Synaptic pathology of spinal anterior horn cells in amyotrophic lateral sclerosis: an immunohistochemical study

Patterns of synaptic loss in human amyotrophic lateral sclerosis spinal cord: a clinicopathological study

Amyotrophic Lateral Sclerosis (ALS) is mainly characterized by the degeneration of corticospinal neurons and spinal α-motoneurons; vulnerable cells display prominent pTDP-43 inclusions. Evidence gathered from genetics, murine models, and iPSC-derived neurons point to the early involvement of synapses in the disease course and their crucial role in the pathogenic cascade. However, pathology studies, with specimens from large post-mortem cohorts, mapping the pattern of synaptic disturbances over clinical and neuropathological hallmarks of disease progression, are currently not available. Thus, the appearance and progression of synaptic degeneration in human ALS patients are currently not known, preventing a full validation of the murine and in vitro models. Here, we investigated the loss of synaptophysin-positive terminals in cervical, thoracic, and lumbar spinal cord samples from a retrospective cohort of n = 33 ALS patients and n = 8 healthy controls, and we correlated the loss of synapses against clinicodemographic features and neuropathological ALS stage. We found that, although dorsal and intermediate spinal cord laminae do not lose synapses, ALS patients displayed a substantial but variable loss of synapses in the ventral horn of lumbar and cervical spinal cord. The amount of synaptic loss was predicted by disease duration, by the clinical site of onset, and by the loss of α-motoneurons, although not by the fraction of pTDP-43-immunopositive α-motoneurons. Taken together, our findings validate the synaptic pathology observed in other models and suggest that pathogenic pathways unfolding in the spinal microenvironment are critical to the progressive disassembly of local synaptic connectivity.

Elucidating the Role of Cerebellar Synaptic Dysfunction in C9orf72-ALS/FTD - a Systematic Review and Meta-Analysis

A hexanucleotide repeat expansion in the C9orf72 gene is the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) with synaptic dysfunction identified as an early pathological hallmark. Although TDP-43 pathology and overt neurodegeneration are largely absent from the cerebellum, the pathological hallmarks of RNA foci and dipeptide repeat protein (DPR) inclusions are most abundant. Here, we present a systematic literature search in the databases of PubMed, Scopus, Embase, Web of Science and Science Direct up until March 5, 2021, which yielded 19,515 publications. Following the exclusion criteria, 72 articles were included having referred to C9orf72, synapses and the cerebellum. Meta-analyses were conducted on studies which reported experimental and control groups with means and standard deviations extracted from figures using the online tool PlotDigitizer. This revealed dendritic defects (P = 0.03), reduced C9orf72 in human patients (P = 0.005) and DPR-related neuronal loss (P = 0.0006) but no neuromuscular junction abnormalities (P = 0.29) or cerebellar neuronal loss (P = 0.23). Our results suggest that dendritic arborisation defects, synaptic gene dysregulation and altered synaptic neurotransmission may drive cerebellar synaptic dysfunction in C9-ALS/FTD. In this review, we discuss how the chronological appearance of the different pathological hallmarks alters synaptic integrity which may have profound implications for disease progression. We conclude that a reduction in C9orf72 protein levels combined with the accumulation of RNA foci and DPRs act synergistically to drive C9 synaptopathy in the cerebellum of C9-ALS/FTD patients.

Sarm1 knockout modifies biomarkers of neurodegeneration and spinal cord circuitry but not disease progression in the mSOD1G93A mouse model of ALS

The mechanisms underlying the loss of motor neuron axon integrity in amyotrophic lateral sclerosis (ALS) are unclear. SARM1 has been identified as a genetic risk variant in sporadic ALS, and the SARM1 protein is a key mediator of axon degeneration. To investigate the role of SARM1 in ALS-associated axon degeneration, we knocked out Sarm1 (Sarm1^KO) in mSOD1^G93ATg (mSOD1) mice. Animals were monitored for ALS disease onset and severity, with motor function assessed at pre-symptomatic and late-stage disease and lumbar spinal cord and sciatic nerve harvested for immunohistochemistry at endpoint (20 weeks). Serum was collected monthly to assess protein concentrations of biomarkers linked to axon degeneration (neurofilament light (NFL) and tau), and astrogliosis (glial fibrillary acidic protein (GFAP)), using single molecule array (Simoa®) technology. Overall, loss of Sarm1 in mSOD1 mice did not slow or delay symptom onset, failed to improve functional declines, and failed to protect motor neurons. Serum NFL levels in mSOD1 mice increased between 8 -12 and 16-20 weeks of age, with the later increase significantly reduced by loss of SARM1. Similarly, loss of SARM1 significantly reduced an increase in serum GFAP between 16 and 20 weeks of age in mSOD1 mice, indicating protection of both global axon degeneration and astrogliosis. In the spinal cord, Sarm1 deletion protected against loss of excitatory VGluT2-positive puncta and attenuated astrogliosis in mSOD1 mice. In the sciatic nerve, absence of SARM1 in mSOD1 mice restored the average area of phosphorylated neurofilament reactivity towards WT levels. Together these data suggest that Sarm1^KO in mSOD1 mice is not sufficient to ameliorate functional decline or motor neuron loss but does alter serum biomarker levels and provide protection to axons and glutamatergic synapses. This indicates that treatments targeting SARM1 could warrant further investigation in ALS, potentially as part of a combination therapy.

Glial Contribution to Excitatory and Inhibitory Synapse Loss in Neurodegeneration

Synapse loss is an early feature shared by many neurodegenerative diseases, and it represents the major correlate of cognitive impairment. Recent studies reveal that microglia and astrocytes play a major role in synapse elimination, contributing to network dysfunction associated with neurodegeneration. Excitatory and inhibitory activity can be affected by glia-mediated synapse loss, resulting in imbalanced synaptic transmission and subsequent synaptic dysfunction. Here, we review the recent literature on the contribution of glia to excitatory/inhibitory imbalance, in the context of the most common neurodegenerative disorders. A better understanding of the mechanisms underlying pathological synapse loss will be instrumental to design targeted therapeutic interventions, taking in account the emerging roles of microglia and astrocytes in synapse remodeling.

The role of mutated SOD1 gene in synaptic stripping and MHC class I expression following nerve axotomy in ALS murine model

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by motoneuron death. Several cellular pathways have been described to be involved in ALS pathogenesis; however, the involvement of presynaptic stripping and the related MHC class I molecules in mutant SOD1 motoneurons remains to be clarified. To this purpose, we here investigated, for the first time, the motoneurons behavior, di per se and after facial axonal injury, in terms of synaptic stripping and MHC class I expression in wild-type (Wt) mice and in a murine model of ALS, the SOD1(G93A) mice, at the presymptomatic and symptomatic stage of the disease. Concerning Wt animals, we found a reduction in synaptophysin immunoreactivity and an increase of MHC class I molecules in facial motoneurons after axotomy. In uninjured motoneurons of SOD1(G93A) mice, an altered presynaptic framework was evident, and this phenomenon increased during the disease course. The alteration in the presynaptic input is related to excitatory fibers. Moreover, after injury, a further decrease of excitatory input was not associated to an upregulation of MHC class I molecules in motoneuron soma. This study demonstrates, for the first time, that the presence of mutated SOD1 protein affects the MHC class I molecules expression, altering the presynaptic input in motoneurons. Nevertheless, a positive MHC class I immunolabeling was evident in glial cells around facial injured motoneurons, underlying an involvement of these cells in synaptic stripping. This study contributes to better understand the involvement of the mutated SOD1 protein in the vulnerability of motoneurons after damage.

Synaptic Failure: Focus in an Integrative View of ALS

From early description by Charcot, the classification of the Amyotrophic Lateral Sclerosis (ALS) is evolving from a subtype of Motor Neuron (MN) Disease to be considered rather a multi-systemic, non-cell autonomous and complex neurodegenerative disease. In the last decade, the huge amount of knowledge acquired has shed new insights on the pathological mechanisms underlying ALS from different perspectives. However, a whole vision on the multiple dysfunctional pathways is needed with the inclusion of information often excluded in other published revisions. We propose an integrative view of ALS pathology, although centered on the synaptic failure as a converging and crucial player to the etiology of the disease. Homeostasis of input and output synaptic activity of MNs has been proved to be severely and early disrupted and to definitively contribute to microcircuitry alterations at the spinal cord. Several cells play roles in synaptic communication across the MNs network system such as interneurons, astrocytes, microglia, Schwann and skeletal muscle cells. Microglia are described as highly dynamic surveying cells of the nervous system but also as determinant contributors to the synaptic plasticity linked to neuronal activity. Several signaling axis such as TNFα/TNFR1 and CX3CR1/CX3CL1 that characterize MN-microglia cross talk contribute to synaptic scaling and maintenance, have been found altered in ALS. The presence of dystrophic and atypical microglia in late stages of ALS, with a decline in their dynamic motility and phagocytic ability, together with less synaptic and neuronal contacts disrupts the MN-microglia dialogue, decreases homeostatic regulation of neuronal activity, perturbs “on/off” signals and accelerates disease progression associated to impaired synaptic function and regeneration. Other hotspot in the ALS affected network system is the unstable neuromuscular junction (NMJ) leading to distal axonal degeneration. Reduced neuromuscular spontaneous synaptic activity in ALS mice models was also suggested to account for the selective vulnerability of MNs and decreased regenerative capability. Synaptic destabilization may as well derive from increased release of molecules by muscle cells (e.g. NogoA) and by terminal Schwann cells (e.g. semaphorin 3A) conceivably causing nerve terminal retraction and denervation, as well as inhibition of re-connection to muscle fibers. Indeed, we have overviewed the alterations on the metabolic pathways and self-regenerative capacity presented in skeletal muscle cells that contribute to muscle wasting in ALS. Finally, a detailed footpath of pathologic changes on MNs and associated dysfunctional and synaptic alterations is provided. The oriented motivation in future ALS studies as outlined in the present article will help in fruitful novel achievements on the mechanisms involved and in developing more target-driven therapies that will bring new hope in halting or delaying disease progression in ALS patients.

4-Aminopyridine Induced Activity Rescues Hypoexcitable Motor Neurons from Amyotrophic Lateral Sclerosis Patient-Derived Induced Pluripotent Stem Cells

Despite decades of research on amyotrophic lateral sclerosis (ALS), there is only one approved drug, which minimally extends patient survival. Here, we investigated pathophysiological mechanisms underlying ALS using motor neurons (MNs) differentiated from induced pluripotent stem cells (iPSCs) derived from ALS patients carrying mutations in FUS or SOD1. Patient-derived MNs were less active and excitable compared to healthy controls, due to reduced Na(+) /K(+) ratios in both ALS groups accompanied by elevated potassium channel (FUS) and attenuated sodium channel expression levels (FUS, SOD1). ALS iPSC-derived MNs showed elevated endoplasmic reticulum stress (ER) levels and increased caspase activation. Treatment with the FDA approved drug 4-Aminopyridine (4AP) restored ion-channel imbalances, increased neuronal activity levels and decreased ER stress and caspase activation. This study provides novel pathophysiological data, including a mechanistic explanation for the observed hypoexcitability in patient-derived MNs and a new therapeutic strategy to provide neuroprotection in MNs affected by ALS. Stem Cells 2016;34:1563-1575.

Human iPSC-derived motoneurons harbouring TARDBP or C9ORF72 ALS mutations are dysfunctional despite maintaining viability

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease for which a greater understanding of early disease mechanisms is needed to reveal novel therapeutic targets. We report the use of human induced pluripotent stem cell (iPSC)-derived motoneurons (MNs) to study the pathophysiology of ALS. We demonstrate that MNs derived from iPSCs obtained from healthy individuals or patients harbouring TARDBP or C9ORF72 ALS-causing mutations are able to develop appropriate physiological properties. However, patient iPSC-derived MNs, independent of genotype, display an initial hyperexcitability followed by progressive loss of action potential output and synaptic activity. This loss of functional output reflects a progressive decrease in voltage-activated Na(+) and K(+) currents, which occurs in the absence of overt changes in cell viability. These data implicate early dysfunction or loss of ion channels as a convergent point that may contribute to the initiation of downstream degenerative pathways that ultimately lead to MN loss in ALS.

Anatomy and function of cholinergic C bouton inputs to motor neurons

Motor control circuitry of the central nervous system must be flexible so that motor behaviours can be adapted to suit the varying demands of different states, developmental stages, and environments. Flexibility in motor control is largely provided by neuromodulatory systems which can adjust the output of motor circuits by modulating the properties and connectivity of neurons within them. The spinal circuitry which controls locomotion is subject to a range of neuromodulatory influences, including some which are intrinsic to the spinal cord. One such intrinsic neuromodulatory system, for which a wealth of anatomical information has recently been combined with new physiological data, is the C bouton system. C boutons are large, cholinergic inputs to motor neurons which were first described over 40 years ago but whose source and function have until recently remained a mystery. In this review we discuss how the convergence of anatomical, molecular genetic and physiological data has recently led to significant advances in our understanding of this unique neuromodulatory system. We also highlight evidence that C boutons are involved in spinal cord injury and disease, revealing their potential as targets for novel therapeutic strategies.

Early presymptomatic cholinergic dysfunction in a murine model of amyotrophic lateral sclerosis

Sporadic and familiar amyotrophic lateral sclerosis (ALS) cases presented lower cholinergic activity than in healthy individuals in their still preserved spinal motoneurons (MNs) suggesting that cholinergic reduction might occur before MN death. To unravel how and when cholinergic function is compromised, we have analyzed the spatiotemporal expression of choline acetyltransferase (ChAT) from early presymptomatic stages of the SOD1(G93A) ALS mouse model by confocal immunohistochemistry. The analysis showed an early reduction in ChAT content in soma and presynaptic boutons apposed onto MNs (to 76%) as well as in cholinergic interneurons in the lumbar spinal cord of the 30-day-old SOD1(G93A) mice. Cholinergic synaptic stripping occurred simultaneously to the presence of abundant surrounding major histocompatibility complex II (MHC-II)-positive microglia and the accumulation of nuclear Tdp-43 and the appearance of mild oxidative stress within MNs. Besides, there was a loss of neuronal MHC-I expression, which is necessary for balanced synaptic stripping after axotomy. These events occurred before the selective raise of markers of denervation such as ATF3. By the same time, alterations in postsynaptic cholinergic-related structures were also revealed with a loss of the presence of sigma-1 receptor, a Ca2+ buffering chaperone in the postsynaptic cisternae. By 2 months of age, ChAT seemed to accumulate in the soma of MNs, and thus efferences toward Renshaw interneurons were drastically diminished. In conclusion, cholinergic dysfunction in the local circuitry of the spinal cord may be one of the earliest events in ALS etiopathogenesis.

Reduction in the motoneuron inhibitory/excitatory synaptic ratio in an early-symptomatic mouse model of amyotrophic lateral sclerosis

Excitotoxicity is a widely studied mechanism underlying motoneuron degeneration in amyotrophic lateral sclerosis (ALS). Synaptic alterations that produce an imbalance in the ratio of inhibitory/excitatory synapses are expected to promote or protect against motoneuron excitotoxicity. In ALS patients, motoneurons suffer a reduction in their synaptic coverage, as in the transition from the presymptomatic (2-month-old) to early-symptomatic (3-month-old) stage of the hSOD1(G93A) mouse model of familial ALS. Net synapse loss resulted from inhibitory bouton loss and excitatory synapse gain. Furthermore, in 3-month-old transgenic mice, remaining inhibitory but not excitatory boutons attached to motoneurons showed reduction in the active zone length and in the spatial density of synaptic vesicles in the releasable pool near the active zone. Bouton degeneration/loss seems to be mediated by bouton vacuolization and by mechanical displacement due to swelling vacuolated dendrites. In addition, chronic treatment with a nitric oxide (NO) synthase inhibitor avoided inhibitory loss but not excitatory gain. These results indicate that NO mediates inhibitory loss occurring from the pre- to early-symptomatic stage of hSOD1(G93A) mice. This work contributes new insights on ALS pathogenesis, recognizing synaptic re-arrangement onto motoneurons as a mechanism favoring disease progression rather than as a protective homeostatic response against excitotoxic events.

NO orchestrates the loss of synaptic boutons from adult "sick" motoneurons: modeling a molecular mechanism

Synapse elimination is the main factor responsible for the cognitive decline accompanying many of the neuropathological conditions affecting humans. Synaptic stripping of motoneurons is also a common hallmark of several motor pathologies. Therefore, knowledge of the molecular basis underlying this plastic process is of central interest for the development of new therapeutic tools. Recent advances from our group highlight the role of nitric oxide (NO) as a key molecule triggering synapse loss in two models of motor pathologies. De novo expression of the neuronal isoform of NO synthase (nNOS) in motoneurons commonly occurs in response to the physical injury of a motor nerve and in the course of amyotrophic lateral sclerosis. In both conditions, this event precedes synaptic withdrawal from motoneurons. Strikingly, nNOS-synthesized NO is "necessary" and "sufficient" to induce synaptic detachment from motoneurons. The mechanism involves a paracrine/retrograde action of NO on pre-synaptic structures, initiating a downstream signaling cascade that includes sequential activation of (1) soluble guanylyl cyclase, (2) cyclic guanosine monophosphate-dependent protein kinase, and (3) RhoA/Rho kinase (ROCK) signaling. Finally, ROCK activation promotes phosphorylation of regulatory myosin light chain, which leads to myosin activation and actomyosin contraction. This latter event presumably contributes to the contractile force to produce ending axon retraction. Several findings support that this mechanism may operate in the most prevalent neurodegenerative diseases.

Glycinergic innervation of motoneurons is deficient in amyotrophic lateral sclerosis mice: a quantitative confocal analysis

Altered motoneuron excitability is involved in amyotrophic lateral sclerosis pathobiology. To test the hypothesis that inhibitory interneuron innervation of spinal motoneurons is abnormal in an amyotrophic lateral sclerosis mouse model, we measured GABAergic, glycinergic, and cholinergic immunoreactive terminals on spinal motoneurons in mice expressing a mutant form of human superoxide dismutase-1 with a Gly93-->Ala substitution (G93A-SOD1) and in controls at different ages. Glutamic acid decarboxylase, glycine transporter-2, and choline acetyltransferase were used as markers for GABAergic, glycinergic, and cholinergic terminals, respectively. Triple immunofluorescent labeling of boutons contacting motoneurons was visualized by confocal microscopy and analyzed quantitatively. Glycine transporter-2-bouton density on lateral motoneurons was decreased significantly in G93A-SOD1 mice compared with controls. This reduction was absent at 6 weeks of age but present in asymptomatic 8-week-old mice and worsened with disease progression from 12 to 14 weeks of age. Motoneurons lost most glycinergic innervation by 16 weeks of age (end-stage) when there was a significant decrease in the numbers of motoneurons and choline acetyltransferase-positive boutons. No significant differences in glutamic acid decarboxylase-bouton densities were found in G93A-SOD1 mice. Reduction of glycinergic innervation preceded mitochondrial swelling and vacuolization. Calbindin-positive Renshaw cell number was decreased significantly at 12 weeks of age in G93A-SOD1 mice. Thus, either the selective loss of inhibitory glycinergic regulation of motoneuron function or glycinergic interneuron degeneration contributes to motoneuron degeneration in amyotrophic lateral sclerosis.

Morphofunctional characteristics of the lumbar enlargement of the spinal cord in rats

The topography of the lumbar enlargement of the spinal cord in rats was studied; an immunohistochemical method was used to determine the distribution of synaptophysin--a membrane protein of synaptic vesicles. Synaptophysin-immunoreactive structures were detected in the gray matter of all Rexed laminae, around most neurons and in the neuropil. Previously undescribed subpial synaptic contacts were detected immunohistochemically in the white matter and confirmed by electron microscopy. A non-myelinated component of the corticospinal tract, including axonal varicosities and synaptic contacts, was observed in the dorsal part of the white matter of the lumbar enlargement of the spinal cord.

RNAi knockdown of Par-4 inhibits neurosynaptic degeneration in ALS-linked mice

Evidence from human amyotrophic lateral sclerosis (ALS) patients and ALS-linked Cu/Zn superoxide dismutase (Cu/Zn-SOD) transgenic mice bearing the mutation of glycine to alanine at position 93 (G93A) suggests that the pro-apoptotic protein prostate apoptosis response-4 (Par-4) might be a critical link in the chain of events leading to motor neuron degeneration. We now report that Par-4 is enriched in synaptosomes and post-synaptic density from the ventral horn of the spinal cord. Levels of Par-4 in synaptic compartments increased significantly during rapid and slow declining stages of muscle strength in hSOD1 G93A mutant mice. In the pre-muscle weakness stage, hSOD1 G93A mutation sensitized synaptosomes from the ventral horn of the spinal cord to increased levels of Par-4 expression following excitotoxic and apoptotic insults. In ventral spinal synaptosomes, Par-4-mediated production of pro-apoptotic cytosolic factor(s) was significantly enhanced by the hSOD1 G93A mutation. RNA interference (RNAi) knockdown of Par-4 inhibited mitochondrial dysfunction and caspase-3 activation induced by G93A mutation in synaptosomes from the ventral horn of the spinal cord, and protected spinal motor neurons from apoptosis. These results identify the synapse as a crucial cellular site for the cell death promoting actions of Par-4 in motor neurons, and suggest that targeted inhibition of Par-4 by RNAi may prove to be a neuroprotective strategy for motor neuron degeneration.

Synaptic lesions and synaptophysin distribution change in spinal motoneurons at early stages following sciatic nerve transection in neonatal rats

The purpose of this investigation was to evaluate the rate of synaptic stripping, changes in the synaptophysin distribution, and synapses ultrastructure of spinal motoneurons at early stages of sciatic nerve axotomy in newborn rats. Seven groups were used in the experiment, which were sacrificed after 1, 3, 6, 12, 24, 48 and 72 h. L4-L6 spinal segments from the animals of the above groups were prepared and processed for indirect immunoperoxidase. Accordingly, tissue samples were prepared from similar groups for routine electron microscopy. Synaptophysin-labeled motoneurons were classified into intact, partial, cytoplasmic and negative patterns. Synaptophysin immunoreactivity in both the axotomized and non-axotomized sides showed no negative pattern at the first three time points, while this pattern significantly increased in the 12, 24, 48 and 72 h groups at the axotomized side, moreover, there was a progressive reduction in the percentage of the intact pattern at the axotomized side. The percentages of the cytoplasmic and partial patterns also increased during the time course. The rate of synaptic stripping was five time higher in the axotomized side than that of non-axotomized side. The results of the ultrastructural study showed synaptic membranes irregularity, synaptic vesicles displacement, synaptic membrane detachment and ensheathment of degenerated synapses. The conclusion of the study was that early synaptophysin immunoreactivity changes were seen in both the axotomized and non-axotomized sides, but the rate of change in the axotomized side was more rapid than that of the non-axotomized side.

Cell death and decreased synaptic protein expression in the ventral horn of Holstein-Friesian calves with spinal muscular atrophy

A neuropathological study of Holstein-Friesian calves with spinal muscular atrophy (SMA) demonstrated decreased numbers of motor neurons in the brachial and lumbo-sacral regions of the spinal cord, together with swelling and accumulation of phosphorylated neurofilaments, and neuronophagia in most of the remaining motor neurons. The pyramidal tracts, motor cortex and thalamus were not affected. Synaptophysin immunohistochemistry revealed a marked reduction of punctate terminals but only around swollen neurones, suggesting loss of terminal afferents on motor neurons at advanced stages of the degenerative process. An immunohistochemical study of proteins linked with cell death and cell survival demonstrated reduced expression of Fas, Fas-L, Bcl-2 and Bax in swollen motor neurons. Punctate cytochrome C immunoreactivity, consistent with mitochondrial localization, was detected in the soma of normal motor neurons, but not in swollen motor neurons. Finally, no labelling of motor neurons with antibodies to cleaved (active) caspase-3 (17kD) was detected, suggesting a lack of involvement of the apoptotic pathways in motor neuron death. Taken together, the present findings point to necrosis as a major cause of motor neuron death in the advanced stages of SMA in Holstein-Friesian calves.

Disconnection of cerebellar Purkinje cells in Kearns-Sayre syndrome

Kearns-Sayre syndrome (KSS) is a sporadic multisystem disorder due to rearrangements in mitochondrial DNA (mtDNA). To gain further insight into the pathogenesis of cerebellar dysfunction in KSS, antibodies against synaptophysin (SY) were used to identify presynaptic terminals and antibodies to calbindin D (CB) to identify Purkinje cells in the cerebellar cortex and in the dentate nucleus from two autopsied cases of KSS. By conventional neuropathology we found marked spongiform degeneration and by immunohistochemistry a disruption of presynaptic terminals and of the terminal arborizations of Purkinje cell axons on multipolar neurons of the dentate nucleus in the KSS patients. We suggest that a disconnection of Purkinje cells at the dentate nucleus may play a role in the pathogenesis of cerebellar ataxia in KSS.

Synaptophysin staining in normal brain: importance for diagnosis of ganglioglioma

Neuronal and mixed glioneuronal tumors traditionally have comprised a very small percentage of intrinsic central nervous system neoplasms, although they are somewhat more common among juvenile brain tumors and in the temporal lobe. Neuronal differentiation increasingly is recognized in pleomorphic xanthoastrocytoma, intraventricular neurocytoma, and subependymal giant cell astrocytoma. However, the diagnostic distinctions between subtle ganglioglioma (with rare neurons) and infiltrating glioma with entrapped neurons and between infiltrating oligodendroglioma and parenchymal neurocytoma are problematic but may be clinically important. Recently, it was proposed that perisomatic synaptophysin immunostaining in the human central nervous system reliably and selectively discriminates neoplastic from nonneoplastic neurons. Using this criterion, the number of brain stem and spinal cord gangliogliomas could be increased substantially. We canvassed synaptophysin immunostaining patterns in the normal brain stem, cerebellum, and forebrain, and found that synaptophysin-positive neurons are distributed broadly in the normal human brain. In disturbed neocortical tissue, such as near vascular malformations, synaptophysin-positive neurons and irregular white-matter synaptophysin immunostaining are visualized. Although synaptophysin-positive neurons are found in gangliogliomas and archipelagos of synaptophysin reactivity are found in neurocytomas, these patterns clearly are not pathognomonic for glioneuronal tumors and must be interpreted with caution whenever other histologic or ultrastructural evidence of neuronal differentiation is lacking.

Ultrastructural study of synapses in the anterior horn neurons of patients with amyotrophic lateral sclerosis

This report concerns an ultrastructural examination of the synapses present on the surface of somata of anterior horn neurons of the lumbar spinal cord of seven patients with amyotrophic lateral sclerosis (ALS). Specimens from six age-matched, neurologically normal control individuals were included for comparison. Examination of presynaptic terminals revealed a wide range of changes not only in degenerated neurons (central chromatolytic neurons), but, to a lesser extent, in normal-appearing neurons. The alterations included dense conglomerates of aggregated dark mitochondria and presynaptic vesicles, bundles of neurofilaments, as well as marked increase of presynaptic vesicles. Our observations suggest that in patients with ALS a substantial synaptic alteration does take place in the early stages of anterior horn neuron degeneration and degeneration of axosomatic synapses of anterior horn neurons in ALS may be of consequence on lower motor neuron degeneration.

Abnormal excitability of the corticospinal pathway in patients with amyotrophic lateral sclerosis: a single motor unit study using transcranial magnetic stimulation

The pathophysiology of corticospinal tract degeneration in amyotrophic lateral sclerosis (ALS) was investigated by studying the effect of transcranial magnetic stimulation on discharge characteristics of single motor units during voluntary activation. The motor units were recorded from the first dorsal interosseus muscles of 12 patients with ALS, 14 healthy subjects, 12 patients with upper motor neuron lesions and 9 with pure lower motor neuron diseases. More than 100 magnetic stimuli were delivered over the scalp during minimal muscle contraction. The occurrence of motor unit discharges was plotted in a peristimulus time histogram. An increase in discharge probability at latencies of 20-30 msec, that represents monosynaptic activation (primary peak) was found in normal units. Motor units from ALS patients with short disease durations had significantly increased discharge probabilities in the primary peak (P < 0.001). Motor units from 4 ALS patients with upper motor neuron signs showed double primary peaks: an initial synchronized peak followed by a dispersed peak. The latter was ascribed to a slow corticospinal pathway, which remains undetected or is functionally insignificant in healthy subjects. We conclude that the excitabilities of the surviving corticospinal tract pathways are abnormally increased in ALS, especially in the early stage.

Structural changes of anterior horn neurons and their synaptic input caudal to a low thoracic spinal cord hemisection in the adult rat: a light and electron microscopic study

Structural changes in lumbosacral ventral horn neurons and their synaptic input were studied at 3, 10, 21, 42, and 90 days following low thoracic cord hemisection in adult rats by light microscopic examination of synaptophysin immunoreactivity (SYN-IR) and by electron microscopy. There was an ipsilateral transient decrease in SYN-IR at the somal and proximal dendritic surfaces of anterior horn neurons which extended caudally from the site of injury over a postoperative (p.o.) period of 42 days. Concomitantly, at 21 days p.o., perineuronal SYN-IR started to recover in upper lumbar segments. By 90 days p.o., a normal staining pattern of SYN was noted in upper and mid lumbar segments, but the perineuronal SYN-IR was still slightly below normal levels in low lumbar and sacral segments. Electron microscopy revealed ultrastructural changes coincident with the alterations in SYN-IR. At 3 days p.o., phagocytosis of degenerating axon terminals by activated microglial cells was observed at the somal and proximal dendritic surfaces of ventral horn neurons. These changes were most prominent up to two segments caudal to the lesion. At 10 days p.o., advanced stages of bouton phagocytosis were still detectable in all lumbosacral motor nuclei. Additionally, abnormal axon terminals, with a few dispersed synaptic vesicles and accumulations of large mitochondria, appeared at the scalloped somal surfaces of anterior horn neurons. At 21 days p.o., several large lumbosacral motoneurons had developed chromatolysis-like ultrastructural alterations and motoneuronal cell bodies had become partially covered by astrocytic lamellae. At 42 days p.o., there was a transient appearance of polyribosomes in some M-type boutons. In addition, at 42 and 90 days p.o., a few degenerating motoneurons were detected in all lumbosacral segments, but most displayed normal neuronal cell bodies contacted by numerous intact synapses as well as by astrocytic processes. In contrast to these striking alterations of synaptic input at somal and proximal dendritic surfaces of motoneurons, relatively few degenerating boutons were detected in the neuropil of motor nuclei at all the p.o. times studied. We suggest that the preferential disturbance of the predominantly inhibitory axosomatic synapses on ventral horn neurons may be involved in the mechanisms which influence the well-established increase in motoneuronal excitability after spinal cord injury.

Synaptic loss in the proximal axon of anterior horn neurons in motor neuron disease

This report deals with an ultrastructural investigation of the synapses of the proximal axons of normal-appearing anterior horn neurons of 7 patients with amyotrophic lateral sclerosis (ALS) and 4 patients with motor neuron disease who had no upper motor neuron and corticospinal tract involvement (lower motor neuron disease, LMND). Specimens from 12 age-matched individuals who died of non-neurological diseases served as controls. Proximal axons directly emanating from the normal-appearing neurons were examined: 42 axons were from ALS patients, 43 from LMND patients and 87 from controls. Our results show that the number of synapses on axon hillocks, as well as the lengths of the synaptic contact and of the active zone were reduced in both groups of patients (P < 0.0001), but no significant differences were seen between patients and controls with respect to the synaptic parameters of initial axon segments. There was no overall difference between ALS and LMND patients. These findings suggest that the electrophysiological functions pertaining to integration of electrical inputs into the axon and information transduction on the axon may be greatly impaired in the early stages of motor neuron diseases, and that the observed synaptic alterations may be pathological events, likely to be due to anterior horn neuron degeneration.

Synaptic vesicle proteins, synaptophysin and chromogranin A in amyotrophic lateral sclerosis

In amyotrophic lateral sclerosis (ALS) it is not known which motoneuron is affected first. The study of synaptic proteins may contribute to the clarification of the problem. Fifteen cases of ALS and five control cases were studied with the immunohistochemical demonstration of synaptophysin (Sy) and chromogranin A (CgA). Sy is a typical membrane protein of small synaptic vesicles (SSV), whereas CgA is found in large dense core vesicles (LDCV) and in neurosecretory granules. In controls, Sy is distributed as dots on the neuronal surface, on proximal dendrites and in neuropil, whereas CgA is found in perikarya and dendrites and as puncta in the neuropil. In ALS there is a marked decrease of Sy-positive dots. In chromatolytic neurons and spheroids a diffuse reaction may occur. CgA-positive dots disappear in ALS, sometimes replaced by a dust-like positivity. CgA is produced by Golgi apparatus and its reduction in ALS corresponds to the fragmentation of the Golgi complex, described in the literature. The findings are interpreted as secondary to the lower motoneuron degeneration and discussed in relation to our knowledge on vesicle production and migration in the neuron and on synapses in the anterior horns of spinal cord.