Induction of cholinergic function in cultured sympathetic neurons by periosteal cells: cellular mechanisms

Using tissue clearing and light sheet fluorescence microscopy for the three-dimensional analysis of sensory and sympathetic nerve endings that innervate bone and dental tissue of mice

Bone and dental tissues are richly innervated by sensory and sympathetic neurons. However, the characterization of the morphology, molecular phenotype, and distribution of nerves that innervate hard tissue has so far mostly been limited to thin histological sections. This approach does not adequately capture dispersed neuronal projections due to the loss of important structural information during three-dimensional (3D) reconstruction. In this study, we modified the immunolabeling-enabled imaging of solvent-cleared organs (iDISCO/iDISCO+) clearing protocol to image high-resolution neuronal structures in whole femurs and mandibles collected from perfused C57Bl/6 mice. Axons and their nerve terminal endings were immunolabeled with antibodies directed against protein gene product 9.5 (pan-neuronal marker), calcitonin gene-related peptide (peptidergic nociceptor marker), or tyrosine hydroxylase (sympathetic neuron marker). Volume imaging was performed using light sheet fluorescence microscopy. We report high-quality immunolabeling of the axons and nerve terminal endings for both sensory and sympathetic neurons that innervate the mouse femur and mandible. Importantly, we are able to follow their projections through full 3D volumes, highlight how extensive their distribution is, and show regional differences in innervation patterns for different parts of each bone (and surrounding tissues). Mapping the distribution of sensory and sympathetic axons, and their nerve terminal endings, in different bony compartments may be important in further elucidating their roles in health and disease.

Hallmarks of peripheral nerve function in bone regeneration

Skeletal tissue is highly innervated. Although different types of nerves have been recently identified in the bone, the crosstalk between bone and nerves remains unclear. In this review, we outline the role of the peripheral nervous system (PNS) in bone regeneration following injury. We first introduce the conserved role of nerves in tissue regeneration in species ranging from amphibians to mammals. We then present the distribution of the PNS in the skeletal system under physiological conditions, fractures, or regeneration. Furthermore, we summarize the ways in which the PNS communicates with bone-lineage cells, the vasculature, and immune cells in the bone microenvironment. Based on this comprehensive and timely review, we conclude that the PNS regulates bone regeneration through neuropeptides or neurotransmitters and cells in the peripheral nerves. An in-depth understanding of the roles of peripheral nerves in bone regeneration will inform the development of new strategies based on bone-nerve crosstalk in promoting bone repair and regeneration.

CRLF1 and CLCF1 in Development, Health and Disease

Cytokines and their receptors have a vital function in regulating various processes such as immune function, inflammation, haematopoiesis, cell growth and differentiation. The interaction between a cytokine and its specific receptor triggers intracellular signalling cascades that lead to altered gene expression in the target cell and consequent changes in its proliferation, differentiation, or activation. In this review, we highlight the role of the soluble type I cytokine receptor CRLF1 (cytokine receptor-like factor-1) and the Interleukin (IL)-6 cytokine CLCF1 (cardiotrophin-like cytokine factor 1) during development in physiological and pathological conditions with particular emphasis on Crisponi/cold-induced sweating syndrome (CS/CISS) and discuss new insights, challenges and possibilities arising from recent studies.

The sympathies of the body: functional organization and neuronal differentiation in the peripheral sympathetic nervous system

During the last 30 years, our understanding of the development and diversification of postganglionic sympathetic neurons has dramatically increased. In parallel, the list of target structures has been critically extended from the cardiovascular system and selected glandular structures to metabolically relevant tissues such as white and brown adipose tissue, lymphoid tissues, bone, and bone marrow. A critical question now emerges for the integration of the diverse sympathetic neuron classes into neural circuits specific for these different target tissues to achieve the homeostatic regulation of the physiological ends affected.

Neurobiology of Cancer: the Role of β-Adrenergic Receptor Signaling in Various Tumor Environments

The development and progression of cancer depends on both tumor micro- and macroenvironments. In addition, psychosocial and spiritual “environments” might also affect cancer. It has been found that the nervous system, via neural and humoral pathways, significantly modulates processes related to cancer at the level of the tumor micro- and macroenvironments. The nervous system also mediates the effects of psychosocial and noetic factors on cancer. Importantly, data accumulated in the last two decades have clearly shown that effects of the nervous system on cancer initiation, progression, and the development of metastases are mediated by the sympathoadrenal system mainly via β-adrenergic receptor signaling. Here, we provide a new complex view of the role of β-adrenergic receptor signaling within the tumor micro- and macroenvironments as well as in mediating the effects of the psychosocial and spiritual environments. In addition, we describe potential preventive and therapeutic implications.

Clearing method for 3-dimensional immunofluorescence of osteoarthritic subchondral human bone reveals peripheral cholinergic nerves

The cholinergic system plays a major anti-inflammatory role in many diseases through acetylcholine (Ach) release after vagus nerve stimulation. Osteoarthritis (OA) is associated with local low-grade inflammation, but the regulatory mechanisms are unclear. Local Ach release could have anti-inflammatory activity since articular cells express Ach receptors involved in inflammatory responses. Using the 3DISCO clearing protocol that allows whole-sample 3-dimensional (3D) analysis, we cleared human OA cartilage-subchondral bone samples to search for cholinergic nerve fibres able to produce Ach locally. We analysed 3 plugs of knee cartilage and subchondral bone from 3 OA patients undergoing arthroplasty. We found no nerves in the superficial and intermediate articular cartilage layers, as evidenced by the lack of Peripherin staining (a peripheral nerves marker). Conversely, peripheral nerves were found in the deepest layer of cartilage and in subchondral bone. Some nerves in the subchondral bone samples were cholinergic because they coexpressed peripherin and choline acetyltransferase (ChAT), a specific marker of cholinergic nerves. However, no cholinergic nerves were found in the cartilage layers. It is therefore feasible to clear human bone to perform 3D immunofluorescence. Human OA subchondral bone is innervated by cholinergic fibres, which may regulate local inflammation through local Ach release.

Nerves in Bone: Evolving Concepts in Pain and Anabolism

The innervation of bone has been described for centuries, and our understanding of its function has rapidly evolved over the past several decades to encompass roles of subtype-specific neurons in skeletal homeostasis. Current research has been largely focused on the distribution and function of specific neuronal populations within bone, as well as their cellular and molecular relationships with target cells in the bone microenvironment. This review provides a historical perspective of the field of skeletal neurobiology that highlights the diverse yet interconnected nature of nerves and skeletal health, particularly in the context of bone anabolism and pain. We explore what is known regarding the neuronal subtypes found in the skeleton, their distribution within bone compartments, and their central projection pathways. This neuroskeletal map then serves as a foundation for a comprehensive discussion of the neural control of skeletal development, homeostasis, repair, and bone pain. Active synthesis of this research recently led to the first biotherapeutic success story in the field. Specifically, the ongoing clinical trials of anti-nerve growth factor therapeutics have been optimized to titrated doses that effectively alleviate pain while maintaining bone and joint health. Continued collaborations between neuroscientists and bone biologists are needed to build on this progress, leading to a more complete understanding of neural regulation of the skeleton and development of novel therapeutics. © 2019 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals, Inc.

Periosteum Metabolism and Nerve Fiber Positioning Depend on Interactions between Osteoblasts and Peripheral Innervation in Rat Mandible

The sympathetic nervous system controls bone remodeling by regulating bone formation and resorption. How nerves and bone cells influence each other remains elusive. Here we modulated the content or activity of the neuropeptide Vasoactive Intestinal Peptide to investigate nerve-bone cell interplays in the mandible periosteum by assessing factors involved in nerve and bone behaviors. Young adult rats were chemically sympathectomized or treated with Vasoactive Intestinal Peptide or Vasoactive Intestinal Peptide_10-28, a receptor antagonist. Sympathectomy depleted the osteogenic layer of the periosteum in neurotrophic proNerve Growth Factor and neurorepulsive semaphorin3a; sensory Calcitonin-Gene Related Peptide-positive fibers invaded this layer physiologically devoid of sensory fibers. In the periosteum non-osteogenic layer, sympathectomy activated mast cells to release mature Nerve Growth Factor while Calcitonin-Gene Related Peptide-positive fibers increased. Vasoactive Intestinal Peptide treatment reversed sympathectomy effects. Treating intact animals with Vasoactive Intestinal Peptide increased proNerve Growth Factor expression and stabilized mast cells. Vasoactive Intestinal Peptide_10-28 treatment mimicked sympathectomy effects. Our data suggest that sympathetic Vasoactive Intestinal Peptide modulate the interactions between nervous fibers and bone cells by tuning expressions by osteogenic cells of factors responsible for mandible periosteum maintenance while osteogenic cells keep nervous fibers at a distance from the bone surface.

Development of non-catecholaminergic sympathetic neurons in para- and prevertebral ganglia of cats

Expression of vasoactive intestinal peptide (VIP), neuronal nitric oxide synthase (nNOS), choline acetyltransferase (ChAT) and calcitonin gene-related peptide (CGRP) in the sympathetic ganglia was investigated by immunohistochemistry in the superior cervical ganglion (SCG), stellate ganglion (SG) and celiac ganglion (CG) from cats of different ages (newborn, 10-day-old, 20-day-old, 30-day-old and 2-month-old). Non-catecholaminergic TH-negative VIP-immunoreactive (IR) and nNOS-IR sympathetic ganglionic neurons are present from the moment of birth. In all studied age groups, substantial populations of VIP-IR (up to 9.8%) and nNOS-IR cells (up to 8.3%) was found in the SG, with a much smaller population found in the SCG (<1%) and only few cells observed in the CG. The percentage of nNOS-IR and VIP-IR neurons in the CG and SCG did not significantly change during development. The proportion of nNOS-IR and VIP-IR neuron profiles in the SG increased in first 20 days of life from 2.3±0.15% to 8.3±0.56% and from 0.3±0.05% to 9.2±0.83%, respectively. In the SG, percentages of nNOS-IR sympathetic neurons colocalizing VIP increased in the first 20 days of life. ChAT-IR and CGRP-IR neurons were not observed in the sympathetic ganglia of newborn animals and did not appear until 10 days after birth. In the SG of newborn and 10-day-old kittens, the majority of NOS-IR neurons were calbindin (CB)-IR, whereas in the SCG and CG of cats of all age groups and in the SG of 30-day-old and older kittens, the vast majority of NOS-IR neurons lacked CB. We conclude that the development of various non-catecholaminergic neurons in different sympathetic ganglia has its own time dynamics and is concluded at the end of the second month of life.

The transcription factor Hmx1 and growth factor receptor activities control sympathetic neurons diversification

The sympathetic nervous system relies on distinct populations of neurons that use noradrenaline or acetylcholine as neurotransmitter. We show that fating of the sympathetic lineage at early stages results in hybrid precursors from which, genetic cell-lineage tracing reveals, all types progressively emerge by principal mechanisms of maintenance, repression and induction of phenotypes. The homeobox transcription factor HMX1 represses Tlx3 and Ret, induces TrkA and maintains tyrosine hydroxylase (Th) expression in precursors, thus driving segregation of the noradrenergic sympathetic fate. Cholinergic sympathetic neurons develop through cross-regulatory interactions between TRKC and RET in precursors, which lead to Hmx1 repression and sustained Tlx3 expression, thereby resulting in failure of TrkA induction and loss of maintenance of Th expression. Our results provide direct evidence for a model in which diversification of noradrenergic and cholinergic sympathetic neurons is based on a principle of cross-repressive functions in which the specific cell fates are directed by an active suppression of the expression of transcription factors and receptors that direct the alternative fate.

Interneuronal synapses formed by motor neurons appear to be glutamatergic

Acetylcholine release at motor neuron synapses has been long established; however, recent discoveries indicate that synaptic transmission by motor neurons is more complex than previously thought. Using whole-cell patch clamp, we show that spontaneous excitatory postsynaptic currents of rat motor neurons in primary ventral horn cultures are entirely glutamatergic, although the cells respond to exogenous acetylcholine. Motor neurons in cultures express the vesicular glutamate transporter VGlut2, and culturing motor neurons for weeks with glutamate receptors blocked upregulates glutamate signaling without increasing cholinergic signaling. In spinal cord slices, motor neurons showed no decrease in spontaneous excitatory synaptic potentials after blocking acetylcholine receptors. Our results suggest that motor neuron synapses formed on other neurons are largely glutamatergic in culture and the spinal cord.

Different sympathetic pathways control the metabolism of distinct bone envelopes

Bone remodeling, the mechanism that modulates bone mass adaptation, is controlled by the sympathetic nervous system through the catecholaminergic pathway. However, resorption in the mandible periosteum envelope is associated with cholinergic Vasoactive Intestinal Peptide (VIP)-positive nerve fibers sensitive to sympathetic neurotoxics, suggesting that different sympathetic pathways may control distinct bone envelopes. In this study, we assessed the role of distinct sympathetic pathways on rat femur and mandible envelopes. To this goal, adult male Wistar rats were chemically sympathectomized or treated with agonists/antagonists of the catecholaminergic and cholinergic pathways; femora and mandibles were sampled. Histomorphometric analysis showed that sympathectomy decreased the number of preosteoclasts and RANKL-expressing osteoblasts in mandible periosteum but had no effect on femur trabecular bone. In contrast, pharmacological stimulation or repression of the catecholaminergic cell receptors impacted the femur trabecular bone and mandible endosteal retromolar zone. VIP treatment of sympathectomized rats rescued the disturbances of the mandible periosteum and alveolar wall whereas the cholinergic pathway had no effect on the catecholaminergic-dependent envelopes. We also found that VIP receptor-1 was weakly expressed in periosteal osteoblasts in the mandible and was increased by VIP treatment, whereas osteoblasts of the retromolar envelope that was innervated only by tyrosine hydroxylase-immunoreactive fibers, constitutively expressed beta-2 adrenergic receptors. These data highlight the complexity of the sympathetic control of bone metabolism. Both the embryological origin of the bone (endochondral for the femur, membranous for the mandibular periosteum and the socket wall) and environmental factors specific to the innervated envelope may influence the phenotype of the sympathetic innervation. We suggest that an origin-dependent imprint of bone cells through osteoblast-nerve interactions determines the type of autonomous system innervating a particular bone envelope.

Calcium signaling in neuronal development

The development of the nervous system involves the generation of a stunningly diverse array of neuronal subtypes that enable complex information processing and behavioral outputs. Deciphering how the nervous system acquires and interprets information and orchestrates behaviors will be greatly enhanced by the identification of distinct neuronal circuits and by an understanding of how these circuits are formed, changed, and/or maintained over time. Addressing these challenging questions depends in part on the ability to accurately identify and characterize the unique neuronal subtypes that comprise individual circuits. Distinguishing characteristics of neuronal subgroups include but are not limited to neurotransmitter phenotype, dendritic morphology, the identity of synaptic partners, and the expression of constellations of subgroup-specific proteins, including ion channel subtypes.

Non-neuronal regulation and repertoire of cholinergic receptors in organs

Many studies on the cholinergic pathway have indicated that cholinergic receptors, which are widely expressed in various cells, play an important role in all body organs. In this review, we present the concept that cholinergic responses are regulated through a neuronal or non-neuronal mechanism. The neuronal mechanism is a system in which acetylcholine binds to cholinergic receptors on target cells through the nerves. In the non-neuronal mechanism, acetylcholine, produced by neighboring cells in an autocrine/paracrine manner, binds to cholinergic receptors on target cells. Both mechanisms subsequently lead to physiological and pathophysiological responses. We also investigated the subunits/subtypes of cholinergic receptors on target cells, physiological and pathophysiological responses of the organs via cholinergic receptors, and extracellular factors that alter the subtypes/subunits of cholinergic receptors. Collectively, this concept will elucidate how cholinergic responses occur and will help us conduct further experiments to develop new therapeutic agents.

Functional role of acetylcholine and the expression of cholinergic receptors and components in osteoblasts

Recent studies have indicated that acetylcholine (ACh) plays a vital role in various tissues, while the role of ACh in bone metabolism remains unclear. Here we demonstrated that ACh induced cell proliferation and reduced alkaline phosphatase (ALP) activity via nicotinic (nAChRs) and muscarinic acetylcholine receptors (mAChRs) in osteoblasts. We detected mRNA expression of several nAChRs and mAChRs. Furthermore, we showed that cholinergic components were up-regulated and subunits/subtypes of acetylcholine receptors altered during osteoblast differentiation. To our knowledge, this is the first report demonstrating that osteoblasts express specific acetylcholine receptors and cholinergic components and that ACh plays a possible role in regulating the proliferation and differentiation of osteoblasts.

Generating diversity: Mechanisms regulating the differentiation of autonomic neuron phenotypes

Sympathetic and parasympathetic postganglionic neurons innervate a wide range of target tissues. The subpopulation of neurons innervating each target tissue can express unique combinations of neurotransmitters, neuropeptides, ion channels and receptors, which together comprise the chemical phenotype of the neurons. The target-specific chemical phenotype shown by autonomic postganglionic neurons arises during development. In this review, we examine the different mechanisms that generate such a diversity of neuronal phenotypes from the pool of apparently homogenous neural crest progenitor cells that form the sympathetic ganglia. There is evidence that the final chemical phenotype of autonomic postganglionic neurons is generated by both signals at the level of the cell body that trigger cell-autonomous programs, as well as signals from the target tissues they innervate.

Re-innervation pattern of the 'neovagina' created from the bladder flap in patients with Mayer-Rokitanski-Kistner-Hauser syndrome: an immunochemical study

BACKGROUND

Cystovaginoplasty (CVP) is a method of vaginal reconstruction in women with Mayer-Rokitansky-Kistner-Hauser Syndrome (MRKHS). The neo-vagina allows normal sexual intercourses, but after CVP, the sexual life of patients with MRKHS does not differ significantly from normal females. Therefore, we decided to elucidate the pattern of sensory re-innervation of the bladder flap used for the surgery.

METHODS

Biopsies were taken from vaginal vestibule and urinary bladder during the CVP and 1 year later in four patients with MRKHS. The following neurotransmitters were studied calcitonin gene-related peptide (CGRP), galanin (GAL), vasoactive intestinal polypeptide (VIP) and pituitary adenylate cyclase-activating peptide (PACAP).

RESULTS

CGRP and PACAP nerve fibres were sparse under the urothelium and in submucosal layer of the neovagina, they were more numerous around blood vessels and in the vicinity of smooth muscles. This was similar to the pattern observed in the urinary bladder. VIP- and GAL-positive nerve fibres were most numerous in the submucosa around blood vessels and in smooth muscle bundles of neovagina. They were distinctly less numerous beneath the epithelium. This innervation pattern mimicked that seen in normal vagina and in vaginal vestibule of patients with MRKHS.

CONCLUSIONS

Our findings demonstrate considerable nervous system plasticity in the bladder flap. Distribution of presumably sensory CGRP and PACAP immunoreactive nerve fibers was similar to the pattern observed within the intact bladder wall, and VIP or GAL immunoreactive nerve fibers (vasomotor functions) were distributed in a manner similar to that observed in the intact vaginal wall.

Modulation of rat parasympathetic cardiac ganglion phenotype and NGF synthesis by adrenergic nerves

Cardiac function is regulated by interactions among intrinsic and extrinsic autonomic neurons, and the mechanisms responsible for organizing these circuits are poorly understood. Parasympathetic neurons elsewhere synthesize the neurotrophin NGF, which may promote postganglionic axonal associations where parasympathetic axons inhibit sympathetic transmitter release. Previous studies have shown that parasympathetic NGF content and neurochemical phenotype are regulated by sympathetic innervation. In this study we assessed contributions of sympathetic input on cardiac ganglion neuronal phenotype and NGF expression. Because cardiac ganglia are reported to contain putative noradrenergic neurons, we eliminated sympathetic input both surgically (extrinsic) and chemically (extrinsic plus intrinsic). In controls, most cardiac ganglion neurons expressed vesicular acetylcholine transporter, frequently colocalized with vesicular monoamine transporter, but lacked catecholamine histofluorescence. Most cardiac ganglion neurons expressed NGF transcripts, and 40% contained mature and 47% proNGF immunoreactivity. Guanethidine treatment for 7 days decreased numbers of neurons expressing vesicular acetylcholine transporter, NGF transcripts and NGF immunoreactivity, but did not affect proNGF or vesicular monoamine transporter immunoreactivity. Stellate ganglionectomy had comparable effects on neurochemical phenotype and mature NGF immunoreactivity, but proNGF expression was additionally reduced. These findings show that individual cardiac ganglion neurons display markers of both cholinergic and noradrenergic transmission. Sympathetic noradrenergic innervation maintains levels of cholinergic but not noradrenergic marker protein. Sympathetic innervation also promotes cardiac ganglion neuronal NGF synthesis. Because chemical blockade of all noradrenergic transmission is no more effective than extrinsic sympathectomy, local intrinsic noradrenergic transmission is not a factor in regulating ganglion neuron phenotype.

Crisponi syndrome is caused by mutations in the CRLF1 gene and is allelic to cold-induced sweating syndrome type 1

Crisponi syndrome is a severe autosomal recessive condition that is phenotypically characterized by abnormal, paroxysmal muscular contractions resembling neonatal tetanus, large face, broad nose, anteverted nares, camptodactyly, hyperthermia, and sudden death in most cases. We performed homozygosity mapping in five Sardinian and three Turkish families with Crisponi syndrome, using high-density single-nucleotide polymorphism arrays, and identified a critical region on chromosome 19p12-13.1. The most prominent candidate gene was CRLF1, recently found to be involved in the pathogenesis of cold-induced sweating syndrome type 1 (CISS1). CISS1 belongs to a group of conditions with overlapping phenotypes, also including cold-induced sweating syndrome type 2 and Stuve-Wiedemann syndrome. All these syndromes are caused by mutations of genes of the ciliary neurotrophic factor (CNTF)-receptor pathway. Here, we describe the identification of four different CRLF1 mutations in eight different Crisponi-affected families, including a missense mutation, a single-nucleotide insertion, and a nonsense and an insertion/deletion (indel) mutation, all segregating with the disease trait in the families. Comparison of the mutation spectra of Crisponi syndrome and CISS1 suggests that neither the type nor the location of the CRLF1 mutations points to a phenotype/genotype correlation that would account for the most severe phenotype in Crisponi syndrome. Other, still-unknown molecular factors may be responsible for the variable phenotypic expression of the CRLF1 mutations. We suggest that the syndromes can comprise a family of "CNTF-receptor-related disorders," of which Crisponi syndrome would be the newest member and allelic to CISS1.

Leukemia inhibitory factor inhibits neuronal development and disrupts synaptic organization in the mouse retina

Leukemia inhibitory factor (LIF) belongs to the interleukin-6 cytokine family, all members of which signal through the common gp130 receptor. Neurotrophic members of this cytokine family are known to arrest photoreceptor maturation and are likely to regulate maturation of other retinal neurons as well. We have used transgenic mice that constitutively express LIF beginning in embryonic development to determine its effects on synaptic organization and molecular maturation of all classes of retinal neurons. LIF reduced the numbers of cells showing markers characteristic of mature cells of all neuronal classes and caused synaptic ectopia. The net effect was disrupted morphological development and disturbed synaptic organization. Our study suggests that cytokines signaling through gp130 are capable of regulating many aspects of neuronal differentiation in the retina, including synaptic targeting.

Role for calcium/calmodulin-dependent protein kinase II in the p75-mediated regulation of sympathetic cholinergic transmission

Neurotrophins regulate sympathetic neuron cotransmission by modulating the activity-dependent release of norepinephrine and acetylcholine. Nerve growth factor promotes excitatory noradrenergic transmission, whereas brain-derived neurotrophic factor (BDNF), acting through the p75 receptor, increases inhibitory cholinergic transmission. This regulation of corelease by target-derived factors leads to the functional modulation of myocyte beat rate in neuron-myocyte cocultures. Calcium/calmodulin-dependent protein kinase II (CaMKII) has been implicated in the control of both pre- and postsynaptic mechanisms of synaptic plasticity. We demonstrate that CaMKII acts in conjunction with p75 signaling to regulate cholinergic transmission between sympathetic neurons and heart cells. Inhibition of presynaptic CaMKII prevents the BDNF-dependent shift to inhibitory neurotransmission, whereas presynaptic expression of a constitutively active CaMKII results in inhibitory neurotransmission in the absence of added BDNF, suggesting that activation of presynaptic CaMKII is both necessary and sufficient for a shift from excitatory to inhibitory transmission. Several isozymes of CaMKII are expressed in sympathetic neurons, with the delta-CaMKII being activated by BDNF and nerve growth factor. Activated CaMKII is less effective at promoting cholinergic transmission in the absence of p75 signaling, demonstrating that p75 and CaMKII act to coordinate neurotransmitter selection in sympathetic neurons.

Target-dependent specification of the neurotransmitter phenotype: cholinergic differentiation of sympathetic neurons is mediated in vivo by gp 130 signaling

Sympathetic neurons are generated through a succession of differentiation steps that initially lead to noradrenergic neurons innervating different peripheral target tissues. Specific targets, like sweat glands in rodent footpads, induce a change from noradrenergic to cholinergic transmitter phenotype. Here, we show that cytokines acting through the gp 130 receptor are present in sweat glands. Selective elimination of the gp 130 receptor in sympathetic neurons prevents the acquisition of cholinergic and peptidergic features (VAChT, ChT1, VIP) without affecting other properties of sweat gland innervation. The vast majority of cholinergic neurons in the stellate ganglion, generated postnatally, are absent in gp 130-deficient mice. These results demonstrate an essential role of gp 130-signaling in the target-dependent specification of the cholinergic neurotransmitter phenotype.

Growth and survival signals controlling sympathetic nervous system development

The precise coordination of the many events in nervous system development is absolutely critical for the correct establishment of functional circuits. The postganglionic sympathetic neuron has been an amenable model for studying peripheral nervous system formation. Factors that control several developmental events, including multiple stages of axon extension, neuron survival and death, dendritogenesis, synaptogenesis, and establishment of functional diversity, have been identified in this neuron type. This knowledge allows us to integrate the various intricate processes involved in the formation of a functional sympathetic nervous system and thereby create a paradigm for understanding neuronal development in general.

Mechanisms and perspectives on differentiation of autonomic neurons

Neurons share many features in common but are distinguished by expression of phenotypic characteristics that define their specific function, location, or connectivity. One aspect of neuronal fate determination that has been extensively studied is that of neurotransmitter choice. The generation of diversity of neuronal subtypes within the developing nervous system involves integration of extrinsic and intrinsic instructive cues resulting in the expression of a core set of regulatory molecules. This review focuses on mechanisms of growth and transcription factor regulation in the generation of peripheral neural crest-derived neurons. Although the specification and differentiation of noradrenergic neurons are the focus, I have tried to integrate these into a larger picture providing a general roadmap for development of autonomic neurons. There is a core of DNA binding proteins required for the development of sympathetic, parasympathetic, and enteric neurons, including Phox2 and MASH1, whose specificity is regulated by the recruitment of additional transcriptional regulators in a subtype-specific manner. For noradrenergic neurons, the basic helix-loop-helix DNA binding protein HAND2 (dHAND) appears to serve this function. The studies reviewed here support the notion that neurotransmitter identity is closely linked to other aspects of neurogenesis and reveal a molecular mechanism to coordinate expression of pan-neuronal genes with cell type-specific genes.