title: Ontogeny of the corticotrophin-releasing hormone system in slow- and fast-growing chicks (Gallus gallus).
abstract: Selective breeding has caused striking phenotypic differences among chickens. For example, the broiler, a fast-growing phenotype, is a relatively heavy bird selected for meat production while the layer, a slower-growing, lighter bird, was developed for egg production. Broilers are prone to early obesity and show physiological and behavioural differences in response to stressors compared with layers. However, the genetic causes of the differences in the responses to stressors between them have not been determined. The purpose of the present study was to compare the ontogeny of the corticotropin-releasing hormone (CRH) system between broilers and layers, because the CRH system plays a major role in regulating stress. We found that fast-growing broilers showed significantly lower levels of diencephalic CRH mRNA expression at post-hatch days 8 and 15 and pituitary CRH receptor 1 mRNA expression from the embryonic to post-hatch stage than slower-growing layers. However, a significantly higher level of CRH-binding protein (CRH-BP), which inactivates CRH and prevents pituitary-adrenal stimulation, was found in broilers compared with layers. Indeed, broilers showed significantly lower levels of plasma corticosterone (CORT) than layers. Subjecting birds to isolation stress did not alter the CORT level of broilers, but increased that of layers. Collectively, the stress-coping actions of the CRH system via the hypothalamic-pituitary-adrenal (HPA) axis might be less responsive in broilers than in layers due to differential gene expression. Together, the present results provide evidence that genetic selection has altered gene expression in the CRH system of the fast-growing broiler, causing blunted HPA axis activity in response to stressors.
authors.affiliation: Department of Agrobiological Science, Faculty of Agriculture, Ehime University, Matsuyama 790-8566, Japan; Department of Anatomy and Embryology, Ehime University Graduate School of Medicine, Toon 791-0295, Ehime, Japan. Electronic address: sakirul@m.ehime-u.ac.jp.
authors.forename: Md Sakirul Islam
authors.initials: MS
authors.lastname: Khan
authors.affiliation: Department of Agrobiological Science, Faculty of Agriculture, Ehime University, Matsuyama 790-8566, Japan.
authors.forename: Chisa
authors.initials: C
authors.lastname: Shigeoka
authors.affiliation: Department of Agrobiological Science, Faculty of Agriculture, Ehime University, Matsuyama 790-8566, Japan.
authors.forename: Yuriko
authors.initials: Y
authors.lastname: Takahara
authors.affiliation: Department of Anatomy and Embryology, Ehime University Graduate School of Medicine, Toon 791-0295, Ehime, Japan.
authors.forename: Seiji
authors.initials: S
authors.lastname: Matsuda
authors.affiliation: Department of Agrobiological Science, Faculty of Agriculture, Ehime University, Matsuyama 790-8566, Japan.
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Tachibana
mesh_terms: D000818:Animals; D030161:Avian Proteins / Q000378:metabolism*; D001786:Blood Glucose / Q000502:physiology; D002645:Chickens / Q000254:growth & development* / Q000502:physiology*; D003345:Corticosterone / Q000097:blood; D003346:Corticotropin-Releasing Hormone / Q000378:metabolism*; D004027:Diencephalon / Q000254:growth & development / Q000502:physiology; D005230:Fatty Acids, Nonesterified / Q000097:blood; D010641:Phenotype; D010902:Pituitary Gland / Q000254:growth & development / Q000502:physiology; D012333:RNA, Messenger / Q000378:metabolism; D018019:Receptors, Corticotropin-Releasing Hormone / Q000378:metabolism; D012934:Social Isolation; D013045:Species Specificity; D013315:Stress, Psychological / Q000503:physiopathology
chemical_list: D030161:Avian Proteins; D001786:Blood Glucose; D005230:Fatty Acids, Nonesterified; D012333:RNA, Messenger; D018019:Receptors, Corticotropin-Releasing Hormone; D003346:Corticotropin-Releasing Hormone; D003345:Corticosterone
keywords: Broiler; Corticotropin-releasing hormone system; HPA axis; Layer; Ontogenetic; Stress response