Oculomotor nuclear pathology in amyotrophic lateral sclerosis

Cellular and axonal transport phenotypes due to the C9ORF72 HRE in iPSC motor and sensory neurons

Induced pluripotent stem cell (iPSC)-derived motor neurons (MNs) from patients with amyotrophic lateral sclerosis (ALS) and the C9ORF72 hexanucleotide repeat expansion (HRE) have multiple cellular phenotypes, but which of these accurately reflect the biology underlying the cell-specific vulnerability of ALS is uncertain. We therefore compared phenotypes due to the C9ORF72 HRE in MNs with sensory neurons (SNs), which are relatively spared in ALS. The iPSC models were able to partially reproduce the differential gene expression seen between adult SNs and MNs. We demonstrated that the typical hallmarks of C9ORF72-ALS, including RNA foci and dipeptide formation, as well as specific axonal transport defects, occurred equally in MNs and SNs, suggesting that these in vitro phenotypes are not sufficient to explain the cell-type selectivity of ALS in isolation.

Molecular and cellular mechanisms of selective vulnerability in neurodegenerative diseases

The selective vulnerability of specific neuronal subtypes is a hallmark of neurodegenerative diseases. In this Review, I summarize our current understanding of the brain regions and cell types that are selectively vulnerable in different neurodegenerative diseases and describe the proposed underlying cell-autonomous and non-cell-autonomous mechanisms. I highlight how recent methodological innovations - including single-cell transcriptomics, CRISPR-based screens and human cell-based models of disease - are enabling new breakthroughs in our understanding of selective vulnerability. An understanding of the molecular mechanisms that determine selective vulnerability and resilience would shed light on the key processes that drive neurodegeneration and point to potential therapeutic strategies to protect vulnerable cell populations.

Identification of molecular signatures defines the differential proteostasis response in induced spinal and cranial motor neurons

Amyotrophic lateral sclerosis damages proteostasis, affecting spinal and upper motor neurons earlier than a subset of cranial motor neurons. To aid disease understanding, we exposed induced cranial and spinal motor neurons (iCrMNs and iSpMNs) to proteotoxic stress, under which iCrMNs showed superior survival, quantifying the transcriptome and proteome for >8,200 genes at 0, 12, and 36 h. Two-thirds of the proteome showed cell-type differences. iSpMN-enriched proteins related to DNA/RNA metabolism, and iCrMN-enriched proteins acted in the endoplasmic reticulum (ER)/ER chaperone complex, tRNA aminoacylation, mitochondria, and the plasma/synaptic membrane, suggesting that iCrMNs expressed higher levels of proteins supporting proteostasis and neuronal function. When investigating the increased proteasome levels in iCrMNs, we showed that the activity of the 26S proteasome, but not of the 20S proteasome, was higher in iCrMNs than in iSpMNs, even after a stress-induced decrease. We identified Ublcp1 as an iCrMN-specific regulator of the nuclear 26S activity.

Selective vulnerability of motor neuron types and functional groups to degeneration in amyotrophic lateral sclerosis: review of the neurobiological mechanisms and functional correlates

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative condition characterised by a progressive loss of motor neurons controlling voluntary muscle activity. The disease manifests through a variety of motor dysfunctions related to the extent of damage and loss of neurons at different anatomical locations. Despite extensive research, it remains unclear why some motor neurons are especially susceptible to the disease, while others are affected less or even spared. In this article, we review the neurobiological mechanisms, neurochemical profiles, and morpho-functional characteristics of various motor neuron groups and types of motor units implicated in their differential exposure to degeneration. We discuss specific cell-autonomous (intrinsic) and extrinsic factors influencing the vulnerability gradient of motor units and motor neuron types to ALS, with their impact on disease manifestation, course, and prognosis, as revealed in preclinical and clinical studies. We consider the outstanding challenges and emerging opportunities for interpreting the phenotypic and mechanistic variability of the disease to identify targets for clinical interventions.

Different saccadic profile in bulbar versus spinal-onset amyotrophic lateral sclerosis

Two clinical phenotypes characterize the onset of amyotrophic lateral sclerosis (ALS): the spinal variant, with symptoms beginning in the limbs, and the bulbar variant, affecting firstly speech and swallowing. The two variants show some distinct features in the histopathology, localization and prognosis, but to which extent they really differ clinically and pathologically remains to be clarified. Recent neuropathological and neuroimaging studies have suggested a broader spreading of the neurodegenerative process in ALS, extending beyond the motor areas, toward other cortical and deep grey matter regions, many of which are involved in visual processing and saccadic control. Indeed, a wide range of eye movement deficits have been reported in ALS, but they have never been used to distinguish the two ALS variants. Since quantifying eye movements is a very sensitive and specific method for the study of brain networks, we compared different saccadic and visual search behaviours across spinal ALS patients (n = 12), bulbar ALS patients (n = 6) and healthy control subjects (n = 13), along with cognitive and MRI measures, with the aim to define more accurately the two patients subgroups and possibly clarify a different underlying neural impairment. We found separate profiles of visually-guided saccades between spinal (short saccades) and bulbar (slow saccades) ALS, which could result from the pathologic involvement of different pathways. We suggest an early involvement of the parieto-collicular-cerebellar network in spinal ALS and the fronto-brainstem circuit in bulbar ALS. Overall, our data confirm the diagnostic value of the eye movements analysis in ALS and add new insight on the involved neural networks.

The Cell Autonomous and Non-Cell Autonomous Aspects of Neuronal Vulnerability and Resilience in Amyotrophic Lateral Sclerosis

Simple Summary

Amyotrophic lateral sclerosis (ALS) is a fatal disease characterized by a progressive paralysis due to the loss of particular neurons in our nervous system called motor neurons, that exert voluntary control of all our skeletal muscles. It is not entirely understood why motor neurons are particularly vulnerable in ALS, neither is it completely clear why certain groups of motor neurons, including those that regulate eye movement, are rather resilient to this disease. However, both vulnerability and resilience to ALS likely reflect cell intrinsic properties of different motor neuron subpopulations as well as non-cell autonomous events regulated by surrounding cell types. In this review we dissect the particular properties of different motor neuron types and their responses to disease that may underlie their respective vulnerabilities and resilience. Disease progression in ALS involves multiple cell types that are closely connected to motor neurons and we here also discuss their contributions to the differential vulnerability of motor neurons.

Abstract

Amyotrophic lateral sclerosis (ALS) is defined by the loss of upper motor neurons (MNs) that project from the cerebral cortex to the brain stem and spinal cord and of lower MNs in the brain stem and spinal cord which innervate skeletal muscles, leading to spasticity, muscle atrophy, and paralysis. ALS involves several disease stages, and multiple cell types show dysfunction and play important roles during distinct phases of disease initiation and progression, subsequently leading to selective MN loss. Why MNs are particularly vulnerable in this lethal disease is still not entirely clear. Neither is it fully understood why certain MNs are more resilient to degeneration in ALS than others. Brain stem MNs of cranial nerves III, IV, and VI, which innervate our eye muscles, are highly resistant and persist until the end-stage of the disease, enabling paralyzed patients to communicate through ocular tracking devices. MNs of the Onuf’s nucleus in the sacral spinal cord, that innervate sphincter muscles and control urogenital functions, are also spared throughout the disease. There is also a differential vulnerability among MNs that are intermingled throughout the spinal cord, that directly relate to their physiological properties. Here, fast-twitch fatigable (FF) MNs, which innervate type IIb muscle fibers, are affected early, before onset of clinical symptoms, while slow-twitch (S) MNs, that innervate type I muscle fibers, remain longer throughout the disease progression. The resilience of particular MN subpopulations has been attributed to intrinsic determinants and multiple studies have demonstrated their unique gene regulation and protein content in health and in response to disease. Identified factors within resilient MNs have been utilized to protect more vulnerable cells. Selective vulnerability may also, in part, be driven by non-cell autonomous processes and the unique surroundings and constantly changing environment close to particular MN groups. In this article, we review in detail the cell intrinsic properties of resilient and vulnerable MN groups, as well as multiple additional cell types involved in disease initiation and progression and explain how these may contribute to the selective MN resilience and vulnerability in ALS.

Amyotrophic lateral sclerosis and delayed onset muscle soreness in light of the impaired blink and stretch reflexes – watch out for Piezo2

Amyotrophic lateral sclerosis (ALS) is a fatal, multisystem neurodegenerative disease that causes the death of motoneurons (MNs) progressively and eventually leads to paralysis. In contrast, delayed onset muscle soreness (DOMS) is defined as delayed onset soreness, muscle stiffness, loss of force-generating capacity, reduced joint range of motion, and decreased proprioceptive function. Sensory deficits and impaired proprioception are common symptoms of both ALS and DOMS, as impairment at the proprioceptive sensory terminals in the muscle spindle is theorized to occur in both. The important clinical distinction is that extraocular muscles (EOM) are relatively spared in ALS, in contrast to limb skeletal muscles; however, the blink reflex goes through a gradual impairment in a later stage of disease progression. Noteworthy is, that, the stretch of EOM induces the blink reflex. The current authors suggest that the impairment of proprioceptive sensory nerve terminals in the EOM muscle spindles are partially responsible for lower blink reflex, beyond central origin, and implies the critical role of Piezo2 ion channels and Wnt-PIP2 signaling in this pathomechanism. The proposed microinjury of Piezo2 on muscle spindle proprioceptive terminals could provide an explanation for the painless dying-back noncontact injury mechanism theory of ALS.

Stem cell-derived cranial and spinal motor neurons reveal proteostatic differences between ALS resistant and sensitive motor neurons

In amyotrophic lateral sclerosis (ALS) spinal motor neurons (SpMN) progressively degenerate while a subset of cranial motor neurons (CrMN) are spared until late stages of the disease. Using a rapid and efficient protocol to differentiate mouse embryonic stem cells (ESC) to SpMNs and CrMNs, we now report that ESC-derived CrMNs accumulate less human (h)SOD1 and insoluble p62 than SpMNs over time. ESC-derived CrMNs have higher proteasome activity to degrade misfolded proteins and are intrinsically more resistant to chemically-induced proteostatic stress than SpMNs. Chemical and genetic activation of the proteasome rescues SpMN sensitivity to proteostatic stress. In agreement, the hSOD1 G93A mouse model reveals that ALS-resistant CrMNs accumulate less insoluble hSOD1 and p62-containing inclusions than SpMNs. Primary-derived ALS-resistant CrMNs are also more resistant than SpMNs to proteostatic stress. Thus, an ESC-based platform has identified a superior capacity to maintain a healthy proteome as a possible mechanism to resist ALS-induced neurodegeneration.

Eyelid Drive System: An Assistive Technology Employing Inductive Sensing of Eyelid Movement

This paper presents the design, development, and validation of the eyelid drive system (EDS), an assistive technology comprising a specialized pair of glasses and millimeter-sized passive resonators, attached to the user's eyelids, that transduce eyelid movement (blinking and winking) through inductive sensing. The theory of operation and design optimization with simulations are presented. A proof-of-concept prototype EDS was constructed using a pair of nonprescription glasses and commercial-off-the-shelf components. In benchtop tests with model eyelids, the EDS demonstrated basic functionality. Initial trials were performed involving six human subjects interacting with custom designed graphical user interfaces on a computer. A group mean accuracy of 96.3% was achieved using a set of four different commands at a response rate of 3 s. A mean information transfer rate (ITR) of 56.1 b/min over all subjects was achieved with a set of six different commands at a response rate of 1.5 s. This proof-of-concept device consumes 51.6 mW of power. The EDS compares favorably with related eye-interfacing assistive technologies and provides a unique combination of advantages, including high accuracy and ITR, wearability, insensitivity to lighting and noise conditions, obviation of facial electrodes, and the use of nonexaggerated gestures.

Selective Motor Neuron Resistance and Recovery in a New Inducible Mouse Model of TDP-43 Proteinopathy

Motor neurons (MNs) are the neuronal class that is principally affected in amyotrophic lateral sclerosis (ALS), but it is widely known that individual motor pools do not succumb to degeneration simultaneously. Because >90% of ALS patients have an accumulation of cytoplasmic TDP-43 aggregates in postmortem brain and spinal cord (SC), it has been suggested that these inclusions in a given population may trigger its death. We investigated seven MN pools in our new inducible rNLS8 transgenic (Tg) mouse model of TDP-43 proteinopathy and found striking differences in MN responses to TDP-43 pathology. Despite widespread neuronal expression of cytoplasmic human TDP-43, only MNs in the hypoglossal nucleus and the SC are lost after 8 weeks of transgene expression, whereas those in the oculomotor, trigeminal, and facial nuclei are spared. Within the SC, slow MNs survive to end stage, whereas fast fatigable MNs are lost. Correspondingly, axonal dieback occurs first from fast-twitch muscle fibers, whereas slow-twitch fibers remain innervated. Individual pools show differences in the downregulation of endogenous nuclear TDP-43, but this does not fully account for vulnerability to degenerate. After transgene suppression, resistant MNs sprout collaterals to reinnervate previously denervated neuromuscular junctions concurrently with expression of matrix metalloproteinase 9 (MMP-9), a marker of fast MNs. Therefore, although pathological TDP-43 is linked to MN degeneration, the process is not stochastic and mirrors the highly selective patterns of MN degeneration observed in ALS patients.

SIGNIFICANCE STATEMENT

Because TDP-43 is the major pathological hallmark of amyotrophic lateral sclerosis (ALS), we generated mice in which mutant human TDP-43 expression causes progressive neuron loss. We show that these rNLS8 mice have a pattern of axonal dieback and cell death that mirrors that often observed in human patients. This finding demonstrates the diversity of motor neuron (MN) populations in their response to pathological TDP-43. Furthermore, we demonstrate that resistant MNs are able to compensate for the loss of their more vulnerable counterparts and change their phenotype in the process. These findings are important because using a mouse model that closely models human ALS in both the disease pathology and the pattern of degeneration is critical to studying and eventually treating progressive paralysis in ALS patients.

Pathological TDP-43 changes in Betz cells differ from those in bulbar and spinal α-motoneurons in sporadic amyotrophic lateral sclerosis

Two nerve cells types, Betz cells in layer Vb of the primary motor neocortex and α-motoneurons of the lower brainstem and spinal cord, become involved at the beginning of the pathological cascade underlying sporadic amyotrophic lateral sclerosis (sALS). In both neuronal types, the cell nuclei forfeit their normal (non-phosphorylated) expression of the 43-kDa transactive response DNA-binding protein (TDP-43). Here, we present initial evidence that in α-motoneurons the loss of normal nuclear TDP-43 expression is followed by the formation of phosphorylated TDP-43 aggregates (pTDP-43) within the cytoplasm, whereas in Betz cells, by contrast, the loss of normal nuclear TDP-43 expression remains mostly unaccompanied by the development of cytoplasmic aggregations. We discuss some implications of this phenomenon of nuclear clearing in the absence of cytoplasmic inclusions, namely, abnormal but soluble (and, thus, probably toxic) cytoplasmic TDP-43 could enter the axoplasm of Betz cells, and following its transmission to the corresponding α-motoneurons in the lower brainstem and spinal cord, possibly contribute in recipient neurons to the dysregulation of the normal nuclear protein. Because the cellular mechanisms that possibly inhibit the aggregation of TDP-43 in the cytoplasm of involved Betz cells are unknown, insight into such mechanisms could disclose a pathway by which the development of aggregates in this cell population could be accelerated, thereby opening an avenue for a causally based therapy.

Sigma-1 Receptor in Motoneuron Disease

Amyotrophic Lateral Sclerosis (ALS ) is a neurodegenerative disease affecting spinal cord and brain motoneurons , leading to paralysis and early death. Multiple etiopathogenic mechanisms appear to contribute in the development of ALS , including glutamate excitotoxicity, oxidative stress , protein misfolding, mitochondrial defects, impaired axonal transport, inflammation and glial cell alterations. The Sigma-1 receptor is highly expressed in motoneurons of the spinal cord, particularly enriched in the endoplasmic reticulum (ER) at postsynaptic cisternae of cholinergic C-terminals. Several evidences point to participation of Sigma-1R alterations in motoneuron degeneration. Thus, mutations of the transmembrane domain of the Sigma-1R have been described in familial ALS cases. Interestingly, Sigma-1R KO mice display muscle weakness and motoneuron loss. On the other hand, Sigma-1R agonists promote neuroprotection and neurite elongation through activation of protein kinase C on motoneurons in vitro and in vivo after ventral root avulsion. Remarkably, treatment of SOD1 mice, the most usual animal model of ALS , with Sigma-1R agonists resulted in significantly enhanced motoneuron function and preservation, and increased animal survival. Sigma-1R activation also reduced microglial reactivity and increased the glial expression of neurotrophic factors. Two main interconnected mechanisms seem to underlie the effects of Sigma-1R manipulation on motoneurons: modulation of neuronal excitability and regulation of calcium homeostasis. In addition, Sigma-1R also contributes to regulating protein degradation, and reducing oxidative stress. Therefore, the multi-functional nature of the Sigma-1R represents an attractive target for treating aspects of ALS and other motoneuron diseases .

Eye-tracking in amyotrophic lateral sclerosis: A longitudinal study of saccadic and cognitive tasks

A relative preservation of eye movements is notable in ALS, but saccadic functions have not been studied longitudinally. ALS overlaps with FTD, typically involving executive dysfunction, and eye-tracking offers additional potential for the assessment of extramotor pathology where writing and speaking are both impaired. Eye-tracking measures (including anti-saccade, trail-making and visual search tasks) were assessed at six-monthly intervals for up to two years in a group of ALS (n = 61) and primary lateral sclerosis (n = 7) patients, compared to healthy age-matched controls (n = 39) assessed on a single occasion. Task performance was explored speculatively in relation to resting-state functional MRI (R-FMRI) network connectivity. Results showed that ALS patients were impaired on executive and visual search tasks despite normal basic saccadic function, and impairments in the PLS patients were unexpectedly often more severe. No significant progression was detected longitudinally in either group. No changes in R-FMRI network connectivity were identified in relation to patient performance. In conclusion, eye-tracking offers an objective means to assess extramotor cerebral involvement in ALS. The relative resistance of pure oculomotor function is confirmed, and higher-level executive impairments do not follow the same rate of decline as physical disability. PLS patients may have more cortical dysfunction than has been previously appreciated.

Amyotrophic lateral sclerosis: Current perspectives from basic research to the clinic

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by progressive degeneration of upper and lower motoneurons, leading to muscle weakness and paralysis, and finally death. Considerable recent advances have been made in basic research and preclinical therapeutic attempts using experimental models, leading to increasing clinical and translational research in the context of this disease. In this review we aim to summarize the most relevant findings from a variety of aspects about ALS, including evaluation methods, animal models, pathophysiology, and clinical findings, with particular emphasis in understanding the role of every contributing mechanism to the disease for elucidating the causes underlying degeneration of motoneurons and the development of new therapeutic strategies.

Calbindin-D28K is increased in the ventral horn of spinal cord by neuroprotective factors for motor neurons

Slow glutamate-mediated neuronal degeneration is implicated in the pathophysiology of motor neuron diseases such as amyotrophic lateral sclerosis (ALS). The calcium-binding proteins calbindin-D28K and parvalbumin have been reported to protect neurons against excitotoxic insults. Expression of calbindin-D28K is low in adult human motor neurons, and vulnerable motor neurons additionally may lack parvalbumin. Thus, it has been speculated that the lack of calcium-binding proteins may, in part, be responsible for early degeneration of the population of motor neurons most vulnerable in ALS. Using a rat organotypic spinal cord slice system, we examined whether the most potent neuroprotective factors for motor neurons can increase the expression of calbindin-D28K or parvalbumin proteins in the postnatal spinal cord. After 4 weeks of incubation of spinal cord slices with 1) glial cell line-derived neurotrophic factor (GDNF), 2) neurturin, 3) insulin-like growth factor I (IGF-I), or 4) pigment epithelium-derived factor (PEDF), the number of calbindin-D28K -immunopositive large neurons (>20 μm) in the ventral horn was higher under the first three conditions, but not after PEDF, compared with untreated controls. Under the same conditions, parvalbumin was not upregulated by any neuroprotective factor. The same calbindin increase was true of IGF-I and GDNF in a parallel glutamate toxicity model of motor neuron degeneration. Taken together with our previous reports from the same model, which showed that all these neurotrophic factors can potently protect motor neurons from slow glutamate injury, the data here suggest that upregulation of calbindin-D28K by some of these factors may be one mechanism by which motor neurons can be protected from glutamate-induced, calcium-mediated excitotoxicity.

Reductions of docosahexaenoic acid-containing phosphatidylcholine levels in the anterior horn of an ALS mouse model

In this study, we analyzed the spatiotemporal alterations of phospholipid composition in the spinal cord of an amyotrophic lateral sclerosis (ALS) mouse model (G93A-mutated human superoxide dismutase 1 transgenic mice [SOD1(G93A) mice]) using imaging mass spectrometry (IMS), a powerful method to visualize spatial distributions of various types of molecules in situ. Using this technique, we deciphered the phospholipid distribution in the pre-symptomatic stage, early stage after disease onset, and terminal stages of disease in female SOD1(G93A) mouse spinal cords. These experiments revealed a significant decrease in levels of docosahexaenoic acid (DHA)-containing phosphatidylcholines (PCs), such as PC (diacyl-16:0/22:6), PC (diacyl-18:0/22:6), and PC (diacyl-18:1/22:6) in the L5 anterior horns of terminal stage (22-week-old) SOD1(G93A) mice. The reduction in PC (diacyl-16:0/22:6) level could be reflecting the loss of motor neurons themselves in the anterior horn of the spinal cord in ALS model mice. In contrast, other PCs, such as PC (diacyl-16:0/16:0), were observed specifically in the L5 dorsal horn gray matter, and their levels did not vary between ALS model mice and controls. Thus, our study showed a significant decrease in DHA-containing PCs, but not other PCs, in the terminal stage of ALS in model mice, which is likely to be a reflection of neuronal loss in the anterior horns of the spinal cords. Given its enrichment in dorsal sensory regions, the preservation of PC (diacyl-16:0/16:0) may be the result of spinal sensory neurons being unaffected in ALS. Taken together, these findings suggest that ALS spinal cords show significant alterations in PC metabolism only at the terminal stage of the disease, and that these changes are confined to specific anatomical regions and cell types.

Clinicopathologic report of ocular involvement in ALS patients with C9orf72 mutation

Our objective was to present clinicopathologic evidence of anterior visual pathway involvement in patients with amyotrophic lateral sclerosis (ALS) secondary to a C9orf72 mutation. Two related patients from an extended pedigree with ALS and GGGGCC hexanucleotide repeat expansion in the C9orf72 gene (C9-ALS) underwent neuro-ophthalmologic examination. Following death and tissue donation of the younger ALS patient, histopathologic examination of the retina, optic nerve and central nervous system (CNS) was performed. Ophthalmologic examination revealed contrast sensitivity impairment in the younger C9-ALS patient. Immunohistochemistry performed on this patient's donor tissue demonstrated p62-positive, pTDP43-negative perinuclear inclusions in the inner nuclear layer of the retina and CNS. Further colocalization with GLT-1 and recoverin suggested that the majority of retinal p62-positive inclusions are found within cone bipolar cells as well as some amacrine and horizontal cells. In conclusion, this is the first report that identifies disease-specific pathologic inclusions in the anterior visual pathway of a patient with a C9orf72 mutation. Cone bipolar cell involvement within the inner nuclear layer of the retina may explain the observed subtle visual function deficiencies in this patient. Further clinical and histopathologic studies are needed to fully characterize a larger population of C9-ALS patients and explore these findings in other forms of ALS.

Wnt and extraocular muscle sparing in amyotrophic lateral sclerosis

PURPOSE

The extraocular muscles (EOM) and their motor neurons are spared in amyotrophic lateral sclerosis (ALS). In limb muscle, axon retraction from the neuromuscular junctions occurs early in the disease. Wnts, a conserved family of secreted signaling molecules, play a critical role in neuromuscular junction formation. This is the first study to examine Wnt signaling for its potential involvement in maintenance of normal morphology in EOM in ALS.

METHODS

Extraocular muscle and limb muscle axons, neuromuscular junctions, and myofibers from control, aging, and ALS subjects and the SOD1(G93A) mouse model of ALS were quantified for their expression of Wnt1, Wnt3a, Wnt5a, Wnt7a, and β-catenin.

RESULTS

All four Wnt isoforms were expressed in most axon profiles in all human EOM. Significantly fewer were positive for Wnt1, Wnt3a, and Wnt7a in the human limb muscles. Similar differential patterns in Wnt myofiber expression were also seen except in the case of Wnt7a, where expression was elevated. In the SOD1(G93A) mouse, all four Wnt isoforms were significantly decreased in the neuromuscular junctions at the terminal stage compared to values in age-matched controls. β-Catenin was activated in a subset of myofibers in EOM and limb muscle in all subjects.

CONCLUSIONS

The differences in expression of Wnts in EOM and limb muscle, particularly at the neuromuscular junction level, suggest that they play a role in the pathophysiology of ALS. Collectively, the data support a role for signaling of Wnts in the preservation of the EOM in ALS and their dysregulation and the subsequent development of pathology in the ALS limb muscles.

Bunina bodies in motor and non-motor neurons revisited: a pathological study of an ALS patient after long-term survival on a respirator

Bunina bodies (BBs) are small eosinophilic neuronal cytoplasmic inclusions (NCIs) found in the remaining lower motor neurons (LMNs) of patients with sporadic amyotrophic lateral sclerosis (SALS), being a specific feature of the cellular pathology. We examined a case of SALS, unassociated with TDP-43 or C9ORF72 mutation, of 12 years duration in a 75-year-old man, who had received artificial respiratory support for 9 years, and showed widespread multisystem degeneration with TDP-43 pathology. Interestingly, in this patient, many NCIs reminiscent of BBs were observed in the oculomotor nucleus, medullary reticular formation and cerebellar dentate nucleus. As BBs in the cerebellar dentate nucleus have not been previously described, we performed ultrastructural and immunohistochemical studies of these NCIs to gain further insight into the nature of BBs. In each region, the ultrastructural features of these NCIs were shown to be identical to those of BBs previously described in LMNs. These three regions and the relatively well preserved sacral anterior horns (S1 and S2) and facial motor nucleus were immunostained with antibodies against cystatin C (CC) and TDP-43. Importantly, it was revealed that BBs exhibiting immunoreactivity for CC were a feature of LMNs, but not of non-motor neurons, and that in the cerebellar dentate nucleus, the ratio of neurons with BBs and TDP-43 inclusions/neurons with BBs was significantly lower than in other regions. These findings suggest that the occurrence of BBs with CC immunoreactivity is intrinsically associated with the particular cellular properties of LMNs, and that the mechanism responsible for the formation of BBs is distinct from that for TDP-43 inclusions.

Oxidative stress and autophagic alteration in brainstem of SOD1-G93A mouse model of ALS

Amyotrophic lateral sclerosis (ALS) is a progressive and fatal neurodegenerative disease involving both upper and lower motor neurons. The mechanism of motor neuron degeneration is still unknown. Although many studies have been performed on spinal motor neurons, few have been reported on brainstem and its motor nuclei. The aim of this study was to investigate oxidative stress and autophagic changes in the brainstem and representative motor nuclei of superoxide dismutase 1 (SOD1)-G93A mouse model of ALS. The expression levels of cluster of differentiation molecule 11b (CD11b), glial fibrillary acidic protein, glutamate-cysteine ligase catalytic subunit, heme oxygenase-1, NAD(P)H: quinone oxidoreductase 1, voltage-dependent anion-selective channel protein 1, Sequestosome 1/p62 (p62), microtubule-associated protein 1 light chain 3B (LC3), and SOD1 proteins in brainstem were examined by Western blot analysis. Immunohistochemistry and immunofluorescence were performed to identify the cellular localization of SOD1, p62, and LC3B, respectively. The results showed that there were progressive asctrocytic proliferation and microglial activation, induction of antioxidant proteins, and increased p62 and LC3II expression in brainstem of SOD1-G93A mice. Additionally, SOD1 and p62 accumulated in hypoglossal, facial, and red nuclei, but not in oculomotor nucleus. Furthermore, electron microscope showed increased autophagic vacuoles in affected brainstem motor nuclei. Our results indicate that brainstem share similar gliosis, oxidative stress, and autophagic changes as the spinal cord in SOD1-G93A mice. Thus, SOD1 accumulation in astrocytes and neurons, oxidative stress, and altered autophagy are involved in motor neuron degeneration in the brainstem, similar to the motor neurons in spinal cord. Therefore, therapeutic trials in the SOD1G93A mice need to target the brainstem in addition to the spinal cord.

Stages of pTDP-43 pathology in amyotrophic lateral sclerosis

OBJECTIVE

To see whether the distribution patterns of phosphorylated 43kDa TAR DNA-binding protein (pTDP-43) intraneuronal inclusions in amyotrophic lateral sclerosis (ALS) permit recognition of neuropathological stages.

METHODS

pTDP-43 immunohistochemistry was performed on 70 μm sections from ALS autopsy cases (N = 76) classified by clinical phenotype and genetic background.

RESULTS

ALS cases with the lowest burden of pTDP-43 pathology were characterized by lesions in the agranular motor cortex, brainstem motor nuclei of cranial nerves V, VII, and X-XII, and spinal cord α-motoneurons (stage 1). Increasing burdens of pathology showed involvement of the prefrontal neocortex (middle frontal gyrus), brainstem reticular formation, precerebellar nuclei, and the red nucleus (stage 2). In stage 3, pTDP-43 pathology involved the prefrontal (gyrus rectus and orbital gyri) and then postcentral neocortex and striatum. Cases with the greatest burden of pTDP-43 lesions showed pTDP-43 inclusions in anteromedial portions of the temporal lobe, including the hippocampus (stage 4). At all stages, these lesions were accompanied by pTDP-43 oligodendroglial aggregates. Ten cases with C9orf72 repeat expansion displayed the same sequential spreading pattern as nonexpansion cases but a greater regional burden of lesions, indicating a more fulminant dissemination of pTDP-43 pathology.

INTERPRETATION

pTDP-43 pathology in ALS possibly disseminates in a sequential pattern that permits recognition of 4 neuropathological stages consistent with the hypothesis that pTDP-43 pathology is propagated along axonal pathways. Moreover, the finding that pTDP-43 pathology develops in the prefrontal cortex as part of an ongoing disease process could account for the development of executive cognitive deficits in ALS.

PACAP signaling exerts opposing effects on neuroprotection and neuroinflammation during disease progression in the SOD1(G93A) mouse model of amyotrophic lateral sclerosis

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a pleiotropic peptide with autocrine neuroprotective and paracrine anti-inflammatory properties in various models of acute neuronal damage and neurodegenerative diseases. Therefore, we examined a possible beneficial role of endogenous PACAP in the superoxide dismutase 1, SOD1(G93A), mouse model of amyotrophic lateral sclerosis (ALS), a lethal neurodegenerative disease particularly affecting somatomotor neurons. In wild-type mice, somatomotor and visceromotor neurons in brain stem and spinal cord were found to express the PACAP specific receptor PAC1, but only visceromotor neurons expressed PACAP as a potential autocrine source of regulation of these receptors. In SOD1(G93A) mice, only a small subset of the surviving somatomotor neurons showed induction of PACAP mRNA, and somatomotor neuron degeneration was unchanged in PACAP-deficient SOD1(G93A) mice. Pre-ganglionic sympathetic visceromotor neurons were found to be resistant in SOD1(G93A) mice, while pre-ganglionic parasympathetic neurons degenerated during ALS disease progression in this mouse model. PACAP-deficient SOD1(G93A) mice showed even greater pre-ganglionic parasympathetic neuron loss compared to SOD1(G93A) mice, and additional degeneration of pre-ganglionic sympathetic neurons. Thus, constitutive expression of PACAP and PAC1 may confer neuroprotection to central visceromotor neurons in SOD1(G93A) mice via autocrine pathways. Regarding the progression of neuroinflammation, the switch from amoeboid to hypertrophic microglial phenotype observed in SOD1(G93A) mice was absent in PACAP-deficient SOD1(G93A) mice. Thus, endogenous PACAP may promote microglial cytodestructive functions thought to drive ALS disease progression. This hypothesis was consistent with prolongation of life expectancy and preserved tongue motor function in PACAP-deficient SOD1(G93A) mice, compared to SOD1(G93A) mice. Given the protective role of PACAP expression in visceromotor neurons and the opposing effect on microglial function in SOD1(G93A) mice, both PACAP agonism and antagonism may be promising therapeutic tools for ALS treatment, if stage of disease progression and targeting the specific auto- and paracrine signaling pathways are carefully considered.

Unravelling the enigma of selective vulnerability in neurodegeneration: motor neurons resistant to degeneration in ALS show distinct gene expression characteristics and decreased susceptibility to excitotoxicity

A consistent clinical feature of amyotrophic lateral sclerosis (ALS) is the sparing of eye movements and the function of external sphincters, with corresponding preservation of motor neurons in the brainstem oculomotor nuclei, and of Onuf’s nucleus in the sacral spinal cord. Studying the differences in properties of neurons that are vulnerable and resistant to the disease process in ALS may provide insights into the mechanisms of neuronal degeneration, and identify targets for therapeutic manipulation. We used microarray analysis to determine the differences in gene expression between oculomotor and spinal motor neurons, isolated by laser capture microdissection from the midbrain and spinal cord of neurologically normal human controls. We compared these to transcriptional profiles of oculomotor nuclei and spinal cord from rat and mouse, obtained from the GEO omnibus database. We show that oculomotor neurons have a distinct transcriptional profile, with significant differential expression of 1,757 named genes (q < 0.001). Differentially expressed genes are enriched for the functional categories of synaptic transmission, ubiquitin-dependent proteolysis, mitochondrial function, transcriptional regulation, immune system functions, and the extracellular matrix. Marked differences are seen, across the three species, in genes with a function in synaptic transmission, including several glutamate and GABA receptor subunits. Using patch clamp recording in acute spinal and brainstem slices, we show that resistant oculomotor neurons show a reduced AMPA-mediated inward calcium current, and a higher GABA-mediated chloride current, than vulnerable spinal motor neurons. The findings suggest that reduced susceptibility to excitotoxicity, mediated in part through enhanced GABAergic transmission, is an important determinant of the relative resistance of oculomotor neurons to degeneration in ALS.

Cross-sectional evaluation of clinical neuro-ophthalmic abnormalities in an amyotrophic lateral sclerosis population

OBJECTIVE

Ocular motility abnormalities may be a marker of neuro-degeneration beyond motor neurons in amyotrophic lateral sclerosis (ALS). We formally compared clinical neuro-ophthalmic abnormalities in ALS patients and a control population.

METHODS

Patients attending a multidisciplinary ALS clinic (n=63, age 60.8+/-16.4 years) and their caregivers serving as controls (n=37, ages 55.0+/-12.7 years) participated in this cross-sectional study. Visual acuity was assessed. Video recordings of a standardized ocular motility exam including gaze fixation, voluntary saccades, reflex saccades, smooth pursuit, eyelid opening and Bell's phenomenon were rated by two senior neuro-ophthalmologists who were masked to subject group.

RESULTS

Visual acuity was lower in ALS patients versus control subjects (OR 0.81 (0.71-0.93), p=0.003, logistic regression). Inter- and intra-rater reliability for ocular motility examination ratings were good (Cohen's Kappa>0.6). Findings observed only in ALS subjects included gaze impersistence (14%, p=0.01), moderately or severely restricted voluntary upgaze (13%, p=0.01), and moderate or severe eyelid opening apraxia (27%, p=0.0002). Accounting for age, moderately or severely saccadic horizontal smooth pursuits distinguished ALS from control subjects (OR 3.6 (1.2-10.9), p=0.02, logistic regression).

CONCLUSIONS

Clinical findings of decreased visual acuity, gaze impersistence, voluntary upgaze restriction, eyelid opening apraxia, and saccadic horizontal smooth pursuits are more frequent in patients with ALS than in similar-aged controls. These findings are potential clinical markers of neurodegeneration beyond upper and lower motor neuron disease in ALS. Further study is warranted regarding their application to disease categorization and outcomes assessment.

Transition from the locked in to the completely locked-in state: a physiological analysis

OBJECTIVE

To clarify the physiological and behavioral boundaries between locked-in (LIS) and the completely locked-in state (CLIS) (no voluntary eye movements, no communication possible) through electrophysiological data and to secure brain-computer-interface (BCI) communication.

METHODS

Electromyography from facial muscles, external anal sphincter (EAS), electrooculography and electrocorticographic data during different psychophysiological tests were acquired to define electrophysiological differences in an amyotrophic lateral sclerosis (ALS) patient with an intracranially implanted grid of 112 electrodes for nine months while the patient passed from the LIS to the CLIS.

RESULTS

At the very end of the LIS there was no facial muscle activity, nor external anal sphincter but eye control. Eye movements were slow and lasted for short periods only. During CLIS event related brain potentials (ERP) to passive limb movements and auditory stimuli were recorded, vibrotactile stimulation of different body parts resulted in no ERP response.

CONCLUSIONS

The results presented contradict the commonly accepted assumption that the EAS is the last remaining muscle under voluntary control and demonstrate complete loss of eye movements in CLIS. The eye muscle was shown to be the last muscle group under voluntary control. The findings suggest ALS as a multisystem disorder, even affecting afferent sensory pathways.

SIGNIFICANCE

Auditory and proprioceptive brain-computer-interface (BCI) systems are the only remaining communication channels in CLIS.

(C)overt attention and visual speller design in an ERP-based brain-computer interface

BACKGROUND

In a visual oddball paradigm, attention to an event usually modulates the event-related potential (ERP). An ERP-based brain-computer interface (BCI) exploits this neural mechanism for communication. Hitherto, it was unclear to what extent the accuracy of such a BCI requires eye movements (overt attention) or whether it is also feasible for targets in the visual periphery (covert attention). Also unclear was how the visual design of the BCI can be improved to meet peculiarities of peripheral vision such as low spatial acuity and crowding.

METHOD

Healthy participants (N = 13) performed a copy-spelling task wherein they had to count target intensifications. EEG and eye movements were recorded concurrently. First, (c)overt attention was investigated by way of a target fixation condition and a central fixation condition. In the latter, participants had to fixate a dot in the center of the screen and allocate their attention to a target in the visual periphery. Second, the effect of visual speller layout was investigated by comparing the symbol Matrix to an ERP-based Hex-o-Spell, a two-levels speller consisting of six discs arranged on an invisible hexagon.

RESULTS

We assessed counting errors, ERP amplitudes, and offline classification performance. There is an advantage (i.e., less errors, larger ERP amplitude modulation, better classification) of overt attention over covert attention, and there is also an advantage of the Hex-o-Spell over the Matrix. Using overt attention, P1, N1, P2, N2, and P3 components are enhanced by attention. Using covert attention, only N2 and P3 are enhanced for both spellers, and N1 and P2 are modulated when using the Hex-o-Spell but not when using the Matrix. Consequently, classifiers rely mainly on early evoked potentials in overt attention and on later cognitive components in covert attention.

CONCLUSIONS

Both overt and covert attention can be used to drive an ERP-based BCI, but performance is markedly lower for covert attention. The Hex-o-Spell outperforms the Matrix, especially when eye movements are not permitted, illustrating that performance can be increased if one accounts for peculiarities of peripheral vision.

A systematic study of brainstem motor nuclei in a mouse model of ALS, the effects of lithium

Transgenic mice expressing the human superoxide dismutase 1 (SOD-1) mutant at position 93 (G93A) develop a phenotype resembling amyotrophic lateral sclerosis (ALS). In fact, G93A mice develop progressive motor deficits which finally lead to motor palsy and death. This is due to the progressive degeneration of motor neurons in the ventral horn of the spinal cord. Although a similar loss is reported for specific cranial motor nuclei, only a few studies so far investigated degeneration in a few brainstem nuclei. We recently reported that chronic lithium administration delays onset and duration of the disease, while reducing degeneration of spinal motor neuron. In the present study, we extended this investigation to all somatic motor nuclei of the brain stem in the G93A mice and we evaluated whether analogous protective effects induced by lithium in the spinal cord were present at the brain stem level. We found that all motor but the oculomotor nuclei were markedly degenerated in G93A mice, and chronic treatment with lithium significantly attenuated neurodegeneration in the trigeminal, facial, ambiguus, and hypoglossal nuclei. Moreover, in the hypoglossal nucleus, we found that recurrent collaterals were markedly lost in G93A mice while they were rescued by chronic lithium administration.

Bunina bodies in amyotrophic lateral sclerosis

Bunina bodies, which are small eosinophilic intraneuronal inclusions in the remaining lower motor neurons, are generally considered to be a specific pathologic hallmark of amyotrophic lateral sclerosis (ALS). One year before a publication by Bunina, van Reeth et al. described similar intracytoplasmic inclusions in the anterior horn cells in a patient with Pick's dementia with atypical ALS. At present, only two proteins have been shown to be present in Bunina bodies, one is cystatin C and the other is transferrin. Bunina bodies consist of amorphous electron-dense material surrounded by tubular and vesicular structures on electron microscopy. Although the nature and significance of Bunina bodies in ALS are not yet clear, the bodies may be abnormal accumulations of unknown proteinous materials.

Ascending neuropathology in the CNS of a mutant SOD1 mouse model of amyotrophic lateral sclerosis

Transgenic mice expressing a mutated human Cu/Zn superoxide dismutase (SOD1) gene develop a motor neuron disease similar to familial amyotrophic lateral sclerosis (FALS). While the histopathology and the inflammatory reactions in the spinal cord of these mice are well described, their spatiotemporal extension into brain areas and the relationship between degenerative and inflammatory events remain obscure. In the present study, we investigated the time course and extent of degenerative changes and inflammatory reactions in the CNS during progression of the disease in a transgenic FALS model, the SOD1-G93A mouse with histological and immunohistochemical methods. Compared to non-transgenic littermates, the SOD1-G93A transgenics developed widespread degeneration in both motor and extra-motor regions up to telencephalic regions, including the cerebral cortex but sparing distinct regions like the striatum and hippocampus. We provide evidence that these degenerative processes are accompanied by intense inflammatory reactions in the brain, which spatiotemporally correlate with degeneration and comprise besides strong astro- and microgliotic reactions also an influx of peripheral immune cells such as T-lymphocytes and dendritic cells. Both degeneration and inflammatory reactions spread caudocranially, starting at 2 months in the spinal cord and reaching the telencephalon at 5 months of age. Since the corticospinal tract lacked any signs of degeneration, we conclude that the upper and the lower motor neurons degenerate independently of each other.

Motor neuronopathy with dropped hands and downbeat nystagmus: a distinctive disorder? A case report

Background

Eye movements are clinically normal in most patients with motor neuron disorders until late in the disease course. Rare patients are reported to show slow vertical saccades, impaired smooth pursuit, and gaze-evoked nystagmus. We report clinical and oculomotor findings in three patients with motor neuronopathy and downbeat nystagmus, a classic sign of vestibulocerebellar disease.

Case presentation

All patients had clinical and electrodiagnostic features of anterior horn cell disease. Involvement of finger and wrist extensors predominated, causing finger and wrist drop. Bulbar or respiratory dysfunction did not occur. All three had clinically evident downbeat nystagmus worse on lateral and downgaze, confirmed on eye movement recordings using the magnetic search coil technique in two patients. Additional oculomotor findings included alternating skew deviation and intermittent horizontal saccadic oscillations, in one patient each. One patient had mild cerebellar atrophy, while the other two had no cerebellar or brainstem abnormality on neuroimaging. The disorder is slowly progressive, with survival up to 30 years from the time of onset.

Conclusion

The combination of motor neuronopathy, characterized by early and prominent wrist and finger extensor weakness, and downbeat nystagmus with or without other cerebellar eye movement abnormalities may represent a novel motor neuron syndrome.

Frontotemporal and motor neurone degeneration with neurofilament inclusion bodies: additional evidence for overlap between FTD and ALS

We present the case of a patient who had clinical frontal lobe dementia without apparent motor neurone disease (MND), with pathologic findings not typical of any single currently classified frontotemporal degeneration (FTD). At autopsy, the brain had frontal and temporal atrophy with neuronal loss, gliosis, and superficial spongiosis, typical of all FTDs. There were at least three different morphologic types of intracytoplasmic neuronal inclusions in a variety of brain and brainstem regions, including the hippocampal dentate gyrus and pyramidal neurones, the neocortex (in particular, the motor cortex), basal ganglia, thalamus, subthalamic nucleus, basis pontis, and inferior olivary nuclei. Inclusions had the morphologies of Pick-like bodies, pleomorphic inclusions, and hyaline conglomerate (HC)-like inclusions. None of these were positive with tau immunostains. Pick-like bodies in the dentate gyrus were labelled with ubiquitin. The pleomorphic inclusions in the neocortex and dentate gyrus and the HC-like inclusions in the motor and parietal cortex were strongly positive with immunostains for neurofilament. We discuss the differential diagnosis and compare this case with those disorders to which it is most similar. In particular, we compare the unique neurofilament-positive inclusions to the inclusions of FTD-MND, to Pick bodies, and to the basophilic and HC inclusions that are occasionally seen in amytrophic lateral sclerosis (ALS). Although FTD-MND may be found in ALS, the findings in this case may have additional implications for a link between FTD and ALS.

Ubiquitin-only intraneuronal inclusion in the substantia nigra is a characteristic feature of motor neurone disease with dementia

Two types of ubiquitinated inclusions have been described in motor neurone disease (MND). (1) Skein or globular ubiquitinated inclusions in the motor neurones (more frequently in the lower motor neurones). This is a characteristic feature of all motor neurone disease categories. (2) Dot-shape or crescentric ubiquitinated inclusions in the upper layers of cortex and dentate gyrus described in cases of motor neurone disease with dementia (DMND). We investigated the substantia nigra (SN) in MND cases; two cases of motor neurone disease inclusion body (MND-IB) dementia, six cases of DMND, 14 cases of MND (including one case from Guam and two cases of familial SOD1 mutation), four cases of Parkinson's disease (PD), and 10 cases of age-matched normal controls. SN and spinal cord sections were stained with ubiquitin (alpha-synuclein, tau, PGM1, SMI-31 and SOD1 antibodies). The neuronal density in SN was quantified by using a computer-based image analysis system. Four out of six DMND cases showed rounded ubiquitin positive inclusions with irregular frayed edges, associated with neuronal loss, reactive astrocytosis and a large number of activated microglia cells. These inclusions are negative with antibodies to (alpha-synuclein, tau, SMI-31 and SOD1). The SN in cases from MND-IB dementia and MND showed occasional neuronal loss and no inclusions. The ubiquitin-only inclusions in SN of DMND cases are similar (but not identical) to the ubiquitinated inclusions described previously in the spinal cord of MND cases and are distinct from Lewy bodies (LBs). The degeneration of SN is most likely a primary neurodegenerative process of motor neurone disease type frequently involving the DMND cases. MND disease is a spectrum and multisystem disorder with DMND located at the extreme end of a spectrum affecting the CNS more widely than just the motor system.

Differential susceptibility of the ocular motor system to disease

This review summarizes an alternative approach to the understanding of neuromuscular disease. By contrasting disease susceptibility of extraocular muscle and ocular motor neurons, it is hoped that unique insights into disease mechanisms may be identified. Disorder of eye movements leads to dramatic symptoms for patients and the ocular motor system is relatively limited in its ability to compensate rapidly for such disruptions. However, more profound reasons exist as to why myasthenia gravis compromises neuromuscular transmission at ocular muscle synapses as well as why Graves' ophthalmopathy exists. In contrast, muscular dystrophies spare the eye muscles while devastating all other skeletal muscles; the same is true for motor neuron diseases. It is hoped that this review will encourage others to view the world of neuromuscular diseases as delineated into those that spare the ocular motor system and those that do not.

Differential vulnerability of oculomotor, facial, and hypoglossal nuclei in G86R superoxide dismutase transgenic mice

In recent years, several mouse models of amyotrophic lateral sclerosis (ALS) have been developed. One, caused by a G86R mutation in the superoxide dismutase-1 (SOD-1) gene associated with familial ALS, has been subjected to extensive quantitative analyses in the spinal cord. However, the human form of ALS includes pathology elsewhere in the nervous system. In the present study, analyses were extended to three motor nuclei in the brainstem. Mutant mice and control littermates were evaluated daily, and mutants, along with their littermate controls, were killed when they were severely affected. Brains were removed after perfusion and processed for Nissl staining, the samples were randomized, and the investigators were blinded to their genetic status. Stereologic methods were used to estimate the number of neurons, mean neuronal volumes, and nuclear volume in three brainstem motor nuclei known to be differentially involved in the human form of the disease, the oculomotor, facial, and hypoglossal nuclei. In the facial nucleus, neuron number consistently declined (48%), an effect that was correlated with disease severity. The nuclear volume of the facial nucleus was smaller in the SOD-1 mutant mice (45.7% difference from control mice) and correlated significantly with neuron number. The oculomotor and hypoglossal nuclei showed less extreme involvement (<10% neuronal loss overall), with a trend toward fewer neurons in the hypoglossal nucleus of animals with severe facial nucleus involvement. In the oculomotor nucleus, neuronal loss was seen only once in five mice, associated with very severe disease. There was no significant change in the volume of individual neurons in any of these three nuclei in any transgenic mouse. These results suggest that different brainstem motor nuclei are differentially affected in this SOD-1 mutant model of ALS. The relatively moderate and late involvement of the hypoglossal nucleus indicates that, although the general patterns of neuronal pathology match closely those seen in ALS patients, some differences exist in this transgenic model compared with the progression of the disease in humans. However, these patterns of cellular vulnerability may provide clues for understanding the differential susceptibility of neural structures in ALS and other neurodegenerative diseases.

Fragmentation of the Golgi apparatus of Betz cells in patients with amyotrophic lateral sclerosis

The Golgi apparatus (GA) of the large pyramidal motor neurons in the cerebral cortex (Betz cells), was examined in sixteen patients with sporadic amyotrophic lateral sclerosis (ALS), in one patient with familial ALS (FALS), and in ten non-ALS age matched controls including one patient with Huntington's disease and one patient with a brain infarct. The GA was immunostained with an antibody against the MG-160 protein, a conserved sialoglycoprotein of the medial cisternae of the organelle. In ALS, 13.2% of counted Betz cells had fragmented GA in contrast to 0.6% in the ten non-ALS controls. The fragmentation of the GA of Betz cells was identical to that previously reported in spinal cord motor neurons from patients with sporadic ALS and in transgenic mice expressing the G93A mutation of the gene encoding the Cu/Zn superoxide dismutase. The striking morphological similarity between the fragmentation of the GA observed in Betz cells and in spinal cord motor neurons suggests that a similar pathogenic mechanism is responsible for both, and that the fragmentation of the GA of the spinal cord motor neurons is not a consequence of deafferentation due to the degeneration of the Betz cells.

Slow vertical saccades in motor neuron disease: correlation of structure and function

We studied eye movements and brainstem pathology in 2 patients with slow vertical saccades and autopsy-proven amyotrophic lateral sclerosis (ALS). In both patients, the main ocular motor finding was supranuclear vertical gaze impairment with slow vertical saccades. The second patient had difficulty opening his eyes on command, with preserved spontaneous eyelid opening. Postmortem examination in both patients demonstrated cell loss in the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF) and substantia nigra, along with histopathological findings consistent with ALS. The extent of the pathological changes in the riMLF correlated well with the degree of functional impairment as reflected in the slow vertical saccades. We suggest that motor neuron disease with early involvement of vertical saccades represents a distinct clinicopathological entity.

Brainstem motoneuron pools that are selectively resistant in amyotrophic lateral sclerosis are preferentially enriched in parvalbumin: evidence from monkey brainstem for a calcium-mediated mechanism in sporadic ALS

Some brainstem motoneuron groups appear more resistant to the process of neurodegeneration in ALS (for example, oculomotor, trochlear, and abducens nuclei) than others (for example, trigeminal, facial, ambiguus, and hypoglossal nuclei). The possibility that the differential presence of the calcium-chelating protein parvalbumin might underlie this difference in vulnerability was examined immunohistochemically as a way to determine whether a calcium-mediated mechanism might be involved in ALS. In normal monkey brainstem, we found that the abundance of parvalbumin-containing neurons in the oculomotor, trochlear, and abducens nuclei was approximately 90% of the abundance of choline acetyltransferase (CHAT)-containing motoneurons. In contrast, the abundance of parvalbumin-containing neurons in the other brainstem motor nuclei innervating skeletal muscle (trigeminal, facial, ambiguus, and hypoglossal) was only about 30-60% of the abundance of CHAT-containing motoneurons. Since some of these motoneuron pools contain nonmotoneuron internuclear neurons that might be parvalbumin-containing, we also carried out double-label studies to specifically determine the percentage of cholinergic motoneurons that contained parvalbumin in each of these motoneuron pools. We found that 85-100% of the oculomotor, trochlear, and abducens motoneurons were parvalbumin-containing. In contrast, only 20-30% of the trigeminal, facial, ambiguus, and hypoglossal motoneurons were parvalbumin-containing. These results raise the possibility that motoneuron death in sporadic ALS is related to some defect that promotes cytosolic calcium accumulation in motoneurons. This excess calcium entry may promote cell death via an excitotoxic pathway. Motoneurons rich in parvalbumin may resist the deleterious effects of this putative calcium gating defect because they are better able to sequester the excess calcium.

The role of calcium-binding proteins in selective motoneuron vulnerability in amyotrophic lateral sclerosis

The factors contributing to selective motoneuron loss in amyotrophic lateral sclerosis (ALS) remain undefined. To investigate whether calcium-binding proteins contribute to selective motoneuron vulnerability in ALS, we compared calbindin-D28K and parvalbumin immunoreactivity in motoneuron populations in human ALS, and in a ventral spinal cord hybrid cell line selectively vulnerable to the cytotoxic effects of ALS IgG. In human autopsy specimens, immunoreactive calbindin-D28k and parvalbumin were absent in motoneuron populations lost early in ALS (i.e., cortical and spinal motoneurons, lower cranial nerve motoneurons), while motoneurons damaged late or infrequently in the disease (i.e., Onuf's nucleus motoneurons, oculomotor, trochlear, and abducens nerve neurons) expressed markedly higher levels of immunoreactive calbindin-D28K and/or parvalbumin. Motoneuron-neuroblastoma VSC 4.1 hybrid cells lost immunoreactive calbindin-D28k and parvalbumin following dibutyryl-cyclic AMP-induced differentiation and were killed by IgG from ALS patients. Undifferentiated calbindin/parvalbumin-reactive VSC 4.1 cells were not killed, nor were other cell lines expressing high levels of calbindin-D28K and parvalbumin immunoreactivity (substantia nigra-neuroblastoma hybrid cells and N18TG2 neuroblastoma parent cells). These studies suggest that decreased calbindin-D28K and parvalbumin immunoreactivity may help explain the selective vulnerability of motoneurons in ALS.

An immunohistochemical study of the neuronal expression of manganese superoxide dismutase in sporadic amyotrophic lateral sclerosis

Neuronal expression of manganese superoxide dismutase (MnSOD) in sporadic amyotrophic lateral sclerosis (sALS) was investigated by an immunohistochemical method. The brains and spinal cords from 11 patients with sALS and 20 normal controls (NCs) were used, and the following four nuclei (three motor nuclei and one autonomic nucleus) were examined: the oculomotor nucleus; the hypoglossal nucleus; the cervical motor nucleus; and Onuf's nucleus. Serial sections were stained by the Klüver-Barrera (KB) method and with human-MnSOD-specific antibodies. We counted the total number of neurons visible after KB staining and the total number of positive neurons after immunostaining. The average total number of neurons after KB staining was similar in sALS patients and NCs in both the oculomotor nucleus and Onuf's nucleus, but the number in the hypoglossal and cervical motor nuclei was significantly lower in sALS. The ratio of MnSOD-positive neurons to total neurons visible after KB staining, calculated as an index of the expression of MnSOD, was significantly higher in the oculomotor nucleus and Onuf's nucleus, and lower in the hypoglossal nucleus in sALS patients than in NCs. In the cervical motor nucleus, the ratio in sALS patients did not differ from that in NCs. These results suggest that production of toxic superoxide radicals might be increased in sALS, and that neurons that successfully induce the expression of sufficient MnSOD can survive the disease process, while those failing to activate adequate expression of the enzyme succumb to the toxic effects of the radicals and die.

New pathological findings in amyotrophic lateral sclerosis

There have been recent developments in the pathology of sporadic ALS. A new filamentous neuronal inclusion body in ALS detected by immunohistochemical localisation of the protein ubiquitin has been characterised at the light microscopic and ultrastructural level and appears specific for the disease. The molecular composition of underlying filaments remains unresolved but the quest for this is a major aim in ALS research. Despite being a progressive degenerative process which primarily affects motor systems, ALS is now recognised to involve several non-motor systems and in long survivors affects many subcortical structures. There is also accumulating evidence that the neurodegenerative process underlying ALS may present as a non-motor clinical syndrome, particularly as a frontal lobe dementia with characteristic inclusions present in the non-motor cortex. Considering ALS as a multisystem disease rather than simply a disease of motor neurones has major implications for research into pathogenesis.