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Peripheral nerve section with subsequent disconnection of motor neuron (MN) cell bodies from their skeletal muscle targets leads to a rapid reactive response involving the recruitment and activation of microglia. In addition, the loss of afferent synapses on MNs occurs in concomitance with microglial reaction by a process described as synaptic stripping. However, the way in which postaxotomy‐activated microglia adjacent to MNs are involved in synaptic removal is less defined. Here, we used confocal and electron microscopy to examine interactions between recruited microglial cells and presynaptic terminals in axotomized MNs between 1 and 15 days after sciatic nerve transection in mice. We did not observe any bulk engulfment of synaptic boutons by microglia. Instead, microglial cells internalized small membranous‐vesicular fragments which originated from the acute disruption of synaptic terminals involving the activation of the necroptotic pathway. The presence of abundant extracellular vesicles in the perineuronal space after axotomy, together with the increased expression of phospho‐mixed lineage kinase domain‐like protein and, later, of extracellular vesicle markers, such as CD9, CD63, and flotillin, indicate that the vesicles mainly originated in synapses and were transferred to microglia. The upregulation of Rab7 and Rab10 in microglia interacting with injured MNs, indicated the activation of endocytosis. As activated microglia and synaptic boutons displayed positive C1q immunoreactivity, a complement‐mediated opsonization may also contribute to microglial‐mediated synaptic disruption. In addition to the relevance of our data in the context of neuroinflammation and MN disease, they should also be taken into account for understanding functional recovery after peripheral nerve injury., Main Points Early after axotomy, microglia recruited near injured motor neurons, emit processes that tend to contact their afferent synaptic terminals.Extracellular vesicles resulting from necroptotic synaptic disruption are removed by microglia.

Background The cellular mechanisms underlying the age‐associated loss of muscle mass and function (sarcopenia) are poorly understood, hampering the development of effective treatment strategies. Here, we performed a detailed characterization of age‐related pathophysiological changes in the mouse neuromuscular system. Methods Young, adult, middle‐aged, and old (1, 4, 14, and 24-30 months old, respectively) C57BL/6J mice were used. Motor behavioural and electrophysiological tests and histological and immunocytochemical procedures were carried out to simultaneously analyse structural, molecular, and functional age‐related changes in distinct cellular components of the neuromuscular system. Results Ageing was not accompanied by a significant loss of spinal motoneurons (MNs), although a proportion (~15%) of them in old mice exhibited an abnormally dark appearance. Dark MNs were also observed in adult (~9%) and young (~4%) animals, suggesting that during ageing, some MNs undergo early deleterious changes, which may not lead to MN death. Old MNs were depleted of cholinergic and glutamatergic inputs (~40% and ~45%, respectively, P < 0.01), suggestive of age‐associated alterations in MN excitability. Prominent microgliosis and astrogliosis [~93% (P < 0.001) and ~100% (P < 0.0001) increase vs. adults, respectively] were found in old spinal cords, with increased density of pro‐inflammatory M1 microglia and A1 astroglia (25‐fold and 4‐fold increase, respectively, P < 0.0001). Ageing resulted in significant reductions in the nerve conduction velocity and the compound muscle action potential amplitude (~30%, P < 0.05, vs. adults) in old distal plantar muscles. Compared with adult muscles, old muscles exhibited significantly higher numbers of both denervated and polyinnervated neuromuscular junctions, changes in fibre type composition, higher proportion of fibres showing central nuclei and lipofuscin aggregates, depletion of satellite cells, and augmented expression of different molecules related to development, plasticity, and maintenance of neuromuscular junctions, including calcitonin gene‐related peptide, growth associated protein 43, agrin, fibroblast growth factor binding protein 1, and transforming growth factor‐β1. Overall, these alterations occurred at varying degrees in all the muscles analysed, with no correlation between the age‐related changes observed and myofiber type composition or muscle topography. Conclusions Our data provide a global view of age‐associated neuromuscular changes in a mouse model of ageing and help to advance understanding of contributing pathways leading to development of sarcopenia. This work was supported by Abbott and a grant from the Ministerio de Ciencia, Innovación y Universidades cofinancedby Fondo Europeo de Desarrollo Regional (RTI2018-099278-B-I00 to J.C. and J.E.)

Early misfolded superoxide dismutase 1 (mfSOD1) accumulation, motor neuron (MN) degeneration, and microgliosis are hallmark pathological features in SOD1

C-type synaptic boutons (C-boutons) provide cholinergic afferent input to spinal cord motor neurons (MNs), which display an endoplasmic reticulum (ER)–related subsurface cistern (SSC) adjacent to their postsynaptic membrane. A constellation of postsynaptic proteins is clustered at C-boutons, including M2 muscarinic receptors, potassium channels, and s-1 receptors. In addition, we previously found that neuregulin (NRG)1 is associated with C-boutons at postsynaptic SSCs, whereas its ErbB receptors are located in the presynaptic compartment. Cbouton–mediated regulation of MN excitability has been implicated in MN disease, but NRG1-mediated functions and the impact of various pathologic conditions on C-bouton integrity have not been studied in detail. Here, we investigated changes inC-boutons after electrical stimulation,pharmacological treatment, and peripheral nerve axotomy. SSC-linked NRG1 clusters were severely disrupted in acutely stressedMNs and after tunicamycin-induced ER stress. In axotomized MNs, C-bouton loss occurred in concomitance with microglial recruitment and was prevented by the ER stress inhibitor salubrinal.Activatedmicroglia displayed apositive chemotaxis to C-boutons.Analysis of transgenicmice overexpressing NRG1 type I and type III isoforms in MNs indicated that NRG1 type III acts as an organizer of SSC-like structures, whereas NRG1 type I promotes synaptogenesis of presynaptic cholinergic terminals.Moreover,MN-derived NRG1 signals may regulate the activity of perineuronal microglial cells. Together, these data provide new insights into the molecular and cellular pathology of C-boutons in MN injury and suggest that distinct NRG1 isoform–mediated signaling functions regulate the complex matching between pre- and postsynaptic C-bouton elements. The authors thank Klaus A. Nave (Max-Planck-Institute of Experimental Medicine, Göttingen, Germany) for advice and for supplying neuregulin-1–mutant mice; Jesús María López (Universidad Complutense de Madrid, Madrid, Spain), Ester Desfilis, and José Antonio Moreno for providing spinal cord samples from nonrodent animals; Anaïs Panosa and Xavier Calomarde (all from Universitat de Lleida−Institut de Recerca Biomèdica de Lleida) for technical support with confocal and electron microscopy; and the Serveis Científico-Tècnics Anima Facility of the University of Lleida for mouse care and housing. This work was supported by grants to J.E.E. and J.C. from the Spanish Ministerio de Economía y Competitividad cofinanced by the Fondo Europeo de Desarrollo Regional (FEDER; SAF2015-70801-R). S.S. holds a grant from Spanish Ministerio de Educación, Cultura, y Deporte (FPU). M.H.S. holds a Heisenberg Fellowship from the Deutsche Forschungsgemeinschaft (DFG) and acknowledges funding by a DFG research grant (SCHW741/4-1). The authors declare no conflicts of interest.

This work was supported by Abbott and a grant from the Spanish Ministerio de Ciencia, Innovacion y Universidades cofinanced by Fondo Europeo de Desarrollo Regional (RTI2018-099278-B-I00 to JC and JE) ., Besides skeletal muscle wasting, sarcopenia entails morphological and molecular changes in distinct components of the neuromuscular system, including spinal cord motoneurons (MNs) and neuromuscular junctions (NMJs); moreover, noticeable microgliosis has also been observed around aged MNs. Here we examined the impact of two flavonoid-enriched diets containing either green tea extract (GTE) catechins or cocoa flavanols on age-associated regressive changes in the neuromuscular system of C57BL/6J mice. Compared to control mice, GTE- and cocoa-supplementation significantly improved the survival rate of mice, reduced the proportion of fibers with lipofuscin aggregates and central nuclei, and increased the density of satellite cells in skeletal muscles. Additionally, both supplements significantly augmented the number of innervated NMJs and their degree of maturity compared to controls. GTE, but not cocoa, prominently increased the density of VAChT and VGluT2 afferent synapses on MNs, which were lost in control aged spinal cords; conversely, cocoa, but not GTE, significantly augmented the proportion of VGluT1 afferent synapses on aged MNs. Moreover, GTE, but not cocoa, reduced aging-associated microgliosis and increased the proportion of neuroprotective microglial phenotypes. Our data indicate that certain plant flavonoids may be beneficial in the nutritional management of age-related deterioration of the neuromuscular system., Abbott Laboratories, Spanish Ministerio de Ciencia, Innovacion y Universidades, European Commission RTI2018-099278-B-I00

Spinal muscular atrophy (SMA) is characterized by the loss of α-motoneurons (MNs) with concomitant muscle denervation. MN excitability and vulnerability to disease are particularly regulated by cholinergic synaptic afferents (C-boutons), in which Sigma-1 receptor (Sig1R) is concentrated. Alterations in Sig1R have been associated with MN degeneration. Here, we investigated whether a chronic treatment with the Sig1R agonist PRE-084 was able to exert beneficial effects on SMA. We used a model of intermediate SMA, the Smn2B/− mouse, in which we performed a detailed characterization of the histopathological changes that occur throughout the disease. We report that Smn2B/− mice exhibited qualitative differences in major alterations found in mouse models of severe SMA: Smn2B/− animals showed more prominent MN degeneration, early motor axon alterations, marked changes in sensory neurons, and later MN deafferentation that correlated with conspicuous reactive gliosis and altered neuroinflammatory M1/M2 microglial balance. PRE-084 attenuated reactive gliosis, mitigated M1/M2 imbalance, and prevented MN deafferentation in Smn2B/− mice. These effects were also observed in a severe SMA model, the SMNΔ7 mouse. However, the prevention of gliosis and MN deafferentation promoted by PRE-084 were not accompanied by any improvements in clinical outcome or other major pathological changes found in SMA mice. This work was supported by grants from the Ministerio de Economía y Competitividad co-financed by FEDER (SAF2015-70801).

C boutons are large, cholinergic, synaptic terminals that arise from local interneurons and specifically contact spinal α-motoneurons (MNs). C boutons characteristically display a postsynaptic specialization consisting of an endoplasmic reticulum-related subsurface cistern (SSC) of unknown function. In the present work, by using confocal microscopy and ultrastructural immunolabeling, we demonstrate that neuregulin-1 (NRG1) accumulates in the SSC of mouse spinal MNs. We also show that the NRG1 receptors erbB2 and erbB4 are presynaptically localized within C boutons, suggesting that NRG1-based retrograde signaling may occur in this type of synapse. In most of the cranial nuclei, MNs display the same pattern of NRG1 distribution as that observed in spinal cord MNs. Conversely, MNs in oculomotor nuclei, which are spared in amyotrophic lateral sclerosis (ALS), lack both C boutons and SSC-associated NRG1. NRG1 in spinal MNs is developmentally regulated and depends on the maintenance of nerve-muscle interactions, as we show after nerve transection experiments. Changes in NRG1 in C boutons were also investigated in mouse models of MN diseases: i.e., spinal muscular atrophy (SMNΔ7) and ALS (SOD1(G93A)). In both models, a transient increase in NRG1 in C boutons occurs during disease progression. These data increase our understanding of the role of C boutons in MN physiology and pathology.

In the chick embryo, in ovo application of NMDA from embryonic day (E) 5 to E9 results in selective damage to spinal cord motoneurons (MNs) that undergo a long-lasting degenerative process without immediate cell death. This contrasts with a single application of NMDA on E8, or later, which induces massive necrosis of the whole spinal cord. Chronic MN degeneration after NMDA implies transient incompetence to develop programmed cell death, altered protein processing within secretory pathways, and late activation of autophagy. Chronic NMDA treatment also results in an enlargement of thapsigargin-sensitive Ca(2+) stores. In particular MN pools, such as sartorius-innervating MNs, the neuropeptide CGRP is accumulated in somas, peripheral axons and neuromuscular junctions after chronic NMDA treatment, but not in embryos paralyzed by chronic administration of curare. Intramuscular axonal branching is also altered severely after NMDA: it usually increases, but in some cases a marked reduction can also be observed. Moreover, innervated muscle postsynaptic sites increase by NMDA, but to a lesser extent than by curare. Because some of these results show interesting homologies with MN pathology in human sporadic ALS, the model presented here provides a valuable tool for advancing in the understanding of some cellular and molecular processes particularly involved in this disease.

Stereological techniques using the optical disectors require estimation of final section thickness, but frozen tissue irregularities may interfere with this estimation. Cryostat slices from rodent nerve tissues (dorsal root ganglia, spinal cord, and brain), cut at 16, 40, and 50 μm, were digitized with a confocal microscope and visualized through 3D software. Geometric section thickness of tissue (Tgeom) was defined as tissue volume/area. Maximal section thicknesses (Tmax), from the top to the bottom of the section, were measured in a random sample of vertical ZX planes. Irregularities were mostly related to blood vessels traversing the tissue and neuronal somas protruding over the cut surfaces, with other neuron profiles showing a fragmented appearance. Irregularities contributed to increasing the distance between the tops and bottoms of slices sectioned in different laboratories. Significant differences were found between Tmax and Tgeom for all thickness studies and counting frames (pTgeom/Tmax average rate was 68.4–85.7% in volumes around cell profiles (∼600–1,200 μm2) and 83.3–91.8% in subcellular samples (∼25–160 μm2). Confocal microscopy may help to assess tissue irregularities, which might lead to an overestimation of tissue volume if section thickness is estimated by focusing on the top and bottom of the sections.

Amyotrophic lateral sclerosis (ALS) is an adult-onset progressive neurodegenerative disease affecting upper and lower motoneurons (MNs). Although the motor phenotype is a hallmark for ALS, there is increasing evidence that systems other than the efferent MN system can be involved. Mutations of superoxide dismutase 1 (SOD1) gene cause a proportion of familial forms of this disease. Misfolding and aggregation of mutant SOD1 exert neurotoxicity in a noncell autonomous manner, as evidenced in studies using transgenic mouse models. Here, we used the SOD1(G93A) mouse model for ALS to detect, by means of conformational-specific anti-SOD1 antibodies, whether misfolded SOD1-mediated neurotoxicity extended to neuronal types other than MNs. We report that large dorsal root ganglion (DRG) proprioceptive neurons accumulate misfolded SOD1 and suffer a degenerative process involving the inflammatory recruitment of macrophagic cells. Degenerating sensory axons were also detected in association with activated microglial cells in the spinal cord dorsal horn of diseased animals. As large proprioceptive DRG neurons project monosynaptically to ventral horn MNs, we hypothesise that a prion-like mechanism may be responsible for the transsynaptic propagation of SOD1 misfolding from ventral horn MNs to DRG sensory neurons. The authors would like to thank Montse Ortega for her technical assistance and Claudia Cervero, Alexandra Eritja and Ariadna Salvador for their help with some of the experiments in this study. This work was supported by grants from the Ministerio de Ciencia y Tecnologia and Ministerio de Economia y Competitividad and cofinanced by FEDER (SAF2011-22908; SAF2012-31831).

During a developmental study of the expression of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) -type glutamate receptor subunits in rat spinal cord, we observed the existence of cytoplasmic inclusion bodies with positive immunoreactivity to glutamate receptor subunit 1 (GluR1) but not to other glutamate receptor subunits. GluR1-positive bodies have a diameter of between 1 and 3 microm and can be seen widely distributed throughout spinal cord gray matter, with the exception of the ventral horn region. They transiently appear within a definite developmental time-period between embryonic day 19 and postnatal day 17 and are only associated with neuronal cells. Ultrastructural analysis revealed that these inclusions were located adjacent to the nucleus and consisted of amorphous material without any limiting membrane. Immunocytochemical analysis revealed that the inclusions displayed positive immunoreactivity to ubiquitin, HSP70, and 20S proteasome. All these data indicate that GluR1-containing inclusions display all the ultrastructural and immunocytochemical characteristics of the recently described structure, which have been given the name aggresomes. Further studies are needed to determine the biological significance of these normally occurring aggresome-like inclusions, because aggresomes are usually considered in a pathologic context.

Motoneurons respond to peripheral nerve transection by either regenerative or degenerative events depending on their state of maturation. Since the expression of c-Jun has been involved in the early signalling of the regenerative process that follows nerve transection in adults, we have investigated c-Jun on rat neonatal axotomized motoneurons during the period in which neuronal death is induced. Changes in levels of c-Jun protein and its mRNA were determined by means of quantitative immunocytochemistry and in situ hybridization. Three hours after nerve transection performed on postnatal day (P)3, c-Jun protein and mRNA is induced in axotomized spinal cord motoneurons, and high levels were reached between 1 and 10 days after. This response is associated with a detectable c-Jun activation by phosphorylation on serine 63. No changes were found in the levels of activating transcription factor -2. Most of dying motoneurons were not labelled by either a specific c-Jun antibody or a c-jun mRNA probe. However, dying motoneurons were specifically stained by a polyclonal anti c-Jun antibody, indicating that some c-Jun antibodies react with unknown epitopes, probably distinct from c-Jun p39, that are specifically associated with apoptosis. J. Neurosci. Res. 63:469–479, 2001. © 2001 Wiley-Liss, Inc.

We previously showed that some antipurinergic receptor P2X4 antibodies cross react with misfolded forms of amyotrophic lateral sclerosis (ALS)-linked mutant Cu/Zn superoxide dismutase (SOD1). Cross reactivity might be caused by abnormal exposure of an epitope in the inner hydrophobic region of SOD1 that shares structural homology with the P2X4-immunizing peptide. Here, we raised antibodies against the human SOD1 epitope mimicked by the P2X4 immunizing peptide. One of these antibodies, AJ10, is a recognized mutant/misfolded form of ALS-linked mutant SOD1. This was demonstrated in the hybrid motoneuron cell line NSC34 expressing enhanced green fluorescent protein-tagged G943A or A4V mutant SOD1. We also found AJ10 immunoreactivity to be selectively associated with degenerating neurons but not with glial cells in mice overexpressmg either SOD1G93A or SOD1G85R mutants. Neurons with strongly positive AJ10 immunostaining were often associated with activated microglia displaying neuronophagic activity. AJ10-immunopositive SOD1 aggregates were also found in spinal cord tissue from a patient with a SOD1-linked familial ALS. AJ10-immunoreactive mutant SOD1 conformers were localized in large intracellular protein aggregates with a filamentous amyloid-like organization by ultrastructural immunolabeling and were also detected in neuronal organelles. These data are consistent with the ability of the AJ10 antibody to recognize misfolded conformations of SOD1 shared by different ALS-linked SOD1 mutations but not with the native protein. The neuronal mutant SOD1 conformers detected with AJ10 may promote neuroinflammation and may define a new epitope in SOD1 for ALS research.

Individuals with Down syndrome (DS) present important motor deficits that derive from altered motor development of infants and young children. DYRK1A, a candidate gene for DS abnormalities has been implicated in motor function due to its expression in motor nuclei in the adult brain, and its overexpression in DS mouse models leads to hyperactivity and altered motor learning. However, its precise role in the adult motor system, or its possible involvement in postnatal locomotor development has not yet been clarified. During the postnatal period we observed time-specific expression of Dyrk1A in discrete subsets of brainstem nuclei and spinal cord motor neurons. Interestingly, we describe for the first time the presence of Dyrk1A in the presynaptic terminal of the neuromuscular junctions and its axonal transport from the facial nucleus, suggesting a function for Dyrk1A in these structures. Relevant to DS, Dyrk1A overexpression in transgenic mice (TgDyrk1A) produces motor developmental alterations possibly contributing to DS motor phenotypes and modifies the numbers of motor cholinergic neurons, suggesting that the kinase may have a role in the development of the brainstem and spinal cord motor system. The laboratory of MD is supported by Departament d’Universitats, Recerca i Societat de la Informació (DURSI) (Grups consolidats 09 2009SGR1313). This work was supported by FCT-08-0782, SAF2007-60827, SAF2010-16427, SAF2007-31093-E, Fondo de Investigación Sanitaria (FIS) (PI 082038), Marató TV3, Jerome Lejeune, Reina Sofia and Areces Foundations and EU (LSHG-CT-2006-037627; CureFXS ERare-EU/FIS PS09102673). The CIBER of Enfermedades Raras is an initiative of the ISCIII. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

A detailed pathologic analysis was performed on Smn(-/-);SMN2 mice as a mouse model for human type I spinal muscular atrophy (SMA). We provide new data concerning changes in the spinal cord, neuromuscular junctions and muscle cells, and in the organs of the immune system. The expression of 10 synaptic proteins was analyzed in 3-dimensionally reconstructed neuromuscular junctions by confocal microscopy. In addition to defects in postsynaptic occupancy, there was a marked reduction in calcitonin gene-related peptide and Rab3A in the presynaptic motor terminals of some, but not all, of the skeletal muscles analyzed. Defects in the organization of presynaptic nerve terminals were also detected by electron microscopy. Moreover, degenerative changes in muscle cells, defective postnatal muscle growth, and prominent muscle satellite cell apoptosis were also observed. All of these changes occurred in the absence of massive loss of spinal cord motoneurons. On the other hand, astroglia, but not microglia, increased in the ventral horn of newborn SMA mice. In skeletal muscles, the density of interstitial macrophages was significantly reduced, and monocyte chemotactic protein-1 was downregulated. These findings raise questions regarding the primary contribution of a muscle cell defect to the SMA phenotype.

Amyotrophic lateral sclerosis (ALS) is a neuromuscular disease characterized by the selective loss of both upper and lower motoneurons (MNs). The familial form of the illness is associated with mutations in the gene encoding Cu/Zn superoxide dismutase 1 (SOD-1) enzyme, but it accounts for fewer than 10% of cases; the rest, more than 90%, correspond to the sporadic form of ALS. Although many proposals have been suggested over the years, the mechanisms underlying the characteristic selective killing of MN in ALS remain unknown. In this study we tested the effect of sera from sporadic ALS patients on NMDA receptors (NMDAR). We hypothesize that an endogenous seric factor is implicated in neuronal death in ALS, mediated by the modulation of NMDAR. Sera from ALS patients and from healthy subjects were pretreated to inactivate complement pathways and dialyzed to remove glutamate and glycine. IgGs from ALS patients and healthy subjects were obtained by affinity chromatography and dialyzed against phosphate-buffered saline. Human NMDAR were expressed in Xenopus laevis oocytes, and ionic currents were recorded using the two-electrode voltage clamp technique. Sera from sporadic ALS patients induced transient oscillatory currents in oocytes expressing NMDAR with a significantly higher total electrical charge than that induced by sera from healthy subjects. Sera from patients with other neuromuscular diseases did not exert this effect. The currents were inhibited by MK-801, a noncompetitive blocker of NMDAR. The PLC inhibitor, U-73122, and the IP 3 receptor antagonist, 2-APB, also inhibited the sera-induced currents. The oscillatory signal recorded was due to internal calcium mobilization. Isolated IgGs from ALS patients significantly affected the activity of oocytes injected with NMDAR, causing a 2-fold increase over the response recorded for IgGs from healthy subjects. Our data support the notion that ALS sera contain soluble factors that mobilize intracellular calcium, not opening directly the ionic conductance, but through the non-canonical activation of NMDAR.

We recently reported that degenerating motor neurons of superoxide dismutase mutant 1 (SOD1) rodents exhibit immunoreactivity to P2X(4) antibodies. Neurons with strong P2X(4)-like immunoreactivity (P2X(4)-LIR) do not show an apoptotic phenotype and are often associated with microglial cells that display neuronophagic activity. Western blot analysis showed that P2X(4) antibodies recognize not only the P2X(4) adenosine triphosphate receptor protein but also a hitherto unidentified low-molecular weight band. Here, we identify the molecular counterpart of the strong P2X(4)-LIR observed in association with neuronal degeneration in SOD1 animals. After matrix-assisted laser desorption/ionization time-of-flight, we found that the low-molecular weight P2X(4)-immunoreactive protein was SOD1. Further analysis demonstrated that the P2X(4) antibody recognizes a form of misfolded mutant SOD1 that is expressed in neuronal cells undergoing degeneration but not in glial cells. Cross-reactivity could have been caused by the abnormal exposure of an epitope in the inner hydrophobic region of SOD1 that shared structural homology with the P2X(4)-immunizing peptide used for raising the antibody. No positive P2X(4) immunostaining was detected in mice overexpressing human wild-type SOD1. Intracerebral injections of affinity chromatography-isolated P2X(4)-immunoreactive SOD1 species promote microglial and astroglial activation. We conclude that neuronal SOD1 conformers with P2X(4)-LIR may have pathogenetic relevance in the promotion of neuroinflammation.

Massive programmed cell death (PCD) of developing chick embryo motoneurons (MNs) occurs in a well defined temporal and spatial sequence between embryonic day (E) 6 and E10. We have found that, when administered in ovo, either circulating immunoglobulins G (IgGs) or cerebrospinal fluid from patients with MN disease can rescue a significant number of chick embryo MNs from normally occurring PCD. An increase of branching of intramuscular nerves was also observed that may account for the rescuing effects of pathologic IgGs. Proteomic analysis and further analysis by ELISA indicated that these effects may be mediated by the interaction of circulating human immunoglobulins with proteins of the semaphorin family. (C) 2010 Elsevier B.V. All rights reserved.

The distribution of the P2X family of ATP receptors was analyzed in a rat model for amyotrophic lateral sclerosis (ALS) expressing mutated human superoxide dismutase (mSOD1G93A). We showed that strong P2X4 immunoreactivity was selectively associated with degenerating motoneurons (MNs) in spinal cord ventral horn. Degenerating P2X4-positive MNs did not display apoptotic features such as chromatin condensation, positive TUNEL reaction, or active caspase 3 immunostaining. In contrast, these neurons showed other signs of abnormality, such as loss of the neuronal marker NeuN and recruitment of microglial cells with neuronophagic activity. Similar changes were observed in MNs from the cerebral cortex and brainstem in mSOD1G93A in both rat and mice. In addition, P2X4 immunostaining demonstrated the existence of neuronal degeneration in the locus coeruleus, reticular formation, and Purkinje cells of the cerebellar cortex. It is suggested that abnormal trafficking and proteolytic processing of the P2X4 receptor protein may underlie these changes. J. Comp. Neurol. 506:75–92, 2008. © 2007 Wiley-Liss, Inc.

The electric activity of lower motor neurons (MNs) appears to play a role in determining cell-vulnerability in MN diseases. MN excitability is modulated by cholinergic inputs through C-type synaptic boutons, which display an endoplasmic reticulum-related subsurface cistern (SSC) adjacent to the postsynaptic membrane. Besides cholinergic molecules, a constellation of proteins involved in different signal-transduction pathways are clustered at C-type synaptic sites (M2 muscarinic receptors, Kv2.1 potassium channels, Ca2+ activated K+ [SK] channels, and sigma-1 receptors [S1R]), but their collective functional significance so far remains unknown. We have previously suggested that neuregulin-1 (NRG1)/ErbBs-based retrograde signalling occurs at this synapse. To better understand signalling through C-boutons, we performed an analysis of the distribution of C-bouton-associated signalling proteins. We show that within SSC, S1R, Kv2.1 and NRG1 are clustered in highly specific, non-overlapping, microdomains, whereas ErbB2 and ErbB4 are present in the adjacent presynaptic compartment. This organization may define highly ordered and spatially restricted sites for different signal-transduction pathways. SSC associated proteins are disrupted in axotomised MNs together with the activation of microglia, which display a positive chemotactism to C-bouton sites. This indicates that C-bouton associated molecules are also involved in neuroinflammatory signalling in diseased MNs, emerging as new potential therapeutic targets. We would like to thank Dr. Ronald W. Oppenheim for his critical reading of the manuscript and for helpful comments and suggestions. We would also like to thank Marta Hereu for her technical assistance, Lidia Delgado, Gema Marta Martínez and M. Yolanda Muela, from the Unitat de Criomicroscòpia Electrònica (Centres Científics i Tecnològics de la Universitat de Barcelona), for their technical support with ultrastructural immunolabelling, Daniel Cabezas for his help in some experiments, and the SCT animal facility of the Universitat de Lleida for mouse care and housing. This work was supported by grants from the Ministerio de Economía y Competitividad cofinanced by FEDER (SAF2015–70801-R to J.E.E. and J.C.), and from Jack Van den Hoek a la investigació de l’ELA - Fundació Miquel Valls (to J.E.E.).