Neurofilament function and dysfunction: involvement in axonal growth and neuronal disease

Stathmin-2 loss leads to neurofilament-dependent axonal collapse driving motor and sensory denervation

The mRNA transcript of the human STMN2 gene, encoding for stathmin-2 protein (also called SCG10), is profoundly impacted by TAR DNA-binding protein 43 (TDP-43) loss of function. The latter is a hallmark of several neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS). Using a combination of approaches, including transient antisense oligonucleotide-mediated suppression, sustained shRNA-induced depletion in aging mice, and germline deletion, we show that stathmin-2 has an important role in the establishment and maintenance of neurofilament-dependent axoplasmic organization that is critical for preserving the caliber and conduction velocity of myelinated large-diameter axons. Persistent stathmin-2 loss in adult mice results in pathologies found in ALS, including reduced interneurofilament spacing, axonal caliber collapse that drives tearing within outer myelin layers, diminished conduction velocity, progressive motor and sensory deficits, and muscle denervation. These findings reinforce restoration of stathmin-2 as an attractive therapeutic approach for ALS and other TDP-43-dependent neurodegenerative diseases.

Exploration of Neurofilament Light Chain and Nerve Ultrasound in Leprotic Neuropathy

OBJECTIVES

To explore neurofilament light chain (NfL) levels in leprotic neuropathy compared to controls, and to determine if the changes correlate with ultrasonographic nerve findings.

METHODS

Individuals with leprosy with signs or symptoms suggestive of peripheral nerve involvement were recruited. They were evaluated by clinical examination, functional scores, laboratory assessments (including NfL), nerve conduction studies (NCS), and ultrasound. Ultrasound was conducted in bilateral median, ulnar, tibial, fibular, sural, and vagus nerves as well as cervical roots 5 and 6. Results were compared to age, sex, and body mass index matched healthy controls.

RESULTS

A total of 320 nerves from 20 patients and 480 nerves from 30 controls were evaluated. NfL was significantly elevated in those with leprosy with a mean and standard deviation of 7.50 + 2.83 compared with 3.42 + 1.18 in controls (P < .001). Ultrasound showed focal enlargement of the nerves, particularly at entrapment sites. Additionally, there were noticeable changes in neural Doppler signal, echogenicity, and epineural thickness among the measured nerve sites. NfL levels in those with leprosy correlated closely with nerve cross-sectional area at all sites (P < .05). Functional and clinical assessment scores correlated with NfL and sonographic cross-sectional area as well (P ≤ .05).

CONCLUSIONS

NfL is elevated in leprotic neuropathy. Ultrasound showed specific morphological changes in individuals with leprosy, and nerve enlargement correlated with NfL levels. Thus, both modalities may be useful for the diagnosis, prognosis, and disease monitoring in those with leprotic neuropathy, and further investigations are warranted.

The Heterogeneous Multiple Sclerosis Lesion: How Can We Assess and Modify a Degenerating Lesion?

Multiple sclerosis (MS) is a heterogeneous disease of the central nervous system that is governed by neural tissue loss and dystrophy during its progressive phase, with complex reactive pathological cellular changes. The immune-mediated mechanisms that promulgate the demyelinating lesions during relapses of acute episodes are not characteristic of chronic lesions during progressive MS. This has limited our capacity to target the disease effectively as it evolves within the central nervous system white and gray matter, thereby leaving neurologists without effective options to manage individuals as they transition to a secondary progressive phase. The current review highlights the molecular and cellular sequelae that have been identified as cooperating with and/or contributing to neurodegeneration that characterizes individuals with progressive forms of MS. We emphasize the need for appropriate monitoring via known and novel molecular and imaging biomarkers that can accurately detect and predict progression for the purposes of newly designed clinical trials that can demonstrate the efficacy of neuroprotection and potentially neurorepair. To achieve neurorepair, we focus on the modifications required in the reactive cellular and extracellular milieu in order to enable endogenous cell growth as well as transplanted cells that can integrate and/or renew the degenerative MS plaque.

Nucleoredoxin Plays a Key Role in the Maintenance of Retinal Pigmented Epithelium Differentiation

Nucleoredoxin (Nrx) belongs to the Thioredoxin protein family and functions in redox-mediated signal transduction. It contains the dithiol active site motif Cys-Pro-Pro-Cys and interacts and regulates different proteins in distinct cellular pathways. Nrx was shown to be catalytically active in the insulin assay and recent findings indicate that Nrx functions, in fact, as oxidase. Here, we have analyzed Nrx in the mammalian retina exposed to (perinatal) hypoxia-ischemia/reoxygenation, combining ex vivo and in vitro models. Our data show that Nrx regulates cell differentiation, which is important to (i) increase the number of glial cells and (ii) replenish neurons that are lost following the hypoxic insult. Nrx is essential to maintain cell morphology. These regulatory changes are related to VEGF but do not seem to be linked to the Wnt/β-catenin pathway, which is not affected by Nrx knock-down. In conclusion, our results strongly suggest that hypoxia-ischemia could lead to alterations in the organization of the retina, related to changes in RPE cell differentiation. Nrx may play an essential role in the maintenance of the RPE cell differentiation state via the regulation of VEGF release.

Microstructure of Human Corpus Callosum across the Lifespan: Regional Variations in Axon Caliber, Density, and Myelin Content

The myeloarchitecture of the corpus callosum (CC) is characterized as a mosaic of distinct differences in fiber density of small- and large-diameter axons along the anterior-posterior axis; however, regional and age differences across the lifespan are not fully understood. Using multiecho T2 magnetic resonance imaging combined with multi-T2 fitting, the myelin water fraction (MWF) and geometric-mean of the intra-/extracellular water T2 (geomT2IEW) in 395 individuals (7-85 years; 41% males) were examined. The approach was validated where regional patterns along the CC closely resembled the histology; MWF matched mean axon diameter and geomT2IEW mirrored the density of large-caliber axons. Across the lifespan, MWF exhibited a quadratic association with age in all 10 CC regions with evidence of a positive linear MWF-age relationship among younger participants and minimal age differences in the remainder of the lifespan. Regarding geomT2IEW, a significant linear age × region interaction reflected positive linear age dependence mostly prominent in the regions with the highest density of small-caliber fibers-genu and splenium. In all, these two indicators characterize distinct attributes that are consistent with histology, which is a first. In addition, these results conform to rapid developmental progression of CC myelination leveling in middle age as well as age-related degradation of axon sheaths in older adults.

In VitroStudies of Acrylamide Neurotoxicity in Rat Pheochromocytoma (PC12) Cells

This review discusses our studies on molecular mechanisms of acrylamide neurotoxicity by using the rat pheochromocytoma (PC12) cell line. The results showed that: a) acrylamide altered the gross morphology of PC12 cells; b) acrylamide induced neurofilament accumulation in PC12 cells; c) the effects of acrylamide on PC12 cells are consistent with its neurotoxicity in vivo; d) acrylamide stimulated neurofilament protein synthesis in PC12 cells; e) acrylamide did not act via nerve growth factor (NGF) receptor gp140trk to regulate neurofilament synthesis in PC12 cells; f) dexamethasone antagonised NGF and/or acrylamide-induced neurofilament protein synthesis and expression; and g) acrylamide differentially regulated the mRNA levels of three neurofilament subunit genes in PC12 cells. These molecular studies provide the first evidence that: a) there are distinctive and convergent signalling pathways for NGF-regulated and acrylamide-regulated neurofilament expression; b) acrylamide may differentially regulate the expression of each subunit, resulting in aberrant accumulation of neurofilament proteins; and c) there is a dexamethasone-sensitive signalling step common to NGF and acrylamide. These results could partially explain the mechanisms of neurofilament accumulation in distal axonal swellings, a pathognomonic feature of acrylamide neurotoxicity.

Diagnostic performance of new and classic CSF biomarkers in age-related dementias

The identification of diagnostic-prognostic biomarkers of dementia has become a global priority due to the prevalence of neurodegenerative diseases in aging populations. The objective of this study was to assess the diagnostic performance of cerebrospinal fluid (CSF) biomarkers across patients affected by either Alzheimer’s disease (AD), tauopathies other than AD (TP), or vascular dementia (VD), and cognitively normal subjects (CNS). One hundred fifty-three patients were recruited and tested for classical AD CSF biomarkers- Amyloid-ß42 and tau proteins - and novel candidate biomarkers - neurofilament (NF-) light and microRNA (miR) -21, -125b, -146a, and -222.

All dementia patients had significantly higher concentrations of NF-light compared to CNS, with the TP group displaying the highest NF-light values. A significant inverse correlation was also observed between NF-light and cognitive impairment. Of the four miRNAs analyzed, miR-222 levels were significantly increased in VD patients compared to both CNS and AD. In addition, while NF-light showed a better diagnostic performance than miR-222 and classical AD biomarkers in differentiating TP and VD from CNS, classical AD biomarkers revealed higher performance in discriminating AD from non-AD disorders.

Overall, our results suggest that CSF NF-light and miR-222 are promising biomarkers that may help to diagnose non-AD disorders.

Neurofilaments: The C-Reactive Protein of Neurology

Neurofilaments (NFs) are quickly becoming the biomarkers of choice in the field of neurology, suggesting their use as an unspecific screening marker, much like the use of elevated plasma C-reactive protein (CRP) in other fields. With sensitive techniques being readily available, evidence is growing regarding the diagnostic and prognostic value of NFs in many neurological disorders. Here, we review the latest literature on the structure and function of NFs and report the strengths and pitfalls of NFs as markers of neurodegeneration in the context of neurological diseases of the central and peripheral nervous systems.

The Networks of Genes Encoding Palmitoylated Proteins in Axonal and Synaptic Compartments Are Affected in PPT1 Overexpressing Neuronal-Like Cells

CLN1 disease (OMIM #256730) is an early childhood ceroid-lipofuscinosis associated with mutated CLN1, whose product Palmitoyl-Protein Thioesterase 1 (PPT1) is a lysosomal enzyme involved in the removal of palmitate residues from S-acylated proteins. In neurons, PPT1 expression is also linked to synaptic compartments. The aim of this study was to unravel molecular signatures connected to CLN1. We utilized SH-SY5Y neuroblastoma cells overexpressing wild type CLN1 (SH-p.wtCLN1) and five selected CLN1 patients’ mutations. The cellular distribution of wtPPT1 was consistent with regular processing of endogenous protein, partially detected inside Lysosomal Associated Membrane Protein 2 (LAMP2) positive vesicles, while the mutants displayed more diffuse cytoplasmic pattern. Transcriptomic profiling revealed 802 differentially expressed genes (DEGs) in SH-p.wtCLN1 (as compared to empty-vector transfected cells), whereas the number of DEGs detected in the two mutants (p.L222P and p.M57Nfs*45) was significantly lower. Bioinformatic scrutiny linked DEGs with neurite formation and neuronal transmission. Specifically, neuritogenesis and proliferation of neuronal processes were predicted to be hampered in the wtCLN1 overexpressing cell line, and these findings were corroborated by morphological investigations. Palmitoylation survey identified 113 palmitoylated protein-encoding genes in SH-p.wtCLN1, including 25 ones simultaneously assigned to axonal growth and synaptic compartments. A remarkable decrease in the expression of palmitoylated proteins, functionally related to axonal elongation (GAP43, CRMP1 and NEFM) and of the synaptic marker SNAP25, specifically in SH-p.wtCLN1 cells was confirmed by immunoblotting. Subsequent, bioinformatic network survey of DEGs assigned to the synaptic annotations linked 81 DEGs, including 23 ones encoding for palmitoylated proteins. Results obtained in this experimental setting outlined two affected functional modules (connected to the axonal and synaptic compartments), which can be associated with an altered gene dosage of wtCLN1. Moreover, these modules were interrelated with the pathological effects associated with loss of PPT1 function, similarly as observed in the Ppt1 knockout mice and patients with CLN1 disease.

Effect of carotid endarterectomy on brain damage markers

OBJECTIVES

Carotid endarterectomy (CEA) is a recommended treatment in the prevention of ischemic stroke. However, this procedure may cause neurological complications caused by cerebrovascular damage. While YKL-40 is a proinflammatory protein, neurofilament light polypeptide (NEFL) and brain lipid-binding protein (FABP7) are structural components of the brain. The aim of the study was to investigate YKL-40, NEFL, and FABP7 in the serum of patients undergoing CEA.

MATERIALS AND METHODS

The study included 25 participants who underwent CEA due to internal carotid artery stenosis. Blood samples were taken from each patient at three different intervals: prior to the surgery, 12 h after the surgery, and 48 h after the surgery. Serum levels of these brain damage markers were measured by enzyme-linked immunosorbent assay (ELISA).

RESULTS

The study showed that the serum YKL-40 level was significantly increased 48 h after CEA when compared to the level prior to surgery and also when compared to levels 12 h after surgery. There were no statistically significant differences in serum NEFL and FABP7 levels between all three recorded measurements.

CONCLUSIONS

Data from our study showed that CEA affects serum YKL-40 but not NEFL and FABP7 levels. This implicates that YKL-40 may be a valuable serum marker of brain damage after CEA. However, the observed change in serum YKL-40 level in patients after CEA does not necessarily warrant a change in recommendations concerning the use of this treatment in patients with high-grade internal carotid artery stenosis.

Neurofilament heavy chain expression and neuroplasticity in rat auditory cortex after unilateral and bilateral deafness

Deafness induces many plastic changes in the auditory neural system. For instance, dendritic changes cause synaptic changes in neural cells. SMI-32, a monoclonal antibody reveals auditory areas and recognizes non-phosphorylated epitopes on medium- and high-molecular-weight subunits of neurofilament proteins in cortical pyramidal neuron dendrites. We investigated SMI-32-immunoreactive (-ir) protein levels in the auditory cortices of rats with induced unilateral and bilateral deafness. Adult male Sprague-Dawley rats were divided into unilateral deafness (UD), bilateral deafness (BD), and control groups. Deafness was induced by cochlear ablation. All rats were sacrificed, and the auditory cortices were harvested for real-time quantitative polymerase chain reaction (RT-qPCR) and western blot analyses at 2, 4, 6, and 12 weeks after deafness was induced. Immunohistochemical staining was performed to evaluate the location of SMI-32-ir neurons. Neurofilament heavy chain (NEFH) mRNA expression and SMI-32-ir protein levels were increased in the BD group. In particular, SMI-32-ir protein levels increased significantly 6 and 12 weeks after deafness was induced. In contrast, no significant changes in protein level were detected in the right or left auditory cortices at any time point in the UD group. NEFH mRNA level decreased at 4 weeks after deafness was induced in the UD group, but recovered thereafter. Taken together, BD induced plastic changes in the auditory cortex, whereas UD did not affect the auditory neural system sufficiently to show plastic changes, as measured by neurofilament protein level.

Increased frequencies of serum antibodies to neurofilament light in patients with primary chronic progressive multiple sclerosis

We investigated whether serum and cerebrospinal fluid (CSF) antibodies to the light subunit of the NF protein (NF-L), a main component of the axonal cytoskeleton, may serve as biological markers for axonal pathology and/or disease progression in multiple sclerosis (MS). IgG to NF-L was measured in sera and CSF of MS patients, patients with inflammatory demyelinating diseases of the PNS, with acute inflammatory neurological diseases (including bacterial and viral meningitis), with neurodegenerative diseases, with acute noninflammatory neurological diseases (including stroke, headache and backache) and healthy controls by enzyme-linked immunosorbent assay. We found that serum anti-NF-L IgG antibodies were significantly elevated in MS patients with primary progressive disease course and we provide evidence for an intrathecal production of these antibodies. Our findings support the use of serum antibodies to NF-L as a marker for axonal destruction.

Selective regional alterations in the content or distribution of neuronal and glial cytoskeletal proteins in brain of rats chronically exposed to 2,5-hexanedione

Hexane is used in many industrial processes and induces neurotoxic effects in the central and peripheral nervous system. Hexane is metabolized to 2,5-hexanedione, which is the neurotoxic agent. Continued exposure to hexane or 2,5-hexanedione results in loss of sensorial and motor function in arms and legs and to alterations in axonal neurofilament proteins. The effects of 2,5-hexanedione on different cytoskeletal proteins in different brain areas have not been studied in detail. The aim of this work was to study the effects of chronic exposure of rats to 2,5-hexanedione (1% in the drinking water) on tubulin, neurofilament NF-L, microtubule-associated protein MAP-2, and on glial fibrillary acidic protein (GFAP), in cerebellum, hippocampus and cerebral cortex. The amount of each protein was determined by immunoblotting and its distribution was analysed by immunohistochemistry. The results obtained show a regional selectivity in the 2,5-hexanedione effects on cytoskeletal proteins. NF-L content decreased in all brain areas. MAP-2 decreased in cerebellum and hippocampus and tubulin decreased only in cerebellum. GFAP decreased only in cerebral cortex, but its distribution was altered in cerebellum, with increased content in the granular layer and decreased content in the molecular layer. The area most affected was the cerebellum, where all the proteins analysed were altered. These cytoskeletal proteins alterations may impair the transfer of information involved in the regulation by the cerebellum of motor function and contribute to the altered motor performance in rats exposed to 2,5-hexanedione and humans exposed to hexane.

Semi-in situ atomic force microscopy imaging of intracellular neurofilaments under physiological conditions through the 'sandwich' method

Neurofilaments are intermediate filament proteins specific for neurons and characterized by formation of biochemically stable, obligate heteropolymers in vivo While purified or reassembled neurofilaments have been subjected to morphological analyses by electron microscopy and atomic force microscopy, there has been a need for direct imaging of cytoplasmic genuine intermediate filaments with minimal risk of artefactualization. In this study, we applied the modified 'cells on glass sandwich' method to exteriorize intracellular neurofilaments, reducing the risk of causing artefacts through sample preparation. SW13vim(-) cells were double transduced with neurofilament medium polypeptide (NF-M) and alpha-internexin (α-inx). Cultured cells were covered with a cationized coverslip after prestabilization with tannic acid to form a sandwich and then split into two. After confirming that neurofilaments could be deposited on ventral plasma membranes exposed via unroofing, we performed atomic force microscopy imaging semi-in situ in aqueous solution. The observed thin filaments, considered to retain native structures of the neurofilaments, exhibited an approximate periodicity of 50-60 nm along their length. Their structural property appeared to reflect the morphology formed by their constituents, i.e. NF-M and α-inx. The success of semi-in situ atomic force microscopy of exposed bona fide assembled neurofilaments through separating the sandwich suggests that it can be an effective and alternative method for investigating cytoplasmic intermediate filaments under physiological conditions by atomic force microscopy.

ENU mutagenesis identifies mice modeling Warburg Micro Syndrome with sensory axon degeneration caused by a deletion in Rab18

Mutations in the gene of RAB18, a member of Ras superfamily of small G-proteins, cause Warburg Micro Syndrome (WARBM) which is characterized by defective neurodevelopmental and ophthalmological phenotypes. Despite loss of Rab18 had been reported to induce disruption of the endoplasmic reticulum structure and neuronal cytoskeleton organization, parts of the pathogenic mechanism caused by RAB18 mutation remain unclear. From the N-ethyl-N-nitrosourea (ENU)-induced mutagenesis library, we identified a mouse line whose Rab18 was knocked out. This Rab18(-/-) mouse exhibited stomping gait, smaller testis and eyes, mimicking several features of WARBM. Rab18(-/-) mice were obviously less sensitive to pain and touch than WT mice. Histological examinations on Rab18(-/-) mice revealed progressive axonal degeneration in the optic nerves, dorsal column of the spinal cord and sensory roots of the spinal nerves while the motor roots were spared. All the behavioral and pathological changes that resulted from abnormalities in the sensory axons were prevented by introducing an extra copy of Rab18 transgene in Rab18(-/-) mice. Our results reveal that sensory axonal degeneration is the primary cause of stomping gait and progressive weakness of the hind limbs in Rab18(-/-) mice, and optic nerve degeneration should be the major pathology of progressive optic atrophy in children with WARBM. Our results indicate that the sensory nervous system is more vulnerable to Rab18 deficiency and WARBM is not only a neurodevelopmental but also neurodegenerative disease.

Adenoviral-mediated expression of G2019S LRRK2 induces striatal pathology in a kinase-dependent manner in a rat model of Parkinson's disease

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene cause late-onset, autosomal dominant Parkinson's disease (PD). LRRK2 contains functional GTPase and kinase domains. The most common G2019S mutation enhances the kinase activity of LRRK2 in vitro whereas G2019S LRRK2 expression in cultured neurons induces toxicity in a kinase-dependent manner. These observations suggest a potential role for kinase activity in LRRK2-associated PD. We have recently developed a novel rodent model of PD with progressive neurodegeneration induced by the adenoviral-mediated expression of G2019S LRRK2. In the present study, we further characterize this LRRK2 model and determine the contribution of kinase activity to LRRK2-mediated neurodegeneration. Recombinant human adenoviral vectors were employed to deliver human wild-type, G2019S or kinase-inactive G2019S/D1994N LRRK2 to the rat striatum. LRRK2-dependent pathology was assessed in the striatum, a region where LRRK2 protein is normally enriched in the mammalian brain. Human LRRK2 variants are robustly expressed throughout the rat striatum. Expression of G2019S LRRK2 selectively induces the accumulation of neuronal ubiquitin-positive inclusions accompanied by neurite degeneration and the altered distribution of axonal phosphorylated neurofilaments. Importantly, the introduction of a kinase-inactive mutation (G2019S/D1994N) completely ameliorates the pathological effects of G2019S LRRK2 in the striatum supporting a kinase activity-dependent mechanism for this PD-associated mutation. Collectively, our study further elucidates the pathological effects of the G2019S mutation in the mammalian brain and supports the development of kinase inhibitors as a potential therapeutic approach for treating LRRK2-associated PD. This adenoviral rodent model provides an important tool for elucidating the molecular basis of LRRK2-mediated neurodegeneration.

Nanofibrous scaffolds releasing a small molecule BDNF-mimetic for the re-direction of endogenous neuroblast migration in the brain

Brain tissue engineering has the potential to harness existing elements of neurogenesis within the adult brain to overcome a microenvironment that is otherwise inhibitory to regeneration, especially following severe tissue damage. This study investigates the ability of electrospun poly ε-caprolactone (PCL) to re-direct the migratory pathway of endogenous neuroblasts from the disrupted subventricular zone (SVZ). A small molecule non-peptide ligand (BDNF-mimetic) that mimicked the trophic properties of brain-derived neurotrophic factor (BDNF) was incorporated into electrospun PCL scaffolds to improve neuroblast survival and promote neuroblast migration towards the implant. PCL scaffolds were able to support neuroblast infiltration and migration along the implant tract. In the presence of the BDNF-mimetic, neuroblasts were able to migrate towards the implant via the parenchyma, and their persistence within the implants was prolonged. In addition, the BDNF-mimetic improved implant integration and increased local neuronal plasticity by increasing neurite sprouting at the tissue-implant interface. SMI32+ neurites were observed inside scaffolds at 21 days but not 8 days post implantation, indicating that at least some of the infiltrated neuroblasts had differentiated into neurons.

Coordinated development of voltage-gated Na+ and K+ currents regulates functional maturation of forebrain neurons derived from human induced pluripotent stem cells

Like embryonic stem (ES) cells, human induced pluripotent stem (hiPS) cells can differentiate into neuronal cells. However, it is unclear how their exquisite neuronal function is electrophysiologically coordinated during differentiation and whether they are functionally identical to human ES cell-derived neurons. In this study, we differentiated hiPS and ES cells into pyramidal-like neurons and conducted electrophysiological characterization over the 4-week terminal differentiation period. The human neuron-like cells express forebrain pyramidal cell markers NeuN, neurofilament, the microtubule-associated protein 2 (MAP2), the paired box protein Pax-6 (PAX6), Tuj1, and the forkhead box protein G1 (FoxG1). The size of developing neurons increased continuously during the 4-week culture, and cell-resting membrane potentials (RMPs) underwent a negative shift from -40 to -70 mV. Expression of the muscarinic receptor-modulated K(+) currents (IM) participated in the development of cell RMPs and controlled excitability. Immature neurons at week 1 could only fire abortive action potentials (APs) and the frequency of AP firing progressively increased with neuronal maturation. Interestingly, the developmental change of voltage-gated Na(+) current (INa) did not correlate with the change in the AP firing frequency. On the other hand, the transient outward K(+) current (IA), but not the delayed rectifier current (IK) contributed to the high frequency firing of APs. Synaptic activities were observed throughout the 4-week development. These morphological and electrophysiological features were almost identical between iPS and ES cell-derived neurons. This is the first systematic investigation showing functional evidence that hiPS cell-derived neurons possess similar neuronal activities as ES cell-derived neurons. These data support that iPS cell-derived neural progenitor cells have the potential for replacing lost neurons in cell-based therapy.

The discontinuous nature of neurofilament transport accommodates both establishment and repair of the axonal neurofilament array

Neurofilaments (NFs) provide structural support to axons. Timely and regional deposition of NFs is essential during axonogenesis, since progressive stabilization of proximal axons is essential to support continued pathfinding of distal axonal regions. NFs undergo short bursts of microtubule-mediated axonal transport interspersed by prolonged pauses. We demonstrate herein that it is this unique "on-off" method of axonal transport, coupled with the ability of NFs to form cation-dependent, phosphomediated lateral associations that allow neurons to mediate the orderly transition from exploratory process to stabilized axon following synaptogenesis. We further demonstrate how this transport method provides for NF maintenance following maturation and encompasses the potential for regeneration.

Calcium-dependent neutral cysteine protease and organophosphate-induced delayed neuropathy

A few organophosphorus compounds (OPs) can cause toxic neuropathy known as organophosphorus ester-induced delayed neuropathy (OPIDN). Although the incidents of OPIDN have been documented for over a century, its molecular mechanisms underlying the axonopathy are still unclear. Recently, increasing evidences suggest that proteases are closely associated with OPIDN. Herein, we have summarized the roles of calcium-dependent cysteine proteases (calpains) in OPIDN. The activation of calpains should be an early molecular event during the onset and development of OPIDN. However, the understanding of the mechanism underlying the disruption of Ca(2+) homeostasis and the activation of calpain by neurotoxic OPs is still limited. Therefore, a better understanding of molecular mechanisms that can prevent the disturbance in cellular Ca(2+) homeostasis can facilitate to establish the novel therapeutic strategies for OPIDN.

2,5-hexanedione altered the degradation of low-molecular-weight neurofilament in rat nerve tissues

Occupational exposure to n-hexane produces a central-peripheral distal axonopathy, which is characterized by giant axonal swellings filled with neurofilaments (NFs). To investigate the change of NFs degradation and their possible role in n-hexane neuropathy, adult male Wistar rats were administered intraperitoneally at a dosage of 400 mg/kg/day 2,5-hexanedione (2,5-HD) for 4 weeks. The time course of low-molecular-weight neurofilament (NF-L) degradation and autophagy-related protein in rat sciatic nerves and spinal cords was determined by Western blotting. The results demonstrated that the administration of 2,5-HD inhibited NF-L degradation to an undetectable level in sciatic nerves. Furthermore, a significant reduction of NF-L degradation in spinal cords was observed in the early stage of 2,5-HD exposure. In the meantime, 2,5-HD significantly decreased the level of Beclin-1, a key autophagy-regulated protein in sciatic nerves of rats while increased the level of P62, a selective substrate of autophagy degrading pathway, which indicated a dysfunctional autophagy in rat nerve tissues. Collectively, our findings suggested that the inhibition of autophagy by 2,5-HD might be responsible for the reduction of NF-L degradation in rat sciatic nerves, and involved in the pathogenesis of 2,5-HD-induced axonopathy.

Neonatal MeCP2 is important for the organization of sex differences in vasopressin expression

Several neurodevelopmental disorders are marked by atypical Methyl-CpG-binding protein 2 (MeCP2) expression or function; however, the role of MeCP2 is complex and not entirely clear. Interestingly, there are sex differences in some of these disorders, and it appears that MeCP2 has sex-specific roles during development. Specifically, recent data indicate that a transient reduction in MeCP2 within developing amygdala reduces juvenile social play behavior in males to female-typical levels. These data suggest that MeCP2 within the amygdala is involved in programming lasting sex differences in social behavior. In the present study, we infused MeCP2 or control siRNA into the amygdala of male and female rats during the first three days of postnatal life in order to assess the impact of a transient reduction in MeCP2 on arginine vasopressin (AVP), a neural marker that is expressed differentially between males and females and is linked to a number of social behaviors. The expression of AVP, as well as several other genes, was measured in two-week old and adult animals. Two-week old males expressed more AVP and galanin mRNA in the amygdala than females, and a transient reduction in MeCP2 eliminated this sex difference by reducing the expression of both gene products in males. A transient reduction in MeCP2 also decreased androgen receptor (AR) mRNA in two-week old males. In adulthood, control males had more AVP-immunoreactive (AVP-ir) cells than females in the centromedial amygdala (CMA), bed nucleus of the stria terminalis (BST) and in the fibers that project from these cells to the lateral septum (LS). A transient reduction in MeCP2 eliminated this sex difference. Interestingly, there were no lasting differences in galanin or AR levels in adulthood. Reducing MeCP2 levels during development did not alter estrogen receptorα, neurofilament or Foxg1. We conclude that a transient reduction in MeCP2 expression in the developing male amygdala has a transient impact on galanin and AR expression but a lasting impact on AVP expression, highlighting the importance of MeCP2 in organizing sex differences in the amygdala.

Water extract from the leaves of Withania somnifera protect RA differentiated C6 and IMR-32 cells against glutamate-induced excitotoxicity

Glutamate neurotoxicity has been implicated in stroke, head trauma, multiple sclerosis and neurodegenerative disorders. Search for herbal remedies that may possibly act as therapeutic agents is an active area of research to combat these diseases. The present study was designed to investigate the neuroprotective role of Withania somnifera (Ashwagandha), also known as Indian ginseng, against glutamate induced toxicity in the retinoic acid differentiated rat glioma (C6) and human neuroblastoma (IMR-32) cells. The neuroprotective activity of the Ashwagandha leaves derived water extract (ASH-WEX) was evaluated. Cell viability and the expression of glial and neuronal cell differentiation markers was examined in glutamate challenged differentiated cells with and without the presence of ASH-WEX. We demonstrate that RA-differentiated C6 and IMR-32 cells, when exposed to glutamate, undergo loss of neural network and cell death that was accompanied by increase in the stress protein HSP70. ASH-WEX pre-treatment inhibited glutamate-induced cell death and was able to revert glutamate-induced changes in HSP70 to a large extent. Furthermore, the analysis on the neuronal plasticity marker NCAM (Neural cell adhesion molecule) and its polysialylated form, PSA-NCAM revealed that ASH-WEX has therapeutic potential for prevention of neurodegeneration associated with glutamate-induced excitotoxicty.

Age-related changes of myelin basic protein in mouse and human auditory nerve

Age-related hearing loss (presbyacusis) is the most common type of hearing impairment. One of the most consistent pathological changes seen in presbyacusis is the loss of spiral ganglion neurons (SGNs). Defining the cellular and molecular basis of SGN degeneration in the human inner ear is critical to gaining a better understanding of the pathophysiology of presbyacusis. However, information on age-related cellular and molecular alterations in the human spiral ganglion remains scant, owing to the very limited availably of human specimens suitable for high resolution morphological and molecular analysis. This study aimed at defining age-related alterations in the auditory nerve in human temporal bones and determining if immunostaining for myelin basic protein (MBP) can be used as an alternative approach to electron microscopy for evaluating myelin degeneration. For comparative purposes, we evaluated ultrastructural alternations and changes in MBP immunostaining in aging CBA/CaJ mice. We then examined 13 temporal bones from 10 human donors, including 4 adults aged 38-46 years (middle-aged group) and 6 adults aged 63-91 years (older group). Similar to the mouse, intense immunostaining of MBP was present throughout the auditory nerve of the middle-aged human donors. Significant declines in MBP immunoreactivity and losses of MBP(+) auditory nerve fibers were observed in the spiral ganglia of both the older human and aged mouse ears. This study demonstrates that immunostaining for MBP in combination with confocal microscopy provides a sensitive, reliable, and efficient method for assessing alterations of myelin sheaths in the auditory nerve. The results also suggest that myelin degeneration may play a critical role in the SGN loss and the subsequent decline of the auditory nerve function in presbyacusis.

Distribution of SMI-32-immunoreactive neurons in the central auditory system of the rat

SMI-32 antibody recognizes a non-phosphorylated epitope of neurofilament proteins, which are thought to be necessary for the maintenance of large neurons with highly myelinated processes. We investigated the distribution and quantity of SMI-32-immunoreactive(-ir) neurons in individual parts of the rat auditory system. SMI-32-ir neurons were present in all auditory structures; however, in most regions they constituted only a minority of all neurons (10-30%). In the cochlear nuclei, a higher occurrence of SMI-32-ir neurons was found in the ventral cochlear nucleus. Within the superior olivary complex, SMI-32-ir cells were particularly abundant in the medial nucleus of the trapezoid body (MNTB), the only auditory region where SMI-32-ir neurons constituted an absolute majority of all neurons. In the inferior colliculus, a region with the highest total number of neurons among the rat auditory subcortical structures, the percentage of SMI-32-ir cells was, in contrast to the MNTB, very low. In the medial geniculate body, SMI-32-ir neurons were prevalent in the ventral division. At the cortical level, SMI-32-ir neurons were found mainly in layers III, V and VI. Within the auditory cortex, it was possible to distinguish the Te1, Te2 and Te3 areas on the basis of the variable numerical density and volumes of SMI-32-ir neurons, especially when the pyramidal cells of layer V were taken into account. SMI-32-ir neurons apparently form a representative subpopulation of neurons in all parts of the rat central auditory system and may belong to both the inhibitory and excitatory systems, depending on the particular brain region.

Anti-alpha-internexin autoantibody from neuropsychiatric lupus induce cognitive damage via inhibiting axonal elongation and promote neuron apoptosis

BACKGROUND

Neuropsychiatric systemic lupus erythematosus (NPSLE) is a major complication for lupus patients, which often leads to cognitive disturbances and memory loss and contributes to a significant patient morbidity and mortality. The presence of anti-neuronal autoantibodies (aAbs) has been identified; as examples, anti-NMDA receptors and anti-Ribsomal P aAbs have been linked to certain pathophysiological features of NPSLE.

METHODS AND FINDINGS

In the current study, we used a proteomic approach to identify an intermediate neurofilament alpha-internexin (INA) as a pathogenetically relevant autoantigen in NPSLE. The significance of this finding was then validated in an expanded of a cohort of NPSLE patients (n = 67) and controls (n = 270) by demonstrating that high titers of anti-INA aAb was found in both the serum and cerebrospinal fluid (CSF) of approximately 50% NPSLE. Subsequently, a murine model was developed by INA immunization that resulted in pronounced cognitive dysfunction that mimicked features of NPSLE. Histopathology in affected animals displayed cortical and hippocampal neuron apoptosis. In vitro studies further demonstrated that anti-INA Ab mediated neuronal damage via inhibiting axonal elongation and eventually driving the cells to apoptosis.

CONCLUSIONS

Taken together, this study identified a novel anti-neurofilament aAb in NPSLE, and established a hitherto undescribed mechanism of aAb-mediated neuron damage that could have relevance to the pathophysiology of NPSLE.

Neuroprotective effects of Epigallocatechin-3-gallate (EGCG) in optic nerve crush model in rats

Epigallocatechin-3-gallate (EGCG), the major catechin found in green tea, is a powerful antioxidant and has anti-inflammatory with neuroprotective potential. This study aims to investigate the neuroprotective effects of EGCG in an optic nerve crush (ONC) model in rats. Seventy-two Wistar rats were randomly divided into four groups: normal control (group A), sham operation+EGCG (group B), ONC+vehicle (group C), and ONC+EGCG (group D). The rats were treated intraperitoneally and orally with either vehicle or EGCG (25 mg/kg, injected daily for 5 days and 2 mg/kg orally daily afterwards). Two days after the first injection, an ONC injury was performed by using a micro optic nerve clipper with 40 g power at approximately 2 mm from the optic nerve head for 60 s. Fluorogold was injected into the bilateral superior colliculi 5 days before sacrifice and fluorescent gold-labelled retinal ganglion cells (RGCs) were counted under fluorescence microscopy on days 7, 14 and 28 after ONC. The expression of Neurofilament triplet L (NF-L) was measured via immunohistochemical and Western blotting analysis. In group C, a progressive loss of RGCs was observed after ONC. In contrast, the density of RGCs was significantly higher in group D (p=0.009, independent samples t-test) on day 7 after ONC, and statistical differences were obtained on days 14 and 28 (p=0.026 and p=0.019, respectively, independent samples t-test). The results of immunohistochemical and Western blotting analysis showed significantly higher NF-L protein expression in group D in comparison with group C on days 7, 14 and 28 after ONC. These findings suggest that there are protective effects of EGCG on RGCs after ONC, indicating EGCG might be a potential therapeutic agent for optic nerve diseases.

Focal cortical infarcts alter intrinsic excitability and synaptic excitation in the reticular thalamic nucleus

Focal cortical injuries result in death of cortical neurons and their efferents and ultimately in death or damage of thalamocortical relay (TCR) neurons that project to the affected cortical area. Neurons of the inhibitory reticular thalamic nucleus (nRT) receive excitatory inputs from corticothalamic and thalamocortical axons and are thus denervated by such injuries, yet nRT cells generally survive these insults to a greater degree than TCR cells. nRT cells inhibit TCR cells, regulate thalamocortical transmission, and generate cerebral rhythms including those involved in thalamocortical epilepsies. The survival and reorganization of nRT after cortical injury would determine recovery of thalamocortical circuits after injury. However, the physiological properties and connectivity of the survivors remain unknown. To study possible alterations in nRT neurons, we used the rat photothrombosis model of cortical stroke. Using in vitro patch-clamp recordings at various times after the photothrombotic injury, we show that localized strokes in the somatosensory cortex induce long-term reductions in intrinsic excitability and evoked synaptic excitation of nRT cells by the end of the first week after the injury. We find that nRT neurons in injured rats show (1) decreased membrane input resistance, (2) reduced low-threshold calcium burst responses, and (3) weaker evoked excitatory synaptic responses. Such alterations in nRT cellular excitability could lead to loss of nRT-mediated inhibition in relay nuclei, increased output of surviving TCR cells, and enhanced thalamocortical excitation, which may facilitate recovery of thalamic and cortical sensory circuits. In addition, such changes could be maladaptive, leading to injury-induced epilepsy.

Axonal pathology and loss precede demyelination and accompany chronic lesions in a spontaneously occurring animal model of multiple sclerosis

Axonal damage has been highlighted recently as a cause of neurological disability in various demyelinating diseases, including multiple sclerosis, either as a primary pathological change or secondary due to myelin loss. To characterize and quantify axonal damage and loss in canine distemper demyelinating leukoencephalomyelitis (DL), formalin-fixed paraffin-embedded cerebella were investigated histochemically and immunohistochemically using the modified Bielschowsky's silver stain as well as antibodies against nonphosphorylated (n-NF), phosphorylated neurofilament (p-NF) and beta-amyloid precursor protein (beta-APP). Injured axons characterized by immunoreactivity against n-NF and beta-APP were detected in early distemper lesions without demyelination. In subacute and chronic demyelinating lesions the number of injured axons increased. Moreover, a significant decrease in axonal density was observed within lesions and in the normal appearing white matter in DL as determined by morphometric analyses using Bielschowsky's silver stain and p-NF immunohistochemistry. Summarized, the observed findings indicate that axonal damage (i) occurs early in DL; (ii) can be detected before myelin loss; and (iii) represents a pivotal feature in advanced lesions. It must be postulated that axonal damage plays an important role in the initial phase as a primary event and during progression of nervous distemper as a result of demyelination.

Phenylmethylsulfonyl fluoride protects against the degradation of neurofilaments in tri-ortho-cresyl phosphate (TOCP) induced delayed neuropathy

Tri-ortho-cresyl phosphate (TOCP) is an organophosphorus ester, which can cause a type of neurotoxicity known as organophosphate-induced delayed neuropathy (OPIDN). Our recent study has shown that the enhanced degradation of neurofilament (NF) in peripheral nerve of hens is an early event of TOCP-induced OPIDN (Song et al., 2009). The main objective of this investigation is to study the effect of TOCP administration on NF content and NF degradation when OPIDN is blocked by pretreatment with phenylmethylsulfonyl fluoride (PMSF). The hens were pretreated 24h earlier with PMSF and subsequently treated with a single dosage of 750 mg/kg TOCP, then sacrificed on the corresponding time points of 0, 1, 5, 10, and 21 days after dosing TOCP, respectively. The tibial nerves were dissected, homogenized, and centrifuged at 100,000 x g. The level of NF triplet protein in both pellet and supernatant fractions of tibial nerves was determined. Western blotting analysis showed a significant increase of three NF subunits in hens treated with PMSF and TOCP compared with the control. These changes were observed within 24h of PMSF administration and then followed by an obvious recovery. Furthermore, accompanied with the increase of NF content, a significant decline in NF-L degradation rate was observed in both fractions of tibial nerves. Taken together, these results demonstrated the pretreatment with PMSF could inhibit TOCP-induced NF degradation while it protected hens against the development of OPIDN, which suggested the inhibition of NF-associated protease in peripheral nerves might be an underlying protective mechanism of PMSF against OPIDN.

Motor neuron disease and model systems: aetiologies, mechanisms and therapies

The phenotypes of many neurological diseases, including motor neuron disease (amyotrophic lateral sclerosis; ALS) and Alzheimer's disease (AD), are determined by the vulnerabilities of populations of nerve cells and the character/ evolution of cellular abnormalities. Because different cell types respond selectively to individual trophic factors, these factors may be useful in ameliorating pathology in cells that express their cognate receptors. To test therapies for ALS and AD, investigators require model systems. Although there are a variety of models of ALS, two models are particularly attractive: transgenic mice that express human superoxide dismutase 1 (SOD-1) mutations linked to familial ALS develop paralysis associated with a gain of adverse property of the mutant SOD; and axotomy of facial axons in neonatal rats, a manipulation that causes retrograde cell degeneration, which can be ameliorated by several trophic factors.

Selective overexpression of gamma1 laminin in astrocytes in amyotrophic lateral sclerosis indicates an involvement in ALS pathology

Our earlier studies indicate that the KDI tripeptide of gamma1 laminin reverts paralysis and protects adult rat CNS from excitotoxicity of glutamate and from oxidative stress. Here we show that gamma1 laminin is selectively overexpressed in reactive astrocytes of the amyotrophic lateral sclerosis (ALS) spinal cord, with both gray and white matter astrocytes overexpressing gamma1 laminin. Intensely gamma1 laminin-positive, aggressive-looking reactive astrocytes of the lateral columns of both cervical and thoracic spinal cord surround the lateral ventral horns and roots and extend into the area of the lateral corticospinal tract. In the cervical ALS spinal cord, large numbers of strongly gamma1 laminin-immunoreactive astrocytes are also present in the dorsal columns of the ascending sensory pathways. No other laminin or any other ALS-associated protein localizes in this manner. This unique distribution of gamma1 laminin-immunoreactive astrocytes in the ALS white matter together with our recent results on the efficacy of the KDI domain as a neuronal protector strongly suggest that gamma1 laminin may be expressed by astrocytes of the ALS spinal cord as a protective measure intended to aid neuronal survival. Further comparative studies on ALS spinal cord tissues and those of the animal models of ALS are needed to clarify the specific role of gamma1 laminin and its KDI domain in ALS and its putative interactions with the additional ALS-associated factors, such as excitotoxicity, oxidative stress, and neurofilament accumulation. Most importantly, further studies are urgently needed to test the potential of the KDI tripeptide as a therapeutic treatment for ALS.

Time-dependent Alteration of Cytoskeletal Proteins in Cerebral Cortex of Rat During 2,5-Hexanedione-induced Neuropathy

To investigate the mechanisms of the axonopathy induced by 2,5-hexanedione (2,5-HD), male Wistar rats were administered at a dosage of 400 mg/kg/day 2,5-HD (five times per week). The rats produced a slightly, moderately, or severely abnormal neurological changes, respectively, after 2, 4, or 8 weeks of treatment. The cerebrums were Triton-extracted and ultracentrifuged to yield a pellet fraction and a corresponding supernatant fraction. The relative levels of six cytoskeletal proteins (NF-L, NF-M, NF-H, alpha-tubulin, beta-tubulin, and beta-actin) in both fractions were determined by immunoblotting. The results showed that NFs content in HD-treated rats demonstrated a progressive decline as the intoxication of HD continued. As for microtubule proteins, the levels of alpha-tubulin and beta-tubulin demonstrated some inconsistent changes. The content of alpha-tubulin kept unchangeable, while the content of beta-tubulin increased significantly at the late stage of HD exposure. Furthermore, the content of beta-actin in both fractions remained unaffected throughout the study. These findings suggest that HD intoxication resulted in a progressive decline of NFs, which was highly correlated with the development of HD-induced neuropathy.

Neuronal intermediate filaments and ALS: a new look at an old question

One of the pathological hallmarks of ALS is the presence of axonal spheroids and perikaryal accumulations/aggregations comprised of the neuronal intermediate filament proteins, neurofilaments and peripherin. These abnormalities represent a point of convergence of both familial and sporadic forms of the disease and understanding their formation may reveal shared pathways in what is otherwise considered a highly heterogeneous disorder. Here we provide a review of the basic biology of neurofilaments and peripherin and the evidence linking them with ALS disease pathogenesis.

The Changes of Cytoskeletal Proteins in Plasma of Acrylamide-Induced Rats

Acrylamide (ACR) is a known industrial neurotoxic chemical that can induce neurodegeneration. Cytoskeletal protein aggregation is a pathological hallmark of neurodegenerative disorders. This study was an initial exploration on cytoskeletal proteins in plasma as potential biomarkers of ACR neurotoxicity. Low and high ACR groups received 20 mg/kg and 40 mg/kg ACR by intraperitoneal injection in adult Wistar rats and control group received physiological saline. Rats were all killed after 8 weeks to evaluate the levels of neurofilament(NF)-L, NF-M, NF-H, beta-actin, alpha-tubulin, beta-tubulin, tau, MAP2 proteins in plasma using both SDS-PAGE and western blotting. Compared with the control, the levels of NF-L, NF-M, NF-H, beta-actin, tau, MAP2 proteins decreased and the level of alpha-tubulin increased in high ACR group, the levels of alpha-tubulin, beta-tubulin and MAP2 increased in low ACR group. The results suggested that the changes of these proteins might be relevant to the neurotoxicity of ACR. Some of the cytoskeletal proteins in plasma might be used as marker of biological effect in ACR induced neuropathy.

Diphenyl ditelluride- and methylmercury-induced hyperphosphorilation of the high molecular weight neurofilament subunit is prevented by organoselenium compounds in cerebral cortex of young rats

Organotellurides are important intermediates in organic synthesis and, consequently, the occupational exposure to them is a constant risk for laboratory workers. These compounds can elicit many neurotoxic events in the central nervous system (CNS) that are associated with several neurological symptoms. In contrast, organoselenium compounds are considered to exert neuroprotective actions on such effects. Neurofilaments (NF) are important cytoskeletal proteins and phosphorylation/dephosphorylation of NF is important to stabilize the cytoskeleton. In this work we investigated the potential protective ability of the selenium compounds ebselen and diphenyl diselenide (PhSe)(2) against the effect of diphenyl ditelluride (PhTe)(2) and methylmercury (MeHg) on the total (phosphorylated plus nonphosphorylated) and phosphorylated immunocontent of the high molecular weight neurofilament subunit (NF-H) from slices of cerebral cortex of 17-day-old rats. We observed that 1muM MeHg induced hyperphosphorylation, increasing the total immunocontent of this subunit of the high-salt Triton insoluble NF-H. Otherwise, 15muM (PhTe)(2) induced hyperphosphorylation of the high-salt Triton insoluble NF-H without altering the total immunocontent of this protein into the cytoskeletal fraction. Concerning the selenium compounds, 15muM (PhSe)(2) and 5muM ebselen did not induce alteration per se on the in vitro phosphorylation of NF-H. In addition, (PhSe)(2) and ebselen at these concentrations, presented a protective effect against the action of (PhTe)(2) and MeHg, on the immunoreactivity of NF-H. Considering that hyperphosphorylation of NF-H is associated with neuronal dysfunction it is probable that the effects of (PhTe)(2) and MeHg could be related to the remarkable neurotoxicity of these organocalcogenides. Furthermore the neuroprotective action of selenium compounds against (PhTe)(2) and MeHg effects could be a promising route to be exploited for a possible treatment of calcogenides poisoning.

An immunohistochemical study of the development of sensorimotor components of the early fetal human spinal cord

Sections from all spinal cord levels from 20 human fetuses, age range 7.5-17 gestational weeks (GW) were immunostained for non-phosphorylated neurofilaments (to reveal motoneurones, spinocerebellar neurones and other large neurones), the calcium-binding protein parvalbumin (large proprioreceptive afferents), growth-associated protein 43 kDa (growing axons), glial fibrillary acidic protein (radial glia), synaptophysin (synaptic terminals) the cell-cell recognition molecule ephrin A4 (EphA4) and the ETS transcription factor Er81 (subclasses of motoneurone and proprioreceptive neurone). Muscle afferents crossed the dorsal horn by 7.5 GW and innervated motoneurones by 9 GW. An alignment of glial fibres guided them from dorsal columns to ventral horn, at right angles to the radial glia. They continued to provide a dense innervation of motoneurone pools up to 17 GW. By 13 GW motoneurones were segregated into distinct columns, all of which expressed EphA4 although only certain lateral groups expressed Er81. However, Er81 expression was more widespread amongst dorsal root ganglion neurones. From 9 GW Clarke's column neurones were identified and by 14 GW were heavily innervated by parvalbumin-positive afferents whilst their efferent axons could be traced to the lateral funiculus. This investigation contributes towards a timetable for the functional development of human motor control and makes comparisons with well-studied rodent models.

Carbon Disulfide-Induced Changes in Cytoskeleton Protein Content of Rat Cerebral Cortex

To investigate the mechanism of carbon disulfide-induced neuropathy, male wistar rats were administrated by gavage at dosage of 300 or 500 mg/kg carbon disulfide, five times per week for 12 weeks. By the end of the exposure, the animals produced a slight or moderate level of neurological deficits, respectively. Cerebrums of carbon disulfide-intoxicated rats and their age-matched controls were Triton-extracted and centrifuged at a high speed (100,000 x g) to yield a pellet fraction of NF polymer and a corresponding supernatant fraction, which presumably contained mobile monomer. Then, the contents of six cytoskeletal protein (NF-L, NF-M, NF-H, alpha-tubulin, beta-tubulin, and beta-actin) in both fractions were determined by immunoblotting. Results showed that the contents of the three neurofilament subunits in the pellet and the supernatant fraction decreased significantly regardless of dose levels (P<0.01). As for microtubule proteins, in the pellet fraction of cerebrum, the levels of alpha-tubulin and beta-tubulin demonstrated some inconsistent changes. However, in the supernatant fractions, the content of alpha-tubulin and beta-tubulin increased significantly in both two dose groups (P<0.01). In comparison to neurofilament and tubulin proteins, the content of beta-actin changed less markedly, only the supernatant fraction of the high dose group displayed significant increase (P<0.01), but the others remained unaffected. These findings suggested that the changes of cytoskeleton protein contents in rat cerebrum were associated with the intoxication of carbon disulfide, which might be involved in the development of carbon disulfide neurotoxicity.

Transient ischemia-induced changes of neurofilament 200 kDa immunoreactivity and protein content in the main olfactory bulb in gerbils

This study was carried out to investigate alterations of neurofilament 200 kDa (NF-200) and its polyphosphorylation form (RT97) immunoreactivity and protein content in the main olfactory bulb (MOB) after 5 min of transient forebrain ischemia in gerbils. In the sham-operated group, weak NF-200 immunoreactivity was detectable in a few somata of mitral cells, which projected weak NF-200-immunoreactive processes to the external plexiform layer (EPL). At 1-5 days after ischemia, strong NF-200 and RT97 immunoreactivity was shown by the mitral cell processes; however, somata of mitral cells did not show NF-200 immunoreactivity. At this time point, strong NF-200-immunoreactive mitral cell processes ran to the EPL and glomerular layer (GL). Thereafter, NF-200 and RT97 immunoreactivity was decreased up to 30 days after ischemia. In the 15 days post-ischemic group, the distribution pattern of NF-200 and RT97 immunoreactivity was slightly lower than that in the 1-5 days post-ischemic groups. In the 30 days post-ischemic group, moderate NF-200 and RT97 immunoreactivity was found in the mitral cells processes, but the immunoreactivity in the EPL and GL nearly disappeared. A Western blot study showed a pattern of NF-200 and RT97 expression at all post-ischemic time points similar to that of immunohistochemistry after ischemia. This result indicates that NF-200 and RT97 accumulates in injured mitral cell processes a few days after transient ischemia, which suggests that the axonal transport in the MOB may be disturbed during this period after transient ischemia.

Acrylamide-Induced Changes in the Neurofilament Protein of Rat Cerebrum Fractions

Acrylamide (ACR) is known to produce central-peripheral distal axonopathy, which is characterized by distal swellings and secondary degeneration both in experimental animals and human. Ultrastructurally, excessive accumulation of neurofilaments (NFs) in the distal swollen axon is a major pathological hallmark. However, the mechanisms of ACR axonopathy remain unknown. Twenty seven male Wistar rats were randomly divided into three groups. Lower and higher ACR groups were received 20 and 40 mg/kg ACR by i.p. injection respectively. The control group received physiological saline. All rats were sacrificed after 8 weeks of treatment and their cerebrums were dissected, homogenized and used for the determination of the NF proteins. In general, the levels of light NF (NF-L) and medium NF (NF-M) subunits increased consistently in the supernatant, whereas they decreased consistently in the pellet from rats treated with ACR. Compared to that of the control group, the levels of NF-L increased respectively by 104% and 45% (P<0.01) in the supernatant and decreased by 16% and 11% (P<0.01) in the pellet of rat cerebrums in lower and higher groups. The enhancement of NF-M was 76% and 147% (P<0.05, P<0.01) in supernatant, and the reduction was 26% and 36% (P<0.01) in pellet in lower and higher group respectively. The heavy NF (NF-H) level changed slightly. The present results suggested that the change of NF-L and NF-M levels in cerebrum might be relevant to the mechanisms of the neurofilamentous axonopathies induced by ACR.