Proportions of melanocyte stimulating hormone‐immunoreactive cells in the adenohypophysis of Silky fowl and hyperpigmentation‐free cockerels

Abstract

Alpha‐melanocyte stimulating hormone (α‐MSH) is one of the main regulators for melanocytes, and the adenohypophysis is one of the major tissues for the synthesis of this hormone. The Silky fowl is a characteristic breed of chicken with hyperpigmentation throughout the body. The involvement of the adenohypophysis in the hyperpigmentation of this breed is not known. In the present study, the proportion of melanocyte stimulating hormone‐immunopositive cells (MSH cells) in the adenohypophysis was immunocytochemically compared between Silky, Red Cornish × New Hampshire (RN) crossbred and Japanese bantam cockerels at 15 weeks of age. After the body and gland were weighed, the adenohypophyseal cells were enzymatically dispersed and immunostained for α‐MSH, and the immunopositive MSH cells were counted. The weights of the body and adenohypophysis were heaviest in the RN crossbred, followed by the Silky and lightest in the bantam cockerels. In contrast, the ratio between adenohypophysis and bodyweight was much larger in the Silky and the bantam than in the RN crossbreed (P < 0.05). The population of MSH cells in the adenohypophysis was larger in the Silky (14.3%) than in the RN crossbreed (8.0%) and the bantam (8.1%) cockerels (P < 0.05). From these results, it was concluded that prepubertal Silky cockerel have numerous MSH cells in the adenohypophysis suggesting a relationship to hyperpigmentation.

Role of α-MSH-MC1R-cAMP Signaling Pathway in Regulating the Melanin Synthesis in Silky Fowl

“…However, the regulatory effects of α-MSH and MC1R on melanin synthesis in avian species, and the mechanisms involved, are still poorly understood. Nishimura et al found that the number of α-MSH secreting cells in the anterior pituitary of silky fowl was significantly higher than common chickens with either low, or no melanin deposition, suggesting that α-MSH was closely related to deposition of melanin in the tissues [11]. Takeuchi et al cloned the MC1R gene, located on chromosome 11, for α-MSH (melanocyte-stimulating hormone) receptor from chickens for the first time in 1996 [12].…”