Extrinsic innervation of the pelvic organs in the lesser pelvis of human embryos

Realistic models to understand the developmental appearance of the pelvic nervous system in mammals are scarce. We visualized the development of the inferior hypogastric plexus and its preganglionic connections in human embryos at 4–8 weeks post-fertilization, using Amira 3D reconstruction and Cinema 4D-remodelling software. We defined the embryonic lesser pelvis as the pelvic area caudal to both umbilical arteries and containing the hindgut. Neural crest cells (NCCs) appeared dorsolateral to the median sacral artery near vertebra S1 at ~5 weeks and had extended to vertebra S5 1 day later. Once para-arterial, NCCs either formed sympathetic ganglia or continued to migrate ventrally to the pre-arterial region, where they formed large bilateral inferior hypogastric ganglionic cell clusters (IHGCs). Unlike more cranial pre-aortic plexuses, both IHGCs did not merge because the 'pelvic pouch', a temporary caudal extension of the peritoneal cavity, interposed. Although NCCs in the sacral area started to migrate later, they reached their pre-arterial position simultaneously with the NCCs in the thoracolumbar regions. Accordingly, the superior hypogastric nerve, a caudal extension of the lumbar splanchnic nerves along the superior rectal artery, contacted the IHGCs only 1 day later than the lumbar splanchnic nerves contacted the inferior mesenteric ganglion. The superior hypogastric nerve subsequently splits to become the superior hypogastric plexus. The IHGCs had two additional sources of preganglionic innervation, of which the pelvic splanchnic nerves arrived at ~6.5 weeks and the sacral splanchnic nerves only at ~8 weeks. After all preganglionic connections had formed, separate parts of the inferior hypogastric plexus formed at the bladder neck and distal hindgut.     

Preganglionic fibers in the rat hypogastric nerve project bilaterally to pelvic ganglia

Stimulation of the hypogastric nerve (HGN) often evokes bilateral responses in some pelvic organs. Retrograde labeling studies indicate that axons of postganglionic neurons often cross to the opposite side. However, there is little information available as to whether preganglionic fibers in the HGN have a contralateral projection to pelvic ganglia. A retrograde tracer was injected into the left major pelvic ganglion (MPG) in rats receiving various lesions of preganglionic nerves (HGN and pelvic nerve, PN). The lumbar spinal cord was then examined for location and number of dye-filled neurons. In a second approach, the incidence of synaptophysin immunoreactivity (SN-IR) perineuronal profiles (baskets) was examined in the MPG and in the accessory pelvic ganglia (APG) after nerve lesions. Labeled neuronal profiles were found in spinal cord nuclei (Lumbar_1–2) after dye injection of the MPG in animals with an intact contralateral HGN. Cutting both HGNs virtually eliminated dye labeling in the lumbar cord, as did severing commissural branches (CB) between pelvic ganglia (leaving the contralateral HGN intact). Some SN-IR baskets were found in the left APG when only the contralateral HGN was intact, but baskets were rare when all four preganglionic nerves were cut. It could not be determined whether the HGN projects to the contralateral MPG, since SN-IR baskets were numerous in the MPG even when all four nerves were cut. This study has shown that some preganglionic fibers in the HGN synapse on neurons in contralateral pelvic ganglia. Both the APG and MPG receive contralateral innervation, but it is likely that neurons in the APG are the primary target of this input. Thus, in addition to crossing postganglionic fibers, a portion of the bilateral control of pelvic tissues is accomplished by preganglionic fibers which target autonomic neurons in contralateral ganglia. Anat. Rec. 252:229–234, 1998. © 1998 Wiley-Liss, Inc.     

Remodelling of connections in pelvic ganglia after hypogastric nerve crush

Pelvic ganglia innervate the urogenital organs and contain both sympathetic and parasympathetic neurons. Previous studies have shown that within days of cutting either the lumbar or sacral preganglionic axons that innervate pelvic ganglia, many axon collaterals grow and appear to form specific connections with denervated pelvic neurons. Here we have examined the longer term consequences of partial deafferentation by studying pelvic ganglia up to 7 weeks after hypogastric nerve (HGN) crush, a lesion which also allows faster regeneration of spinal axons. Noradrenergic neurons were denervated by HGN crush, as demonstrated by loss of varicosities immunostained for the synaptic proteins, synaptophysin and synapsin. A week after HGN crush, axon collaterals grew from parasympathetic pelvic ganglion neurons, shown by the presence of numerous varicose fibers immunostained for vasoactive intestinal peptide (VIP). These VIP fibers were poorly stained or unstained for synaptophysin, even after 7 weeks. At early post-operative times the VIP fibers grew irregularly; however, with longer post-operative times they appeared to target particular VIP-negative, noradrenergic neurons. Our results also indicate that some lumbar preganglionic axons regenerated during the post-operative period, although this only affected a minority of sympathetic neurons. These reinnervated sympathetic neurons were not associated with VIP fibers, suggesting that the new intrinsic connections may have precluded regeneration or targeting of preganglionic axons. Together these results demonstrate that there is considerable remodelling within pelvic ganglia after partial deafferentation. This occurs under conditions where spinal preganglionic axons can regenerate. New intra-ganglionic connectivity may be permanent and may impact on this regeneration.     

The hypogastric nerve innervates a population of penile neurons in the pelvic plexus

Retrograde dye staining, enkephalin immunocytochemistry and nerve lesion paradigms were used to determine if penile neurons in the pelvic plexus are innervated by fibers in the hypogastric nerve. In the intact major pelvic ganglion of the rat, some 80% of penile neurons are enclosed by an enkephalin-positive fiber plexus. Following surgical interruption of the pelvic nerve, 20% of penile neurons were still surrounded by an enkephalin plexus. After interruption of the pelvic nerve and the hypogastric nerve, the enkephalin plexus in the ganglion was virtually absent, including the plexus around penile neurons. Therefore, possible intrinsic sources of the enkephalin fibers such as enkephalin-positive principal neurons and small intensely fluorescent cells, do not account for the delicate enkephalin fiber system in the pelvic ganglion. It is concluded that the pelvic nerve is the major source of preganglionic innervation to penile neurons in the major pelvic ganglion. However, it is significant that the hypogastric nerve is preganglionic to about 20% of penile neurons. The pathway through the hypogastric nerve may represent an alternate vasodilator system to penile erectile tissue.     

Functional segregation within the pelvic nerve of male rats: a meso- and microscopic analysis

The pelvic splanchnic nerves are essential for pelvic organ function and have been proposed as targets for neuromodulation. We have focused on the rodent homologue of these nerves, the pelvic nerves. Our goal was to define within the pelvic nerve the projections of organ-specific sensory axons labelled by microinjection of neural tracer (cholera toxin, subunit B) into the bladder, urethra or rectum. We also examined the location of peptidergic sensory axons within the pelvic nerves to determine whether they aggregated separately from sacral preganglionic and paravertebral sympathetic postganglionic axons travelling in the same nerve. To address these aims, microscopy was performed on the major pelvic ganglion (MPG) with attached pelvic nerves, microdissected from young adult male Sprague–Dawley rats (6–8 weeks old) and processed as whole mounts for fluorescence immunohistochemistry. The pelvic nerves were typically composed of five discrete fascicles. Each fascicle contained peptidergic sensory, cholinergic preganglionic and noradrenergic postganglionic axons. Sensory axons innervating the lower urinary tract (LUT) consistently projected in specific fascicles within the pelvic nerves, whereas sensory axons innervating the rectum projected in a complementary group of fascicles. These discrete aggregations of organ-specific sensory projections could be followed along the full length of the pelvic nerves. From the junction of the pelvic nerve with the MPG, sensory axons immunoreactive for calcitonin gene-related peptide (CGRP) showed several distinct patterns of projection: some projected directly to the cavernous nerve, others projected directly across the surface of the MPG to the accessory nerves and a third class entered the MPG, encircling specific cholinergic neurons projecting to the LUT. A subpopulation of preganglionic inputs to noradrenergic MPG neurons also showed CGRP immunoreactivity. Together, these studies reveal new molecular and structural features of the pelvic nerves and suggest functional targets of sensory nerves in the MPG. These anatomical data will facilitate the design of experimental bioengineering strategies to specifically modulate each axon class.     

A study of the inferior mesenteric and pelvic ganglia of guinea-pigs with intracellular electrodes

1. Ganglion cells in the inferior mesenteric ganglion (IMG) and the pelvic plexus of the guinea-pig were studied using intracellular micro-electrodes.2. Ganglion cells had resting membrane potentials of 55-65 mV. Threshold for initiation of an action potential ranged from 10 to 20 mV depolarization. Action potentials often exceeded 100 mV in amplitude and were followed by an after-hyperpolarization of up to 20 mV.3. Synaptic responses were recorded from cells in the IMG in response to stimulation of the right and left hypogastric nerves, ascending mesenteric, inferior splanchnic and colonic nerves. It has been established that more than forty preganglionic fibres converge on any one cell. Preganglionic fibres to the IMG were also observed in the pelvic nerves.4. In contrast to the IMG, ganglion cells in the pelvic plexus received up to ten preganglionic fibres.5. Ganglion cells responded to supramaximal preganglionic stimulation with up to four action potentials.6. In the IMG, action potentials in response to synaptic action were followed by a prolonged period of hyperpolarization (after-hyperpolarization) and a later phase of prolonged depolarization (after-depolarization). The time course of these after potentials depended on the pattern of firing of action potentials during the period of stimulation. In the presence of dihydro-beta-erythroidine, or if synaptic action was insufficient to evoke action potentials, only the after-depolarization was observed.7. Other cells were impaled whose properties differed from those described above. In one group of cells the resting membrane potentials were higher (up to 85 mV), input resistances lower and the threshold for initiation of an action potential was higher. The other group were inexcitable, had high resting membrane potentials (up to 85 mV), low input resistances and underwent a slow depolarization in response to repetitive stimulation of preganglionic fibres.8. This study indicates that marked convergence of presynaptic fibres occurs on to ganglion cells of the IMG. The ganglion cells in the pelvic plexus receive a relatively small number of fibres, many of which exert intense synaptic activity ensuring a direct connexion to the central nervous system.     

Demonstration of paracervical ganglion origin for the vasoactive intestinal peptide-containing nerves of the rat uterus using retrograde tracing techniques combined with immunocytochemistry and denervation procedures

The origin of the abundant vasoactive intestinal peptide (VIP)-immunoreactive nerves in the uterus has not been fully determined. In this study, a fluorescent dye, True Blue was injected into the uterus of rat and 6 days later, neuronal cell bodies of the paracervical ganglion were found to be labelled by this dye. Some of these labelled ganglion cells were also found to contain VIP immunoreactivity by immunocytochemistry. When the preganglionic pelvic and/or hypogastric nerves of rats were sectioned, the VIP-immunoreactive nerves in the uteri were not depleted, indicating that these nerves did not originate from the splanchnic ganglion, dorsal root ganglion or the spinal cord. Therefore it is concluded that VIP-immunoreactive nerves in the uterus originate from the paracervical ganglion.     

Effects of chronic deafferentation on adrenergic ganglion cells and small intensely fluorescent cells

Summary To determine the reaction of adrenergic ganglion cells and small intensely fluorescent (SIF) cells to chronic deafferentation, catecholamine fluorescence of the major pelvic ganglion (MPG) of the rat has been studied following section of the hypogastric nerve, pelvic nerve and sympathetic trunk. Only minor changes occurred following section of the hypogastric nerve; the fluorescence surrounding a few adrenergic ganglion cells became brighter. In contrast, pelvic neurectomy resulted in the appearance of numerous varicose fibres and an increase in the fluorescent intensity of fibres enclosing many ganglion cells. Varicose fibres seem to originate from adrenergic ganglion cells and SIF cells. In many instances, nests of SIF cells gave rise to radially oriented fibres. Removal of the sympathetic trunk appeared to have no effect on the MPG. It is suggested that the appearance of varicose fibres from SIF cells following deafferentation may be due to collateral sprouting of these cells or to the increased fluorescence of pre-existing processes.     

Localization of hindlimb vasomotor neurones in the lumbar spinal cord of the guinea pig

After retrograde labelling with horseradish peroxidase, sympathetic preganglionic neurones projecting to paravertebral ganglion cells with destinations primarily in the hindlimb were found to lie laterally in the intermediate region of the lumbar spinal cord. The majority of the labelled cell bodies were located near the edge of the grey matter or lateral to it within the white matter. In the most caudal segments (L3-L4) neurons extended right across the lateral funiculi. This distribution of neurones with predominantly vasoconstrictor functions differs markedly from that observed after labelling preganglionic fibres that project in the hypogastric nerve to the pelvic viscera.     

Human pelvic extramural ganglion cells: a semiquantitative and immunohistochemical study

In pelvic surgery, much attention is paid to nerve bundles but not to ganglion cells. Using serial section histology of 14 postmortem-treated hemipelvis (eight males, six females; mean, 79 years old), we examined the population number, distribution, and tyrosine hydroxylase-immunoreactivity (TH-IR; suggesting sympathetic neurons) of extramural pelvic ganglion cells. All pelvic ganglion cells were uniformly sized (25–30 μm) contrasting with small intramural rectal neurons. Abundant ganglion cells (30,000–140,000 unilaterally) existed not only along the pelvic viscera except for the rectum, but also along the hypogastric nerve, pelvic splanchnic nerve, pelvic plexus, and associated branches excluding those within the mesorectum. The intrapelvic ganglion cells outside the sympathetic trunk did not form macroscopically identifiable ganglia, but made small clusters (0.1–2.0 mm of maximum diameter) or were diffusely scattered within nerve bundles. More than half of these cells appeared TH-IR positive, although the positive/negative proportion differed between nerves and specimens. Greater numbers of ganglion cells were found in dorsosuperior sites (e.g., around the seminal vesicle) rather than in ventroinferior sites (e.g., along the urethra) in males, and vice versa in females. However, in total cell numbers, interindividual variations were evident rather than intergender difference. Due to significant interindividual variations in cell number, differences are likely to exist between patients in “resistance” to surgical stresses. We hypothesized that pelvic ganglion cells are liable to be damaged due to drying along the surgical margin, hypoxia in venous bleeding, pressure from surgical retractors, extension stress with taping and excess traction and/or direct injury with electrical scalpels.     

Nerve contributions to the pelvic plexus and the umbilical cord

Serial sections of human embryos and fetuses reveal that the sacral nerves which contribute fibers to the pelvic plexus often have dorsal, ventral, and oblique communicating rami. The ventral rami resemble the white rami of upper thoracic nerves and some of their fibers pass close by or through the chain ganglia and into the pelvic plexus. The sizes of the ventral rami are often in inverse proportion to that of the pelvic splanchnic nerves. That is, when the pelvic splanchnic nerves are poorly developed, the ventral rami are large, and conversely, when the pelvic splanchnic nevers are well developed, these rami are small. The pelvic plexus was found to receive fibers from the sympathetic trunk and its ganglia in addition to those from the hypogastric plexus and the pelvic splanchnic nerves. Analysis of the observations made in this study together with a review of the literature in light of the present day classification of nerve fibers raises serious doubts concerning the limits set for the outflow of preganglionic nerve fibers from the spinal cord and the distribution of gray and white rami as described in recent textbooks in terms of their histological and physiological significance. Nerve fibers from the pelvic plexus can be traced along the walls of the bladder and the urachus and along the umbilical arteries into the umbilical cord. In embryos, only a few scattered nerve fibers were found distal to the umbilicus, but in fetuses at term, distinct nerve bundles were identified in the cord. These bundles sent branches to the walls of the umbilical arteries; other branches terminated as “end-nets” in Wharton's jelly. These nets appeared as fine fibers with nodular swellings at irregular intervals. Innervation of the umbilical arteries was richest within the first few inches of the cord. Beyond this region, the nerves rapidly decreased in number. “End-nets” were present as far as four inches from the umbilicus. Granular cells resembling Langerhans' cells were found in the cord. Often these cells were closely associated with fine nerve fibers.     

Origin of peptide-containing fibers in the inferior mesenteric ganglion of the guinea-pig: Immunohistochemical studies with antisera to substance P,enkephalin, vasoactive intestinal polypeptide,cholecystokinin and bombesin

After different denervation procedures the guinea-pig inferior mesenteric ganglion was analysed by immunohistochemistry using antisera to substance P, enkephalin, vasoactive intestinal polypeptide, cholecystokinin and bombesin. The results demonstrate that each of the nerve trunks connected to the ganglion carries specific peptidergic pathways. Thus, the lumbar splachnic nerves contain substance P-immunoreactive primary afferent neurons, which to a large extent traverse the ganglion, and enkephalin-immunoreactive preganglionic neurons; the colonie nerves carry vasoactive intestinal polypeptide-, cholecystokinin- and bombesin-immunoreactive fibers from the distal colon to the ganglion; the hypogastric nerves contain vasoactive intestinal polypeptide-positive fibers from the pelvic plexus; and the intermesenteric nerve contains vasoactive intestinal polypeptide, cholecystokinin, substance P and enkephalin from divergent sources. By studying accumulations of peptides in ligated lumbar splanchnic, intermesenteric, hypogastric and colonic nerves the existence of these major peptidergic pathways was confirmed and evidence was obtained for additional, not so prominent, peptidergic projections. The results are discussed in view of earlier morphological and physiological studies.     

Spinal neurons involved in the control of the seminal vesicles: a transsynaptic labeling study using pseudorabies virus in rats

The seminal vesicles are male accessory sex glands that mainly contribute the seminal fluid of the ejaculate. Previous studies have suggested that seminal vesicles are supplied by both sympathetic and parasympathetic nerves. However, this conclusion was mainly based on studies in pelvic major ganglions and direct neuroanatomical evidence of spinal neurons innervating the seminal vesicles is still lacking. In order to map the spinal nerve circuit innervating the seminal vesicles, the present study used the pseudorabies virus (PRV) retrograde tracing technique in combination with immunohistochemistry. Three groups of rats were prepared: (1) nerves intact; (2) right hypogastric nerve and bilateral pelvic nerves sectioned; (3) right pelvic and bilateral hypogastric nerves sectioned. For the intact group, 3 to 5 days after injection of PRV into the left seminal vesicle in male rats, immunohistochemistry for PRV was performed to map the control circuit. Double immunofluorescence experiments against PRV and choline acetyltransferase (ChAT) were performed to discriminate preganglionic neurons and interneurons. Double detection of PRV and galanin (GAL) was also performed to identify lumbar spinothalamic (LSt) cells. Three days after virus injection, both sympathetic and parasympathetic preganglionic neurons were retrograde-labeled. Four days after injection of PRV into the seminal vesicles, PRV-infected neurons were found in the dorsal horn, ventral horn, dorsal gray commissure (DGC), medial gray matter and intermediolateral cell column (IML) from T13 to S1. For the group with an intact hypogastric nerve, 4 days after injection of PRV into the seminal vesicles, PRV-infected neurons were mainly located in DGC and IML of spinal lumbar segments (L) 1-L2. However, in the group with an intact pelvic nerve, PRV-infected neurons were mainly located in DGC of L5-S1 spinal segments. At the L3-L4 level, most of the virus-labeled neurons around the central canal expressed immunoreactivity for GAL, strongly suggesting that they could be LSt cells. These anatomical data support the idea that the sympathetic and parasympathetic nervous system are both involved in the control of the seminal vesicles and we demonstrated a connection between preganglionic neurons innervating the seminal vesicles and LSt cells which play a crucial role in coordinating the spinal control of ejaculation.     

Postnatal maturational changes in rat pelvic autonomic ganglion cells: a mixture of steroid-dependent and -independent effects

Androgens have potent effects on the maturation and maintenance of a number of neural pathways involved in reproductive behaviors in males. Most studies in this area have focused on central pathways, but androgen receptors are expressed by many peripheral neurons innervating reproductive organs, and previous studies have demonstrated structural and chemical changes in these neurons at puberty and after castration. We have performed the first electrophysiological comparison of pelvic autonomic ganglion neurons in male rats before and after puberty and following pre- or postpubertal castration. Studies were performed in vitro on intact ganglia with hypogastric and pelvic nerves attached to allow synaptic activation of sympathetic or parasympathetic neurons, respectively. Pelvic ganglion neurons underwent many changes in their passive and active membrane properties over the pubertal period, and some of these changes were dependent on exposure to circulating androgens. The most pronounced steroid-dependent effects were on membrane capacitance (soma size) in sympathetic neurons and duration of the action potential afterhyperpolarization in tonic neurons. Our study also showed that rat pelvic ganglion cells and their synaptic inputs were more diverse than previously reported. In conclusion, this study demonstrated that rat pelvic ganglion neurons undergo considerable postnatal changes in their electrophysiological properties. The steroid dependence of some of these changes indicates that circulating androgens may influence reproductive behaviors at many locations within the nervous system not just in the brain and spinal cord.     

Organization of lumbar spinal outflow to distal colon and pelvic organs

The lumbar sympathetic outflow projects through the lumbar splanchnic, lumbar colonic, and hypogastric nerves (and to a lesser degree through the sacral sympathetic chain and pelvic nerves). It is thought to be involved in the regulation of the storage and evacuation functions of the following three organ systems: lower urinary tract, hindgut, and reproductive organs. In addition, it controls vascular resistance and capacitance. Thus the target tissues of the postganglionic neurons are vascular smooth muscle, visceral smooth muscles, probably secretory epithelia, and also neurons in the enteric nervous system and the pelvic ganglia. The preganglionic neurons are situated in the caudal part of the spinal representation, neurons associated with the colon being located rostral to those associated with the pelvic organs. Most lie medial to the classical intermediolateral cell column that may contain mainly vasoconstrictor neurons. Most (if not all) preganglionic neurons are cholinergic; some also contain an identified peptide. Most of the postganglionic neurons are situated in the inferior mesenteric ganglion (or equivalent structures); again, those projecting to the colon lie rostral to those projecting to the pelvic organs. Others lie in intercalated prevertebral ganglia, in the pelvic plexus, and in sacral paravertebral ganglia. The majority is noradrenergic, and most also contain one or several peptides, the topographical distribution of which appears to characterize functional subgroups of neurons. The terminations of noradrenergic axons in many pelvic organs probably make close contact with both vascular and nonvascular effectors. In the colon, most endings are located in the enteric plexuses. The responses of these organs to electrical stimulation of visceral nerves, and their reflex responses (together with those observed in the efferent axons of visceral nerve trunks) to electrical and natural stimulation of afferent fibers, lead to the general conclusion that several distinct classes of pre- and postganglionic neurons exist. 1) Vasoconstrictor neurons demonstrate ongoing activity with cardiac rhythm and appropriate reflexes to stimulation of cardiovascular afferent receptors and respond only weakly to natural stimulation of visceral receptors. 2) MR neurons respond to visceral stimuli but are not influenced from arterial baro- and chemoreceptors. These show at least two different response patterns consistent with their separate involvement in the reciprocal behavior of the colon and bladder. 3) Other neurons are silent in anesthetized animals and do not respond to any stimuli used thus far.(ABSTRACT TRUNCATED AT 400 WORDS)     

Reflex firing in the lumbar sympathetic outflow to activation of vesical afferent fibres

1. Activation of vesical afferent fibres in the Aγδ range by electrical stimulation of the pelvic nerve or by bladder distension elicited reflex firing in hypogastric nerves and in preganglionic nerves to the inferior mesenteric ganglion.

2. The multisynaptic reflex was present in cats with an intact spinal cord and in acute and chronic spinal animals (transections at T10—T12). The reflex pathway was partially crossed in the sacral cord, and in the periphery at the level of the inferior mesenteric ganglia. In contrast, an inhibitory response to raised intravesical pressure was mediated by a supraspinal inhibitory mechanism which was activated in parallel with the micturition reflex.

3. Since enhancement as well as depression of sympathetic firing accompanied reflex micturition, it is concluded that at least two distinct populations of lumbar preganglionic neurones are responsive to vesical afferent activity: one population being excited, the other depressed, during micturition. The latter population may be involved in an inhibitory feed-back mechanism on to the bladder.

     

Observations on the anatomy and amine histochemistry of the nerves and ganglia which supply the pelvic viscera and on the associated chromaffin tissue in the guinea-pig

Summary The organs of the lower abdominal and pelvic regions of the guinea-pig receive nerves from the inferior mesenteric ganglia and pelvic plexuses. The inferior mesenteric ganglia connect with the sympathetic chains, the superior mesenteric ganglia, the pelvic plexuses via the hypogastric nerves, and with the gut. Each pelvic plexus consists of anterior and posterior parts which send filaments to the internal generative organs and to the rectum, internal anal sphincter and other pelvic organs. The pelvic nerves enter the posterior plexuses, which also receive rami from the sacral sympathetic chains. The adrenergic neurons of the pelvic plexuses are monopolar, do not have dendrites and are supplied by few varicose adrenergic axons. Nearly all the nerves contain adrenergic fibres. After exposure to formaldehyde vapour the chromaffin cells appear brightly fluorescent with one or two long, often varicose, processes. Most of the chromaffin cells are in Zuckerkandl's organ or in chromaffin bodies associated with the inferior mesenteric ganglia. Groups of chromaffin cells are found along the hypogastric nerves and in the pelvic plexuses; they become smaller and fewer as regions more posterior to Zuckerkandl's organ are approached.This work was supported by grants from the Australian Research Grants Committee and the National Health and Medical Research Council. We thank Professor G. Burnstock for his generous support.     

Origin of sympathetic efferent axons in the renal nerves of the cat

The origin of efferent axons in the renal nerves of the cat was examined using retrograde transport of horseradish peroxidase (HRP). Nerves on the surface of the left renal blood vessels were dissected 5-7 horseradish mm proximal to the medial margin of the kidney, transected and the central cut ends exposed to HRP. Labeled neurons were typically identified in three locations: (1) centrally along the renal nerve, (2) in the superior mesenteric ganglion, and (3) in the ipsilateral sympathetic chain ganglia (T12-L3). HRP was not detected in preganglionic neurons in the thoracolumbar spinal cord. Labeled cells ranged in size from 15 to 50 micrometers, with those in the renal nerve at the smaller end of the spectrum and those in the superior mesenteric ganglion at the larger end. In the superior mesenteric ganglion labeled cells were typically localized to a small region in the caudal pole of the ganglion around the origin of the renal nerve. The results show that the sympathetic efferent innervation of the kidney is derived from both paravertebral and prevertebral ganglia. In the latter (superior mesenteric ganglion), renal efferent neurons exhibited a topographic distribution.     

Adrenergic and Cholinergic Innervation of the Rat Urinary Bladder

The autonomic innervation of the rat urinary bladder was studied using histochemical methods and nerve stimulations. A sparse adrenergic innervation of the detrusor muscle was found. It was supposed to originate from long adrenergic neurones. The trigonum area had a rich supply of adrenergic fibres, probably derived from short adrenergic neurones. A uniformly rich supply of acetylcholine-esterase (AChE)-positive nerves was found in the whole bladder. Postganglionic sympathetic denervation caused no detectable change of adrenergic or AChE-positive nerves in the bladder, while parasympathetic decentralization or denervation produced a total disappearance of adrenergic fibres. The AChE-positive nerves were appreciably reduced in number after parasympathetic decentralization and not detectable after postganglionic denervation. Neither adrenergic nor AChE-positive ganglion cells could be demonstrated in the bladder wall. Electrical stimulation of the hypogastric nerves or the pelvic nerves distal to the pelvic ganglia elicited contraction of the detrusor muscle. The responses were not affected by hexamethonium, dihydroergotamine or propranolol but were slightly reduced by guanethidine, reduced to about 40% by atropine and potentiated by eserine. Stimulation of the pelvic nerve proximal to the pelvic ganglion was partially blocked by hexamethonium. It is concluded that the urinary bladder of the rat is supplied by postganglionic adrenergic fibres mainly via the pelvic nerves and only to a lesser extent via the hypogastric nerves. Probably cholinergic fibres pass to the bladder mainly via the pelvic nerves but also via the hypogastric nerves, having their cellbodies outside the bladder wall, partly proximal to the pelvic ganglia.