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PubMed1988

Ganglioside treatment of diabetic rats; effects on nerve adenosine triphosphatase activity and motor nerve conduction velocity.

Ouabain-sensitive ATPase activity (expressed as nmol ADP produced/h/mg (wet) nerve +/- SEM) was measured in homogenates of sciatic nerve from control rats and rats with streptozotocin-induced diabetes of 8 wk duration. Nerves from diabetic rats showed activity (21.7 +/- 2.0) which was significantly (p less than 0.05) less than that of controls (34.6 +/- 4.8). These animals also showed a deficit in conduction velocity (m/sec +/- SEM) of sciatic nerve motoneurones (50.7 +/- 0.4 vs. 57.7 +/- 0.7 in controls; p less than 0.001). In parallel, matched control and diabetic groups were treated daily with mixed gangliosides extracted from bovine brain (10 mg/kg i.p.). After such treatment for 8 wk the deficit in ouabain-sensitive ATPase activity did not develop in the diabetic group (treated diabetics, 31.9 +/- 3.7; treated controls, 34.5 +/- 3.8). However, the treatment did not affect the deficit in motor nerve conduction velocity (treated diabetics, 50.9 +/- 1.1 vs. treated controls, 57.9 +/- 0.5; p less than 0.001). Accumulations of the polyol pathway metabolites--sorbitol and fructose--together with depletion of nerve myo-inositol were similar in both diabetic groups. These data indicate an etiology for the conduction velocity deficit which differs from that of the deficit in ouabain-sensitive ATPase.

Adenosine Triphosphatases↗
PubMed1994

Further evidence for two types of corticopulvinar neurons.

Retrograde tracing experiments suggest that corticopulvinar connections originate from at least two subpopulations: medium and giant pyramids in layer 5, each with distinctive dendritic and local axonal arborizations. The present study used extracellular injections of PHA-L to delineate extrinsic axon arbors and to assess the possibility of categories that might correlate with these specific neuronal subpopulations. Two distinct types of terminations were found. Type I have smaller caliber preterminal axons, are generally elongate, and are studded with spinelike terminal specializations. Type II have larger axons (> 1.0 microns), spherical arbors, and mainly beaded specializations, some of which are conspicuously large (approximately 3.0 microns). These two axon types may differ in conduction velocity and membrane properties, and the interactions of these different features may be important for pulvinar function.

Animals↗
PubMed1985

The detection of monosynaptic connexions from inspiratory bulbospinal neurones to inspiratory motoneurones in the cat.

Simultaneous recordings were made of the discharges of inspiratory bulbospinal neurones and phrenic or external intercostal alpha-motoneurones in the anaesthetized cat. The connexions between these neurones were studied by the construction of cross-correlation histograms from their discharges. Peaks observed in the cross-correlation histograms were divided into three groups on the basis of their time courses: narrow, medium-width and high-frequency oscillations (h.f.o.). Narrow peaks were defined as having half-widths less than 1.1 ms and medium-width peaks as having half-widths greater than this, while h.f.o. was characterized by periodic waves in the range 60-120 Hz. H.f.o. peaks were interpreted as being derived from the well known periodic synchronization of medullary inspiratory neurones in this frequency range. The time courses and latencies of the medium-width peaks could be quantitatively explained by a simple model representing excitation of the motoneurones by bulbospinal neurones whose discharges showed synchronization within +/- 1 ms of the reference spike, together with temporal dispersion in bulbospinal axons having a distribution of conduction velocities given by the measurements of this study. Such an explanation was essential for some of the medium-width peaks, whose latencies were short compared to the conduction times to the spinal cord for their own axons, but for other medium-width peaks oligosynaptic excitation of the motoneurones from the identified bulbospinal neurones was another possible explanation. The narrow peaks were of appropriate durations for monosynaptic connexions and were all at appropriate latencies (0.6-2.4 ms after the calculated arrival time of the bulbospinal impulse in the segment concerned). It is concluded from the observations of narrow peaks that monosynaptic excitation exists between inspiratory bulbospinal neurones and both phrenic and external intercostal motoneurones. However, because of the existence of presynaptic synchronization, as shown by the presence of the medium-width peaks, such a conclusion is predicated upon being able to discriminate against such an effect. The model showed that this restriction applies just as much to the measurements of excitatory post-synaptic potentials (e.p.s.p.s) by spike-triggered averaging as it does to cross-correlation measurements. We suggest that the discrimination against presynaptic synchronization here was possible only because the long conduction distance created temporal dispersion in the synchronized presynaptic impulses.

Action Potentials↗
PubMedDate not supplied

Duration, configuration and amplitude of the motor response evoked by magnetic brain stimulation in patients with multiple sclerosis.

Analysis of motor evoked potentials (MEP) after magnetic brain stimulation is often restricted to measurement of latency and amplitude. In the present study, which was conducted in healthy controls and in patients with multiple sclerosis (MS), the additional value of MEP duration and configuration was evaluated. Recordings were made from distal muscles of the upper and lower extremity. In the MS group, mean MEP duration was found to be prolonged, while amplitudes were reduced. MEP of abnormally prolonged duration, as compared to normative data derived from the control group, were found even in presence of normal central motor conduction times. These findings are compatible with increased temporal dispersion of the impulses arriving at the spinal motoneurone pool. Thus, analysis of MEP duration may provide additional information about impulse propagation along the descending motor tracts, indicating disturbed conduction properties even in the presence of normal central motor conduction time. In contrast, MEP configuration was of no value for differentiating between the two groups.

Adolescent↗
PubMed1964

OBSERVATIONS ON THE MODE OF ACTION OF SOME CENTRAL DEPRESSANT DRUGS ON TRANSMISSION THROUGH THE CAT SUPERIOR CERVICAL GANGLION.

Methylpentynol, paraldehyde, amylobarbitone and procainamide blocked transmission through the cat superior cervical ganglion, and antagonized the ganglion-stimulating actions of acetylcholine and carbachol injected intra-arterially to the ganglion. Comparison with the effects of tetraethylammonium indicated that the impaired response to acetylcholine could not wholly account for the failure of transmission, which suggested that an impaired release of transmitter substance was a contributory factor. Methylpentynol, paraldehyde and procainamide also blocked the ganglion-stimulating action of potassium chloride. In contrast, amylobarbitone and pentobarbitone did not block the stimulating action of potassium chloride, but antagonized specifically the actions of acetylcholine and carbachol. The anti-acetylcholine activities of the two barbiturate drugs at this site accord with their relative ganglion-blocking activities. It is concluded that the ganglion-blocking action of methylpentynol, paraldehyde and procainamide arises from a nonspecific depression of both presynaptic and postsynaptic elements in the ganglion, but that barbiturate compounds act more specifically on the acetylcholine receptor.

Acetylcholine↗
PubMed1996

Perinatal maturation of the auditory brain stem response: changes in path length and conduction velocity.

OBJECTIVE: The goal of this study was to correlate developmental data on brain stem auditory path length with data on auditory brain stem response (ABR) conduction time. This was done to estimate changing axonal conduction velocity during the perinatal period. DESIGN: Pathway length was determined by three-dimensional reconstruction of postmortem fetal and infant brain stems in an AutoCAD system. Brain stem conduction time was obtained from previous ABR studies of premature, term, and post-term infants. The process of correlation of path length and conduction time was based on a model of ABR generation (Ponton, Moore, & Eggermont, this issue) that assumes that the III-IV interpeak interval represents activity in an asynaptic pathway and, thus, consists of only axonal conduction time. RESULTS: Brain stem conduction time is adult-like by the time of term birth. However, the brain stem auditory pathway continues to lengthen postnatally, with portions of the pathway not reaching adult dimensions until 3 yr of age. We determined lengths at various perinatal ages for three different segments of the auditory pathway. Each segment began at the cochlear nucleus (site of wave III generation) and ended at a more rostral location that is a possible site of wave IV generation. Conduction velocity was estimated by dividing path length by axonal conduction time (III-IV interpeak interval). All three assumed sites of generation of wave IV gave estimates of a threefold increase in conduction velocity between 29 wk CA and adulthood. However, three highly discrepant measures of absolute conduction velocity were obtained for the different path segments. The most reasonable conduction velocity estimates, from 5 m/sec at 29 wk conceptional age to 20 m/sec in adults, were produced by assuming a site of generation for wave IV near the contralateral medial superior olivary nucleus. CONCLUSIONS: Prenatally, increasing conduction velocity more than compensates for increasing path length, causing ABR conduction time to decrease. Postnatally, increasing conduction velocity exactly compensates for increasing path length while ABR conduction time remains stable. Different aspects of myelin development may underlie these two phenomena.

Evoked Potentials, Auditory, Brain Stem↗
PubMed2005

Non-uniform olivocerebellar conduction time in the vermis of the rat cerebellum.

It has been proposed that the conduction velocities of cerebellar climbing fibre (olivocerebellar) axons are tuned according to length, in order to precisely fix the conduction time between the inferior olive and cerebellar cortex. Some data conflict with this view. We have re-evaluated this issue using the climbing fibre reflex. The white matter of the tip of one folium in lobule VI or VII was stimulated electrically 0.5-1 mm below the surface and recordings were made from Purkinje cells in lobules VIII and IX. Reflex evoked climbing fibre (CF) responses (33 units) were recorded at different depths from Purkinje cells found in a narrow sagittal zone of cortex as complex spikes. The responses had latencies ranging from 4.3 ms to 11.3 ms. A consistent trend was that Purkinje cell responses recorded at greater depth had shorter CF reflex latencies than those recorded more superficially, both in individual experiments and in grouped data. These data show that the CF reflex latency is not constant, but is directly proportional to the distance an action potential has to travel along a CF. These data are not consistent with tuning of CF conduction velocities to normalize olivocerebellar conduction time, but are consistent with a CF conduction velocity in the cortex of approximately 0.6 m s-1. This suggests that climbing fibres projecting to different parts of the cerebellar cortex may have differences in spike conduction time of a few milliseconds, and that submillisecond precision is not an important element of the climbing fibre signal.

Action Potentials↗
PubMed1998

Cervical and reticular projections of neurones located in S1 and S2 segments of the cat's spinal cord.

Sacral neurones (S1 and S2 segments) projecting to the cervical cord (C6 segment) and to the contralateral gigantocellular reticular nucleus (coGRN) were electrophysiogically studied on 7 adult cats under alpha-chloralose anaesthesia. Antidromic action potentials were recorded from 48 neurones following stimulation of their axons in both the C6 segment and coGRN. Two groups of investigated cells were distinguished in the gray matter of sacral segments: one distributed in laminae V-VI (12 neurones), the other located in medial part of lamina VII and lamina VIII (36 neurones). All cells from the first group projected to C6. The latter group consisted of three types of neurones: projecting to C6 (n = 9), to coGRN (n = 1) as well as to both C6 and coGRN (n = 26). Axons of all identified neurones ran in lateral funiculi ipsilaterally, contralaterally or bilaterally. Conduction velocities were comprised in the ranges 35-81 m/s and 34-70 m/s for neurones projecting to the reticular formation and the cervical spinal cord, respectively. Decrease in conduction velocities was found in some axons in their distal parts suggesting more extensive divergence to various segments in the spinal cord or supraspinal centres.

Animals↗
PubMed1976

[Activity of the expiratory laryngeal motor neurons].

The activity of the whole recurrent nerve branch to expiratory laryngeal muscles, along with unitary activity of fibres from this branch were studied in cats. Conduction velocities of fibres ranged between 19.5-93 m/s. We used two types of preparations: low "encephale isole " (at C7 level) cats with concomitant light Dial anesthesia or without any anesthesia, or cats deeply anesthetized with Dial or chloralose-urethane. The vagus nerves were preserved. Under normocapnic conditions, the delay of recruitment (i.e. the lag between the interruption of phrenic nerve activity and the start of unitary expiratory recurrent nerve activity) increases as the residual phrenic nerve activity increases; in fact, the delay is nearly zero with unanesthetized or lightly anesthetized preparations (small residual phrenic activity), but can extend up to 800 ms with deeply anesthetized preparations (large and long-lasting residual activity) (fig. 4). Recurrent nerve units show a maximum firing rate at the beginning of a discharge; the rate then decreases (fig. 5). The maximum frequency is strongly reduced when residual phrenic activity is present (fig. 7). The discharge duration does not reach the expiratory pause duration. Rapidly conducting fibres are the firs ones to cease activity (fig. 5)...

Action Potentials↗
PubMed1988

Spike propagation and conduction failure in the rat neural lobe.

1. Single units were recorded from the rat hypothalamo-neurohypophysial system in vivo to test the hypothesis that action potential conduction failure might contribute to the relative inefficiency of neurohypophysial hormone release at low frequencies of stimulation, and following prolonged stimulation. 2. Recordings were made from the cell bodies of supraoptic neurones which project to the neural lobe of the pituitary. Stimuli applied to the neural lobe evoked antidromic action potentials (in ten of forty cells) at times when the axonal membrane at the site of stimulation should have been refractory following the passage of a spontaneous, orthodromically conducted action potential. This observation suggests that failure of orthodromic action potentials may occur intermittently in the neural lobe. 3. Recordings from single units in the neural lobe showed similar spontaneous patterns of activity to those seen from cell bodies in the supraoptic nucleus. 4. Stimuli applied to the neural stalk evoked orthodromically conducted spikes in these single units: evoked spikes followed stimulation faithfully at 50-80 Hz for 1 s or at 20 Hz for 1 min. Such stimulation was accompanied by a reduction in spike height and a prolongation of latency. 5. Comparable changes were seen in the latency and amplitude of evoked potentials recorded from the neural lobe with low-resistance electrodes. 6. Stalk stimulation at 50 Hz for 1 s was accompanied by a reduction in the threshold for initiation of action potentials, suggesting an increase in the excitability of neural lobe axons. 7. We conclude that, during low-frequency activation, spike failure occurs intermittently in neurohypophysial axons, and that changes in the excitability of the axons during activation at high frequencies may contribute to the facilitation of neurohypophysial hormone release that occurs with increasing frequencies of stimulation.

Action Potentials↗
PubMed1987

The duplex character of the corticofugal pathway from the striate cortex to the lateral geniculate complex of the cat.

From studies on signal conduction times in the corticofugal pathway from the striate cortex of the cat it has been proposed that S cells project to the LGN and C cells to the PGN. This concept has not received support from the histological examination of axons projecting to the two nuclei. The physiological experiments pointed to a clear segregation not apparent in the distribution of axonal diameters. A larger sample of signal conduction times, collected in the present study, is more consistent with the findings on the morphology of the pathway.

Animals↗