Elicited activity of the sensorimotor cortex after chronic unilateral exclusion of the spinocervical tract

Elicited potentials of the sensorimotor cortex were investigated in chronic experiments before and after unilateral injury to the spinocervical tract at the C₃ level. Such injury led to a considerable disturbance of tactile and proprioceptive reactions but did not lower the amplitude of potentials elicited in the cerebral cortex by irritation of a limb on the injured side. On the intact side, there was an increase in the amplitude of the early response components to irritation of the extremity on this side. In 1–2 months after the operation proprioceptive sensitivity and motor activity had returned to normal, but the reactions to tactile irritation failed to reappear. Apparently the presence of a high level of afferent input into the cerebral cortex is insufficient for retention of somatic sensitivity. It is suggested that an inflow over several channels plays a role in providing the spatial-temporal sequence required for activating cortical neurons.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences, USSR, Moscow. Translated from Neirofiziologiya, Vol. 2, No. 5, pp. 469–474, September–October, 1970.     

Role of tonic motor units in flexor reflex evoked by impulsation from a focus of inflammation

The reactions of single motor units (MU) of the flexor muscles (musculus tibialis anterior and musculus biceps femoris) to tactile (light touch), nociceptive (strong compression), and electrical stimulation of the skin of the same extremity were investigated in unanesthetized spinal rats and cats. These reactions were compared with the reactions of the same MU to impulsation from a focus of inflammation evoked on the same extremity. It is shown that the smaller the motor units (judging by the amplitude of its action potential), the higher its sensitivity to exciting and the lower its sensitivity to inhibitory effects from the flexor reflex afferents (FRA), the longer its after-discharges and the more pronounced its capacity for prolonged discharges in response to prolonged stimulation of the FRA. These functional properties of the small MU are characteristic of the tonic motor neurons and the slow muscle fibers innervated by them. It is shown that prolonged impulsation from a focus of inflammation evokes the continuous activity of precisely these (tonic) MU. The activity of the large (phasic) MU ceases 2–3 min after injury which causes a focus of inflammation. Such selective activation of only some of the tonic MU is evidently due to the fact that the prolonged exciting synaptic effect of impulsation from the focus of inflammation causes accommodation of the phasic motor neurons.Institute of Normal and Pathological Physiology, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 3, No. 3, pp. 308–315, May–June 1971.     

Motor unit recruitment strategy of knee antagonist muscles in a step-wise, increasing isometric contraction

The purpose of this study was to determine if differences exist between the control strategies of two antagonist thigh muscles during knee flexion and extension muscular coactivation. Surface myoelectric signal (MES) of the quadriceps (rectus femoris) and the hamstrings (semitendinosus) were obtained from both muscles while performing step-wise increasing contractions during flexion and extension with the knee at 1.57 rad of flexion (90 degrees). The median frequency of the power density spectrum, which is related to the average muscle fiber action potential conduction velocity and therefore to motor unit recruitment, was calculated from each MES. The results suggest that, in all the subjects tested, when the muscle acts as antagonist most motor units are recruited up to 50% of the maximal voluntary force, whereas when the muscle acts as antagonist motor units are recruited up to 40% of the maximal voluntary force. The force range past 40–50% of the maximal force is also characterized by differences between the agonist/antagonist.     

Frequency analysis of motor responses evoked in unanesthetized cats by stimulation of the motor cortex

Frequency characteristics of motor responses evoked by stimulation of the motor cortex by amplitude- and frequency-modulated stimulus sequences were investigated in chronic experiments on unanesthetized cats. The variable component of evoked muscular contraction was studied. Frequency characteristic curves were plotted by the harmonic linearization method. Transformation of controlling signals in the motor system was shown to take place by low-frequency filtration and to be characterized by nonstationary, nonlinear, and frequency-dependent properties. Phase delay of the principal harmonic of the variable component of evoked muscular contraction was minimal at a frequency of 0.2 Hz and it varied in different experiments from 40 to 90°. The increase in the phase delay and decline of the amplitude-frequency characteristic curves were particularly marked if the frequency exceeded 1–2 Hz. The mean phase delay at a frequency of 5 Hz was about 108°; the mean slope of the amplitude characteristic curves in the 2–10 Hz region was –12 dB/decade. It is suggested that definite correlation between the dynamic properties of the motor system may be determined, in particular, by the adaptive properties of the spike discharge of neurons concerned in the transmission of motor command signals.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 12, No. 6, pp. 571–579, November–December, 1980.     

Voluntary control of muscle tension in lengthened and intact limbs in different ranges of force load

Data confirming the hypothesis that there is a range of isometric loads where subjects organize voluntary control of muscle tension with the maximum precision and minimum specific energy expenditure are presented, the energy expenditure being estimated indirectly by the ratio of the area (integral) of the summary electromyogram (EMG) to the force momentum impulse. The asymmetries of the integrated estimates of visuomotor tracking with the use of isometric control organs have been analyzed in 23 patients (6 men and 17 women) aged 15–35 years in different periods, after surgical elimination of the difference between the lengths of their lower extremities. A slightly distinct zone of minimization of the integrated estimates of discrete visuomotor tracking in the range of 25–35% of the maximum force of the muscle group tested (foot dorsal flexors) has been found in healthy subjects (26 healthy men aged 19–39 years) and orthopedic patients (the intact extremity). The zone of optimal loads is more distinct in patents on the side of lengthening; this zone tends to shift towards the region of weaker forces.     

Electromyography Parameters of Muscular Fatigue and Recovery in Patients with Parkinson’s Disease before and on Medication

The effect of medication (Nakom, Cyclodol, and Bromocriptine for 3–6 months) on the electromyogram (EMG) parameters of muscular fatigue and recovery after exercise was studied in patients with Parkinson’s disease (PD). Healthy age-matched subjects served as a control group. In the patients on medication, tolerance to exercise increased approximately twofold and the maximum strength during fatigue and recovery was lower than before medication. In the control subjects, the number of flexions was twofold higher than in the patients on medication. In the patients before medication, the turn count and the mean EMG amplitude were higher and the turn-amplitude peak ratio was lower than on medication, suggesting a treatment-induced decrease in muscular rigidity. Medication changed the EMG parameters of fatigue and recovery to values more characteristic of healthy young subjects than of healthy elderly ones. Thus, the increased tolerance to exercise revealed in the PD patients on medication by turn-amplitude and muscular strength analyses could lead to an increased working capacity and deeper fatigue.__________Translated from Fiziologiya Cheloveka, Vol. 31, No. 4, 2005, pp. 81–87.Original Russian Text Copyright © 2005 by Antonen, Meigal, Lupandin.     

Regeneration of motor axons in crayfish limbs: Distal stump activation followed by synaptic reformation

Summary Servered distal stumps of limb motor axons in the crayfish Procambarus clarkii remain ultrastructurally intact for at least 2–3 ms after being severed from their cell body. Initial regeneration of a motor axon is associated with the appearance of up to 200 small profiles (satellite axons) having no glial sheath adjacent to the large surviving stump for about 1 cm distal to the lesion at 4–5 wks postoperatively. These satellite axons are seen 2–4 cm distally at the target muscles 3–4 ms postoperatively. By 14–15 ms postoperative, the motor sheaths from the lesion site to the target muscles contain small axonal processes having thick glial sheaths. Behavioral tests show that some axons that are reconnected to the CNS at 4–5 wks may not be connected at 14–15 ms, whereas other axons not connected by 3–4 ms may be connected at 14–15 ms when the original distal stumps have degenerated.We suggest that all these data can best be explained by the view that motor axons in crayfish limbs initially regenerate via activation of the surviving distal stump by satellite axons which grow out from proximal stump. In most cases, these satellite axons continue to activate the surviving distal stump as they slowly grow to the target muscle. Eventually the satellite axons reform synapses on the target muscle and the original distal stump degenerates.This work was supported by NSF grants BNS 77-27678 and 80-22248 and an NIH RCDA 00070 to GDB. The authors would like to thank Mr. Martis Ballinger, Mr. Robert Reiss, and Mrs. Mary Raymond for their excellent technical assistance. We would also like to thank Dr. Wesley Thompson and Mr. Douglas Baxter for helpful discussions.     

Fatigue Effect on Low-Frequency Force Fluctuations and Muscular Oscillations during Rhythmic Isometric Contraction

Continuous force output containing numerous intermittent force pulses is not completely smooth. By characterizing force fluctuation properties and force pulse metrics, this study investigated adaptive changes in trajectory control, both force-generating capacity and force fluctuations, as fatigue progresses. Sixteen healthy subjects (20–24 years old) completed rhythmic isometric gripping with the non-dominant hand to volitional failure. Before and immediately following the fatigue intervention, we measured the gripping force to couple a 0.5 Hz sinusoidal target in the range of 50–100% maximal voluntary contraction. Dynamic force output was off-line decomposed into 1) an ideal force trajectory spectrally identical to the target rate; and 2) a force pulse trace pertaining to force fluctuations and error-correction attempts. The amplitude of ideal force trajectory regarding to force-generating capacity was more suppressed than that of the force pulse trace with increasing fatigue, which also shifted the force pulse trace to lower frequency bands. Multi-scale entropy analysis revealed that the complexity of the force pulse trace at high time scales increased with fatigue, contrary to the decrease in complexity of the force pulse trace at low time scales. Statistical properties of individual force pulses in the spatial and temporal domains varied with muscular fatigue, concurrent with marked suppression of gamma muscular oscillations (40–60 Hz) in the post-fatigue test. In conclusion, this study first reveals that muscular fatigue impairs the amplitude modulation of force pattern generation more than it affects the amplitude responsiveness of fine-tuning a force trajectory. Besides, motor fatigue results disadvantageously in enhancement of motor noises, simplification of short-term force-tuning strategy, and slow responsiveness to force errors, pertaining to dimensional changes in force fluctuations, scaling properties of force pulse, and muscular oscillation.     

Changes in intra-abdominal pressure, trunk muscle activation and force during isokinetic lifting and lowering

Intra-abdominal pressure (IAP), force and electromyographic (EMG) activity from the abdominal (intra-muscular) and trunk extensor (surface) muscles were measured in seven male subjects during maximal and sub-maximal sagittal lifting and lowering with straight arms and legs. An isokinetic dynamometer was used to provide five constant velocities (0.12–0.96 m·s^–1) of lifting (pulling against the resistance of the motor) and lowering (resisting the downward pull of the motor). For the maximal efforts, position-specific lowering force was greater than lifting force at each respective velocity. In contrast, corresponding IAPs during lowering were less than those during lifting. Highest mean force occurred during slow lowering (1547 N at 0.24 m·s^–1) while highest IAP occurred during the fastest lifts (17.8 kPa at 0.48–0.96 m·s^–1). Among the abdominal muscles, the highest level of activity and the best correlation to variations in IAP (r=0.970 over velocities) was demonstrated by the transversus abdominis muscle. At each velocity the EMG activity of the primary trunk and hip extensors was less during lowering (eccentric muscle action) than lifting (concentric muscle action) despite higher levels of force (r between –0.896 and –0.851). Sub-maximal efforts resulted in IAP increasing linearly with increasing lifting or lowering force (r=0.918 and 0.882, respectively). However, at any given force IAP was less during lowering than lifting. This difference was negated if force and IAP were expressed relative to their respective lifting and lowering maxima. It appears that the IAP increase primarily accomplished by the activation of the transversus abdominis muscle can have the dual function of stabilising the trunk and reducing compression forces in the lumbar spine via its extensor moment. The neural mechanisms involved in sensing and regulating both IAP and trunk extensor activity in relation to the type of muscle action, velocity and effort during the maximal and sub-maximal loading tasks are unknown.     

Dynamic characteristics of motor responses evoked by stimulation of the motor cortex in unanesthetized cats

Temporal characteristics of motor responses evoked in unanesthetized cats by stimulation of the motor cortex through bipolar needle electrodes were investigated in chronic experiments. Isometric and isotonic contractions of the flexor muscles of the hip and knee joints of the limb contralateral to the point of stimulation were recorded. The latent period of response varied from 100 msec or more in the case of low-frequency (100–150 Hz) and low-threshold (1.1–1.2 thresholds) stimulation of the motor cortex to 30–35 msec in the case of "optimal" parameters of stimulation (300–400 Hz, 1.5–1.6 thresholds). If the intensity of stimulation was high enough the rising time constant of evoked contraction was 50–80 msec; values of the falling time constant of muscular contraction after cessation of stimulation were much greater, namely 150–300 msec. The rising time constant of contraction decreased with an increase in both the frequency and strength of motor cortical stimulation. The results are examined and discussed from the standpoint of methods of automatic control theory.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 12, No. 5, pp. 451–458, September–October, 1980.     

The targeted force steps developed by a human wrist: Cyclic components in the motor program

The targeted flexor isometric force steps developed by a wrist and corresponding EMG activity of the flexor muscles were studied in healthy volunteers. In 82.3–97.5% of trials, the main component of the force trajectory (before the postcorrections of the force level) showed complex dynamics: several (from two to five)dF/dt peaks were observed at this section of the trajectory. The distribution of time intervals from the initiation of the force trajectory todF/dt peaks was polymodal in all cases. The mean interval between successivedF/dt peaks varied from 56.7 msec to 84.4 msec in different individuals (the average group value was 70.5 msec). All tested subjects exhibited amplitude modulation of integrated EMG at the section reflecting the force step development; the averaged interval between the successive first-order EMG peaks calculated for the group of five persons was 78.6 msec. Strict temporal correlation ofdF/dt peaks and EMG peaks was found (coefficient of correlation averaged 0.94). It is concluded that the motor command ensuring performance of isometric force step includes a cyclic component; this feature must be taken into account when mechanisms controlling such motor events are interpreted. The frequency of the component is near the upper limit of a normal tremor frequency band. At the same time, it is impossible to regard the cyclic component in the motor command as a result of simple superposition of tremor on the targeted force development because the cyclic component is clearly synchronized with the force step initiation.Neirofiziologiya/Neurophysiology, Vol. 25, No. 6, pp. 455–462, November–December, 1993.     

Characteristics of the Integrated Electromyogram in Individuals Exposed to Long-Term Vibration

The functional state of the forearm muscles in individuals exposed to long-term vibration (dressers with a duration of current employment of 7–15 years, n = 12) was assessed using turn–amplitude analysis of the integrated surface electromyogram (EMG), the nerve conduction velocity test, and the conventional motor unit action potential electromyographic test. A significant increase in the EMG amplitude and the number of turns upon graded effort, as well as a decrease in the maximal ratio of the number of turns to the average amplitude of the electromyogram from the right m. flexor carpi radialis of the dressers, was revealed, which is indicative of secondary muscular disorders connected with the specific features of the occupational movement pattern and long-term exposure to vibration.     

Sprouting and formation of new synapses in motor structures of the central nervous system

The investigations of sprouting and reactive synaptogenesis in motor structures of the spinal cord, brain stem, thalamus, and cerebral cortex are reviewed. The reactions of the neurons and neuronal connections to injury and the ability of the nervous system to recover the impaired connections in the early postnatal period are compared with those in adult animals. The sprouting phenomenon appearing in the intact central nervous system is analyzed too. The mechanisms of synaptic reorganization of the nervous centers are discussed.Neirofiziologiya/Neurophysiology, Vol. 26, No. 4, pp. 299–314, June–July, 1994.     

Evoked Potentials of the Somatic Cortex and EMG Reactions of the Shoulder Muscles Elicited by Passive Extension of the Elbow Joint in Unanesthetized Cats

We recorded electromyographic (EMG) reactions from the flexors of the elbow joint and evoked potentials (EP) from the somatic cortex (fields 3, 4, and 6) of unanesthetized cats. These reactions were elicited by perturbation of an external extensor loading applied to the arm and evoking passive extension of the elbow joint. Perturbation of the loading was performed in two modes: (i) with different fixed force moments within a 0.04–0.2 N·m range, but with a constant rate of change in this moment (3.2 N·m·sec^–1), and (ii) with a constant force moment magnitude (0.2 N·m), but with different rates of change in this moment (from 0.1 to 6.4 N·m·sec^–1). When the elbow joint was passively extended, an EMG response was generated in the m. biceps brachii. The amplitude of this response correlated with the amplitude of perturbation of the external loading, and the time course of the response was rather close to that of the evoked passive moment. It was possible to differentiate several (up to seven) successive components in EP recorded from the three above-mentioned cortical fields; among them, the component N(50–60) was the most stable and clearly manifested. Its amplitude did not depend on the level of external loading and decreased with a decrease in the rate of loading perturbation. The time course of the N(50–60) changed insignificantly with variation of temporal parameters of the stimulus and of the evoked movement. We conclude that the spinal level and the cortical level responsible for formation of the stretch reflex differ significantly from each other in their functional roles. Reactions of the spinal level (which could be characterized by changes in EMG) are to a greater extent related to a change in the position of the limb link, while reactions of the cortical level (EP) are determined by the arrival of information about changes in the forces applied to the joint. Neurons of the somatic cortex, which are excited in the course of the stretch reflex, cannot be considered the main source responsible for generation of the M2 component of the myographic response. It is supposed that the cortical level predetermines the formation of non-reflex motor commands related to motor reflexes closed in the somatic brain cortex.     

Altered Nucleotide-Microtubule Coupling and Increased Mechanical Output by a Kinesin Mutant

Kinesin motors hydrolyze ATP to produce force and do work in the cell – how the motors do this is not fully understood, but is thought to depend on the coupling of ATP hydrolysis to microtubule binding by the motor. Transmittal of conformational changes from the microtubule- to the nucleotide-binding site has been proposed to involve the central β-sheet, which could undergo large structural changes important for force production. We show here that mutation of an invariant residue in loop L7 of the central β-sheet of the Drosophila kinesin-14 Ncd motor alters both nucleotide and microtubule binding, although the mutated residue is not present in either site. Mutants show weak-ADP/tight-microtubule binding, instead of tight-ADP/weak-microtubule binding like wild type – they hydrolyze ATP faster than wild type, move faster in motility assays, and assemble long spindles with greatly elongated poles, which are also produced by simulations of assembly with tighter microtubule binding and faster sliding. The mutated residue acts like a mechanochemical coupling element – it transmits changes between the microtubule-binding and active sites, and can switch the state of the motor, increasing mechanical output by the motor. One possibility, based on our findings, is that movements by the residue and the loop that contains it could bend or distort the central β-sheet, mediating free energy changes that lead to force production.     

Effect of exogenous acetylcholine on potassium currents in the frog motor nerve ending during acetylcholinesterase inhibition

The effect of exogenous acetylcholine (ACh) on potassium currents in the motor nerve ending (NE) has been studied in neuromuscular preparations of the frog cutaneous-sternal muscle by extracellular recording of evoked electrical potentials from the NE. The investigation was performed during inhibition of acetylcholinesterase (AChE) activity by specific inhibitors and AChE removal from the synaptic cleft by collagenase. After AChE inhibition by either armine or proserine, or after treatment of the preparation with collagenase, no effect of exogenous ACh in concentrations of 1·10^–4–6·^–4 mole/liter was observed, in contrast to results from preparations with intact AChE. However, under the same conditions, as in the case of active AChE, ACh in concentrations of 7·10^–4–2·10^–3 mole/liter inhibited Ca-activated potassium current of the NE membrane. Experiments with dipyroxim, a synaptic AChE reactivator, have shown that the ACh effect on the potential-dependent potassium current is mediated by specific AChE. The role of AChE is discussed in respect to its significance for realization of the ACh action on potential-dependent potassium current in NE.Translated from Neirofiziologiya, Vol. 25, No. 2, pp. 146–149, March–April, 1993.     

High temperature induced alterations in energy transfer in phycobilisomes of the cyanobacterium Spirulina platensis

Exposure of intact cells of Spirulina to high temperature (HT) stress (40–60 °C) caused decrease in absorption spectrum and fluorescence emission spectrum. Low temperature emission spectra were altered at phycocyanin (PC) level. Room and low temperature emission spectra of intact phycobilisomes showed that PC was the main target in this cyanobacterium for the altered energy transfer under HT.This revised version was published online in March 2005 with corrections to the page numbers.     

Selective Vulnerability of Spinal and Cortical Motor Neuron Subpopulations in delta7 SMA Mice

Loss of the survival motor neuron gene (SMN1) is responsible for spinal muscular atrophy (SMA), the most common inherited cause of infant mortality. Even though the SMA phenotype is traditionally considered as related to spinal motor neuron loss, it remains debated whether the specific targeting of motor neurons could represent the best therapeutic option for the disease. We here investigated, using stereological quantification methods, the spinal cord and cerebral motor cortex of ∆7 SMA mice during development, to verify extent and selectivity of motor neuron loss. We found progressive post-natal loss of spinal motor neurons, already at pre-symptomatic stages, and a higher vulnerability of motor neurons innervating proximal and axial muscles. Larger motor neurons decreased in the course of disease, either for selective loss or specific developmental impairment. We also found a selective reduction of layer V pyramidal neurons associated with layer V gliosis in the cerebral motor cortex. Our data indicate that in the ∆7 SMA model SMN loss is critical for the spinal cord, particularly for specific motor neuron pools. Neuronal loss, however, is not selective for lower motor neurons. These data further suggest that SMA pathogenesis is likely more complex than previously anticipated. The better knowledge of SMA models might be instrumental in shaping better therapeutic options for affected patients.     

The impact of vitamin D3 supplementation on muscle function among HIV-infected children and young adults: a randomized controlled trial

Objectives:

We tested the hypothesis that daily vitD₃ supplementation increases neuromuscular motor skills, jump power, jump energy, muscular force, and muscular strength.

Methods:

This was a secondary analysis of a randomized controlled trial of 12-months of oral 7,000 IU/day vitD₃ supplementation or placebo among 56 persons living with HIV aged 9-25 years. Neuromuscular motor skills were quantified using the Bruininks-Oseretsky Test of Motor Proficiency. Power was quantified using peak jump power, and energy was quantified using peak jump height. Muscular force was quantified using isometric ankle plantar- and dorsiflexion, isokinetic knee flexion and extension. Muscular strength was quantified using isometric handgrip strength.

Results:

After 12-months, serum 25-hydroxyvitamin D [25(OH)D] was higher with supplementation versus placebo (β=12.1 ng/mL; P<0.001). In intention-to-treat analyses, supplementation improved neuromuscular motor skills versus placebo (β=1.14; P=0.041). We observed no effect of supplementation on jump power, jump energy, muscular force, or muscular strength outcomes versus placebo.

Conclusions:

Among HIV-infected children and young adults supplementation with daily high-dose vitD₃ increased concentration of serum 25(OH)D and improved neuromuscular motor skills versus placebo.     

Dynamic properties of neurons sensitive to visible movement in scarabaeid beetles (coleoptera scarabaeidae)

The responses of individual neurons of the optic lobe of beetles to moving light stimuli were studied. It was established that the reactions of neurons to the movement of a single light band in a preferred direction at a rate of 1–150 deg/sec are proportional to the logarithm of the angular velocity. The reactions to the movement of a striped pattern vary nonlinearly with the angular velocity. After an initial volley of discharges, the reaction to steady movement of the pattern drops more sharply than during a single movement of the band. When the pattern is stopped, an inhibitory pause occurs in the neuron's activity. The properties of the transitional processes can be explained by adaptation of local areas of the receptive field and by mutual inhibition between neuron systems sensitive to counter-oriented movements. The neurons which detect rotation of the optical environment have binocular receptive fields. The system for transmitting a turning command to the motor neurons has a time constant of 3–5 sec.Institute of Zoology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 3, No. 3, pp. 325–330, May–June, 1971.