Expression of Agouti-related Protein (Agrp) and its mRNA in the Hypothalamus and the Adrenal Gland of the duck (Anas platyrhynchos).

Introduction: Agouti-related protein (AGRP) is a neuropeptide involved in the control of body weight. Morphological and pharmacological studies have shown that AGRP is implicated in the central control of feeding behaviour acting as an endogenous antagonist of the alpha-melanocyte stimulating hormone (-MSH), a potent satiety-inducing factor, at the melanocortin 3 (MC3)- and four (MC4)-receptors. Aim: The aim of the present study was to investigate the expression of AGRP and its mRNA in the hypothalamus and adrenal gland of the duck and, in particular, to establish which type of adrenal tissue is involved in the AGRP synthesis. Methods: Immunohistochemistry, western blotting, reverse transcriptase (RT)-polimerase chain reaction (PCR). Results and Discussion: AGRP-immunoreactivity was observed in neurons and nerve fibres in a restricted area of the hypothalamus. AGRP-ir neurons were located in the nucleus infundibularis and distributed ventromedially to the third ventricle in the hypothalamic tuberal region. These neurons were round or, with a lesser extent, elongated in shape. AGRP-ir fibres were seen to project to the median eminence (ME) and anterior periventricular hypothalamus. The AGRP ir-fibres in the ME were distributed in the external layer in close vicinity to the capillaries of the hypothalamo-hypophysial portal system. In the avian adrenal gland, AGRP immunoreactivity was observed in the medullary tissue. A partial sequence of AGRP cDNA was identified using RT-PCR cloning and sequencing. This sequence was highly homologous to the corresponding fragment of the chicken AGRP gene. The western blotting analysis of adrenal gland and hypothalamus tissue extracts showed a well-defined single band with an electrophoretic mobility consistent with the molecular weight of the avian AGRP protein. These results demonstrate that AGRP is expressed in the hypothalamus and adrenal glands of the duck and suggest an involvement of this peptide in the regulation of the melanocortin system in birds.