PHYLOGENETIC AND ONTOGENIC STUDY OF NEUROPEPTIDE Y-CONTAINING NERVES IN THE LIVER

The distribution of neuropeptide Y was investigated by light and elect ron microscopic immunohistochemistry in the liver of various vertebrat es including the eel, carp, bullfrog, turtle, chicken, mouse, rat, gui nea-pig, dog, monkey and human. The ontogenetic development of neurope ptide Y was also studied in the mouse liver. In all species examined e xcept the eel, neuropeptide Y-like immunoreactivity was detected in ne rve fibres. In the carp, bullfrog, turtle, chicken, mouse and rat, pos itive fibres were distributed around the wall of hepatic vessels and t he bile duct of the Glisson's sheath. The density of the positive fibr es increased with evolution. On the other hand, in the guinea-pig, dog , monkey and human, numerous neuropeptide Y-positive fibres were obser ved not only in the Glisson's sheath but also in the liver parenchyma. Positive fibres formed a dense network to surround hepatocytes. The p resent immunoelectron microscopic study has confirmed that neuropeptid e Y-positive terminals are closely apposing to hepatocytes. Ontogeneti cally, neuropeptide Y-positive fibres were first found in embryonic li ver of 19-day-old mice. Positive fibres increased with age and the hig hest peak was seen one week after birth. This ontogenetic pattern has suggested that neuropeptide Y plays a certain role in developing liver .