Amyotrophic lateral sclerosis: macro-EMG and twitch forces of single motor units

Macro-EMG potentials (MEP)s and twitch contractions (spike-triggered-averaging) of single motor units (MUs) have been recorded in the first dorsal interosseus muscle (FDI) of 10 control subjects and 20 patients with amyotrophic lateral sclerosis (ALS). MUs over the full range of voluntary recruitment thresholds were studied. Patients with slightly affected FDIs (5) mainly showed MUs with enlarged MEPs and increased twitch forces. In contrast, the patients with more severely affected FDIs (15) revealed decreased twitch forces, especially in the MUs with higher thresholds. The corresponding MEPs could be enlarged as well as normal. It appears that MU sprouting and the resulting increase of twitch force can compensate for the loss of motoneuron in early stages of ALS. In more advanced stages, however, a decline of the force of the surviving MUs, especially of those with higher thresholds, seems to contribute to the progressive muscle weakness, in addition to the corticospinal degeneration and the reduction in the number of motoneurons.

[Hyp3]-bradykinin and [Hyp3]-Lys-bradykinin interact with B2-bradykinin receptors and stimulate inositol phosphate production in cultured human fibroblasts

The recently isolated, naturally occurring peptide hormones [Hyp3]-bradykinin and [Hyp3]-Lys-bradykinin were investigated for their agonist activity on solubilized binding sites from human fibroblasts. Both ligands competed with [3H]bradykinin binding in a dose-dependent fashion with potencies similar to bradykinin (BK) and Lys-BK. Biological activity was assessed by determination of inositol phosphate accumulation and cyclic 3',5'-adenosine monophosphate synthesis in intact cultured cells. Stimulation by the hydroxylated peptides resulted in a pronounced accumulation of both parameters with similar effectiveness as BK and Lys-BK. These results indicate that [Hyp3]-BK and [Hyp3]-Lys-BK are agonists at the bradykinin receptor system with properties comparable to their non-hydroxylated analogues. This suggests that hydroxylation of kinins does not alter receptor interaction or signal transduction in cultured human fibroblasts.

The impact of paired motor unit discharges on tremor

We studied paired discharges (PDs) of single motor units (MUs) of the first dorsal interosseus muscle in parkinsonian and essential tremor. The number of PDs increased with increasing tremor strength and the duration of their intervals shortened. The amplitudes of the single tremor beats showed a significant negative correlation to the duration of the intervals of the preceding PDs. It is concluded that PDs play an important role as tremor amplifiers. The basic mechanism is probably the more than linear summation of two twitch contractions with short interval which is known from animal experiments.

Collateral nerve sprouting and twitch forces of single motor units in conditions with partial denervation in man

Single motor units (MUs) were studied in the first dorsal interosseus muscle of 7 patients with slight partial denervation and in 10 controls. MU action potentials were recorded using the macro-EMG technique and their size was taken to assess collateral nerve sprouting. Simultaneously, the muscle force was monitored to determine the voluntary recruitment thresholds of the MUs and spike-triggered-averaging was applied to measure their twitch forces. At comparable force recruitment thresholds, both macro-EMG potentials and twitch forces were increased in the patients. We conclude, that collateral nerve sprouting increases MU force and can compensate for MU loss.

Silent periods in single orbicularis oculi motoneurones

The activity of single motor units (MUs) of the orbicularis oculi muscle was recorded in normal volunteers. While the subject maintained a constant firing rate, electrical stimuli were applied to the ipsilateral supraorbital nerve. Peristimulus histograms were constructed showing 2 periods of discharge accumulation at times corresponding to the R1 and R2 component of the blink reflex, each followed by a silent period, called SP1 and SP2, respectively. Whereas SP1 may merely result from the synchronisation of discharges in the preceding R1, SP2 can only be explained by an inhibition of the motoneurone activity. These findings confirm the existence of silent periods in the orbicularis oculi muscle in spite of the absence of mechanisms probably responsible for silent periods in load-bearing muscles.

[Double discharges of motor units and tremor strength]

The relationship between the double-discharges (DDs) of single motor units (MUs) and the tremor strength was studied in 7 patients with parkinsonism and 3 with essential tremor. The potentials of single MUs and the force of the first dorsal interosseus muscle were recorded during slight isometric contractions. The rate of DDs and their interval duration were correlated with the global tremor strength and the amplitudes of the single tremor beats. With increasing tremor strength, the rate of DDs increased and the duration of their intervals decreased. It is concluded that DDs act as tremor amplifiers. This effect is probably accounted for by a more than linear summation of two consecutive MU contractions with short interval which is known from animal experiments.

Axonal conduction velocity and force of single human motor units

Tungsten microelectrodes of the type used for microneurography have been used to record motor units selectively from the first dorsal interosseous and abductor pollicis brevis muscles of normal subjects and patients who had had complete sections of the ulnar or median nerve. After determining the recruitment threshold and the twitch tension (spike-triggered averaging) of a single unit, its nerve was stimulated at the wrist and the elbow using surface electrodes. By adjusting the position of the surface electrode and the stimulus intensity and by using computerized subtraction of responses just above and below threshold for a given unit, the same motor unit could often be identified in response to stimulation at both sites and its conduction velocity determined. The twitch tension and recruitment threshold of the motor units were closely correlated with the conduction velocity of the motor axons in normal subjects. Preliminary data from patients suggests that this method should be applicable to patients with a number of neuromuscular disorders.

[Direct measurement of the conduction velocity of single motor axons in man]

The conduction velocity (CV) of single motor axons was measured in the ulnar and median nerve. Stimuli of submaximal intensities were delivered at the wrist and at the elbow using surface electrodes. The responses of single motor units were recorded by tungsten or steel microelectrodes. Changes of the stimulus intensity and of the position of the stimulation electrodes and subtraction of the responses frequently allowed the potential of the same motor unit to be identified following stimulation at both sites and to calculate its axonal CV. In all individuals, axonal CV's from the low to the high velocity range (40 to 63 m/s) could be measured. The method may provide a new approach to the investigation of various disorders of the peripheral nerve.

[Disorders of motor unit discharge activity in parkinsonism]

The discharge activity of single motor units (MUs) of the first dorsal interosseus muscle was recorded in slight stationary isometric contractions. Normal subjects and patients with parkinsonism of various degrees were investigated. The purpose was to study disturbances of the discharge pattern in the patients and their potential diagnostic role. Automatic signal recognition and statistical analysis of the interval distribution were used. Most MUs of the patients revealed considerable irregularities of their discharge sequences best marked by the so called "floating standard deviation". All patients, also 2 without tremor, showed a characteristic synchronization of their MU discharges ("broad-peak" type). Since the above changes were also seen in the patients with only slight symptoms, these investigations, if methodically simplified, could be of diagnostic value.

Discharge pattern of single motor units in basal ganglia disorders

We studied the discharge pattern of motor units (MUs) from the first dorsal interosseous muscle during slight stationary isometric contraction. In six controls, seven patients with parkinsonism, and five patients with choreic disorders, we analyzed 78 MUs. About one-half of the MUs in both patient groups fired irregularly as shown by interval histograms, joint interval histograms, and corresponding statistical calculations. Cross-correlation techniques revealed a characteristic type of MU synchronization in parkinsonism. Analysis of the MU discharge pattern can be useful in clinical assessment of these disorders.

Changes in the recruitment pattern of single motor units in the blink reflex of patients with parkinsonism and hemiplegia

The recruitment pattern of single motor units (SMUs) was studied in the early (R1) and late (R2) blink reflex components in normal subjects (15), patients with parkinsonism (10) and with hemiplegia due to hemispheral lesions (5). Reflexes were evoked by constant current stimuli applied to the supraorbital nerve. SMU discharges were recorded in the preseptal part of the lower eyelid using a bipolar needle electrode. Thresholds of R1 and R2, latencies at the thresholds and the number of discharges in R2 were determined. In parkinsonism, the recruitment of SMUs in R1 was impaired, suggesting that the malfunction of the basal ganglia in this disorder is associated with a reduced excitability of neurons in the pontine brain-stem. In hemiplegia, the recruitment in both R1 and R2 could be impaired. The orderly function of neurones in the pontine and medullary pathways of these components appears to require facilitatory hemispheral influences. Signs of disinhibition occasionally found in R1 may point to an imbalance between facilitatory and inhibitory hemispheral influences upon the pontine pathway.

Synchronous discharges in pairs of steadily firing motor units tend to form clusters

Discharges of several motor units (MU) were simultaneously recorded during slight isometric contractions of the first dorsal interosseus muscle using bipolar needle electrodes. Correlograms constructed by counting the relative discharge intervals (1-ms binwidth) between two MU frequently showed narrow central peaks reflecting the occurrence of more synchronies than expected by chance. Diagrams of the temporal distribution of these synchronies revealed that they tend to form clusters consisting of several subsequent events associated with an adjustment of the firing pattern of the two MU. The synchronization described here may be explained by similar mechanisms as the so-called 'short-term synchronization'.

[Function of early and late components of the blink reflex--study of discharge behavior of single motor units]

The discharge pattern of single motor units in the early (R1) and late (R2) component of the electrically evoked trigemino-facial blink reflex was investigated by means of selective EMG-recording techniques. At low rate stimulation (0,1 Hz) the stimulus threshold of motor unit discharges in R1 was clearly above that in R2. Higher stimulation rates (1 Hz) were associated with an attenuation of motor unit discharges in R2 according to the well known habituation. The same motor units, however, revealed stable discharges in R1 or even signs of facilitation. These differences of motor unit recruitment in the two components indicate that R1 cannot be simply interpreted as a protective reflex like R2. At higher stimulus intensities, the characteristical firing pattern consisted of single discharges in R1 followed by high frequency multi-discharges of the same motor units in R2. This means that the motor unit discharges in R1 do not only evoke a single twitch of the eyelids but initiate a vigorous tetanic contraction with short latency. Thus, R1 yet reveals a protective function shortening the latency of the reflex blink upon stronger stimuli on the side of the affected eye.

Two cases of adynamia episodica hereditaria: in vitro investigation of muscle cell membrane and contraction parameters

Membrane potentials, current-voltage relationships, and contractile parameters were studied in intact muscle cell bundles obtained from two patients with adynamia episodica hereditaria. In a normal extracellular medium, the cell membranes had resting potentials of about -80 mV and their current-voltage relationships were not significantly different from control curves. In contrast to normal muscles the afflicted cells were paralyzed in a medium having 6-10 mmol/liter potassium. The mechanisms of paralysis in the two specimens were different from each other. Many fibers from one patient were spontaneously active even in normal solution. In high potassium solution spontaneous activity was increased and the cells gradually depolarized to values at which excitatory sodium current is normally inactivated. This depolarization was connected with an increased sodium conductance and was reversed by the application of tetrodotoxin (TTX). The fibers from the other patient were not spontaneously active. In high potassium solution they were paralyzed at membrane potential values at which normal fibers would still contract. The reason for this paralysis was a reduced excitability.

Recruitment of single motor units in the human blink reflex

The recruitment of single motor units (MU) in the early (R1) and late (R2) components of the electrically evoked human blink reflex (BR) was studied using bipolar needle electrodes with a limited take-off area. It could be shown that the same MUs can discharge in R1 and R2 of a BR as well as during voluntary eyelid contraction. At repetitive stimulation (1 Hz), facilitation of MU discharges in R1 and habituation in R2 became apparent. The visible reflex eyelid contraction may mainly be due to repetitive MU discharges in R2. The discharges of the same MUs in R1, however, contribute to it and shorten the latency between stimulus and reflex response.

Unilateral reduction of the early and late blink reflex component in hemiparkinson syndrome

Electrically evoked blink reflexes were recorded in 10 patients with unilateral tremor and/or rigor, mostly diagnosed as hemiparkinson syndrome. Five of the patients could be investigated before and after stereotaxic thalamo-subthalamotomy. The EMG activity of the early and late components was quantified by means of averaging and integrations techniques. In addition, the latencies of the reflex components were determined. The major finding was a unilateral decrease of the EMG activity of both the early and late components confined to the clinically affected side. This pattern points to a lowered state of excitability of neurons in or close to the facial nucleus, probably due to a dysfunction of contralateral EPMS structures. A loss of facilitatory influences from EPMS centers, e.g. the nigro-striatal system, on brain stem neurons in the area of the facial nucleus appears most probable. The latencies of the early and late components were mostly normal. After stereotaxic surgery, the BR activity was decreased bilaterally. The difference between the affected and unaffected sides, however, was nearly unchanged. At present an unspecific postoperative effect cannot be excluded.

Quantitative analysis of blink reflexes in patients with hemiplegic disorders

Electrically evoked blink reflexes were investigated in 18 patients with hemiplegia and in 15 control subjects, using common electromyographic techniques. The EMG activities of the early and late components were quantitatively and integration. In addition, the latencies of the single components were determined. Regarding the EMG activity of the late components two major types of BR alteration could be distinguished. In type I stimulation of the clinically affected side evoked significantly decreased late components on both the affected and the unaffected sides. This pattern points to a lowered excitability of the brain stem trigeminal systems and may be associated with predominantly sensory disorders. In type II the decrease of the late components was confined to the affected side independent of the side of stimulation. This pattern may indicate a lowered excitability of the brain stem facial systems and/or of the lateral bulbar reticular formation and may be correlated with predominantly motor deficits. Both types are presumably due to a loss of facilitatory influences associated with the hemispheral lesion. Although the early component was frequently decreased on the affected side there was no consistent pattern and no relation to the alterations of the late components. The latencies of both responses, predominantly of the late ones were frequently prolonged, in particular following stimulation of the affected side. Comparison of the seemingly normal components in the patients with the corresponding control values pointed to a generally lowered blink reflex excitability in hemiplegic patients.

Peripheral and central conduction times in hereditary pressure-sensitive neuropathy

Seven members of a family with histologically proven hereditary pressure-sensitive neuropathy (HPSN) agreed to be examine clinically and electrophysiologically. A sural nerve biopsy specimen taken from the propositus who suffered from a partial brachial plexus palsy showed typical 'sausage-like' myelin sheath thickenings reflecting a failure of axon-adjusted myelination. Reduced motor and sensory conduction velocities involving several nerves were found in the four family members with clinical signs of HPSN. In addition, central conduction times in the auditory and somatosensory pathways were determined measuring the interwave latency I-V in brainstem auditory-evoked potentials and the interpeak latency N14-N20 in median nerve sensory-evoked potentials. Central conduction times in both afferent systems were within normal limits. The absolute delay of peak N14 and N20 in median and P40 in tibial nerve-evoked potentials was probably due to an impaired conduction in the peripheral branch of the bipolar ganglion cell. Whether the central axon branch in the dorsal columns was also involved could not be decided.

Membrane defects in paramyotonia congenita with and without myotonia in a warm environment

Three patients with paramyotonia congenita and 3 control persons were biopsied for an in vitro investigation of the sarcolemmal membrane parameters and of the contractile properties of paramyotonic muscle. At 37 degrees C, paramyotonic muscle fibers had normal resting potentials, but on cooling to 27 degrees C they depolarized. Depolarization to -60 mV caused spontaneous activity, and further depolarization to -40 mV caused inexcitability. Depolarization could be prevented by the application of tetrodotoxin, a finding suggesting a defect in the Na channels. Analysis of the membrane current densities using voltage clamps with 3 microelectrodes revealed that in paramyotonic patients at 37 degrees C all component conductances were normal, except for a decreased Cl conductance in the patient who had myotonia in a warm environment. At 27 degrees C, the Na and Cl conductances were abnormally high. The K conductance was always normal. The results explain the clinical symptoms of weakness and paralysis. Potassium- and caffeine-contracture experiments gave normal results. The clinical symptom of paramyotonic stiffness, therefore, has not been explained by these studies.