Histology of the hepatopancreas of puffer fish (Takifugu rubripes) in relation to the localization of tetrodotoxin

The “liver” of puffer fish had both a hepatic portion and a pancreatic portion. The hepatic portion had the parenchyma and the portal area as mammalian livers such as human or mouse or rat. However, the hepatic lobule was not obvious histologically in the puffer liver. In the hepatic parenchyma, both parenchymal cells (hepatocytes) and non-parenchymal cells such as liver sinusoidal endothelial cells and hepatic stellate cells (vitamin A-storing cells, Ito cells) were demonstrated to exist. Cytoplasm of the parenchymal cells was filled with large fat droplets, namely, the liver was in steatosis, but neither hepatic fibrosis nor liver cirrhosis was identified. In the pancreatic portion, pancreatic acinar cells containing zymogen granules were seen. Tetrodotoxin was demonstrated mainly in the acinar cells of the pancreatic portion; hepatic parenchymal cells, liver sinusoidal endothelial cells, and hepatic stellate cells were also shown to contain tetrodotoxin by immunohistochemistry using specific antibody against tetrodotoxin. This is the first report demonstrating the localization of tetrodotoxin in acinar cells of the pancreatic portion and non-parenchymal cells of the hepatic portion in the hepatopancreas of the puffer fish.