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Am J Physiol Regul Integr Comp Physiol 281: R76-R90, 2001;
0363-6119/01 $5.00
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Vol. 281, Issue 1, R76-R90, July 2001

Hypothalamic control of photoperiod-induced cycles in food intake, body weight, and metabolic hormones in rams

Gerald A. Lincoln1, Stewart M. Rhind2, Sueli Pompolo3, and Iain J. Clarke3

1 Medical Research Council Human Reproductive Sciences Unit, Centre for Reproductive Biology, Edinburgh EH3 9ET; 2 The Macaulay Land Use Research Institute, Craigiebuckler, Aberdeen AB15 8QH, United Kingdom; 3 Prince Henry's Institute for Medical Research, Clayton, VIC 3168, Australia

This study used a hypothalamo-pituitary disconnected (HPD) sheep model to investigate the central regulation of long-term cycles in voluntary food intake (VFI) and body weight (BW). VFI, BW, and circulating concentrations of metabolic hormones [alpha -melanocyte-stimulating hormone (alpha -MSH), insulin-like growth factor-1 (IGF-1), insulin, and leptin] were measured in HPD and control Soay rams exposed to alternating 16 weekly periods of long and short days for 80 wk. In the controls, the physiology was cyclical with a 32-wk periodicity corresponding to the lighting regimen. VFI and BW increased under long days to a maximum early into short days, and there were associated increases in blood concentrations of alpha -MSH, insulin, and leptin. In the HPD rams, there were no significant photoperiod-induced changes in any of the parameters. VFI increased after surgery for 8 wk and then gradually declined, although BW increased progressively and the HPD rams became obese. Concentrations of alpha -MSH, insulin, and leptin in peripheral blood were permanently increased (>200%), and levels of IGF-1 decreased (<55%). The HPD lesion effectively destroyed the entire median eminence [no nerve terminals immunostained for tyrosine hydroxylase (TH) and gonadotropin-releasing hormone] and the adjacent arcuate nucleus (no perikarya immunostained for proopiomelanocortin or TH, and no cells expressed neuropeptide Y mRNA). The results support the conclusion that arcuate hypothalamic systems generate long-term rhythms in VFI, BW, and energy balance.

adipose; appetite; energy balance; hypothalamus; melatonin; pars intermedia; seasonal cycles; sheep


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