Submitted on June 15, 2006
Accepted on July 25, 2006
Influence of photoperiod and gonadal status on food intake, adiposity and gene expression of hypothalamic appetite regulators in a seasonal mammal
Chantacha Anukulkitch1, Alexandra Rao2, Frank R. Dunshea3, Dominique Blache4, Gerald A Lincoln5, and Iain J. Clarke6*
1 Prince Henry's Institute of Medical Research, Clayton, Victoria, Australia
2 Prince Henry's Institute of Medical Research, Victoria, Victoria, Australia
3 Department of Primary Industries, Werribee, Victoria, 3030, Australia
4 Animal Biology, University of Western Australia, Crawley, Western Australia, Australia
5 University of Edinburgh, Edinburgh, United Kingdom
6 Physiology, Monash University, Monash University, Victoria, Australia
* To whom correspondence should be addressed. E-mail: iain.clarke{at}med.monash.edu.au.
We have studied the effects of photoperiod on metabolic profiles, adiposity and gene expression of hypothalamic appetite regulating peptides in gonad-intact and castrated Soay rams. Groups of 5-6 animals were studied 6, 18 or 30 weeks after switching from long photoperiod (LP: 16h light) to short photoperiod (SP: 8h light). Reproductive and metabolic indices were measured in blood plasma. Expression of neuropeptide Y (NPY), pro-opiomelanocortin (POMC) and leptin receptor (ObRb) in the arcuate nucleus was measured by in situ hybridization. Testosterone levels of intact animals were low under LP, increased to a peak at 16 weeks SP and then declined. Voluntary food intake (VFI) was high under LP in both intact and castrated animals, decreased to a nadir at 12-16 weeks under SP and then recovered, but only in the intact rams as the reproductive axis became photorefractory to SP. NPY gene expression varied positively and POMC expression varied negatively with the cycle in VFI, with differences between intact and castrate rams in the refractory phase. ObRb expression decreased under SP, unrelated the changes in VFI. Visceral fat weight also varied between the intact and castrated animals across the cycle. We conclude that: 1) photoperiodic changes in VFI reflect changes in NPY and POMC gene expression, 2) changes in Ob-Rb gene expression are not necessarily determinants of changes in VFI, 3) gonadal status affects the pattern of VFI that changes with photoperiod and 4) in the absence of gonadal factors animals can eat less but gain adiposity.
