The effects of acute and prolonged muscle vibration on the function of the muscle spindle’s reflex arc

Abstract

Purpose:?Localized mechanical vibration, applied directly to a muscle, is known to have powerful, duration-dependent effects on the muscle spindle’s reflex arc. Here, the conditioning of the function of the spindle reflex arc via vibration was examined with considerations for use as a non-invasive, sensorimotor research tool.

Methods:?Muscle spindle function was examined with patellar tendon taps prior to and following exposure to muscle vibration applied to the quadriceps femoris for acute (<5?s) and prolonged (20?min) durations. Surface electromyography (sEMG), torque, and accelerometry signals were obtained during the taps to quantify various measures of reflex magnitude and latency.

Results:?Our findings suggest that acute vibration had no effect on normalized reflex torque or sEMG amplitude (p?>?0.05), but increased total reflex latency (p?=?0.022). Alternatively, prolonged vibration reduced normalized reflex torque and sEMG amplitude (p?<?0.001), and increased reflex latency (p?<?0.001).

Conclusions:?Our findings support the use of prolonged vibration as a practical means to decrease the function of the muscle spindle’s reflex arc. Overall, this suppressive effect was evident in the majority of subjects, but the extent was variable. This approach could potentially be used to help delineate the muscle spindle’s role in various sensory or motor tasks in which more direct measures are not feasible. Acute vibration, however, did not potentiate muscle spindle function as hypothesized. Rather, our results suggest that acute vibration increased total reflex latency. Accordingly, potential mechanical and neurophysiological mechanisms are discussed.     

The occurrence of “wasting disease” of Zostera in Ireland in the 1930's

There is only one publication quoted in connection with “wasting disease” of Zostera marina L. in Ireland. This was examined and it was concluded that in fact, it did not describe “wasting disease”, but merely the normal seasonal changes of Zostera. However, another report which has not been quoted before did give an account of the disease in County Down. Evidence that the disease occurred in County Mayo is presented for the first time.     

Neurotrophic control of the transmembrane Cl− pump in mammalian muscle fibers

Resting membrane potential of both innervated and denervated rat diaphragm muscle fibers was investigated when the concentration of potential-producing ions was changed in the external fluid and following treatment with furosemide. It was found that equilibrium potential ( ) equalled resting potential level in innervated muscle for Cl^–, but shifts to more positive values compared with resting membrane potential following section of the nerve. Furosemide retards development of post-denervation depolarization of the muscle membrane. It is deduced that trophic influences originating from the motor nerve activates the furosemide-sensitive Cl^– influx system, leading to raised intracellular concentration of Cl^–, a shift in (E_Cl) and depolarization of the muscle membrane.S. V. Kurashov Medical Institute, Minsitry of Health of the RSFSR, Kazan'. Translated from Neirofiziologiya, Vol. 19, No. 6, pp. 766–771, November–December, 1987.     

Does the speed of shortening affect steady-state force depression in cat soleus muscle?

It has been stated repeatedly for the past 50 years that the steady-state force depression following shortening of an activated muscle depends on the speed of shortening. However, these statements were based on results from experiments in which muscles were shortened at different speeds but identical activation levels. Therefore, the force during shortening was changed in accordance with the force-velocity relationship of muscles: that is, increasing speeds of shortening were associated with decreasing forces, and vice versa. Consequently, it is not possible at present to distinguish whether force depression is caused by the changes in speed, as frequently stated, or the associated changes in force, or both. The purpose of this study was to test if force depression depends on the speed of shortening. We hypothesized that force depression was dependent on the force but not the speed of contraction. Our prediction is that the amount of force depression after shortening contractions at different speeds could be similar if the force during contraction was controlled at a similar level. Cat soleus muscles (n=7) were shortened by 9 or 12 mm at speeds of 3, 9, and 27 mm/s, first with a constant activation during shortening (30Hz), then with activation levels that were reduced (<30Hz) for the slow speeds (3 and 9 mm/s) to approximate the shortening forces of the fast speed contractions (27 mm/s). If done properly, force depression could be precisely matched at the three different speeds, indicating that force depression was related to the force during the shortening contraction but not to the speed. However, in order to match force depression, the forces during shortening had to be systematically greater for the slow compared to the fast speeds of shortening, suggesting that force depression also depends on the level of activation, as force depression at constant activation levels can only be matched if the force during shortening, evaluated by the mechanical work, is identical. Therefore, we conclude that force depression depends on the force and activation level during shortening, but does not depend on the speed of shortening as has been assumed for half a century. These results support, but do not prove, the current hypothesis that force depression is caused by a stress-related cross-bridge inhibition in the actin-myosin overlap zone that is newly formed during muscle shortening.     

The role of PGC-1α in the regulation of skeletal muscle metabolism

The purpose of this review was to provide an understanding of the role of PGC-1α in the regulation of skeletal muscle metabolism and to describe the results of studies on the association of the polymorphism gene PPARGC1A with human muscle performance.     

The occurrence of the brown alga Streblonema oligosporum Strömfelt in Britain

The small brown alga Streblonema oligosporum Strömfelt (Ectocarpaceae, Ectocarpales) is reported for the first time in Britain growing on a toxic test panel in Langstone Harbour, south coast of England. An account of the vegetative and reproductive features of the plant is given along with its life history in laboratory culture.     

System identification of muscle–joint interactions of the cat hind limb during locomotion

Neurophysiological experiments in walking cats have shown that a number of neural control mechanisms are involved in regulating the movements of the hind legs during locomotion. It is experimentally hard to isolate individual mechanisms without disrupting the natural walking pattern and we therefore introduce a different approach where we use a model to identify what control is necessary to maintain stability in the musculo-skeletal system. We developed a computer simulation model of the cat hind legs in which the movements of each leg are produced by eight limb muscles whose activations follow a centrally generated pattern with no proprioceptive feedback. All linear transfer functions, from each muscle activation to each joint angle, were identified using the response of the joint angle to an impulse in the muscle activation at 65 postures of the leg covering the entire step cycle. We analyzed the sensitivity and stability of each muscle action on the joint angles by studying the gain and pole plots of these transfer functions. We found that the actions of most of the hindlimb muscles display inherent stability during stepping, even without the involvement of any proprioceptive feedback mechanisms, and that those musculo-skeletal systems are acting in a critically damped manner, enabling them to react quickly without unnecessary oscillations. We also found that during the late swing, the activity of the posterior biceps/semitendinosus (PB/ST) muscles causes the joints to be unstable. In addition, vastus lateralis (VL), tibialis anterior (TA) and sartorius (SAT) muscle-joint systems were found to be unstable during the late stance phase, and we conclude that those muscles require neuronal feedback to maintain stable stepping, especially during late swing and late stance phases. Moreover, we could see a clear distinction in the pole distribution (along the step cycle) for the systems related to the ankle joint from that of the other two joints, hip or knee. A similar pattern, i.e., a pattern in which the poles were scattered over the s-plane with no clear clustering according to the phase of the leg position, could be seen in the systems related to soleus (SOL) and TA muscles which would indicate that these muscles depend on neural control mechanisms, which may involve supraspinal structures, over the whole step cycle.     

Calcium signaling in isolated skeletal muscle fibers investigated under “silicone voltage-clamp” conditions

In skeletal muscle, release of calcium from the sarcoplasmic reticulum (SR) represents the major source of cytoplasmic Ca²⁺ elevation. SR calcium release is under the strict command of the membrane potential, which drives the interaction between the voltage sensors in the t-tubule membrane and the calcium-release channels. Either detection or control of the membrane voltage is thus essential when studying intracellular calcium signaling in an intact muscle fiber preparation. The silicone-clamp technique used in combination with intracellular calcium measurements represents an efficient tool for such studies. This article reviews some properties of the plasma membrane and intracellular signals measured with this methodology in mouse skeletal muscle fibers. Focus is given to the potency of this approach to investigate both fundamental aspects of excitation-contraction coupling and potential alterations of intracellular calcium handling in some muscle diseases.     

Variation of the immunolabelling of the α1-isotubulin in the mitotic spindle ofPhysarum polycephalum

Summary Immunofluorescent labelling ofPhysarum microtubules with a new antibody specific for the ₁-isotubulin has been compared with the labelling with an antibody specific for -isotubulins and an antibody with recognizes tubulin chains terminated by an aromatic amino-acid. In agreement with the known presence of only one -isotype in amoebae and several -isotypes in plasmodia, the immunofluorescence of the mitotic spindle was qualitatively identical, but lower in plasmodia than in amoebae. In all cases except one, there were no relative variations of immuno-fluorescence staining with the three antibodies, from metaphase to telophase, in spindles sampled. In plasmodia grown at optimal temperature, both during normal or perturbed mitosis, the immunostaining of the ₁isotype decreased sharply after metaphase, while the staining obtained with the two other antibodies did not vary significantly. The immunologic determination of the relative amount of the ₁-isotubulin in the tubulin pool and in isolated mitotic microtubules could not account for this observation.     

The ultrastructure of the “difference factor” in the myelin

Summary Electron-microscopic studies of peripheral nerves as prepared by the freezeetching method show the myelin lamella to be 185 Å thick. This is the same dimension found by x-ray diffraction analysis of natural myelin. In contrast to the appearance of osmiumfixed material, the cytoplasmic surfaces of the paired membranes in the myelin lamella are apposed to two fine, separate lines, while the outer membrane sides are fused into a broader single line. The finding of a decidedly different structure for the outer and for the inner membrane surfaces appears to be the cause of the difference factor.This work was supported by the Swiss National Foundation (Nr. 4065). — Acknowledgement: We thank the Balzers AG. (9496 Balzers, Fürstentum Liechtenstein) for providing us with the High Vakuum Device.     

Propagation of activity along the “stepping strip” of the cat spinal cord

Three points located approximately 8 mm apart were identified in a dorsolateral funiculus of the lower thoracic spinal cord in mesencephalic cats, each producing stepping movements on the ipsilateral hindlimb when stimulated. An area 5–17 mm caudal to the caudal stepping point (SP) was scanned for neurons responding synaptically to stimulating the rostral or caudal SP prior and subsequent to electrolytic coagulation of the medial SP. Relative incidence of neurons excited by stimulating the caudal SP did not change following this type of lesioning, although stimulation of the rostral SP at the rate of 4 Hz induced response 5 times less frequently than before. Even stimulation of the rostral SP at the rate of 40–60 Hz, which had considerably increased firing index prior to coagulation, could only produce excitation in tiny numbers of neurons. This indicates that synaptic excitation of neurons becomes considerably more difficult once the stepping strip between stimulation and recording sites has been damaged.Institute for Research into Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 20, No. 6, pp. 763–769, November–December, 1988.