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At least 775 records · Page 43Linked to original sources
PubMed1981

Hypothetical role of long-loop reflex pathways.

It is nowadays well known that there are reflex loops starting in the spinal cord, relaying in various supraspinal structures and descending back to the cord. These long-loops regulate motor responses and work in cooperation with segmental mono- and polysynaptic reflexes. The role of certain well-documented long-loop reflexes is reviewed. The existence of additional long-loop reflexes is hypothesized and preliminary results supporting this view are presented. In discussing the mode of action of spinal cord stimulation, the various ascending and descending pathways involved in long-loop regulation of motricity are to be taken into account.

Electromyography↗
PubMed1997

Autosomal dominant late-onset leukoencephalopathy. Clinical report of a new Italian family.

The adult-onset autosomal dominant leukoencephalopathies are rare disorders. Very few pedigrees have been extensively described and no biochemical or genetic marker has been identified so far. The present study was aimed to characterized an autosomal dominant late-onset leukoencephalopathy occurring in a large Italian kindred. A genealogic method was adopted to ascertain 51 affected individuals among nearly 400 subjects in 8 generations. Medical records were obtained from 11 deceased patients. We personally examined 8 symptomatic and 9 asymptomatic at-risk individuals who underwent a standardized clinical, biochemical, radiological and neurophysiological study. The mean age at onset of the disease was 46.6 years and the mean duration of disease 9.9 years. The clinical picture was characterized by progressive pyramidal and pseudobulbar signs, urinary incontinence and, sometimes, action tremor of the head and/or hands. No relevant mental deterioration was noted. In all the symptomatic and in 1 asymptomatic subject, brain MRI showed marked symmetrical hyperintensity on T2-weighted images of the white matter of the cerebral hemispheres, with constant sparing of the cerebellum. In these subjects, evoked potentials revealed altered central neural conduction. Nerve conduction velocity, biochemical (including lysosomal enzymatic activities) and biopsy (peripheral tissue specimens) examination were normal. The clinical and neuroradiological data are consistent with an autosomal dominant adult-onset leukoencephalopathy whose features are unusual when compared to those previously reported.

Adult↗
PubMed1992

NG-methyl-L-arginine, an inhibitor of L-arginine-derived nitric oxide synthesis, stimulates renal sympathetic nerve activity in vivo. A role for nitric oxide in the central regulation of sympathetic tone?

Continuous production of endothelium-derived nitric oxide (NO) in peripheral vessels has been shown to modulate vascular resistance and blood pressure. NO is also formed in the brain upon activation of glutamate receptors, which are thought to mediate central autonomic reflexes. In the present study we assessed whether NO plays a role in central autonomic regulation. For this, we have investigated the effects of NG-methyl-L-arginine (NMA), a selective inhibitor of NO synthesis from L-arginine, on sympathetic renal nerve activity (RNA), blood pressure, and heart rate in the anesthetized rat. NMA elicited a dose-dependent sustained increase in blood pressure (approximately 20 and 30 mm Hg, 5 minutes after 10 and 50 mumol/kg i.v., respectively). Heart rate and RNA decreased transiently (15 beats per minute and 40%, respectively); RNA subsequently increased (100%) while blood pressure remained elevated. Baroreceptor deafferentation markedly altered these responses to NMA; the transient decreases in heart rate and RNA were abolished, whereas the increases in RNA and blood pressure were significantly potentiated. After spinal C-1-C-2 transection, there was no increase in RNA, and blood pressure increased to a smaller extent. L-Arginine blocked the NMA-induced increases in blood pressure and RNA. Thus, in addition to modulating vascular resistance by a peripheral action, NO may also play a role in the central regulation of sympathetic tone.

Animals↗
PubMed2001

Dual information representation with stable firing rates and chaotic spatiotemporal spike patterns in a neural network model.

Although various means of information representation in the cortex have been considered, the fundamental mechanism for such representation is not well understood. The relation between neural network dynamics and properties of information representation needs to be examined. We examined spatial pattern properties of mean firing rates and spatiotemporal spikes in an interconnected spiking neural network model. We found that whereas the spatiotemporal spike patterns are chaotic and unstable, the spatial patterns of mean firing rates (SPMFR) are steady and stable, reflecting the internal structure of synaptic weights. Interestingly, the chaotic instability contributes to fast stabilization of the SPMFR. Findings suggest that there are two types of network dynamics behind neuronal spiking: internally-driven dynamics and externally driven dynamics. When the internally driven dynamics dominate, spikes are relatively more chaotic and independent of external inputs; the SPMFR are steady and stable. When the externally driven dynamics dominate, the spiking patterns are relatively more dependent on the spatiotemporal structure of external inputs. These emergent properties of information representation imply that the brain may adopt a dual coding system. Recent experimental data suggest that internally driven and externally driven dynamics coexist and work together in the cortex.

Action Potentials↗
PubMed1995

Synchrony in excitatory neural networks.

Synchronization properties of fully connected networks of identical oscillatory neurons are studied, assuming purely excitatory interactions. We analyze their dependence on the time course of the synaptic interaction and on the response of the neurons to small depolarizations. Two types of responses are distinguished. In the first type, neurons always respond to small depolarization by advancing the next spike. In the second type, an excitatory postsynaptic potential (EPSP) received after the refractory period delays the firing of the next spike, while an EPSP received at a later time advances the firing. For these two types of responses we derive general conditions under which excitation destabilizes in-phase synchrony. We show that excitation is generally desynchronizing for neurons with a response of type I but can be synchronizing for responses of type II when the synaptic interactions are fast. These results are illustrated on three models of neurons: the Lapicque integrate-and-fire model, the model of Connor et al., and the Hodgkin-Huxley model. The latter exhibits a type II response, at variance with the first two models, that have type I responses. We then examine the consequences of these results for large networks, focusing on the states of partial coherence that emerge. Finally, we study the Lapicque model and the model of Connor et al. at large coupling and show that excitation can be desynchronizing even beyond the weak coupling regime.

Computer Simulation↗
PubMed1994

Bradykinin-induced contraction of human peripheral airways mediated by both bradykinin beta 2 and thromboxane prostanoid receptors.

Bradykinin (BK) induces bronchoconstriction in asthmatic but not in normal individuals. Studies in vivo in the human suggest that BK causes cholinergic nerve activation, release of prostanoids, and local axon reflexes with release of tachykinins in the airways. To determine the mechanisms of BK-induced airway narrowing, we investigated the effects of epithelium removal, inhibition of the enzymes neutral endopeptidase (NEP) and cyclooxygenase, and blockade of neural conductance with tetrodotoxin (TTX) on BK-induced responses of human isolated peripheral airways. Responses to BK were recorded from airways with spontaneous intrinsic tone and from airways precontracted with methacholine. Furthermore, we measured the BK-induced release of the prostanoids PGE2, PGI2, and TXA2 from airways with and without epithelium in the absence and presence of indomethacin by radioimmunoassay. Finally, we examined the effect of the bradykinin beta 2 receptor antagonist Hoe 140 and the thromboxane prostanoid (TP) receptor blocking drug GR32191 on BK-induced responses. BK contracted intact and epithelium-denuded airways with spontaneous intrinsic tone, whereas precontracted airways either relaxed or contracted to BK. Removal of the epithelium increased the sensitivity to BK sevenfold without changing the direction of the response. The NEP inhibitor phosphoramidon tended to increase the sensitivity to BK (NS) and did not change the direction of the response. Both contractile and relaxation responses to BK and the release of the prostanoids PGE2, PGI2, and TXA2 by the airway tissues were largely inhibited by indomethacin, whereas TTX had no effect. PGE2, PGI2, and TXA2 were released by both intact and epithelium-denuded airways.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed2002

Auditory brain stem and midbrain development after cochlear implantation in children.

Input to the central auditory system through a cochlear implant promotes psychophysical improvement of auditory skills. However, the developmental changes along the pathways have never been characterized in children with hearing loss who use implants. We aimed to measure auditory development in such children by using the electrically evoked auditory brain stem response (EABR). We made repeated measures of the EABR in 41 nonsedated children with implants before chronic stimulation and after 2, 6, and 12 months of consistent implant use. The results show that EABRs were present in all of the children even before chronic auditory stimulation, and that EABR wave latencies decreased from the time of initial activation throughout the first year of cochlear implant use. These findings reflect auditory development to the level of the midbrain as a result of the cochlear implant. The decreasing latencies likely reflect decreased neural conduction times at this level, in part because of increased synaptic efficacy.

Adolescent↗
PubMedDate not supplied

Course of the peripheral gustatory nerves.

The multiple variations of the course of the gustatory nerves still considered possible are discussed. Recent investigations lead to the conclusion that there is only one path for the gustatory fibers for each gustatory area: 1) from the anterior part of the tongue via the tympanic cord and facial nerve to the medulla oblongata; 2) for the posterior part of the tongue in the IX cranial nerve; and 3) from the soft palate via the greater superficial petrosal nerve to the facial nerve. The trigeminal nerve carries no gustatory fibers to the brain.

Animals↗
PubMedDate not supplied

Acoustic reflex latency test in the evaluation of nontumor patients with abnormal brainstem latencies.

The acoustic reflex latency test (ARLT), an indirect measure of neural conduction time utilizing the electroimpedance method, was used to evaluate 43 highly suspect, nontumor patients who demonstrated abnormal latency results on brainstem electric response audiometry (BERA), false-positive for tumor. Normative values and criteria for tumor-positive ARLT results were established on a control group using a second generation test unit, comprised of dual impedance bridges and a digital signal averager, designed especially to perform the ARLT. When cut-off criteria for both absolute reflex latency and interaural latency difference (ILD) values were applied to this BERA false positive population, the ARLT correctly identified 93% of patients as having end-organ lesions. Differences in ARLT and BERA test results are attributed to differences in 1) method of measurement, 2) characteristics of the eliciting signal, and 3) generation of the response. These factors are discussed as sources of variability. Both ARLT and BERA are recommended as tandem procedures when screening for acoustic or angle tumors.

Audiometry↗
PubMedDate not supplied

Electrocochleography and auditory brainstem electric responses in patients with pontine angle tumors.

In 45 patients with surgically proven pontine angle tumors, compound action potential (AP) and summating potential (SP) were recorded with transtympanic electrocochleography (ECochG) together with brainstem electric responses (BSER). The aims were to quantify the mechanism by which tumors cause hearing loss and evaluate the diagnostic potentials of ECochG and BSER for detecting eighth nerve and brainstem tumors. Except for AP latency and narrow band AP waveform, response parameters recorded by ECochG are uncorrelated. Four uncorrelated parameters were abnormal in only 10% of the cases, three in 25%, two in 40%, and one in 90%. The BSER criterion was the latency delay between waves I and IV and resulted in about 90% detection, improving to 95% when used in combination with ther interaural wave V delay criterion. ECochG results provide evidence that, for hearing losses up to 60 dB HL, the origin is cochlear, resembling that caused by Meniere's disease. Evidence is presented that the increase in I-V delay in the BSERs is caused by differential action of the tumor upon low and high frequency fibers in the auditory nerve and that desynchronization of the firings of the nerve fibers is of more importance than an increase in neural conduction time. ECochG as the sole test for detection of pontine angle tumors appears to be of limited value. Brainstem response on its own has great merits; however, it should be emphasized that no wave I was detected in about 30% of the cases. The 95% detection score obtained with BSER depends on specifying the latency of wave I. For these cases, we substituted the latency of the AP recorded by ECochG.

Acoustic Stimulation↗
PubMedDate not supplied

Implications of Ewald's second law for evaluation of vestibular function.

The significance of Ewald's second law in the evaluation of the vestibulo-ocular reflex (VOR) was investigated using the transfer characteristics of the vestibular and VOR systems in normal rabbits and rabbits in which one horizontal semicircular canal had been blocked. The transfer characteristics of the vestibular system were derived from the experimental results reported by Goldberg and Fernández in 1971. A comparison was made of the properties of the bilateral and monolateral VOR systems with the predictions of a piecewise linear model of the vestibular system. The data received quantitatively collaborate the prediction of Ewald's second law as it applies to the VOR responses.

Animals↗
PubMed2001

Neural network classification of nerve activity recorded in a mixed nerve.

Whole-nerve cuff electrodes can be used to record electrical nerve activity in peripheral nerves and are suitable for chronic implantation in animals or humans. If the whole nerve innervates multiple target organs or muscles then the recorded activity will be the superposition of the activity of different nerve fibers innervating these organs. In certain cases it is desirable to monitor mixed nerve activity and to determine the origin (modality) of the recorded activity. A method using the autocorrelation function of recorded nerve activity and an artificial neural network was developed to classify the modality of nerve signals. The method works in cases where different end organs are innervated by nerve fibers having different diameter distributions. The electrical activity in the cat S1 sacral spinal root was recorded using a cuff electrode during the activation of cutaneous, bladder, and rectal mechanoreceptors. Using the classification method, 87.5% of nerve signals were correctly classified. This result demonstrates the effectiveness of the neural network classification method to determine the modality of the nerve activity arising from activation of different receptors.

Action Potentials↗
PubMed2005

Effects of conditioning peripheral repetitive magnetic stimulation in patients with complex regional pain syndrome.

OBJECTIVES: We tested whether repetitive magnetic stimulation (rMS) induces an afferent input to the spinocerebral tract in patients with complex regional pain syndrome (CRPS). METHODS: Cortical and spinal motor evoked potentials (cMEP and sMEP), as well as the contra- and ipsilateral silent period (cCSP and iCSP), were recorded in patients with CRPS type I before and after conditioning rMS, applied at cervical nerve roots innervating affected muscles. Patients were compared with a group of healthy subjects. RESULTS: In the group of patients we found that cMEP amplitudes were always significantly smaller for both hemispheres. In the group of healthy subjects we found a significant prolongation of the cCSP and iCSP after rMS. This was absent in patients. SMEP were always unchanged in both groups. DISCUSSION: This led us to the explanation that the afferent input to the motor cortical system in CRPS patients is less effective than in healthy subjects.

Adult↗