The effects of thiamylal sodium on the tonic vibration reflex in man

Investigation of The Neural Drive During Vibration Exercise by High-density Surface-electromyography

Mechanical vibration applied directly to the muscle belly or tendon has been reported to elicit a specific reflex loop named tonic vibration reflex (TVR), which involves motor unit (MU) activation synchronized and un-synchronized within the vibration cycle. Indirect application of vibration to the muscle by vibration exercise (VE) has also been suggested to evoke TVR, as evidenced by the spectral peaks observed at the vibration frequency in the surface electromyography (sEMG). However, other studies interpreted these spectral peaks as the result of motion artifacts (MAs). The aim of the present study is, therefore, to investigate MU activation patterns during VE in order to clarify the nature of those spectral peaks. To this end, low-intensity isometric contractions were executed with and without VE, and high-density sEMG measurements were performed during the contraction tasks. MU action potential (MUAP) trains were extracted by decomposing the recorded high-density sEMG signals. The spectra of the MUAP trains were then calculated and compared between vibration and no-vibration conditions. Clear MU synchronization was observed during VE, confirming the spectral peaks at the vibration frequency to be mainly due to the reflex loop rather than MAs.

Does vibration superimposed on low-level isometric contraction alter motor unit recruitment strategy?

OBJECTIVE

Beneficial effects, including improved muscle strength and power performance, have been observed during vibration exercise (VE) and partially ascribed to a specific reflex mechanism referred to as Tonic vibration reflex (TVR). TVR involves motor unit (MU) activation synchronized and un-synchronized with the vibration cycle; this suggests VE to alter the temporal MU recruitment strategy. However, the effects of VE on MU recruitment remain poorly understood. This study aims to elucidate the influence of VE on MU recruitment indirectly, by investigating the effects of low-intensity VE on muscle activation.

APPROACH

Twenty volunteers performed isometric contractions on the biceps brachii of the right arm at a baseline (low) force equal to 30% of the maximum voluntary contraction without vibration (control) and with vibration at 20, 30, 40, and 55 Hz. Three vibration amplitudes were employed at 12.5%, 25%, and 50% of the baseline. Mean muscle-fiber conduction velocity (mCV), mean frequency (MF), and root mean square (RMS) value were estimated from surface electromyography as indicators of the alteration in MU recruitment strategies.

MAIN RESULTS

The mCV estimates during VE were significantly (p  <  0.05) higher compared to the control condition. Furthermore, six VE conditions produced significantly larger RMS values compared to control condition. The estimated MF did not show any consistent trend.

SIGNIFICANCE

These results suggest that vibration superimposed on low-level isometric contraction alters the MU recruitment strategy, activating larger and faster MUs.

Analysis of Vibration Exercise at Varying Frequencies by Different Fatigue Estimators

Vibration exercise (VE) has been suggested to improve muscle strength and power performance, due to enhanced neuromuscular demand. However, understanding of the most appropriate VE protocols is lacking, limiting the optimal use of VE in rehabilitation programs. In this study, the fatiguing effect of vibration at different frequencies was investigated by employing a force-modulation VE system. Twenty volunteers performed 12-s isometric contractions of the biceps brachii with a load consisting of a baseline force of 80% of their maximum voluntary contraction (MVC) and a superimposed sinusoidal force at 0 (control condition with no vibration), 20, 30, and 40 Hz. Mechanical fatigue was estimated by assessment of MVC decay after each task while myoelectric fatigue was estimated by analysis of multichannel electromyography (EMG) signals recorded during VE. EMG conduction velocity, spectral compression, power, and fractal dimension were estimated as indicators of myoelectric fatigue. Our results suggest vibration, in particular at 30 Hz, to produce a larger degree of fatigue as compared to control condition. These results motivate further research aiming at introducing VE in rehabilitation programs with improved training protocols.

Citosol (thiamylal sodium) triggers apoptosis and affects gene expressions of murine leukemia RAW 264.7 cells

Citosol (thiamylal sodium) is one of generally used anesthetic–sedative agents for clinical patients, and it has not been reported to show induction of cytotoxic effects in cancer cells, especially in mice leukemia RAW 264.7 cells in vitro. In the present study, we investigated the cytotoxic effects of citosol on mice leukemic RAW 264.7 cells, including the effects on protein and gene expression levels which are determined by Western blotting and DNA microarray methods, respectively. Results indicated that citosol induced cell morphological changes, cytotoxic effect, and induction of apoptosis in RAW 264.7 cells. Western blotting analysis demonstrated that citosol promoted the levels of Fas, cytochrome c, caspase 9 and 3 active form and Bax levels, but it suppressed Bcl-xl protein level that may lead to apoptotic death in RAW 264.7 cells. Furthermore, DNA microarray assay indicated that citosol significantly promoted the expression of 5 genes (Gm4884, Gm10883, Lce1c, Lrg1, and LOC100045878) and significantly inhibited the expression of 24 genes (Gm10679, Zfp617, LOC621831, Gm5929, Snord116, Gm3994, LOC380994, Gm5592, LOC380994, LOC280487, Gm4638, Tex24, A530064D06Rik, BC094916, EG668725, Gm189, Hist2h3c2, Gm8020, Snord115, Gm3079, Olfr198, Tdh, Snord115, and Olfr1249). Based on these observations, citosol induced cell apoptosis and influenced gene expression in mice leukemia RAW 264.7 cells in vitro.

Muscle vibration and prefrontal repetitive transcranial magnetic stimulation

We previously demonstrated that prefrontal subthreshold repetitive transcranial magnetic stimulation (rTMS) may reduce motor cortex excitability. We have now examined whether muscle vibration (MV) can compensate for this depression. We enrolled 25 healthy volunteers (aged 22 to 37 years) who received 5 HZ, 10% subthreshold prefrontal rTMS for 12 s. The extensor carpi radialis muscle was vibrated with an electromagnetic mechanical stimulator with a stimulation frequency of 120 HZ and 0.5 mm amplitude. Motor evoked potentials (MEPs) from the flexor carpi radialis muscle (FCR) following single-pulse transcranial magnetic stimulation (TMS) were recorded at baseline, and after 4, 8, and 12 s. During prefrontal rTMS, MEPs of the FCR exhibited a serial depression (P = 0.001). This effect did not occur during MV. We conclude that rTMS of the prefrontal cortex may inhibit the corticospinal system. This depression may be compensated by MV, suggesting that vibration changes motor cortex excitability. The underlying mechanism might be an input from Ia sensory afferents to the motor and prefrontal cortex.

Age-dependent effects of muscle vibration and the Jendrassik maneuver on the patellar tendon reflex response

OBJECTIVE

To explore possible effects of aging on the excitability of spinal reflexes.

DESIGN

Using a cross-sectional design, the influences of muscle vibration and the Jendrassik maneuver on patellar tendon reflex function were compared between 30 young adults and 15 older adults.

SETTING

Motor control research laboratory.

SUBJECTS

The young adults were volunteers of college age. The older adults (74.5 +/- 4.14 yr) were volunteers from the local community. All subjects were free of medications and neurological conditions that would affect normal neuromuscular responses.

MAIN OUTCOME MEASURES

A force-time curve analysis of the patellar tendon reflex response was used to assess the inhibition and facilitation of spinal reflexes. In the experimental protocol to assess spinal reflex inhibition, 100 Hz vibration was applied to the right quadriceps muscle. In another experimental protocol, spinal reflex facilitation was assessed using the Jendrassik maneuver. To perform the Jendrassik maneuver, subjects were instructed to grasp their hands together and to pull as hard as possible while breathing normally. After a 2-second count, the tendon tap was delivered to the right leg and the subject was instructed to relax. In both experimental protocols, control patellar tendon reflexes were collected.

RESULTS

Analysis of variance for reflex peak force revealed a significant 30% reduction in the amount of vibration-induced reflex inhibition with increasing age, and a similar 33% reduction in the amount of Jendrassik maneuver facilitation observed for the older adults as compared with the younger adults.

CONCLUSION

These results support the hypothesis that inhibitory and excitatory influences acting on the alpha motoneuron pool are different in young and older adults.

Differential activation of motor units in the wrist extensor muscles during the tonic vibration reflex in man

1. Single motor unit activity was recorded in the extensor carpi radialis longus and extensor carpi radialis brevis muscles of five healthy human subjects, using metal microelectrodes. 2. Motor units were characterized on the basis of their twitch contraction times and their force recruitment thresholds during voluntary imposed-ramp contractions. 3. The discharge patterns of forty-three motor units were studied during tonic vibration reflex elicited by prolonged (150 s) trains of vibration (30 Hz) applied to the distal tendons of the muscles. The temporal relationships between the individual small tendon taps of the vibratory stimulus and the motor unit impulses were analysed on dot raster displays and post-stimulus time histograms. 4. After tendon taps, the impulses of motor units with long twitch contraction times (mean +/- S.D., 47.2 +/- 10.7 ms) and low recruitment thresholds (0.88 +/- 0.6 N) formed a single narrow peak (P1) with a latency (22.7 +/- 1.4 ms) which was comparable to that of the tendon jerk in the extensor carpi radialis muscles. These motor units were named 'P1 units'. On the other hand, the response of motor units with shorter twitch contraction times (31.1 +/- 3.3 ms) and higher recruitment thresholds (3.21 +/- 1.3 N) showed two peaks: a short latency (23.4 +/- 1.3 ms) P1 peak similar to the previous one and a P2 peak occurring 9.4 +/- 1.2 ms later. These motor units were named 'P1-P2 units'. 5. When the reflex contraction increased slowly, the P1 peaks of 'P1-P2 units' were clearly predominant at the beginning of the contraction, during the rising phase of the motor unit discharge frequency, while the P2 peaks became predominant when the units had reached their maximal discharge frequency. 6. Increasing the tendon vibration frequency (35, 55, 75, 95 Hz) did not modify the 'P1 unit' discharge pattern. Due to interference between vibration period and peak latencies, increasing the vibration frequency caused the P1 and P2 peaks of 'P1-P2 units' to overlap. 7. Superficial cutaneous stimulation of the dorsal side of the forearm during tendon vibration noticeably decreased the P1 peaks in both types of motor units. In the P2 peaks it could result in either a decrease or an increase but the average effect was a slight increase. 8. When applied 10 s before tendon vibration, cutaneous stimulation considerably suppressed the tonic vibration reflex.(ABSTRACT TRUNCATED AT 400 WORDS)