Photoperiodic effects on seasonal physiology, reproductive status and hypothalamic gene expression in young male F344 rats

F. M. Tavolaro, L. M. Thomson, A. W. Ross, P. J. Morgan, G. Helfer

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Seasonal or photoperiodically sensitive animals respond to altered day length with changes in physiology (growth, food intake and reproductive status) and behaviour to adapt to predictable yearly changes in the climate. Typically, different species of hamsters, voles and sheep are the most studied animal models of photoperiodism. Although laboratory rats are generally considered nonphotoperiodic, one rat strain, the inbred Fischer 344 (F344) rat, has been shown to be sensitive to the length of daylight exposure by changing its physiological phenotype and reproductive status according to the season. The present study aimed to better understand the nature of the photoperiodic response in the F344 rat. We examined the effects of five different photoperiods on the physiological and neuroendocrine responses. Young male F344 rats were held under light schedules ranging from 8 h of light/day to 16 h of light/day, and then body weight, including fat and lean mass, food intake, testes weights and hypothalamic gene expression were compared. We found that rats held under photoperiods of ≥ 12 h of light/day showed increased growth and food intake relative to rats held under photoperiods of ≤ 10 h of light/day. Magnetic resonance imaging analysis confirmed that these changes were mainly the result of a change in lean body mass. The same pattern was evident for reproductive status, with higher paired testes weight in photoperiods of ≥ 12 h of light/day. Accompanying the changes in physiological status were major changes in hypothalamic thyroid hormone (Dio2 and Dio3), retinoic acid (Crabp1 and Stra6) and Wnt/b-Catenin signalling genes (sFrp2 and Mfrp). Our data demonstrate
that a photoperiod schedule of 12 h of light/day is interpreted as a stimulatory photoperiod by the neuroendocrine system of young male F344 rats.
Original languageEnglish
Pages (from-to)79-87
Number of pages9
JournalJournal of Neuroendocrinology
Issue number2
Early online date26 Jan 2015
Publication statusPublished - Feb 2015

Bibliographical note

Funded by:
Scottish Government
Biotechnology and Biological Science Research Council (BBSRC). Grant Number: BB/G014272/1

The authors thank the British Society for Neuroendocrinology (BSN) for providing the Student Laboratory Experience Grant to FMT. This work was further supported by the Scottish Government (LMT, AWR and PJM) and the Biotechnology and Biological Science Research Council (BBSRC) grant number BB/G014272/1 (GH, AWR and PJM). We also thank Donna Wallace and the animal house staff for their excellent help with the animal studies. The authors have no conflicts of interest to declare


  • photoperiod
  • F344 rat
  • body weight
  • reproduction
  • hypothalamic gene expression


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