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At least 955 records · Page 53Linked to original sources
PubMed1993

Peripheral proprioceptive modulation in crayfish walking leg by serotonin.

In vitro serotoninergic modulation of intracellularly recorded sensory responses was examined in primary afferent terminals of a crayfish leg proprioceptor, the coxo-basal chordotonal organ (CB CO). The effects of different concentrations of serotonin (5-HT) on static and dynamic sensory responses were analysed following bath or pressure applications of the monoamine directly on the strand of the mechanoreceptor. Consequently, the reported effects result from the direct peripheral action of 5-HT on the sensory organ itself. Serotonin modulates the sensory activity by modifying the sensory discharge frequency. The firing discharge of the primary afferents is increased in a dose-dependent manner. The maximal effect is obtained with a concentration of 10(-6) M. Higher concentrations are less effective, and for 20% of the recorded cells, 10(-4) M 5-HT induces a decrease of the sensory discharge, i.e. has an inhibitory effect. Alteration in the pattern of sensory firing, resulting in bursting discharge, was observed in some units. All the recorded sensory units were responsive to the neuromodulator whatever their functional properties. The effects of 5-HT lasted as long as the amine was applied and were reversible after wash. The results suggest that 5-HT could exert a modulatory action on the proprioceptive feedback, by peripheral action on the sensory organ. The natural modalities of 5-HT action are discussed on the basis of immunohistochemistry data suggesting: (i) connections between CB CO and central serotoninergic cells, (ii) 5-HT content in sensory cells of the CB CO. Since the CB CO is involved in the control of leg movement and position, the modulation of its primary afferents might influence the organization of the locomotor pattern. The functional significance of this peripheral sensory neuromodulation was approached by the analysis of the motor reflex activity.

Animals↗
PubMed1999

The role of capsaicin-sensitive muscle afferents in fatigue-induced modulation of the monosynaptic reflex in the rat.

1. The role of group III and IV afferent fibres of the lateral gastrocnemious muscle (LG) in modulating the homonymous monosynaptic reflex was investigated during muscle fatigue in spinalized rats. 2. Muscle fatigue was induced by a series of increasing tetanic electrical stimuli (85 Hz, 600 ms) delivered to the LG muscle nerve. Series consisted of increasing train numbers from 1 to 60. 3. Potentials from the spinal cord LG motor pool and from the ventral root were recorded in response to proprioceptive afferent stimulation and analysed before and during tetanic muscle activations. Both the pre- and postsynaptic waves showed an initial enhancement and, after a '12-train' series, an increasing inhibition. 4. The enhancement of the responses to muscle fatiguing stimulation disappeared after L3-L6 dorsal root section, while a partial reflex inhibition was still present. Conversely, after section of the corresponding ventral root, there was only a reduction in the inhibitory effect. 5. The monosynaptic reflex was also studied in animals in which a large number of group III and IV muscle afferents were eliminated by injecting capsaicin (10 mM) into the LG muscle. As a result of capsaicin treatment, the fatigue-induced inhibition of the pre- and postsynaptic waves disappeared, while the response enhancement remained. 6. We concluded that the monosynaptic reflex inhibition, but not the enhancement, was mediated by those group III and IV muscle afferents that are sensitive to the toxic action of capsaicin. The afferents that are responsible for the response enhancement enter the spinal cord through the dorsal root, while those responsible for the inhibition enter the spinal cord through both the ventral and dorsal roots.

Animals↗
PubMed1995

Neurotrophin-3 reverses experimental cisplatin-induced peripheral sensory neuropathy.

Cisplatin, a widely used chemotherapeutic agent, induces a sensory neuropathy with selective loss of vibration sense and proprioception. Here we demonstrate that neurotrophin-3 (NT-3), a member of the nerve growth factor family of neurotrophic factors, restored to normal levels the reduced H-reflex-related sensory nerve conduction velocity induced by cisplatin in rats. NT-3 treatment corrected an abnormal cytoplasmic distribution of neurofilament protein in large sensory neurons in dorsal root ganglia and the reduction in the numbers of myelinated fibers in sural nerves caused by cisplatin. The NT-3-dependent reversal of cisplatin neurotoxicity thus suggests the possible use of NT-3 in the treatment of peripheral sensory neuropathy.

Animals↗
PubMed2003

Somatosensory graviception inhibits soleus H-reflex during erect posture in humans as revealed by parabolic flight experiment.

The purpose of this study was to investigate how gravity level affects the excitability of the soleus muscle (SOL) motoneuron pool to Ia afferent input while erect posture is maintained in humans. Three healthy male subjects participated in an experiment whereby three different gravity conditions [microgravity (MG), normal gravity (NG), and hypergravity (HG)] were imposed using a parabolic flight procedure. The SOL H-reflex was evoked every 2 s while the subjects kept an erect posture. The stimulus intensity was controlled automatically on a real-time basis by personal computer to induce the constant amplitude of M-wave (10+/-5% of maximal M-wave amplitude). The background electromyographic activity (BGA) of the SOL was largest during HG, while it was almost absent during MG. The SOL H-reflex amplitude was significantly larger during HG and MG than during NG ( P<0.05). During NG and HG, there was a linear relationship between the BGA and the H-reflex amplitude; the difference in the SOL H-reflex amplitude between both gravity conditions could be explained in terms of the BGA level. However, during MG, despite the absence of BGA, the SOL H-reflex amplitude was larger than that during NG. Furthermore, when the subjects voluntarily activated the SOL by applying a load to the lower limb joints and spine by pulling a handle upward, this H-reflex enhancement almost disappeared. These results suggest that the somatosensory systems detecting a load at the lower limbs and/or vertebral column might play a role in reducing the excitability of the SOL motoneuron pool to Ia afferent inputs by presynaptic inhibition.

Adult↗
PubMed1987

Neuromuscular control of posture in the infant and child: is vision dominant?

This study explored the effects of vision and maturation on the characteristics of neuromuscular responses underlying balance control in both seated and standing children of five age groups (3 1/2-5 months, 8-14 months, 2-3 years, 4-6 years, and 7-10 years). A platform was used to unexpectedly disturb the child's balance in the anterior or posterior direction. Responses of the leg, trunk, and neck muscles were recorded using surface electromyograms. Vision was not required for the activation of these responses in any of the age groups tested. However, comparison of the muscle response latencies of standing children to posterior platform translation in the two visual conditions showed a significant reduction in latency for neck flexors in the 2- to 3-year-olds with vision removed and ann increase in the total number of monosynaptic reflexes. No reduction in latency was found in the older age groups. The hypothesis of a shift from an early long latency visual dominance to a shorter latency proprioceptive one during childhood is discussed. Postural control showed a cephalo-caudal developmental gradient with postural responses appearing first in the neck, then trunk, and finally, legs, as children developed from 3 to 14 months of age. A wide variety of response patterns was seen in the 3- to 5-month-olds, indicating that postural responses are not functional prior to experience with stabilizing the center of mass.

Journal Article↗
PubMed2007

Insect walking is based on a decentralized architecture revealing a simple and robust controller.

Control of walking in rugged terrain requires one to incorporate different issues, such as the mechanical properties of legs and muscles, the neuronal control structures for the single leg, the mechanics and neuronal control structures for the coordination between legs, as well as central decisions that are based on external information and on internal states. Walking in predictable environments and fast running, to a large degree, rely on muscle mechanics. Conversely, slow walking in unpredictable terrain, e.g. climbing in rugged structures, has to rely on neuronal systems that monitor and intelligently react to specific properties of the environment. An arthropod model system that shows the latter abilities is the stick insect, based on which this review will be focused. An insect, when moving its six legs, has to control 18 joints, three per leg, and therefore has to control 18 degrees of freedom (d.f.). As the body position in space is determined by 6 d.f. only, there are 12 d.f. open to be selected. Therefore, a fundamental problem is as to how these extra d.f. are controlled. Based mainly on behavioural experiments and simulation studies, but also including neurophysiological results, the following control structures have been revealed. Legs act as basically independent systems. The quasi-rhythmic movement of the individual leg can be described to result from a structure that exploits mechanical coupling of the legs via the ground and the body. Furthermore, neuronally mediated influences act locally between neighbouring legs, leading to the emergence of insect-type gaits. The underlying controller can be described as a free gait controller. Cooperation of the legs being in stance mode is assumed to be based on mechanical coupling plus local positive feedback controllers. These controllers, acting on individual leg joints, transform a passive displacement of a joint into an active movement, generating synergistic assistance reflexes in all mechanically coupled joints. This architecture is summarized in the form of the artificial neural network, Walknet, that is heavily dependent on sensory feedback at the proprioceptive level. Exteroceptive feedback is exploited for global decisions, such as the walking direction and velocity.

Animals↗
PubMed1991

[Striatal involvement on MRI in adrenomyeloneuropathy].

Adrenomyeloneuropathy (AMN), a clinical variant of child adrenoleukodystrophy (ALD), is an adult-onset progressive disorder which presents spastic paraparesis with peripheral nerve involvement and affects mainly the pyramidal tracts from the brainstem to the spinal cord. We report a case of AMN in which serial MRI showed unusual development of areas of high signal in the right striatum. The patient was in good health until the age of 12, when he began to lose his hair. At age 25 he started to have progressive gait disturbance and erectile impotence. In his first admission to our hospital at age 33, he showed diffuse baldness. He was intelligent but childish. His cranial nerves were normal. Muscle strength was weak (3-4/5) in the lower extremities. Deep tendon reflexes were hyperactive in the lower extremities while normal in the upper extremities. Babinski signs were elicited bilaterally. Pinprick and vibratory sensation was impaired in the lower legs. Proprioceptive sensations were normal. Co-ordination was intact. There were urinary incontinence and impairment of erection with preserved libido and ejaculation. Routine laboratory data including hematological studies, serum chemistry and urinalysis were all normal except for mild hyperlipidemia. Serum cortisol response to ACTH was low and serum levels of very long chain fatty acids were increased. Nerve conduction studies were abnormal and consistent with peripheral polyneuropathy. A biopsy specimen of left sural nerve revealed a mild loss of myelinated fibers with thinning of the myelin. These findings and the clinical features confirmed the diagnosis of AMN. MRI in SE2000/40 scans at age 34 disclosed areas of high signal in the bilateral internal capsules.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenoleukodystrophy↗
PubMed1994

Muscle spindle and periodontal trigeminal afferents modulate the hypoglossal motoneuronal activity.

Hypoglossal responses to electrical or natural activation of the afferent fibers of the masseteric nerve and to periodontal mechanoreceptors were recorded in rats. Electrical stimulation of the masseteric nerve, at an intensity adequate to excite prevalently the primary spindle afferents, induced various sequences of excitation-inhibition and inhibition-excitation in 55% of the tested hypoglossal motoneurons. Responses were characterized by excitation, inhibition or excitation-inhibition sequences occurring at short and long latencies. Different pattern of responses were evoked in both the protrusive and the retractive motoneurons of the homolateral hypoglossal nucleus. Moreover, jaw lowering and pressure on the incisor tooth induced antagonistic and synergistic effects on the electrical activity of the same hypoglossal motoneurons. The results show for the first time that afferent signals from both muscle spindles and periodontal receptors modulate the activity of the hypoglossal motoneurons aimed at controlling the tongue position in the mouth during mastication.

Action Potentials↗
PubMed1978

The biphasic acoustic reflex: a new perspective.

The anatomic, neurologic, and physiologic characteristics of the middle ear structures have created confusion concerning the nature of the intraaural muscle reflex. After reviewing the relevant literature, we correlated this information with our studies of human temporal bones and computer analyses of the acoustic reflex responses of individuals with normal hearing. Our hypothesis is that although the stapedius is the initiator of the reflex and the primary contributor to ossicular chain fixation, the tensor tympani is responsible for the major observed response. The negative deflection present in normals tested on the impedance bridge is caused by the stapedius, whereas the large positive deflection is the result of the tensor tympani contraction. We postulate that proprioceptive feedback mechanisms located within the stapedius muscle and tendon permit and/or initiate tensor tympani contraction during acoustic stimulation.

Acoustic Stimulation↗
PubMed1992

Spinothalamic and propriospinal neurones in the upper cervical cord of the rat: terminations of primary afferent fibres on soma and primary dendrites.

Experiments were performed on rats to determine whether primary afferents from the upper cervical region terminate directly on spinothalamic and propriospinal neurones. The central terminations of primary afferents from the upper cervical region were identified by diffusely filling their axons with horseradish peroxidase. Spinothalamic neurones or propriospinal neurones were identified in the same experimental animals by using retrograde transport of wheat germ agglutinin conjugated to horseradish peroxidase. Approximately 3-11% of spinothalamic cells in laminae 4-6 of spinal segments C2-4 received apparent synaptic contacts from primary afferents on the soma or primary dendrites. Approximately 18-36% of propriospinal neurones with axons descending to lower thoracic or lumbar levels received apparent synaptic contacts on the soma or primary dendrites. These data provide anatomical evidence that spinothalamic and long propriospinal neurones in the upper cervical cord are excited directly by primary afferents. The data also help to clarify the neural circuitry underlying somatic sensation and reflex movements evoked by neck receptors.

Animals↗
PubMed1986

Somatosensory activity relevant for motor output. A summary of presentations and discussion.

Several aspects of the function of receptors which contribute to somatic sensations are reviewed. First, there is evidence for a role of large-diameter cutaneous afferents in the reflex regulation of precision movements by the hand. Second, large-diameter muscle afferents from the intrinsic muscles of the hand, probably from primary muscle spindle afferents, can evoke specific sensations of finger movement. Third, the variable relationship between discharges in human C fibers from the hand and the specific sensation of pain is investigated. Activity in large-diameter cutaneous afferents can probably modify this sensation. Finally, the properties of small-diameter afferent fibers innervating joints are shown to be consistent with a role in the reflex regulation of joint integrity.

Afferent Pathways↗
PubMed1997

Proprioceptive control of wrist movements in Parkinson's disease. Reduced muscle vibration-induced errors.

The effects upon the trajectories of practised slow (approximately 9 degrees/s) voluntary wrist-extension movements of applying vibration to the tendon of an antagonist muscle (flexor carpi radialis) during the course of the movement have been studied in patients with idiopathic Parkinson's disease and age-matched healthy individuals. In both patient and control groups, flexor vibration elicited undershooting of wrist-extension movements. Wrist extensor and flexor surface EMG recordings indicated that, in patients and controls, such undershooting resulted principally from sustained reductions in extensor (prime mover) activity. Small vibration reflexes were commonly elicited in the wrist flexors which, in both Parkinson's disease and healthy subjects, were usually otherwise virtually quiescent during these slow extension movements. The amplitudes of such vibration reflexes did not differ systematically between patient and control groups and appeared inadequate to have exerted an appreciable braking action upon the extension trajectories. However, the extent of vibration-induced undershooting was, on average, significantly less in the Parkinson's disease group. In a subgroup of patients with asymmetrical parkinsonism the effects of antagonist vibration upon wrist movements of the more and less affected limb were compared. The degree of vibration-induced undershooting was significantly smaller on the more affected side. This finding suggests that disturbed proprioceptive guidance of voluntary movements in Parkinson's disease is related to the severity of clinical motor deficits. A small number Parkinson's disease patients were studied 'ON' and 'OFF' their routine anti-parkinsonian medication. A non-significant tendency was found for vibration-induced errors to be less marked in the 'OFF' state. In a separate series of experiments, under isometric conditions, vibration-induced EMG changes were recorded whilst subjects attempted to maintain a steady (15% maximum) voluntary wrist extensor effort. Results in control subjects suggested that prolonged flexor vibration produced significant tonic reflex reciprocal inhibition of the extensor muscles. However, the strength of reflex inhibition appeared sufficient to account for only a small fraction of the undershooting observed during the movement tasks. Thus, our results are consistent with the existence of an abnormality of higher-level proprioceptive integration in Parkinson's disease in which there is a mismatch of sensory (proprioceptive) and motor (corollary discharge) information.

Aged↗
PubMed1989

Stereotaxic Vim thalamotomy for treatment of tremor.

Pathological tremor is alleviated almost totally and immediately, also sustainedly, by a selective surgical lesion within the ventral part of the Vim thalamus. Since the Vim receives its proprioceptive sense from the periphery, tremor is interpreted as the phenomenon based on the circuit involving both central and peripheral mechanisms. The importance of the role of the spinal reflex mechanisms is discussed.

Humans↗
PubMed1981

Syndrome of postoperative depression of vital functions in poor-risk patients: its treatment.

Loss of proprioception due to depressed neuromuscular transmitter following continued action of skeletomuscular relaxant drugs may not be the main cause of stupor, respiratory depression, and suppression of motor and sensory reflex activity in the immediate or delayed post-operative period in surgical patients. Those with a chronic history of suffering (termed poor-risk types because of other associated derangements in electrolytes, body water, etc.), hyper-react to surgical stress as well as postoperative pain and apprehension. This leads to the release of large quantities of stress products (noradrenaline and its cognates) into the central nervous system (CNS), thus inducing a phase of depression of the cerebral cortex and other vulnerable parts of the CNS in such a way that the stupor analgesic stage is induced in the affected persons (called the "syndrome of post-operative depression of vital functions"). Treatment of such a syndrome thus involved removal of the stress products from the CNS as well as from peripheral circulation by extraction therapy (20% mannitol administration), coupled with judicious use of atropine and neostigmine to stimulate the CNS itself, i.e., the production of acetylcholine in the mesencephalic reticulo-activating system.

Catheterization↗
PubMedDate not supplied

Modulation by head and trunk positions of the vestibulo-spinal reflexes evoked by galvanic stimulation of the labyrinth. Observations by labyrinthine evoked EMG.

Modulation by head and trunk positions of the vestibulo-spinal reflexes was studied in the soleus muscle activities induced by galvanic stimulation of the labyrinth. The stimulation was applied using a bipolar-biaural method with the cathode on the right ear and the anode on the left ear. The intensity was 1 mA and duration 3 s. 1) When the labyrinth was stimulated with the head facing forward, soleus muscle activities increased on the right side and decreased on the left, with a latency of about 100 ms. In spite of the same stimulation, activities of the soleus muscle on both sides decreased with the head rotated to the right and increased with the head rotated to the left. 2) The responses in upper-body rotation were the same as in the case of head rotation. 3) In trunk rotation, some cases showed the same responses as with the trunk facing forward in rotation to the right and left, while others showed changes in muscular activities with the head rotation caused by rotating the trunk. 4) Changes in labyrinthine evoked EMG by head and trunk positions were considered to be due to interaction of vestibular and proprioceptive inputs on the interneurons of the spinal cord.

Ear, Inner↗