Coexpression of cholinergic and noradrenergic phenotypes in human and nonhuman autonomic nervous system

Desensitizing the autonomic nervous system to mitigate anti-GD2 monoclonal antibody side effects

Background

Anti-GD2 monoclonal antibodies (mAbs) have shown to improve the overall survival of patients with high-risk neuroblastoma (HR-NB). Serious adverse events (AEs), including pain, within hours of antibody infusion, have limited the development of these therapies. In this study, we provide evidence of Autonomic Nervous System (ANS) activation as the mechanism to explain the main side effects of anti-GD2 mAbs.

Methods

Through confocal microscopy and computational super-resolution microscopy experiments we explored GD2 expression in postnatal nerves of infants. In patients we assessed the ANS using the Sympathetic Skin Response (SSR) test. To exploit tachyphylaxis, a novel infusion protocol (the Step-Up) was mathematically modelled and tested.

Results

Through confocal microscopy, GD2 expression is clearly visible in the perineurium surrounding the nuclei of nerve cells. By computational super-resolution microscopy experiments we showed the selective expression of GD2 on the cell membranes of human Schwann cells in peripheral nerves (PNs) significantly lower than on NB. In patients, changes in the SSR were observed 4 minutes into the anti-GD2 mAb naxitamab infusion. SSR latency quickly shortened followed by gradual decrease in the amplitude before disappearance. SSR response did not recover for 24 hours consistent with tachyphylaxis and absence of side effects in the clinic. The Step-Up protocol dissociated on-target off-tumor side effects while maintaining serum drug exposure.

Conclusion

We provide first evidence of the ANS as the principal non-tumor target of anti-GD2 mAbs in humans. We describe the development and modeling of the Step-Up protocol exploiting the tachyphylaxis phenomenon we demonstrate in patients using the SSR test.

Electrophysiology and 3D-imaging reveal properties of human intracardiac neurons and increased excitability with atrial fibrillation

Altered autonomic input to the heart plays a major role in atrial fibrillation (AF). Autonomic neurons termed ganglionated plexi (GP) are clustered on the heart surface to provide the last point of neural control of cardiac function. To date the properties of GP neurons in humans are unknown. Here we have addressed this knowledge gap in human GP neuron structure and physiology in patients with and without AF. Human right atrial GP neurons embedded in epicardial adipose tissue were excised during open heart surgery performed on both non-AF and AF patients and then characterised physiologically by whole cell patch clamp techniques. Structural analysis was also performed after fixation at both the single cell and at the entire GP levels via three-dimensional confocal imaging. Human GP neurons were found to exhibit unique properties and structural complexity with branched neurite outgrowth. Significant differences in excitability were revealed between AF and non-AF GP neurons as measured by lower current to induce action potential firing, a reduced occurrence of low action potential firing rates, decreased accommodation and increased synaptic density. Visualisation of entire GPs showed almost all neurons are cholinergic with a small proportion of noradrenergic and dual phenotype neurons. Phenotypic distribution differences occurred with AF including decreased cholinergic and dual phenotype neurons, and increased noradrenergic neurons. These data show both functional and structural differences occur between GP neurons from patients with and without AF, highlighting that cellular plasticity occurs in neural input to the heart that could alter autonomic influence on atrial function. KEY POINTS: The autonomic nervous system plays a critical role in regulating heart rhythm and the initiation of AF; however, the structural and functional properties of human autonomic neurons in the autonomic ganglionated plexi (GP) remain unknown. Here we perform the first whole cell patch clamp electrophysiological and large tissue confocal imaging analysis of these neurons from patients with and without AF. Our data show human GP neurons are functionally and structurally complex. Measurements of action potential kinetics show higher excitability in GP neurons from AF patients as measured by lower current to induce action potential firing, reduced low firing action potential rates, and decreased action potential accommodation. Confocal imaging shows increased synaptic density and noradrenergic phenotypes in patients with AF. Both functional and structural differences occur in GP neurons from patients with AF that could alter autonomic influence on atrial rhythm.

Arterio-venous Anastomoses of the Sucquet-Hoyer Type: Complexity and Distribution in the Human Dermis

Our study aims at providing detailed information on numbers, form, and spatial distribution of arterio-venous anastomoses of the Sucquet-Hoyer type in the dermis of the nail bed, nail fold corner, thumb pad, arm, nose, glabella, lip, and ear. It further aims at providing a system, which relies on objective morphologic criteria for classifying Sucquet-Hoyer canals (SHCs). Using high-resolution episcopic microscopy (HREM), digital volume data of eight samples of each skin region were produced. Virtual three-dimensional (3D) models of the dermally located SHCs were created, and their 3D tortuosity (τ) values were determined. Dermal SHCs were identified in all 24 finger samples and in 1 lip sample. Beneath a field of 2 × 2 mm2, an average of four were located in the nail bed, three in the dermis of the thumb pad, and one in the dermis of the nail fold corner. Only a single dermal SHC was found in one lip sample. No SHCs were observed in the dermis of the other samples. The τ values of the SHCs ranged from 1.11 to 10. Building on these values, a classification system was designed, which distinguishes four SHC classes. The dermal distribution of the SHCs of different classes was similar in all specimens.

Comparative specialization of intrinsic cardiac neurons in humans, mice, and pigs

Intrinsic cardiac neurons (ICNs) play a crucial role in the proper functioning of the heart; yet a paucity of data pertaining to human ICNs exists. We took a multidisciplinary approach to complete a detailed cellular comparison of the structure and function of ICNs from mice, pigs, and humans. Immunohistochemistry of whole and sectioned ganglia, transmission electron microscopy, intracellular microelectrode recording and dye filling for quantitative morphometry were used to define the neurophysiology, histochemistry, and ultrastructure of these cells across species. The densely packed, smaller ICNs of mouse lacked dendrites, formed axosomatic connections, and had high synaptic efficacy constituting an obligatory synapse. At Pig ICNs, a convergence of subthreshold cholinergic inputs onto extensive dendritic arbors supported greater summation and integration of synaptic input. Human ICNs were tonically firing, with synaptic stimulation evoking large suprathreshold excitatory postsynaptic potentials like mouse, and subthreshold potentials like pig. Ultrastructural examination of synaptic terminals revealed conserved architecture, yet small clear vesicles (SCVs) were larger in pigs and humans. The presence and localization of ganglionic neuropeptides was distinct, with abundant VIP observed in human but not pig or mouse ganglia, and little SP or CGRP in pig ganglia. Action potential waveforms were similar, but human ICNs had larger after-hyperpolarizations. Intrinsic excitability differed; 93% of human cells were tonic, all pig neurons were phasic, and both phasic and tonic phenotypes were observed in mouse. In combination, this publicly accessible, multimodal atlas of ICNs from mice, pigs, and humans identifies similarities and differences in the evolution of ICNs.

A century of exercise physiology: concepts that ignited the study of human thermoregulation. Part 3: Heat and cold tolerance during exercise

In this third installment of our four-part historical series, we evaluate contributions that shaped our understanding of heat and cold stress during occupational and athletic pursuits. Our first topic concerns how we tolerate, and sometimes fail to tolerate, exercise-heat stress. By 1900, physical activity with clothing- and climate-induced evaporative impediments led to an extraordinarily high incidence of heat stroke within the military. Fortunately, deep-body temperatures > 40 °C were not always fatal. Thirty years later, water immersion and patient treatments mimicking sweat evaporation were found to be effective, with the adage of cool first, transport later being adopted. We gradually acquired an understanding of thermoeffector function during heat storage, and learned about challenges to other regulatory mechanisms. In our second topic, we explore cold tolerance and intolerance. By the 1930s, hypothermia was known to reduce cutaneous circulation, particularly at the extremities, conserving body heat. Cold-induced vasodilatation hindered heat conservation, but it was protective. Increased metabolic heat production followed, driven by shivering and non-shivering thermogenesis, even during exercise and work. Physical endurance and shivering could both be compromised by hypoglycaemia. Later, treatments for hypothermia and cold injuries were refined, and the thermal after-drop was explained. In our final topic, we critique the numerous indices developed in attempts to numerically rate hot and cold stresses. The criteria for an effective thermal stress index were established by the 1930s. However, few indices satisfied those requirements, either then or now, and the surviving indices, including the unvalidated Wet-Bulb Globe-Thermometer index, do not fully predict thermal strain.

Vesicular monoamine transporter (VMAT) regional expression and roles in pathological conditions

Vesicular monoamine transporters (VMATs) are key regulators of neurotransmitter release responsible for controlling numerous physiological, cognitive, emotional, and behavioral functions. They represent important therapeutic targets for numerous pathological conditions. There are two isoforms of VMAT transporter proteins that function as secondary active transporters into the vesicle for storage and release via exocytosis: VMAT1 (SLC18A1) and VMAT2 (SLC18A2) which differ in their function, quantity, and regional expression. VMAT2 has gained considerable interest as a therapeutic target and diagnostic marker. Inhibitors of VMAT2 have been used as an effective therapy for a range of pathological conditions. Additionally, the functionality and phenotypic classification of classical and nonclassical catecholaminergic neurons are identified by the presence of VMAT2 in catecholaminergic neurons. Dysregulation of VMAT2 is also implicated in many neuropsychiatric diseases. Despite the complex role of VMAT2, many aspects of its function remain unclear. Therefore, our aim is to expand our knowledge of the role of VMAT with a special focus on VMAT2 in different systems and cellular pathways which may potentially facilitate development of novel, more specific therapeutic targets. The current review provides a summary demonstrating the mechanism of action of VMAT, its functional role, and its contribution to disease progression and utilization as therapeutic targets.

Neurochemical alterations of intrinsic cardiac ganglionated nerve plexus caused by arterial hypertension developed during ageing in spontaneously hypertensive and Wistar Kyoto rats

The acknowledged hypothesis of the cause of arterial hypertension is the emerging disbalance in sympathetic and parasympathetic regulations of the cardiovascular system. This disbalance manifests in a disorder of sustainability of endogenous autonomic and sensory neural substances including calcitonin gene-related peptide (CGRP). This study aimed to examine neurochemical alterations of intrinsic cardiac ganglionated nerve plexus (GP) triggered by arterial hypertension during ageing in spontaneously hypertensive rats of juvenile (prehypertensive, 8-9 weeks), adult (early hypertensive, 12-18 weeks) and elderly (persistent hypertensive, 46-60 weeks) age in comparison with the age-matched Wistar-Kyoto rats as controls. Parasympathetic, sympathetic and sensory neural structures of GP were analysed and evaluated morphometrically in tissue sections and whole-mount cardiac preparations. Both the elevated blood pressure and the evident ultrasonic signs of heart failure were identified for spontaneously hypertensive rats and in part for the aged control rats. The amount of adrenergic and immunoreactive to CGRP neural structures was increased in the adult group of spontaneously hypertensive rats along with the significant alterations that occurred during ageing. In conclusion, the revealed chemical alterations of GP support the hypothesis about the possible disbalance of efferent and afferent heart innervation and may be considered as the basis for the emergence and progression of arterial hypertension and perhaps even as a consequence of hypertension in the aged spontaneously hypertensive rats. The determined anatomical changes in the ageing Wistar-Kyoto rats suggest this breed being as inappropriate for its use as control animals for hypertension studies in older animal age.

A comparative evaluation of resting state proxies of sympathetic and parasympathetic nervous system activity in adolescent major depression

Major depressive disorder (MDD) is associated with autonomic nervous system (ANS) dysfunction, characterized by decreased parasympathetic (PNS) and increased sympathetic (SNS) activity. Although findings on reduced PNS activity in adult MDD have been replicated in adolescents, comprehensive studies assessing PNS and SNS proxies in underage patients with MDD are scarce. Proxies of resting PNS (heart rate variability (HRV) and SNS activity (skin conductance response [SCR] and salivary alpha amylase [sAA], as well as mixed activity (heart rate [HR]) were collected in adolescents with MDD (n = 29) and non-depressed controls (n = 29). Primary analyses addressed differences between groups and correlations with depression severity. Patients with MDD showed significantly decreased HRV (g = - 0.87; 95% CI [- 1.39; - 0.35]) and increased HR (g = 0.66; 95% CI [0.14; 1.18]). Proxies of pure SNS activity showed no significant differences between groups. HR (positive) and HRV (negative) were significantly correlated with self- and clinician-rated depression severity. Alterations of ANS activity are evident in adolescent MDD, but characterized by decreased PNS activity only. We found no evidence for altered SNS activity. Findings suggest that ANS dysfunction early in the course of MDD might be predominantly driven by decreased PNS activity.

Vagally-mediated heart block after myocardial infarction associated with plasticity of epicardial neurons controlling the atrioventricular node

Imbalances in the opposing actions of sympathetic and parasympathetic nerves controlling the heart enhance risk for arrhythmia and sudden cardiac death after myocardial infarction (MI). Plasticity in peripheral neuron function may underlie the observed changes in cardiomotor nerve activity. We studied vagal control of the heart in pigs after chronic infarction of the left ventricle. Stimulation of the cervical vagus nerve produced greater bradycardic responses 8-weeks after MI. Recordings of epicardial electrocardiograms demonstrate increased severity and duration of atrioventricular (AV) block in MI-pigs during 20 Hz vagal stimulation. Intracellular voltage recordings from isolated neurons of the inferior vena cava-inferior left atrium (IVC-ILA) ganglionated plexus, a cluster of epicardial neurons receiving innervation from the vagus known to regulate the AV node, were used to assess plasticity of membrane and synaptic physiology of intrinsic cardiac neurons (ICNs) after MI. Changes to both passive and active membrane properties were observed, including more negative resting membrane potentials and greater input resistances in MI-pig ICNs, concomitant with a depression of neuronal excitability. Immunoreactivity to pituitary adenylate cyclase-activating polypeptide (PACAP), a cardiotropic peptide known to modulate cardiac neuron excitability, was localized to perineuronal varicosities surrounding pig IVC-ILA neurons. Exogenous application of PACAP increased excitability of control but not MI-ICNs. Stimulation (20 Hz) of interganglionic nerves in the ex vivo whole-mount preparations elicited slow excitatory postsynaptic potentials (sEPSPs) which persisted in hexamethonium (500 μM), but were blocked by atropine (1 μM), indicating muscarinic receptor-mediated inhibition of M-current. Extracellular application of 1 mM BaCl₂ to inhibit M-current increased neuronal excitability. The muscarine-sensitive sEPSPs were observed more frequently and were of larger amplitude in IVC-ILA neurons from MI animals. In conclusion, we suggest the increased probability of muscarinic sEPSPs play a role in the potentiation of the vagus nerve mediated-slowing of AV nodal conduction following chronic MI. We identify both a novel role of a muscarinic sensitive current in the regulation of synaptic strength at ICNs projecting to the AV node, and demonstrate changes to both intrinsic plasticity and synaptic plasticity of IVC-ILA neurons which may contribute to greater risk for heart block and sudden cardiac death after MI.

Prenatal development of sympathetic innervation of the human pancreas

BACKGROUND

The sympathetic nervous system plays an important role in the regulation of pancreatic exocrine and endocrine secretion. The results of experimental studies also demonstrate the involvement of the sympathetic nervous system in the regulation of endocrine cell differentiation and islet formation during the development of the pancreas. However, the prenatal development of sympathetic innervation of the human pancreas has not yet been studied.

MATERIAL AND METHODS

Pancreatic autopsy samples from 24 human fetuses were examined using immunohistochemistry with antibodies to tyrosine hydroxylase (TH). The density, concentration, and size (width, length, perimeter and area) of the TH-positive sympathetic nerves were compared in four developmental periods: pre-fetal (8-11 weeks post conception (w.p.c.), n = 6), early fetal (13-20 gestational weeks (g.w.), n = 7), middle fetal (21-28 g.w., n = 6) and late fetal (29-40 g.w., n = 5) using morphometric methods and statistical analysis (Multiple Comparisons p values). Double immunofluorescence with antibodies to TH and either insulin or glucagon and confocal microscopy were applied to analyze the interaction between the sympathetic nerves and endocrine cells, and the co-localization of TH with hormones.

RESULTS

TH-positive sympathetic nerves were detected in the fetal pancreas starting from the early stages (8 w.p.c.). The developmental dynamics of sympathetic nerves was follows: from the pre-fetal period, the amount of TH-positive nerves gradually increased and their branching occurred reaching the highest density and concentration in the middle fetal period, followed by a decrease in these parameters in the late fetal period. From the 14th g.w. onwards, thin TH-positive nerve fibers were mainly distributed in the vicinity of blood vessels and around the neurons of intrapancreatic ganglia, which is similar in adults. There were only rare TH-positive nerve fibers adjacent to acini or located at the periphery of some islets. The close interactions between the TH-positive nerve fibers and endocrine cells were observed in the neuro-insular complexes. Additionally, non-neuronal TH-containing cells were found in the pancreas of fetuses from the pre-fetal and early fetal periods. Some of these cells simultaneously contained glucagon.

CONCLUSIONS

The results demonstrate that sympathetic innervation of the human pancreas, including the formation of perivascular and intraganglionic nerve plexuses, extensively develops during prenatal period, while some processes, such as the formation of sympathetic innervation of islet capillaries, may occur postnatally. Non-neuronal TH-containing cells, as well as the interactions between the sympathetic terminals and endocrine cells observed in the fetal pancreas may be necessary for endocrine pancreas development in humans.

Correlation of neurological level and sweating level of injury in persons with spinal cord injury

Objective: Thermoregulatory dysfunction after spinal cord injury (SCI) impairs quality of life and predisposes persons to life-threatening sequela of heat-related illness (HRI) in conditions of high ambient temperature. SCI clinicians currently have no objective way to predict which persons are at greatest risk of HRI. Evaporative cooling via sweating is the body's most efficient mechanism of heat dissipation. The relationship between the neurological level of injury (NLOI) and the degree of sudomotor dysfunction is not well defined. This study examines the relationship between the NLOI and sweating level of injury (SwLOI). This information can assist SCI clinicians in identifying individuals with SCI who have most impaired sudomotor function and thus highest risk of HRI.Design: Observational.Setting: Human physiology laboratory.Participants: 10 persons with tetraplegia (TP), 14 with paraplegia (PP) and 10 able-bodied (AB).Intervention: Passive heat stress (1°C rise in core temperature) with sweat responses (SR) quantified with the starch iodine test.Outcome measures: The most caudal dermatomal level in which sweating was visualized was recorded as the SwLOI, which was compared to the NLOI. Minimum, maximum and median differences between NLOI and SwLOI were calculated.Results: Persons with tetraplegia demonstrated no SR. Persons with paraplegia demonstrated SR at a median of 1 level below NLOI. Able-bodied controls demonstrated sweating on all skin surface areas.Conclusions: Persons with motor complete tetraplegia lack evaporative cooling capacity through SR during passive heat stress predisposing them to HRI. Meanwhile, persons with paraplegia sweat on average 1 dermatomal level below their NLOI.

Asymmetry and Heterogeneity: Part and Parcel in Cardiac Autonomic Innervation and Function

The cardiac autonomic nervous system (cANS) regulates cardiac adaptation to different demands. The heart is an asymmetrical organ, and in the selection of adequate treatment of cardiac diseases it may be relevant to take into account that the cANS also has sidedness as well as regional differences in anatomical, functional, and molecular characteristics. The left and right ventricles respond differently to adrenergic stimulation. Isoforms of nitric oxide synthase, which plays an important role in parasympathetic function, are also distributed asymmetrically across the heart. Treatment of cardiac disease heavily relies on affecting left-sided heart targets which are thought to apply to the right ventricle as well. Functional studies of the right ventricle have often been neglected. In addition, many principles have only been investigated in animals and not in humans. Anatomical and functional heterogeneity of the cANS in human tissue or subjects is highly valuable for understanding left- and right-sided cardiac pathology and for identifying novel treatment targets and modalities. Within this perspective, we aim to provide an overview and synthesis of anatomical and functional heterogeneity of the cANS in tissue or subjects, focusing on the human heart.

A single cell transcriptomics map of paracrine networks in the intrinsic cardiac nervous system

We developed a spatially-tracked single neuron transcriptomics map of an intrinsic cardiac ganglion, the right atrial ganglionic plexus (RAGP) that is a critical mediator of sinoatrial node (SAN) activity. This 3D representation of RAGP used neuronal tracing to extensively map the spatial distribution of the subset of neurons that project to the SAN. RNA-seq of laser capture microdissected neurons revealed a distinct composition of RAGP neurons compared to the central nervous system and a surprising finding that cholinergic and catecholaminergic markers are coexpressed, suggesting multipotential phenotypes that can drive neuroplasticity within RAGP. High-throughput qPCR of hundreds of laser capture microdissected single neurons confirmed these findings and revealed a high dimensionality of neuromodulatory factors that contribute to dynamic control of the heart. Neuropeptide-receptor coexpression analysis revealed a combinatorial paracrine neuromodulatory network within RAGP informing follow-on studies on the vagal control of RAGP to regulate cardiac function in health and disease.

Parasympathetic neurons in the human submandibular ganglion

The submandibular ganglion (SMG) contains parasympathetic neurons which innervate the submandibular gland. In this study, immunohistochemistry for vasoactive intestinal polypeptide (VIP), neuropeptide Y (NPY), choline acetyltransferase (ChAT), dopamine β-hydroxylase (DBH), tyrosine hydroxylase (TH), and the transient receptor potential cation channel subfamily V members 1 (TRPV1) and 2 (TRPV2) was performed on the human SMG. In the SMG, 17.5 % and 8.9 % of parasympathetic neurons were immunoreactive for VIP and TRPV2, respectively. SMG neurons mostly contained ChAT- and DBH-immunoreactivity. In addition, subpopulations of SMG neurons were surrounded by VIP (69.6 %)-, TRPV2 (54.4 %)- and DBH (9.5 %)-immunoreactive (-ir) nerve fibers. SMG neurons with pericellular VIP- and TRPV2-ir nerve fibers were significantly larger than VIP- and TRPV2-ir SMG neurons, respectively. Other neurochemical substances were rare in the SMG. In the human submandibular gland, TRPV1- and TRPV2-ir nerve fiber profiles were seen around blood vessels. Double fluorescence method also demonstrated that TRPV2-ir nerve fiber profiles were located around myoepithelial and acinar cells in the submandibular gland. VIP and TRPV2 are probably expressed by both pre- and post-ganglionic neurons innervating the submandibular and sublingual glands. VIP, DBH and TRPV2 may have functions about regulation of salivary components in the salivary glands and neuronal activity in the SMG.

Psychophysiological concomitants of personality pathology in development

Psychophysiological research methods allow important insights into normative and pathological functioning of the human organism. This position paper briefly reviews existing studies, investigating the psychophysiological concomitants of personality pathology, with an emphasis on developmental aspects. Focussing on measures, indexing autonomic nervous system (ANS) activity at rest, and its reactivity to experimental challenge, the narrative synthesis of the literature highlights current challenges in the field. Findings on the psychophysiological concomitants of personality pathology are mixed. Inconsistencies among studies arise from differences between disorders and heterogeneity within distinct diagnostic categories. The majority of studies addressed borderline personality disorder, illustrating robust alterations in ANS function linked to severe experiences of early maltreatment and trauma, and associated symptoms of dissociation. However, important life-style and secondary health-related factors (i.e. physical activity, smoking) influencing ANS function are frequently neglected. Adapting a dimensional approach to personality pathology and longitudinal research designs seem promising to advance the filed in the years to come.

Cholinergic- rather than adrenergic-induced sweating play a role in developing and developed rat eccrine sweat glands

Both cholinergic and adrenergic stimulation can induce sweat secretion in human eccrine sweat glands, but whether cholinergic and adrenergic stimulation play same roles in rat eccrine sweat glands is still controversial. To explore the innervations, and adrenergic- and cholinergic-induced secretory response in developing and developed rat eccrine sweat glands, rat hind footpads from embryonic day (E) 15.5-20.5, postanal day (P) 1-14, P21 and adult were fixed, embedded, sectioned and subjected to immunofluorescence staining for general fiber marker protein gene product 9.5 (PGP 9.5), adrenergic fiber marker tyrosine hydroxylase (TH) and cholinergic fiber marker vasoactive intestinal peptide (VIP), and cholinergic- and adrenergic-induced sweat secretion was detected at P1-P21 and adult rats by starch-iodine test. The results showed that eccrine sweat gland placodes of SD rats were first appeared at E19.5, and the expression of PGP 9.5 was detected surrounding the sweat gland placodes at E19.5, TH at P7, and VIP at P11. Pilocarpine-induced sweat secretion was first detected at P16 in hind footpads by starch-iodine test. There was no measurable sweating when stimulated by alpha- or beta-adrenergic agonists at all the examined time points. We conclude that rat eccrine sweat glands, just as human eccrine sweat glands, co-express adrenergic and cholinergic fibers, but different from human eccrine sweat glands, cholinergic- rather than adrenergic-induced sweating plays a role in the developing and developed rat eccrine sweat glands.

Sweating Disorders

PURPOSE OF REVIEW

This article reviews disorders of sweating, including hyperhidrosis and anhidrosis due to central or peripheral autonomic nervous system causes.

RECENT FINDINGS

Disorders of thermoregulation and sweating may manifest with hyperhidrosis or hypohidrosis/anhidrosis. Primary disorders of hyperhidrosis may significantly impact quality of life yet tend to be benign. Many sweating disorders present with compensatory hyperhidrosis due to areas of anhidrosis. Anhidrosis may occur due to either central or peripheral damage to the autonomic nervous system. The thermoregulatory control of sweating involves central pathways from the hypothalamus to the brainstem and then spinal cord as well as projections to peripheral structures, including the sympathetic chain ganglia, peripheral nerves, and eccrine sweat glands. Disruption at any point of this pathway may lead to impaired sweating. Characterization of sweating dysfunction helps localize different autonomic disorders to guide diagnosis and may allow for evaluation of treatment effect.

SUMMARY

Sweating dysfunction manifests in myriad ways, including essential hyperhidrosis, complete anhidrosis with heat intolerance, and compensatory hyperhidrosis due to anhidrosis, and often indicates involvement of underlying central or peripheral autonomic dysfunction.

Does the iontophoretic application of bretylium tosylate modulate sweating during exercise in the heat in habitually trained and untrained men?

NEW FINDINGS

What is the central question of this study? Does the administration of the adrenergic presynaptic release inhibitor bretylium tosylate modulate sweating during exercise in the heat, and does this response differ between habitually trained and untrained men? What is the main finding and its importance? Iontophoretic administration of bretylium tosylate attenuates sweating during exercise in the heat in habitually trained and untrained men. However, a greater reduction occurred in trained men. The findings demonstrate a role for cutaneous adrenergic nerves in the regulation of eccrine sweating during exercise in the heat and highlight a need to advance our understanding of neural control of human eccrine sweat gland activity.

ABSTRACT

We recently reported an influence of cutaneous adrenergic nerves on eccrine sweat production in habitually trained men performing an incremental exercise bout in non-heat stress conditions. Based on an assumption that increasing heat stress induces cholinergic modulation of sweating, we evaluated the hypothesis that the contribution of cutaneous adrenergic nerves on sweating would be attenuated during exercise in the heat. Twenty young habitually trained and untrained men (n = 10/group) underwent three successive bouts of 15 min of light-, moderate- and vigorous-intensity cycling (equivalent to 30, 50, and 70% of peak oxygen uptake ( V ̇ O 2 peak ) respectively), each separated by a 15 min recovery while wearing a perfusion suit perfused with warm water (43°C). Sweat rate (ventilated capsule) was measured continuously at two bilateral forearm skin sites treated with 10 mm bretylium tosylate (an inhibitor of neurotransmitter release from adrenergic nerve terminals) and saline (control) via transdermal iontophoresis. A greater sweat rate was measured during vigorous exercise only in trained as compared to untrained men (P = 0.014). In both groups, sweating was reduced at the bretylium tosylate versus control sites, albeit the magnitude of reduction was greater in the trained men (P ≤ 0.024). These results suggest that cutaneous adrenergic nerves modulate sweating during exercise performed under a whole-body heat stress, albeit a more robust response occurs in trained men. While it is accepted that a cholinergic mechanism plays a primary role in the regulation of sweating during an exercise-heat stress, our findings highlight the need for additional studies aimed at understanding the neural control of human eccrine sweating.

Does α1-adrenergic receptor blockade modulate sweating during incremental exercise in young endurance-trained men?

PURPOSE

Human eccrine sweat glands respond to α₁-adrenergic receptor agonists. We recently reported that adrenergic mechanisms contribute to sweating in endurance-trained men during an incremental exercise to volitional fatigue. However, it remains unclear if this response is mediated by α₁-adrenergic receptor activation.

METHODS

Twelve endurance-trained men performed an incremental cycling bout until exhaustion while wearing a water-perfused suit to clamp skin temperature at ~ 34 °C. Bilateral forearm sweat rates were measured wherein the distal area was treated with either 1% terazosin (α₁-adrenergic receptor antagonist) or saline solution on the opposite limb (Control) via transdermal iontophoresis. We also measured proximal bilateral forearm sweat rate in untreated sites to confirm that no between-limb differences in forearm sweat rate occurred. Once sweat rate returned to pre-exercise resting levels at ~ 20 min postexercise, 0.25% phenylephrine (α₁-adrenergic receptor agonist) was iontophoretically administered to skin to verify α₁-adrenergic receptor blockade.

RESULTS

Sweat rates at the proximal untreated right and left forearm sites were similar during exercise (interaction, P = 0.581). Similarly, no effect of terazosin on sweat rate was measured relative to control site (interaction, P = 0.848). Postexercise administration of phenylephrine increased sweat rate at the control site (0.08 ± 0.09 mg cm^-2 min^-1), which was suppressed by ~ 90% at the terazosin-treated site (0.01 ± 0.02 mg cm^-2 min^-1) (P = 0.026), confirming that α₁-adrenergic receptor blockade was intact.

CONCLUSION

Our findings demonstrate that α₁-adrenergic receptors located at eccrine sweat glands do not contribute to eccrine sweating during incremental exercise in young endurance-trained men.

Distribution pattern and molecular signature of cholinergic tuft cells in human gastro-intestinal and pancreatic-biliary tract

Despite considerable recent insight into the molecular phenotypes and type 2 innate immune functions of tuft cells in rodents, there is sparse knowledge about the region-specific presence and molecular phenotypes of tuft cells in the human digestive tract. Here, we traced cholinergic tuft cells throughout the human alimentary tract with immunohistochemistry and deciphered their region-specific distribution and biomolecule coexistence patterns. While absent from the human stomach, cholinergic tuft cells localized to villi and crypts in the small and large intestines. In the biliary tract, they were present in the epithelium of extra-hepatic peribiliary glands, but not observed in the epithelia of the gall bladder and the common duct of the biliary tract. In the pancreas, solitary cholinergic tuft cells were frequently observed in the epithelia of small and medium-size intra- and inter-lobular ducts, while they were absent from acinar cells and from the main pancreatic duct. Double immunofluorescence revealed co-expression of choline acetyltransferase with structural (cytokeratin 18, villin, advillin) tuft cell markers and eicosanoid signaling (cyclooxygenase 1, hematopoietic prostaglandin D synthase, 5-lipoxygenase activating protein) biomolecules. Our results indicate that region-specific cholinergic signaling of tuft cells plays a role in mucosal immunity in health and disease, especially in infection and cancer.

The autonomic innervation of hairy skin in humans: an in vivo confocal study

The autonomic innervation of the skin includes different subsets of adrenergic and cholinergic fibers both in humans and animals. The corresponding chemical code is complex and often difficult to ascertain. Accordingly, a detailed histochemical description of skin autonomic fiber subtypes is lacking in humans. To characterize skin autonomic nerve subtypes may help to better understand the selective damage of specific skin autonomic fibers affecting human diseases such as the adrenergic fibers directed to skin vessels in Parkinson’s disease or the cholinergic sudomotor fibers in Ross Syndrome. The present study aimed at characterizing subtypes of autonomic fibers in relation to their target organs by means of an immunofluorescent technique and confocal microscopy. We studied 8 healthy subjects (5 males and 3 females) aged 45 ± 2 (mean ± SE) years without predisposing causes for peripheral neuropathy or autonomic disorders. They underwent skin biopsy from proximal (thigh) and distal (leg) hairy skin. A combination of adrenergic (i.e. tyrosine-hydroxylase- TH and dopamine beta-hydroxylase- DbH) and cholinergic (vesicular acetylcholine transporter- VACHT) autonomic markers and neuropeptidergic (i.e. neuropeptide Y- NPY, calcitonin gene-related peptide- CGRP, substance P- SP, and vasoactive intestinal peptide- VIP) markers were used to characterize skin autonomic fibers. The analysed skin autonomic structures included: 58 sweat glands, 91 skin arterioles and 47 arrector pili muscles. Our results showed that all skin structures presented a sympathetic adrenergic but also cholinergic innervation although in different proportions. Sympathetic adrenergic fibers were particularly abundant around arterioles and arrector pili muscles whereas sympathetic cholinergic fibers were mainly found around sweat glands. Neuropeptides were differently expressed in sympathetic fibers: NPY were found in sympathetic adrenergic fibers around skin arterioles and very seldom sweat glands but not in adrenergic fibers of arrector pili muscles. By contrast CGRP, SP and VIP were expressed in sympathetic cholinergic fibers. Cholinergic fibers expressing CGRP, SP or VIP without TH or DbH staining were found in arterioles and arrector pili muscles and they likely represent parasympathetic fibers. In addition, all skin structures contained a small subset of neuropeptidergic fibers devoid of adrenergic and cholinergic markers with a likely sensory function. No major differences were found between males and females and proximal and distal sites. In summary hairy skin contains sympathetic adrenergic and cholinergic fibers differently distributed around skin structures with a specific distribution of neuropeptides. The autonomic skin innervation also contains a small amount of fibers, likely to be parasympathetic and sensory.

Distributions and relationships of chemically defined enteroendocrine cells in the rat gastric mucosa

This paper provides quantitative data on the distributions of enteroendocrine cells (EEC), defined by the hormones they contain, patterns of colocalisation between hormones and EEC relations to nerve fibres in the rat gastric mucosa. The rat stomach has three mucosal types: non-glandular stratified squamous epithelium of the fundus and esophageal groove, a region of oxyntic glands in the corpus, and pyloric glands of the antrum and pylorus. Ghrelin and histamine were both contained in closed cells, not contacting the lumen, and were most numerous in the corpus. Gastrin cells were confined to the antrum, and 5-hydroxytryptamine (5-HT) and somatostatin cells were more frequent in the antrum than the corpus. Most somatostatin cells had basal processes that in the antrum commonly contacted gastrin cells. Peptide YY (PYY) cells were rare and mainly in the antrum. The only numerous colocalisations were 5-HT and histamine, PYY and gastrin and gastrin and histamine in the antrum, but each of these populations was small. Peptide-containing nerve fibres were found in the mucosa. One of the most common types was vasoactive intestinal peptide (VIP) fibres. High-resolution analysis showed that ghrelin cells were closely and selectively approached by VIP fibres. In contrast, gastrin cells were not selectively innervated by VIP or CGRP fibres. The study indicates that there are distinct populations of gastric EEC and selective innervation of ghrelin cells. It also shows that, in contrast to EEC of the small intestine, the majority of EEC within the stomach contained only a single hormone.

Distribution of postganglionic neurons which contain dopamine β-hydroxylase, tyrosine hydroxylase, neuropeptide Y and vasoactive intestinal polypeptide in the human middle cervical ganglion

The middle cervical ganglion (MCG) has been shown to contain neurotransmitters and related substances in the cat, dog and sheep. However, little is known about their presence or distribution in the human MCG. In this study, immunohistochemistry for catecholamine-synthesizing enzymes and neuropeptides was performed on the MCG in human cadavers. In 4 samples of human cadavers, MCG swellings contained numerous postganglionic neurons. In another sample, a distinct swelling of the MCG could not be detected. However, neuronal cell bodies were present within the sympathetic nerve trunk between the superior cervical and stellate ganglia. The cell size analysis demonstrated that cell bodies of postganglionic neurons measured 94.1-1774.1 μm² (mean ± S.D. = 578.1 ± 127.7 μm²) in the MCG. Postganglionic neurons in the MCG were immunoreactive for dopamine β-hydroxylase (DBH, 92.1%), tyrosine hydroxylase (TH, 59.3%), neuropeptide Y (NPY, 71.9%) and vasoactive intestinal polypeptide (VIP, 19.3%). TH-positive neurons in the human MCG appear to be infrequent compared to the sheep MCG in a previous study. In the superior cervical (SCG) and stellate ganglia (SG), 91.0% and 94.2%, respectively, of postganglionic neurons showed DBH-immunoreactivity. A total of 83.8% and 70.4%of them contained TH-immunoreactivity in the SCG and SG. However, expression of NPY in the SG (78.2%) was more abundant than in the SCG (59.1%). Only 16.4% and 13.8% of postganglionic neurons were immunoreactive for VIP in the SCG and SG, respectively. VIP-immunoreactivity was also expressed by nerve fibers surrounding some postganglionic neurons in the MCG (8.7%), SCG (11.5%) and SG (5.9%). The present study suggests that catecholamine, NPY and VIP are neurotransmitters in the MCG, SCG and SG of the human.

The Investigation of the Cardiovascular and Sudomotor Autonomic Nervous System-A Review

The autonomic nervous system as operating system of the human organism permeats all organ systems with its pathways permeating that it is involved with virtually all diseases. Anatomically a central part, an afferent part and sympathetic and parasympathetic efferent system can be distinguished. Among the different functional subsystems of the autonomic nervous system, the cardiovascular autonomic nervous system is most frequently examined with easily recordable cardiovascular biosignals as heart rate and blood pressure. Although less widely established, sudomotor tests pose a useful supplement to cardiovascular autonomic assessment as impaired neurogenic sweating belongs to the earliest clinical signs of various autonomic neuropathies as well as neurodegenerative disorders and significantly reduces quality of life. Clinically at first, the autonomic nervous system is assessed with a detailed history of clinical autonomic function and a general clinical examination. As a lof of confounding factors can influence autonomic testing, subjects should be adequately prepared in a standardized way. Autonomic testing is usually performed in that way that the response of the autonomic nervous system to a well-defined challenge is recorded. As no single cardiovascular autonomic test is sufficiently reliable, it is recommended to use a combination of different approaches, an autonomic test battery including test to measure parasympathetic and sympathetic cardiovascular function (deep breathing test, Valsalva maneuver, tilt, or pressor test). More specialized tests include carotid sinus massage, assessment of baroreceptor reflex function, pharmacological tests or cardiac, and regional hemodynamic measurements. Techniques to measure functional integrity of sudomotor nerves include the quantitative sudomotor axon reflex sweat test, analysis of the sympathetic skin response as well as the thermoregulatory sweat test. In addition to these rather established techniques more recent developments have been introduced to reduce technical demands and interindividual variability such as the quantitative direct and indirect axon reflex testing or sudoscan. However, diagnostic accuracy of these tests remains to be determined. We reviewed the current literature on currently available autonomic cardiovascular and sudomotor tests with a focus on their physiological and technical mechanisms as well as their diagnostic value in the scientific and clinical setting.

Cutaneous adrenergic nerve blockade attenuates sweating during incremental exercise in habitually trained men

It remains unknown whether cutaneous adrenergic nerves functionally contribute to sweat production during exercise. This study examined whether cutaneous adrenergic nerve blockade attenuates sweating during incremental exercise, specifically in habitually trained individuals. Accordingly, 10 habitually trained and 10 untrained males (V̇o_2max: 56.7 ± 5.4 and 38.9 ± 6.7 ml·kg^-1·min^-1, respectively; P < 0.001) performed incremental semirecumbent cycling (20 W/min) until exhaustion. Sweat rates (ventilated capsule) were measured at two bilateral forearm skin sites on which either 10 mM bretylium tosylate (BT) (an inhibitor of neurotransmitter release from sympathetic adrenergic nerve terminals) or saline (Control) was transdermally administered via iontophoresis. BT treatment delayed sweating onset in both groups (∼0.66 min; P = 0.001) and suppressed the sweat rate relative to the Control treatment at ≥70% relative total exercise time in trained individuals (each 10% increment; all P ≤ 0.009) but not in untrained counterparts ( P = 0.122, interaction between relative time × treatment). Changes in total sweat production at the BT site relative to the Control site were greater in trained individuals than in untrained counterparts (area under the curve, -0.86 ± 0.67 and -0.22 ± 0.39 mg/cm², respectively; P = 0.023). In conclusion, we demonstrated that cutaneous adrenergic nerves do modulate sweating during incremental exercise, which appeared to be more apparent in habitually trained men (e.g., ≥70% maximum workload). Although our results indicated that habitual exercise training may augment neural adrenergic sweat production during incremental exercise, additional studies are required to confirm this possibility. NEW & NOTEWORTHY We demonstrated for the first time that cutaneous adrenergic nerves do modulate sweating during high-intensity exercise in humans (≥70% maximum workload). In addition, neural adrenergic sweating appeared to be greater in habitually trained individuals than in untrained counterparts, although further studies are necessary to confirm such a possibility. Nonetheless, the observations presented herein advance our understanding on human thermoregulation while providing new evidence for the neutral mediation of adrenergic sweating during exercise.

A brain within the heart: A review on the intracardiac nervous system

Cardiac function is under the control of the autonomic nervous system, composed by the parasympathetic and sympathetic divisions, which are finely tuned at different hierarchical levels. While a complex regulation occurs in the central nervous system involving the insular cortex, the amygdala and the hypothalamus, a local cardiac regulation also takes place within the heart, driven by an intracardiac nervous system. This complex system consists of a network of ganglionic plexuses and interconnecting ganglions and axons. Each ganglionic plexus contains numerous intracardiac ganglia that operate as local integration centres, modulating the intricate autonomic interactions between the extrinsic and intracardiac nervous systems. Herein, we summarize the current understanding on the intracardiac nervous system, and acknowledge its role in the pathophysiology of cardiovascular diseases.

Feasibility of monitoring stress using skin conduction measurements during intubation of newborns

The objective of this study was to assess the feasibility of monitoring stress responses in newborns during naso-tracheal intubation after two different premedication regimens, using skin conductance measurements (SCM). Twenty-two newborns were randomised and premedicated with morphine + vecuronium or propofol. SCM (peaks/s) were collected prior to, during and after the procedure. Threshold for interpreting responses as stressful was 0.21 peaks/s. Intubation conditions and physiological parameters were registered. Intubation conditions were good in all newborns. Administration of morphine (range 1.4-10.3 min) before administration of vecuronium did not affect SCM when a stressful stimulus was applied. Within 1.6 min (range 0.8-3 min) after administration of vecuronium, SCM disappeared in 10 of 11 newborns. Propofol reduced SCM in 10 of 11 newborns at the first attempt. Further attempts were associated with increasing SCM, mostly above a threshold of 0.21 peaks/s. There were no significant changes in physiological parameters during the procedure for either premedication regimen.

CONCLUSION

The variation in SCM between individual newborns limits the usefulness of SCM as stress monitor during intubation. The use of neuromuscular blockers for premedication precludes monitoring of SCM completely in newborns.

WHAT IS KNOWN

Skin conductance measurements have been used successfully to monitor pain in awake newborn infants.

WHAT IS NEW

Premedicated newborns display significant interindividual variation in skin conductance measurements during an intubation procedure. Neuromuscular blockade causes skin conductance measurements to disappear completely.

Innervation of the rabbit cardiac ventricles

The rabbit is widely used in experimental cardiac physiology, but the neuroanatomy of the rabbit heart remains insufficiently examined. This study aimed to ascertain the architecture of the intrinsic nerve plexus in the walls and septum of rabbit cardiac ventricles. In 51 rabbit hearts, a combined approach involving: (i) histochemical acetylcholinesterase staining of intrinsic neural structures in total cardiac ventricles; (ii) immunofluorescent labelling of intrinsic nerves, nerve fibres (NFs) and neuronal somata (NS); and (iii) transmission electron microscopy of intrinsic ventricular nerves and NFs was used. Mediastinal nerves access the ventral and lateral surfaces of both ventricles at a restricted site between the root of the ascending aorta and the pulmonary trunk. The dorsal surface of both ventricles is supplied by several epicardial nerves extending from the left dorsal ganglionated nerve subplexus on the dorsal left atrium. Ventral accessing nerves are thicker and more numerous than dorsal nerves. Intrinsic ventricular NS are rare on the conus arteriosus and the root of the pulmonary trunk. The number of ventricular NS ranged from 11 to 220 per heart. Four chemical phenotypes of NS within ventricular ganglia were identified, i.e. ganglionic cells positive for choline acetyltransferase (ChAT), neuronal nitric oxide synthase (nNOS), and biphenotypic, i.e. positive for both ChAT/nNOS and for ChAT/tyrosine hydroxylase. Clusters of small intensely fluorescent cells are distributed within or close to ganglia on the root of the pulmonary trunk, but not on the conus arteriosus. The largest and most numerous intrinsic nerves proceed within the epicardium. Scarce nerves were found near myocardial blood vessels, but the myocardium contained only a scarce meshwork of NFs. In the endocardium, large numbers of thin nerves and NFs proceed along the bundle of His and both its branches up to the apex of the ventricles. The endocardial meshwork of fine NFs was approximately eight times denser than the myocardial meshwork. Adrenergic NFs predominate considerably in all layers of the ventricular walls and septum, whereas NFs of other neurochemical phenotypes were in the minority and their amount differed between the epicardium, myocardium and endocardium. The densities of NFs positive for nNOS and ChAT were similar in the epicardium and endocardium, but NFs positive for nNOS in the myocardium were eight times more abundant than NFs positive for ChAT. Potentially sensory NFs positive for both calcitonin gene-related peptide and substance P were sparse in the myocardial layer, but numerous in epicardial nerves and particularly abundant within the endocardium. Electron microscopic observations demonstrate that intrinsic ventricular nerves have a distinctive morphology, which may be attributed to remodelling of the peripheral nerves after their access into the ventricular wall. In conclusion, the rabbit ventricles display complex structural organization of intrinsic ventricular nerves, NFs and ganglionic cells. The results provide a basic anatomical background for further functional analysis of the intrinsic nervous system in the cardiac ventricles.

[Autonomic angiotensinergic fibres in the human heart with an efferent sympathetic cophenotype]

AIM

The autonomic innervation of the heart consists of sympathetic and parasympathetic nerve fibres, and fibres of the intrinsic ganglionated plexus with noradrenaline and acytylcholine as principal neurotransmitters. The fibres co-release neuropeptides to modulate intracardiac neurotransmission by specific presynaptic and postsynaptic receptors. The coexpression of angiotensin II in sympathetic fibres of the human heart and its role are not known so far.

METHODS

Autopsy specimens of human hearts were studied (n=3; ventricles). Using immunocytological methods, cryostat sections were stained by a murine monoclonal antibody (4B3) directed against angiotensin II and co-stained by polyclonal antibodies against tyrosine hydroxylase, a catecholaminergic marker. Visualisation of the antibodies was by confocal light microscopy or laser scanning microscopy.

RESULTS

Angiotensin II-positive autonomic fibres with and without a catecholaminergic cophenotype (hydroxylase-positive) were found in all parts of the human ventricles. In the epicardium, the fibres were grouped in larger bundles of up to 100 and more fibres. They followed the preformed anatomic septa and epicardial vessels towards the myocardium and endocardium where the bundles dissolved and the individual fibres spread between myocytes and within the endocardium. Generally, angiotensinergic fibres showed no synaptic enlargements or only a few if they were also catecholaminergic. The exclusively catechalominergic fibres were characterised by multiple beaded synapses.

CONCLUSION

The autonomic innervation of the human heart contains angiotensinergic fibres with a sympathetic efferent phenotype and exclusively angiotensinergic fibers representing probably afferents. Angiotensinergic neurotransmission may modulate intracardiac sympathetic and parasympathetic activity and thereby influence cardiac and circulatory function.

New approach to the understanding of keloid: psychoneuroimmune-endocrine aspects

The skin is a dynamic and complex organ that relies on the interrelation among different cell types, macromolecules, and signaling pathways. Further, the skin has interactions with its own appendages and other organs such as the sebaceous glands and hair follicles, the kidney, and adrenal glands; systems such as the central nervous system; and axes such as the hypothalamic–pituitary–adrenal axis. These continuous connections give the skin its versatility, and when an injury is caused, some triggers start a cascade of events designed to restore its integrity. Nowadays, it is known that this psychoneuroimmune–endocrine intercommunication modulates both the homeostatic condition and the healing process. In this sense, the skin conditions before a trauma, whether of endogenous (acne) or exogenous origin (injury or surgical incision), could regulate the process of tissue repair. Most skin diseases such as psoriasis and atopic dermatitis, among others, have in their pathophysiology a psychogenic component that triggers integrated actions in the nervous, immune, and endocrine systems. However, fibroproliferative disorders of wound healing, such as hypertrophic scar and keloid, are not yet included in this listing, despite showing correlation with stress, especially with the psychosocial character. This review, by understanding the “brain–skin connection”, presents evidence that allows us to understand the keloid as a psychomediated disease.

Satb2-independent acquisition of the cholinergic sudomotor phenotype in rodents

Expression of Satb2 (Special AT-rich sequence-binding protein-2) elicits expression of the vesicular acetylcholine transporter (VAChT) and choline acetyltransferase (ChAT) in cultured rat sympathetic neurons exposed to soluble differentiation factors. Here, we determined whether or not Satb2 plays a similar role in cholinergic differentiation in vivo, by comparing the postnatal profile of Satb2 expression in the rodent stellate ganglion to that of VAChT and ChAT. Throughout postnatal development, VAChT and ChAT were found to be co-expressed in a numerically stable subpopulation of rat stellate ganglion neurons. Nerve fibers innervating rat forepaw sweat glands on P1 were VAChT immunoreactive, while ChAT was detectable at this target only after P5. The postnatal abundance of VAChT transcripts in the stellate ganglion was at maximum already on P1, whereas ChAT mRNA levels increased from low levels on P1 to reach maximum levels between P5 and P21. Satb2 mRNA was detected in cholinergic neurons in the stellate ganglion beginning with P8, thus coincident with the onset of unequivocal detection of ChAT immunoreactivity in forepaw sweat gland endings. Satb2 knockout mice exhibited no change in the P1 cholinergic VAChT/ChAT co-phenotype in stellate ganglion neurons. Thus, cholinergic phenotype maturation involves first, early target (sweat-gland)-independent expression and trafficking of VAChT, and later, potentially target- and Satb2-dependent elevation of ChAT mRNA and protein transport into sweat gland endings. In rat sudomotor neurons that, unlike mouse sudomotor neurons, co-express calcitonin gene-related peptide (CGRP), Satb2 may also be related to the establishment of species-specific neuropeptide co-phenotypes during postnatal development.

Dermatological and immunological conditions due to nerve lesions

Some syndromes are of interest to both neurologists and dermatologists, because cutaneous involvement may harbinger symptoms of a neurological disease. The aim of this review is to clarify this aspect. The skin, because of its relationships with the peripheral sensory nervous system, autonomic nervous system and central nervous system, constitutes a neuroimmunoendocrine organ. The skin contains numerous neuropeptides released from sensory nerves. Neuropeptides play a precise role in cutaneous physiology and pathophysiology, and in certain skin diseases. A complex dysregulation of neuropeptides is a feature of some diseases of both dermatological and neurological interest (e.g. cutaneous and nerve lesions following herpes zoster infection, cutaneous manifestations of carpal tunnel syndrome, trigeminal trophic syndrome). Dermatologists need to know when a patient should be referred to a neurologist and should consider this option in those presenting with syndromes of unclear etiology.

Epidermal innervation in diabetes

The skin is innervated by small sensory and autonomic fibers. In the epidermis, sensory fibers are present as unmyelinated C fibers that terminate as free nerve endings. The determination of epidermal nerve fiber (ENF) density using the immunohistochemical method is a powerful tool that provides insight into a population of nerve fibers that is prominently altered in small fiber neuropathy. The superficial location of epidermal nerve fibers allows repeated sampling of these nerves in a relatively noninvasive fashion, and in sites that cannot be assessed through conventional electrodiagnostic techniques. These features have allowed investigators to diagnose diabetic neuropathy earlier in the course of disease. ENF density holds promise as a biomarker for neuropathic pain and is a sensitive indicator of neuropathic progression. Finally, the ability to injure these fibers in a standardized fashion has led to novel measures of human axonal regeneration that may provide a more sensitive ruler by which to assess promising regenerative compounds in clinical trials.

Autonomic cardiac innervation: development and adult plasticity

Autonomic cardiac neurons have a common origin in the neural crest but undergo distinct developmental differentiation as they mature toward their adult phenotype. Progenitor cells respond to repulsive cues during migration, followed by differentiation cues from paracrine sources that promote neurochemistry and differentiation. When autonomic axons start to innervate cardiac tissue, neurotrophic factors from vascular tissue are essential for maintenance of neurons before they reach their targets, upon which target-derived trophic factors take over final maturation, synaptic strength and postnatal survival. Although target-derived neurotrophins have a central role to play in development, alternative sources of neurotrophins may also modulate innervation. Both developing and adult sympathetic neurons express proNGF, and adult parasympathetic cardiac ganglion neurons also synthesize and release NGF. The physiological function of these “non-classical” cardiac sources of neurotrophins remains to be determined, especially in relation to autocrine/paracrine sustenance during development.

 

Cardiac autonomic nerves are closely spatially associated in cardiac plexuses, ganglia and pacemaker regions and so are sensitive to release of neurotransmitter, neuropeptides and trophic factors from adjacent nerves. As such, in many cardiac pathologies, it is an imbalance within the two arms of the autonomic system that is critical for disease progression. Although this crosstalk between sympathetic and parasympathetic nerves has been well established for adult nerves, it is unclear whether a degree of paracrine regulation occurs across the autonomic limbs during development. Aberrant nerve remodeling is a common occurrence in many adult cardiovascular pathologies, and the mechanisms regulating outgrowth or denervation are disparate. However, autonomic neurons display considerable plasticity in this regard with neurotrophins and inflammatory cytokines having a central regulatory function, including in possible neurotransmitter changes. Certainly, neurotrophins and cytokines regulate transcriptional factors in adult autonomic neurons that have vital differentiation roles in development. Particularly for parasympathetic cardiac ganglion neurons, additional examinations of developmental regulatory mechanisms will potentially aid in understanding attenuated parasympathetic function in a number of conditions, including heart failure.

Species-specific vesicular monoamine transporter 2 (VMAT2) expression in mammalian pancreatic beta cells: implications for optimising radioligand-based human beta cell mass (BCM) imaging in animal models

AIMS/HYPOTHESIS

Imaging of beta cell mass (BCM) is a major challenge in diabetes research. The vesicular monoamine transporter 2 (VMAT2) is abundantly expressed in human beta cells. Radiolabelled analogues of tetrabenazine (TBZ; a low-molecular-weight, cell-permeant VMAT2-selective ligand) have been employed for pancreatic islet imaging in humans. Since reports on TBZ-based VMAT2 imaging in rodent pancreas have been fraught with confusion, we compared VMAT2 gene expression patterns in the mouse, rat, pig and human pancreas, to identify appropriate animal models with which to further validate and optimise TBZ imaging in humans.

METHODS

We used a panel of highly sensitive VMAT2 antibodies developed against equivalently antigenic regions of the transporter from each species in combination with immunostaining for insulin and species-specific in situ hybridisation probes. Individual pancreatic islets were obtained by laser-capture microdissection and subjected to analysis of mRNA expression of VMAT2.

RESULTS

The VMAT2 protein was not expressed in beta cells in the adult pancreas of common mouse or rat laboratory strains, in contrast to its expression in beta cells (but not other pancreatic endocrine cell types) in the pancreas of pigs and humans. VMAT2- and tyrosine hydroxylase co-positive (catecholaminergic) innervation was less abundant in humans than in rodents. VMAT2-positive mast cells were identified in the pancreas of all species.

CONCLUSIONS/INTERPRETATION

Primates and pigs are suitable models for TBZ imaging of beta cells. Rodents, because of a complete lack of VMAT2 expression in the endocrine pancreas, are a 'null' model for assessing interference with BCM measurements by VMAT2-positive mast cells and sympathetic innervation in the pancreas.

Neuronal vulnerability, pathogenesis, and Parkinson's disease

Although there have been significant advances, pathogenesis in Parkinson's disease (PD) is still poorly understood. Potential clues about pathogenesis that have not been systematically pursued are suggested by the restricted pattern of neuronal pathology in the disease. In addition to dopaminergic neurons in the substantia nigra pars compacta (SNc), a significant number of other central and peripheral neuronal populations exhibit Lewy pathology (LP), phenotypic dysregulation, or frank degeneration in PD patients. Drawing on this literature, there appears to be a small number of risk factors contributing to vulnerability. These include autonomous activity, broad action potentials, low intrinsic calcium buffering capacity, poorly myelinated long highly branched axons and terminal fields, and use of a catecholamine neurotransmitter, often with the catecholamine-derived neuromelanin pigment. Of these phenotypic traits, only the physiological ones appear to provide a reachable therapeutic target at present.

The cutaneous nerve biopsy: technical aspects, indications, and contribution

Skin biopsy with a 3mm disposable circular punch is easy to perform and allows, after proper processing, the visualization of epidermal, dermal, and sweat gland nerve fibers. A technique of sampling the epidermis alone by applying a suction capsule, the "blister" technique, has also been developed. It is most common to stain immunohistochemically for the pan-axonal marker protein gene product 9.5 (PGP 9.5), an ubiquitin C-terminal hydroxylase. The sections are then observed and analyzed with bright-field microscopy or with indirect immunofluorescence with or without confocal microscopy. Most studies report quantification of intraepidermal nerve fiber density displayed in bright-field microscopy. Normative values have been established, particularly from the distal part of the leg, 10cm above the external malleolus. In diabetes mellitus early degeneration of intraepidermal nerve fibers is induced and there is slower regeneration even when there is no evidence of neuropathy. Skin biopsy is of particular value in the diagnosis of small fiber neuropathy when nerve conduction studies are normal. It may also be repeated in order to study the progressive nature of the disease and also has the potential of studying regeneration of nerve fibers and thus the effects of treatment. Inflammatory demyelinating neuropathies may also involve loss of small-diameter nerve fibers and IgM deposits in dermal myelinated nerve fibers in anti-MAG neuropathy. In some cases the presence of vasculitis in skin may indicate a nonsystemic vasculitic neuropathy and in HIV neuropathy intraepidermal nerve fiber density is reduced in a length-dependent manner. In several hereditary neuropathies intraepidermal nerve fiber density may be reduced but other abnormalities can also be demonstrated in dermal myelinated fibers. Some small swellings and varicosities may be present in the distal leg skin biopsy of healthy individuals but large axonal swellings are considered as evidence of a pathological process affecting the normal structure of nerves. The indirect immunofluorescence technique with confocal microscopy provides the opportunity to study the complex structure of sensory receptors and cutaneous myelinated fibers and the innervation of sweat glands, arrector pilorum muscles, and vessels.

Localization and expression of VMAT2 aross mammalian species: a translational guide for its visualization and targeting in health and disease

VMAT2 is the vesicular monoamine transporter that allows DA, NE, Epi, His, and 5-HT uptake into neurons and endocrine cells. A second isoform, VMAT1, has similar structure and function, but does not recognize histamine as a substrate. VMAT1 is absent from neurons, and its major function appears to be in endocrine cells, that is, enterochromaffin cells, which scavenge 5-HT, but not histamine, from dietary sources. This chapter provides an update on the neuroanatomical distribution of VMAT2 across various mammalian species, including human, primate, pig, rat, and mouse. When necessary, VMAT1 expression is provided as a contrast. The main purpose of this chapter is to allow clinicians, in particular endocrinologists and diagnosing neuroradiologists and neuropathologists, an acquaintanceship with the possibilities for VMAT2 as a target for in vivo imaging, and drug development, based on this updated information.

Peripheral choline acetyltransferase in rat skin demonstrated by immunohistochemistry

Conventional choline acetyltransferase immunohistochemistry has been used widely for visualizing central cholinergic neurons and fibers but not often for labeling peripheral structures, probably because of their poor staining. The recent identification of the peripheral type of choline acetyltransferase (pChAT) has enabled the clear immunohistochemical detection of many known peripheral cholinergic elements. Here, we report the presence of pChAT-immunoreactive nerve fibers in rat skin. Intensely stained nerve fibers were distributed in association with eccrine sweat glands, blood vessels, hair follicles and portions just beneath the epidermis. These results suggest that pChAT-positive nerves participate in the sympathetic cholinergic innervation of eccrine sweat glands. Moreover, pChAT also appears to play a role in cutaneous sensory nerve endings. These findings are supported by the presence of many pChAT-positive neuronal cells in the sympathetic ganglion and dorsal root ganglion. Thus, pChAT immunohistochemistry should provide a novel and unique tool for studying cholinergic nerves in the skin.

Efferent projections of C3 adrenergic neurons in the rat central nervous system

C3 neurons constitute one of three known adrenergic nuclei in the rat central nervous system (CNS). While the adrenergic C1 cell group has been extensively characterized both physiologically and anatomically, the C3 nucleus has remained relatively obscure. This study employed a lentiviral tracing technique that expresses green fluorescent protein behind a promoter selective to noradrenergic and adrenergic neurons. Microinjection of this virus into the C3 nucleus enabled the selective tracing of C3 efferents throughout the rat CNS, thus revealing the anatomical framework of C3 projections. C3 terminal fields were observed in over 40 different CNS nuclei, spanning all levels of the spinal cord, as well as various medullary, mesencephalic, hypothalamic, thalamic, and telencephalic nuclei. The highest densities of C3 axon varicosities were observed in Lamina X and the intermediolateral cell column of the thoracic spinal cord, as well as the dorsomedial medulla (both commissural and medial nuclei of the solitary tract, area postrema, and the dorsal motor nucleus of the vagus), ventrolateral periaqueductal gray, dorsal parabrachial nucleus, periventricular and rhomboid nuclei of the thalamus, and paraventricular and periventricular nuclei of the hypothalamus. In addition, moderate and sparse projections were observed in many catecholaminergic and serotonergic nuclei, as well as the area anterior and ventral to the third ventricle, Lamina X of the cervical, lumbar, and sacral spinal cord, and various hypothalamic and telencephalic nuclei. The anatomical map of C3 projections detailed in this survey hopes to lay the first steps toward developing a functional framework for this nucleus.

Psychological Stress and the Cutaneous Immune Response: Roles of the HPA Axis and the Sympathetic Nervous System in Atopic Dermatitis and Psoriasis

Psychological stress, an evolutionary adaptation to the fight-or-flight response, triggers a number of physiological responses that can be deleterious under some circumstances. Stress signals activate the hypothalamus-pituitary-adrenal (HPA) axis and the sympathetic nervous system. Elements derived from those systems (e.g., cortisol, catecholamines and neuropeptides) can impact the immune system and possible disease states. Skin provides a first line of defense against many environmental insults. A number of investigations have indicated that the skin is especially sensitive to psychological stress, and experimental evidence shows that the cutaneous innate and adaptive immune systems are affected by stressors. For example, psychological stress has been shown to reduce recovery time of the stratum corneum barrier after its removal (innate immunity) and alters antigen presentation by epidermal Langerhans cells (adaptive immunity). Moreover, psychological stress may trigger or exacerbate immune mediated dermatological disorders. Understanding how the activity of the psyche-nervous -immune system axis impinges on skin diseases may facilitate coordinated treatment strategies between dermatologists and psychiatrists. Herein, we will review the roles of the HPA axis and the sympathetic nervous system on the cutaneous immune response. We will selectively highlight how the interplay between psychological stress and the immune system affects atopic dermatitis and psoriasis.

Neuronal vulnerability, pathogenesis, and Parkinson's disease

Although there have been significant advances, pathogenesis in Parkinson's disease (PD) is still poorly understood. Potential clues about pathogenesis that have not been systematically pursued are suggested by the restricted pattern of neuronal pathology in the disease. In addition to dopaminergic neurons in the substantia nigra pars compacta (SNc), a significant number of other central and peripheral neuronal populations exhibit Lewy pathology (LP), phenotypic dysregulation, or frank degeneration in PD patients. Drawing on this literature, there appear to be a small number of risk factors contributing to vulnerability. These include autonomous activity, broad action potentials, low intrinsic calcium-buffering capacity, poorly myelinated long highly branched axons and terminal fields, and use of a monoamine neurotransmitter, often with the catecholamine-derived neuromelanin pigment. Of these phenotypic traits, only the physiological ones appear to provide a reachable therapeutic target at present.