DEVELOPMENT OF NEUROPEPTIDE-Y INNERVATION IN THE LIVER

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.