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PubMed1997

Short and long latency cortical potentials evoked by electrical stimulation of the oesophageal mucosa in normal alert humans.

Cerebral responses from the oesophagus were investigated in 16 normal male and female volunteers ranging in age from 20 to 54 years. The stimulus was applied by a naso-oesophageal probe equipped with bipolar ring electrodes. Short and long latency EP (SLEP and LLEP) were observed in all the subjects examined. SLEP consisted in a low threshold potential of 30 to 70 microV amplitude, biphasic or triphasic in shape and of approximately 5 to 10 ms duration; mean latency at the largest peak was 4.5 +/- 1.7 at 25 cm from the nostrils. Early components at about 2.5-3.5 ms and of small amplitude are also present. Recording from the neck at C7 with a common non-cephalic reference, SLEP components occurred from 2 to 6 ms earlier than that from the scalp, suggesting an oligo-synaptic transmission of the excitement via ganglion and lemniscal pathways to the cortex. SLEP was always followed by a complex potential formed of a succession of negative and positive waves with latencies ranging from 20 to 300 ms: the LLEP. This LLEP was usually not very stable and reproducible during the course of successive recordings and in the same subject because it tended to adjust. Preliminary observations concerning the topographical cortical distribution of oesophageal evoked potentials show a circumscribed localization of the SLEP in the parieto-temporal region of the hemisphere whereas LLEP was more widespread. It is the authors' opinion that oesophageal evoked potentials are generated both by the excitation of myelinic fibres with a wide range of conduction speed and of amyelinic fibres from the oesophageal mucosa and the paraoesophageal peripheral nerves of vagal origin.

Adult↗
PubMed1975

Electrophysiology of the peripheral nerve net in the polyclad flatworm Freemania litoricola.

1. A diffuse-conducting system close to the dorsal epithelium of the polyclad flatworm Freemania litoricola is described. Tactile stimuli elicit small action potentials which can be conducted around lesions through the body wall. The potentials can occur in bursts or barrages. 2. This conducting system appears to be insensitive to Mg2+ ions. 3. Conduction velocities (0-26--71 m/sec) vary over the animal. Conduction spread in the anterior half of the animal appears to be greater than that in the posterior portion. 4. Response decrement to repeated stimulation can be recorded in the peripheral system but it is not clear if this is due to habituation or fatigue. 5. Conduction from the peripheral net to the brain occurs. Some central units appear to pick up information only, or mainly, through the anterior nerves, while other units can respond to information conducted through the network to nerves of the contralateral side. 6. Different possibilities to account for this system are discussed, and it is suggested that the animals either possess a unique Mg2+ insensitive synaptic nerve-net or else the network is electrically coupled.

Action Potentials↗
PubMed1985

Neuronal connections in the primary auditory cortex: an electrophysiological study in the cat.

Neuronal connections in the primary auditory cortex (AI) of the cat were studied electrophysiologically by using intracellular recording techniques. Fast-conducting fibers from the medial geniculate nucleus (MG) projected monosynaptically onto AI neurons in layers III-VI (mainly in layer IV), whereas slow-conducting MG-fibers projected monosynaptically onto AI neurons in layer I. AI neurons which received monosynaptic inputs from the auditory association cortices (AII and Ep) and/or from the contralateral AI were distributed in all layers of the AI; the commissural fibers from the contralateral AI were divided into fast- and slow-conducting ones. AI neurons were categorized into seven types: type I neurons which received monosynaptic inputs from slow-conducting MG-fibers were located in layer I. Type II neurons which received polysynaptic inputs from the MG were located in layers II-VI. Type III neurons which sent their axons to the AII or Ep were mainly located in layer III. Type IV neurons which sent their axons to the contralateral AI were located mainly in layer III. Type V neurons which received monosynaptic inputs from fast-conducting MG-fibers were located mainly in layer IV. Type VI neurons which projected onto the inferior colliculus were located in the upper part of the layer V. Type VII neurons which projected onto the MG were located in layers V and VI.

Animals↗
PubMed1986

Electrophysiological characteristics of neurons in forebrain regions implicated in self-stimulation of the medial forebrain bundle in the rat.

In an attempt to identify neurons likely to play a role in self-stimulation of the medial forebrain bundle (MFB), action potentials of single neurons in the septum and basal forebrain of anesthetized rats were recorded by means of extracellular electrodes. Refractory period estimates were obtained from cells antidromically activated by stimulation of the lateral hypothalamus or ventral tegmental area, and estimates of interelectrode conduction time were obtained from cells that were driven by stimulation of both sites. The results show that some descending MFB axons arising in the medial septum, diagonal band of Broca and neighboring forebrain structures have characteristics comparable to properties of MFB reward neurons inferred from behavioral experiments.

Animals↗
PubMed1980

Neurophysiological study of subacute combined degeneration.

Three patients with subacute combined degeneration of the spinal cord due to vitamin B12 deficiency showed a characteristic pattern of abnormalities on neurophysiological tests which corresponded to the clinical signs and symptoms. Peripheral nerve conduction studies showed an axonal degeneration peripheral neuropathy. Brain stem auditory evoked responses were normal; visual evoked responses were mildly abnormal and somatosensory evoked responses were moderately abnormal. These studies shed light on the pathology of this disorder and can aid in its diagnosis.

Aged↗
PubMed1985

Axonal branching patterns and funicular trajectories of raphespinal sympathoinhibitory neurons.

We studied axonal branching patterns and funicular trajectories of cat medullary raphespinal neurons with spontaneous activity related to inferior cardiac postganglionic sympathetic nerve discharge (as demonstrated with spike-triggered averaging). These neurons were excited by raising carotid sinus pressure. We have classified these neurons as sympathoinhibitory in function and refer to them here as RS neurons. Microstimulation of the second thoracic spinal segment (T2) antidromically activated RS neurons (as determined with time-controlled collision of spontaneous and evoked action potentials). The longest-latency antidromic responses were elicited with the lowest-threshold current from sites in the intermediolateral nucleus (IML). This observation suggests that RS neurons innervated IML. Most RS neurons activated from T2 were also antidromically activated by stimulation of a more caudal thoracic spinal segment (T6 or T12). Time-controlled collision of action potentials evoked by stimulation at two thoracic levels allowed us to distinguish activation of an axonal branch in T2 from that of the main axon coursing through T2 to the more caudal thoracic level. Of those RS axons that branched in T2, 78% descended at least as far caudal as T6, whereas 65% reached T12. The axonal projections of other RS neurons that innervated T2 were restricted to no more than two consecutive thoracic spinal segments (as determined by stimulation in T3). Antidromic mapping of T2 further revealed that the axons of RS neurons coursed through the dorsolateral, ventral, or ventrolateral funiculus to innervate the ipsilateral and/or contralateral IML. The conduction velocities of dorsolateral and ventral RS axons indicated that they were finely myelinated. The data demonstrate the existence of RS neurons with restricted and widespread axonal branching patterns, thereby supporting the view that the medullary raphe complex is capable of regional as well as global inhibitory control over spinal sympathetic outflow.

Animals↗
PubMed1979

Functional relationships between the hippocampus and the cerebellum: an electrophysiological study of the cat.

1. Functional interrelationships between the hippocampus and the cerebellum have been investigated in the anaesthetized cat. Plots of the stimulating and recording sites as well as the latency range of the responses indicated the extent of ascending and descending lines of operation between these two structures. 2. Stimulation of the fastigial nucleus evoked the discharge of single hippocampal units on both sides of the brain. Early responses had a mean latency of 12 msec and late responses had a mean latency of 21 msec. Increasing the intensity of the stimulus had little effect on the patterns of discharge. 3. There was no topographical organization within the hippocampus. On the other hand, the activity evoked by a cutaneous stimulus was shown to be greatly depressed by a preceding cerebellar stimulus, particularly at intervals 30--40 msec between the two stimuli. 4. Cerebellar responses evoked by stimulating the hippocampus were found mainly in lobule VI of the posterior lobe. Early and late responses were frequently recorded in the same trace, ipsilateral stimulation yielding the shortest latencies. Increasing the intensity of the stimulus increased the likelihood of there being a response and increased the number of spikes in each discharge. Hippocampal stimulation also had a profound influence on resting cerebellar discharges. 5. Symmetrical points in the two hippocampi were chosen for conditioning and testing sequences. The conditioning stimulus had a long-lasting inhibitory effect on the test response followed by a slow recovery. 6. The location and extent of hippocampal influences on the cerebellum were determined by plotting the presence or absence of a response at each stimulated site. The results indicated the existence of bilateral descending projections containing fast and slow components in conformity with the known conduction properties of mossy fibre and climbing fibre inputs. 7. The physiological significance of interrelationship between the hippocampus and the cerebellum is discussed. It seems that there are many similarities as well as fundamental differences in the cerebellar control of movement under normal circumstances and in conditions of stress.

Animals↗
PubMed1985

An intracellular study of the synaptic input to sympathetic preganglionic neurones of the third thoracic segment of the cat.

In chloralose anaesthetized, paralyzed and artificially ventilated cats intracellular recordings were obtained from sympathetic preganglionic neurones (SPN) of the third thoracic segment of the spinal cord identified by antidromic stimulation of the white ramus T3. The synaptic input to SPNs was assessed, in cats with intact neuraxis or spinalized at C3, by electrical stimulation of segmental afferent fibres in intercostal nerves and white rami of adjacent thoracic segments and by stimulation of the ipsi- and contralateral dorsolateral funiculus and of the dorsal root entry zone of the cervical spinal cord. In both preparations SPNs showed on-going synaptic activity which predominantly consisted of excitatory post-synaptic potentials (EPSPs). Inhibitory post-synaptic potentials (IPSPs) were rarely observed. EPSPs were single step (5 mV) or, less frequently, large (up to 20 mV) summation EPSPs. The proportion of SPNs showing very low levels of on-going activity was markedly higher in spinal than in intact cats. Stimulation of somatic and sympathetic afferent fibres evoked early EPSPs (amplitude 3 mV, latency 5-22.3 ms), and late, summation EPSPs (amplitude up to 20 mV, latency 27-55 ms). Early and late EPSPs were evoked in nearly all SPNs in which this synaptic input was tested in the intact preparation (from 79-93% of the SPNs). In spinal cats, early EPSPs were evoked in 88% of the SPNs, whereas late EPSPs were recorded only in half of the neurones. No evidence for a monosynaptic pathway from these segmental afferent fibres to SPNs was obtained. In both intact and spinal cats, stimulation of the dorsolateral funiculus evoked early and late EPSPs in SPNs. Late EPSPs were recorded in 70% and 37% of the SPNs in intact and spinal cats, respectively. Early EPSPs, however, were evoked in all neurones. The early EPSPs evoked by stimulation of the dorsolateral funiculus had several components which are suggested to arise from stimulation of descending excitatory pathways with different conduction velocities. The following conduction velocities were calculated in intact (spinal) cats: 9.5-25 m/s (7.8-13.2 m/s), 5.7-9.5 m/s (5.5-7.8 m/s), 3.8-5.7 m/s (3.2-5.5 m/s), and 2.6-3.8 m/s (2.1-3.2 m/s). EPSPs of these various groups were elicited in a varying percentage in SPNs. EPSPs of the most rapidly conducting pathway were subthreshold for the generation of action potentials; some EPSPs of this group had a constant latency suggesting a monosynaptic pathway to SPNs. Stimulation of the dorsal root entry zone at the cervical level yielded essentially the same results as stimulation of the dorsolateral funiculus.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

Site of motor pathway excitation during cervical spinal stimulation.

In a set of 25 normal subjects the probable site of activation of the motor pathway was looked for using transcutaneous cervical spinal stimulation. The motor conduction time in the fastest fibres between the "spinal cord" and the wrist reached 10.79 (SD 1.17) ms when using this technique and this value was compared to the same parameter obtained with other methods: F wave mean conduction time in the established distance was 11.0 (SD 0.96) ms; the conversion of sensory to motor conduction showed 11.0 (SD 1.1) ms and H wave 10.97 (SD 1.03) ms. The conduction time through the fastest motor fibres with the spinal stimulation corresponds to the activation of the alpha-motoneuron axons near their bodies. When interpreting the results of the cortical and spinal stimulation, it is necessary to take this fact into account.

Adult↗
PubMed1981

Properties of medullary respiratory neurons.

A summary of recently published results dealing with the intrinsic and extrinsic properties of medullary respiratory neurons is presented. These neurons are organized into two anatomically separate populations, one associated with the ventrolateral nucleus of the solitary tract and the other with nucleus ambiguus and retroambigualis. Procion yellow dye injection studies have shown that respiratory neurons are medium-sized cells, their dendrites are selectively oriented, there is considerable dendritic overlap, but axon collaterals could not be demonstrated. Axonal conduction velocities vary widely, and input resistance is higher than that of alpha motoneurons. Extrinsic properties reveal a variety of firing patterns and membrane potential trajectories. Evidence is presented and a model proposal suggesting that reciprocal inhibition as well as recurrent inhibition and excitation may be important extrinsic inputs onto medullary respiratory neurons.

Animals↗
PubMed1976

[Reticular structures and reticulospinal pathways participating in initiation and inhibition of spino-bulbo-spinal activity].

Efferent discharges in intercostal nerves and activity of reticulospinal fibres during stimulation of the brain stem reticular formation, intercostal splanchnic nerves were recorded in cats anesthetized with chloralose (50 mg/kg). It is found that the structures involved in the transmission of spino-bulbo-spinal activity are located in the medial bulbar and pontine reticular formation as well as in its lateral regions. The structures producing long-lasting (300-800 ms) inhibition of spino-bulbo-spinal reflexes are also wide distributed in the brain stem, especially in the pontine region. Recording of activity of single reticulospinal fibres in the ventral (conduction velocity 16-120 m/s) and lateral (17-100 m/s) funiculi during spino-bulbo-spinal reflexes showed that both medial and lateral reticulospinal tracts may be involved into this reflex mechanism. New evidence is obtained that the inhibition of spino-bulbo-spinal reflexes may be located at supraspinal level.

Animals↗
PubMed2005

Experimental muscle pain decreases voluntary EMG activity but does not affect the muscle potential evoked by transcutaneous electrical stimulation.

OBJECTIVE: The aim of this human study was to investigate if voluntary EMG activity and supra-maximal M-wave are affected by injection of hypertonic saline to experimentally induce muscle pain. METHODS: Surface EMG signals were recorded with an electrode array from the tibialis anterior muscle of 12 subjects. Two sets of 6 contractions, 3 electrically elicited and 3 voluntary (30% of the maximal force), alternated, were performed with each leg. During the second set of 6 contractions, hypertonic (painful; right leg) or isotonic (non-painful; left leg) saline was injected 3 times (0.2, 0.5, 0.9 ml), separated by 140 s, into the tibialis anterior. RESULTS: In the voluntary contractions, EMG average rectified value (ARV) significantly decreased (mean+/-SE, 13.2 +/- 4.2%) with increasing pain, although the exerted torque was unaltered. Conduction velocity (CV) (4.2 +/- 0.2 and 4.4 +/- 0.3 m/s, right and left leg, respectively) and mean power spectral frequency (MPF) (119.0 +/- 8.4 and 119.5+/-8.9 Hz) were not affected by the injection of hypertonic saline. In the electrically elicited contractions, M-wave CV (4.6 +/- 0.3 and 4.7 +/- 0.2 m/s), ARV (748.6 +/- 101.8 and 822.3 +/- 104.4 microV), and MPF (72.0+/-5.1 and 76.9+/-4.8 Hz) did not change with pain. CONCLUSIONS: Injection of hypertonic saline did not change muscle fiber conduction velocity or impaire neuromuscular transmission. The decrease in voluntary EMG activity with injection of hypertonic saline was thus due to central factors. SIGNIFICANCE: The injection of hypertonic saline provides a model for exciting nociceptive afferents without affecting muscle fiber electrophysiological properties.

Action Potentials↗
PubMed2005

On the human sensorimotor-cortex beta rhythm: sources and modeling.

Cortical oscillations in the beta band (13-35 Hz) are known to be modulated by the GABAergic agonist benzodiazepine. To investigate the mechanisms generating the approximately 20-Hz oscillations in the human cortex, we administered benzodiazepines to healthy adults and monitored cortical oscillatory activity by means of magnetoencephalography. Benzodiazepine increased the power and decreased the frequency of beta oscillations over rolandic areas. Minimum current estimates indicated the effect to take place around the hand area of the primary sensorimotor cortex. Given that previous research has identified sources of the beta rhythm in the motor cortex, our results suggest that these same motor-cortex beta sources are modulated by benzodiazepine. To explore the mechanisms underlying the increase in beta power with GABAergic inhibition, we simulated a conductance-based neuronal network comprising excitatory and inhibitory neurons. The model accounts for the increase in the beta power, the widening of the spectral peak, and the slowing down of the rhythms with benzodiazepines, implemented as an increase in GABAergic conductance. We found that an increase in IPSCs onto inhibitory neurons was more important for generating neuronal synchronization in the beta band than an increase in IPSCs onto excitatory pyramidal cells.

Adult↗
PubMed1986

Noninvasive measurement of spinal cord conduction: review of presently available methods.

The ability to measure spinal cord conduction velocity noninvasively is limited by available methodology. Surface recording of small spinal potentials, although feasible in infants and young children, is problematical in adults, especially when recording over the cervical spine. On the other hand, indirect methods designed to improve the signal-to-noise ratio, which include recording of somatosensory cortical evoked potentials, F-waves, or other muscle responses, are limited by the unproven assumptions necessary in calculating spinal conduction. Additionally, each method has its own particular limitations. The majority of presently available noninvasive methods take a restricted, or no, account of conduction through the motor pathways. Despite these often serious limitations, each of the reviewed methods does play a useful clinical role in the electrophysiologic investigation of cord disease that is not visible radiologically. Knowledge of them allows for sufficient diversity to tackle most relevant problems until an ideal physiologic method is developed.

Biophysical Phenomena↗
PubMed1986

Electrophysiology of the corticomotoneurone pathways in patients with movement disorders.

The corticomotoneurone pathways were examined in 21 patients with movement disorders, using the technique of percutaneous electrical stimulation of the motor cortex. Conduction in these pathways was assessed by measuring the latency to onset of electromyographic activity in the muscles of the upper limb after cortical stimulation. In all patients [five with primary (idiopathic) torsion dystonia and two with secondary (symptomatic) hemidystonia, seven with Huntington's disease, four with essential tremor, and three with Parkinson's disease] central motor conduction was normal. This and other evidence suggests that the origin of the disorder of movement in these conditions lies in the delivery of abnormal motor commands to a normal corticomotoneuronal system.

Adult↗
PubMed1975

Direction-selective units in the rabbit's nucleus of the optic tract.

A class of direction-selective (DS) units, histologically localized within the nucleus of the optic tract (NOT) was isolated in the rabbit's pretectum. These units typically had a maintained discharge of 25-50 action potentials/sec and large receptive fields (up to 40 X 150 degrees) in the visual streak area of the contralateral eye. They were excited by a visual pattern moving in one direction and inhibited by motion in the opposite direction. The reactions were sustained. Excitatory and inhibitory acceptance angles were each 180 degrees. Most units were excited by anterior motion of the stimulus and reacted to a wide range of velocities (0.01-20 degrees/sec). Random checkerboard patterns (elements 0.8 degrees), grids of black and white stripes (1, 2 and 4 degrees wide) and single black and white edges were all effective, with a decreasing response magnitude in roughly this order. A stimulus area of 2 X 2 degrees was already effective; response increased with area and was maximal for 15 X 15 degrees and larger stimuli. Latency for visual stimulation was 60 +/- 10 (S.D.) msec, for electrical stimulation of the chiasm 2.2 +/- 0.3 (S.D.) msec. Synaptic latency and presynaptic conduction velocity were estimated at 0.7 msec and 13m/sec, respectively. A strong convergence of retinal DS fibers upon NOT units is postulated. Since most properties of NOT units are compatible with those of optokinetic nystagmus, and electrical stimulation of the NOT elicits vigorous nystagmus, these data suggest that these cells are the essential afferent link in the optokinetic reflex arc.

Animals↗
PubMed2002

Only minor spinal motor reflex effects from feline group IV muscle nociceptors.

The contribution of group III and IV muscle nociceptors activated by injection of KCl or bradykinin into the muscle artery (i.a.) of the gastrocnemius-soleus muscle to spinal motor reflex pathways was investigated in high spinal cats. Group I-III fibres were completely blocked by TTX, leaving group IV-fibre conduction intact. Thus, effects from i.a. KCl or bradykinin injection persisting after TTX were attributed to TTX resistant group IV fibres while the contribution of group III fibres was approximately defined by the difference between those effects and the control effects before TTX. Confirming former findings the chemical activation of group III and IV muscle afferents induced distinct reflex facilitation of the flexor posterior biceps semitendinosus and inhibition of the extensor quadriceps. After the block of all myelinated fibres by TTX the same stimuli induced only minor reflex effects mediated by the persistently conducting TTX resistant group IV afferents. It is concluded that the main functional meaning of group IV muscle afferents, which respond preferentially with a higher threshold to mechanical stimuli, is probably less related to reflex motor control than that of group III afferents.

Afferent Pathways↗