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PubMed1992

[Postnatal development of central motor pathways. An electrophysiological study].

The percutaneous electrical stimulation of the brain and spinal cord has been used to study the central motor pathways in 19 healthy full-term newborns and in 19 infants. The evoked compound muscle action potential were recorded by bipolar surface electrodes fixed on the skin overlying the thenar eminence muscles and the tibialis anterior muscle. In full-term newborns, the responses of lower limb muscles to cortical stimulation are more difficult to obtain that those of upper limb muscles. At birth, the conduction velocity of central motor fibres along the spinal cord are around 10 m/s, 4 or 5 times lower that the lowest values published for adult subjects. Thus, as has been demonstrated in animals, there seems to exist in man a very clear dissociation between myelination of central motor pathways and that of peripheral motor fibres.

Action Potentials↗
PubMed1994

A segmental chronic pain syndrome in rats associated with intrathecal infusion of NMDA: evidence for selective action in the dorsal horn.

We explored the effects of chronic lumbar intrathecal NMDA infusion (mini-osmotic pumps) in Sprague-Dawley rats on motor and sensory axon integrity. Several different infusion protocols, each given over a 4 week period were examined: 0.15 M NMDA in phosphate buffered saline; phosphate buffered saline without NMDA; and 0.20 M magnesium sulfate plus 0.15 M NMDA; 0.35 M NMDA. In two additional protocols, 0.15 M NMDA or phosphate buffered saline were infused for a total of 8 weeks. Within 1-2 weeks of the onset of NMDA, but not phosphate buffered saline infusions, the rats exhibited irritability, circling, biting and excessive grooming resulting in loss of hair, and skin ulcerations from autotomy localized to lumbar and sacral innervated dermatomes. Co-infusion of NMDA with magnesium sulfate almost completely prevented these findings. The behavioural changes were not associated with abnormalities of sensory or motor conduction. Intrathecal infusion of NMDA induces a chronic "central" experimental pain disorder in rats, localized to the cord segment with the greatest exposure to the infusion, without involvement of peripheral sensory axons and sparing the axonal integrity of anterior horn cells.

Animals↗
PubMed1976

Regulation of neuronal properties by afferent connections. I. Functional changes in snail neurons following section of presysnaptic nerve fibers.

The left cerebral connective of snail ganglia containing afferent inputs to a particular neuron was sectioned. One week after the operation synaptic potentials were not obtained when the connective was stimulated, and they had not reappeared after 60 days. The current-voltage relationship of denervated cells showed a rectification in the hyperpolarizing direction, whereas that of control cells had an ohmic behavior. Depolarization or conductance changes produced by ACh or carbachol showed a supersensitivity in denervated cells, evidenced by a shift to the left of the dose-response curve and an increase of the maximal responses obtained. The reversal potential of ACh shifted from--22 mV in the control to--8 mV in denervated cells. Depolarization produced by serotonin was similar in control and denervated cells.

Acetylcholine↗
PubMed1993

The dynamic clamp: artificial conductances in biological neurons.

The dynamic clamp is a novel method that uses computer simulation to introduce conductances into biological neurons. This method can be used to study the role of various conductances in shaping the activity of single neurons, or neurons within networks. The dynamic clamp can also be used to form circuits from previously unconnected neurons. This approach makes computer simulation an interactive experimental tool, and will be useful in many applications where the role of synaptic strengths and intrinsic properties in neuronal and network dynamics is of interest.

Animals↗
PubMed1995

Motor evoked potentials by magnetic stimulation in hereditary and sporadic ataxia.

We report the study of motor evoked potentials by magnetic stimulation in 26 subjects with hereditary or sporadic ataxia. The subjects included 15 cases of late onset cerebellar ataxia (12 classified as olivopontocerebellar atrophy (OPCA), 3 as spinocerebellar atrophy (SCA)) and 11 cases of early onset cerebellar ataxia (4 Friedreich's ataxia (FA) and 7 unclassifiable in Friedreich's ataxia (NFA)). All subjects with FA and SCA had delayed central motor conduction times, more accentuated in corticospinal tracts directed to lumbar motoneurons. A similar but less marked slowing was observed in about half of the subjects with OPCA and NFA. In the last two groups the anomalies are more frequent in hereditary than in sporadic forms.

Adolescent↗
PubMedDate not supplied

Efficient computation of branched nerve equations.

Three simple improvements are presented which, for a given accuracy, result in a 10-20-fold decrease in computation time for simulation of arbitrarily branched active cables with Hodgkin Huxley (HH) kinetics. The first improvement takes advantage of the essentially tridiagonal character of the matrix equation for each branch of a 'tree' network and solves the equations as efficiently as for an unbranched cable. The second improvement evaluates the HH membrane conductances at the midpoint of a time step, delta t, to maintain full second order accuracy, 0(delta t2), with no increase in the number of computational steps. The third improvement makes use of 'premultiplied' HH rate function tables for very efficient second order correct integration of HH membrane conductance.

Electrophysiology↗
PubMed1983

Baclofen blocks postsynaptic inhibition but not the effect of muscimol in the olfactory cortex.

1 The olfactory cortex slice preparation from the guinea-pig brain was used to study the effects of baclofen on inhibition using intracellular recording. Stimulation of the lateral olfactory tract activities sequentially excitatory and inhibitory pathways. Inhibition is manifest as a period of increased membrane conductance (termed postsynaptic inhibitory conductance, IPSC). 2 Bath application of baclofen (0.2-500 muM) reversibly blocked the IPSC. Baclofen also produced a secondary increase in the amplitude and duration of the initial excitatory postsynaptic potential. 3 Baclofen (0.5-500 muM) slightly augmented the ability of bath-applied muscimol to increase the resting membrane conductance. Baclofen had no effect on cell excitability and membrane potential and no effect on the action of gamma-aminobutyric acid (GABA), noradrenaline, glycine, taurine or 5-hydroxytrypamine. 4 These results confirm previous suggestions that baclofen at low concentrations acts outside the GABA receptor mediating the IPSC perhaps by reducing the release of the excitatory transmitter activating the inhibitory interneurones.

Animals↗
PubMed1986

Synaptic organization of inhibitory circuits in the pigeon's optic tectum.

The synaptic organization of inhibitory systems in the pigeon's optic tectum was studied with intracellular recording techniques. An extrapolation procedure based on response latency was used to determine the synaptic delay of the postsynaptic potentials (PSPs) and the velocity of conduction of the associated retinal axons. Tectal cells receive mostly disynaptic, trisynaptic or polysynaptic inhibition from retinal ganglion cells. However, evidence was found which together with previous studies raised the possibility of the existence of a direct inhibitory retino-tectal path. Our present results also suggest that inhibition is transmitted from the retina to the tectal cells by way of both, feedforward and feedback pathways.

Animals↗
PubMed1985

Projection of morphologically identified superior colliculus neurons to the lateral posterior nucleus in the cat.

Using the intracellular recording and staining techniques we studied types of superior colliculus cells which project to the ipsilateral nucleus lateralis posterior (LP) and the nature of retinal afferent inputs to them. Five morphologically identified colliculus cells were antidromically driven by stimulation of the tectorecipient zone of the LP. The nature of retinal afferent inputs to these cells was determined by measuring conduction velocity between the optic chiasm and the optic tract. Four of the five, innervated by W-retinal ganglion cells, were narrow-field vertical and wide-field vertical cells, located in the upper and lower parts of the superficial gray layer. The remaining one, innervated by Y-fibers, was a large narrow-field vertical cell, located in the lower part of the same layer.

Action Potentials↗
PubMed1993

Longitudinal study of central motor conduction time following stroke. 1. Natural history of central motor conduction.

A 12 month longitudinal study has been performed on 118 subjects following first-ever stroke to determine changes in central motor conduction time (CMCT) to upper limb muscles. The responses to electromagnetic stimulation of the motor cortex and cervical motor roots were recorded bilaterally in the surface electromyograms of pectoralis major, biceps and triceps brachii and thenar muscles. The CMCTs obtained from these recordings in stroke patients have been compared with those obtained in 53 normal healthy subjects of a similar age. The first measurements were made within the immediate post-stroke period (12-72 h of the onset of symptoms) and repeated at set time intervals over 12 months. The first assessment of CMCT identified three groups: those with normal responses, delayed responses and absent responses. During the first 12 months following stroke various changes in CMCT occurred. Central motor conduction time may remain unchanged, delayed CMCT may return to normal and previously absent responses may reappear and be delayed or normal. Using electromagnetic stimulation of the motor cortex the thresholds for motor evoked responses in the different muscles were initially high and fell over 12 months.

Adult↗
PubMed2000

Preserved slow conducting corticomotoneuronal projections in amyotrophic lateral sclerosis with autosomal recessive D90A CuZn-superoxide dismutase mutation.

Recently, a subgroup of the amyotrophic lateral sclerosis (ALS) syndrome associated with mutations in the gene encoding the free radical scavenging enzyme CuZn-superoxide dismutase (CuZn-SOD, SOD1) has been identified. Some 67 different mutations have been reported worldwide to date, comprising about one-fifth of familial ALS cases in the populations studied. The autosomal recessively inherited D90A CuZn-SOD mutation has been associated with a very slowly progressive, clinically distinct phenotype, and is neurophysiologically characterized by very slow central motor conduction. It is not known which physiological and/or biochemical mechanisms are responsible for the different clinical course. To delineate ALS associated with this particular CuZn-SOD mutation from ALS without mutations, we performed a detailed neurophysiological study of the corticomotoneuronal function using peristimulus time histograms (PSTHs) in eight ALS patients homozygous for the D90A CuZn-SOD mutation. The results were compared with those obtained in 12 non-hereditary ALS patients and 11 healthy subjects. PSTHs were constructed from three to seven different, voluntarily recruited motor units of the extensor digitorum communis muscle (EDC) in each patient. The onset latency, number of excess bins, duration and synchrony of the primary peak were analysed. All measurements differed significantly between healthy controls and the D90A patients (P < 0.0007). The mean onset latency of the primary peak in D90A patients was 35.3 ms, compared with 24.2 ms for non-hereditary ALS patients and 19.3 ms for normal subjects (P < 0.0000). Delayed primary peaks in the D90A patients were desynchronized and characteristically preceded by a marked suppression phase. This suppression phase was not seen in non-hereditary ALS patients. We conclude that the mainly slow conducting and/or polysynaptic corticomotoneuronal connections are preserved in the D90A homozygous cases, and that the cortical and possibly spinal inhibitory circuitry is preserved. These events may partially protect the motor neurons, slowing down the degenerative process.

Adult↗
PubMed1997

Properties of individual embryonic primary afferents and their spinal projections in the rat.

Embryonic (E19-E20) and early postnatal (P2) spinal cords with intact saphenous and sciatic nerves were isolated and placed in aerated artificial cerebral spinal fluid (CSF). Intracellular recordings were made from cells in the L2-L6 dorsal root ganglia using microelectrodes filled with 3 M potassium acetate or 5% neurobiotin (NB) in 1 M potassium acetate. Several physiological properties of adequately impaled cells were measured, including peripheral conduction velocity, action potential (AP) amplitude and duration, duration of afterhyperpolarization (AHP), input impedance, rheobase, presence of inward rectifying current, and maximum somal firing frequency. The extent to which these properties are correlated also was determined. One cell per ganglion was injected with NB. Stained somata and their central projections in the spinal cord were visualized in serial 50 microm sections. Cell size was determined and the central morphology of the central projections examined. Although some fibers were in the process of growing into the spinal cord, others had established projections over several millimeters in the dorsal columns. Although most of these fibers supported projections in the gray matter, 22% only maintained fibers in the dorsal columns. Fibers with projections in the dorsal horn exhibited three types of morphology: projections confined to the superficial dorsal horn (laminae I, II); terminals confined to laminae III-V; and projections spanning laminae II-V. In addition, some embryonic fibers maintained projections to the dorsal horn that extended over five lumbar segments. Somal APs could be divided into two groups: broad spikes with inflections on their falling phase and narrow spikes without inflections. On average, cells with broad spikes (BS) had the following characteristics: slower peripheral conduction velocity, larger amplitude, higher rheobase and input impedance, longer AHP duration, and lower maximum firing frequency. There were significant correlations between conduction velocity and several of the physiological properties. Conduction velocity was negatively correlated with AP duration, rheobase, and input impedance and positively correlated with maximum firing frequency. Comparisons between spike shape and central morphology revealed that cells lacking collaterals in the gray matter and those with projections in the superficial dorsal horn always had broad somal spikes with inflections. Those with projections confined to laminae III-V always had narrow somal spikes (NS).

Animals↗
PubMed1992

Preservation of atrioventricular nodal conduction during radiofrequency current catheter ablation of midseptal accessory pathways.

BACKGROUND: Septal accessory atrioventricular (AV) pathways may be located in close vicinity of the His bundle-AV nodal conduction system. Attempts at surgical or electrical interruption of these pathways may therefore result in impairment of normal AV conduction. This study focuses on a subset of septal pathways with an atrial insertion located inside the triangle of Koch. In this study, they were called "midseptal." METHODS AND RESULTS: Six patients with a midseptal accessory pathway (mean +/- SD age, 40 +/- 12 years; five with Wolff-Parkinson-White syndrome and one with a concealed accessory pathway) underwent attempts at ablation of their pathway using 500-kHz radiofrequency current applied to the atrial insertion of the accessory connection. Guided by the recording of accessory pathway activation potentials, the ablation catheter was positioned in all patients in an area bounded anteriorly by the tip electrode of the His bundle catheter and posteriorly by the coronary sinus ostium. All pathways were successfully ablated without the induction of complete heart block. First-degree AV conduction block occurred in one patient in whom a concealed accessory connection was located closer to the AV node than to the coronary sinus ostium. CONCLUSIONS: Radiofrequency current catheter ablation may be used effectively for midseptal accessory pathways and should be preferred in experienced centers as a safe alternative to surgical therapy.

Adult↗
PubMed1978

Efferent system in the retina of the frog, Rana catesbiana.

Single units were recorded through glass microelectrodes placed on the optic disk or on the retina of the opened eye of the frog (Rana catesbiana). Units were classified as A-, B-, and C-fibers according to conduction velocities. By the method of collision between naturally elicited and electrically elicited impulses, many of the B-fibers and some A- and C-fibers, which showed unusual behavior to photic stimulation, were found to be efferent fibers. Retinal effects of the efferent nerves were studied by repetitive stimulation and cooling of the optic nerve. The effects were found to be both inhibitory and excitatory.

Animals↗
PubMed1984

Electrophysiological identification of neurons in ventrolateral medulla sending collateral axons to paraventricular and supraoptic nuclei in the cat.

Experiments were done in chloralosed, paralyzed and artificially ventilated cats to identify single units in the ventrolateral medulla (VLM) that send collateral axons directly to the region of the paraventricular (PVH) and supraoptic (SON) nuclei, and responding to peripheral inputs carrying cardiovascular afferent information. Twenty-six single units were antidromically activated in the VLM to stimulation of both the PVH and SON, and in each case the antidromic potential evoked by stimulation of one site was cancelled by stimulation of the other site. These units responded with latencies corresponding to conduction velocities of 5.1 +/- 0.4 m/s. Of these 26 units, 10 responded orthodromically to stimulation of either the carotid sinus or aortic depressor nerves. These data have demonstrated the existence of VLM neurons which send collateral axons to the PVH and SON and have provided evidence for their role in mediating cardiovascular afferent information directly to hypothalamic regions involved in autonomic and neuroendocrine regulation.

Animals↗
PubMed1985

Nucleus basalis neurons exhibit axonal branching with decreased impulse conduction velocity in rat cerebrocortex.

Single neurons in the basal forebrain (nucleus basalis area) were antidromically activated from the frontal or parietal cortex in anesthetized rats. Wide ranges of antidromic latencies were observed overall, with frontal and parietal stimulation yielding values ranging from 1.0 to 26.0 ms and 1.6-24.0 ms, respectively. Individual neurons often exhibited multiple antidromic latencies, such that deeper sites of stimulation or greater stimulation amplitudes generally yielded discretely different, shorter latencies than more superficial sites or lower amplitudes of stimulation. Single neurons were also often driven from neighboring sites (1-2 mm apart) within the frontal cortex, but no cell was coactivated from both frontal and parietal cortices. Finally, patterns and rates of spontaneous activity varied markedly among these cortically projecting neurons, with some cells being non-spontaneous and others exhibiting tonic rates of 30-40 Hz. Impulse waveforms also differed among driven cells, from relatively low-amplitude, negative spikes to large-amplitude, entirely positive spikes in unfiltered signals. These results indicate that cortically projecting, putatively cholinergic neurons in the basal fore-brain form a physiologically heterogeneous population in terms of impulse conduction velocity, spontaneous discharge, and spike waveforms. Our finding of multiple antidromic latencies and driving from neighboring sites indicate that these fibers may be highly branched in local terminal fields, but that individual cells may project exclusively to a single cortical area. Faster conduction velocities for deep compared to superficial cortical stimulation sites imply that these fibers may become non-myelinated upon entering cortical terminal fields, or that they may become markedly thinner as they travel within the cortex. This system of cholinergic cortical afferents differs in many physiologic aspects from the other non-thalamic cortical input systems of catecholamine or indoleamine neurons.

Animals↗
PubMed1988

The use of radiofrequency lesions for pain relief in failed back patients.

If conservative measures fail in the treatment of the failed back patient and if there is no indication for further surgery, interruption of nerve pathways conducting noxious stimuli may be attempted. The indication for such treatment is made on the result of a series of prognostic blocks analysing the conduction pattern of noxious stimuli. A new technique is described to interrupt the grey communicating ramus, conducting afferent fibres from the anterolateral and anterior parts of the annulus fibrosus. Results indicate a discrepancy between the result of radiofrequency lesions and the outcome of prognostic blocks. The discrepancy is more pronounced in failed back patients. Treatment with radiofrequency lesions is well tolerated and it has few adverse effects. It has a measure of success in a group of patients who are very difficult to manage otherwise.

Autonomic Nerve Block↗
PubMed1985

Electrophysiological investigation of IDPN neuropathy--initial studies.

beta,beta'-iminodipropionitrile (IDPN) causes giant axon swellings in proximal internodes of spinal motor axons and in stem processes of dorsal root ganglia neurons. The electrophysiological consequences of the swellings were investigated in cats given IDPN (50 mg/kg i.p.) weekly for 0 (control), 1 (7 days), 2 (14 days), or 5 (35 days) weeks; some additional animals were studied 15 (50 days) or 65 (100 days) days following the fifth injection. Extracellular recordings of the spinal monosynaptic reflex revealed amplitudes of efferent responses to be equally reduced at 35, 50 and 100 days. Single stimulation of dorsal roots, or soleus or medial gastrocnemius afferents often evoked doublet efferent responses which arose intraspinally. Similar repetitive responses were observed in dorsal root (afferent) input upon single stimulation of peripheral nerves. Latencies to monosynaptic responses became progressively prolonged over 100 days; spinal cord contribution to the increased latencies was maximal by 35 days. Conduction velocities in single soleus and medial gastrocnemius axons declined to 70 and 64% of normal by 50 days and to 56 and 50% of normal by 100 days respectively. Maximal recurrent inhibition was reduced 42-49% by 35 days and quantitatively similar at 50 and 100 days. Intracellular recordings from spinal motoneurons revealed that, at 35 days, action potentials could be elicited by orthodromic but not by antidromic stimulation in 14% of cells tested. This was taken as evidence of block of impulse conduction by the intervening axonal swelling upon antidromic stimulation. The possibility of abnormal electrical interactions between swollen and demyelinated intraparenchymal axons was tested by determining the number of ventral root fibers via which antidromic stimulation would elicit an action potential in the same motoneuron perikaryon. Electrical crosstalk, never seen in normal animals, varied in incidence during the evolution of the neuropathy (7-35 days), reaching a maximum of 30% at 14 days. Many motoneuron action potentials were remarkably similar to those observed in chromatolytic motoneurons, exhibiting, among other features, decreased SD thresholds and IS conduction times, reduced amplitudes and durations of afterhyperpolarization, delayed depolarizations and an enhanced propensity to fire repetitively upon single stimulation. There was no morphological evidence of chromatolysis in the motoneurons. The concept of "functional axotomy" is introduced to accommodate these findings and discussed in terms of altered dendritic excitability. Not all motoneuron types are equally compromised in the neuropathy.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗