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
.