Food intake in birds: hypothalamic mechanisms
Feeding behavior is a complex trait that is regulated by various hypothalamic neuropeptides and neuronal populations (nuclei). Understanding the physiological regulation of food intake is important for improving nutrient utilization efficiency in agricultural species and for understanding and treating eating disorders. Knowledge about appetite in birds has agricultural and biomedical relevance and provides evolutionary perspective. I thus investigated hypothalamic molecular mechanisms associated with appetite in broilers, layers, chicken lines selected for low (LWS) or high (HWS) body weight, and Japanese quail, which provide a unique perspective to understanding appetite. Broiler-type chicks have been genetically selected for rapid growth and consume much more feed than do layer-type chicks which have been selected for egg production. Long-term selection has caused the LWS chicks to have different severities of anorexia while the HWS chicks become obese, thus making these lines a valuable model for metabolic disorders. Lastly, the Japanese quail have not undergone as extensive artificial selection as the chicken, thus this model may provide insights on how human intervention has changed the mechanisms that regulate feeding behavior in birds. This research involved applying a variety of different treatments including fasting and refeeding, diets differing in macronutrient composition, and/or central administration of neuropeptide Y, xenopsin, neuropeptide K, oxytocin, mesotocin, gonadotropin-inhibitory hormone, and prolactin-releasing peptide, after which I measured feeding behavior and various aspects of hypothalamic physiology. I measured nuclei activation in hypothalamic appetite-associated regions including the lateral hypothalamus, paraventricular nucleus, ventromedial hypothalamus, dorsomedial nucleus, and arcuate nucleus and I measured gene expression of various appetite-associated factors in the whole hypothalamus and individual nuclei. These data provided information about the regions of the brain involved in mediating effects on appetite and the molecular pathways involved in the effect on appetite. There were differences in dose threshold sensitivity to various injected factors in the different stocks, differential responses to fasting and refeeding, and differences in nuclei and genes that were activated in response to the various treatments. These data provide valuable insights on the molecular mechanisms that are associated with the short-term regulation of feeding behavior and pathways that may be genetically stock-dependent.