RESUMEN
The marine microturbellarian Macrostomum lignano (Platyhelminthes, Rhabditophora) is an emerging laboratory model used by a growing community of researchers because it is easy to cultivate, has a fully sequenced genome, and offers multiple molecular tools for its study. M. lignano has a compartmentalized brain that receives sensory information from receptors integrated in the epidermis. Receptors of the head, as well as accompanying glands and specialized epidermal cells, form a compound sensory structure called the frontal glandular complex. In this study, we used semi-serial transmission electron microscopy (TEM) to document the types, ultrastructure, and three-dimensional architecture of the cells of the frontal glandular complex. We distinguish a ventral compartment formed by clusters of type 1 (multiciliated) sensory receptors from a central domain where type 2 (collar) sensory receptors predominate. Six different types of glands (rhammite glands, mucoid glands, glands with aster-like and perimaculate granula, vacuolated glands, and buckle glands) are closely associated with type 1 sensory receptors. Endings of a seventh type of gland (rhabdite gland) define a dorsal domain of the frontal glandular complex. A pair of ciliary photoreceptors is closely associated with the base of the frontal glandular complex. Bundles of dendrites, connecting the receptor endings with their cell bodies which are located in the brain, form the (frontal) peripheral nerves. Nerve fibers show a varicose structure, with thick segments alternating with thin segments, and are devoid of a glial layer. This distinguishes platyhelminths from larger and/or more complex invertebrates whose nerves are embedded in prominent glial sheaths.
Asunto(s)
Imagenología Tridimensional , Platelmintos , Animales , Platelmintos/ultraestructura , Células Receptoras Sensoriales/ultraestructuraRESUMEN
The evolution of new traits enables expansion into new ecological and behavioural niches. Nonetheless, demonstrated connections between divergence in protein structure, function and lineage-specific behaviours remain rare. Here we show that both octopus and squid use cephalopod-specific chemotactile receptors (CRs) to sense their respective marine environments, but structural adaptations in these receptors support the sensation of specific molecules suited to distinct physiological roles. We find that squid express ancient CRs that more closely resemble related nicotinic acetylcholine receptors, whereas octopuses exhibit a more recent expansion in CRs consistent with their elaborated 'taste by touch' sensory system. Using a combination of genetic profiling, physiology and behavioural analyses, we identify the founding member of squid CRs that detects soluble bitter molecules that are relevant in ambush predation. We present the cryo-electron microscopy structure of a squid CR and compare this with octopus CRs1 and nicotinic receptors2. These analyses demonstrate an evolutionary transition from an ancestral aromatic 'cage' that coordinates soluble neurotransmitters or tastants to a more recent octopus CR hydrophobic binding pocket that traps insoluble molecules to mediate contact-dependent chemosensation. Thus, our study provides a foundation for understanding how adaptation of protein structure drives the diversification of organismal traits and behaviour.
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Conducta Animal , Decapodiformes , Octopodiformes , Receptores Nicotínicos , Células Receptoras Sensoriales , Gusto , Tacto , Animales , Conducta Animal/fisiología , Sitios de Unión , Microscopía por Crioelectrón , Decapodiformes/química , Decapodiformes/fisiología , Decapodiformes/ultraestructura , Evolución Molecular , Interacciones Hidrofóbicas e Hidrofílicas , Neurotransmisores/metabolismo , Octopodiformes/química , Octopodiformes/fisiología , Octopodiformes/ultraestructura , Receptores Nicotínicos/química , Receptores Nicotínicos/metabolismo , Receptores Nicotínicos/ultraestructura , Gusto/fisiología , Tacto/fisiología , Células Receptoras Sensoriales/química , Células Receptoras Sensoriales/metabolismo , Células Receptoras Sensoriales/ultraestructuraRESUMEN
Chemotactile receptors (CRs) are a cephalopod-specific innovation that allow octopuses to explore the seafloor via 'taste by touch'1. CRs diverged from nicotinic acetylcholine receptors to mediate contact-dependent chemosensation of insoluble molecules that do not readily diffuse in marine environments. Here we exploit octopus CRs to probe the structural basis of sensory receptor evolution. We present the cryo-electron microscopy structure of an octopus CR and compare it with nicotinic receptors to determine features that enable environmental sensation versus neurotransmission. Evolutionary, structural and biophysical analyses show that the channel architecture involved in cation permeation and signal transduction is conserved. By contrast, the orthosteric ligand-binding site is subject to diversifying selection, thereby mediating the detection of new molecules. Serendipitous findings in the cryo-electron microscopy structure reveal that the octopus CR ligand-binding pocket is exceptionally hydrophobic, enabling sensation of greasy compounds versus the small polar molecules detected by canonical neurotransmitter receptors. These discoveries provide a structural framework for understanding connections between evolutionary adaptations at the atomic level and the emergence of new organismal behaviour.
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Evolución Molecular , Octopodiformes , Células Receptoras Sensoriales , Animales , Microscopía por Crioelectrón , Ligandos , Octopodiformes/química , Octopodiformes/fisiología , Octopodiformes/ultraestructura , Receptores Nicotínicos/química , Receptores Nicotínicos/fisiología , Receptores Nicotínicos/ultraestructura , Células Receptoras Sensoriales/química , Células Receptoras Sensoriales/fisiología , Células Receptoras Sensoriales/ultraestructura , Tacto/fisiología , Transmisión Sináptica , Sitios de Unión , Interacciones Hidrofóbicas e HidrofílicasRESUMEN
The internal ultrastructure of the scolex and the histochemical composition of the apical glands of two South American proteocephalideans cestodes, Monticellia magna and Proteocephalus pimelodi, were described for the first time. The study included the use of scanning and transmission electron microscopy to observe the tegumental ultrastructure, and histochemical techniques to detect types of gland secretion. Two types of glands were found in the scolex of M. magna and P. pimelodi. The pattern of microtriches described for M. magna was confirmed and that of P. pimelodi was described for the first time. Also, the internal ultrastructure of the microtriches in both species was described. Indications of the presence of sensory receptors were also found in M. magna. Finally, the systematic value of the characters studied is discussed, such as the internal structure of the gladiate spinitriches and the apocrine gland of M. magna.
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Cestodos , Animales , Cestodos/ultraestructura , Microscopía Electrónica de Transmisión , Histocitoquímica , Células Receptoras Sensoriales/ultraestructuraRESUMEN
Processing bodies (p-bodies) are a prototypical phase-separated RNA-containing granule. Their abundance is highly dynamic and has been linked to translation. Yet, the molecular mechanisms responsible for coordinate control of the two processes are unclear. Here, we uncover key roles for eEF2 kinase (eEF2K) in the control of ribosome availability and p-body abundance. eEF2K acts on a sole known substrate, eEF2, to inhibit translation. We find that the eEF2K agonist nelfinavir abolishes p-bodies in sensory neurons and impairs translation. To probe the latter, we used cryo-electron microscopy. Nelfinavir stabilizes vacant 80S ribosomes. They contain SERBP1 in place of mRNA and eEF2 in the acceptor site. Phosphorylated eEF2 associates with inactive ribosomes that resist splitting in vitro. Collectively, the data suggest that eEF2K defines a population of inactive ribosomes resistant to recycling and protected from degradation. Thus, eEF2K activity is central to both p-body abundance and ribosome availability in sensory neurons.
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Quinasa del Factor 2 de Elongación/metabolismo , Factor 2 de Elongación Peptídica/metabolismo , Cuerpos de Procesamiento/metabolismo , Ribosomas/metabolismo , Animales , Línea Celular Tumoral , Microscopía por Crioelectrón , Quinasa del Factor 2 de Elongación/genética , Ganglios Espinales/citología , Humanos , Masculino , Ratones , Ratones Noqueados , Nelfinavir/farmacología , Fosforilación/efectos de los fármacos , Cultivo Primario de Células , Biosíntesis de Proteínas/efectos de los fármacos , Biosíntesis de Proteínas/fisiología , Células Receptoras Sensoriales/metabolismo , Células Receptoras Sensoriales/ultraestructuraRESUMEN
BACKGROUND: Toll-like receptor 7 (TLR7) is an innate immune receptor that detects viral single-stranded RNA and triggers the production of proinflammatory cytokines and type 1 interferons in immune cells. TLR7 agonists also modulate sensory nerve function by increasing neuronal excitability, although studies are conflicting whether sensory neurons specifically express TLR7. This uncertainty has confounded the development of a mechanistic understanding of TLR7 function in nervous tissues. METHODS: TLR7 expression was tested using in situ hybridization with species-specific RNA probes in vagal and dorsal root sensory ganglia in wild-type and TLR7 knockout (KO) mice and in guinea pigs. Since TLR7 KO mice were generated by inserting an Escherichia coli lacZ gene in exon 3 of the mouse TLR7 gene, wild-type and TLR7 (KO) mouse vagal ganglia were also labeled for lacZ. In situ labeling was compared to immunohistochemistry using TLR7 antibody probes. The effects of influenza A infection on TLR7 expression in sensory ganglia and in the spleen were also assessed. RESULTS: In situ probes detected TLR7 in the spleen and in small support cells adjacent to sensory neurons in the dorsal root and vagal ganglia in wild-type mice and guinea pigs, but not in TLR7 KO mice. TLR7 was co-expressed with the macrophage marker Iba1 and the satellite glial cell marker GFAP, but not with the neuronal marker PGP9.5, indicating that TLR7 is not expressed by sensory nerves in either vagal or dorsal root ganglia in mice or guinea pigs. In contrast, TLR7 antibodies labeled small- and medium-sized neurons in wild-type and TLR7 KO mice in a TLR7-independent manner. Influenza A infection caused significant weight loss and upregulation of TLR7 in the spleens, but not in vagal ganglia, in mice. CONCLUSION: TLR7 is expressed by macrophages and satellite glial cells, but not neurons in sensory ganglia suggesting TLR7's neuromodulatory effects are mediated indirectly via activation of neuronally-associated support cells, not through activation of neurons directly. Our data also suggest TLR7's primary role in neuronal tissues is not related to antiviral immunity.
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Ganglios Espinales/metabolismo , Macrófagos/metabolismo , Glicoproteínas de Membrana/biosíntesis , Neuroglía/metabolismo , Células Receptoras Sensoriales/metabolismo , Receptor Toll-Like 7/biosíntesis , Animales , Femenino , Ganglios Espinales/ultraestructura , Expresión Génica , Cobayas , Macrófagos/ultraestructura , Glicoproteínas de Membrana/genética , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Neuroglía/ultraestructura , Células Receptoras Sensoriales/ultraestructura , Receptor Toll-Like 7/genéticaRESUMEN
We report that the neurotrophin receptor p75 contributes to sensory neuron survival through the regulation of cholesterol metabolism in Schwann cells. Selective deletion of p75 in mouse Schwann cells of either sex resulted in a 30% loss of dorsal root ganglia (DRG) neurons and diminished thermal sensitivity. P75 regulates Schwann cell cholesterol biosynthesis in response to BDNF, forming a co-receptor complex with ErbB2 and activating ErbB2-mediated stimulation of sterol regulatory element binding protein 2 (SREBP2), a master regulator of cholesterol synthesis. Schwann cells lacking p75 exhibited decreased activation of SREBP2 and a reduction in 7-dehydrocholesterol (7-DHC) reductase (DHCR7) expression, resulting in accumulation of the neurotoxic intermediate, 7-dehyrocholesterol in the sciatic nerve. Restoration of DHCR7 in p75 null Schwann cells in mice significantly attenuated DRG neuron loss. Together, these results reveal a mechanism by which the disruption of lipid metabolism in glial cells negatively influences sensory neuron survival, which has implications for a wide range of peripheral neuropathies.SIGNIFICANCE STATEMENT Although expressed in Schwann cells, the role of p75 in myelination has remained unresolved in part because of its dual expression in sensory neurons that Schwann cells myelinate. When p75 was deleted selectively among Schwann cells, myelination was minimally affected, while sensory neuron survival was reduced by 30%. The phenotype is mainly due to dysregulation of cholesterol biosynthesis in p75-deficient Schwann cells, leading to an accumulation of neurotoxic cholesterol precursor, 7-dehydrocholesterol (7-DHC). Mechanism-wise, we discovered that in response to BDNF, p75 recruits and activates ErbB2 independently of ErbB3, thereby stimulating the master regulator, sterol regulatory element binding protein 2 (SREBP2). These results together highlight a novel role of p75 in Schwann cells in regulating DRG neuron survival by orchestrating proper cholesterol metabolism.
Asunto(s)
Receptores de Factor de Crecimiento Nervioso/deficiencia , Receptores de Factor de Crecimiento Nervioso/genética , Células de Schwann/metabolismo , Células Receptoras Sensoriales/metabolismo , Animales , Supervivencia Celular/fisiología , Células Cultivadas , Femenino , Células HEK293 , Humanos , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Ratas , Células de Schwann/ultraestructura , Células Receptoras Sensoriales/ultraestructuraRESUMEN
Hereditary sensory neuropathy type 1 (HSN1) is caused by mutations in the SPTLC1 or SPTLC2 sub-units of the enzyme serine palmitoyltransferase, resulting in the production of toxic 1-deoxysphingolipid bases (DSBs). We used induced pluripotent stem cells (iPSCs) from patients with HSN1 to determine whether endogenous DSBs are neurotoxic, patho-mechanisms of toxicity and response to therapy. HSN1 iPSC-derived sensory neurons (iPSCdSNs) endogenously produce neurotoxic DSBs. Complex gangliosides, which are essential for membrane micro-domains and signaling, are reduced, and neurotrophin signaling is impaired, resulting in reduced neurite outgrowth. In HSN1 myelinating cocultures, we find a major disruption of nodal complex proteins after 8 weeks, which leads to complete myelin breakdown after 6 months. HSN1 iPSC models have, therefore, revealed that SPTLC1 mutation alters lipid metabolism, impairs the formation of complex gangliosides, and reduces axon and myelin stability. Many of these changes are prevented by l-serine supplementation, supporting its use as a rational therapy.
Asunto(s)
Axones/metabolismo , Gangliósidos/metabolismo , Neuropatías Hereditarias Sensoriales y Autónomas/patología , Células Madre Pluripotentes Inducidas/patología , Modelos Biológicos , Neuroglía/metabolismo , Serina/farmacología , Envejecimiento/patología , Axones/efectos de los fármacos , Axones/ultraestructura , Secuencia de Bases , Caspasa 3/metabolismo , Línea Celular , Regulación de la Expresión Génica/efectos de los fármacos , Neuropatías Hereditarias Sensoriales y Autónomas/genética , Humanos , Células Madre Pluripotentes Inducidas/ultraestructura , Microdominios de Membrana/efectos de los fármacos , Microdominios de Membrana/metabolismo , Microdominios de Membrana/ultraestructura , Vaina de Mielina/metabolismo , Factores de Crecimiento Nervioso/metabolismo , Neuroglía/efectos de los fármacos , Proyección Neuronal/efectos de los fármacos , Proteína Nodal/metabolismo , Células Receptoras Sensoriales/efectos de los fármacos , Células Receptoras Sensoriales/metabolismo , Células Receptoras Sensoriales/patología , Células Receptoras Sensoriales/ultraestructura , Transducción de Señal/efectos de los fármacos , Esfingolípidos/metabolismo , Transcriptoma/genéticaRESUMEN
Dorsal root ganglion (DRG) neurons are the predominant cell type that innervates the vertebrate skin. They are typically described as pseudounipolar cells that have central and peripheral axons branching from a single root exiting the cell body. The peripheral axon travels within a nerve to the skin, where free sensory endings can emerge and branch into an arbor that receives and integrates information. In some immature vertebrates, DRG neurons are preceded by Rohon-Beard (RB) neurons. While the sensory endings of RB and DRG neurons function like dendrites, we use live imaging in zebrafish to show that they have axonal plus-end-out microtubule polarity at all stages of maturity. Moreover, we show both cell types have central and peripheral axons with plus-end-out polarity. Surprisingly, in DRG neurons these emerge separately from the cell body, and most cells never acquire the signature pseudounipolar morphology. Like another recently characterized cell type that has multiple plus-end-out neurites, ganglion cells in Nematostella, RB and DRG neurons maintain a somatic microtubule organizing center even when mature. In summary, we characterize key cellular and subcellular features of vertebrate sensory neurons as a foundation for understanding their function and maintenance.
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Ganglios Espinales/ultraestructura , Microtúbulos/ultraestructura , Células Receptoras Sensoriales/ultraestructura , Piel/inervación , Animales , Animales Modificados Genéticamente , Axones/fisiología , Axones/ultraestructura , Cuerpo Celular/ultraestructura , Polaridad Celular , Dendritas/fisiología , Drosophila/citología , Drosophila/crecimiento & desarrollo , Ganglios Espinales/fisiología , Centro Organizador de los Microtúbulos/ultraestructura , Anémonas de Mar/citología , Anémonas de Mar/crecimiento & desarrollo , Anémonas de Mar/ultraestructura , Células Receptoras Sensoriales/fisiología , Pez CebraRESUMEN
Neuroendocrine systems in animals maintain organismal homeostasis and regulate stress response. Although a great deal of work has been done on the neuropeptides and hormones that are released and act on target organs in the periphery, the synaptic inputs onto these neuroendocrine outputs in the brain are less well understood. Here, we use the transmission electron microscopy reconstruction of a whole central nervous system in the Drosophila larva to elucidate the sensory pathways and the interneurons that provide synaptic input to the neurosecretory cells projecting to the endocrine organs. Predicted by network modeling, we also identify a new carbon dioxide-responsive network that acts on a specific set of neurosecretory cells and that includes those expressing corazonin (Crz) and diuretic hormone 44 (Dh44) neuropeptides. Our analysis reveals a neuronal network architecture for combinatorial action based on sensory and interneuronal pathways that converge onto distinct combinations of neuroendocrine outputs.
Asunto(s)
Conectoma , Drosophila melanogaster/ultraestructura , Interneuronas/ultraestructura , Sistemas Neurosecretores/ultraestructura , Células Receptoras Sensoriales/ultraestructura , Sinapsis/ultraestructura , Animales , Animales Modificados Genéticamente , Dióxido de Carbono/metabolismo , Proteínas de Drosophila/genética , Proteínas de Drosophila/metabolismo , Drosophila melanogaster/genética , Drosophila melanogaster/metabolismo , Hormonas de Insectos/genética , Hormonas de Insectos/metabolismo , Interneuronas/metabolismo , Microscopía Electrónica de Transmisión , Neuropéptidos/genética , Neuropéptidos/metabolismo , Sistemas Neurosecretores/metabolismo , Células Receptoras Sensoriales/metabolismo , Sinapsis/metabolismoRESUMEN
TMEM132D is a human gene identified with multiple risk alleles for panic disorders, anxiety and major depressive disorders. Defining a conserved family of transmembrane proteins, TMEM132D and its homologs are still of unknown molecular functions. By generating loss-of-function mutants of the sole TMEM132 ortholog in C. elegans, we identify abnormal morphologic phenotypes in the dopaminergic PDE neurons. Using a yeast two-hybrid screen, we find that NAP1 directly interacts with the cytoplasmic domain of human TMEM132D, and mutations in C. elegans tmem-132 that disrupt interaction with NAP1 cause similar morphologic defects in the PDE neurons. NAP1 is a component of the WAVE regulatory complex (WRC) that controls F-actin cytoskeletal dynamics. Decreasing activity of WRC rescues the PDE defects in tmem-132 mutants, whereas gain-of-function of TMEM132D in mammalian cells inhibits WRC, leading to decreased abundance of select WRC components, impaired actin nucleation and cell motility. We propose that metazoan TMEM132 family proteins play evolutionarily conserved roles in regulating NAP1 protein homologs to restrict inappropriate WRC activity, cytoskeletal and morphologic changes in the cell.
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Proteínas de Caenorhabditis elegans/fisiología , Citoesqueleto/ultraestructura , Neuronas Dopaminérgicas/ultraestructura , Proteínas de la Membrana/metabolismo , Morfogénesis/genética , Neurogénesis/genética , Células Receptoras Sensoriales/ultraestructura , Actinas/metabolismo , Animales , Evolución Biológica , Caenorhabditis elegans/citología , Caenorhabditis elegans/genética , Proteínas de Caenorhabditis elegans/genética , Forma de la Célula , Secuencia Conservada , Neuronas Dopaminérgicas/metabolismo , Mutación con Ganancia de Función , Genes Reporteros , Células HEK293 , Humanos , Mutación con Pérdida de Función , Familia de Multigenes , Complejos Multiproteicos/fisiología , Trastorno de Pánico/genética , Dominios Proteicos , Mapeo de Interacción de Proteínas , Proteínas Recombinantes de Fusión/metabolismo , Células Receptoras Sensoriales/metabolismo , Técnicas del Sistema de Dos HíbridosRESUMEN
Pain is a common non-motor symptom of Parkinson's disease (PD), with current limited knowledge of its pathophysiology. Here, we show that peripheral inoculation of mouse alpha-synuclein (α-Syn) pre-formed fibrils, in a transgenic mouse model of PD, elicited retrograde trans-synaptic spreading of α-Syn pathology (pSer129) across sensory neurons and dorsal nerve roots, reaching central pain processing regions, including the spinal dorsal horn and the projections of the anterolateral system in the central nervous system (CNS). Pathological peripheral to CNS propagation of α-Syn aggregates along interconnected neuronal populations within sensory afferents, was concomitant with impaired nociceptive response, reflected by mechanical allodynia, reduced nerve conduction velocities (sensory and motor) and degeneration of small- and medium-sized myelinated fibers. Our findings show a link between the transneuronal propagation of α-Syn pathology with sensory neuron dysfunction and neuropathic impairment, suggesting promising avenues of investigation into the mechanisms underlying pain in PD.
Asunto(s)
Neuralgia/etiología , Neuralgia/fisiopatología , Degeneración Retrógrada/patología , Degeneración Retrógrada/fisiopatología , Células Receptoras Sensoriales/patología , Sinucleinopatías/patología , Sinucleinopatías/fisiopatología , Animales , Modelos Animales de Enfermedad , Femenino , Ratones , Ratones Transgénicos , Microscopía Electrónica de Transmisión , Enfermedad de Parkinson/fisiopatología , Células Receptoras Sensoriales/metabolismo , Células Receptoras Sensoriales/ultraestructura , Transmisión Sináptica , alfa-Sinucleína/metabolismoRESUMEN
To investigate circuit mechanisms underlying locomotor behavior, we used serial-section electron microscopy (EM) to acquire a synapse-resolution dataset containing the ventral nerve cord (VNC) of an adult female Drosophila melanogaster. To generate this dataset, we developed GridTape, a technology that combines automated serial-section collection with automated high-throughput transmission EM. Using this dataset, we studied neuronal networks that control leg and wing movements by reconstructing all 507 motor neurons that control the limbs. We show that a specific class of leg sensory neurons synapses directly onto motor neurons with the largest-caliber axons on both sides of the body, representing a unique pathway for fast limb control. We provide open access to the dataset and reconstructions registered to a standard atlas to permit matching of cells between EM and light microscopy data. We also provide GridTape instrumentation designs and software to make large-scale EM more accessible and affordable to the scientific community.
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Envejecimiento/fisiología , Drosophila melanogaster/ultraestructura , Microscopía Electrónica de Transmisión , Neuronas Motoras/ultraestructura , Células Receptoras Sensoriales/ultraestructura , Animales , Automatización , Conectoma , Extremidades/inervación , Nervios Periféricos/ultraestructura , Sinapsis/ultraestructuraRESUMEN
The ability to perceive and interact with the world depends on a diverse array of neural circuits specialized for carrying out specific computations. Each circuit is assembled using a relatively limited number of molecules and common developmental steps, from cell fate specification to activity-dependent synaptic refinement. Given this shared toolkit, how do individual circuits acquire their characteristic properties? We explore this question by comparing development of the circuitry for seeing and hearing, highlighting a few examples where differences in each system's sensory demands necessitate different developmental strategies.
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Vías Auditivas/embriología , Núcleo Coclear/embriología , Neurogénesis , Retina/embriología , Vías Visuales/embriología , Animales , Audición/fisiología , Ratones , Células Receptoras Sensoriales/ultraestructura , Sinapsis/ultraestructura , Visión Ocular/fisiologíaRESUMEN
The scolex ultrastructure was studied in Grillotia (Christianella) carvajalregorum (Cestoda: Trypanorhyncha) using histochemistry and transmission electron microscopy. We show for the first time the presence of scolex glands arranged in two longitudinal acini at the pars vaginalis parenchyma. These glands, along with those scattered in bothrial parenchyma, produce potentially adhesive glycoprotein secretions that are discharged via ducts to the bothrial grooves and apex. A particular type of sensory receptor was found around frontal gland pores, with a possible function in regulating their secretion activity. The internal structure of microtriches varies according to their morphotype and distribution on the scolex, this study providing the first description of the ultrastructure of serrate lanceolate spinitriches. The projections that form serrate margins are an extension of the medulla, differing from similar projections of other spinitriches. The large caps observed in serrate lanceolate spinitriches may reflect their specialization in attachment to and abrasion of intestinal mucosa, while the short caps and large bases of acicular filitriches may reflect their involvement in nutrient absorption. We also describe the rhyncheal apparatus ultrastructure, showing a similar basic structure of tentacular walls than that of other trypanorhynchs. Some differences among species in the number of fibrous layers, composition of the apical cytoplasm and presence of microvilli-like projections were discussed. Finally, our study describes in detail the internal ultrastructure of hollow hooks, evidencing the presence of cytoplasm, mitochondria and fibrils. The location of these fibrils may increase the area of contact surface of hooks on tentacles, possibly allowing for a higher tensile strength than that of solid hooks. We consider that gland location and shape, composition of tentacular wall layers, and hook internal structure may serve as useful characters for the taxonomy and phylogeny of Trypanorhyncha. RESEARCH HIGHLIGHTS: This is the first description of scolex internal ultrastructure in Grillotia carvajalregorum, showing the presence of glands arranged in two longitudinal acini at the pars vaginalis parenchyma, with potentially adhesive functions. The internal ultrastructure of serrate lanceolate spinitriches and acicular filitriches may reflect their specialization in attachment to the host intestinal mucosa and their involvement in nutrient absorption, respectively. Internally, hollow hooks have cytoplasm with mitochondria and fibrils, which are more widely distributed than in solid hooks, possibly increasing their tensile strength.
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Cestodos/anatomía & histología , Cestodos/ultraestructura , Animales , Cestodos/citología , Histocitoquímica , Filogenia , Células Receptoras Sensoriales/citología , Células Receptoras Sensoriales/ultraestructuraRESUMEN
The output from the peripheral terminals of primary nociceptive neurons, which detect and encode the information regarding noxious stimuli, is crucial in determining pain sensation. The nociceptive terminal endings are morphologically complex structures assembled from multiple branches of different geometry, which converge in a variety of forms to create the terminal tree. The output of a single terminal is defined by the properties of the transducer channels producing the generation potentials and voltage-gated channels, translating the generation potentials into action potential (AP) firing. However, in the majority of cases, noxious stimuli activate multiple terminals; thus, the output of the nociceptive neuron is defined by the integration and computation of the inputs of the individual terminals. Here, we used a computational model of nociceptive terminal tree to study how the architecture of the terminal tree affects the input-output relation of the primary nociceptive neurons. We show that the input-output properties of the nociceptive neurons depend on the length, the axial resistance (Ra), and location of individual terminals. Moreover, we show that activation of multiple terminals by a capsaicin-like current allows summation of the responses from individual terminals, thus leading to increased nociceptive output. Stimulation of the terminals in simulated models of inflammatory or neuropathic hyperexcitability led to a change in the temporal pattern of AP firing, emphasizing the role of temporal code in conveying key information about changes in nociceptive output in pathologic conditions, leading to pain hypersensitivity.SIGNIFICANCE STATEMENT Noxious stimuli are detected by terminal endings of primary nociceptive neurons, which are organized into morphologically complex terminal trees. The information from multiple terminals is integrated along the terminal tree, computing the neuronal output, which propagates toward the CNS, thus shaping the pain sensation. Here, we revealed that the structure of the nociceptive terminal tree determines the output of nociceptive neurons. We show that the integration of noxious information depends on the morphology of the terminal trees and how this integration and, consequently, the neuronal output change under pathologic conditions. Our findings help to predict how nociceptive neurons encode noxious stimuli and how this encoding changes in pathologic conditions, leading to pain.
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Nociceptores/fisiología , Nociceptores/ultraestructura , Nervios Periféricos/fisiología , Nervios Periféricos/ultraestructura , Terminales Presinápticos/fisiología , Terminales Presinápticos/ultraestructura , Células Receptoras Sensoriales/fisiología , Células Receptoras Sensoriales/ultraestructura , Potenciales de Acción/fisiología , Capsaicina/farmacología , Simulación por Computador , Humanos , Modelos Neurológicos , Neuralgia/fisiopatología , Nocicepción , Enfermedades del Sistema Nervioso Periférico/fisiopatología , Canales de Sodio/efectos de los fármacos , Transmisión Sináptica/efectos de los fármacos , Transmisión Sináptica/fisiologíaRESUMEN
BACKGROUND: Recent physiological and experimental data highlight the role of the sensory nervous system in bone repair, but its precise role on angiogenesis in a bone regeneration context is still unknown. Our previous work demonstrated that sensory neurons (SNs) induce the osteoblastic differentiation of mesenchymal stem cells, but the influence of SNs on endothelial cells (ECs) was not studied. METHODS: Here, in order to study in vitro the interplay between SNs and ECs, we used microfluidic devices as an indirect co-culture model. Gene expression analysis of angiogenic markers, as well as measurements of metalloproteinases protein levels and enzymatic activity, were performed. RESULTS: We were able to demonstrate that two sensory neuropeptides, calcitonin gene-related peptide (CGRP) and substance P (SP), were involved in the transcriptional upregulation of angiogenic markers (vascular endothelial growth factor, angiopoietin 1, type 4 collagen, matrix metalloproteinase 2) in ECs. Co-cultures of ECs with SNs also increased the protein level and enzymatic activity of matrix metalloproteinases 2 and 9 (MMP2/MMP9) in ECs. CONCLUSIONS: Our results suggest a role of sensory neurons, and more specifically of CGRP and SP, in the remodelling of endothelial cells extracellular matrix, thus supporting and enhancing the angiogenesis process. Video abstract.
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Células Endoteliales/metabolismo , Matriz Extracelular/metabolismo , Ganglios Espinales/metabolismo , Células Receptoras Sensoriales/metabolismo , Animales , Péptido Relacionado con Gen de Calcitonina/metabolismo , Células Endoteliales/ultraestructura , Matriz Extracelular/ultraestructura , Femenino , Ganglios Espinales/ultraestructura , Regulación de la Expresión Génica , Metaloproteinasas de la Matriz/biosíntesis , Microfluídica , Modelos Biológicos , Neuritas/metabolismo , Osteogénesis , Ratas Wistar , Células Receptoras Sensoriales/ultraestructura , Sustancia P/metabolismoRESUMEN
Neurotoxicity is a common side effect of chemotherapeutics that often leads to the development of chemotherapy-induced peripheral neuropathy (CIPN). The peptide Prokineticin 2 (PK2) has a key role in experimental models of CIPN and can be considered an insult-inducible endangering mediator. Since primary afferent sensory neurons are highly sensitive to anticancer drugs, giving rise to dysesthesias, the aim of our study was to evaluate the alterations induced by vincristine (VCR) and bortezomib (BTZ) exposure in sensory neuron cultures and the possible preventive effect of blocking PK2 signaling. Both VCR and BTZ induced a concentration-dependent reduction of total neurite length that was prevented by the PK receptor antagonist PC1. Antagonizing the PK system also reduced the upregulation of PK2, PK-R1, TLR4, IL-6, and IL-10 expression induced by chemotherapeutic drugs. In conclusion, inhibition of PK signaling with PC1 prevented the neurotoxic effects of chemotherapeutics, suggesting a promising strategy for neuroprotective therapies against the sensory neuron damage induced by exposure to these drugs.
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Antineoplásicos/toxicidad , Bortezomib/toxicidad , Hormonas Gastrointestinales/antagonistas & inhibidores , Proteínas del Tejido Nervioso/antagonistas & inhibidores , Neuropéptidos/antagonistas & inhibidores , Fármacos Neuroprotectores/farmacología , Síndromes de Neurotoxicidad/prevención & control , Células Receptoras Sensoriales/efectos de los fármacos , Triazinas/farmacología , Vincristina/toxicidad , Animales , Células Cultivadas , Relación Dosis-Respuesta a Droga , Regulación hacia Abajo , Evaluación Preclínica de Medicamentos , Hormonas Gastrointestinales/fisiología , Regulación de la Expresión Génica/efectos de los fármacos , Masculino , Ratones , Ratones Endogámicos C57BL , Proteínas del Tejido Nervioso/fisiología , Neuritas/efectos de los fármacos , Neuritas/ultraestructura , Neuroinmunomodulación/efectos de los fármacos , Neuropéptidos/fisiología , Fármacos Neuroprotectores/uso terapéutico , ARN Mensajero/biosíntesis , Células Receptoras Sensoriales/fisiología , Células Receptoras Sensoriales/ultraestructura , Triazinas/uso terapéuticoRESUMEN
OBJECTIVE: Pain, temperature, and itch are conventionally thought to be exclusively transduced by the intraepidermal nerve endings. Although recent studies have shown that epidermal keratinocytes also participate in sensory transduction, the mechanism underlying keratinocyte communication with intraepidermal nerve endings remains poorly understood. We sought to demonstrate the synaptic character of the contacts between keratinocytes and sensory neurons and their involvement in sensory communication between keratinocytes and sensory neurons. METHODS: Contacts were explored by morphological, molecular, and functional approaches in cocultures of epidermal keratinocytes and sensory neurons. To interrogate whether structures observed in vitro were also present in the human epidermis, in situ correlative light electron microscopy was performed on human skin biopsies. RESULTS: Epidermal keratinocytes dialogue with sensory neurons through en passant synaptic-like contacts. These contacts have the ultrastructural features and molecular hallmarks of chemical synaptic-like contacts: narrow intercellular cleft, keratinocyte synaptic vesicles expressing synaptophysin and synaptotagmin 1, and sensory information transmitted from keratinocytes to sensory neurons through SNARE-mediated (syntaxin1) vesicle release. INTERPRETATION: By providing selective communication between keratinocytes and sensory neurons, synaptic-like contacts are the hubs of a 2-site receptor. The permanent epidermal turnover, implying a specific en passant structure and high plasticity, may have delayed their identification, thereby contributing to the long-held concept of nerve endings passing freely between keratinocytes. The discovery of keratinocyte-sensory neuron synaptic-like contacts may call for a reassessment of basic assumptions in cutaneous sensory perception and sheds new light on the pathophysiology of pain and itch as well as the physiology of touch. ANN NEUROL 2020;88:1205-1219.
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Queratinocitos/ultraestructura , Células Receptoras Sensoriales/ultraestructura , Sinapsis/ultraestructura , Adulto , Anciano , Animales , Técnicas de Cocultivo , Epidermis/inervación , Femenino , Humanos , Queratinocitos/metabolismo , Masculino , Microscopía Electrónica , Persona de Mediana Edad , Proteínas Qa-SNARE/metabolismo , Ratas , Vesículas Sinápticas/metabolismo , Sinaptofisina/metabolismo , Sinaptotagmina I/metabolismoRESUMEN
Imaging neuronal networks provides a foundation for understanding the nervous system, but resolving dense nanometer-scale structures over large volumes remains challenging for light microscopy (LM) and electron microscopy (EM). Here we show that X-ray holographic nano-tomography (XNH) can image millimeter-scale volumes with sub-100-nm resolution, enabling reconstruction of dense wiring in Drosophila melanogaster and mouse nervous tissue. We performed correlative XNH and EM to reconstruct hundreds of cortical pyramidal cells and show that more superficial cells receive stronger synaptic inhibition on their apical dendrites. By combining multiple XNH scans, we imaged an adult Drosophila leg with sufficient resolution to comprehensively catalog mechanosensory neurons and trace individual motor axons from muscles to the central nervous system. To accelerate neuronal reconstructions, we trained a convolutional neural network to automatically segment neurons from XNH volumes. Thus, XNH bridges a key gap between LM and EM, providing a new avenue for neural circuit discovery.