A comparative histochemical and immunohistochemical study of aminergic, cholinergic and peptidergic innervation in rat, hamster, guinea pig, dog and human livers

Anatomy of efferent hepatic nerves

The role of neural elements in regulating blood flow through the hepatic sinusoids, solute exchange, and parenchymal function is incompletely understood. This is due in part to limited investigation in only a few species whose hepatic innervation may differ significantly from humans. For example, most experimental studies have used rats and mice having livers with little or no intralobular innervation. In contrast, most other mammals, including humans, have aminergic and peptidergic nerves extending from perivascular plexus in the portal space into the lobule, where they course in Disse's space in close relationship to stellate cells (fat storing cells of Ito) and hepatic parenchymal cells. While these fibers extend throughout the lobule, they predominate in the periportal region. Cholinergic innervation, however, appears to be restricted to structures in the portal space and immediately adjacent hepatic parenchymal cells. Neuropeptides have been colocalized with neurotransmitters in both adrenergic and cholinergic nerves. Neuropeptide Y (NPY) has been colocalized in aminergic nerves supplying all segments of the hepatic-portal venous and the hepatic arterial and biliary systems. Nerve fibers immunoreactive for substance P and somatostatin follow a similar distribution. Intralobular distribution of all of these nerve fibers is species-dependent and similar to that reported for aminergic fibers. Vasoactive intestinal peptide and calcitonin gene-related peptide (CGRP) are reported to coexist in cholinergic and sensory afferent nerves innervating portal veins and hepatic arteries and their branches, but not the other vascular segments or the bile ducts. Nitrergic nerves immunoreactive for neuronal nitric oxide (nNOS) are located in the portal tract where nNOS colocalizes with both NPY- and CGRP-containing fibers. In summary, the liver is innervated by aminergic, cholinergic, peptidergic, and nitrergic nerves. While innervation of structures in the portal tract is relatively similar between species, the extent and distribution of intralobular innervation are highly variable as well as species-dependent and may be inversely related to the density of gap junctions between contiguous hepatic parenchymal cells.

Cocaine increases inducible nitric oxide synthase expression in rats: effects of acute and binge administration

The present studies assessed the effects of acute and binge cocaine administration on the in vivo production of inducible nitric oxide synthase in a rat model of endotoxemia. Inducible nitric oxide synthase is a key enzyme involved in host defense and inflammatory responses consequent to infection through its production of nitric oxide. Male Lewis rats received subcutaneous injections of saline or selected doses of cocaine (7.5-30 mg/kg) at the same time as a 50 microg/kg dose of lipopolysaccharide (LPS). Animals in the binge cocaine experiments received two additional injections of cocaine or saline at 2 and 4 h after the initial injections. All animals were sacrificed 6 h after initial drug administration and tissues harvested for determination of iNOS protein levels. Plasma nitrite/nitrate levels were also assayed to assess any treatment-related differences in the degradative by-products of nitric oxide metabolism. Western blot analyses of iNOS expression indicated that both acute and binge cocaine treatment resulted in significant increases in iNOS expression in all tissues assayed. Furthermore, acute and binge cocaine treatment also dose-dependently increased plasma nitrite levels. These data suggest that cocaine may impact resistance to gram-negative infections and severity of these infections via modulation of nitric oxide parameters.

Cloning of a C-terminally truncated NK-1 receptor from guinea-pig nervous system

In order to examine the possibility that some actions of substance P may be mediated by a variant of the neurokinin-1 (NK-1) receptor, we isolated and sequenced the cDNA encoding a truncated NK-1 receptor from guinea-pig celiac ganglion and brain mRNA by two-step RT-PCR based on the 3'RACE method. The truncated NK-1 receptor sequence corresponded to a splice variant missing the final exon 5, and encoded a 311-amino acid protein that was truncated just after transmembrane domain 7, in an identical position to a truncated variant of the human NK-1 receptor. Thus, the truncated NK-1 receptor lacked the intracellular C-terminus sequence required for the phosphorylation and internalisation of the full-length NK-1 receptor. Using a sensitive one-step semi-quantitative RT-PCR assay, we detected mRNA for both the full length and truncated NK-1 receptors throughout the brain, spinal cord, sensory and autonomic ganglia, and viscera. Truncated NK-1 receptor mRNA was present in lower quantities than mRNA for the full-length NK-1R in all tissues. Highest levels of mRNA for the truncated NK-1 receptor were detected in coeliac ganglion, spinal cord, basal ganglia and hypothalamus. An antiserum to the N-terminus of the NK-1 receptor labelled dendrites of coeliac ganglion neurons that were not labelled with antisera to the C-terminus of the full length NK-1 receptor. These results show that a C-terminally truncated variant of the NK-1 receptor is likely to be widespread in central and peripheral nervous tissue. We predict that this receptor will mediate actions of substance P on neurons where immunohistochemical evidence for a full-length NK-1 receptor is lacking.

The nitrergic autonomic innervation of the liver

Using immunohistochemical approaches, the nitrergic innervation of the liver has been studied in mammals and in fish. The morphofunctional relationships described here indicate a high degree of evolutionary conservation of the hepatic nitrergic transmission and its possible involvement in the neural control of the hepatic function in health and disease.

Neuronal nitric oxide synthase immunoreactivity in the guinea-pig liver: distribution and colocalization with neuropeptide Y and calcitonin gene-related peptide

AIMS/BACKGROUND

The innervation pattern of the guinea-pig liver is similar to that of the human liver. However, many aspects of the distribution of the neuronal isoform of the enzyme nitric oxide synthase (nNOS) in the guinea-pig liver and its colocalization with neuropeptides remain to be elucidated.

METHODS

The distribution of nNOS was studied in fixed guinea-pig liver by light microscopic immunohistochemistry. Confocal analysis was used to determine its colocalization with neuropeptide Y (NPY) or calcitonin gene-related peptide (CGRP).

RESULTS

nNOS-immunoreactive (nNOS-IR) nerves were observed in relation to hilar and interlobar vessels and in Glisson's capsule. A few nNOS-IR ganglia were observed in the extrahepatic bile duct and close to the interlobar portal triads. In addition, nNOS-IR fibers were located in the interlobular portal triads and pervading the parenchyma. Moreover, nNOS-IR nerves were demonstrated for the first time in the larger central veins and in the hepatic vein. nNOS-NPY and nNOS-CGRP colocalizations were detected in the fibromuscular layer of the bile duct and periductal plexus, respectively.

CONCLUSIONS

These results support the phylogenetic conservation of the nNOS-IR hepatic innervation and its possible contribution to the regulation of hepatic blood flow and certain hepatic functions.

Immunocytochemical study on the liver innervation in patients with cirrhosis

In the liver, the autonomic nervous system plays an important role in degenerative and inflammatory changes. The aim of the present study was to investigate the distribution of neuronal fibres containing neuropeptides in livers of 5 patients with cirrhosis by immunocytochemical localization at the light and electron microscopical level of substance P (SP), neuropeptide Y (NPY), somatostatin (SOM), and calcitonin gene-related peptide (CGRP). In patients with alcoholic cirrhosis, a decreased number of neuronal fibres was found in the portal tract and fibrous septa as well as in the sinusoids of regenerative nodules. NPY- and SP-immunoreactive neuronal fibres were more numerous than CGRP-containing fibres. They were located mainly in portal tracts. These findings led to the conclusion that peptidergic innervation plays a role in inflammatory and fibrotic changes in cirrhotic liver.

Immunolocalization of the HNK-1 epitope in the autonomic innervation to the liver and upper digestive tract of the developing rat embryo

The immunohistochemical analysis of the HNK-1 epitope presence in the liver and upper digestive tract nerves was carried out in 12- to 18-day-old rat embryos embedded in acrylamide-agarose and observed with laser scanning confocal microscopy. The vagus and sympathetic trunk were intensely immunostained at all ages; branches of both structures were also HNK-1 positive, and ramified ventrocaudally following the course of the thoracic and abdominal aorta, caval vein, portal vein and ductus venosus. As early as day 12, some immunostained cells were seen in the mesentery that formed the enteric nervous system. Clearly immunostained HNK-1-immunoreactive fibres were detected innervating the digestive wall after day 14, forming both myenteric and submucosal plexuses. After day 16, the Glisson sheath showed streams of HNK-1-positive fibres coming from dorsal areas, lining the peritoneal surface of the diaphragm, invading the capsule, and ramifying superficially around the lobes of the liver. We saw no immunoreactive structures pervading the hepatic lobes at all ages studied, with the exception of occasional HNK-l-positive cells in the superficial parenchyma, which were visualized after 16 days of gestation. Our findings can help to understand the development of the gastrointestinal and liver innervation in the rat.

Peptides and other neuronal markers in transplanted pancreatic islets

Functional alterations are developed in transplanted islets over time. Because islets in situ are densely innervated and isolation disconnects the endocrine organ from extrinsic nerves and from ganglia in the exocrine pancreas, it is important to examine the reinnervation of islet grafts. This review describes the patterns of appearances of intrinsic perikarya and reinnervating fibers demonstrating markers for parasympathetic, sympathetic or sensory nerve substances, most notably neuropeptides, in islet transplants. An altered innervation pattern, as compared to normal islets, develops. Presumably the expression of neuronal markers in the grafts is related to factors both in the islets and in the ectopic environment offered by the implantation organ.