A COMPARATIVE HISTOCHEMICAL AND IMMUNOHISTOCHEMICAL STUDY OF AMINERGIC, CHOLINERGIC AND PEPTIDERGIC INNERVATION IN RAT, HAMSTER, GUINEA-PIG, DOG AND HUMAN LIVERS

Aims/Background: The mammalian liver receives both sympathetic and par asympathetic nerves that contain aminergic, cholinergic and peptidergi c components. The intrahepatic distribution of nerve fibers are highly species-dependent; and also, even within one species, there are notab le variations. To reveal the pattern and type of hepatic innervation i n different species, we examined the distribution and density of these nerve fibers. Methods. The livers of rats, golden hamsters, guinea pi gs, dogs and humans were used. Aminergic and peptidergic nerve fibers were identified by immunohistochemistry for tyrosine hydroxylase (TH), neuropeptide Y (NPY), substance P (SP), vasoactive intestinal polypep tide (VIP), calcitonin gene-related peptide (CGRP), and galanin (GAL), and cholinergic fibers were identified by the acetylcholinesterase (A ChE) neurohistochemistry method. Results: AChE-, TH-, NPY-, CGRP-, VIP - and SP-positive nerves were observed in the connective tissue of the portal region, and they were in close contact with hepatic arteries, portal veins and bile ducts in all five species, Within the parenchyma of guinea pig, dog and human livers, TH-, NPY- and SP-positive fibers were observed, but no AChE- and CGRP-positive fibers were observed. I n rat and hamster livers, no parenchymal nerve fibers could be demonst rated, but CGRP-, NPY- and SP-positive fibers were observed in the bor der of periportal areas. The density of CGRP-positive nerve fibers wer e slightly higher around bile ducts than around hepatic arteries and p ortal veins, GAL-positive fibers were not detected in any animal. Conc lusions: These data indicate that there were differences in the patter ns of hepatic innervation among rats, golden hamsters, guinea pigs, do gs and humans. The data also show that: 1) in rat and hamster livers, hepatic functions may be regulated by both sympathetic and parasympath etic nerves in the portal region; 2) in guinea pig, dog and human live rs they may be regulated by these fibers both in the interlobular regi on (parasympathetic and sympathetic systems) and in the intraparenchym al region (sympathetic system); and thus, 3) in the latter three speci es, hepatocytes and sinusoidal cells may be innervated by sympathetic nerves.