Lines of evidence suggest that hypothalamic neuropeptides have a physiological role in the regulation of food intake in mammals. However, little is known about the age-dependent change of hypothalamic neuropeptides in chicks. In this study, we investigated the age-dependent changes in hypothalamic mRNA levels of neuropeptide Y (NPY, an orexigenic neuropeptide), proopiomelanocortin (POMC, the precursor of anorexigenic neuropeptides), and corticotropin-releasing factor (CRF, a possible mediator in the POMC-induced anorexigenic pathway) in growing broiler chicks. The weights of body and abdominal adipose tissue of chicks were measured at 7, 14, 21, and 28 days of age, and the hypothalamic mRNA levels of NPY, POMC, and CRF were analyzed by real-time PCR. Hypothalamic NPY mRNA levels at 14 and 28 days of age were significantly (P<0.05) lower than that at 7 days of age. Hypothalamic POMC mRNA level at 28 days of age was significantly lower than that at 7 days of age. Hypothalamic CRF mRNA level was not affected throughout the experimental period. Abdominal adipose tissue weight was significantly increased after 14 days of age in chicks. Our findings demonstrated that the expressions of NPY and POMC are dependent on age in boiler chicken hypothalamus.
Glucagon-related peptides, such as glucagon-like peptide (GLP)-1, GLP-2 and oxyntomodulin (OXM), are processed from an identical precursor proglucagon. In mammals, all of these peptides are suggested to be involved in the central regulation of food intake. We previously showed that intracerebroventricular administration of chicken OXM and GLP-1 significantly suppressed food intake in chicks. Here, we show that central administration of chicken GLP-2 potently suppresses food intake in chicks. Male 8-day-old chicks (Gallus gallus domesticus) were used in all experiments. Intracerebroventricular administration of chicken GLP-2 significantly suppressed food intake in chicks. Plasma glucose concentration was significantly decreased by chicken GLP-2, whereas plasma nonesterified fatty acid concentration was significantly increased. Intracerebroventricular administration of chicken GLP-2 did not affect plasma corticosterone concentration. In addition, the anorexigenic effect of GLP-2 was not reversed by the corticotropin-releasing factor (CRF) receptor antagonist α-helical CRF, suggesting that CRF is not a downstream mediator of the anorexigenic pathway of GLP-2 in chicks. Intracerebroventricular administration of an equimolar amount of GLP-1 and GLP-2, but not OXM, significantly suppressed food intake in both broiler and layer chicks. All our findings suggest that GLP-2 functions as a potent anorexigenic peptide in the brain, as well as GLP-1, in chicks.
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