A clinical study of motor evoked potentials using a triple stimulation technique.
Amplitudes of motor evoked potentials (MEPs) are usually much smaller than those of motor responses to maximal peripheral nerve stimulation, and show marked variation between normal subjects and from one stimulus to another. Consequently, amplitude measurements have low sensitivity to detect central motor conduction failures due to the broad range of normal values. Since these characteristics are mostly due to varying desynchronization of the descending action potentials, causing different degrees of phase cancellation, we applied the recently developed triple stimulation technique (TST) to study corticospinal conduction to 489 abductor digiti minimi muscles of 271 unselected patients referred for possible corticospinal dysfunction. The TST allows resynchronization of the MEP, and thereby a quantification of the proportion of motor units activated by the transcranial stimulus. TST results were compared with those of conventional MEPs. In 212 of 489 sides, abnormal TST responses suggested conduction failure of various degrees. By contrast, conventional MEPs detected conduction failures in only 77 of 489 sides. The TST was therefore 2.75 times more sensitive than conventional MEPs in disclosing corticospinal conduction failures. When the results of the TST and conventional MEPs were combined, 225 sides were abnormal: 145 sides showed central conduction failure, 13 sides central conduction slowing and 67 sides both conduction failure and slowing. It is concluded that the TST is a valuable addition to the study of MEPs, since it improves detection and gives quantitative information on central conduction failure, an abnormality which appears to be much more frequent than conduction slowing. This new technique will be useful in following the natural course and the benefit of treatments in disorders affecting central motor conduction. (+info)
Nitric oxide, mitochondria and neurological disease.
Damage to the mitochondrial electron transport chain has been suggested to be an important factor in the pathogenesis of a range of neurological disorders, such as Parkinson's disease, Alzheimer's disease, multiple sclerosis, stroke and amyotrophic lateral sclerosis. There is also a growing body of evidence to implicate excessive or inappropriate generation of nitric oxide (NO) in these disorders. It is now well documented that NO and its toxic metabolite, peroxynitrite (ONOO-), can inhibit components of the mitochondrial respiratory chain leading, if damage is severe enough, to a cellular energy deficiency state. Within the brain, the susceptibility of different brain cell types to NO and ONOO- exposure may be dependent on factors such as the intracellular reduced glutathione (GSH) concentration and an ability to increase glycolytic flux in the face of mitochondrial damage. Thus neurones, in contrast to astrocytes, appear particularly vulnerable to the action of these molecules. Following cytokine exposure, astrocytes can increase NO generation, due to de novo synthesis of the inducible form of nitric oxide synthase (NOS). Whilst the NO/ONOO- so formed may not affect astrocyte survival, these molecules may diffuse out to cause mitochondrial damage, and possibly cell death, to other cells, such as neurones, in close proximity. Evidence is now available to support this scenario for neurological disorders, such as multiple sclerosis. In other conditions, such as ischaemia, increased availability of glutamate may lead to an activation of a calcium-dependent nitric oxide synthase associated with neurones. Such increased/inappropriate NO formation may contribute to energy depletion and neuronal cell death. The evidence available for NO/ONOO--mediated mitochondrial damage in various neurological disorders is considered and potential therapeutic strategies are proposed. (+info)
The role of immunophilins in mutant superoxide dismutase-1linked familial amyotrophic lateral sclerosis.
It has been reported that expression of familial amyotrophic lateral sclerosis (FALS)-associated mutant Cu/Zn superoxide dismutase-1 (SOD) induces apoptosis of neuronal cells in culture associated with an increase in reactive oxygen species. SOD recently has been shown to prevent calcineurin inactivation, initiating the present investigations examining the role of calcineurin in mutant SOD-induced cell death. Wild-type or mutant SOD was expressed in neuronal cells by infection with replication-deficient adenoviruses. PC12 cells overexpressing human wild-type SOD exhibited higher calcineurin activity than cells expressing FALS-related mutant SOD (SODV148G); however, cells expressing SODV148G had calcineurin activity equal to mock-infected cells, suggesting that cell death induced by mutant SOD was not related to a decrease in calcineurin activity. Calcineurin antagonists such as cyclosporin A and FK506, as well as nonimmunosuppressant analogs of cyclosporin A, significantly enhanced SODV148G- and SODA4V-induced cell death. Because both groups of drugs inhibit the rotamase activity of cyclophilins (CyP), but only the immunosuppressant analogs inhibit calcineurin activity, these data suggest that rotamase inhibition underlies the enhanced cell death after SODV148G expression. The importance of rotamase activity in mutant SOD-mediated apoptosis was supported by experiments showing that overexpressed wild-type cyclophilin A (CyPA), but not CyPA with a rotamase active site point mutation, protected cells from death after SODV148G expression. These data suggest that mutant SOD produces a greater need for rotamase and, also, highlights possible new therapeutic strategies in FALS. (+info)
Release of copper ions from the familial amyotrophic lateral sclerosis-associated Cu,Zn-superoxide dismutase mutants.
Point mutations of Cu,Zn-superoxide dismutase (SOD) have been linked to familial amyotrophic lateral sclerosis (FALS). We reported that the Swedish FALS Cu,Zn-SOD mutant, D90A, exhibited an enhanced hydroxyl radical-generating activity, while its dismutation activity was identical to that of the wild-type enzyme (Kim et al. 1998a; 1998b). Transgenic mice that express a mutant Cu,Zn-SOD, Gly93 --> Ala (G93A), have been shown to develop amyotrophic lateral sclerosis (ALS) symptoms. We cloned the cDNA for the FALS G93A mutant, overexpressed the protein in E. coli cells, purified the protein, and studied its enzymic activities. Our results showed that the G93A, the D90A, and the wild-type enzymes have identical dismutation activity. However, the hydroxyl radical-generating activity of the G93A mutant was enhanced relative to those of the D90A and the wild-type enzyme (wild-type < D90A < G93A). These higher free radical-generating activities of mutants facilitated the release of copper ions from their own molecules (wild-type < D90A < G93A). The released copper ions can enhance the Fenton-like reaction to produce hydroxyl radicals and play a major role in the oxidative damage of macromolecules. Thus, the FALS symptoms may be associated with the enhancements in both the free radical-generating activity and the releasing of copper ions from the mutant enzyme. (+info)
Amyotrophic lateral sclerosis (ALS), commonly called Lou Gehrig's disease, is a progressive neuromuscular condition characterized by weakness, muscle wasting, fasciculations and increased reflexes. Approximately 30,000 Americans currently have the disease. The annual incidence rate is one to two cases per 100,000. The disease is most commonly diagnosed in middle age and affects more men than women. It usually presents with problems in dexterity or gait resulting from muscle weakness. Difficulty in speaking or swallowing is the initial symptom in the bulbar form of the disease. Over a period of months or years, patients with ALS develop severe, progressive muscular weakness and other symptoms caused by loss of function in both upper and lower motor neurons. Sphincter control, sensory function, intellectual abilities and skin integrity are preserved. Patients become completely disabled, often requiring ventilatory support and gastrostomy. Death usually occurs within five years of diagnosis and is attributed to respiratory failure or cachexia. The etiology of the disease is unknown. Current research is focused on abnormalities of neuronal cell metabolism involving glutamate and the role of potential neurotoxins and neurotrophic factors. New drugs are being developed based on these theories. Current management involves aggressive, individualized alleviation of symptoms and complications. (+info)
Atypical form of amyotrophic lateral sclerosis.
OBJECTIVE: To investigate patients with an unusual type of muscular atrophy confined to the upper limbs (proximally dominant) and the shoulder girdle, while sparing the face and the legs until the terminal stage. METHODS: Eight patients (six men and two women) were clinically examined. The age at onset ranged from 42 to 73 years, and the clinical course varied from 28 to 81 months. There was no family history of motor neuron disease in any of these patients. Necropsy was performed in two of them. RESULTS: All eight patients basically showed a similar distribution of muscular weakness and atrophy. Subluxation of the shoulder joints was found in all patients. Reflexes were absent in the upper limbs in all patients, but were almost normal in the face and legs in most patients. Pathological reflexes could be elicited in only one patient. Electromyography showed typical neurogenic changes in the limbs of all patients. Cervical MRI disclosed moderate spondylotic changes in seven patients. Antiganglioside antibodies were negative in six patients tested. Abnormal trinucleotide (CAG) repeat expansion of androgen receptor gene was not recognised in five patients examined. Bulbar involvement developed in three patients during the course of the disease. At necropsy, one patient showed degeneration of the pyramidal tracts and motor cortex including Betz cells as well as loss of spinal anterior horn cells and brainstem motor neurons, which is consistent with ALS; in another patient there was neuronal loss of anterior horn cells at the spinal cord accompanied by astrogliosis, whereas the motor cortex and brainstem motor nuclei were relatively well preserved. Intracytoplasmic inclusions such as Bunina bodies, skein-like inclusions, and Lewy body-like inclusions were found in both patients. CONCLUSION: These patients with their peculiar pattern of muscular atrophy seem to have ALS or a subtype of ALS. (+info)
Variation in the biochemical/biophysical properties of mutant superoxide dismutase 1 enzymes and the rate of disease progression in familial amyotrophic lateral sclerosis kindreds.
Mutations in superoxide dismutase 1 (SOD1) polypeptides cause a form of familial amyotrophic lateral sclerosis (FALS). In different kindreds, harboring different mutations, the duration of illness tends to be similar for a given mutation. For example, patients inheriting a substitution of valine for alanine at position four (A4V) average a 1.5 year life expectancy after the onset of symptoms, whereas patients harboring a substitution of arginine for histidine at position 46 (H46R) average an 18 year life expectancy after disease onset. Here, we examine a number of biochemical and biophysical properties of nine different FALS variants of SOD1 polypeptides, including enzymatic activity (which relates indirectly to the affinity of the enzyme for copper), polypeptide half-life, resistance to proteolytic degradation and solubility, in an effort to determine whether a specific property of these enzymes correlates with clinical progression. We find that although all the mutants tested appear to be soluble, the different mutants show a remarkable degree of variation with respect to activity, polypeptide half-life and resistance to proteolysis. However, these variables do not stratify in a manner that correlates with clinical progression. We conclude that the basis for the different life expectancies of patients in different kindreds of sod1-linked FALS may result from an as yet unidentified property of these mutant enzymes. (+info)
Extrapyramidal involvement in amyotrophic lateral sclerosis: backward falls and retropulsion.
Three patients with sporadic amyotrophic lateral sclerosis (ALS) presented with a history of backward falls. Impaired postural reflexes and retropulsion accompanied clinical features of ALS. Hypokinesia, decreased arm swing, and a positive glabellar tap were noted in two of these three patients. Cognitive impairment, tremor, axial rigidity, sphincter dysfunction, nuchal dystonia, dysautonomia, and oculomotor dysfunction were absent. Brain MRI disclosed bilateral T2 weighted hyperintensities in the internal capsule and globus pallidus in one patient. Necropsy studies performed late in the course of ALS have shown degeneration in extrapyramidal sites-for example, the globus pallidus, thalamus, and substantia nigra. Clinically, backward falls and retropulsion may occur early in ALS. This may reflect extrapyramidal involvement. (+info)