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PubMed1975

Pulmonary afferent activity recorded from sympathetic nerves.

This study in mongrel dogs, anesthetized with sodium pentobarbital, verified the existence of pulmonary receptors whose afferents traverse the right and left upper thoracic white rami communicantes. These receptors responded to lung inflation as well as pinching of the lung parenchyma and were nonadapting in nature. In some fibers, increases in afferent activity were also observed when the pulmonary artery and veins were mechanically stimulated by probing. Conduction velocities of these afferents were measured in single-fiber preparations and were of the Adelta fiber type.

Animals↗
PubMed1984

Autoreceptor-mediated changes in dopaminergic terminal excitability: effects of striatal drug infusions.

The neurophysiological correlates of autoinhibition at the terminals of nigrostriatal dopaminergic neurons were studied by measuring the changes in antidromic excitability of nigrostriatal neurons following local infusions of various catecholamine agonists and antagonists into the neostriatum. Infusions of apomorphine or amphetamine reduced terminal excitability whereas the dopamine antagonists, haloperidol, fluphenazine or sulpiride, led to increases in terminal excitability. Alterations in antidromic excitability were constrained to the terminal regions and were not observed when infusions and excitability testing were performed in the medial forebrain bundle. The alpha-2 agonist, clonidine, did not alter dopaminergic terminal excitability. Our results indicate that pharmacological manipulations which have been shown to reduce the amount of stimulation-induced transmitter release from dopaminergic terminals are associated with a dopamine autoreceptor-mediated hyperpolarization and/or alteration in ionic conductance of the terminal membranes. These results are discussed with respect to mechanisms of autoinhibition in the central nervous system.

Animals↗
PubMed1976

An electrophysiological study of the sacral parasympathetic pathway to the colon of the cat.

1. Electrophysiological techniques were used to study the sacral parasympathetic pathway to the colon of the cat. 2. Electrical stimulation of the sacral ventral roots or the pelvic nerve elicited contractions of the colon and firing in nerve filaments on the serosal surface of the colon. Both responses were markedly reduced by the administration of ganglionic blocking agents. It is concluded that sacral preganglionic fibres to the colon make synaptic contacts with extramural ganglion cells. These cells were identified histologically in small ganglia on the serosal surface of the distal colon and rectum. 3. Transmission in extramural colonic ganglia was cholinergic and mediated by nicotinic receptors. Colonic ganglia did not exhibit large recruiting responses during repetitive (1-4 c/s) preganglionic nerve stimulation or an adrenergic inhibitory mechanism, both of which have been identified in bladder parasympathetic ganglia. It is concluded that colonic ganglia unlike bladder function primarily as simple relay stations and have little potential for modulating the neral activity arising in the central nervus system. 4. The preganglionic input to colonic ganglia was mediated by C fibres with maximal conduction velocities ranging from 0-5 to 1-4 m/sec. Bladder ganglia, on the other hand, received a preganglionic input composed of B fibres with maximal conduction velocities ranging from 8 to 10 m/sec. The possible physiological significance of different types of preganglionic fibres in the sacral outflow is discussed.

Action Potentials↗
PubMed1985

Connections between pericruciate cortex and the medullary reticulospinal neurons in cat: an electrophysiological study.

The connections between the pericruciate cortex and the medullary reticulospinal (RS) neurons were studied in anesthetized cat. Intracellular recordings were made from reticulospinal neurons and the effects of stimulating different areas of the pericruciate cortex were compared. EPSPs were elicited in all the 93 neurons studied which were antidromically activated by spinal stimulation and had an IS-SD notch on the ascending limb of their antidromic spikes. According to the conduction velocity (c.v.) of the axon and the minimal EPSP latency to cortical stimulation, the neurons could be divided into two groups, i.e. fast-conducting RS neurons (FRS neurons, c.v. greater than 45 m/s) and slow-conducting RS neurons (SRS neurons, c.v. less than 45 m/s). The minimal latencies of FRS neurons were equal to or shorter than 2 ms whereas those of SRS neurons were longer than 2 ms. EPSPs with short latency (less than 2 ms) could be evoked in FRS neurons by stimulating a relatively wide cortical area including the major part of precruciate area 4 and area 6, with a central area of strongest excitatory effect located in area 4 slightly medial to the tip of the cruciate sulcus. Stimulation of the postcruciate area 4 only produced long latency EPSPs. By extrapolation from the cortical and peduncular latencies and the conducting distances it was revealed that the earliest part of the minimal latency EPSPs were monosynaptically evoked in FRS neurons and were mediated by fast-conducting corticobulbar fibers. FRS neurons could be excited by stimuli applied to both ipsilateral and contralateral pericruciate cortex. The influence from the contralateral cortex was slightly stronger.

Animals↗
PubMed1981

Spinal cord conduction pathway for cerebellar evoked potentials from C-fibers.

Evoked responses from saphenous nerve C fiber stimulation were identified on the ipsilateral intermediate cerebellar cortex. This late potential has a latency between 180 and 250 msec, duration 50-70 msec, and an amplitude 10-20 micro V. The potential is conducted in the ipsilateral dorsal quadrant as determined by differential section of the spinal cord. The probable pathway is assigned to the dorsal spinocerebellar tract.

Animals↗
PubMed2004

Location and magnitude of conductance changes produced by Renshaw recurrent inhibition in spinal motoneurons.

The mean location of Renshaw synapses on spinal motoneurons and their synaptic conductance were estimated from changes in impedance magnitude produced by sustained recurrent inhibition. Motoneuron impedance was determined by injecting quasi-white noise current into lumbosacral motoneurons of pentobarbital-anesthetized cats. Synaptic location and conductance were estimated by comparing observed impedance changes to simulation results obtained using standard motoneuron models and compartmental models fit to each impedance function. Estimated synaptic locations ranged from 0.10 to 0.41lambda, with a mean of 0.19 or 0.24lambda, depending on the estimation method. Average dendritic path length was 262 microm. Average synaptic conductance was 23 to 27 nS (range: 6.7 to 57.9 nS), corresponding to conductance changes of 78 to 88% of resting membrane conductance. Estimated accuracy was supported by consistency using different estimation methods, agreement with Fyffe's 1991 morphological data, and comparisons of observed and simulated recurrent IPSP amplitudes. Synaptic location, but not synaptic conductance, was correlated with rheobase, a measure of motoneuron excitability. Synaptic conductance did not depend on synaptic location. A regression analysis demonstrated that synaptic conductance and cell impedance were the principal factors determining recurrent IPSP amplitude. Simulations using the observed values and locations of Renshaw conductance demonstrate that recurrent inhibition can require as much as an additional 14 to 18% sustained excitatory synaptic conductance to depolarize motoneurons sufficiently to activate somatic or dendritic inward currents and recruit motoneurons or amplify excitatory synaptic currents.

Animals↗
PubMed1987

Conduction block in hereditary neuropathy with susceptibility to pressure palsies.

Slow nerve conduction velocities, temporal dispersion of action potentials and conduction block occur in polyneuropathies with segmental demyelination. Conduction block has been reported in focal compressive neuropathies and in acute and chronic autoimmune polyneuropathy but not in hereditary motor and sensory demyelinating neuropathy. We report conduction block in five nerves of four patients from two families with a hereditary neuropathy with susceptibility to pressure palsies and pathologic changes of segmental demyelination and tomaculous swellings. Conduction block that may be long lasting is a feature of this type of hereditary neuropathy, which should be considered in the differential diagnosis of this electrophysiologic finding.

Action Potentials↗
PubMed1990

[Ageing and central motor conduction time].

The corticomotoneuronal pathway in the aged was studied using the technique of percutaneous electrical stimulation of the brain and the spinal cord. Central motor conduction time (CMCT) from the cerebral motor cortex to the cervical segment of the spinal cord (C-CMCT) was measured in 26 intact volunteers (20-85 years old) by substracting the latency to onset of EMG activity of the thenar muscle after cervical stimulation from the latency to onset of EMG activity of the same muscle after cortical stimulation. The latencies to onset of action potential of the anterior tibial muscle after cortical stimulation and the onset of action potential of the same muscle after lumbar stimulation were also measured in 11 volunteers (aged 46-67 years), and the difference between the two latencies was evaluated as the central motor conduction time from the cortex to the lumbar segment of the spinal cord (L-CMCT). Mean C-CMCT was 5.1 ms. and mean L-CMCT was 12.8 ms. Neither was related to the patient's height or age. There was no difference in either C-CMCT or L-CMCT between males and females. The results suggested that the conduction of the pyramidal tract is not affected by age, and this must be recognised when motor functions in the aged are studied.

Adult↗
PubMed1985

[Electrophysiological identification of neurons of the substantia innominata].

Recently in senile dementia of Alzheimer type, neuronal loss of cholinergic neurons in the substantia innominata is described. However these findings are based on morphological studies and, so far, these neurons have not been identified physiologically. In this study we tried to record these neurons electrophysiologically by antidromic activation. Cats were anesthetized with sodium pentobarbital and paralyzed with gallamine triethiodide. Three arreys of 3 or 4 silver-ball stimulating electrodes were fixed to the surface of the cerebral cortex. Each electrode was stimulated by rectangular pulses of 1 msec duration. Recording electrodes were glass micropipettes filled with 2 M NaCl saturated with fast green FCF and inserted into the ipsilateral substantia innominata stereotaxically. Twenty-eight neurons were constituted of mainly negative component; suggesting that they were recorded from cell bodies, not from axons. Also they responded in an all-or-none manner and showed constant latencies when stimulus intensities were at threshold level. When paired stimuli were applied, the latency of the action potential to the second stimulus was equal to that of the first one. These neurons were, therefore, considered to be activated antidromically. These neurons had axons of very slow conduction velocities. They are divided into two groups according to conduction velocities. The first group had mean conduction velocity of 2.3 m/sec and they responded to rather high frequency stimuli. The second group had mean conduction velocity of 1.0 m/sec and neurons belonging to this group showed quite long refractory periods. Based on conduction velocity analysis, the former is thought to include neurons with myelinated axons and the latter those with unmyelinated ones.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Axonal projections from the rostral expiratory neurones of the Bötzinger complex to medulla and spinal cord in the cat.

Axonal projections of eighty-four rostral medullary expiratory neurones of the Bötzinger complex were tested using antidromic mapping techniques in anaesthetized cats. A projection to the ventral respiratory neurones of the medulla (n.r.a.) was shown in eleven out of twelve tested neurones. Also a spinal projection to the C5-C6 cervical segments was evident in more than 72% of tested neurones; probably near 100% project to cervical cord. These axonal projections were found bilaterally in both brain stem and spinal cord. The majority of Bötzinger complex expiratory neurones were seen to have two to four axonal collaterals to the ventro-lateral (v.l.) nucleus of the solitary tract (n.t.s.) and/or the n.r.a. and/or the spinal cord. In eight out of twelve of the tested neurones, electrophysiological evidence of axonal arborization in more than one of n.r.a. inspiratory, n.r.a. expiratory or v.l. n.t.s. regions was obtained. Similar evidence for the terminal arborization was found for 26% of tested neurones in the phrenic motor nucleus. The descending spinal expiratory axons of the Bötzinger complex neurones are located in the dorsal and medial parts of the lateral funiculus in C4 and C5 segments. Conduction velocity measurements indicate that these are large myelinated axons. We propose that the Bötzinger complex expiratory neurones are a source of synaptic inhibition for n.r.a. inspiratory neurones and phrenic motoneurones.

Animals↗
PubMed1989

[Transcranial and spinal stimulation of motor pathways using conventional stimulator].

In a group of 31 subjects with a normal locomotor system in the area of the upper extremities transcutaneous cortical and spinal stimulation was administered using a conventional stimulator with an electromyographic tracing on the contralateral tenar and a common investigation of the motor conduction of the median nerve. The mean latency on stimulation on the calva was 20.0 +/- SD 0.9 ms, the mean amplitude 3.8 +/- SD 1.6 mV. The conduction time between cortex and the cervical spinal area was on average 4.8 +/- SD 0.5 ms, between cortex and wrist 16.26 +/- SD 0.8 ms, the mean latency on spinal stimulation 15.2 +/- SD 0.9 ms. The authors found a statistically significant relationship between the latencies from the calva, and spinal stimulation, with the height of the subject and with the length of the upper extremity, while there was no relationship between the conduction time in the central portion of the motor pathway and these anthropometric parameters. The authors evaluate the risk and tolerance of transcranial stimulation in man.

Adolescent↗
PubMed1987

Responses of neurones in the brainstem raphe nuclei to stimulation of the cerebellar fastigial nuclei in the cat.

Stimulation of the fastigial nuclei of the cerebellum was found to excite units located throughout the raphe nuclei of the brainstem. Raphe spinal units with axons conducting at velocities below 20 m/s were either unaffected by fastigial nucleus stimulation or inconsistently excited at long latency. In contrast units with faster conducting spinal axons throughout the raphe and more dorsally in the reticular formation were excited by stimulation of the fastigial nuclei. Many of these units responded at short latency and followed high rates of repetitive stimulation.

Action Potentials↗
PubMed1975

Supraspinal interactions resulting from experimental dorsal column stimulation.

Experiments were performed on rhesus monkeys to examine the hypothesis that stimulation with dorsal column electrodes of the type implanted clinically could alter the responses evoked in supraspinal nuclei through pathways in the ventral quadrant of the spinal cord. Dorsal column stimulation did produce changes in responses evoked in supraspinal nuclei; this effect could not be ascribed to a conduction block in ascending pathways. These results suggest that the mechanism of action of the dorsal column stimulator need not be dependent on interactions in the dorsal horn.

Animals↗