Ventral root afferent and dorsal root efferent fibres in dog and human lower sacral nerve roots.

Two pairs of wire electrodes were used to record single afferent action potentials from ventral roots and single efferent action potentials from dorsal roots of dogs and humans. A human lower sacral ventral root contained about 20 to 30% afferents among fibres with a diameter larger than 5 microns; a comparable ventral root of a dog contained about 1% afferents. Human S3, S4 and S5 dorsal roots contained 3, 18, and 20 to 30% efferent fibres respectively; a comparable dorsal root of the dog contained less than 1% efferent fibres. Primary and secondary muscle spindle afferents, Golgi tendon organ afferents, and afferents from the mechanoreceptors of the urinary bladder and anal canal mucosa were activated in a dog ventral root by pulling bladder and anal catheters. Their peak group conduction velocities were 82, 57, 71 and 18 m/s at 34 degrees C respectively. The dog afferents conducted more than 30% faster than did comparable human nerve fibres. By strongly pulling the bladder catheter, the static human dorsal root gamma 21-motoneurons increased their activity for about 7 s which in turn strongly increased the dorsal root spindle afferent activity for more than 10 min; the human static intrafusal gamma-motoneurons seemed to show cumulative properties.     

In vivo measurement of conduction velocities in afferent and efferent nerve fibre groups in mice

Electrophysiological investigations in mice, particularly with altered myelination, require reference data of the nerve conduction velocity (CV). CVs of different fibre groups were determined in the hindlimb of anaesthetized adult mice. Differentiation between afferent and efferent fibres was performed by recording at dorsal roots and stimulating at ventral roots, respectively. Correspondingly, recording or stimulation was performed at peripheral hindlimb nerves. Stimulation was performed with graded strength to differentiate between fibre groups. CVs of the same fibre groups were different in different nerves of the hindlimb. CVs for motor fibres were for the tibial nerve (Tib) 38.5±4.0 m/s (Agamma: 16.7±3.0 m/s), the sural nerve (Sur) 39.3±3.1 m/s (12.0±0.8 m/s) and the common peroneal nerve (Per) 46.7±4.7 m/s (22.2±4.4 m/s). CVs for group I afferents were 47.4±3.1 m/s (Tib), 43.8±3.8 m/s (Sur), 55.2±6.1 m/s (Per) and 42.9±4.3 m/s for the posterior biceps (PB). CVs of higher threshold afferents, presumably muscle and cutaneous, cover a broad range and do not really exhibit nerve specific differences. Ranges are for group II 22-38 m/s, for group III 9-19 m/s, and for group IV 0.8-0.9 m/s. Incontrovertible evidence was found for the presence of motor fibres in the sural nerve. The results are useful as references for further electrophysiological investigations particularly in genetically modified mice with myelination changes.     

IGF-I deficient mice show reduced peripheral nerve conduction velocities and decreased axonal diameters and respond to exogenous IGF-I treatment

Although insulin-like growth factor-I (IGF-I) can act as a neurotrophic factor for peripheral neurons in vitro and in vivo following injury, the role IGF-I plays during normal development and functioning of the peripheral nervous system is unclear. Here, we report that transgenic mice with reduced levels (two genotypes: heterozygous Igf1+/- or homozygous insertional mutant Igf1m/m) or totally lacking IGF-I (homozygous Igf1-/-) show a decrease in motor and sensory nerve conduction velocities in vivo. In addition, A-fiber responses in isolated peroneal nerves from Igf1+/- and Igf1-/- mice are impaired. The nerve function impairment is most profound in Igf1-/- mice. Histopathology of the peroneal nerves in Igf1-/- mice demonstrates a shift to smaller axonal diameters but maintains the same total number of myelinated fibers as Igf1+/+ mice. Comparisons of myelin thickness with axonal diameter indicate that there is no significant reduction in peripheral nerve myelination in IGF-I-deficient mice. In addition, in Igf1m/m mice with very low serum levels of IGF-I, replacement therapy with exogenous recombinant hIGF-I restores both motor and sensory nerve conduction velocities. These findings demonstrate not only that IGF-I serves an important role in the growth and development of the peripheral nervous system, but also that systemic IGF-I treatment can enhance nerve function in IGF-I-deficient adult mice.     

On the relation between fibre diameter and conduction velocity in myelinated nerve fibres

Myelinated fibres less than 1 micrometer in diameter are rare in the peripheral nervous system; but fibres down to 0.2 micrometer in diameter exist in the central nervous system. These observations are consistent with Rushton's theory on the effects of fibre size on conduction in myelinated nerve when the different processes of myelination in the peripheral and central nervous systems are taken into account.     

Control of defecation in patients with spinal injuries by stimulation of sacral anterior nerve roots.

OBJECTIVE--To observe the effects of stimulation of the sacral anterior roots on anorectal and low colonic pressures and to programme implanted stimulators to produce defecation. DESIGN--Prospective study of 12 consecutive patients. SETTING--Spinal injuries unit and university gastrointestinal physiology department. PATIENTS--12 Patients with complete supraconal spinal cord lesions. Their injuries had been sustained at least two years before the study. INTERVENTIONS--A Brindley-Finetech intradural sacral anterior root stimulator was implanted in all patients. Three months postoperatively the stimulator settings were adjusted after measurement of simultaneous anorectal and low colonic pressures. MAIN OUTCOME MEASURES--Full defecation. RESULTS--Six patients achieved complete rectal evacuation of faeces using the implant and subsequently did not require manual help for defecation. For all but one of the patients the total time taken to complete defecation was reduced, and all were free from constipation, the most prevalent gastrointestinal symptom in patients with spinal injuries. CONCLUSIONS--Sacral anterior root stimulators can be programmed to achieve complete unassisted defecation and can considerably improve the quality of life of patients with spinal injuries.     

Effects of nickel ion on the conduction of action potentials in non-myelinated nerve fibre of crayfish.

Effects of NiCL2 and PCMB (p-chloromercuribenzoate) on the action potential were examined by the method of extra- and intracellular electrodes, using a single nerve fibre of crayfish. The results obtained were as follows : The conduction of the action potential was blocked by treating the nerve fibre with Ni ion or PCMB. The blockade was easily recovered by replacement with cysteine. The process of the blockade and recovery, which could be repeated several times, was fairly characteristic such that the more repetition led the sooner blockade and the harder recovery. No conduction block was observed by treatment with Ni-cysteine mixed solution nor with PCMB-cysteine solution. The critical concentration for blocking was 1.1 x 10(-4)M for NiCL2 and 5.6 x 10(-6) M for PCMB. The action potential was disappeared without any change in the resting potential by treatment with the chemicals, which gave significant effects on the rising and falling phases of the action potential before the blockade.     

Motor and sensory conduction velocities and amplitude of nerve or muscle potentials in the normal rat according to age

The relative changes in sensory and motor nerve conductions and SNAP and CMAP amplitudes were studied on the sural and tibial posterior nerves in anesthetized male rats, between the 1st and the 23rd month. Neural growth was controlled with the measure of the nerve path length on the skin, between stimulating and recording cathodes for the sural nerve and proximal and distal stimulating cathodes for the tibial posterior nerve. The sural SCV and SNAP amplitude are consistent with a more accurate method than the H-reflex one. Similar changes were observed in both parameters. During the maturation of the peripheral nervous system, between the 1st and the 5th month, parameters rapidly increased. Over 14 months old, parameters decrease: the diminution of SNAP and CMAP amplitudes is characteristic of aging. The results were analyzed through quadratic and linear regression and were similar to those in young and elderly human patients. Parabola curves fitted the best way to represent the evolution of parameters. Moreover, the linear regression permitted to divide the rat life in 3 parts and to distinguish a period between the 6th and 13th months during which studied parameters are considered as constant. SCV, MCV, SNAP and CMAP amplitudes from the 1st to the 5th, from 6th to 13th and over the 14th month, could be used as reference.     

Diameters and conduction velocities of fibers in the cat auditory pathways

The diameters of nerve fibers in the brachium colliculi inferioris and geniculo-cortical tract were measured. The thickness of these fibers ranges from 0.5 to 6.0 µ, and in 82–88% of them it is 1.0–3.0 µ. About 100,000 nerve fibers were found in cross-sections through the brachium colliculi inferioris. The velocity of conduction along centripetal fibers of the geniculo-cortical tract was determined. It varied from 11 to 28.6 m/sec in different fibers, and in 71% of them it was between 15 and 22 m/sec. The composition of the fibers of the geniculo-cortical tract was compared relative to their thickness and conduction velocity.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 6, pp. 608–611, November–December, 1972.     

Long-range afferents in the rat spinal cord. 1. Numbers, distances and conduction velocities.

The caudal extent of the penetration of primary afferent axons from the T12 and L1 dorsal roots and sural nerve has been investigated in adult decerebrate spinal rats. Microelectrode stimulation at the root entry zone (REZ) and at further caudal points in the spinal cord was used to generate antidromic action potentials in single fibres recorded in dorsal roots or peripheral nerves. A total of 209 units were recorded in T12 and L1 dorsal roots and 27% of these could be antidromically activated 10 mm caudal to the REZ. Fifteen percent of the units could be stimulated at the L4-5 border, 15 mm caudal to the T12 segment whereas 4.5% of the axons could be stimulated 25 mm caudally in the S4 segment, 11 segments caudal to the entry segment. Similar recordings made from units in the sural nerve showed that of all the sural axons that penetrated to the L6 segment 50%, 18% and 2% of these reached the S1, S2 and S4 segments respectively. The conduction velocities of these units were clearly in the A-beta range when recorded in the nerve but decreased on entering the spinal cord and were reduced by 83% at their caudal end point. The results show that substantial numbers of primary afferents have long-ranging caudal branches in areas beyond the regions of known postsynaptic effects. The functions of these caudal projections are unclear but they may represent a potential substrate for the development of functional connections under conditions of disease or denervation.     

Effect of vitamin C and E supplementation in modulating the peripheral nerve conduction following cold exposure in humans

Exposure to an extremely cold environment without proper protection leading to hypothermia is an emergency, one of the several complications of which is impairment in nerve conduction. Our previous work in the rat model has shown the beneficial effect of vitamin C in modulating the effect of hypothermia on nerve conduction. The present study aimed to evaluate the effect of vitamins C and E, administered alone or in combination, in modulating the effect of mild hypothermia on human ulnar nerve conduction. The study was carried out on 26 volunteers divided into three groups: group I received vitamin C supplementation (2000 mg/day in a single dose and 1,000 mg/day for the next 6 days), group II received vitamins C and E in combination (1,000 mg and 800 mg respectively in a single dose and 500 mg and 400 mg respectively for the next 6 days) and group III received vitamin E (800 mg in a single dose and the same for the next 6 days). The recordings were carried out before and after single and weekly supplementation in each group. There was a fall in ulnar nerve conduction velocity with a reduction in the oral temperature of 2–2.5 °C. Vitamin C administered alone and in combination with vitamin E reduced the fall in ulnar nerve conduction velocity. Prior supplementation with vitamin C and E could help ameliorate the impairment in human ulnar nerve conduction due to hypothermia.     

Validation of improved recording site to measure phrenic conduction from surface electrodes in humans.

Phrenic nerve stimulation, electrical (ES) or from cervical magnetic stimulation (CMS), allows one to assess the diaphragm contractile properties and the conduction time of the phrenic nerve (PNCT) through recording of an electromyographic response, traditionally by using surface electrodes. Because of the coactivation of extradiaphragmatic muscles, signal contamination can jeopardize the determination of surface PNCTs. To address this, we compared PNCTs with ES and CMS from surface and needle diaphragm electrodes in five subjects (10 phrenic nerves). At a modified recording site, lower and more anterior than usual (lowest accessible intercostal space, costochondral junction) with electrodes 2 cm apart, surface and needle PNCTs were similar (CMS: 6.0 +/- 0.25 ms surface vs. 6.2 +/- 0.13 ms needle, not significant). Electrodes recording the activity of the most likely sources of signal contamination, i.e., the serratus anterior and pectoralis major, showed distinct responses from that of the diaphragm, their earlier occurrence strongly arguing against contamination. With ES and CMS, apparently uncontaminated signals could be consistently recorded from surface electrodes.     

Blood supply and the atrioventricular conduction system of the dog heart

In 30 experiments in order to specify the blood supply and conducting system in the dog heart, coronal arteries were injected with a contrasting mass that was followed by roentgenography and preparation of the coronal arteries. The topography and blood supply of the atrioventricular conducting system with application of prevital blood supply, and the left coronal artery is the main source of blood supply for all the parts of the cardiac atrioventricular conducting system.     

Batrachotoxin-modified sodium channels from squid optic nerve in planar bilayers. Ion conduction and gating properties

Squid optic nerve sodium channels were characterized in planar bilayers in the presence of batrachotoxin (BTX). The channel exhibits a conductance of 20 pS in symmetrical 200 mM NaCl and behaves as a sodium electrode. The single-channel conductance saturates with increasing the concentration of sodium and the channel conductance vs. sodium concentration relation is well described by a simple rectangular hyperbola. The apparent dissociation constant of the channel for sodium is 11 mM and the maximal conductance is 23 pS. The selectivity determined from reversal potentials obtained in mixed ionic conditions is Na+ approximately Li+ greater than K+ greater than Rb+ greater than Cs+. Calcium blocks the channel in a voltage-dependent manner. Analysis of single-channel membranes showed that the probability of being open (Po) vs. voltage relation is sigmoidal with a value of 0.5 between -90 and -100 mV. The fitting of Po requires at least two closed and one open state. The apparent gating charge required to move through the whole transmembrane voltage during the closed-open transition is four to five electronic charges per channel. Distribution of open and closed times are well described by single exponentials in most of the voltage range tested and mean open and mean closed times are voltage dependent. The number of charges associated with channel closing is 1.6 electronic charges per channel. Tetrodotoxin blocked the BTX-modified channel being the blockade favored by negative voltages. The apparent dissociation constant at zero potential is 16 nM. We concluded that sodium channels from the squid optic nerve are similar to other BTX-modified channels reconstituted in bilayers and to the BTX-modified sodium channel detected in the squid giant axon.     

Internal axial light conduction in the stems and roots of herbaceous plants

In order to reveal any roles played by stems and roots of herbaceous plants in responding to the surrounding light environment, the optical properties of the stem and root tissues of 18 herbaceous species were investigated. It was found that light was able to penetrate through to the interior of the stem and was then conducted towards the roots. Light conduction was carried out within the internodes and across the nodes of the stem, and then in the roots from the tap root to lateral roots. Light conduction in both the stem and root occurred in the vascular tissue, usually with fibres and vessels serving as the most efficient axial light conductors. The pith and cortex in many cases were also involved in axial light conduction. Investigation of the spectral properties of the conducted light made it clear that only the spectral region between 710 nm and 940 nm (i.e. far-red and near infra-red light) was the most efficiently conducted in both the stem and the root. It was also found that there were light gradients in the axial direction of the stem or root, and the light intensity generally exhibited a linear attenuation in accord with the distance of conduction. These results revealed that tissues of the stem and root are bathed in an internal light environment enriched in far-red light, which may be involved in phytochrome-mediated metabolic activities. Thus, it appears that light signals from above-ground directly contribute to the regulation of the growth and development of underground roots via an internal light-conducting system from the stem to the roots.     

Axolemmal and septal conduction in the impedance of the earthworm medial giant nerve fiber.

Ionic conduction in the axolemmal and septal membranes of the medial giant fiber (MGF) of the earthworm (EW) Lumbricus terrestris was assessed by impedance spectroscopy in the frequency range 2.5-1000 Hz. Impedance loci in the complex plane were described by two semi-circular arcs, one at a lower characteristic frequency (100 Hz) and the other at a higher frequency (500 Hz). The lower frequency arc had a chord resistance of 53 k omega and was not affected by membrane potential changes or ion channel blockers [tetrodotoxin (TTX), 3,4-diaminopyridine (3,4-DAP), 4-aminopyridine (4-AP), and tetraethylammonium (TEA)]. The higher frequency arc had a chord resistance of 274 k omega at resting potential, was voltage-dependent, and was affected by the addition of TTX, 3,4-DAP, 4-AP, and TEA to the physiological EW salines. When all four blockers were added to the bathing solution, the impedance locus was described by two voltage-independent arcs. Considering the effects of these and other (i.e., Cd and Ni) ion channel blockers, we conclude that: 1) the higher frequency locus reflects conduction by voltage-sensitive ion channels in the axolemmal membrane, which contains at least four ion channels selective for sodium, calcium, and potassium (delayed rectifier and calcium-dependent), and 2) the lower frequency locus reflects voltage-insensitive channels in the septal membrane, which separates adjacent MGFs.     

Frequency distribution of axon diameters in the left aortic nerve of the rat raised in space--Neurolab Program.

Introduction: To study development of the aortic baroreflex mechanisms under conditions of microgravity, we carried out the various experiments in the neonate rats aged 25 days raised in microgravity for 16 days (flight: FLT group) in Neurolab program (STS-90, space shuttle Columbia, launch date: Apr 17, '98. Some results of the experiments were already reported. The results of histological examination of the aortic nerve which is the afferent of the aortic baroreflex showed that the number of unmyelinated fibers in FLT was significantly less in than those in two control groups and there was no difference between FLT and each control group in the analysis of myelin. In the present paper, the frequency distribution of axon diameters of the left aortic nerves in FLT was compared to that in two ground control groups to examine the growth of the aortic nerve fibers in space. Methods: After breeding Sprague-Dawley rats for 16 days in the shuttle in space and in the animal center in the Kennedy space center, a total of 43 deeply anesthetized rats were perfused with 1% parahormaldehyde and 1% glutaraldehyde or 4% parahormaldehyde solution buffered at pH7.4 with 0.12 M phosphate solution. Concerning the control groups, one group was the asynchronous ground control (AGC) group in which the rats were housed in the same cages as those on the shuttle, and the other was the vivarium ground control (VIV) group in which the rats were housed in commercial cages. The cervical region of the left aortic nerve which is a branch of the vagus was cut off and stored in the same fixative as that used for perfusion, and postfixed in the solution of 1% OsO4, for 2 hours within 24 hours after the perfusion. The fixed specimens were embedded in epoxy resin blocks by the usual method for electron microscopy following dehydration. Electron microscopic montages of transverse sections of these nerve trunks were made from the five left aortic nerves in each group. The magnification of the montages was approximately 13400 times. The long and short axes (a and b) of the nerve fibers and the myelin thickness (T) were measured with a caliper and the axon diameters (R were calculated by following formula: R2=[(a-2T)2+(b-2T)2]/2.     

Effect of nitrogen addition on the decomposition and release of compounds from fine roots with different diameters: the importance of initial substrate chemistry

Plant and Soil - Initial substrate chemical characteristics are the most important factor in the regulation of fine root decomposition. However, it remains unclear how nitrogen (N) deposition...