reproductive cycle of photoperiodic rodents is conceptualized as a series of discrete melatonin-dependent neuroendocrine transitions. Least understood is the springtime restoration of responsiveness to winter-like melatonin signals (breaking of refractoriness) that enables animals to once again respond appropriately to winter photoperiods the following year. This has been posited to require many weeks of long days based on studies employing static photoperiods instead of the annual pattern of continually changing photoperiods under which these mechanisms evolved. Maintaining Siberian hamsters under simulated natural photoperiods, we demonstrate that winter refractoriness is broken within six weeks after the spring equinox. We then test whether a history of natural photoperiod exposure can eliminate the requirement for long-day melatonin signalling. Hamsters pinealectomized at the spring equinox and challenged 10 weeks later with winter melatonin infusions exhibited gonadal regression, indicating that refractoriness was broken. A photostimulatory effect on body weight is first observed in the last four weeks of winter. Thus, the seasonal transition to the summer photosensitive phenotype is triggered prior to the equinox without exposure to long days and is thereafter melatonin-independent. Distinctions between photoperiodic and circannual seasonal organization erode with the incorporation in the laboratory of ecologically relevant day length conditions.
Original language | English (US) |
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Pages (from-to) | 2867-2874 |
Number of pages | 8 |
Journal | Proceedings of the Royal Society B: Biological Sciences |
Volume | 277 |
Issue number | 1695 |
DOIs | |
State | Published - Sep 22 2010 |
Externally published | Yes |
Keywords
- Melatonin
- Season
- Simulated natural photoperiod
ASJC Scopus subject areas
- General Biochemistry, Genetics and Molecular Biology
- General Immunology and Microbiology
- General Environmental Science
- General Agricultural and Biological Sciences