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At least 91 records · Page 5Linked to original sources
PubMed1988

Electrophysiologic evaluation of the facial nerve in Bell's palsy. A review.

Facial nerve paralysis is the most common mononeuropathy and idiopathic facial paralysis (Bell's palsy) the most common seventh nerve disease electromyographers may be asked to evaluate. The electrophysiologic method of choice to assess the facial nerve is side-to-side evoked amplitude comparison with the affected side expressed as a percentage of the nonaffected side. This examination should be performed on days 3, 5, 7, 9, 11 and 13 after onset of paralysis. If the percentage of surviving axons falls below 10% within the first 14 days, an incomplete recovery is suggested. Electromyography may assist in prognosticating a functional return, determining neural conduction across the site of injury and following reinervation in the recovery period. The persistence or early return of an absent R1 component of the blink reflex may qualitatively suggest a satisfactory functional outcome in facial paralysis. Supramaximally exciting the facial nerve at the stylomastoid foramen and comparing the clinical response on the affected and nonaffected side, maximum stimulation test, can also predict eventual seventh nerve return. Observing a minimal twitch, utilizing the nerve excitability test or measuring the facial nerve latency have yielded poor correlations with functional return and are of limited usefulness in the prognostication of acute facial palsies. Trigeminal somatosensory evoked potentials can be employed to evaluate the status of the trigeminal nerve as approximately 50% of patients with Bell's palsy also have lesions involving the fifth nerve. Side-to-side amplitude comparison and electromyography are the two most valuable electrophysiologic methods of assessing facial nerve functioning.

Action Potentials↗
PubMed1987

The effects of carbamazepine and sodium valproate on SEPs and BAEPs.

SEPs and BAEPs were studied in 36 previously untreated epileptics receiving either carbamazepine (CBZ) or sodium valproate (VPA) monotherapy. CBZ prolonged central conduction times in SEPs and BAEPs. SEP latency prolongation correlated with serum CBZ levels. VPA had minimal effects on evoked potentials. The present study gives evidence of similar effects of carbamazepine and phenytoin on central neural conduction.

Adult↗
PubMed1979

Visual resolution in a patient exhibiting a visual fatigue or saturation-like effect: probable multiple sclerosis.

A rapid visual resolution test conducted on available equipment reveals the presence of rapid falloff in acuity in a case of probable multiple sclerosis. Intense large field illumination was used, and grating acuity was tested using laser red light. The effect is so large that minor anomalies (not subjectively appreciated) or the residuum of earlier minor attacks of retrobulbar optic neuritis can be readily detected. A related "visual fatigue or saturation-like syndrome" was described earlier. In bright environments these patients' vision fades. Briefly closing the eyes restores visual sensitivity. Providing filters or lowering the light level tends to maintain vision. This test must be studied intensively. It offers a noninvasive simple means of showing underlying anomalies in neural conduction of the visual signal. Such anomalies can be prognostic and previously have been revealed only with sophisticated electrophysiological techniques.

Adult↗
PubMed1988

Beta-adrenoceptors on duodenal mucosal cells mediate venous serotonin release.

We have previously documented predominant intraluminal release of serotonin (5-HT) following activation of muscarinic receptors on enterochromaffin cells. Gronstad et al. reported that portal venous release of 5-HT in response to vagal stimulation was mediated by beta-adrenergic receptors. The purpose of this study was to determine whether 5-HT release induced by the beta-adrenergic agonist, isoproterenol, is mediated by enteric nerves or is a direct action at the enterochromaffin cell level. We mounted rabbit duodenal mucosal sheets stripped of muscularis in modified Ussing chambers and measured release of 5-HT in response to 10(-5) M isoproterenol, in the presence and absence of the neural conduction blocker tetrotoxin, 10(-6) M. Serotonin was measured in the buffer bathing the mucosal and submucosal surfaces by HPLC. In the presence of isoproterenol, total (mucosal and submucosal) 5-HT release (21.0 +/- 4.9 ng/cm2/45 min) was significantly (P less than 0.05) greater than that in untreated controls (7.8 +/- 2.7 ng/cm2/45 min); release was predominantly toward the submucosal surface. In the presence of tetrodotoxin alone, net 5-HT release was significantly (P less than 0.05) increased to 12.8 +/- 2.8 ng/cm2/45 min. In tetrodotoxin-treated mucosa, isoproterenol increased 5-HT release to 28.6 +/- 5.3 ng/cm2/45 min which was significantly greater (P less than 0.05) than that with tetrodotoxin alone. Since 5-HT release was increased even in the presence of neural blockade, these results suggest that activation of beta-adrenergic receptors on or near enterochromaffin cells induces release of 5-HT predominantly toward the submucosal surface.

Animals↗
PubMed1985

Spinal mechanisms of the analgesic action of electroconvulsive shock.

The present study investigated the spinal systems involved in the analgesic action of electroconvulsive shock (ECS). To identify such systems complete spinal transections and discrete lesions within the dorsal half of the spinal cord were performed. Complete spinal transection eliminated ECS analgesia totally, demonstrating that the observed analgesic effect is attributable to neural conduction. Lesions within the region of the dorsolateral funiculus (DLF) caused a pronounced, but incomplete, attenuation of ECS analgesia. Larger lesions of the dorsal aspects of the spinal cord including both the DLF and the dorsal column area did not result in further attenuation of analgesia. Thus, it appears that within the dorsal cord the area of the DLF contains the fibers mediating the antinociceptive action of ECS. Additional experiments were conducted to determine the neuromediators involved in ECS analgesia. Of a wide range of antagonists injected intraperitoneally (methysergide, phentolamine, haloperidol, diphenhydramine, naloxone, picrotoxin, theophylline and scopolamine), only methysergide produced a significant attenuation of ECS analgesia. In contrast, following intrathecal injections of antagonists a dose-related decrease of analgesia could be seen after the injections of methysergide, phentolamine and naloxone implicating spinal serotonin, noradrenaline and the enkephalins in the analgesic action of ECS. To assess further the interaction between the action of these neurotransmitter systems, we evaluated the effect of drug pair combinations on ECS analgesia. Intrathecal phentolamine + naloxone, methysergide + naloxone and methysergide + phentolamine were injected at doses that caused maximal attenuation of analgesia.(ABSTRACT TRUNCATED AT 250 WORDS)

Analgesia↗
PubMed1977

Auditory evoked brain stem potentials in a case of "locked-in" syndrome.

Auditory evoked brain stem potentials were measured in a patient with occlusion of the basilar artery about 7 mm above its origin, resulting in the "locked-in" syndrome due to infarction at the junction of the lower one third and upper two thirds of the pons. The first three waves of the evoked response originating from the acoustic nerve and auditory nuclei in the caudal pons were normal in wave form, peak latency, and voltage level. Waves IV and V, generated in the region of the lateral lemniscus and inferior colliculus in rostral pons and caudal midbrain, demonstrated prolonged peak latency and reduced voltage, indicative of slowed neural conduction in the pons above the level of the superior olivary complex. These findings suggest that auditory evoked potential recordings may have considerable value in the localization of brain stem disorders.

Acoustic Stimulation↗
PubMed1978

Internuclear ophthalmoplegia. II. Pursuit, optokinetic nystagmus, and vestibulo-ocular reflex.

Smooth pursuit, optokinetic nystagmus (OKN) and the vestibulo-ocular reflex (VOR) were studied in four patients with internuclear ophthalmoplegia (two with bilateral and two with unilateral lesions). Horizontal smooth pursuit by an adducting eye on the side of a medial longitudinal fasciculus (MLF) lesion was normal in three of four patients; vertical pursuit was abnormal in all four. The horizontal VOR gain of slow components made by an adducting eye on the side of an MLF lesion was normal in all four patients. The vertical VOR gain was decreased in the two patients tested. It is concluded that either there are pathways independent of the MLF for horizontal pursuit and vestibular signals that are not available to vertical signals, or vertical pursuit and vestibular eye movements require a higher rate of oculomotor neuron firing than equal-velocity horizontal eye movements.

Adult↗
PubMed1979

Dominant optic atrophy. The clinical profile.

We examined 24 individuals in four family pedigrees with dominantly inherited optic atrophy (DOA); 12 patients met the criteria for diagnosis of DOA and two were suspect. Our data indicate that (1) insidious onset usually occurred in childhood, but subjective visual symptoms may evolve in adulthood; (2) visual function was minimally (20/25) to moderately (20/400) abnormal, could be strikingly asymmetric in an individual (eg, 20/30 in the right eye and 20/200 in the left eye), and showed considerable intrafamilial and interfamilial variation; (3) visual field defects consisted of central and centrocecal scotomas, but no peripheral isopter abnormalities were found; (4) color-vision screening with Hardy-Rand-Rittler plates revealed dyschromotopsias, but only Farnsworth-Munsell 100-hue examination disclosed the typical tritan defects; (5) pattern-reversal visual-evoked responses were characterized by diminished amplitudes and prolonged latencies, consistent with neural conduction defects; (6) disc pallor was limited to the temporal segment in all cases, and 16 of 24 eyes showed focal temporal excavation, which is probably pathognomonic of DOA.

Adolescent↗
PubMed1976

Central vestibular compensation. Effect of the bilateral labyrinthectomy on neural activity in the medial vestibular nucleus.

An attempt was made to reconstruct the central events that occurred in the various stages of vestibular compensation after a bilateral labyrinthectomy in the cat. Bilateral labyrinthectomized cats showed no nystagmus, but had unsteady head movements and wide gaits. Neural activity in both sides of the medial vestibular nuclei (MVN) was depressed during the critical stage of compensation; however, the neural activity was full and normal during the acute and compensated stage. The experimental results suggest that removing crossed inhibitory influence and reducing the cerebellar inhibitory influence by bilateral labyrinthectomy enhances the process of recovering neural activity in the vestibular nuclei during central compensation, and that the contralateral vestibular end organ is not a source of the driving force responsible for regeneration of electrical activity in the deafferented MVN after a unilateral labyrinthectomy.

Animals↗
PubMed1986

Phenytoin: mechanisms of its anticonvulsant action.

Phenytoin is a major anticonvulsant drug that is very effective in controlling a wide variety of seizure disorders while impairing neurological function little, if at all. Early work suggested the hypothesis that the drug's effects were due to a selective block of high-frequency neuronal activity. This theory is reevaluated in the light of accumulated observations on the effects of phenytoin in many neuronal and synaptic preparations. Most of these observations can be explained by a use- and frequency-dependent suppression of the sodium action potential by phenytoin, with a consequent filtering out of sustained high-frequency neuronal discharges and synaptic activity. The molecular mechanism for this is a voltage-dependent blockade of membrane sodium channels responsible for the action potential. Through this action, phenytoin obstructs the positive feedback that underlies the development of maximal seizure activity, while normal brain activity, proceeding at lower neuronal firing rates, is spared its depressant action. Other mechanisms of action that may contribute to the drug's efficacy and selectivity are also discussed.

Action Potentials↗
PubMed1978

Anatomical and physiological properties of ipsilaterally projecting spinothalamic neurons in the second cervical segment of the cat's spinal cord.

Anatomical and electrophysiological methods were used to investigate the projections and response properties of neurons in the second cervical (C2) spinal segment of the cat giving origin to a previously undescribed projection to the ipsilateral thalamus. The method of retrograde axonal transport of horseradish peroxidase (HRP) was used to identify neurons in C2 giving rise to thalamic projections. Following large (3.0 microliter) thalamic HRP injections, a large number of labeled neurons was observed in lateral laminae VII-VIII of C2 ipsilateral to the injections. They occurred as small clusters of cells along the longitudinal axis of C2. Labeled neurons were also observed contralaterally in the lateral cervical nucleus, dorsal horn (especially medial lamina VI), and loosely distributed in the ventral horn. The ipsilaterally projecting neurons were also labeled following small (0.2--0.5 microliter) HRP injections restricted to individual spinothalamic terminal zones (intralaminar nuclei, ventrobasal complex-nucleus ventralis lateralis border zone, medial division of the posterior nuclei), indicating that as a group they project widely throughout the thalamus. Single unit recording methods were used to obtain complementary information on the functional properties of these neurons. The antidromic stimulation method was applied to identify units in C2 projecting to the ipsilateral thalamus in anesthetized, paralyzed cats. Three categories of ipsilaterally projecting C2 units were identified: (1) units not driven by any type of natural stimulation; (2) units having large cutaneous receptive fields (RFs) and wide dynamic response ranges ("widefield"), and (3) units with smaller RFs and varied properties ("other"). Widefield units with bilaterally symmetrical and asymmetrical RFs were observed. Co-stimulation of different portions of an excitatory RF produced summation of the unit response. Inhibitory RF components were identified in one-third of the widefield units. Unit recordings after spinal tract lesions revealed that the afferent input passed via the ipsilateral lateral and/or ventral funiculi. Widefield unit responses to somatosensory stimuli could be inhibited by dorsal column conditioning stimulation. Several "other" units resembled widefield units, while a second group had small RFs restricted to the C2 dermatome. Possible functional roles of the projecting C2 neurons in somatosensory and non-specific systems are discussed.

Animals↗
PubMed1983

A system of rat spinal cord lamina 1 cells projecting through the contralateral dorsolateral funiculus.

The aim of these experiments was to sample the properties of lamina I neurones with long ascending projections. Recordings have been made from 136 units at the L4/5 level, with ascending axons reaching C2. More than 80% of the units projected via the contralateral dorsolateral white matter and only 10% via the contralateral ventral quadrant. None projected via the dorsal columns. Receptive fields were typically 1-2 cm2 and although a substantial number of units responded to a limited range of intense stimuli, a greater number of units were fired by both low- and high-threshold stimulation. In contrast to cells of deeper laminae, the majority of units were excited following activation of descending pathways in the dorsolateral funiculus. The functional role of these units is not obvious, but the location of the ascending projection and the influence of descending pathways does not support the notion that the output of lamina 1 constitutes a simple "pain pathway."

Action Potentials↗
PubMed1978

Intracortical horizontal connections of neurons in cat and monkey motor cortex.

The present paper deals with the study of the structure of horizontal neuron chains, one of the aspects of intracortical intraneuronal relationships. The motor cortex (field 4) of cats and lower monkeys (Papio hamadryas and Macacus rhesus s. M. mullata) was treated by the impregnating method of Golgi--Kopsh. The drawings of neurons from 90-micrometer sections were made by means of a camera lucida. Three possible pathways of impulse transmission along neuron chains in a horizontal direction were revealed. These were: a pyramido-pyramidal system of connections which may possibly spread excitatory influence among several columns; a basket-pyramidal connection system; and connections which arise from successive switchings between neighboring neurons of one layer.

Animals↗
PubMed1991

Inhibition of motoneuron discharge by peripheral nerve stimulation: an F response analysis.

F waves were recorded from the abductor pollicis brevis stimulating the median nerve at the wrist. These data were compared to responses obtained after preceding supramaximal stimulation of digital fibers of the second (II) finger or the median nerve at the wrist. The time between conditioning and test stimuli were 50 msec. Following conditioning stimuli, F wave latencies were significantly increased while F amplitudes, durations, and persistences were all decreased. Chronodispersion was not significantly affected. These changes were associated with increased repetition of individual F responses. The most prominent changes were found after stimulation of fibers of digit II but only at levels of stimulation supramaximal for the sensory nerve action potential. Some, but relatively limited, changes were present after stimulation of digital fibers of the fifth finger. The results are consistent with afferent fiber, probably A delta, inhibition of antidromic motoneuron activation with associated decrease in central motor neuron pool excitability. The study also demonstrates that, except for chronodispersion, changes in F waves found with peripheral nerve injury may also occur due to physiological changes in the central nervous system.

Electric Stimulation↗