Dorsal Root Fibers Research Articles

The synaptic excitation of Renshaw cells

An analysis has been made in spinal cats anaesthetised with pentobarbitone of the firing of Renshaw cells induced by stimulation of ventral roots or by volleys entering the spinal cord via dorsal root fibres. The response to maximal ventral root stimulation consisted of an early high frequency discharge which was blocked by dihydro-β-erythroidine (nicotinic receptors), a depression of spontaneous firing and a subsequent late firing which was specifically depressed by atropine (muscarinic receptors). The intervening depression or pause was associated with a non-specific depression of the sensitivity of these neurones to both acetylcholine and excitant amino acids. It is proposed that these responses may be the consequence of the action of acetylcholine released simultaneously from all of the axon collateral endings upon a Renshaw cell and that the late response may have no functional role. Other possibilities are discussed. The spontaneous activity of these neurones appears to involve muscarinic receptors. The activation of Renshaw cells by dorsal root volleys, which is independent of the prior discharge of motoneurones, does not involve cholinergic mechanisms.

Asphyxial potentials of spinal grey matter, and of ventral and dorsal roots.

1. Asphyxial potentials of short latency (from a few to about 10 sec) were recorded with mono- and bipolar electrodes from the cat's spinal cord. Monopolarly, a zone of maximum negativity was found somewhat dorsal of the central canal in the dorsal horn. With bipolar leads potentials of opposite polarity were observed in the dorsal and ventral horns. In the dorsal horn the more ventral electrode tip became negative with respect to the more dorsal one, in the ventral horn the more ventral tip became more positive. In the centre of the cord where the monopolar potential showed a maximum the bipolar potentials were small in either direction, or reversed during asphyxiation.2. These observations can be explained by the development of two independent dipoles of opposite polarity, located in the dorsal and ventral horn respectively, oriented with their negative poles towards the centre of the cord.3. In the ventral as well as in the dorsal root a negativity of a proximal electrode with respect to a more distal one developed during asphyxiation after the same latency as the asphyxial cord potentials. The asphyxial root potentials continued to grow during periods of asphyxiation as long as 30 min, and recovered promptly upon re-oxygenation.4. Ventral and dorsal root potentials were abolished by asphyxiation of the cord for a period of 60 min, 2 weeks previously. This procedure destroys practically all the neurones, but not the dorsal root fibres. The dorsal root potential, but not the ventral one, was abolished by extradural sectioning of the roots, 2 weeks previously.5. The asphyxial ventral and dorsal root potentials were interpreted as the result of depolarization of the intraspinal part of the motoneurones and primary afferent endings respectively, conducted electrotonically along the roots. The short latency of these potentials suggests that an early depolarization of motoneurone, and of the primary afferent end knobs occurs. The latter, which may have some relation to presynaptic inhibition, explains the early failure of synaptic conduction during acute asphyxiation.

Monosynaptic transmission from afferents of one segment to motoneurons of other segments in the spinal cord

Monosynaptic connections between collaterals of one dorsal root fiber and motoneurons of several adjacent segments were described in 1909. In mammals, however, monosynaptic reflex activity is strictly confined to the motoneurons which supply the muscle from where the stimulated afferents originate. Activation of motoneurons subserving a synergistic muscle occurs in the cat under special conditions only. In this paper successful attempts to establish effective monosynaptic transmission from afferents of one segment to motoneurons of other segments (polysegmental monosynaptic reflex connections) in the spinal cord of frogs are reported. Experiments were designed to demonstrate the monosynaptic character of reflexes recorded from several spinal nerves on stimulation of the tenth dorsal root. Total reflex latency, afferent and efferent conduction time, central reflex time and synaptic delay were measured by classical methods. Reflex latency and synaptic delay were found to be highly dependent on temperature, but were nevertheless comparable with the values for frogs reported in the literature. Effective monosynaptic transmission always occurred from dorsal root X to ipsilateral motoneurons of segment IX, and in some cases to motoneurons of segment VIII. Polysynaptic activity was sometimes observed in ipsilateral spinal nerve VIII (when monosynaptic response was absent) and III, as well as in the contralateral spinal nerve X.

PRESYNAPTIC INHIBITION FROM CONTRALATERAL CUTANEOUS AFFERENT FIBRES.

AbstractDepolarization of the cutaneous nerve terminals by volleys in any contralateral cutaneous nerve has been shown by three experimental procedures: by electrotonic spread of the depolarization along the dorsal root fibres; by intracellular recording from primary cutaneous afferents; and by excitability changes at the fibre terminations. These crossed presynaptic inhibitions were usually less powerful than those from the ipsilateral cutaneous nerves; and had a longer latency, 6 msec instead of 3; and a maximal effect at 30–50 msec instead of at 15–20 msec. Like in the ipsilateral cutaneous nerves, maximum effects with conditioning volleys in cutaneous fibres were obtained with volleys of about four times threshold.

PHARMACOLOGICAL STUDIES ON THE VASOMOTOR CENTER WITH EMPHASIS ON THE VASODILATOR NERVE.

There has been no sufficient investigation about the physiology of the vasomoter nerve, especially about the vasodilator nerve. Folkow 1> 2 > has illustrated that vasomotion is controlled only by sympathetic. Stricker 3> stated that the vasodilator nerve was contained in the dorsal root fibres. Bayliss •> 5> observed that the stimulation of the peripheral end of a cut sensory nerve resulted, in certain animals, in the vasodilatation in the area of skin supplied by the nerve and he investigated that this phenomenon resulted from the antidromic impulse conduction of sensory nerve. Langley 6> 7> dinied the existence of autonomic nerve in the dorsal root, and he also observed the vasodilatation with antidromic impulse conduction of sensory nerve. Since then many investigators s) 9> 10> 11 > 12 > 13> have studied on the same antidromic impulse conduction. Holton and Perry 14> 15> 16 > also observed this phenomenon and investigated on its transmitter. On the other hand, Kure et al.11> have reported the existence of not only sensory nerve fibres but parasympathetic fibres in the dorsal root of cervical and thoracicolumbar cord. Umemoto18> has demonstrated the existence of vasodilator nerve in the rabbit's ear by using a method established by Kanda et al.19> In the present investigation, the existence of active vasodilator nerve was observed in the dorsal root fibres by means of a new experimental method, and furthermore the possibility that the nerve is parasympathetic and cholinergic was proved.

FUSIMOTOR FUNCTION. V. REFLEX REINFORCEMENT UNDER FUSIMOTOR BLOCK IN NORMAL SUBJECTS.

In the previous study 1 we have been unable to confirm the finding of Sommer 2 and others 3,4 that the H reflex in man is not subject to reinforcement in the same manner as the tendon jerk. Nevertheless it remains possible that the efferents to muscle spindle stretch receptors are an essential link in the pathway for the Jendrassik phenomenon. In animals our present knowledge of the gamma efferent fibers to striated muscle has evolved from techniques where ventral root, dorsal root, or muscle nerve fibers are dissected and recorded separately. Such techniques are hardly applicable in man. The motor fibers to extrafusal muscle fibers as well as the afferents from muscle spindles and tendon receptors are the largestdiameter myelinated nerve fibers, largely in the alpha range, while the fusimotor fibers are predominantly in the small myelinated gamma group. This circumstance provides an approach to funcional study, for the

The Terminal Fields of Dorsal Root Fibers in the Lumbosacral Spinal Cord of the Cat, and the Dendritic Organization of the Motor Nuclei

Publisher Summary This chapter describes the pattern of degenerating dorsal root fibers, visualized by means of the Nauta-Laidlaw technique, in the spinal gray matter of the lumbosacral segments of the cat. The pattern, especially of the terminal fields, is related to the cytoarchitectonic laminae determined with the Nissl stain, and to data on synaptic areas revealed by the use of the Golgi method. These anatomical findings have been compared in detail with electrophysiological data on the areas of termination of various muscles and cutaneous nerve fibers, and the distribution of interneurons activated by specific types of peripheral stimulation. The chapter also describes the pattern of dendrites of various motor and interneuron nuclei of the lumbosacral segments by use of the Golgi-Cox technique. The relative independence and overlap of the dendritic territories of the motor nuclei are described in the chapter, and a possible relationship between these and the synaptic linkages formed by the large, sensory fibers of muscle nerves is indicated.

RECURRENT FACILITATION OF FROG MOTONEURONS.

ArticlesRECURRENT FACILITATION OF FROG MOTONEURONSKisou Kubota, and John M. BrookhartKisou Kubota, and John M. BrookhartPublished Online:01 Nov 1963https://doi.org/10.1152/jn.1963.26.6.877MoreSectionsPDF (2 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformationCited ByElectrophysiology of adult rat facial motoneurones: the effects of serotonin (5-HT) in a novel in vitro brainstem sliceJournal of Neuroscience Methods, Vol. 28, No. 1-2Excitatory postsynaptic currents in response to different synaptic inputs of frog spinal motoneuronsNeuroscience Research, Vol. 5, No. 3Effects of changes in osmolality on spinal cord activityExperimental Neurology, Vol. 68, No. 3Intracellular synaptic potentials of primate motor cortex neurons during voluntary movementBrain Research, Vol. 163, No. 1Dual effects of acetylcholine on the spontaneous activity in the isolated perfused spinal cord of the frogNeuropharmacology, Vol. 17, No. 1The pharmacology of the amphibian spinal cordProgress in Neurobiology, Vol. 11, No. 1Electrotonic coupling between frog spinal motoneurons. An electrophysiological and morphological studyBrain Research, Vol. 138, No. 2Dendritic responses of frog motoneurons produced by antidromic activationNeuroscience, Vol. 1, No. 6The morphology of motoneurons and dorsal root fibers in the frog's spinal cordBrain Research, Vol. 103, No. 2Presynaptic modulation of synaptic effectiveness of afferent and ventrolateral tract fibers in the frog spinal cordExperimental Neurology, Vol. 45, No. 3Light and electron microscopy of motoneurons and neuropile in the amphibian spinal cordBrain Research, Vol. 31, No. 1Acetylcholine depolarization of the dorsal root nerve terminals in the amphibian spinal cordInternational Journal of Neuropharmacology, Vol. 8, No. 4Inhibitory interaction between motoneurons of adjacent segments in the frog spinal cordExperimental Neurology, Vol. 23, No. 2Facilitatory and excitatory interaction between motoneurons of adjacent segments in the spinal cord of the frogExperimental Neurology, Vol. 20, No. 4Differences between monosynaptic and polysynaptic excitatory post-synaptic potentials of cat motoneurons during current injectionBrain Research, Vol. 3, No. 4Rubrally evoked unitary potentials in ventro-lateral thalamus of catElectroencephalography and Clinical Neurophysiology, Vol. 21, No. 3 More from this issue > Volume 26Issue 6November 1963Pages 877-893 https://doi.org/10.1152/jn.1963.26.6.877PubMed14084164History Published online 1 November 1963 Published in print 1 November 1963 Metrics

Extracellular Single Fibre Recording Technique for Peripheral Nerves without Section of Nerve or Incision of Perineurium

Two main techniques are at present in use to obtain electrophysiological data from single afferent fibres in mammalian and reptilian nerves. (1) The nerve trunk is severed and successively fractionated until the stage is reached at which a fine strand (or strands) gives a unit response. This method suffers from the disadvantage that the nerve trunk is severely damaged and only a few fibres can be investigated in each experiment—an inevitably non-representative sample of the nerve fibre (or receptor) spectrum. (2) A micro-electrode is inserted into the dorsal root or its ganglion, from which extra- or intra-cellular single unit recordings are made. In this case a representative sample of all dorsal root fibres can be taken, but it is impossible to obtain a true sample of the fibres supplying a particular area of skin. Several isolated reports also describe extracellular1–5 and intra-cellular6 records made with micro-electrodes inserted blindly into nerve trunks, but no generally applicable technique has yet emerged.

The responses of the primary and secondary endings of muscle spindles with intact motor innervation during applied stretch.

The effects of small stretches applied at constant velocities, varying from 8 to 100 mm/sec. on the muscle spindle endings of the cat's soleus were recorded in dorsal root fibres of decerebrate animals with intact motor roots. The primary endings showed a greatly increased and well‐sustained discharge rate during stretch application. They were particularly sensitive to the velocity of stretch and the rates reached were considerably higher than those recorded during the subsequent maintained extensioin of the muscle. The endings often showed some discharge in release of stretch. The secondary endings showed a wide range of thresholds for stretch. The increase of discharge rate during stretch application was very moderate, and might not exceed the steady rate during maintained stretch. On release of stretch impulses were frequently seen. These differences in the behaviour of the two kinds of ending to stretch are considered in relation to the histological structure of a muscle spindle.

The distribution of dorsal root fibres on motor cells in the lumbosacral spinal cord of the cat, and the site of excitatory and inhibitory terminals in monosynaptic pathways.

The degeneration of cut, lumbosacral dorsal roots was traced by means of a silver method to the various sites of termination in the spinal cord of the cat. Particular attention was given to the pattern and distribution of dorsal root fibres terminating on motor cells. An attempt was made to correlate the synaptic organization of these monosynaptic pathways with the presence and distribution of short latency, direct excitation and inhibition (measured on the ventral roots) in comparable segments of the cord. Short latency excitation was found in the lower sacral segments to be correlated with dorsal root fibres terminating on cell bodies and dendrites of the motoneurons. Direct inhibition, largely or entirely uncontaminated by excitation, was identified in lower lumbar and upper and lower sacral segments. In these sites the terminal degeneration of the responsible dorsal root was limited to the dendrites and did not reach the cell bodies of the motoneurons. This consistent correlation between the spatial distribution of direct inhibition and terminals on motor dendrites suggests that this inhibition is monosynaptically and dendritically mediated, at least in part. Certain other interpretations are considered and relevant evidence obtained from intracellular microelectrodes placed in lower sacral motoneurones which were excited by ipsilateral and inhibited by contralateral dorsal root stimulation is discussed. Here, uncontaminated, monosynaptic excitation could be correlated with synaptic terminals on both cell bodies and dendrites of motoneurones.

The relation of antidromic impulses in the dorsal root fibres to the dorsal root potential in the frog.

The Journal of PhysiologyVolume 142, Issue 2 p. 343-359 ArticleFree Access The relation of antidromic impulses in the dorsal root fibres to the dorsal root potential in the frog R. T. Tregear, R. T. TregearSearch for more papers by this author R. T. Tregear, R. T. TregearSearch for more papers by this author First published: 14 July 1958 https://doi.org/10.1113/jphysiol.1958.sp006021Citations: 8AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume142, Issue2July 14, 1958Pages 343-359 RelatedInformation

Variations in the Spinothalamic Tract in Man

T UlS is a report of two cases that illustrate the variability of the pain pathways in the spinal cord of some individuals. Standard textbooks of neuroanatomy 3,5,6 give descriptions and present diagrams indicating that the pain pathway in the spinal cord in man is a discrete bundle of fibers, known as the spinothalamic tract, located in the anterolateral funiculus and consisting of afferent neurons of the second order. Finely myelinated or unmyelinated dorsal root fibers that serve as pain conductors terminate in the gray matter almost at once after entering the cord. From cells in the posterior column of the gray matter fibers arise which, in man, cross to the opposite side of the cord in the anterior white commissure and ascend in the lateral spinothalamic tract to end in the thalamus. Unilateral section of this tract produces complete loss of pain and temperature sensations on the opposite side of the body, extending upward to a level one segment below the level of the lesion, because of the oblique crossing of the spinothalamic fibers. These and similar statements are the result of piecing together fragmentary bits of clinical and experimental facts obtained over a period of many years. Unfortunately, our knowledge of the pain pathways in the spinal cord is still far from exact and the dogmatic statements and diagrams to be found in most textbooks cannot be substantiated by clinical observations. White and Sweet 9 in their extensive monograph on pain have reviewed the knowledge accumulated to date on the pain pathways in man.

Regeneration in the mammalian peripheral nervous system.

Regeneration in the mammalian peripheral nervous system.

Physiology of spinal cord, nerve root and peripheral nerve compression.

The reversible conduction block produced by maintained mechanical pressure around small segments of spinal cord, nerve root or peripheral nerve (dog) is due to mechanical deformation of the neuronal tissue and not to lack of O2. The compressed segment, although ischemic, is not anoxic; O2 from adjacent nonischemic tissue reaches it, presumably by diffusion. The entire pattern of modification of neuronal responses by compression and the postdecompression recovery pattern are distinctly different from the patterns observed during anoxia and recovery from the latter, indicating the difference in mechanisms by which mechanical deformation and O2 lack block conduction. The largest fibers in dorsal columns, roots and peripheral nerves are most susceptible to pressure and the smallest ones are relatively most resistant. Secondary neurons are less vulnerable than the primary afferent ones to light and moderate, but suprasystolic, circumferential spinal cord pressure. All components of the composite spinal cord potential are blocked at about the same time by larger compressive forces. Anoxia, on the other hand, always inactivates secondary neurons before dorsal column fibers and blocks smaller A fibers in peripheral nerves before the larger ones. The latency for complete blocking in each neuronal structure is specific and irreducible in the case of anoxia, whereas in compression it varies over a wide range, depending upon the magnitude of the compressive force.

Intracellular Slow Potential of Dorsal Root Fibers

Intracellular potential changes associated with excitation were recorded from a dorsal root fiber in the funiculus of an isolated spinal cord of a bullfrog or toad. The spike potential of a dorsal root fiber was observed to follow the slow positive (inside) potential. This slow potential was recorded without a spike potential by applying stimuli sub-threshold for the impaled nerve fiber. The size of the slow potential increased gradually with increased strength of dorsal root stimuli, but with no accompanying prolongation of its declining phase. Dorsal root reflex discharges were occasionally superimposed on this slow potential. No summation of the slow potential resulted from two successive supramaximal stimuli. The slow potential induced by a test stimulus showed considerable occlusion even half a second after the conditioning stimulus. The slow positive (inside) potential was also recorded intracellularly by applying antidromic ventral root stimuli. The slow potential recorded here proved to be generated intrinsically by the depolarization of the surface membrane of the impaled nerve fiber. Active depolarization of the membrane of the terminal endings of the dorsal root fiber may spread out electrotonically along the membrane of the nerve fiber and provide this slow potential. The membrane of terminal endings of a single dorsal root fiber may be depolarized secondarily by the activity of other dorsal root fibers or secondary neurons. The relationship between positive deflection of the cord dorsum potential, the dorsal root potential, and the slow potential recorded intracellularly in this experiment has been analyzed.

On Motor and Sensory Nerve Systems in in Lumber Cord in Man

Motor cells exist in the lumbar cord not only in cornu ventrale, but also in pars intermedia and cornu dorsale, and they are clearly distinguishable from the vegetative and sensory cells, through that they are very large in size, show a concave contour and are provided with many stout processes, giving them an appearance of rugged virility. Motor cells incornu ventrale are especially typical in their form. They have usually one long process each, which is thick and strongly stainable, but seeing that the total number of long processes is. larger than that of motor cells on the same cross section, it may be surmised that some cells send out two long processes each, or some of the processes branch out in 2 rami. The short processes number 5 to 7 per cell, are stout but somewhat weakly staining, and after a rather long course, mostly branch out in numerous rami and apparently end freely. Frequently, true anastomosis of short processes is observed between both motor cells. Motor cells in cornu ventrale may be divided into the medial and lateral groups. The cells in the former group are smaller both in number and size than the cells in the latter group. The former can be divided again into the ventral and dorsal subgroups. The dorsal subgroup is especially poor in development. The lateral group, on the other hand, is very well developed, and can be divided into the ventral, middle and dorsal subgroups, and especially in the lumbar swelling the number of motor cells increases, so that they may be justly subdivided further. Motor cells in pars intermedia are arranged sporadically, with prevalence in its medial parts, where 3 cells are usually seen on one cross section. In shape, they resemble the small motor cells in the medial group in cornu ventrale. Motor cells in cornu dorsale are seen in its lateral, medial and basal parts, where 1 or 2 each are found in the respective areas. They are also small in size. Motor cells in cornu ventrale, together with their long and. short processes, are found buried in a plexus of incoming nerve fibres. Of the plexus fibres, the motor fibres penetrate into the motor cell group chiefly through the tractus corticospinalis lateralis, the reflex sensory fibres through the entrance zone of dorsal root fibres, and the minute vegetative fibres from the circumference of the cell group. These fibres are all thinner than the short processes of motor cells. The incoming motor and sensory fibres are both better stainable and stouter than the vegetative fibres, so that the distinction between them is readily made. The end formation of these incoming fibres toward the motor cells is neither represented by pericellular reticular formation nor by annular or pin-head shaped corpuscles, as has been held hitherto, but by an intricate criss-cross run in every direction of the incoming fibres. They seem to end in simple branched endings around the short processes, rather than around the cell bodies. The transmission of stimuli seems to be accomplished by the following process. First, the stimuli carried by the incoming fibres excite the glial cells apparently of endocrinous nature, whose secretion secondarily excites the motor cells, in particular their short processes. The excitement ofthe motor cells is then transmitted by the way of the long processes to the periphery. Sensory cells in the lumbar cord stand midway between the motor and vegetative cells in size, and are morphologically readily distinguishablee from the latter two. Only few of them are rounded and feminine in appearance as those in the sensory nuclei in the brain stem, the majority being either spindleshaped or triangular in form. Their short processess are strongly stainable and stout, but stand behind those of motor cells both in number and length. They apparently end without branching or in a few branches, always sharply. These sensory cells are different in size and shape according to their localisation.

Role of gelatinous substance of spinal cord in conduction of pain.

THE PATHS of the dorsal root fibers into Lissauer's zone and the dorsal funiculus of the spinal cord are well established. The manner of the termination of these fibers within the gray matter of the spinal cord and the pattern of the connecting neurons are not so well understood. This is particularly true of the human spinal cord. Although this problem has been studied by Ramon y Cajal, 1 Ranson, 2 and others, there are still wide gaps in our knowledge of these connections. The majority of the studies on this subject have been based on the lower vertebrate forms, such as the chick and cat, with few observations on the higher mammals and man. Since the early literature on this subject has been reviewed by Barker 3 ; Ranson 4 ; Massazza 5 ; Bok, 6 and Ariens Kappers, Huber, and Crosby, 7 only the more recent investigations will be discussed. MATERIALS

Do dorsal root fibers convey centrally induced vasodilator impulses?

Do dorsal root fibers convey centrally induced vasodilator impulses?

PROJECTION OF DERMATOMES ON THE SUBSTANTIA GELATINOSA

IT IS known that dorsal root neurons conducting different types of sensation run a different course after entering the spinal cord and terminate in different nuclei. Knowledge of the exact course of pathways for the several modalities of sensation, however, is still fragmentary. A wide gap remains especially between the primary sensory root neurons and the better known longer central pathways containing the secondary sensory neurons. It is not known exactly on which ganglion cells the dorsal root fibers subserving different functions terminate and whether this second group of ganglion cells contribute fibers to the long ascending tracts or internuncial ganglion cells with a short axon deliver the sensory impulses to a third group of neurons, with a longer axon. Especially defective is information concerning the exact termination of neurons within the spinal cord and the brain stem which belong to receptors situated in different parts of the sensory segment,