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PubMed1986

Two converging brainstem pathways mediating circling behavior.

Ipsiversive circling results from stimulation of the rostromedial tegmentum (RMT) or medial pons (PONS), and contraversive circling results from stimulation of the superior colliculus (SC). To determine whether these sites are functionally connected, the collision method of Shizgal, Bielajew, Corbett, Skelton and Yeomans (1980) was used in rats. Pairs of stimulation pulses were presented to two sites, and the degree of collision between stimulation-evoked action potentials was assessed by measuring the frequency required for circling at short and long intrapair conditioning-testing (C-T) intervals. Collision was evidenced when the required frequencies were higher at short C-T intervals than at long C-T intervals. Collision of 46-62% was observed between RMT and PONS, and collision of 15-29% was observed between SC and PONS. Sites from which collision was obtained were located along the trajectories of the medial tegmental tract and the crossed tectospinal pathway. Refractory periods in all sites were similar, ranging from 0.3 to 1.7 ms. Conduction velocities of axons connecting RMT and PONS and SC and PONS were comparable, ranging from 0.8 to 13.3 m/s and 1.7 to 13.8 m/s, respectively, with lower conduction velocities associated with more ventral pontine sites. Thus, RMT and PONS, and SC and PONS are connected by myelinated axons that mediate circling.

Animals↗
PubMed1974

Presynaptic inhibition: primary afferent depolarization in crayfish neurons.

Inhibition of transmission between tactile sensory neurons and interneurons in the crayfish was investigated by intracellular recording int the presynaptic processes. Inhibition is correlated with a depolarization of the presynaptic process, as in the mammalian spinal cord; the depolarization is accompanied by a conductance increase, and is mediated by interneurons that can be excited by a variety of routes.

Animals↗
PubMed1993

Sensory nerve conduction velocities are higher on the left than the right hand and motor conduction is faster on the right hand than left in right-handed normal subjects.

Lateralization in the sensory and motor nerve conduction velocities was studied in right-handed normal subjects. The nerve conduction velocities (NCVs) were measured in hands. Sensory NCVs were found to be higher on the left hand than the right hand. The motor NCVs did not show a statistically significant difference between the right and left hands. However, the motor conduction velocity measured from median nerve to the action potential from abductor pollicis brevis muscle was found to be significantly higher in the right hand than the left hand. It was concluded that fast conducting neuromuscular junctions on the right hand muscles would contribute to relatively fast right hand in right-handers. Relatively fast conducting sensory nerves in the left hand may contribute to a relatively better perception by the right cerebral hemisphere in right-handers.

Brain↗
PubMed1976

[Organization of cortico-reticulo-spinal connections in the cat].

Time characteristics of the monosynaptic EPSP evoked by stimulation of the motor cortex in reticulospinal neurons were studied in detail. Negative correlation was revealed between latency duration of EPSP and conduction velocity of the corticobulbar fibres and positive correlation between such characteristics and conduction velocity of axons. Reticulospinal neurons with conduction velocity from 10.8 to 65.0 m/s were activated by fast and slow corticobulbar fibres, but neurons with conduction velocity from 65.0 to 155 m/s were activated only by slow ones. A functional role of different cortico-reticulo-spinal connections is discussed.

Animals↗
PubMed1964

SOME EFFECTS OF LONG CHAIN POLYMETHYLENE BISONIUM SALTS ON JUNCTIONAL TRANSMISSION IN THE PERIPHERAL NERVOUS SYSTEM.

A survey has been made of the effects on junctional transmission of the complete series of polymethylene bis-trimethylammonium (BTM) and bis-triethylammonium (BTE) salts from the decamethylene compounds (BTM 10 and BTE 10) to those with twenty-one methylene groups in the chain. These were tested for their ability to cause contracture of the isolated chick biventer cervicis preparation, and for their ability to block the twitch responses of this preparation, those of the rat isolated diaphragm preparation, and those of the cat tibialis anterior preparation. They were also tested for their ability to block transmission in the cat superior cervical ganglion, to block the actions of acetylcholine on the guinea-pig isolated ileum, and for ability to inhibit the hydrolysis of acetylcholine by acetylcholinesterase. Their electrical conductivity has been measured in aqueous solution. Ability to cause contracture of the chick biventer cervicis is confined to the compounds BTM 10 to 15; BTE 10, 11 and 12 have some weak activity but the other BTE compounds, and the BTM compounds with more than fifteen methylene groups, have virtually no activity. In the BTE series both neuromuscular blocking and ganglion-blocking activities increase with chain length up to a maximum in the region of BTE 15 to 17 and then decline. In the BTM series ganglion-blocking activity increases with chain length in much the same way as in the BTE series, though the maximum activity is at a slightly longer chain length. At the neuromuscular junction an increase in chain length beyond BTM 10 leads to a decline in activity but this returns to some extent at longer chain lengths, reaching a second maximum at BTM 18, above which it declines further. At the ganglion BTE 16 is only slightly more active than BTM 16 and about five-times as active as hexamethonium; at the neuromuscular junction in the cat BTE 16 is about five-times as active as BTM 16 and about eight-times as active as (+)-tubocurarine. The affinity of the BTE compounds for the postganglionic acetylcholine receptors of the guinea-pig ileum reaches a maximum at BTE 14 but does not decline significantly with further increase in chain length. Anticholinesterase activity, likewise, does not alter significantly between BTM 12 and BTM 21 and the activity of the compounds in the BTE series appears to be similar. This property could conceivably be modifying the actions of some of the intermediate compounds but is not likely to be affecting those of the more active ones. The conductivity experiments indicate that micelle formation could be limiting the actions of the compounds with 20 or 21 methylene groups, but is not likely to be affecting those of the other compounds. The results suggest that there is a regular increase with chain length of the affinity of these compounds for the receptors in the ganglia and at the neuromuscular junction but that efficacy in causing contracture is limited to compounds with three methyl groups in the cationic head and a chain of about ten methylene groups. The connexion between this ability to depolarize and the ability to block transmission by desensitization is discussed.

Acetylcholine↗
PubMed1995

Cognitive potentials: ipsilateral corticocortical interconnections in prefrontal human cortex ablations.

The research deals with the possible role of the essentially monosynaptic bidirectional corticocortical connections between occipito-temporo-parietal association cortical areas and frontal areas in the genesis of some contingent negative variation (CNV) components, especially on the supramodal dorsolateral prefrontal regions. With standard and topographic mapping methods of analysis, the multicomponent CNV complex formation was examined in 7 patients with extensive frontal cortex ablations exactly identified through CT/MRI examinations, and in 10 normal subjects. On the scalp over the ablated frontocortical areas, no consistent post-warning auditory N100 a-b-c, P200, P300, early and late CNV components were recordable. The hypothesis is proposed that the bidirectional ipsilateral long-distance pathways which interconnect uni-polymodal occipito-temporo-parietal cortical areas to prefrontal ones, in particular the arcuate-superior longitudinal and superior/inferior occipito-frontal fasciculi, play an important role in the genesis of several CNV complex components, especially the multicomponent post-S1 auditory N100. The posteroanterior sequential latency differences of these neurocognitive components, roughly measured along the scalp or on MRI imagings, is probably accounted for by the transcortical ipsilateral conduction time of about 1 cm/ms (10 m/s).

Brain Mapping↗
PubMed2001

Properties and substrate of slow pathway exposed with a compact node targeted fast pathway ablation in rabbit atrioventricular node.

INTRODUCTION: The properties and substrates of slow and fast AV nodal pathway remain unclear. This applies particularly to the slow pathway (SP), which is largely concealed by fast pathway (FP) conduction. We designed a new FP ablation approach that exposes the SP over the entire cycle length range and allows for its independent characterization and ablation. METHODS AND RESULTS: Premature stimulation was performed before and after FP ablation with 5.4 +/- 1.9 lesions (300-microm diameter each; overall lesion size 1.4 +/- 0.5 mm) targeting the junction between perinodal and compact node tissues in seven rabbit heart preparations. The resulting SP recovery curve and control curve had the same maximum nodal conduction time (165 +/- 22 msec vs 164 +/- 24 msec; P = NS) and effective refractory period (101 +/- 10 msec vs 100 +/- 9 msec; P = NS). The two curves covered the same cycle length range. However, the SP curve was shifted up with respect to control one at intermediate and long cycle lengths and thus showed a longer minimum nodal conduction time (81 +/- 15 msec vs 66 +/- 10 msec; P < 0.01) and functional refractory period (180 +/- 11 msec vs 170 +/- 12 msec; P < 0.05). The SP curve was continuous and closely fitted by a single exponential function. Small local lesions (2 +/- 1) applied to the posterior nodal extension resulted in third-degree nodal block in all preparations. CONCLUSION: The posterior nodal extension can sustain effective atrial-His conduction at all cycle lengths and account for both the manifest and concealed portion of SP. Slow and FP conduction primarily arise from the posterior extension and compact node, respectively.

Animals↗
PubMed1988

Somatosensory evoked potentials in chronic alcoholics with spasticity.

Somatosensory evoked potentials to median and bilateral tibial nerve stimulation were investigated in eight chronic alcoholics with spasticity, 12 patients with alcoholic polyneuropathy, and 11 normal subjects. Central conduction velocities from the third lumbar vertebra to the fifth cervical vertebra and from the 12th thoracic vertebra to the fifth cervical vertebra were significantly lower in the chronic alcoholics with spasticity than in the alcoholic polyneuropathy group and in the healthy nonalcoholic group. The result indicates that chronic alcoholics with spasticity have conduction disturbance in the posterior column and/or the medial lemniscus, which is considered to be due to alcoholic myelopathy and/or a brainstem lesion.

Alcoholism↗
PubMed1985

Two different mechanisms control inhibition of spike discharge in neurons of cat motor cortex after stimulation of the pyramidal tract.

Intracellular recordings were made from neurons of the motor cortex of awake cats while the pyramidal tract (PT) was stimulated at the level of the facial nucleus. In some neurons IPSPs of 35-120 ms peak latency were recorded that diminished in size or reversed with hyperpolarizing current. During these IPSPs a decrease in input resistance reflective of a conductance increase was measured. More often, however, PT stimulation produced IPSPs with comparable latencies that increased in size with hyperpolarizing current. These IPSPs diminished with depolarizing current, and in some instances they appeared to reverse with strong depolarization. During these IPSPs an increased input resistance reflective of a decreased conductance was measured. The results indicate that two different mechanisms control rapid inhibition of spike discharge in neurons of the motor cortex after PT stimulation.

Animals↗
PubMed1987

Locus coeruleus neurons projecting to the forebrain and the spinal cord in the cat.

The intranuclear organization of the cat locus coeruleus neurons was investigated anatomo-physiologically. The locus coeruleus neurons project to the forebrain through the dorsal noradrenergic bundle and to the spinal cord. Horseradish peroxidase, a retrograde tracer, was pressure-injected into either the dorsal noradrenergic bundle or the ventrolateral funiculus of the high cervical cord (C1-C2). The cats (n = 12) were killed after a 2- or 3-day survival period. The frontal sections (100 micron) throughout the locus coeruleus were observed by light microscope after carrying out the diaminobenzidine reaction. The labeled locus coeruleus neurons were located predominantly in the rostral locus coeruleus proper and locus coeruleus alpha when horseradish peroxidase was injected into the dorsal noradrenergic bundle, whereas they were predominantly located in the caudal locus coeruleus alpha and subcoeruleus when horseradish peroxidase was injected into the spinal cord. In the electrophysiological experiments, cats (n = 30) were anesthetized with alpha-chloralose and two stimulating electrodes were placed stereotaxically in the dorsal noradrenergic bundle and the ipsilateral ventrolateral funiculus of the high cervical cord (C1-C2), respectively. Monophasic square-wave pulses (2.5 Hz, 100 microsecond duration, 800 microA) were delivered. A recording glass electrode, filled with 2 M NaCl saturated with Fast Green, was placed in the locus coeruleus. Neurons with different conduction velocities, which were evoked by the antidromic stimulation of the dorsal noradrenergic bundle and spinal cord, were verified in the locus coeruleus and the adjacent areas. The slow conductive neurons with a conduction velocity of less than 1 m/s had a slow firing rate (1.6 +/- 0.9/s). They were located predominantly in the rostral locus coeruleus proper and locus coeruleus alpha by the dorsal noradrenergic bundle stimulation. From the anatomical and electrophysiological experimental results, it was concluded that the conduction velocities of the horseradish peroxidase-labeled neurons observed in locus coeruleus proper and locus coeruleus alpha were mostly slow and less than 1 m/s. Most of the slow conductive neurons were considered to be noradrenergic. Neurons evoked antidromically by both the dorsal noradrenergic bundle and spinal cord stimulation were not observed.

Action Potentials↗
PubMed1990

Electrophysiological characterization of central sensory and motor pathway function in patients with moderate hemiparesis. I. Methodical approach.

The central sensory and motor pathway function in healthy persons and patients with several neurological disorders was selectively characterized by evaluation of latencies of short (R1) and long (R2) latency EMG responses as well as simultaneously recorded somatosensory potentials (N19, N26) evoked by electrical stimulation of N.medianus and N.peroneus. On the basis of these latencies the peripheral and central sensory/motor conduction times were calculated. By using this investigation procedure a selective quantification of central pathway functions is possible.

Adolescent↗