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

Diverse stimuli induce piloerection and yield varied autonomic responses in humans

This research provides an in-depth exploration into the triggers and corresponding autonomic responses of piloerection, a phenomenon prevalent across various species. In non-human species, piloerection occurs in reaction to a variety of environmental changes, including social interactions and temperature shifts. However, its understanding in humans has been confined to emotional contexts. This is problematic because it reflects solely upon subjective experience rather than an objective response to the environment. Further, given our shared evolutionary paths, piloerection should function similarly in humans and other animals. I observed 1198 piloerection episodes from eight participants while simultaneously recording multiple autonomic and body temperature indices, finding that piloerection in humans can be elicited by thermal, tactile, and audio-visual stimuli with equal effectiveness. The data also revealed variations in cardiac reactivity measures: audio-visual piloerection was associated with greater sympathetic arousal, while tactile piloerection was linked to greater parasympathetic arousal. Despite prevailing notions of piloerection as a vestigial response in humans, it does respond to decreases in skin temperature and is associated with a rise in skin temperature during episodes. This research underscores that piloerection in humans is not purely vestigial, nor is it solely an affective response to emotional stimuli. Rather, it is best understood as a reflexive response to environmental changes, suggesting a shared functional similarity with other species.

Skin Innervation

All layers and appendages of the skin are densely innervated by afferent and efferent neurons providing sensory information and controlling skin perfusion and sweating. In mice, neuronal functions have been comprehensively linked to unique single-cell expression patterns and to characteristic arborization of nerve endings in skin and dorsal horn, whereas for humans, specific molecular markers for functional classes of afferent neurons are still lacking. Moreover, bidirectional communication between sensory neurons and local skin cells has become of particular interest, resulting in a broader physiological understanding of sensory function but also of trophic functions and immunomodulation in disease states.

Astragalus polysaccharide-containing 3D-printed scaffold for traumatized skin repair and proteomic study

Astragalus polysaccharide-containing 3D-printed scaffold shows great potential in traumatic skin repair. This study aimed to investigate its repairing effect and to combine it with proteomic technology to deeply resolve the related protein expression changes. Thirty SD rats were divided randomly into three groups (n = 10 per group): the sham-operated group, the model group and the scaffold group. Subsequently, we conducted a comparative analysis on trauma blood perfusion, trauma healing rate, histological changes, the expression of the YAP/TAZ signalling pathway and angiogenesis-related factors. Additionally, neonatal skin tissues were collected for proteomic analysis. The blood perfusion volume and wound healing recovery in the scaffold group were better than that in the model group (p < 0.05). The protein expression of STAT3, YAP, TAZ and expression of vascular-related factor A (VEGFA) in the scaffold group was higher than that in the model group (p < 0.05). Proteomic analysis showed that there were 207 differential proteins common to the three groups. Mitochondrial function, immune response, redox response, extracellular gap and ATP metabolic process were the main groups of differential protein changes. Oxidative phosphorylation, metabolic pathway, carbon metabolism, calcium signalling pathway, etc. were the main differential metabolic pathway change groups. Astragalus polysaccharide-containing 3D-printed scaffold had certain reversals of protein disorder. The Astragalus polysaccharide-containing 3D-printed scaffold may promote the VEGFs by activating the YAP/TAZ signalling pathway with the help of STAT3 into the nucleus, accelerating early angiogenesis of the trauma, correcting the protein disorder of the trauma and ultimately realizing the repair of the wound.

Neuroanatomy of the Cutaneous Nervous System Regarding Wound Healing

Wound healing is an important topic in modern medicine across many disciplines. Healing of all cutaneous wounds, whether accidentally sustained or intentionally created, requires the common yet complex set of interactions between the immune, circulatory, nervous, endocrine, and integumentary systems. Deficits in any of these systems or the molecular factors that mediate their communications can contribute to impaired healing of cutaneous wounds. While the stages of wound repair, angiogenesis, growth factors, and cytokines involved have been extensively studied, the role of the cutaneous nervous system in wound healing has not been well outlined. We have provided a basic overview of cutaneous innervation and wound repair for the dermatologic surgeon by outlining the normal cutaneous nervous anatomy and function and discussing the most important neuropeptides that mediate the wound healing process.

The mind-skin connection: A narrative review exploring the link between inflammatory skin diseases and psychological stress

Inflammatory skin diseases are known to negatively impact patient psychology, with individuals experiencing higher rates of stress and subsequent diminished quality of life, as well as mental health issues including anxiety and depression. Moreover, increased psychological stress has been found to exacerbate existing inflammatory skin diseases. The association between inflammatory skin diseases and psychological stress is a timely topic, and a framework to better understand the relationship between the two that integrates available literature is needed. In this narrative review article, we discuss potential neurobiological mechanisms behind psychological stress due to inflammatory skin diseases, focusing mainly on proinflammatory cytokines in the circulating system (the brain-gut-skin communications) and the default mode network in the brain. We also discuss potential descending pathways from the brain that lead to aggravation of inflammatory skin diseases due to psychological stress, including the central and peripheral hypothalamic-pituitary-adrenal axes, peripheral nerves and the skin barrier function.

Cutaneous-immuno-neuro-endocrine (CINE) system: A complex enterprise transforming skin into a super organ

Skin is now emerging as a complex realm of three chief systems viz. immune system, nervous system, and endocrine system. The cells involved in their intricate crosstalk, namely native skin cells, intra-cutaneous immune cells and cutaneous sensory neurons have diverse origin and distinct functions. However, recent studies have explored their role beyond their pre-defined functional boundaries, such that the cells shun their traditional functions and adopt unconventional roles. For example, the native skin cells, apart from providing for basic structural framework of skin, also perform special immune functions and participate in extensive neuro-endocrine circuitry, which were traditionally designated as functions of cutaneous resident immune cells and sensory neurons respectively. At the cellular level, this unique collaboration is brought out by special molecules called neuromediators including neurotransmitters, neuropeptides, neurotrophins, neurohormones and cytokines/chemokines. While this intricate crosstalk is essential for maintaining cutaneous homeostasis, its disruption is seen in various cutaneous diseases. Recent study models have led to a paradigm shift in our understanding of pathophysiology of many such disorders. In this review, we have described in detail the interaction of immune cells with neurons and native skin cells, role of neuromediators, the endocrine aspect in skin and current understanding of cutaneous neuro-immuno-endocrine loop in one of the commonest skin diseases, psoriasis. An accurate knowledge of this unique crosstalk can prove crucial in understanding the pathophysiology of different skin diseases and allow for generation of targeted therapeutic modalities.

Unparallel improvement patterns of dynamic wrinkles and skin quality after botulinum toxin type A treatment on the upper face

BACKGROUND

Botulinum toxin type A (BoNT-A) can not only reduce the dynamic wrinkles but also improve the skin quality. This study aims to quantitaively and comprehensively assess the improvement of dynamic wrinkles and skin quality following BoNT-A treatment on the upper face.

METHODS

Patients were recruited to receive BoNT-A treatment of the glabellar, frontal, and lateral periorbital wrinkles. Antera 3D camera was used to evaluate the skin quality and dynamic wrinkle severity. Follow-up visits were at 1 week, 1 month, 3 months, and 6 months after treatment. Different filters were utilized to quantitatively detect the severity of fine wrinkles (FWS), the volume of pores (PV), the roughness of skin texture (STR), and the severity of dynamic wrinkles (DWS).

RESULTS

Twenty-four participants (average 30.5 ± 7.2 years) were recruited. The significant improvement of PV, FWS, and STR in different areas usually maintained from 1 to 6 months after injections but of DWS only existed within 3 months. For each area, the improvement rates of FWS, PV, and STR peaked at 3 months or 6 months after treatment while the maximal improvement of DWS was observed at 1 month posttreatment.

CONCLUSION

After BoNT-A treatment for dynamic wrinkles on the upper face, the skin quality of target regions can also be ameliorated. The improvement of skin quality and dynamic wrinkles presented unparallel patterns. The former is with a slower onset but longer duration while the latter exhibits a more rapid onset but shorter duration.

Sympathetic System in Wound Healing: Multistage Control in Normal and Diabetic Skin

In this review, we discuss sympathetic regulation in normal and diabetic wound healing. Experimental denervation studies have confirmed that sympathetic nerve endings in skin have an important and complex role in wound healing. Vasoconstrictor neurons secrete norepinephrine (NE) and neuropeptide Y (NPY). Both mediators decrease blood flow and interact with inflammatory cells and keratinocytes. NE acts in an ambiguous way depending on receptor type. Beta2-adrenoceptors could be activated near sympathetic endings; they suppress inflammation and re-epithelialization. Alpha1- and alpha2-adrenoceptors induce inflammation and activate keratinocytes. Sudomotor neurons secrete acetylcholine (ACh) and vasoactive intestinal peptide (VIP). Both induce vasodilatation, angiogenesis, inflammation, keratinocytes proliferation and migration. In healthy skin, all effects are important for successful healing. In treatment of diabetic ulcers, mediator balance could be shifted in different ways. Beta2-adrenoceptors blockade and nicotinic ACh receptors activation are the most promising directions in treatment of diabetic ulcers with neuropathy, but they require further research.

Neuroendocrine signaling in the skin with a special focus on the epidermal neuropeptides

The skin, which is comprised of the epidermis, dermis, and subcutaneous tissue, is the largest organ in the human body and it plays a crucial role in the regulation of the body's homeostasis. These functions are regulated by local neuroendocrine and immune systems with a plethora of signaling molecules produced by resident and immune cells. In addition, neurotransmitters, endocrine factors, neuropeptides, and cytokines released from nerve endings play a central role in the skin's responses to stress. These molecules act on the corresponding receptors in an intra-, juxta-, para-, or autocrine fashion. The epidermis as the outer most component of skin forms a barrier directly protecting against environmental stressors. This protection is assured by an intrinsic keratinocyte differentiation program, pigmentary system, and local nervous, immune, endocrine, and microbiome elements. These constituents communicate cross-functionally among themselves and with corresponding systems in the dermis and hypodermis to secure the basic epidermal functions to maintain local (skin) and global (systemic) homeostasis. The neurohormonal mediators and cytokines used in these communications regulate physiological skin functions separately or in concert. Disturbances in the functions in these systems lead to cutaneous pathology that includes inflammatory (i.e., psoriasis, allergic, or atopic dermatitis, etc.) and keratinocytic hyperproliferative disorders (i.e., seborrheic and solar keratoses), dysfunction of adnexal structure (i.e., hair follicles, eccrine, and sebaceous glands), hypersensitivity reactions, pigmentary disorders (vitiligo, melasma, and hypo- or hyperpigmentary responses), premature aging, and malignancies (melanoma and nonmelanoma skin cancers). These cellular, molecular, and neural components preserve skin integrity and protect against skin pathologies and can act as "messengers of the skin" to the central organs, all to preserve organismal survival.

The impact of perceived stress on the hair follicle: Towards solving a psychoneuroendocrine and neuroimmunological puzzle

While popular belief harbors little doubt that perceived stress can cause hair loss and premature graying, the scientific evidence for this is arguably much thinner. Here, we investigate whether these phenomena are real, and show that the cyclic growth and pigmentation of the hair follicle (HF) provides a tractable model system for dissecting how perceived stress modulates aspects of human physiology. Local production of stress-associated neurohormones and neurotrophins coalesces with neurotransmitters and neuropeptides released from HF-associated sensory and autonomic nerve endings, forming a complex local stress-response system that regulates perifollicular neurogenic inflammation, interacts with the HF microbiome and controls mitochondrial function. This local system integrates into the central stress response systems, allowing the study of systemic stress responses affecting organ function by quantifying stress mediator content of hair. Focusing on selected mediators in this "brain-HF axis" under stress conditions, we distill general principles of HF dysfunction induced by perceived stress.

The physiological study of emotional piloerection: A systematic review and guide for future research

This paper provides an accessible review of the biological and psychological evidence to guide new and experienced researchers in the study of emotional piloerection in humans. A limited number of studies have attempted to examine the physiological and emotional correlates of piloerection in humans. However, no review has attempted to collate this evidence to guide the field as it moves forward. We first discuss the mechanisms and function of non-emotional and emotional piloerection in humans and animals. We discuss the biological foundations of piloerection as a means to understand the similarities and differences between emotional and non-emotional piloerection. We then present a systematic qualitative review (k = 24) in which we examine the physiological correlates of emotional piloerection. The analysis revealed that indices of sympathetic activation are abundant, suggesting emotional piloerection occurs with increased (phasic) skin conductance and heart rate. Measures of parasympathetic activation are lacking and no definite conclusions can be drawn. Additionally, several studies examined self-reported emotional correlates, and these correlates are discussed in light of several possible theoretical explanations for emotional piloerection. Finally, we provide an overview of the methodological possibilities available for the study of piloerection and we highlight some pressing questions researchers may wish to answer in future studies.

Sensory and autonomic innervation of the local tissues at traditional acupuncture point locations GB14, ST2 and ST6

OBJECTIVE

To visualize and compare the sensory and autonomic innervation of the local tissues at the sites of different traditional acupuncture points in the rat forehead and face by histochemical examination.

METHODS

GB14 (Yangbai), ST2 (Sibai) and ST6 (Jiache) were selected as the representative traditional acupuncture points in this study, and the local tissues at these sites were dissected in rats after perfusion followed by double or triple fluorescent histochemical staining. Here, calcitonin gene-related peptide (CGRP), tyrosine hydroxylase (TH) and vesicular acetylcholine transporter (VAChT) were used to label the sensory, sympathetic and parasympathetic nerve fibers, respectively.

RESULTS

The CGRP⁺ sensory, TH⁺ sympathetic and VAChT⁺ parasympathetic nerve fibers were simultaneously demonstrated in the local tissues at GB14, ST2 and ST6. Although the three kinds of nerve fibers ran in parallel or intermingled with each other, by the analysis from the view of three-dimensional reconstruction, it was clear that each of them distributed in an independent pattern to their corresponding target tissues including the blood vessels, hair follicles, arrector pili and subcutaneous muscles, as well as sebaceous glands.

CONCLUSION

Our study demonstrated the sensory and autonomic innervation of the local tissues at GB14, ST2 and ST6, providing neurochemical evidence indicating that the CGRP⁺ sensory, TH⁺ sympathetic and VAChT⁺ parasympathetic nerve fibers form a neural network at these point locations that may respond to acupuncture stimulation.

Immunohistological study of the density and distribution of human penile neural tissue: gradient hypothesis

Immunohistological patterns of density and distribution of neural tissue in the human penis, including the prepuce, are not fully characterized, and effects of circumcision (partial or total removal of the penile prepuce) on penile sexual sensation are controversial. This study analyzed extra- and intracavernosal innervation patterns on the main penile axes using formalin-fixed, paraffin-embedded human adult and fetal penile tissues, single- and double-staining immunohistochemistry and a variety of neural and non-neural markers, with a special emphasis on the prepuce and potential sexual effects of circumcision. Immunohistochemical profiles of neural structures were determined and the most detailed immunohistological characterizations to date of preputial nerve supply are provided. The penile prepuce has a highly organized, dense, afferent innervation pattern that is manifest early in fetal development. Autonomically, it receives noradrenergic sympathetic and nitrergic parasympathetic innervation. Cholinergic nerves are also present. We observed cutaneous and subcutaneous neural density distribution biases across our specimens towards the ventral prepuce, including a region corresponding in the adult anatomical position (penis erect) to the distal third of the ventral penile aspect. We also describe a concept of innervation gradients across the longitudinal and transverse penile axes. Results are discussed in relation to the specialized literature. An argument is made that neuroanatomic substrates underlying unusual permanent penile sensory disturbances post-circumcision are related to heightened neural levels in the distal third of the ventral penile aspect, which could potentially be compromised by deep incisions during circumcision.

Current Insights Into the Role of Neuropeptide Y in Skin Physiology and Pathology

Neuropeptide Y is widely distributed within the body and has long been implicated as a contributor to skin disease based on the correlative clinical data. However, until recently, there have been few empirical investigations to determine whether NPY has a pathophysiological role in the skin. Due to appearance-altering phenotypes of atopic dermatitis, psoriasis, and vitiligo, those suffering from these diseases often face multiple forms of negative social attention. This often results in psychological stress, which has been shown to exacerbate inflammatory skin diseases - creating a vicious cycle that perpetuates disease. This has been shown to drive severe depression, which has resulted in suicidal ideation being a comorbidity of these diseases. Herein, we review what is currently known about the associations of NPY with skin diseases and stress. We also review and provide educated guessing what the effects NPY can have in the skin. Inflammatory skin diseases can affect physical appearance to have significant, negative impacts on quality of life. No cure exists for these conditions, highlighting the need for identification of novel proteins/neuropetides, like NPY, that can be targeted therapeutically. This review sets the stage for future investigations into the role of NPY in skin biology and pathology to stimulate research on therapeutic targeting NPY signaling in order to combat inflammatory skin diseases.

Signs of sympathetic and endothelial cell activation in the skin of patients with restless legs syndrome

OBJECTIVES

To evaluate skin biopsies of patients with early- and late onset restless legs syndrome (RLS) for concomitant small fiber neuropathy (SFN) and to determine cutaneous sympathetic innervation and microvascularization in comparison to healthy individuals.

METHODS

Density of intraepidermal nerve fibers (IENFD), adrenergic nerve fibers and dermal capillaries was analyzed by immunofluorescence for PGP9.5, tyrosine hydroxylase and endothelial markers CD31 and CD105 in skin biopsies of 11 individuals with RLS and 8 age- and sex-matched controls.

RESULTS

IENFD did not differ between RLS and controls, but two RLS patients with comorbid impaired glucose metabolism fulfilled morphometric criteria of SFN according to published normative values. In contrast, dermal nerve bundles of RLS patients showed an increased density of tyrosine hydroxylase⁺ adrenergic nerve fibers (p < 0.005). Moreover, an increased ratio between immature CD105⁺ and mature CD31⁺ endothelial cells within dermal capillaries was observed in RLS (p < 0.02).

CONCLUSIONS

SFN, as a potential contributing factor for RLS, should be considered in patients with predisposing comorbidities presenting with burning or shooting pain, dysesthesias and impaired sensory and temperature perception. Evidence of an increased adrenergic innervation of the skin in RLS patients is in accordance with sympathetic hyperactivity while signs of endothelial cell activation may reflect an adaptive response to tissue hypoxia.

α-Synuclein Deposition in Sympathetic Nerve Fibers in Genetic Forms of Parkinson's Disease

BACKGROUND

Cytoplasmic inclusions of α-synuclein (α-syn) in brainstem neurons are characteristic of idiopathic Parkinson's disease (PD). PD also entails α-syn buildup in sympathetic nerves. Among genetic forms of PD, the relative extents of sympathetic intraneuronal accumulation of α-syn have not been reported.

OBJECTIVE

This cross-sectional observational study compared magnitudes of intraneuronal deposition of α-syn in common and rare genetic forms of PD.

METHODS

α-Syn deposition was quantified by the α-syn-tyrosine hydroxylase colocalization index in C2 cervical skin biopsies from 65 subjects. These included 30 subjects with pathogenic mutations in SNCA (n = 3), PRKN [biallelic (n = 7) and monoallelic (n = 3)], LRRK2 (n = 7), GBA (n = 7), or PARK7/DJ1 [biallelic (n = 1) and monoallelic (n = 2)]. Twenty-five of the mutation carriers had PD and five did not. Data were also analyzed from 19 patients with idiopathic PD and 16 control participants.

RESULTS

α-Syn deposition varied as a function of genotype (F = 16.7, P < 0.0001). It was above the control range in 100% of subjects with SNCA mutations, 100% with LRRK2 mutations, 95% with idiopathic PD, 83% with GBA mutations, and 0% with biallelic PRKN mutations. α-Syn deposition in the biallelic PRKN group was significantly higher than in the control group. In addition, patients with biallelic PRKN mutations had higher α-syn deposition than their unaffected siblings.

CONCLUSIONS

Individuals with SNCA, DJ-1, LRRK2, or GBA mutations have substantial intraneuronal α-syn deposition in sympathetic noradrenergic nerves in skin biopsies, whereas those with biallelic PRKN mutations do not. Biallelic PRKN patients may have mildly increased α-syn deposition compared with control subjects. © 2021 International Parkinson and Movement Disorder Society.

Convergence of peptidergic and non-peptidergic protein markers in the human dorsal root ganglion and spinal dorsal horn

Peripheral sensory neurons are characterized by their size, molecular profiles, and physiological responses to specific stimuli. In mouse, the peptidergic and non-peptidergic subsets of nociceptors are distinct and innervate different lamina of the spinal dorsal horn. The unique molecular signature and neuroanatomical organization of these neurons supports a labeled line theory for certain types of nociceptive stimuli. However, long-standing evidence supports the polymodal nature of nociceptors in many species. We have recently shown that the peptidergic marker, CGRP, and the non-peptidergic marker, P2X3R, show largely overlapping expression at the mRNA level in human dorsal root ganglion (DRG). Herein, our aim was to assess the protein distribution of nociceptor markers, including their central projections, in the human DRG and spinal cord. Using DRGs obtained from organ donors, we observed that CGRP and P2X3R were co-expressed by approximately 33% of human DRG neurons and TrpV1 was expressed in ~60% of human DRG neurons. In the dorsal spinal cord, CGRP, P2X3R, TrpV1, and Nav1.7 proteins stained the entirety of lamina 1-2, with only P2XR3 showing a gradient of expression. This was confirmed by measuring the size of the substantia gelatinosa using Hematoxylin and Eosin staining of adjacent sections. Our findings are consistent with the known polymodal nature of most primate nociceptors and indicate that the central projection patterns of nociceptors are different between mice and humans. Elucidating how human nociceptors connect to subsets of dorsal horn neurons will be important for understanding the physiological consequences of these species differences.

Piloerection is not a reliable physiological correlate of awe

In scientific and popular literature, piloerection (e.g. goosebumps) is often claimed to accompany the experience of awe, though this correlation has not been tested empirically. Using two pre-registered and independently collected samples (N = 210), we examined the objective physiological occurrence of piloerection in response to awe-inducing stimuli. Stimuli were selected to satisfy three descriptors of awe, including perceptual vastness, virtual reality, and expectancy-violating events. The stimuli reliably elicited self-reported awe to a great extent, in line with previous research. However, awe-inducing stimuli were not associated with the objective occurrence of piloerection. While participants self-reported high levels of goosebumps and "the chills," there was no physical evidence of this response. These results suggest that piloerection is not reliably connected to the experience of awe-at least using stimuli known to elicit awe in an experimental setting.

The diversity of neuronal phenotypes in rodent and human autonomic ganglia

Selective sympathetic and parasympathetic pathways that act on target organs represent the terminal actors in the neurobiology of homeostasis and often become compromised during a range of neurodegenerative and traumatic disorders. Here, we delineate several neurotransmitter and neuromodulator phenotypes found in diverse parasympathetic and sympathetic ganglia in humans and rodent species. The comparative approach reveals evolutionarily conserved and non-conserved phenotypic marker constellations. A developmental analysis examining the acquisition of selected neurotransmitter properties has provided a detailed, but still incomplete, understanding of the origins of a set of noradrenergic and cholinergic sympathetic neuron populations, found in the cervical and trunk region. A corresponding analysis examining cholinergic and nitrergic parasympathetic neurons in the head, and a range of pelvic neuron populations, with noradrenergic, cholinergic, nitrergic, and mixed transmitter phenotypes, remains open. Of particular interest are the molecular mechanisms and nuclear processes that are responsible for the correlated expression of the various genes required to achieve the noradrenergic phenotype, the segregation of cholinergic locus gene expression, and the regulation of genes that are necessary to generate a nitrergic phenotype. Unraveling the neuron population-specific expression of adhesion molecules, which are involved in axonal outgrowth, pathway selection, and synaptic organization, will advance the study of target-selective autonomic pathway generation.

Clinical spectrum and diagnosis of diabetic neuropathies

Neuropathy is the most prevalent microvascular complication of diabetes mellitus; it encompasses distal symmetric polyneuropathy, autonomic neuropathy, radiculoplexus neuropathy, mononeuropathy, and treatment-induced neuropathy. The prevalence rate of diabetic neuropathy in Korea was reported to be approximately 43%, which is similar to rates in other countries. However, the precise pathogenic mechanism underlying diabetic neuropathy is still obscure, and many clinical trials have failed to develop methods to prevent or reduce the progression of diabetic neuropathy. Nevertheless, early diagnosis and proper management of diabetic neuropathy are essential to alleviate disabling symptoms and to improve the quality of life of patients. This review discusses clinical manifestations and classification of diabetic neuropathies, bedside neurological examination, and electrophysiological tests.

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.

Clinical diagnosis and management of small fiber neuropathy: an update on best practice

INTRODUCTION

Small fiber neuropathy (SFN) is a heterogeneous group of disorders affecting thin myelinated Aδ and unmyelinated C fibers. Common symptoms include neuropathic pain and autonomic disturbances, and the typical clinical presentation is that of a length-dependent polyneuropathy, although other distributions could be present.

AREA COVERED

This review focuses on several aspects of SFN including etiology, clinical presentation, diagnostic criteria and tests, management, and future perspectives. Diagnostic challenges are discussed, encompassing the role of accurate and standardized assessment of symptoms and signs and providing clues for the clinical practice. The authors discuss the evidence in support of skin biopsy and quantitative sensory testing as diagnostic tests and present an overview of other diagnostic techniques to assess sensory and autonomic fibers dysfunction. The authors also suggest a systematic approach to the etiology including a set of laboratory tests and genetic examinations of sodium channelopathies and other rare conditions that might drive the therapeutic approach based on underlying cause or symptoms treatment.

EXPERT OPINION

SFN provides a useful model for neuropathic pain whose known mechanisms and cause could pave the way toward personalized treatments.

Skin Biopsy May Help to Distinguish Multiple System Atrophy-Parkinsonism from Parkinson's Disease With Orthostatic Hypotension

BACKGROUND

The differential diagnosis between multiple system atrophy parkinsonism type (MSA-P) and Parkinson's disease with orthostatic hypotension (PD+OH) is difficult because the 2 diseases have a similar clinical picture. The aim of this study is to distinguish MSA-P from PD+OH by immunostaining for abnormal phosphorylated α-synuclein at serine 129 (p-syn) in cutaneous nerves.

METHOD

We recruited 50 patients with parkinsonism and chronic orthostatic hypotension: 25 patients fulfilled the diagnostic criteria for MSA-P and 25 patients for PD+OH. The patients underwent a skin biopsy from the cervical area, thigh, and leg to analyze somatic and autonomic skin innervation and p-syn in skin nerves.

RESULTS

Intraneural p-syn positivity was found in 72% of patients with MSA-P, mainly in distal skin sites. More important, p-syn deposits in MSA-P differed from PD+OH because they were mainly found in somatic fibers of subepidermal plexi, whereas scant autonomic fiber involvement was found in only 3 patients. All patients with PD+OH displayed widely distributed p-syn deposits in the autonomic skin fibers of proximal and distal skin sites, whereas somatic fibers were affected only slightly in 4 patients with PD+OH. Skin innervation mirrored p-syn deposits because somatic innervation was mainly reduced in MSA-P. Sympathetic innervation was damaged in PD+OH but fairly preserved in MSA-P.

CONCLUSIONS

The p-syn in cutaneous nerves allows the differentiation of MSA-P from PD+OH; MSA-P mainly shows somatic fiber involvement with relatively preserved autonomic innervation; and by contrast, PD+OH displays prevalent abnormal p-syn deposits and denervation in autonomic postganglionic nerves. © 2020 International Parkinson and Movement Disorder Society.