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At least 811 records · Page 45Linked to original sources
PubMed2000

Temporal changes in the excitability of the reciprocal inhibitory interneurones preceding cocontraction of the antagonistic muscle in the human wrist.

The supraspinal control of reciprocal inhibitory interneurones preceding cocontraction of antagonistic muscles in the human wrist was investigated in 5 subjects. The method combined a reaction time task paradigm and a technique for conditioning the H-reflex. Unconditioned H-reflexes were elicited from flexor carpi radialis (FCR) and extensor carpi radialis (ECR) muscles by using electrical stimulation to median and radial nerves. The conditioned H-reflex of the FCR muscle was obtained by simultaneous electrical stimulation to the median and the radial nerves. While subjects performed the bilateral isometric cocontraction task, excitabilities of the alpha motoneurone pools and that of the reciprocal inhibitory interneurones were assessed by the unconditioned and conditioned H-reflex, respectively. Alpha mononeuron pools of FCR and ECR muscles were facilitated starting from approximately 50 msec. preceeding EMG activities. Reciprocal inhibitory interneurones which suppressed FCR alpha motoneurones were disinhibited at almost same time. The present results suggested that supraspinal control of the reciprocal inhibitory interneurones preceding antagonist cocontraction is different from that of preceding agonist contraction.

Adult↗
PubMed1979

Auditory fusion: a critical interval test with implications in differential diagnosis.

Pulses of white noise each of uniform duration but adjustable in interpulse spacing were presented to subjects at a comfortable loudness level. Reduction of pulse spacing below a critical interval resulted in a subjective impression of continuous noise. Eighty-four per cent of patients with sensori-neural hearing loss had a longer critical interval than normal subjects. Tentative explanations for this phenomenon are put forward in terms of desynchronisation or impaired interaction between inner and outer hair cells. Longer critical intervals found predominately in neural cases are explicable in terms of a reduction in neural conduction velocities. Interesting similarities in respect of end organ and nerve fibre lesions are apparent between critical intervals and reported electrocochleographic responses.

Diagnosis, Differential↗
PubMed1997

Early diagnosis of rheumatoid cervical myelopathy.

The purpose of this study was to detect early signs of cervical myelopathy on the basis of clinical finding, radiographs, somatosensory evoked potentials (SSEPs) for n. medianus in 56 patients and transcranial dopler (TCD) for vertebral arteries in 35 patients. Radiological findings, SSEPs, and TCD were registered in neutral and functional scanning positions. Forward AA dislocation was verified in 25 patients with mean value 4.7 mm. The total of 12 (3 in neutral and 9 in functional positions) out of 56 patients had pathological findings of SSEPs for n. medianus. Out of 35 patients 13 (8 in standard imaging position and 5 in rotations) had abnormal values of mean blood flow velocities (MBFV). Movements can provoke neural conduction disturbances through spinal cord and interrupt vertebral arteries blood flow. The early detection of the cervical myelopathy is possible when changing the head position during SSEPs and TCD recordings. On the basis of clinical, x-ray, SSEPs and TCD analyses we suggest that patients with risk of developing myelopathy should be separated.

Adult↗
PubMed1989

Spinocervical tract-dorsal column postsynaptic neurons: a double-projection neuronal system.

Evidence is presented for the existence of a newly discovered double-projection spinal neuronal system, the spinocervical tract-dorsal column postsynaptic neurons. The neurons are characterized by axonal bifurcation in the cervico-thoracic junction, by branched axons traveling in the dorsal column and the dorsolateral funiculus, and by double projection to the dorsal column nuclei and the lateral cervical nucleus. The neurons, with longitudinally distributed dendritic trees and local axon collaterals, primarily originate in laminae III-V of the dorsal horn and receive innocuous and noxious inputs transmitted along the A-beta primary afferents from the periphery. These neurons are thought to be an intersection of the spinocervical tract and the dorsal column postsynaptic neurons, and to function as a nonlemniscal system in mediation and modulation of ascending sensory information, including pain.

Action Potentials↗
PubMed1998

Changing central nervous system control following intercostal nerve transfer.

OBJECT: The goal of this study was to find which central nervous system (CNS) pathways are involved in volitional control over reinnervated biceps or pectoral muscles. METHODS: Intercostal nerves (ICNs) were coapted to the musculocutaneous nerve (MCN) or the medial pectoral nerve (MPN) in 23 patients with root avulsions of the brachial plexus to restore biceps or pectoral muscle function. The facilitatory effects of respiration and voluntary contraction on cortical motor-evoked potentials of biceps or pectoral muscles were used to study CNS control over the reinnervated muscles. The time course of the facilitatory effect of respiration and voluntary contraction differed significantly. In the end stage of nerve regeneration, the facilitatory effect of voluntary contraction was significantly larger than that of respiration, indicating that the CNS control network over the muscle comes to resemble that of the recipient nerve (MCN or MPN) rather than that of the donor nerve (ICN). CONCLUSIONS: The strengthening of previously subthreshold synaptic connections in a CNS network connecting ICN to MCN or MPN neurons may underlie changing excitability.

Adult↗
PubMed1999

Axons from anteroventral cochlear nucleus that terminate in medial superior olive of cat: observations related to delay lines.

The differences in path length of axons from the anteroventral cochlear nuclei (AVCN) to the medial superior olive (MSO) are thought to provide the anatomical substrate for the computation of interaural time differences (ITD). We made small injections of biotinylated dextran into the AVCN that produced intracellular-like filling of axons. This permitted three-dimensional reconstructions of individual axons and measurements of axonal length to individual terminals in MSO. Some axons that innervated the contralateral MSO had collaterals with lengths that were graded in the rostrocaudal direction with shorter collaterals innervating more rostral parts of MSO and longer collaterals innervating more caudal parts of MSO. These could innervate all or part of the length of the MSO. Other axons had restricted terminal fields comparable to the size of a single dendritic tree in the MSO. In the ipsilateral MSO, some axons had a reverse, but less steep, gradient in axonal length with greater axonal length associated with more rostral locations; others had restricted terminal fields. Thus, the computation of ITDs is based on gradients of axonal length in both the contralateral and ipsilateral MSO, and these gradients may account for a large part of the range of ITDs encoded by the MSO. Other factors may be involved in the computation of ITDs to compensate for differences between axons.

Animals↗
PubMedDate not supplied

Emergent oscillations in a realistic network: the role of inhibition and the effect of the spatiotemporal distribution of the input.

We have simulated a network of 10,000 two-compartment cells, spatially distributed on a two-dimensional sheet; 15% of the cells were inhibitory. The input to the network was spatially delimited. Global oscillations frequently were achieved with a simple set of connectivity rules. The inhibitory neurons paced the network, whereas the excitatory neurons amplified the input, permitting oscillations at low-input intensities. Inhibitory neurons were active over a greater area than excitatory ones, forming a ring of inhibition. The oscillation frequency was modulated to some extent by the input intensity, as has been shown experimentally in the striate cortex, but predominantly by the properties of the inhibitory neurons and their connections: the membrane and synaptic time constants and the distribution of delays. In networks that showed oscillations and in those that did not, widely distributed inputs could lead to the specific recruitment of the inhibitory neurons and to near zero activity of the excitatory cells. Hence the spatial distribution of excitatory inputs could provide a means of selectively exciting or inhibiting a target network. Finally, neither the presence of oscillations nor the global spike activity provided any reliable indication of the level of excitatory output from the network.

Action Potentials↗
PubMed1999

Central nervous system impairment in diabetic patients.

The aims of this study were to investigate the function of the central motor control system in interaction with the vestibular and auditory systems (measured by H-reflex changes in response to vestibular and acoustic stimulations) in diabetics without clinical data for CNS impairment, in order to establish whether the disease affects these CNS mechanisms; and to assess this approach in detecting subclinical CNS diabetic pathology. The results show the same mode of change of H-reflex amplitude in response to acoustic and vestibular stimulations in diabetics as in normal subjects. However the degree of facilitation and inhibition was significantly (p < 0.001) higher in diabetics which indicates subclinical CNS dysfunction. Therefore it was concluded that the test is useful in early diagnosis of the diabetic CNS impairment.

Acoustic Stimulation↗
PubMed1999

Two subgroups of lung vagal C-fibers with different vulnerabilities to blockades by perivagal capsaicin and vagal cooling in dogs.

Perivagal capsaicin treatment and vagal cooling are two techniques that have been widely used to study the respiratory reflexes mediated by lung vagal C-fibers because they can block the neural conduction of unmyelinated fibers. We hypothesized that there are two subgroups of lung vagal C-fibers which have different vulnerabilities to blockades by these two techniques. To test this hypothesis, afferent activity arising from lung vagal C-fibers was recorded in 29 anesthetized, paralyzed, and artificially ventilated dogs. Afferent C-fiber activity was recorded before and after various concentrations of perivagal capsaicin treatment or before and during various temperatures of vagal cooling. Of the 89 lung vagal C-fibers studied, 73 fibers were classified as the group of "low resistance" to capsaicin, while the other 16 were classified as the group of "high resistance". The former group differed from the latter due to their afferent activity being blocked at relatively low concentrations of perivagal capsaicin and at relatively low temperatures of vagal cooling. Our results suggest that lung vagal C-fibers can be categorized into two subgroups, based upon their different blocking thresholds for perivagal capsaicin and vagal cooling. Our data may provide information for researchers to further differentiate the respiratory reflexes originating from these two subgroups of lung vagal C-fibers.

Animals↗
PubMedDate not supplied

Hyperexcitability of cervical motor neurons during neck flexion in patients with Hirayama disease.

We recorded the motor evoked potentials (MEPs) from the affected thenar muscles during neck flexion in 4 patients in the early progressive phase of Hirayama disease. The MEP size significantly increased during neck flexion in patients compared with normal controls. In 2 patients who were treated with a neck collar, the intrinsic muscle atrophy gradually recovered together with increased grip power, and the time course of changes in MEP during neck flexion became normal after treatment with a neck collar for 7-16 months. The technique described here would be useful for evaluating the vulnerability of cervical motor neurons and the therapeutic effect of the neck collar in Hirayama disease.

Adolescent↗
PubMed2000

Brainstem auditory evoked potential responses in iron-deficient anemic children.

Iron deficiency is a major health problem in developing countries manifesting not only as overt anemia but also involving the CNS resulting in cognitive and behavioral deficits. Iron is an important nutrient and essential element involved in myelin formation and neurotransmitter synthesis and thus contributes to normal neurological activity. Hypomyelination has been reported in iron deficient states with possible neural conduction defects. The brainstem auditory evoked potential response is used extensively to identify lesions associated with various demyelinating diseases and hence has been used in the present study to observe the effect of iron deficiency on sensory brain function. A trend of increased absolute and interpeak latencies and reduced amplitudes of the waves leading to a definite linear correlation between the severity of anemia and the degree of neurophysiological deficit suggests a subclinical involvement of the auditory pathway in the brainstem of iron deficient children.

Adolescent↗
PubMed2000

Effects of delay on the type and velocity of travelling pulses in neuronal networks with spatially decaying connectivity.

We study a one-dimensional model of integrate-and-fire neurons that are allowed to fire only one spike, and are coupled by excitatory synapses with delay. At small delay values, this model describes a disinhibited cortical slice. At large delay values, the model is a reduction of a model of thalamic networks composed of excitatory and inhibitory neurons, in which the excitatory neurons show the post-inhibitory rebound mechanism. The velocity and stability of propagating continuous pulses are calculated analytically. Two pulses with different velocities exist if the synaptic coupling is larger than a minimal value; the pulse with the lower velocity is always unstable. Above a certain critical value of the constant delay, continuous pulses lose stability via a Hopf bifurcation, and lurching pulses emerge. The parameter regime for which lurching occurs is strongly affected by the synaptic footprint (connectivity) shape. A bistable regime, in which both continuous and lurching pulses can propagate. may occur with square or Gaussian footprint shapes but not with an exponential footprint shape. A perturbation calculation is used in order to calculate the spatial lurching period and the velocity of lurching pulses at large delay values. For strong synaptic coupling, the velocity of the lurching pulse is governed by the tail of the synaptic footprint shape. Moreover, the velocities of continuous and lurching pulses have the same functional dependencies on the strength of the synaptic coupling strength gsyn: they increase logarithmically with gsyn for an exponential footprint shape, they scale like (In gsyn)1/2 for a Gaussian footprint shape, and they are bounded for a square footprint shape or any shape with a finite support. We find analytically how the axonal propagation velocity reduces the velocity of continuous pulses; it does not affect the critical delay. We conclude that the differences in velocity and shape between the front of thalamic spindle waves in vitro and cortical paroxysmal discharges stem from their different effective delays.

Algorithms↗
PubMed2000

Peripheral neuropathy with hypomyelination, chronic intestinal pseudo-obstruction and deafness: a developmental "neural crest syndrome" related to a SOX10 mutation.

We describe the case of a girl with an unusual congenital phenotype, combining peculiar peripheral nerve lesions with hypomyelination, chronic intestinal pseudoobstruction, and deafness. She was found to have a de novo heterozygous frameshift mutation in the gene encoding the SOX10 transcription factor. The likely role of SOX10 in determining the fate of Schwann cells during early embryogenesis may explain the peripheral nervous system developmental disorder observed in this patient.

Amino Acid Sequence↗
PubMed2000

[Invasive techniques in chronic pain control].

A wide range of invasive techniques are available for pain treatment. Treatment must be adapted to the severity of the underlying disease and the intensity of pain. Very few controlled studies concerning these techniques have been performed, and it is therefore difficult to assess their short and long term efficacy. Optimal effectiveness will be obtained if the indication is correct. This non exhaustive revue presents the indications, techniques and results of neural conduction blocks as peripheral blocks, Alcock canal block, zygapophysial joint blocks and also central blocks illustrated by epidural and intrathecal injections and finally sympathetic nervous system blocks as celiac plexus block, stellate ganglion block and intravenous blocks for complex regional pain syndromes. The indications, techniques and results of thermal neurolyse (radiofrequency, thermocoagulation), transcutaneous electrical nervous stimulation (TENS) and implant central stimulation are also presented. A multidisciplinary approach is used to evaluate the risk/benefit ratio of these invasive techniques for each patient.

Catheter Ablation↗
PubMed1975

[Relation of excitability cycles of cortical reactions to the qualities of afferent stimuli].

The excitability cycles of neurons of the rabbit visual cortex in response to the optic nerve shock were compared with those in response to small light flashes. The pairs of stimuli consisted either of conditioned shock and testing light flash or of conditioned light flash and testing shock. The inhibitory phase of the response to the nerve shock was unable to depress a powerful reaction to adequate light stimulation. However, the profound inhibition of response to the optic nerve shock was obtained at the end of the response to the preceding light stimulation.

Animals↗