Regulation of energy balance in birds by the neuroendocrine hypothalamus
Boswell, T.(Roslin Inst., Ridlothian (UK))
The physiological regulation of energy homeostasis is critica1 to an animal's longterm survival and is relevant to the poultry industry in relation to animal production and welfare. In mammals, rapid progress has been made over the past decade in identifying the neural circuitry in the hypothalamus involved in the regulation of energy balance. Two neuronal cell groups in the arcuate nucleus (the avian infundibular nucleus) , one of which expresses neuropeptide Y (NPY) and agouti-related protein (AGRP) mRNAs and the other pro-opiomelanocortin (POMC) and cocaine- and amphetamine-regulated transcript (CART) mRNAS are particularly important because their encoded peptides exert potent anabolic (NPY and AGRP) and catabolic (POMC and CART) influences. The expression of these genes is altered in a co-ordinated manner by experimental food deprivation or restriction, and by metabolic hormones such as leptin, insulin and ghrelin, so as to enable energy homeostasis to be maintained in the face of perturbations such as energy shortage. The NPY/AGRP and POMC/CART neurones show striking evolutionary conservation between birds and mammals in their neuroanatomical localization, their behavioural effects, and the regulation of their gene expression by nutritional status. However, orexin/hypocretin and melanin-concentrating hormone (MCH) neuropeptides in the lateral hypothalamic area, that exert anabolic effects on energy homeostasis in mammals, do not appear to fulfil these functions in birds. Collectively these observations provide a neuroanatomical framework in the avian brain for future investigations into the regulation of energy balance in commercially important poultry as well as other avian models.
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