Generating diversity: Mechanisms regulating the differentiation of autonomic neuron phenotypes.

Sympathetic and parasympathetic postganglionic neurons innervate a wide range of target tissues. The subpopulation of neurons innervating each target tissue can express unique combinations of neurotransmitters, neuropeptides, ion channels and receptors, which together comprise the chemical phenotype of the neurons. The target-specific chemical phenotype shown by autonomic postganglionic neurons arises during development. In this review, we examine the different mechanisms that generate such a diversity of neuronal phenotypes from the pool of apparently homogenous neural crest progenitor cells that form the sympathetic ganglia. There is evidence that the final chemical phenotype of autonomic postganglionic neurons is generated by both signals at the level of the cell body that trigger cell-autonomous programs, as well as signals from the target tissues they innervate.

The sympathetic postganglionic and sensory innervation of oviducal magnum in hen: a choleratoxin subunit B-conjugated horseradish peroxidase study.

The anatomy of the extrinsic innervation of the avian magnum has not been accurately demonstrated previously. In the present study, choleratoxin subunit B-conjugated horseradish peroxidase (CB-HRP) was used as a retrograde tracer to determine the sympathetic postganglionic and sensory innervation of the magnum of hens. With regard to the sympathetic postganglionic innervation, following CB-HRP injections under the serosa of the magnum, CB-HRP-positive neurons were found bilaterally in the C12-LS13 ganglia of the sympathetic chain, splanchnic ganglia and adrenal ganglia. The number of labelled neurons in the left ganglia of the sympathetic chain and splanchnic ganglia was approximately 2.1 times that in the right ganglia. This suggests that the unilateral magnum is bilaterally innervated with sympathetic postganglionic nerves, the left nerves being predominant. With regard to the sensory innervation, following tracer injections, CB-HRP-positive neurons were found bilaterally in the spinal ganglia C13-LS12, jugular ganglia and nodose ganglia. The number of positive cells in the left ganglia was about 2.2 times that in the right ganglia. In the spinal ganglia, 85.6% of the labelled neurons were in the T5-LS2 and LS8-LS11 ganglia. These results suggest that the sensory nerve fibres of the magnum reach the central nervous system principally via two groups of spinal ganglia and vagus nerves, and that the innervation is bilateral although the left-hand route predominates. Moreover, 45.7% of all the CB-HRP-labelled neurons were found in the rectal region of the intestinal nerve of Remak (INR), which suggests that the INR plays a very important role in the functional regulation of the magnum.

Sensitive innervation of the copulatory organ in Struthio camelus: comparison to the corresponding district in female proctodeum.

The AA. have studied the nerve component of male copulatory organ and ventral part of female proctodeum in the ostrich. This paper represents the concluding part of the plan of research that aimed to verify some data and hypothesis referred in previous observations. The innervation of the considered districts was always constituted by autonomic and sensitive somatic nerve components. The autonomic innervation was represented by isolated and grouped ganglion cells located along the course of nerve bundles or in the point where different nerve bundles converged. This nerve component was frequently in close connection with the blood vessels. The sensitive somatic innervation was constituted by free and capsulated nerve endings. The latter, always supplied by a typical structure and morphologically classified as Pacini, Pacini-like and genital's corpuscles, could be found either isolated or grouped within the different layers of both the examined anatomical territories. The grouped corpuscles, in particular Pacini's corpuscles, could organize simple and complex flower sprays, opposito-polar corpuscles and poikilomorphous fibres. For the first time the capsule's lamellar organization in Pacini's corpuscles in Birds was documented by means of light microscope. The occurrence of genital corpuscles seemed to be exclusive in the ventral part of female ostrich proctodeum, corresponding to the male site in which lies the copulatory organ.

Chemically distinct preganglionic inputs to iris-projecting postganglionic neurons in the rat: A light and electron microscopic study.

Individual autonomic postganglionic neurons are surrounded by pericellular baskets of preganglionic terminals that are easily identifiable with the light microscope. It has been assumed that the target cell of a pericellular basket of preganglionic terminals is the neuron at the centre of the basket. This assumption has enabled the connectivity of preganglionic neurons to be determined at the light microscopic level. However, if the preganglionic terminals in a pericellular basket make synapses with the dendrites of nearby, but functionally different, postganglionic neurons, then the conclusions of light microscopic studies are far less certain. We have used a serial section ultrastructural study to determine the target of the preganglionic pericellular basket in a situation where the apparent target cell is surrounded by neurons of dissimilar function. In the rat superior cervical ganglion, postganglionic neurons projecting to the iris were identified, using retrograde tracers, as single neurons (i.e., not in clusters). We have used immunohistochemistry to show that iris-projecting neurons are surrounded by preganglionic nerve terminals containing calcitonin gene-related peptide (CGRP). We have demonstrated that the pericellular basket of CGRP-immunoreactive preganglionic terminals provides inputs only to the soma at the centre of the basket and not to the dendrites of surrounding neurons. This suggests that, in autonomic ganglia, light microscopic identification of the preganglionic terminal baskets is likely to be a reliable method for identifying the targets of subclasses of preganglionic neurons.

Small intensely fluorescent cells of the rat paracervical ganglion synthesize adrenaline, receive afferent innervation from postganglionic cholinergic neurones, and contain muscarinic receptors.

In the paracervical ganglion (PCG) of the rat, double-labelling immunofluorescence for catecholamine-synthesizing enzymes and HPLC measurement of catecholamine contents were first performed to evaluate whether intraganglionic small intensely fluorescent (SIF) cells are capable of synthesizing adrenaline. Immunolabelling for tyrosine hydroxylase (TH), dopamine beta-hydroxylase and phenylethanolamine-N-methyl transferase (PNMT) occurred in all SIF cells of the PCG, thus demonstrating the presence of all the enzymes required for adrenaline biosynthesis. Adrenaline levels were undetectable in the PCG but to test the hypothesis that PNMT is active in SIF cells, catecholamines were measured in ganglia of rats pretreated with pargyline, an inhibitor of the monoamine oxidase, the major enzyme involved in the catecholamine degradation. Pargyline treatment increased adrenaline levels in the PCG, thus demonstrating that SIF cells are capable of adrenaline synthesis. The undetectable levels of adrenaline in the PCG of untreated rats suggested a slow rate of biosynthesis of adrenaline in the ganglion. Furthermore, the use of double-labelling showed that SIF cells of the PCG were stained for muscarinic receptors and were approached by varicose ChAT-immunoreactive nerve fibres. Nerve fibres immunoreactive for ChAT were also observed associated with nerve cell bodies of ganglion neurones. Following deafferentation of the PCG, the ChAT-immunoreactive nerve fibres surrounding nerve cell bodies totally disappeared indicating their preganglionic origin, while those associated with SIF cells did not degenerate, which demonstrate that they derived from intraganglionic cholinergic neurones. Taken together, the results show that adrenaline may be a transmitter for SIF cells in the PCG and suggest that cholinergic neurones of the parasympathetic division of the PCG can modulate the SIF cell activity through the activation of muscarinic receptors.

Parasympathetic nerves in penile erectile tissue of the rat contain choline acetyltransferase.

Choline acetyltransferase (ChAT), a biochemical marker of cholinergic neurons, was measured in the erectile tissue of intact rats and in rats in which postganglionic fibers from the pelvic plexus were interrupted. ChAT activity in the denervated erectile tissue fell by 56% compared to control tissues. Acetylcholinesterase positive (AChE+) nerves also fell by about 48%. Penile neurons distal to the lesion probably account for the residual ChAT activity and remaining AChE+ nerve fibers in erectile tissue. These results indicate that acetylcholine is an important neurotransmitter in the regulation of penile erection.

Distribution of neurons in the major pelvic ganglion of the rat which supply the bladder, colon or penis.

In male rats a large number of the postganglionic neurons which innervate the pelvic organs are located in the major pelvic ganglion. In the present study we have identified the location within this ganglion of neurons which project to either of three pelvic organs, the penis, colon or urinary bladder. Two fluorescent retrogradely-transported dyes, Fast Blue and Fluoro-Gold, were used. For most animals one dye was injected into the cavernous space of the penis, the wall of the distal colon or the wall of the urinary bladder. In a small number of animals two organs were injected, each with a different dye. One to six weeks after injection the major pelvic ganglia were fixed in buffered formaldehyde. The distribution of fluorescent dye-labelled cells was observed in whole mounts of complete ganglia and, in most cases, also in small accessory ganglia located between the ureter and the prostate. The studies showed a unique pattern of distribution for each organ-specific group of neurons. Most of the colon neurons are located in the major pelvic ganglion near the entrance of the pelvic nerve, whereas almost all of the penis neurons are near or within the penile nerve. Bladder neurons are relatively evenly distributed throughout the ganglion. These results demonstrate a distinct topographical organization of organ-specific neurons of the major pelvic ganglion of the male rat, a phenomenon which has also been observed in other peripheral ganglia.

Innervation of the gastrointestinal canal of the toad Bufo marinus by neurons containing 5-hydroxytryptamine-like immunoreactivity.

The gut of the toad, Bufo marinus, was examined for evidence of enteric neurons containing 5-hydroxytryptamine-like immunoreactivity. Such neurons were absent from the stomach. They were present in the small intestine, with processes confined to the myenteric plexus. Immunoreactive nerve cell bodies lay on branches of the pelvic nerves supplying the large intestine; fibres were found in the submucosa of the posterior large intestine and in the muscularis external of the anterior large intestine. It is concluded, on morphological grounds, that the neurons in the small intestine are interneurons, whereas those in the large intestine are postganglionic parasympathetic motoneurons.

Sympathetic postganglionic innervation of the cardiac coronary artery in cats.

The localization of the sympathetic postganglionic neurons innervating the cardiac coronary arteries of the cat was investigated using retrograde axonal transport with horseradish peroxidase. We found after the enzyme was applied to the main trunk of the right coronary artery, and to the main trunk and the terminal branch of the ventral descending vessels of the left coronary artery, the peroxidase-labeled sympathetic neurons were localized predominantly in the right stellate ganglia, with a few cells in the left stellate ganglia. There were very few labeled cells in the middle cervical, superior cervical, and T4-7 ganglia on both sides. After peroxidase application to the terminal branch of the dorsal descending vessels of the right coronary artery, labeled cells were mainly in the left stellate ganglia, with only a few cells in the right stellate ganglia.

Anatomical localization of afferent and postganglionic sympathetic neurons innervating the rat ovary.

The fluorescent retrograde tracer, True blue, was applied directly to either the superior ovarian nerve (SON) or the ovarian plexus nerve (OPN) in the rat. Afferent perikarya were located in lower thoracic-upper lumbar dorsal root ganglia and projected to the ovary via both nerve routes. Postganglionic sympathetic efferent perikarya were located in both prevertebral and thoracolumbar paravertebral ganglia and also utilized both the SON and OPN to reach the ovary. The significance of the dual origin of postganglionic sympathetic neurons innervating the rat ovary is not known.

Intramural nerves and interstitial cells revealed by the Champy-Maillet stain in the opossum esophagus.

The 3 layers of smooth muscle of the opossum esophagus exhibit distinctly different and characteristic functions in response to nerve stimulation. These behaviors might be related to differences in patterns of innervation. Serial sections, stained with osmic acid and zinc iodide, were examined from all parts of the esophagus to describe in full the innervation of opossum esophageal smooth muscle. Linear beaded structures identified as terminal nerves were abundant in all 3 layers of smooth muscle. They were aligned with muscle bundles in bundles of 1-5 in mucosal muscle and up to about 10 in the longitudinal layer of muscularis propria. In the circular layer of muscularis propria they were less dense and more arborized and they crossed the muscle obliquely to also innervate bipolar interstitial cells; these cells resembled type III interstitial cells of Cajal, were specific for the circular muscle layer and were uniformly distributed throughout the thickness of that layer. Their distribution density in the circular muscle was slightly greater, 8777/cm2 in the most caudad 1.5 cm of the esophagus (which encompasses the sphincter) than in the 6 cm above that level. Terminal nerves also innervated submucosal glands, vessels and the epithelium. Ganglion cells and nerve bundles in the submucous and myenteric plexuses were variably stained. Ganglia of the latter plexus contained intraganglionic laminar endings as described previously in other species. In the striated muscle there were nerves terminating in motor end-plates. Other leafy stellate cells resembling interstitial cells of Cajal of other types were stained, as were oval interstitial cells.

Use of the fluorescent dye, fast blue, to label sympathetic postganglionic neurones supplying mesenteric arteries and enteric neurones of the rat.

Neuronal pathways in the peripheral nervous system have been traced using the fluorescent dye, Fast blue. Following implantation of a gelatin pellet containing the dye, or direct injection of the dye into the mesentery beside an artery, Fast blue is taken up by both nerve terminals and axons of passage, retrogradely transported by large numbers of sympathetic neurones and retained within the neurones for long periods of time without diffusion. Neurones projecting to both blood vessels of the mesentery and submucosa and to enteric ganglia of the segment supplied by the artery were found labelled in prevertebral and paravertebral ganglia as well as in ganglia lying along the major splanchnic nerves. Attempts to separate the vascular component from those neurones innervating enteric ganglia suggest that the latter are located in the prevertebral, coeliac and superior mesenteric ganglia and to a lesser extent in the splanchnic ganglia, while the vasomotor neurones are located in prevertebral, paravertebral and splanchnic ganglia.

[Morphology of the ciliary ganglion (author's transl)]. / Aspects morphologiques du ganglion ciliaire.

Microscopic examination of the ciliary ganglion shows the presence of large peripheral and moderately-sized central neurones. The appearance of the intraganglionic neurones suggests that they are of the parasympathetic type, sensory fibres and sympathetic fibre bundles passing through the ganglion without synapses. Afferent fibres are long and thin and have no collateral endings, while efferent fibres are short and thick. Afferent nerve fibres have either a very thin or no myelin sheath, whereas post-ganglionic fibres are richly myelinated.