Morphology of extraganglionic fluorescent neurons in the myenteric plexus of the small intestine of the rat

Localization of GABAA receptor immunoreactivity in NO synthase positive myenteric neurones

GABAA receptors were localized within laminar preparations of the rat distal colon myenteric plexus using a monoclonal antibody (mAb 62-3G1) to the affinity purified GABAA receptor/benzodiazepine receptor/Cl- channel complex. The immunofluorescence procedure showed that approximately half of the myenteric ganglion cells displayed extensive GABAA receptor labelling of their soma. This population was further characterised by treating some GABAA-receptor-labelled laminar preparations for the histochemical demonstration of nitric oxide (NO) synthase-related NADPH-dependent diaphorase activity. A subpopulation of the GABAA-receptor-immunoreactive cells (35%) were also found to display intense NO-synthase-related activity. These findings extend our understanding of the GABAA-receptor-related innervation of the rat gut wall herein referred to as 'A-GABAergic' and provides an anatomical basis for the pharmacologically-identified GABA-nitrergic pathway in the mammalian gut.

Immunocytochemical study of tyrosine hydroxylase and dopamine beta-hydroxylase immunoreactivities in the rat pancreas

An immunohistochemical and immunoelectron microscopic study was used to demonstrate tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (DBH) immunoreactivities in the rat pancreas. Small TH immunoreactive cells were found in close contact with large TH immunonegative ganglion cells among the exocrine glands and were occasionally found in some islets. Some of these TH immunoreactive cells were also DBH immunopositive. The immunoreaction product was seen diffusely in the cytoplasm and in the granule cores of TH immunoreactive cells. All intra-pancreatic ganglion cells were immunoreactive for DBH, but not for TH. The TH immunoreactive cells were identified as small intensely fluorescent (SIF) cells due to their localization and morphological characteristics and showed no insulin, glucagon, somatostatin or pancreatic polypeptide immunoreactivities. These results indicate that SIF cells may release dopamine or noradrenaline to adequate stimuli while the intra-pancreatic ganglion cells with only DBH may not synthesize catecholamines in a normal biosynthetic pathway. TH immunoreactive nerve bundles without varicosities and fibers with varicosities, associated or unassociated with blood vessels, were found in both the exocrine and endocrine pancreas. Close apposition of TH immunoreactive nerve fibers to the smooth muscle and endothelial cells of the blood vessels was observed. A close apposition between TH immunoreactive nerve fibers and exocrine acinar cells and islet endocrine cells was sometimes found in the pancreas. The immunoreaction product was seen diffusely in the axoplasm and in the granular vesicles of the immunoreactive nerve fibers. Since no TH immunoreactive ganglion cells were present in the rat pancreas, the present study suggests that noradrenergic nerve fibers in the pancreas may be extrinsic in origin, and may exert an effect on the regulation of blood flow and on the secretory activity of the acinar cells, duct cells and endocrine cells.

Autoradiographic study of the distribution of [3H]gamma-aminobutyrate-accumulating neural elements in guinea-pig intestine: evidence for a transmitter function of gamma-aminobutyrate

High affinity uptake, and the distribution of 3H-radiolabelled gamma-aminobutyrate (GABA), cis-3-aminocyclohexanecarboxylic acid, beta-alanine, proline, and leucine have been examined autoradiographically in laminar preparations of the myenteric plexus from the guinea-pig intestine. Following labelling with [3H]proline and [3H]leucine, which are incorporated into neurons, silver grains were concentrated over recognisable perikarya in the ganglia and meshworks of the plexus, whilst [3H]GABA labelled a smaller proportion of neurons and their processes. Specificity of labelling in the sites of [3H]GABA-uptake was established using combinations of labelled and unlabelled GABA, beta-alanine, and cis-3-aminocyclohexanecarboxylic acid, substrates for glial or neuronal high affinity GABA uptake systems. Only myenteric neurons and their processes were labelled significantly by [3H]GABA and its analogue cis-3-[3H]aminocyclohexanecarboxylic acid. Using autoradiographs of laminar preparations and paraffin sections, [3H]GABA labelling was found over nerve fibre bundles that could be traced from their ganglionic origins through the interconnecting meshworks of the myenteric plexus into the innervation of the deep muscular plexus of the circular muscle layer where GABA is evidently concerned with prejunctional modulation of transmitter release. The extensive but selective distribution of [3H]GABA high affinity uptake sites in neural elements of the guinea-pig myenteric plexus is consistent with GABA being an enteric neurotransmitter.

The presence of extraganglionic fluorescent neurons in the myenteric plexus of the guinea pig small intestine

Fluorescent histochemical observations of the small intestine of the guinea pig demonstrated that single fluorescent cell bodies, separate from the ganglia, were present in the myenteric plexus. These cell bodies gave rise to single processes which entered the ganglia or the interganglionic strands. They were of a very small size, and the intensity of their fluorescence increased by pretreatment with L-DOPA and nialamide. Interruption of extrinsic nerve pathways to the small intestine caused a disappearance of the meshwork of fluorescent fibers in the myenteric plexus; but in some areas a fluorescent fiber which supplied its terminal to the ganglion was seen to remain. A photograph taken from the denervated myenteric plexus revealed that a long process arising from an extraganglionic cell entered the ganglion and ramified into terminal branches.

Neurofilament and glial fibrillary acid protein-related immunoreactivity in rodent enteric nervous system

Using antisera raised against neurofilaments and the glial fibrillary acidic protein (GFAP) we have examined the appearance and distribution of neurofilament- and GFAP-like immunoreactivity in the enteric nervous system of rat, mouse and guinea-pig. In whole mounts of the external circular and longitudinal muscle layers, including the myenteric plexus, a high number of neurofilament-positive perikarya were visualized both in the ganglia and in the circularly running interconnecting strands in all three species. These cells were large, usually with eccentrically placed nuclei and single, relatively thick neurofilament-positive processes. In addition, in guinea-pig myenteric plexus a small number of cells with multiple processes could be seen. Both in the longitudinal and circular interconnecting strands a large number of thin, smooth, neurofilament-positive fibres were observed. This regular network of ganglia and strands was superimposed on a sparse system of thin, usually individual neurofilament-positive fibres in the underlying circular muscle layer. Cryostat sections revealed neurofilament-positive cell bodies in the submucous plexus, whereas fibres showing neurofilament-like immunoreactivity were observed in all layers of the gut wall, with the exception of the epithelium. In whole mounts including rat and mouse myenteric plexus, a large number of cells and fibres showing GFAP-like immunoreactivity were visualized. The GFAP-positive cells were smaller and more numerous than the neurofilament-positive ones. They were present both within the ganglia and in the interconnecting strands. Several short fluorescent processes could frequently be seen emanating from the cell body. Both the strands and the ganglia contained a high number of thin, GFAP-positive fibres. Fluorescent fibres and cells were also observed in the circular muscle layer. In sections of rat and mouse small intestine, cells were observed throughout the gut wall, with the exception of the epithelium. Double labelling experiments clearly showed that neurofilament- and GFAP-positive cells represented separate cell populations. Furthermore, GFAP-positive cells and fibres outlined the neurofilament-positive perikarya. It is thus likely that the GFAP-positive cells represent enteric glial cells. The pre- and postnatal development of neurofilament- and GFAP-like immunoreactivity was studied in whole mounts from rat embryos and pups. Furthermore, the presence of neurofilament and GFAP-positive fibres was observed in whole mount preparations of rat and mouse mesenterium.(ABSTRACT TRUNCATED AT 400 WORDS)

The presence of aromatic L-amino acid decarboxylase in certain intestinal nerve cells

The presence of aromatic 1-amino acid decarboxylase (AADC) in nerve cell bodies of the intrinsic plexuses of the guinea-pig small intestine was demonstrated by incubating segments of intestine with 1-dopa in the presence of an inhibitor of monoamine oxidase, pargyline. After such incubation, some nerve cell bodies gave a fluorescence histochemical reaction indicative of the presence of a decarboxylated product of 1-dopa, probably dopamine. No fluorescence reaction occurred in the unincubated control or if the inhibitor of AADC, RO 4-4602, was included in the incubation mixture. The AADC-containing cell bodies apparently do not take up and store dopamine, because no fluorescence could be detected after incubation with dopamine and a monoamine oxidase inhibitor. The AADC-containing cells were found in about half of the ganglia of the submucous plexus of the guinea-pig small intestine, but were considerably less frequent in the myenteric plexus. They were also found in the other areas examined in this study, that is, in both enteric plexuses of the guinea-pig distal colon and of the small intestines of rabbits and rats.

The altrastructure of Auerbach's plexus in the guinea-pig. I. Neuronal elements

The ultrastructural features of nerve cell bodies and axon profiles within Auerbach's plexus in the stomach, ileum, caecum and colon of the guinea-pig have been examined. Nerve cell bodies have been tentatively classified into nine different types according to their size, distribution of organelles, location and relationship to satellite cells. Except for cell size, no attempt has been made to correlate ultrastructual with light microscopical observations. On the basis of vesicular size, shape and content, eight morphologically distinct types of axon profile have been identified as well as two profile types which are thought to reflect different physiological conditions. The axons contained various populations of small, mostly granular vesicles; small, round agranular vesicles; small, flattened vesicles; large flattened or elongated vesicles; and three types of large vesicle with granular contents distinguished by size. Some correlation between types of axon profile and two types of nerve cell body was recognized. However, more than one type of axon profile usually formed synapses with one type of cell body, and a precise correlation was not determined.