Neuropathology of human sympathetic autonomic ganglia

Sympathetic innervation of the development, maturity, and aging of the gastrointestinal tract

The sympathetic nervous system inhibits gut motility, secretion, and blood flow in the gut microvasculature and can modulate gastrointestinal inflammation. Sympathetic neurons signal via catecholamines, neuropeptides, and gas mediators. In the current review, we summarize the current understanding of the mature sympathetic innervation of the gastrointestinal tract with a focus mainly on the prevertebral sympathetic ganglia as the main output to the gut. We also highlight recent work regarding the developmental processes of sympathetic innervation. The anatomy, neurochemistry, and connections of the sympathetic prevertebral ganglia with different parts of the gut are considered in adult organisms during prenatal and postnatal development and aging. The processes and mechanisms that control the development of sympathetic neurons, including their migratory pathways, neuronal differentiation, and aging, are reviewed.

O-GlcNAcylation is crucial for sympathetic neuron development, maintenance, functionality and contributes to peripheral neuropathy

O-GlcNAcylation is a post-translational modification (PTM) that regulates a wide range of cellular functions and has been associated with multiple metabolic diseases in various organs. The sympathetic nervous system (SNS) is the efferent portion of the autonomic nervous system that regulates metabolism of almost all organs in the body. How much the development and functionality of the SNS are influenced by O-GlcNAcylation, as well as how such regulation could contribute to sympathetic neuron (symN)-related neuropathy in diseased states, remains unknown. Here, we assessed the level of protein O-GlcNAcylation at various stages of symN development, using a human pluripotent stem cell (hPSC)-based symN differentiation paradigm. We found that pharmacological disruption of O-GlcNAcylation impaired both the growth and survival of hPSC-derived symNs. In the high glucose condition that mimics hyperglycemia, hPSC-derived symNs were hyperactive, and their regenerative capacity was impaired, which resembled typical neuronal defects in patients and animal models of diabetes mellitus. Using this model of sympathetic neuropathy, we discovered that O-GlcNAcylation increased in symNs under high glucose, which lead to hyperactivity. Pharmacological inhibition of O-GlcNAcylation rescued high glucose-induced symN hyperactivity and cell stress. This framework provides the first insight into the roles of O-GlcNAcylation in both healthy and diseased human symNs and may be used as a platform for therapeutic studies.

Autonomic failure: Clinicopathologic, physiologic, and genetic aspects

Over the past century, generations of neuroscientists, pathologists, and clinicians have elucidated the underlying causes of autonomic failure found in neurodegenerative, inherited, and antibody-mediated autoimmune disorders, each with pathognomonic clinicopathologic features. Autonomic failure affects central autonomic nervous system components in the α-synucleinopathy, multiple system atrophy, characterized clinically by levodopa-unresponsive parkinsonism or cerebellar ataxia, and pathologically by argyrophilic glial cytoplasmic inclusions (GCIs). Two other central neurodegenerative disorders, pure autonomic failure characterized clinically by deficits in norepinephrine synthesis and release from peripheral sympathetic nerve terminals; and Parkinson's disease, with early and widespread autonomic deficits independent of the loss of striatal dopamine terminals, both express Lewy pathology. The rare congenital disorder, hereditary sensory, and autonomic neuropathy type III (or Riley-Day, familial dysautonomia) causes life-threatening autonomic failure due to a genetic mutation that results in loss of functioning baroreceptors, effectively separating afferent mechanosensing neurons from the brain. Autoimmune autonomic ganglionopathy caused by autoantibodies targeting ganglionic α3-acetylcholine receptors instead presents with subacute isolated autonomic failure affecting sympathetic, parasympathetic, and enteric nervous system function in various combinations. This chapter is an overview of these major autonomic disorders with an emphasis on their historical background, neuropathological features, etiopathogenesis, diagnosis, and treatment.

Pathological classification of equine recurrent laryngeal neuropathy

Recurrent Laryngeal Neuropathy (RLN) is a highly prevalent and predominantly left-sided, degenerative disorder of the recurrent laryngeal nerves (RLn) of tall horses, that causes inspiratory stridor at exercise because of intrinsic laryngeal muscle paresis. The associated laryngeal dysfunction and exercise intolerance in athletic horses commonly leads to surgical intervention, retirement or euthanasia with associated financial and welfare implications. Despite speculation, there is a lack of consensus and conflicting evidence supporting the primary classification of RLN, as either a distal ("dying back") axonopathy or as a primary myelinopathy and as either a (bilateral) mononeuropathy or a polyneuropathy; this uncertainty hinders etiological and pathophysiological research. In this review, we discuss the neuropathological changes and electrophysiological deficits reported in the RLn of affected horses, and the evidence for correct classification of the disorder. In so doing, we summarize and reveal the limitations of much historical research on RLN and propose future directions that might best help identify the etiology and pathophysiology of this enigmatic disorder.

Morphological changes in peri-prostatic sympathetic ganglion cells in aging males

A significant part of morbidity in elderly male patients involves the pelvic organs and their autonomic neural regulation. The aim of the current study was to report the histopathological changes in the peri-prostatic ganglia in elderly males. The sympathetic ganglia from 36 prostatectomy specimens, 26 due to carcinoma of the prostate and 10 prostates from total cystectomies for transitional cell carcinoma, were examined. The age range was 54-88 years. A total of 5,075 ganglion cells were counted in all the specimens. Pathological changes were identified in 1,696 neuron cells as follows: Neuronophagia in 746 neuron cells, neuron cell vacuolization (330 cells), satellite cells vacuolization (423 cells), cell pyknosis (148 cells) and nageotte nodules (49 cells). A number of these changes increased with age. All the changes were more marked in the peri-prostatic ganglion cells of patients with prostatic adenocarcinoma compared with those with benign prostate hyperplasia, which may be due to local environmental changes associated with the presence of malignancy.

Synapses on sympathetic neurons and parasympathetic neurons differ in their vulnerability to diabetes

Synapses in autonomic ganglia represent the final output of various CNS structures that regulate the function of the periphery. Normally, these excitatory cholinergic-nicotinic synapses produce large suprathreshold EPSPs on sympathetic and parasympathetic neurons to convey signals from the CNS. However, in certain disease states, synaptic transmission in autonomic ganglia is depressed and the periphery becomes deregulated. For example, previous work demonstrated that hyperglycemia depresses EPSPs on sympathetic neurons and disrupts sympathetic reflexes by causing an ROS-dependent inactivation of the postsynaptic nAChRs. What is not clear, however, is whether some autonomic neurons are more vulnerable to hyperglycemia than others. One possibility is that sympathetic neurons may be more prone than cholinergic parasympathetic neurons to hyperglycemia-induced elevations in cytosolic ROS because sympathetic neurons contain several pro-oxidant molecules involved in noradrenaline metabolism. To test this hypothesis, we recorded synaptic transmission from different mouse sympathetic and parasympathetic ganglia, as well as from the adrenal medulla. In addition, we used cellular imaging to measure hyperglycemia-induced changes in cytosolic ROS and whole-cell recordings to measure the use-dependent rundown of ACh-evoked currents. Our results demonstrate that hyperglycemia depresses synaptic transmission on sympathetic neurons and adrenal chromaffin cells and elevates cytosolic ROS. Conversely, hyperglycemia has little effect on synaptic transmission at synapses on parasympathetic neurons. We conclude that sympathetic neurons and adrenal chromaffin cells are more vulnerable to diabetes than parasympathetic neurons, a finding that may have implications for both long-term diabetic autonomic neuropathies and insulin-induced hypoglycemia, a serious complication of diabetes.

Stereological and allometric studies on neurons and axo-dendritic synapses in superior cervical ganglia

The superior cervical ganglion (SCG) plays an important role in neuropathies including Horner's syndrome, stroke, and epilepsy. While mammalian SCGs seem to share certain organizational features, they display natural differences related to the animal size and side and the complexity and synaptic coverage of their dendritic arborizations. However, apart from the rat SCG, there is little information concerning the number of SCG neurons and synapses, and the nature of relationships between body weight and the numbers and sizes of neurons and synapses remain uncertain. In the recognition of this gap in the literature, in this chapter, we reviewed the current knowledge on the SCG structure and its remodeling during postnatal development across a plethora of large mammalian species, focusing on exotic rodents and domestic animals. Instrumentally, we present stereology as a state-of-the-art 3D technology to assess the SCG 3D structure unbiasedly and suggest future research directions on this topic.

Reactive oxygen species inactivate neuronal nicotinic acetylcholine receptors through a highly conserved cysteine near the intracellular mouth of the channel: implications for diseases that involve oxidative stress

An intriguing feature of several nicotinic acetylcholine receptors (nAChRs) on neurons is that their subunits contain a highly conserved cysteine residue located near the intracellular mouth of the receptor pore. The work summarized in this review indicates that α3β4-containing and α4β2-containing neuronal nAChRs, and possibly other subtypes, are inactivated by elevations in intracellular reactive oxygen species (ROS). This review discusses a model for the molecular mechanisms that underlie this inactivation. In addition, we explore the implications of this mechanism in the context of complications that arise from diabetes. We review the evidence that diabetes elevates cytosolic ROS in sympathetic neurons and inactivates postsynaptic α3β4-containing nAChRs shortly after the onset of diabetes, leading to a depression of synaptic transmission in sympathetic ganglia, an impairment of sympathetic reflexes. These effects of ROS on nAChR function are due to the highly conserved Cys residues in the receptors: replacing the cysteine residues in α3 allow ganglionic transmission and sympathetic reflexes to function normally in diabetes. This example from diabetes suggests that other diseases involving oxidative stress, such as Parkinson's disease, could lead to the inactivation of nAChRs on neurons and disrupt cholinergic nicotinic signalling.

Diabetes depresses synaptic transmission in sympathetic ganglia by inactivating nAChRs through a conserved intracellular cysteine residue

Most people with diabetes develop severe complications of the autonomic nervous system; yet, the underlying causes of many diabetic-induced dysautonomias are poorly understood. Here we explore the idea that these dysautonomias results, in part, from a defect in synaptic transmission. To test this idea, we investigated cultured sympathetic neurons and show that hyperglycemia inactivates nAChRs through a mechanism involving an elevation in reactive oxygen species and an interaction with highly conserved cysteine residues located near the intracellular mouth of the nAChR channel. Consistent with this, we show that diabetic mice have depressed ganglionic transmission and reduced sympathetic reflexes, whereas diabetic mice expressing mutant postsynaptic nAChRs that lack the conserved cysteine residues on the alpha3 subunit have normal synaptic transmission in sympathetic ganglia and normal sympathetic reflexes. Our work suggests a new model for diabetic-induced dysautonomias and identifies ganglionic nAChRs as targets of hyperglycemia-induced downstream signals.

Vasopressin release induced by hypothension is blunted in patients with diabetic autonomic neuropathy

The response of arginin-vasopressin (AVP) to baroreceptor activation (tilt testing) was investigated in patients with diabetic autonomic neuropathy (DAN). The present data show that hypothension induced by upright position showed a slight increase of AVP in patients with DAN in comparison with normal subjects and diabetic patients without DAN. These findings suggest that the blunted AVP response to hypothension may be due to lesions of afferent autonomic pathways present in DAN and plays a role in the pathogenesis of postural hypothension.

Neuritic dystrophy and neuronopathy in Akita (Ins2(Akita)) diabetic mouse sympathetic ganglia

Diabetic autonomic neuropathy is a debilitating, poorly studied complication of diabetes. Our previous studies of non-obese diabetic (NOD) and related mouse models identified rapidly developing, dramatic pathology in prevertebral sympathetic ganglia; however, once diabetic, the mice did not survive for extended periods needed to examine the ability of therapeutic agents to correct established neuropathy. In the current manuscript we show that the Akita (Ins2(Akita)) mouse is a robust model of diabetic sympathetic autonomic neuropathy with unambiguous, spontaneous, rapidly-developing neuropathology which corresponds closely to the characteristic pathology of other rodent models and man. Akita mice diabetic for 2, 4 or 8 months of diabetes progressively developed markedly swollen axons and dendrites ("neuritic dystrophy") in the prevertebral superior mesenteric (SMG) and celiac ganglia (CG). Comparable changes failed to develop in the superior cervical ganglia (SCG) of the Akita mouse or in any ganglia of non-diabetic mice. Morphometric studies demonstrate an overall increase in presynaptic axon terminal cross sectional area, including those without any ultrastructural features of dystrophy. Neurons in Akita mouse prevertebral sympathetic ganglia show an unusual perikaryal alteration characterized by the accumulation of membranous aggregates and minute mitochondria and loss of rough endoplasmic reticulum. These changes result in the loss of a third of neurons in the CG over the course of 8 months of diabetes. The extended survival of diabetic mice and robust pathologic findings provide a clinically relevant paradigm that will facilitate the analysis of novel therapeutic agents on the reversal of autonomic neuropathy.

Diabetes mellitus-related morphoquantitative changes in the celiac ganglion neurons of the dog

Diabetes mellitus is the most common endocrine disturbance of domestic carnivores and can cause autonomic neurological disorders, although these are still poorly understood in veterinary medicine. There is little information available on the quantitative adaptation mechanisms of the sympathetic ganglia during diabetes mellitus in domestic mammals. By combining morphometric methods and NADPH-diaphorase staining (as a possible marker for nitric oxide producing neurons), type I diabetes mellitus-related morphoquantitative changes were investigated in the celiac ganglion neurons in dogs. Twelve left celiac ganglia from adult female German shepherd dogs were examined: six ganglia were from non-diabetic and six from diabetic subjects. Consistent hypertrophy of the ganglia was noted in diabetic animals with increase of 55% in length, 53% in width, and 61.5% in thickness. The ordinary microstructure of the ganglia was modified leading to an uneven distribution of the ganglionic units and a more evident distribution of axon fascicles. In contrast to non-diabetic dogs, there was a lack of NADPH-diaphorase perikarial labelling in the celiac ganglion neurons of diabetic animals. The morphometric study showed that both the neuronal and nuclear sizes were significantly larger in diabetic dogs (1.3 and 1.39 times, respectively). The profile density and area fraction of NADPH-diaphorase-reactive celiac ganglion neurons were significantly larger (1.35 and 1.48 times, respectively) in non-diabetic dogs compared to NADPH-diaphorase-non-reactive celiac ganglion neurons in diabetic dogs. Although this study suggests that diabetic neuropathy is associated with neuronal hypertrophy, controversy remains over the possibility of ongoing neuronal loss and the functional interrelationship between them. It is unclear whether neuronal hypertrophy could be a compensation mechanism for a putative neuronal loss during the diabetes mellitus.

Age-related structural and neurochemical changes of the human superior cervical ganglion

The aim of this study was to investigate age-related morphological and neurochemical changes in the human superior cervical ganglion (SCG). Thirty-seven superior sympathetic human cervical ganglia of young, adult, and aged subjects were examined using morphometric analysis, biotin-streptavidin immunohistochemistry for detecting neurofilament, myelin protein, protein gene product 9.5, nerve growth factor receptor p75 in sympathetic neurons and nerve fibers. Morphometric parameters of neurons (area, long and short axis, shape factor of the neuron body, nucleus, cytoplasm, and lipofuscin) were investigated in every sixth serial section of the ganglion. Seven hundred neurons with clearly visible nuclei were measured in each studied group. The present study showed that human SCG of older subjects had larger areas of neuron body, cytoplasm and nucleus, a lower shape factor, an increased amount of lipofuscin, and a greater number of large-size neurons, as compared to SCG obtained from young subjects. Neuronal cytoskeletal alterations manifested themselves through a decreased number of neurofilament-positive neurons were detected in old human SCG. The amount of myelinated fibers decreased with age, although the amount of myelinated fibers in the young and the adult subjects varied from few to a moderate number. PGP 9.5 immunoreactivity varied in different age groups. A marked reduction of nerve growth factor receptor p75 in old human sympathetic neurons was detected. In conclusion, the findings of this study confirm age-related morphological changes in the human SCG. Structural neuronal changes may influence the deterioration of neuronal functional capacity, neuronal plasticity, and regenerative characteristics.

Long-term changes in sympathetic innervation in the corpus cavernosum of the STZ-diabetic rat

The noradrenaline (NA) concentration in the rat corpus cavernosum (CC) increased to approximately 350% of control values after about 8 weeks of hyperglycaemia induced by the intraperitoneal injection of streptozotocin (STZ) at 10 weeks of age. These changes were maintained for at least a further 32 weeks of hyperglycaemia and occurred without any significant change in the weight in the tissue. Smaller but significant increases in NA concentration occurred in the glans penis (GP) reaching 150-175% of the control levels during the period of prolonged hyperglycaemia. In contrast, there was no significant change in the NA concentration in the penile urethra. Measurements have also been made that relate to changes in the synthesis and reuptake of NA in the CC during the period during which high NA concentration is maintained. Immunohistochemical studies for the synthetic enzyme tyrosine hydroxylase in the CC indicate that the intensity of staining in the tissue had increased after 10, 20 and 32 weeks of hyperglycaemia, relative to the tissues from control animals. Dilated nerve fibres and engorged endings were present in the CC of the diabetic animals at these times. Reuptake of tritiated NA by the terminal axonal membranes in the CC was raised to 181% of control values after 12 weeks of hyperglycaemia (P<0.05), but later declined to values that are not significantly different from the control levels (after 26 and 64 weeks of hyperglycaemia). There are few studies of the effects of prolonged diabetes on functional aspects of sympathetic postganglionic neurones in the CC, and this paper suggests that the changes described represent remodelling of noradrenergic axonal terminals starting about after 8-10 weeks of hyperglycaemia; this delay in onset of the neuropathic changes is also a feature of type I diabetes in humans.

Macro- and Microstructure of the Superior Cervical Ganglion in Dogs, Cats and Horses during Maturation

The superior cervical ganglion (SCG) provides sympathetic input to the head and neck, its relation with mandible, submandibular glands, eyes (second and third order control) and pineal gland being demonstrated in laboratory animals. In addition, the SCG's role in some neuropathies can be clearly seen in Horner's syndrome. In spite of several studies published involving rats and mice, there is little morphological descriptive and comparative data of SCG from large mammals. Thus, we investigated the SCG's macro- and microstructural organization in medium (dogs and cats) and large animals (horses) during a very specific period of the post-natal development, namely maturation (from young to adults). The SCG of dogs, cats and horses were spindle shaped and located deeply into the bifurcation of the common carotid artery, close to the distal vagus ganglion and more related to the internal carotid artery in dogs and horses, and to the occipital artery in cats. As to macromorphometrical data, that is ganglion length, there was a 23.6% increase from young to adult dogs, a 1.8% increase from young to adult cats and finally a 34% increase from young to adult horses. Histologically, the SCG's microstructure was quite similar between young and adult animals and among the 3 species. The SCG was divided into distinct compartments (ganglion units) by capsular septa of connective tissue. Inside each ganglion unit the most prominent cellular elements were ganglion neurons, glial cells and small intensely fluorescent cells, comprising the ganglion's morphological triad. Given this morphological arrangement, that is a summation of all ganglion units, SCG from dogs, cats and horses are better characterized as a ganglion complex rather than following the classical ganglion concept. During maturation (from young to adults) there was a 32.7% increase in the SCG's connective capsule in dogs, a 25.8% increase in cats and a 33.2% increase in horses. There was an age-related increase in the neuronal profile size in the SCG from young to adult animals, that is a 1.6-fold, 1.9-fold and 1.6-fold increase in dogs, cats and horses, respectively. On the other hand, there was an age-related decrease in the nuclear profile size of SCG neurons from young to adult animals (0.9-fold, 0.7-fold and 0.8-fold in dogs, cats and horses, respectively). Ganglion connective capsule is composed of 2 or 3 layers of collagen fibres in juxtaposition and, as observed in light microscopy and independently of the animal's age, ganglion neurons were organised in ganglionic units containing the same morphological triad seen in light microscopy.

Sympathetic neuroaxonal dystrophy in the aged rat pineal gland

Dysfunction of circadian melatonin production by the pineal gland in aged humans and rats is thought to reflect the functional loss of its sympathetic innervation. Our ultrastructural neuropathologic studies of the sympathetic innervation of the pineal gland of aged (24 months old) Fischer-344 and Sprague-Dawley rats showed loss of nerve terminals as well as the development of neuroaxonal dystrophy (NAD), an ultrastructurally distinctive distal axonopathy, far in excess of that in young control rats. Immunolocalization of tyrosine hydroxylase confirmed the age-related loss of normal noradrenergic innervation and development of NAD. NAD was more frequent in aged female rats compared to males and was particularly severe in aged female Sprague-Dawley rats compared to Fischer-344 rats. Pineal NGF content was significantly increased or unchanged in female and male aged Fischer-344 rats, respectively, compared to young controls. The rat pineal is a sensitive experimental model for the quantitative ultrastructural examination of age-related neuropathological changes in nerve terminals of postganglionic noradrenergic sympathetic axons, changes which may reflect similar changes in the diffusely distributed sympathetic innervation of other targeted endorgans.

Postnatal-related changes in the size and total number of neurons in the caudal mesenteric ganglion of dogs: Total number of neurons can be predicted from body weight and ganglion volume

Aging is mostly characterized by a progressive decline of neuronal function that involves both the central and the peripheral nervous system. The aging process is accompanied by changes in either the number or the size of neurons. However, these data are controversial and not very well known in the sympathetic ganglia of large mammals. Hence, the present investigation aimed to study the dog's caudal mesenteric ganglion (CMG) in three different periods of postnatal development, searching for qualitative and quantitative alterations. The CMG is responsible for the large intestine, internal anal sphincter, and partially the urogenital system innervations. Nine dead male dogs from the Veterinary Hospital of the College of Veterinary Medicine at University of São Paulo were divided into three well-defined age groups (1-2 months old, 1-2 years old, and 5-10 years old). The stereological study was pursued using the physical disector method combined to the Cavalieri principle. The postnatal development was accompanied by an increase in the nonneuronal tissue amount and in ganglion volume. Additionally, the total number of neurons also increased during aging (from 70,140 to 1,204,516), although the neuronal density showed an opposite trend (from 29,911 to 11,500 mm(-3)). Due to the interrelation between either body weight or ganglion volume and aging in the dogs investigated in this study, it was possible to predict the total number of neurons in CMG using both body weight and ganglion volume in an attempt to verify whether or not size and total number of neurons are both allometrically and aging ruled, i.e., if either the animal's body weight and ganglion volume or aging influence these parameters. The prediction of the total number of neurons was very close to the initially estimated values.

Non-obese diabetic mice rapidly develop dramatic sympathetic neuritic dystrophy: a new experimental model of diabetic autonomic neuropathy

To address the pathogenesis of diabetic autonomic neuropathy, we have examined the sympathetic nervous system in non-obese diabetic (NOD) and streptozotocin (STZ)-induced diabetic mice, two models of type 1 diabetes, and the db/db mouse, a model of type 2 diabetes. After only 3 to 5 weeks of diabetes, NOD mice developed markedly swollen axons and dendrites ("neuritic dystrophy") in the prevertebral superior mesenteric and celiac ganglia (SMG-CG), similar to the pathology described in diabetic STZ- and BBW-rat and man. Comparable changes failed to develop in the superior cervical ganglia of the NOD mouse or in the SMG-CG of non-diabetic NOD siblings. STZ-induced diabetic mice develop identical changes, although at a much slower pace and to a lesser degree than NOD mice. NOD-SCID mice, which are genetically identical to NOD mice except for the absence of T and B cells, do not develop diabetes or neuropathology comparable to diabetic NOD mice. However, STZ-treated NOD-SCID mice develop severe neuritic dystrophy, evidence against an exclusively autoimmune pathogenesis for autonomic neuropathy in this model. Chronically diabetic type 2 db/db mice fail to develop neuritic dystrophy, suggesting that hyperglycemia alone may not be the critical and sufficient element. The NOD mouse appears to be a valuable model of diabetic sympathetic autonomic neuropathy with unambiguous, rapidly developing neuropathology which corresponds closely to the characteristic pathology of other rodent models and man.

Electron microscopic study of intrinsic cardiac ganglia in the adult human

The aim of the present study was to describe in detail the ultrastructure of intrinsic cardiac ganglionic cells in the healthy human as these cells appear to be directly involved in the development of tachycardia, atrioventricular block, ventricular fibrillation, and sudden cardiac death. Tissues examined in this study were obtained from hearts of 10 adult humans of either sex aged 22-80 years at autopsy performed no more than 8 h after death. The examined human intrinsic cardiac nerve cells were in most respects typical autonomic neurons surrounded by a sheath of satellite cells that was either uni- or multilayered. In addition to regular unmyelinated axons, prominent large axon terminals containing lamellated dense bodies, mitochondria and vesicles in the cytoplasm were observed in the ganglion neuropil. Synaptic profiles were more common in the ganglion neuropil than on neuronal somata. According to axon terminal contents, synaptic profiles were of three types. The most common Type 1 synaptic profiles contained a predominance of small clear, with a few larger dense-cored vesicles and mitochondria. Type 2 synaptic profiles, in addition to the same components as in Type 1, had glycogen-like particles. Type 3 vesicle-containing profiles clearly differed from both the previous ones as they were the largest in diameter and included plentifiul large clear pleomorphic or dense-cored vesicles together with small clear and larger dense-cored vesicles, mitochondria, dense and multivesicular bodies. Independently of age of the human, the most frequent neuronal abnormality was an abundant accumulation of inclusions inside of somata and dendrites that, in profile, appeared like circular membranous or fine granular bodies variable in electron density. In addition to inclusions, some neuronal somata and dendrites had strongly swollen mitochondria filled up with granular material in spite of their close association with normal looking ganglionic neurons. Structures resembling an axon growth cone in profile were revealed inside of cardiac ganglia derived from an 80 year old man. In conclusion, the present results provide baseline information on the normal ultrastructure of intracardiac ganglia in healthy humans which may be useful for assessing and interpreting the degree of damage of ganglionic cells both in autonomic and sensory neuropathies of the human heart.

Neuropathology and pathogenesis of diabetic autonomic neuropathy

Autonomic neuropathy is a significant complication of diabetes resulting in increased patient morbidity and mortality. A number of studies, which have shown correspondence between neuropathologic findings in experimental animals and human subjects, have demonstrated that axonal and dendritic pathology in sympathetic ganglia in the absence of significant neuron loss represents a neuropathologic hallmark of diabetic autonomic neuropathy. A recurring theme in sympathetic ganglia, as well as in the pot-ganglionic autonomic innervation of various end organs, is the involvement of distal portions of axons and nerve terminals by degenerative or dystrophic changes. In both animals and humans, there is a surprising selectivity of the diabetic process for subpopulations of autonomic ganglia, nerve terminals within sympathetic ganglia and end organs, from end organ to end organ, and between vascular and other targets within individual end organs. Although the involvement or autonomic axons in somatic nerves may reflect an ischemic pathogenesis, the selectivity of the diabetic process confounds simple global explanations of diabetic autonomic neuropathy as the result of diminished blood flow with resultant tissue hypoxia. A single unifying pathogenetic hypothesis has not yet emerged from clinical and experimental animal studies, and it is likely that diabetic autonomic neuropathy will be shown to have multiple causative mechanisms, which will interact to result in the variety of presentations of autonomic injury in diabetes. Some of these mechanisms will be shared with aging changes in the autonomic nervous system. The role of various neurotrophic substances and the polyol pathway in the pathogenesis and treatment of diabetic neuropathy likely represents a two-edged sword with both salutary and exacerbating effects. The basic neurobiologic process underlying the diabetes-induced development of neuroaxonal dystrophy, synaptic dysplasia, defective axonal regeneration, and alterations in neurotrophic substance may be mechanistically related.

Early, selective, and marked loss of sympathetic nerves from the islets of BioBreeder diabetic rats

To discover whether islet sympathetic nerves are damaged during the autoimmune destruction of islet B-cells, we immunostained sections of pancreas from BioBreeder (BB) diabetic rats, using antibodies against vesicular monoamine transporter 2 (VMAT2), a marker of sympathetic nerve terminals. We found a marked decrease in the VMAT2-positive fiber area in the islets of BB rats that had been diabetic for only 1-2 weeks compared with their nondiabetic controls. In contrast, there was no significant decrease in the VMAT2-positive fiber area in the exocrine pancreas in these early diabetic BB rats. Furthermore, streptozotocin-diabetic rats showed no decrease in VMAT2-positive fiber area in their islets compared with controls. The classical diabetic autonomic neuropathy (DAN) that eventually occurs in the heart was not present in BB diabetic rats at this early stage as evidenced by normal cardiac VMAT2 immunostaining and normal cardiac norepinephrine content. Also, in contrast to DAN, this islet neuropathy did not worsen with duration of diabetes. These data provide evidence of a heretofore unrecognized early sympathetic islet neuropathy (eSIN). Because eSIN occurs selectively in the islet, is rapid in onset, and is associated with autoimmune but not chemically induced diabetes, it is distinct from DAN in location, time course, and mechanism.

Age-related sympathetic ganglionic neuropathology: human pathology and animal models

Systematic studies of the autonomic nervous system of human subjects and development of well-defined animal models have begun to substantially improve our understanding of the pathogenesis of autonomic dysfunction in aging and may eventually provide strategies for intervention. Neuropathological studies of the sympathetic ganglia of aged human subjects and rodent models have demonstrated that neuroaxonal dystrophy involving intraganglionic terminal axons and synapses is a robust, unequivocal and consistent neuropathological finding in the aged sympathetic nervous system of man and animals. Quantitative studies have demonstrated that markedly swollen argyrophilic dystrophic axon terminals develop in the prevertebral superior mesenteric (SMG) and coeliac, but to a much lesser degree in the superior cervical ganglia (SCG) as a function of age, sex (males more than females) and diabetes. Dystrophic axons were immunoreactive for neuropeptide Y, tyrosine hydroxylase, dopamine-beta-hydroxylase, trkA and p75NTR, an immunophenotype consistent with their origin from postganglionic sympathetic neurons, and contained large numbers of highly phosphorylated neurofilaments or tubulovesicular elements. The sympathetic ganglia of aged rodents also showed the hallmark changes of neuroaxonal dystrophy as a function of age and location (many more in the SMG than in the SCG). Plasticity-related synaptic remodeling could represent a highly vulnerable target of the aging process. The fidelity of animal models to the neuropathology of aged humans suggests that similar pathogenetic mechanisms may be involved in both and that therapeutic advances in animal studies may have human application.

Effect of NGF and neurotrophin-3 treatment on experimental diabetic autonomic neuropathy

Peripheral neuropathy is a significant complication of diabetes resulting in increased patient morbidity and mortality. Deficiencies of neurotrophic substances (e.g. NGE NT-3, and IGF-I) have been proposed as pathogenetic mechanisms in the development of distal symmetrical sensory diabetic polyneuropathy, and salutary effects of exogenous NGF administration have been reported in animal models. In comparison, relatively little is known concerning the effect of NGF on experimental diabetic sympathetic autonomic neuropathy. We have developed an experimental animal model of diabetic autonomic neuropathy characterized by the regular occurrence of pathologically distinctive dystrophic axons in prevertebral sympathetic ganglia and ileal mesenteric nerves of rats with chronic streptozotocin (STZ)-induced diabetes. Treatment of STZ-diabetic rats for 2-3 months with pharmacologic doses of NGF or NT-3, neurotrophic substances with known effects on the adult sympathetic nervous system, did not normalize established neuroaxonal dystrophy (NAD) in diabetic rats in the prevertebral superior mesenteric ganglia (SMG) and ileal mesenteric nerves as had pancreatic islet transplantation and IGF-I in earlier experiments. NGF treatment of control animals actually increased the frequency of NAD in the SMG. New data suggests that, in adult sympathetic ganglia. NGF may contribute to the pathogenesis of NAD rather than its amelioration, perhaps as the result of inducing intraganglionic axonal sprouts in which dystrophic changes are superimposed. NT-3 administration did not alter the frequency of NAD in diabetic animals, although it resulted in a significant decrease in NAD in control SMG. Although deficiencies of neurotrophic substances may represent the underlying pathogenesis of a variety of experimental neuropathies, delivery of excessive levels of selected substances may produce untoward effects.

Effect of streptozotocin-induced diabetes on NGF, P75(NTR) and TrkA content of prevertebral and paravertebral rat sympathetic ganglia

Diabetic autonomic neuropathy results in significant morbidity and mortality. Both diabetic humans and experimental animals show neuroaxonal dystrophy of autonomic nerve terminals, particularly in the prevertebral superior mesenteric ganglia (SMG) and celiac ganglia (CG) which innervate the hyperplastic/hypertrophic diabetic small intestine. Previously, investigators suggested that disturbances in ganglionic nerve growth factor (NGF) content or transport might play a pathogenetic role in diabetic autonomic pathology. To test this hypothesis, we measured NGF content and NGF receptor expression, p75(NTR) (low affinity neurotrophin receptor) and trkA (high affinity NGF receptor), in control and diabetic rat SMG, CG and superior cervical ganglia (SCG). Surprisingly, rather than a decrease, we observed an approximate doubling of NGF content in the diabetic SMG and CG, a result which reflects increased NGF content in the hyperplastic diabetic alimentary tract. No change in NGF content was detected in the diabetic SCG which is relatively spared in experimental diabetic autonomic neuropathy. NGF receptor expression was not consistently altered in any of the autonomic ganglia. These observations suggest that increased NGF content in sympathetic ganglia innervating the diabetic alimentary tract coupled with intact receptor expression may produce aberrant axonal sprouting and neuroaxonal dystrophy.

Insulin-like growth factor I reverses experimental diabetic autonomic neuropathy

Recent studies have suggested a role for neurotrophic substances in the pathogenesis and treatment of diabetic neuropathy. In this study, the effect of insulin-like growth factor I (IGF-I) on diabetic sympathetic autonomic neuropathy was examined in an experimental streptozotocin-induced diabetic rat model. Two months of IGF-I treatment of chronically diabetic rats with established neuroaxonal dystrophy (the neuropathological hallmark of the disease) involving the superior mesenteric ganglion and ileal mesenteric nerves resulted in nearly complete normalization of the frequency of neuroaxonal dystrophy in both sites without altering the severity of diabetes. Treatment with low-dose insulin (to control for the transient glucose-lowering effects of IGF-I) failed to affect the frequency of ganglionic or mesenteric nerve neuroaxonal dystrophy or the severity of diabetes. The striking improvement in the severity of diabetic autonomic neuropathy shown with IGF-I treatment in these studies and the fidelity of the rat model to findings in diabetic human sympathetic ganglia provide promise for the development of new clinical therapeutic strategies.

Axonal cytoskeletal pathology in aged and diabetic human sympathetic autonomic ganglia

Prevertebral sympathetic ganglia develop markedly enlarged argyrophilic neurites as a function of age, gender and diabetes. Immunolocalization studies demonstrate their preferential labeling with antisera to highly phosphorylated 200 kDa neurofilament (NF-H) epitopes, NPY, peripherin and synapsin I, but not to hypophosphorylated NF-M and NF-H or MAP-2. The immunophenotype of dystrophic neurites in conjunction with the results of histochemical and ultrastructural studies are consistent with the terminal axonal and/or synaptic origin of neuritic dystrophy in the sympathetic ganglia of aged and diabetic human subjects.