Hepatic neuropeptide Y (NPY) innervation was studied by immunohistoche
mistry in various mature vertebrates including the eel, carp, bullfrog
, turtle, chicken, mouse, rat, guinea pig, dog, monkey and human. In a
ddition, an ontogenetic study on hepatic NPY was made in developing mi
ce and guinea pigs. In all species examined except the eel, NPY-like i
mmunoreactivity was detected in nerve fibers. In the carp, bullfrog, t
urtle, chicken, mouse, and rat, NPY-positive fibers were distributed a
round the wall of hepatic vessels and the bile duct of the Glisson's s
heath. The density of NPY-positive fibers increased with evolution. Ho
wever, in the guinea pig, dog, monkey, and human, numerous NPY-positiv
e fibers were observed not only in the Glisson's sheath but also in th
e liver parenchyma. Positive fibers formed a dense network that surrou
nded the hepatocytes. The present immunoelectron microscopic study has
confirmed that NPY-positive terminals are closely apposed to hepatocy
tes. Ontogenically, NPY-positive fibers were first found in the embryo
nic Liver of 19-day-old mice. Positive fibers increased with age, and
the highest peak was seen I week after birth. However, NPY-positive ne
rve fibers were present abundantly in Glisson's sheath and in the hepa
tic parenchyma of neonatal (3 and 7 days old) guinea pigs in a distrib
ution similar to that in mature animals. This ontogenetic pattern sugg
ests that NPY plays a certain role in the developing liver. (C) 1997 W
iley-Liss, Inc.