No abstract available.
Animals ; Cats* ; Muscle Spindles* ; Muscle Weakness*

OBJECTIVETo investigate the changes in the afferent discharge activities of the sensory nerve endings in muscle spindles of rats with hindlimb immobilization.

METHODSPlaster cast was used immobilize the hindllimbs of rats. Using air-gap technique, the spontaneous discharge of the muscle spindles and its responses to perfusion with succinylcholine (0.05 mg/ml) and suspension in an extended position were observed in isolated muscle spindles from rats with hindlimb immobilization for 3, 7, and 14 days.

RESULTSThe muscle spindles of rat soleus showed a sharp decrease in spontaneous discharge frequency (P<0.01) and response to succinylcholine perfusion after 3 days of hindlimb immobilization (P<0.05). Significant changes of the firing rate in an extended position was observed in rats after a 14-day immobilization (P<0.01). The duration of individual spikes was significantly prolonged following hindlimb immobilization (P<0.01).

CONCLUSIONMuscle spindle discharges decrease significantly in rats following hindlimb immobilization, which might be related to reduced contractile properties of the muscle spindle.

Muscle spindle is the key proprioceptor in skeletal muscles and plays important roles in many physiological activities, such as maintaining posture, regulating movement and controlling speed variation. It has significant clinical relevance and is emerging as a promising therapeutic target for the treatment of motor functional impairment and metabolic diseases. In this review, we summarized muscle spindle distribution and the mechanism of mechanical signal transmission, and reviewed the research progress on morphological and structural characteristics of muscle spindles.
Muscle Spindles/physiology* ; Muscle, Skeletal/physiology* ; Clinical Relevance

OBJECTIVETo investigate the characteristics in the topographic distribution of the muscle spindles in human masticatory muscles.

METHODSThe muscle spindles of the masticatory muscles on both sides of 3 human corpses fixed in formalin for more than 1 year were observed histologically and analyzed quantitatively using an image analysis system.

RESULTSThe mean muscle spindle density was 32.11/g in the masseter, significantly higher in the deep muscular fibers (70.76/g) with high proportion of spindle complexes than in the superficial layers of the muscle belly (P<0.05). The mean spindle density in the temporalis was 5.44/g, higher in the anterior portion (7.44/g) than in the posterior portion (3.78/g, P<0.01). The medial pterygoid had a mean spindle density of 4.43/g.

CONCLUSIONThese results indicate a heterogeneous distribution of muscle spindles in the masticatory muscles with different morphologies or in different portions of the same muscle, depending on muscle fiber type and muscular architecture.

The purpose of this study was to investigate any relationship between the geometric factors of synaptic contacts of muscle spindle afferent terminals and masseteric motor neurons in the trigeminal motor nucleus. Terminals from the masseteric muscle spindle afferents were stained with intra-axonal injection of HRP and were examined electronmi-croscopically with serial sections at the central and peripheral regions of trigeminal motor nucleus of the cat. The number of terminals examined were 76 in peripheral and 105 in central region. The results obtained were as follows. 1. Most of the labeled terminals showed simple synaptic connectivity. Each terminals in peripheral and central region made synaptic contact with 1 to 5 neuronal profiles. Two or three labeled terminals were occasionally seen to make synaptic contact with the same dendrite. 2. The average number of postsynaptic proximal dendrite per labeled terminal was higher in the central region than in the peripheral region. In contrast, that of postsynaptic distal dendrite per labeled terminal was higher in the peripheral region than in the central region. 3. The average diameter of postsynaptic dendrites in the central region was larger than that in the peripheral region. This imply terminals in the peripheral region contacted with further distal part of the distal dendrite than that in the central region. These results indicate that synaptic connectivity associated with the spindle afferents from masseteric muscle is different according to their geometric location within the trigeminal motor nucleus and suggest that there will be precise interrelationship between the morphology, pattern of synaptic connectivity and functions of muscle spindle afferents.
Animals ; Cats* ; Dendrites ; Motor Neurons ; Muscle Spindles* ; Neurons

OBJECTIVETo find out the characteristic topographic distribution of the muscle spindles in human masseter and temporal muscle, and to clarify the neurobiology roles of masticatory muscles during chew and adjusting mandibular position.

METHODSThe muscle spindles of masseter and temporal muscle on both sides of 5 human corpses fixed in formalin for more than 1 year were observed and quantitatively analyzed by picture analysis equipment.

RESULTSThe muscle spindles were maldistributed and spindles were commonly clustered in some individual portions, and the muscle spindle figures were diversiform, which were predominantly composed of the spindle simple and spindle complexes. The masseter spindles of the deep portion were obviously more than that of the superficial. Spindles of temporal muscle were concentrated in the anterior approach to the coracoid.

CONCLUSIONThe distribution of muscle spindles in the masseter and temporal muscle is heterogeneous, spindle density in the deep portion of masseter and the anterior of temporolis muscle is greater than others. The deep of masseter and the anterior of temporal muscle play an important part in maintaining mandibular position and balance.

One of the most important and urgent issues in the field of space medicine is to reveal the potential mechanism underlying the disused muscle atrophy during the weightlessness or microgravity environment. It will conduce to find out effective methods for the prevention and treatment of muscle atrophy during a long-term space flight. Increasing data show that muscle spindle discharges are significantly altered following the hindlimb unloading, suggesting a vital role in the progress of muscle atrophy. In the last decades, we have made a series of studies on changes in the morphological structure and function of muscle spindle following simulated weightlessness. This review will discuss our main results and related researches for understanding of muscle spindle activities during microgravity environment, which may provide a theoretic basis for effective prevention and treatment of muscle atrophy induced by weightlessness.
Animals ; Hindlimb Suspension ; Muscle Spindles ; physiopathology ; Muscle, Skeletal ; physiopathology ; Muscular Atrophy ; physiopathology ; Space Flight ; Weightlessness Simulation

Capsule restricts the further study on muscle spindle function and the involved mechanism. The aim of this study was to establish the isolation method of intrafusal fibres from the isolated rat muscle spindle. Intrafusal fibres were harvested from muscle spindle of soleus muscle in rats using neutrase-collagenase digestion. A variety of incubation mediums have been tested to find out an appropriate medium of intrafusal fibers in vitro. Trypan blue staining was used to detect cell death, and patch clamp was used to record resting potential. The results showed that the intrafusal fibres incubated with amine acid-saline solution were almost all dead. DMEM could maintain good condition of the fibres, but excess CO2 ventilation would induce cellular swelling or even death. While Leiboviz's 15 (L-15) medium can guarantee 1-2 h of physiological condition of the intrafusal fibres. Coverslips treated with gelatin, polylysine and serum was the better interfaces for the intrafusal fibres to adhere easily, compared with regularly treated coverslip. The resting potential of intrafusal fibres was (-45.3 ± 5.1) mV, consistent with others obtained from in vivo muscle spindle from cats and frogs. These results suggest that the isolation method of the intrafusal fibres has been successfully established in the present study, providing a new approach in better understanding of muscle spindle activities and the involved mechanism.
Animals ; Cell Culture Techniques ; methods ; Muscle Spindles ; physiology ; Muscle, Skeletal ; physiology ; Rats

OBJECTIVE: To investigate the effects of Jendrassik maneuver on latency and amplitude of the T-reflex and H-reflex of the soleus muscle in normal adults. METHOD: The T-reflex and H-reflex tests were performed on sixty normal adults with standardized technique using the soleus muscle. The shortest latency and the largest peak-to-peak amplitude were chosen for representative values. RESULTS: The results were as follows: 1) There was a significant difference in latency of the T-reflex between with and without Jendrassik maneuver. 2) The increment ratio of the amplitude with Jendrassik maneuver was 88% in the T-reflex and 18% in the H-reflex. There were a significant difference in the amplitude of both reflexes between with and without Jendrassik maneuver. 3) A high correlation was present between the latency of H- & T-reflex and the length. CONCLUSION: According to these results, we suggest that Jendrassik maneuver primarily increases the sensitivity of muscle spindles and decreases the presynaptic inhibition of the Ia terminals at cortical, subcortical and spinal levels. Jendrassik maneuver can be a useful tool in cases of clinically decreased or absent deep tendon reflex.
Adult ; H-Reflex* ; Humans ; Muscle Spindles ; Muscle, Skeletal* ; Reflex ; Reflex, Stretch

In anesthetized cats the effects of lactate-activated muscle spindle upon the group Ia muscular afferent fibers were studied. Laminectomy was done from L5 to Sl spinal cord level. Extracellular recording was done at dorsal root to record the impulse discharge from group Ia muscular afferent fibers. 1) Muscle spindle of Gastrocnemius-Soleus muscle were activated by lactate injection and exhibited increased impulse discharge through group Ia muscular afferent fibers. 2) There was latency of 7-12 seconds before muscle spindle is activated by lactate injection. But the whole response was not dose related. 3) The response pattern after lactate injection was divided into three groups which were excitation, inhibition and inhibition with preceding excitation. 4) Some responses were similar to those of bradykinin, sympathetic stimulation (adrenaline injection) and succinylcholine injection. 5) It was suggested that muscle spindle has characteristics of polymodal receptor which has responses to not only mechanical stimulation but also chemical stimulation.
Animals ; Bradykinin ; Cats ; Lactic Acid ; Laminectomy ; Muscle Spindles ; Spinal Cord ; Spinal Nerve Roots ; Stimulation, Chemical ; Succinylcholine