Immunohistochemical identification of dynorphin A and Kappa opioid receptor-1 in the digestive system of scallop Chlamys farreri

Little is known about the roles of dynorphin and Kappa opioid receptor (KOR) in mollusks. In this study, we aim to determine the distribution of dynorphin A and KOR-1 in the digestive system of the scallop Chlamys farreri . Using immunohistochemical staining, we confirmed the expression of dynorphin A and KOR-1 in the digestive system of C. farreri . Dynorphin A immunopositive cells were identified in intestine and hepatopancreas. In intestine, small and spherical dynorphin A immunopositive cells (4–9 μm in diameter) were scattered among the long columnar epithelial cells (ECs). In hepatopancreas, cells containing masses (5–14 μm in diameter) of dynorphin A immunopositive products were observed in epithelium of acinis. These immunopositive cells may be synthetic and/or secretory cells of dynorphin A. Dynorphin A immunoreactive products were commonly observed in epithelium and connective tissue (CT) of labial palps, mouth labia and stomach, which presented in forms of grains, fibers or flakes. KOR-1 immunoreactive material was observed in ECs and CTs of labial palps, mouth labia and stomach, intestine and hepatopancreas. The distribution of both dynorphin A and KOR-1 in the digestive organs suggests an involvement of dynorphin via KOR-1 in the functional regulation of the digestive system of C. farreri .