Implications for Neuromodulation Therapy to Control Inflammation and Related Organ Dysfunction in COVID-19

COVID-19 is a syndrome that includes more than just isolated respiratory disease, as severe acute respiratory syndrome-coronavirus 2 (SARS-CoV2) also interacts with the cardiovascular, nervous, renal, and immune system at multiple levels, increasing morbidity in patients with underlying cardiometabolic conditions and inducing myocardial injury or dysfunction. Emerging evidence suggests that patients with the highest rate of morbidity and mortality following SARS-CoV2 infection have also developed a hyperinflammatory syndrome (also termed cytokine release syndrome). We lay out the potential contribution of a dysfunction in autonomic tone to the cytokine release syndrome and related multiorgan damage in COVID-19. We hypothesize that a cholinergic anti-inflammatory pathway could be targeted as a therapeutic avenue. Graphical Abstract .

Noninvasive ultrasound stimulation of the spleen to treat inflammatory arthritis

Targeted noninvasive control of the nervous system and end-organs may enable safer and more effective treatment of multiple diseases compared to invasive devices or systemic medications. One target is the cholinergic anti-inflammatory pathway that consists of the vagus nerve to spleen circuit, which has been stimulated with implantable devices to improve autoimmune conditions such as rheumatoid arthritis. Here we report that daily noninvasive ultrasound (US) stimulation targeting the spleen significantly reduces disease severity in a mouse model of inflammatory arthritis. Improvements are observed only with specific parameters, in which US can provide both protective and therapeutic effects. Single cell RNA sequencing of splenocytes and experiments in genetically-immunodeficient mice reveal the importance of both T and B cell populations in the anti-inflammatory pathway. These findings demonstrate the potential for US stimulation of the spleen to treat inflammatory diseases.

Physiology and immunology of the cholinergic antiinflammatory pathway

Cytokine production by the immune system contributes importantly to both health and disease. The nervous system, via an inflammatory reflex of the vagus nerve, can inhibit cytokine release and thereby prevent tissue injury and death. The efferent neural signaling pathway is termed the cholinergic antiinflammatory pathway. Cholinergic agonists inhibit cytokine synthesis and protect against cytokine-mediated diseases. Stimulation of the vagus nerve prevents the damaging effects of cytokine release in experimental sepsis, endotoxemia, ischemia/reperfusion injury, hemorrhagic shock, arthritis, and other inflammatory syndromes. Herein is a review of this physiological, functional anatomical mechanism for neurological regulation of cytokine-dependent disease that begins to define an immunological homunculus.

The cholinergic anti-inflammatory pathway

The regulation of the innate immune response is critical for controlling inflammation and for the prevention and treatment of diseases. We recently demonstrated that the efferent vagus nerve inhibits pro-inflammatory cytokine release and protects against systemic inflammation, and termed this vagal function "the cholinergic anti-inflammatory pathway." The discovery that the innate immune response is regulated partially through this neural pathway provides a new understanding of the mechanisms that control inflammation. In this review, we outline the cholinergic anti-inflammatory pathway and summarize the current insights into the mechanisms of cholinergic modulation of inflammation. We also discuss possible clinical implications of vagus nerve stimulation and cholinergic modalities in the treatment of inflammatory diseases.

Acute Vagotomy Activates the Cholinergic Anti-Inflammatory Pathway

Within minutes of acute myocardial infarction (MI), proinflammatory cytokines increase in the brain, heart, and plasma. We hypothesized that cardiac afferent nerves stimulated by myocardial injury signal the brain to increase central cytokines. Urethane-anesthetized male Sprague-Dawley rats underwent ligation of the left anterior descending coronary artery (LAD) or sham LAD ligation after bilateral cervical vagotomy, sham vagotomy, or application of a 10% phenol solution to the epicardial surface of the myocardium at risk. MI caused a significant increase in tumor necrosis factor (TNF)-α and interleukin (IL)-1β in the plasma and heart, which was blunted by vagotomy. MI also caused a significant increase in hypothalamic TNF-α and IL-1β, which was not affected by vagotomy. In contrast, epicardial phenol blocked MI-induced increases in hypothalamic TNF-α and IL-1β without affecting increases in the plasma and heart. These findings demonstrate that the appearance of proinflammatory cytokines in the brain after MI is independent of blood-borne cytokines and suggest that cardiac sympathetic afferent nerves activated by myocardial ischemia signal the brain to increase cytokine production. In addition, an intact vagus nerve is required for the full expression of proinflammatory cytokines in the injured myocardium and in the circulation. We conclude that the sympathetic and parasympathetic innervation of the heart both contribute to the acute proinflammatory response to MI.

Nonsynaptic noradrenaline release in neuro-immune responses

Evidence has recently been obtained that the branches of the autonomic nervous system, mainly, the sympathetic [25], regulate cytokine production. Not only the primary (thymus, bone marrow) and secondary (spleen, tonsils, and lymph nodes) lymphoid organs, but also many other tissues are involved in immune responses and are heavily influenced by noradrenaline (NA) derived from varicose axon terminals of the sympathetic nervous system [25, 100]. Besides NA released from nonsynaptic varicosities of noradrenergic terminals [92], circulating catecholamines (adrenaline, dopamine, NA) are also able to influence immune responses, the production of pro- and anti-inflammatory cytokines by different immune cells. The sympathetic nervous system (catecholamines) and the hypothalamic-pituitary-adrenal (HPA) axis (cortisol) are the major integrative and regulatory components of different immune responses. In our laboratory convincing evidence has been obtained that NA released non-synaptically [90, 92] from sympathetic axon terminals and enhanced in concentration in the close proximity of immune cells is able to inhibit production of proinflammatory (TNF-alpha, IFN-gamma, IL-12, IL-1) and increase antiinflammatory cytokines (IL-10) in response to LPS [25, 91], indicating a fine-tuning control of the production of TNF-alpha and other cytokines by sympathetic innervation under stressful conditions. This effects are mediated via beta2-adrenoceptors expressed on immune cells and coupled to cAMP levels.

Immunological mechanisms and the spectrum of psychiatric syndromes in Alzheimer's disease

Pathological, genetic and epidemiological studies support the opinion that inflammatory mechanisms are involved in the pathogenesis of Alzheimer's disease (AD). Recent pathological and neuroradiological (PET) data show that activation of microglia is an early pathogenic event that precedes the process of severe neuropil destruction in AD brains. In this paper we review the evidence that inflammatory mediators can play a pathogenic role in some behavioural disorders frequently encountered during the clinical course in AD patients. Motivational disturbances are the most striking of the depressive symptoms in AD and can be present in a preclinical stage of the disease. Experimental animal studies and clinical trials in humans have shown that cytokines can induce similar symptoms which were described as 'sickness behaviour' or 'depressive-like' state. Delirious states are frequently observed in more advanced stages of dementia. Delirium is generally considered the result of an imbalance in neurotransmitter systems with severe deficits of the cholinergic systems. Animal studies show that pro-inflammatory cytokines, such as interleukin-1, induce a reduced activity of the cholinergic system. In AD, the release of cytokines would exacerbate any already existing disturbances in the cholinergic neurotransmission. This could explain the susceptibility of demented patients to delirium provoked by a wide variety of trivial incidents that are accompanied by an acute phase response. The data reviewed in this paper suggest that it could be worthwhile employing a neuroimmunological approach to study at molecular level the pathogenesis of a broad spectrum of behavioural disturbances common in the clinical course of AD patients.

Neural change in Trichinella-infected mice is MHC II independent and involves M-CSF-derived macrophages

Intestinal inflammation due to nematode infection impairs enteric cholinergic nerve function and induces hypercontractility of intestinal muscle. Macrophages have been implicated in the neural changes, but the subpopulation and mechanism involved are unknown. We examined whether macrophages alter nerves by virtue of their ability to activate lymphocytes via major histocompatibility complex (MHC) II-restricted antigen presentation. We also attempted to evaluate the role of macrophage subsets using op/op mice deficient in macrophage colony-stimulating factor (M-CSF). ACh release from the myenteric plexus was measured in MHC II- and M-CSF-deficient (op/op) mice infected with Trichinella spiralis. F4/80-positive macrophages and interleukin-1 beta were constitutively present in op/op and op/? mice but increased only in op/? mice postinfection. After infection, a marked suppression of ACh release occurred only in infected MHC II-deficient and op/? mice. Muscle hypercontractility remained evident in infected op/? mice. Treatment with M-CSF restored macrophage number, and this was accompanied by suppression of cholinergic nerve function during infection. Thus M-CSF plays a critical role in this model by recruiting a subset of macrophages that selectively suppresses enteric neural function.

Neuropeptide Y (NPY) expression is increased in explanted guinea pig parasympathetic cardiac ganglia neurons

While expression of neuropeptides by sympathetic neurons is altered by decentralization and axotomy, it is not known whether similar experimental paradigms also modulate the chemical phenotype of parasympathetic cardiac ganglia neurons. The present study tested whether guinea pig parasympathetic neuron neuropeptide Y (NPY) expression was altered when cardiac ganglia preparations were maintained as organ explants in the presence or absence of colchicine. Two experimental approaches were used to examine NPY expression. First, immunocytochemical techniques were used to quantitate numbers of neurons within the cardiac ganglia exhibiting NPY-immunoreactivity; second, reverse transcription PCR was used to examine proNPY mRNA expression. In control cardiac ganglia preparations, approximately 4% of ganglia neurons exhibited NPY-immunoreactivity. The percentage of NPY-immunopositive neurons in 30- and 72-h explanted cardiac ganglia preparations, maintained in the absence of colchicine, increased to 11 and 16%, respectively. Colchicine treatment of explanted preparations further increased the percentage of NPY-positive ganglia cells 24% (30 h) and 32% (72 h). All NPY-immunoreactive neurons from control ganglia and explanted ganglia were choline acetyltransferase(ChAT)-immunoreactive, indicating retention of the cholinergic phenotype. ProNPY mRNA also was increased following ganglia explantation, consistent with the increase in the numbers of NPY-immunoreactive neurons. NPY transcripts were further increased after 30 h, but not after 72 h in colchicine-treated, explanted cardiac ganglia preparations. These results demonstrate that NPY expression is altered in explanted cardiac ganglia preparations, providing evidence that the chemical phenotype of parasympathetic cardiac neurons can be modulated.

Properties of activated microglia and pharmacologic interference by propentofylline

Ameboid microglia are activated macrophages in the developing brain. With age, these cells undergo gradual transformation into the adult form, known as ramified or resting microglia. In response to neuronal insults, microglia change their morphology and immunophenotype and proliferate to become full-blown brain macrophages. Microglia release a battery of neurotoxic substances. Responses to neuronal damage occur at various intervals after the insult, suggesting that microglia may be an attractive target for pharmacologic intervention. The cerebrospinal fluid (CSF) of Alzheimer disease (AD) patients contains antibodies that recognize activated microglia in the developing rat and in the ischemic gerbil brain. These results suggest that AD shares common mechanisms related to the activation of microglia with both these experimental models. In vitro, the xanthine derivative propentofylline (PPF) depresses the production of reactive oxygen intermediates produced by macrophages. To appreciate in vivo interactions of PPF, two models were employed: developing rats and adult gerbils exposed to ischemia. Newborn rats were administered PPF (10 mg/kg) for 7 days. Gerbils were exposed to 5 min of transient forebrain ischemia and received PPF (10 mg/kg) 24 h later until the day before sacrifice. Animals were sacrificed at 7 or 14 days after reperfusion. Brains were processed for immunocytochemistry. Reactive microglia were visualized with monoclonal antibodies OX18 and OX42 or AD-CSF microglia antibodies. In the case of ischemia, an antibody against the amyloid precursor protein (APP) (residues 676-695) was included. Newborn rats receiving PPF for 7 days displayed a dramatic reduction in the number of activated microglia compared with untreated littermates. Ischemic control in gerbils showed complete nerve death, accumulations of APP, and enhanced microglial reactivity. In gerbils receiving PPF, APP accumulation was absent or very slight, and activated microglia were downregulated. The ability of PPF to interfere with activated microglia suggests that this agent may be useful for slowing progressive nerve cell death associated with AD, which is considered to be largely influenced by pathologic glial reactions.

Antineurofilament antibodies in postpolio syndrome

We determined the levels of antineurofilament antibodies in 29 patients with postpolio syndrome (PPS), 26 stable postpolio (PP) patients, 22 patients with ALS, and 20 normal controls (NCs). Patients with PPS had higher antibody levels to cholinergic neurofilaments than did all other groups. PP patients and those with ALS had antibody levels similar to those of NCs. The antibody binding level showed no relation to the age of the patients, duration of disease, or motor score.

Anti-brain spectrin immunoreactivity in Alzheimer's disease: degradation of spectrin in an animal model of cholinergic degeneration

In a previous work, we described the existence of anti-brain spectrin auto antibodies in Alzheimer's disease (AD) patients (J. Neuroimmunol. 68 (1996) 39-44). In this report, we further support our previous observations, showing that sera from 9 out of 18 AD patients, but none of 14 control subjects, immunoreacted with spectrin synthesized by PC12 cells. In addition, degradation of brain spectrin was found to be greatly enhanced in the frontal cortex of rats subjected to an animal model of cholinergic degeneration. Our data suggest that spectrin degradation and generation of anti-spectrin auto antibodies may be related to the cholinergic degeneration encountered in AD.

Experimental immune-mediated damage of septal cholinergic neurons

Degeneration of cholinergic neurons in the medial septum and the diagonal band of Broca is a frequent neuropathological feature of Alzheimer's disease. To determine whether an immune process can injure these basal forebrain cholinergic neurons, we serially immunized guinea pigs with septal cholinergic hybrid cells (SN-56). Following immunization, a relatively selective damage of septal cholinergic neurons, reduction in septal choline acetyltransferase (ChAT) activity and decrease in acetylcholine release in hippocampus were detected. Serum IgG from guinea pigs immunized with SN-56 cells and stereotactically injected into the medial septal region of rats produced a loss of ChAT activity in the medial septum, frontal cortex and hippocampus, together with impairment of learning and long term spatial memory. These data suggest that relatively selective damage to septal cholinergic neurons can be caused by an immune-mediated process in experimental animals.

Synaptic contacts between cholinergic afferents and suprachiasmatic neurones of the rat

The relationship between cholinergic fibres in the suprachiasmatic nucleus (SCN) and neurones of the cell group was investigated at the light and electron microscopic level using choline acetyltransferase (ChAT) immunocytochemistry for the identification of cholinergic elements. Axosomatic and axodendritic synaptic contacts were found between ChAT-immunopositive axon terminals and SCN neurones. These synapses were asymmetrical. The observations provide the final morphological basis for the view already suggested by neuroanatomical, electrophysiological and pharmacological findings that the cholinergic elements in the SCN may act directly on the neurones of the nucleus.

Distribution of choline acetyltransferase immunoreactivity in the pigeon brain

We have investigated the distribution of cholinergic perikarya and fibers in the brain of the pigeon (Columba livia). With this aim, pigeon brain sections were processed immunohistochemically by using an antiserum specific for chicken choline acetyltransferase. Our results show cholinergic neurons in the pigeon basal telencephalon, the hypothalamus, the habenula, the pretectum, the midbrain tectum, the dorsal isthmus,the isthmic tegmentum, and the cranial nerve motor nuclei. Cholinergic fibers were prominent in the dorsal telencephalon, the striatum, the thalamus, the tectum, and the interpeduncular nucleus. Comparison of our results with previous studies in birds suggests some major cholinergic pathways in the avian brain and clarifies the possible origin of the cholinergic innervation of some parts of the avian brain. In addition, comparison of our results in birds with those in other vertebrate species shows that the organization of the cholinergic systems in many regions of the avian brain (such as the basal forebrain, the epithalamus, the isthmus, and the hindbrain) is much like that in reptiles and mammals. In contrast, however, birds appear largely to lack intrinsic cholinergic neurons in the dorsal ("neocortex-like") parts of the telencephalon.

The innervation of the bovine ductus deferens: comparison of a modified acetylcholinesterase-reaction with immunoreactivities of cholinacetyltransferase and panneuronal markers

The innervation pattern of the bovine deferent duct was studied by acetylcholinesterase (AChE)-histochemistry and by immunohistochemical methods. Using antibodies against protein gene product-9.5 (PGP-9.5) and neuron specific enolase (NSE) the complete innervation pattern can be visualized. Thick nerve bundles in the periductal connective tissue supply the two-layered muscular coat. The inner, mainly circularly arranged muscle bundles are innervated by a particularly dense plexus, whereas the nervous network of the more longitudinally running outer musculature is somewhat looser. Additionally, nerve fibres were observed in the subepithelial space in connection with blood vessels and in close proximity to the basal lamina. An innervation pattern analogous to that of the two panneuronal markers was displayed in the immunoreaction against dopamine-beta-hydroxylase (DBH), indicating that the innervation of the bovine deferent duct is predominantly adrenergic. However, the positive reaction with a monoclonal antibody against cholinacetyltransferase (ChAT) specifically demonstrated for the first time the presence of a cholinergic nerve plexus, restricted to the inner muscular layer and the subepithelial space. A modified, direct-colouring AChE-method is presented, which uses copper chloride as source of cupric ions, acetylthiocholine chloride as substrate and 2-morpholinoethanesulphonic acid (MES) as buffer. After short incubation (1-2 h) our modified method allows the specific visualization of cholinergic nerves, comparable to the results of ChAT-immunoreactivity; following a long incubation time (24 h), it reliably illustrates the autonomous innervation pattern as completely as immunohistochemical panneuronal markers.

A trisialoganglioside containing a sialyl alpha 2-6 N-acetylgalactosamine residue is a cholinergic-specific antigen, Chol-1 alpha

Cholinergic-specific antigens termed the Chol-1 family have been suggested to be of a ganglioside nature by Richardson et al. (J. Neurochem. 38, 1605-1614, 1982). Two molecular species of polysialogangliosides among bovine brain gangliosides were found to react with anti-Chol-1 alpha antiserum. One of them, Chol-1 alpha-a, was isolated and characterized as a trisialoganglioside containing the gangliotetraose backbone in which 1 mol of sialic acid was attached to each of the reducing end galactose, N-acetylgalactosamine and internal galactose residues, respectively. The chemical structure of Chol-1 alpha-a was determined for the first time, being as follows: IV3NeuAc III6NeuAc II3NeuAc-GgOse4 Cer.

Induction of cognitive deficits by immunization with cholinergic cell bodies: the influence of age and integrity of the blood-brain barrier

We have recently shown that prolonged immunization of young rats for one year with cholinergic cell bodies (perikarya, PK) purified from Torpedo electric lobe results in the accumulation of IgG in specific brain areas such as the hippocampus and induces behavioral deficits in spatial orientation and short term memory /1, 7/. We presently studied the rate of development of the cognitive deficit in older (12 months old) Sprague Dawley rats which were immunized for periods of up to one year with either Torpedo cholinergic PK or adjuvant (controls). T-maze alternation and Morris swim maze tests revealed a small deficit in the performance of the PK immunized rats after 6 months whereas significant deficits were observed after 12 months of immunization. These results suggest that the duration of immunization is a more significant factor than the age of the animals in the development of the behavioral deficit. In order to examine whether permeability of the blood-brain barrier to IgG influences the rate of development of the cognitive deficit, we disrupted the blood-brain barrier of PK immunized rats by hypercapnia. This treatment repeated weekly for 2 months was found not to accelerate the rate of appearance of deficits in performance of the rats in the T-maze alternation and Morris swim test. These results suggest that penetration of IgG via the blood-brain barrier does not determine the rate of appearance of the cognitive deficits.

Calretinin immunoreactivity in cholinergic motor neurones, interneurones and vasomotor neurones in the guinea-pig small intestine

Immunoreactivity for calretinin, a calcium-binding protein, was studied in neurones in the guinea-pig small intestine. 26 +/- 1% of myenteric neurones and 12 +/- 3% of submucous neurones were immunoreactive for calretinin. All calretinin-immunoreactive neurones were also immunoreactive for choline acetyltransferase and hence are likely to be cholinergic. In the myenteric plexus, two subtypes of Dogiel type-I calretinin-immunoreactive neurones could be distinguished from their projections and neurochemical coding. Some calretinin-immunoreactive myenteric neurones had short projections to the tertiary plexus, and hence are likely to be cholinergic motor neurones to the longitudinal muscle. Some of these cells were also immunoreactive for substance P. The remaining myenteric neurones, immunoreactive for calretinin, enkephalin, neurofilament protein triplet and substance P, are likely to be orad-projecting, cholinergic interneurones. Calretinin immunoreactivity was also found in cholinergic neurones in the submucosa, which project to the submucosal vasculature and mucosal glands, and which are likely to mediate vasodilation. Thus, calretinin immunoreactivity in the guinea-pig small intestine is confined to three functional classes of cholinergic neurones. It is possible, for the first time, to distinguish these classes of cells from other enteric neurones.

Investigations on auto-antibodies in Alzheimer's and Parkinson's diseases, using defined neuronal cultures

In immunocytochemical studies, the CSF from Parkinson disease (PD) patients and from Alzheimer disease (AD) patients were investigated for the presence of neuron specific antibodies using dopaminergic and cholinergic neuronal cultures from embryonic rat brain, respectively. Dopamine containing cell bodies were labelled by Parkinsonian CSF-IgG, while cholinergic neurons, identified with a-NGF-receptor antibodies, were recognized by CSF from AD-patients. The CSF from PD-patients was investigated after autologous adrenal transplantation. CSF was removed 7 d, 5 months and 1 year after operation. When added to 18 d neuronal cultures for 3 d, the 7 d CSF caused neuronal cell and a glial reaction. The 4 months CSF caused cell death, but markedly less than the 7 d CSF. One year after transplantation the CSF had no toxic effects; these cultures were similar to control cultures. It is concluded that CSF from PD patients may contain aggressive IgG-species specific for DA neurons, and that the amount of such antibodies decrease after adrenal transplant operations. It is suggested that neurodegenerative diseases may become aggravated by autoimmune reactions.

Antibodies in serum of patients with Alzheimer's disease cause immunolysis of cholinergic nerve terminals from the rat cerebral cortex

A blind study showing that serum from patients with Alzheimer's disease causes immunolysis of mammalian brain synaptosomes is reported. Control, aged-matched, sera were largely without effect. The immunolysis was directed mainly against cholinergic synaptosomes. The data support the hypothesis that autoimmune mechanisms may operate in the pathogenesis of Alzheimer's disease.

The immunolysis, isolation, and properties of subpopulations of mammalian brain synaptosomes

Five subpopulations of mammalian brain synaptosomes can be selectively damaged by complement-mediated immunolysis employing antibodies to specific surface markers for each subpopulation. This allows the size of these subpopulations to be estimated. Employing antibodies alone, it has proved possible to isolate three of these subpopulations in very pure preparations which are metabolically viable. The immunoaffinity technique involved (immunomagnetophoresis) uses magnetic microspheres and produces mg (protein) quantities of synaptosomes.

A monoclonal antibody to a parasympathetic neurotrophic factor causes immunoparasympathectomy in mice

A monoclonal antibody capable of blocking the biological activity of the ciliary neurotrophic factor purified from bovine cardiac muscle has been produced. This antibody, when administered perinatally to mice, causes a failure of the normal development of the parasympathetic innervation of the iris as determined by assay for the activity of the cholinergic marker enzyme choline acetyltransferase. The same treatment has no effect on the adrenergic neuronal marker, tyrosine hydroxylase. This immunoparasympathectomy suggests that the ciliary neurotrophic factor has an essential role in regulating the development of the mammalian parasympathetic nervous system.

Evidence for the presence of antibodies to cholinergic neurons in the serum of patients with Alzheimer's disease

A blind study showing that serum from patients with Alzheimer's disease causes immunolysis of mammalian brain synaptosomes is reported. Control, aged-matched, sera were largely without effect. The immunolysis was directed mainly against cholinergic synaptosomes. The data presented support the hypothesis that autoimmune mechanisms may operate in the pathogenesis of Alzheimer's disease.

Cholinergic innervation of the main and the accessory olfactory bulbs of the rat as revealed by a monoclonal antibody against choline acetyltransferase

The main and accessory olfactory bulbs (MOB and AOB) of the rat were immunohistochemically stained with a monoclonal antibody against choline acetyltransferase (ChAT) in order to know the difference in the distribution patterns of cholinergic fibers between these two structures. A few ChAT-immunoreactive cell bodies were found in the superficial and middle parts of the external plexiform layer (EPL) of the MOB, in the granule cell layer (GCL) of the MOB, and in the GCL of the AOB. The frequency in appearance of these cells was 0.9 cells/section in the MOB and 0.3 cells/section in the AOB. While the glomerular layer (GL) and the superficial part of the EPL were most densely innervated in the MOB, the internal plexiform layer received the richest innervation in the AOB. There were no immunoreactive structures in the olfactory nerve layer of the MOB and in the vomeronasal nerve layer and glomerular layer of the AOB. In addition to a relatively homogenous distribution of cholinergic fibers in the MOB and AOB, there were several foci of very dense network of immunoreactive fibers at the posterior level of the OB. These foci formed a part of the modified glomerular complex that was recently identified using 2-deoxyglucose method and was presumed to be related to suckling behaviour in the neonatal rat.

Antibodies to cholinergic neurons in Alzheimer's disease

Alzheimer's disease (AD) is associated with degenerative changes in nuclei of the basal forebrain which provide most of the cholinergic input to the cortex and hippocampus and with a reduction in presynaptic cholinergic parameters in these areas. Although the etiology and pathogenesis of AD are not known, several reports indicate the involvement of immunological mechanisms. In the present work we examined the existence of antibodies in sera of AD patients that bind specifically to cholinergic neurons. As antigens we employed the purely cholinergic electromotor neurons of the electric fish Torpedo which are chemically homogeneous and cross-react antigenically with human and other mammalian cholinergic neurons. Our findings show that immunoglobulins from sera of AD patients bind to a specific antigen (molecular mass 200 kilodaltons) in the cell bodies and axons of Torpedo electromotor neurons and that the levels of such antibodies are significantly higher in AD patients than in controls. The possible role of these antibodies in the cholinergic dysfunction in AD and their diagnostic potential are discussed.

Immunocytochemical evaluation of a cholinergic-specific ganglioside antigen (Chol-1) in the central nervous system of the rat

Previous work from this laboratory has identified gangliosidic surface markers specific for cholinergic neurons. Antibodies to these markers, collectively designated Chol-1, induce complement-mediated lysis of the cholinergic subpopulation of synaptosomes and provide the basis for a new immunocytochemical method for staining cholinergic neurons in rat, guinea pig and human material. The specification and localization of immunocytochemical staining for Chol-1 was investigated in selected areas of the rat central nervous system. The antigen was typically expressed on all neurons previously identified as being cholinergic using monoclonal antibodies to choline acetyltransferase. At spinal levels Chol-1 was present on large and smaller cell bodies in the ventral horn motoneuron area. The preganglionic sympathetic neurons in the thoracic intermediolateral nucleus were also Chol-1-positive. Nerve terminal-like staining was observed in association with stained large Chol-1 positive and smaller unstained Chol-1 negative neurons, and in lamina I and III of the dorsal horn. In the mesencephalon, motoneurons of the oculomotor and trochlear nucleus, as well as neurons within the pedunculopontine tegmental nucleus and the red nucleus were Chol-1-positive. In addition visceromotoneurons of the Edinger-Westphal nucleus were stained with anti-Chol-1 antibodies. In the basal forebrain the antibodies gave a positive reaction on well known cholinergic neurons in the vertical and horizontal limbs of the diagonal bands of Broca and the medial forebrain bundle. In agreement with studies using antibodies to choline acetyltransferase, a small subpopulation of neostriatal neurons (1-2%) was Chol-1-positive. In the rat retina, both anti-Chol-1 and anti-choline acetyltransferase antibodies gave rise to a nerve terminal-like staining in the same bands within the inner plexiform layer. The anti-Chol-1 antibodies also stain normal and pathological human material and could have a useful application in human neuropathology.

Antibodies in cerebrospinal fluid of some Alzheimer disease patients recognize cholinergic neurons in the rat central nervous system

The etiology of Alzheimer disease is unclear. However, immunological aberrations have been suggested to be critical factors in the pathogenesis of this neurodegenerative disease. This study was carried out to investigate if cerebrospinal fluid (CSF) from Alzheimer disease patients contains antibodies that recognize specific neuronal populations in the rat central nervous system. The results indicate that in a subgroup of patients this is indeed the case. The antibodies reported in this study have the following properties: (i) they recognize neuronal populations and components in the medial septum and spinal motor neurons in rats perfused with a mixture that fixes small neurotransmitter molecules; (ii) adsorption of the patient CSF with staphylococcal protein A-Sepharose and using a polyclonal antiserum against human IgG3 indicates that the immunocytochemical reaction in these brain regions is mainly due to the subclass IgG3; and (iii) the CSF immunocytochemical reaction is blocked by preincubation of the sections with a rabbit anti-acetylcholine antiserum. These results provide evidence that antibodies in the CSF of some, but not all, Alzheimer disease patients recognize acetylcholine-like epitopes in cholinergic neurons in the rat central nervous system.

Cholinergic neurons in the human retina

Choline acetyltransferase (ChAT)-like immunoreactivity in the human retina can be demonstrated using a polyclonal antiserum to ChAT isolated from chick brain. There is a population of ChAT-like immunoreactive cells along both margins of the inner plexiform layer (IPL). The labeled cells have a morphology and position characteristic of the cholinergic amacrine- and displaced amacrine cells demonstrated by other workers in the mammalian retina. Non-immune rabbit serum or pre-absorbed antiserum, used in place of the primary antiserum, verified the specificity of the method. Human retinas can also be labeled with the fluorescent dye 4',6-diamidino-2-phenylindole (DAPI), which has been reported to bind selectively to DNA in the nuclei of cholinergic cells. The fluorescent cells are similar in morphology, position, and distribution to the cells which show ChAT-like immunoreactivity. In addition, we have localized the presence of [3H]choline and [3H]choline metabolites in freeze-dried, vapor-fixed tissue using 'dry' autoradiographic techniques. Incubation in [3H]choline was followed by either stimulation or inhibition of calcium-dependent transmitter release during a 1-hr 'chase' period. Using tissue incubated in a chase designed to retain labeled neurotransmitters, silver grains were concentrated over a population of cell bodies at either margin of the IPL (i.e. in the same position as putative ChAT-immunoreactive cells and DAPI-labeled cells). In contrast, tissue incubated in a chase designed to release labeled acetylcholine was labeled uniformly throughout the neural retina, with a heavy band of label over the pigment epithelium. Taken together, the results presented here indicate that three independent markers for cholinergic cells (i.e. ChAT immunoreactivity, DAPI binding, and choline uptake) are present in a population of cells in the human retina. This suggests that acetylcholine may be a neurotransmitter synthesized by amacrine and displaced amacrine cells in the retina.

Evidence for the presence of cholinergic nerves in cerebral arteries: an immunohistochemical demonstration of choline acetyltransferase

The presence of cholinergic nerves in cerebral arteries of several species was investigated by an immunohistochemical method using antibodies against choline acetyltransferase (ChAT). In cats, pigs, rats, and dogs, ChAT immunoreactivities were found to be associated with large bundles and single fibers in the circle of Willis and anterior cerebral, middle cerebral, and basilar arteries. In the rabbit, the ChAT-immunoreactive (ChAT-I) nerves were also observed in the circle of Willis and anterior and middle cerebral arteries, but only few or none were found in the basilar and vertebral arteries. The ChAT-I nerves were found only in the adventitial layer of vessels examined. Superior cervical ganglionectomy did not appreciably affect the distribution of ChAT-I nerves. These results indicate the presence of cholinergic nerves in cerebral arteries. The distribution pattern of ChAT-I nerves was different from that of vasoactive intestinal polypeptide (VIP)-like-immunoreactive nerves and acetylcholinesterase-positive nerves. The possible coexistence of ChAT and VIP-like substance in the same neuron is discussed.

Cross-species and intraspecies reactivities of monoclonal antibodies against choline acetyltransferase

We have previously reported the first successful production of monoclonal antibodies against the cholinergic neuronal marker, choline acetyltransferase (ChAT). We now report some inter-and intraspecies cross-reactivity studies of the monoclonal antibody AB1. This antibody reacted most strongly with bovine ChAT and weakly with sheep and human enzyme. Similar amounts of binding were observed with the two forms of bovine ChAT separated by ion exchange chromatography. The antibody also reacted equally well with human ChAT derived from either brain or placenta.

Immunohistochemical localization of a synaptic-vesicle antigen in a cholinergic neuron under conditions of stimulation and rest

An antiserum against a specific component (a glycosamino glycan) of the cholinergic synaptic-vesicle of Torpedo marmorata has been used to investigate the localization of the component in the cell body, its movement within the electromotor axon and its fate within the nerve terminal upon electrical stimulation. After immunofluorescent staining, spots are observed throughout the cytoplasm of the lobe perikarya, although they are concentrated in the region of the axon hillock. Ligation of the electromotor nerves leading from the lobe to electric organ produces a proximal build-up of material which stains readily with the antivesicle antiserum, indicating that the vesicle antigen is transported from the cell body to the nerve terminal. A marked increase in indirect immunofluorescent staining of the electric organ is observed in the nerve ending upon electrical stimulation. We interpret this result as fusion of the vesicles with the presynaptic plasma membrane and exteriorization of the vesicle antigen to the extracellular space, thereby facilitating its staining. After recovery of the system the fluorescence declines, a result that is consistent with the reinternalization of the vesicle antigen into the core of reformed vesicles. The results support a mechanism whereby vesicles recycle within the nerve terminal and transmitter is released by exocytosis.

Presynaptic plasma membranes and synaptic vesicles of cholinergic nerve endings demonstrated by means of specific antisera

Antisera were raised to cholinergic presynaptic plasma membranes and synaptic vesicles isolated from the electric organ of Torpedo marmorata and tested by immunochemical and immunohistochemical methods. The antisera responded to many antigens not specific to nerve endings, but it was possible to eliminate these antibodies by means of simple absorption procedures with fractions containing the unwanted antigens. After absorption, staining of thin sections of electric organ by immunofluorescence was limited to the region of nerve endings in the tissue. The remaining antibodies responded in the case of the plasma membrane antisera predominantly to a 33,000 molecular-weight polypeptide and a chloroform/methanol-soluble antigen. In cross reactivity studies it was found that this antiserum not only stains cholinergic nerve endings in Torpedo but also those in mammalian tissue. The antigen responsible for the cross reactivity is restricted to the chloroform/methanol-soluble material. The vesicle antiserum labels cholinergic nerve endings in mammalian tissue as well; the relevant antigen in this case is different from the one described above and is likely to be a glycosaminoglycan. The antisera provide valuable markers for cholinergic nerve terminals. In addition, the vesicle antiserum may now be used to study axonal transport and the life cycle of this organelle in the cholinergic neurone.

Postganglionic cholinergic dysautonomia

A 9-year-old boy presented with symptoms and signs of marked postganglionic cholinergic autonomic dysfunction manifested by bilateral internal ophthalmoplegia, impaired secretion of tears and saliva, lack of gastrointestinal motility, atony of the bladder, generalized absence of sweating, and hypertension. Clinical and pharmacological studies confirmed that the abnormalities were restricted mainly to the postganglionic cholinergic autonomic system and showed evidence of postdenervation supersensitivity to parasympathomimetic drugs. The patient was treated in the early phase of his illness by the administration of carbachol, and eventually he made a slow and partial spontaneous recovery. Histoimmunofluorescent studies on a skin biopsy specimen suggested an autoimmune origin for his disease, with IgG antibodies being produced against postganglionic cholinergic autonomic fibers.