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At least 1,621 records · Page 90Linked to original sources
PubMed1979

Binding of radioactively labeled saxitoxin to the squid giant axon.

The binding of saxitoxin, a specific inhibitor of the sodium conductance in excitable membranes, has been measured in giant axons from the squid, Loligo pealei. Binding was studied by labeling saxitoxin with tritium, using a solvent-exchange technique, and measuring the toxin uptake by liquid scintillation counting. Total toxin binding is the sum of a saturable, hyperbolic binding component, with a dissociation constant at 2--4 degrees C of 4.3 +/- 1.7 nM (mean SE), and a linear, nonsaturable component. The density of saturable binding sites is 166 +/- 20.4 micrometers-2. From this density and published values of the maximum sodium conductance, the conductance per toxin site is estimated to be about 7 pS, assuming sequential activation and inactivation processes (F. Bezanilla & C.M. Armstrong, 1977, J. Gen. Physiol. 70:549). This single site conductance value of 7 pS is in close aggreement with estimates of the conductance of one open sodium channel from measurements of gating currents and of noise on squid giant axons and is consistent with the hypothesis that one saxitoxin molecule binds to one sodium channel.

Animals↗
PubMed1985

Two groups of corticofugal neurons identified with the pontine stimulation in the cat parietal association cortex: an intracellular HRP study.

A classification of the parietal corticofugal neurons was performed in cats under Nembutal anesthesia. Eighty-eight neurons were identified with antidromic activation by the pontine stimulation. Thirteen neurons were furthermore identified with intracellular HRP staining. In these neurons, we found the close correlation between morphological features and conduction velocities. The faster conducting group of the neurons had relatively large somata, sparsely spinous apical dendrites, tap root basal dendrites and wide apical dendritic fields. The slower group had small somata and numerous dendritic spines.

Animals↗
PubMed1980

Behavioral methods for inferring anatomical linkage between rewarding brain stimulation sites.

Rats lever pressed for concurrent electrical stimulation of the lateral hypothalamus and ventral tegmentum. The pulse-pair stimulation technique was used, with the first pulse of each pair applied to one electrode and the second to the other electrode; the intrapair interval was varied. The effectiveness of stimulation, measured behaviorally, increased abruptly (within .4 msec) as the intrapair interval was increased in the range from 1.0 to 2.0 msec. These results, which do not resemble single-electrode refractory period results, are interpreted as evidence of collision in the directly stimulated, reward-related neurons linking the two sites. We conclude that self-stimulation of the medial forebrain bundle involves the direct activation of long-axon, longitudinal pathways. Estimates of the conduction velocity in the fibers subserving the collision-like effects are consistent with the properties of small myelinated axons but not central monoaminergic fibers.

Animals↗
PubMed1964

SOME ACTIONS OF CENTRALLY ACTIVE AND OTHER DRUGS ON THE TRANSMISSION OF SINGLE NERVE IMPULSES THROUGH THE ISOLATED SUPERIOR CERVICAL GANGLION PREPARATION OF THE RABBIT.

The effect of some centrally-active and other drugs on the transmission of single nerve impulses through the isolated superior cervical ganglion preparation of the rabbit has been studied by recording both preganglionic and postganglionic action potentials. Block of conduction in the axon could be distinguished from block of the synaptic mechanism. The drugs did not appear to exert any one characteristic form of blocking action. A continuous spectrum of drug action linked an agent such as meprobamate which acted predominantly on the synapse to benactyzine which acted mainly by blocking axonal conduction. The drugs have been divided into three groups. Group I: hexamethonium, meprobamate, paraldehyde, amylobarbitone, methylpentynol and azacyclonal; these acted relatively selectively at the ganglion. Group II: N714C (the cis-isomer of chlorprothixene), prochlorperazine, methylpentynol carbamate, pipradrol, promethazine, perphenazine and procaine; the action of these drugs on the ganglion could be accounted for entirely in terms of their axonal depressant action. Group III: chlorprothixene, promazine, N720 (dihydrochlorprothixene), chlorpromazine, hydroxyzine and benactyzine; these drugs also blocked axonal conduction but in addition they appeared to exert a "facilitating" action at the ganglionic synapse. The actions of adrenaline, adrenochrome, iproniazid, ergotoxine, mescaline and lysergic acid diethylamide on transmission were also studied. The implications of the modifications of ganglionic transmission produced by these drugs is discussed.

Action Potentials↗
PubMedDate not supplied

Neurophysiologic mechanisms of internal inhibition.

The experimental results obtained in the authors' laboratory as a result of multiple recording of slow biopotentials, the recording of neuronal activity and of mathematical modeling, are reviewed. The authors conclude that the elaboration of internal inhibition is followed, and determined to a great extent, by the restriction in conduction of excitations due to the increase of inhibitory hyperpolarization and discordance in the periodicity of slow potentials, reflecting oscillations in excitability of neuronal populations in the cortex and other brain structures.

Animals↗
PubMed1977

Indirect estimation of spinal cord conduction velocity in man.

A method is described for deriving an indirect estimate of the velocity of impulse propagation in the spinal cord of intact man. The estimate is computed from measurements of motor and sensory nerve conduction velocity in the limbs, F-wave latencies, and the latencies of somatosensory evoked potentials. The mean estimated spinal cord conduction velocicy in normal subjects was found to be 55.1 m/sec, with a standard deviation of 9.9. This method appears to have potential application in the electrophysiological evaluation of patients with myelopathic disorders.

Adolescent↗
PubMed1981

[Responses of pericruciate cortex neurons to stimulation of the hypothalamus and reticular formation].

Neurons of the pericruciate cortex revealed a high degree of reactivity to stimulation of posterior hypothalamus (HP) and mesencephalic reticular formation (RF)--94 and 88% resp., and a marked convergence of upward discharges from HP and RF (73.5%) in anesthetized and immobilized cats. Latency and unit responses (2.4--4.0 msec) suggested a monosynaptic input from the two subcortical structures. Out of the corticofugal neurons activated antidromically, 27% were of the "divergent" type with collaterals in both the HP and RF and, therefore, reacting antidromically to stimulation of these structures. A predominance of cortical antidromic responses to stimulation of HP suggested a greater corticofugal influence on hypothalamic rather than on reticular neurons (84% and 42.3% resp.). Mean latency of antidromic reaction of cortico--hypothalamic neurons was 2.4 +/- 0.2 msec (0.8--6.0 msec), of cortico--reticular neurons--3.2 +/- 0.3 msec (1.0--6.0 msec). The conduction velocity (12.5 m/sec) was the same for both the HP and RF. Characteristics of neuronal organization of hypothalamo--cortical and reticulo--cortical systems of integration are discussed.

Animals↗
PubMed1979

Spatial properties of X and Y cells in the lateral geniculate nucleus of the cat and conduction veolcities of their inputs.

Visual neurons in the lateral geniculate nucleus (LGN) of the cat may be separated into distinct X and Y classes based on a test of the linearity of spatial summation. Y cells produce nonlinear responses especially when the visual stimulus is a fine spatial grating. X cells exhibit mainly linear summation properties. X cells respond mainly at the fundamental modulation frequency of a contrast reversal grating while Y cells respond at the fundamental and at the second harmonic of the modulation frequency. The spatial resolution of X cells' fundamental responses and Y cells' second harmonic responses is about the same, and both are two to eight times higher than the spatial resolution of the Y cells' fundamental response. The conduction velocity of the Y optic tract afferents is greater than that of the velocity of the X afferents. However, the LGN latencies of the responses of the two classes of cells to optic chiasm stimulation overlap considerably.

Animals↗
PubMed1985

Nerve impulse propagation along central and peripheral fast conducting motor and sensory pathways in man.

Forty-four limbs from 11 healthy volunteers were examined. Spinal and scalp somatosensory evoked potentials to median and peroneal nerve stimulation were recorded and the peripheral (wrist-Erb, Erb-cervical, knee-thoracic spine) and central (cervical-scalp, thoracic-cervical spine, spine-scalp) conduction times and velocities (CTs, CVs) were calculated. Sensory and mixed trunks of median and peroneal nerves were also stimulated and their motor and sensory CVs in mid-distal districts were measured. Motor responses to scalp (motor areas for hand and leg muscles) and spinal cord stimulation (cervical and lower thoracic levels) were carried out through skin rectangular plate electrodes delivering high voltage (880-1870 V) brief anodal pulses. The intracranial (scalp-cervical) and intraspinal (cervical-thoracic spine) CTs and CVs of motor pathways were measured. The elbow-cervical and knee-thoracic spines CTs of motor fibres were also calculated through the F wave method, which gave values almost superimposable on those obtained through direct spine stimulation. Nerve propagation was faster in sensory than in motor fibres in peripheral nerve mid-distal districts, while this difference was reduced or reversed in more proximal segments, including nerve roots. The scalp-cervical CT was slightly shorter in motor than in sensory fibres after subtraction of synaptic delays (6.12 vs. 6.18 msec). The scalp-lower thoracic spine, as well as the intraspinal, CVs were 7-12% faster in sensory than in motor pathways (45.3 vs. 38.7 m/sec for the former; 62.65 vs. 55.4 m/sec for the latter). The reported method allows the evaluation of fast conducting motor and sensory pathways along 'central' and 'peripheral' nerve structures of the entire body. Preliminary findings on scalp stimulation of brain motor areas with low voltage pulses are also included.

Action Potentials↗
PubMed2002

Activation of kinetically distinct synaptic conductances on inhibitory interneurons by electrotonically overlapping afferents.

Mossy fiber (MF) and CA3 collateral (CL) axons activate common interneurons via synapses comprised of different AMPA receptors to provide feedforward and feedback inhibitory control of the CA3 hippocampal network. Because synapses potentially occur over variable electrotonic distances that distort somatically recorded synaptic currents, it is not known whether the underlying afferent-specific synaptic conductances are associated with different time courses. Using a somatic voltage jump technique to alter the driving force at the site of the synapse, we demonstrate that MF and CL synapses overlap in electrotonic location yet differ in conductance time course. Thus, afferent-specific conductance time courses allow single interneurons to differentially integrate feedforward and feedback information without the need to segregate distinct AMPA receptor subunits to different electrotonic domains.

Afferent Pathways↗
PubMed1977

[Experimental study of neural and neuro-muscular conduction during simulated diving in dogs and rabbits: anatomo-pathologic correlations].

Five dogs and twelve rabbits were submitted to simulated diving at 6 ATA (compressed air) and 13-15 ATA (normoxic oxygen + nitrogen). Progressive decompressions were carried on for the first, rapid for the lasts. Motor nerve conduction velocity and nerve-muscle delays were measured. No variations could be observed neither for nerve conduction velocity nor for muscular and nerve action potentials. Nevertheless optic and electronic microscopy observations shew some nerve, neuronal and a few muscular alterations occuring during rapid decompression.

Action Potentials↗
PubMed1988

Absence of tonic supraspinal control of substance P release in the substantia gelatinosa of the anaesthetized cat.

Antibody microprobes were used to measure immunoreactive substance P (irSP) release in the substantia gelatinosa of the lower lumbar spinal cord of barbiturate-anaesthetized cats. Release of irSP was produced by noxious peripheral stimuli. Such release was not altered by blocking spinal conduction at the first lumbar segment by cooling or transecting the spinal cord. The results suggest that the release of irSP from the central terminals of nociceptors is not subject to tonic supraspinal inhibition.

Animals↗
PubMedDate not supplied

Comparison of the somatosensory evoked potential and the direct cortical response following severe incomplete global ischemia: selective vulnerability of the white matter conduction pathways.

Eight cats were subjected to graded hemorrhagic hypotension following bilateral carotid ligation to produce incomplete global cerebral ischemia. Three additional cats served as controls. The somatosensory evoked potential (SEP) and direct cortical response (DCR) were monitored in all animals and in each case, the cortical component of the SEP was abolished during progressive ischemia while the morphology of the DCR was well-preserved but with reduced amplitude. Determinations of adenosine triphosphate (ATP), phosphocreatine (PCr), and lactate levels in cerebral cortex and white matter were made in five experimental cats and the three controls. At the time of failure of the cortical SEP, PCr was dramatically reduced and lactate moderately elevated in the white matter while ATP remained unchanged. Cortical lactate was only mildly elevated and PCr and ATP were unchanged accounting for preservation of the DCR. In this model of global ischemia, abolition of the cortical SEP is due to a block of stimulus conduction in white matter projection pathways. A hypothesis to explain the observed metabolic changes is presented and correlation is made to clinical situations.

Adenosine Triphosphate↗
PubMed1998

"Threshold-level" multipulse transcranial electrical stimulation of motor cortex for intraoperative monitoring of spinal motor tracts: description of method and comparison to somatosensory evoked potential monitoring.

UNLABELLED: Numerous methods have been pursued to evaluate function in central motor pathways during surgery in the anesthetized patient. At this time, no standard has emerged, possibly because each of the methods described to date requires some degree of compromise and/or lacks sensitivity. OBJECT: The goal of this study was to develop and evaluate a protocol for intraoperative monitoring of spinal motor conduction that: 1) is safe; 2) is sensitive and specific to motor pathways; 3) provides immediate feedback; 4) is compatible with anesthesia requirements; 5) allows monitoring of spontaneous and/or nerve root stimulus-evoked electromyography; 6) requires little or no involvement of the surgical team; and 7) requires limited equipment beyond that routinely used for somatosensory evoked potential (SSEP) monitoring. Using a multipulse electrical stimulator designed for transcranial applications, the authors have developed a protocol that they term "threshold-level" multipulse transcranial electrical stimulation (TES). METHODS: Patients considered at high risk for postoperative deficit were studied. After anesthesia had been induced and the patient positioned, but prior to incision, "baseline" measures of SSEPs were obtained as well as the minimum (that is, threshold-level) TES voltage needed to evoke a motor response from each of the muscles being monitored. A brief, high-frequency pulse train (three pulses; 2-msec interpulse interval) was used for TES in all cases. Data (latency and amplitude for SSEP; threshold voltage for TES) were collected at different times throughout the surgical procedure. Postoperative neurological status, as judged by evaluation of sensory and motor status, was compared with intraoperative SSEP and TES findings for determination of the sensitivity and specificity of each electrophysiological monitoring technique. Of the 34 patients enrolled, 32 demonstrated TES-evoked responses in muscles innervated at levels caudal to the lesion when examined after anesthesia induction and positioning but prior to incision (that is, baseline). In contrast, baseline SSEPs could be resolved in only 25 of the 34 patients. During surgery, significant changes in SSEP waveforms were noted in 12 of these 25 patients, and 10 patients demonstrated changes in TES thresholds. Fifteen patients experienced varying degrees and durations of postoperative neurological deficit. Intraoperative changes in TES thresholds accurately predicted each instance of postoperative motor weakness without error, but failed to predict four instances of postoperative sensory deficit. Intraoperative SSEP monitoring was not 100% accurate in predicting postoperative sensory status and failed to predict five instances of postoperative motor deficit. As a result of intraoperative TES findings, the surgical plan was altered or otherwise influenced in six patients (roughly 15% of the sample population), possibly limiting the extent of postoperative motor deficit experienced by these patients. CONCLUSIONS: This novel method for intraoperative monitoring of spinal motor conduction appears to meet all of the goals outlined above. Although the risk of postoperative motor deficit is relatively low for the majority of spine surgeries (for example, a simple disc), high-risk procedures, such as tumor resection, correction of vascular abnormalities, and correction of major deformities, should benefit from the virtually immediate and accurate knowledge of spinal motor conduction provided by this new monitoring approach.

Adolescent↗
PubMed1990

[Evoked motor potentials in the diagnosis of multiple sclerosis].

The authors examined evoked motor potentials (MEP) of the upper extremities in a group of 43 patients with multiple sclerosis using transcranial cortical and spinal stimulation. As abnormal they rated a prolongation of the motor conduction time by more than 3 sigma above the mean value recorded in the control group or when the response could not be evoked. The central motor conduction time between the cortex and cervical spine was abnormal in 76.7% of patients. The authors did not find a correlation between the severity of the paresis and the degree of electrophysiological abnormality. In frust and mild pareses the sensitivity was 80%. The frequency of abnormalities correlated with the degree of the diagnostic certainty. In patients with a probable diagnosis (according to Poser) abnormalities were present in 41.6%, when the diagnosis was certain, in 90.3%. In prolongation of the time of central motor conduction among all abnormalities 65.1% were due to prolonged motor conduction and in 27.9% the response could not be evoked. MEP examination is a sensitive technique for the detection of clinical and subclinical lesions and as to its sensitivity it is better than visual EP.

Adult↗
PubMedDate not supplied

Optimizing conductance parameters of cortical neural models via electrotonic partitions.

Development of automated methods for fitting computational models to observed biological data is an important challenge of neural modeling. Previous work has focused on generalized search techniques combined with distance measures tuned to specific neural morphologies. We propose general analysis techniques to guide construction of distance measures across a broader range of cell types. Specifically, we evaluate the use of multiple external stimuli to evoke characteristic behaviors of underlying active channel densities on a simple three-compartment model. We also examine the use of frequency analysis to smooth search space distortions induced by temporal shifts in recorded voltage traces. We propose a novel method of parameter optimization that is characterized by linear regression over the conductance densities using channel permissiveness as a basis of ionic current. We derive this method and demonstrate, given known anatomy and kinetics, it will solve all conductance densities in an N compartment model given N spatially distinct membrane potential traces with minimal error. We compare the regression method with the covariance matrix adaptation evolutionary strategy (CMA-ES) over a two-compartment cortical neuron and empirically show that regression over electrotonic partitions solves the cortical model near-optimally. We also show that electronic partitioning significantly improves search performance of CMA-ES on the cortical model.

Algorithms↗