Meeting Abstract
For many migrants the annual increase in day length initiates development of behavioral and physiological traits requisite for long distance flight. One such trait is hyperphagia leading to increased body mass and fuel (fat) deposition. A number of neuropeptides are known to regulate energy balance in mammals and domestic fowl but how photoinduction influences gene expression that enhances food intake in migratory birds is poorly understood. To gain insight we measured body mass and daily food intake in 3 groups of Gambel’s White-crowned Sparrows: short-day controls held on a winter photoperiod, 9L:15D, long-day experimentals that included one and two day exposure to a long photoperiod 20L:4D to record the effect of photoinduction on premigratory hyperphagia. Photoinduction was associated with increased food intake (P<0.05) and body mass (P<0.05). Additionally, mean agouti-related protein (AGRP) mRNA was increased (P=0.02) on the first long day that was accompanied by a respective decrease (p=0.003) and increase (p=0.015) in the alpha 1 and alpha 2 catalytic subunits of the cellular energy sensor AMP-activated protein kinase (AMPK). Exposure to long days also significantly increased the mean ratio of iodothyronine deiodinase 2/deiodinase 3 mRNA by 17-fold on the first long day (p=0.001) and by 97-fold on the second long day (p=0.001) compared to the short day level. These results suggest that photostimulation coordinates changes in expression within the basal hypothalamus of deiodinase and AMPK enzymes to stimulate AGRP gene expression. The consequent increased signaling activity of AGRP neurons may promote premigratory changes in feeding and metabolism.
