Motoneuron Somata Research Articles

Cholinergic enzyme activity in neurons of the developing anuran spinal cord.

Cholinergic enzyme activity was investigated over the course of spinal cord development from early larval (tadpole) stages to adult life in bullfrogs (Rana catesbeiana). Acetylcholinesterase (AChE) activity examined histochemically in spinal neurons and AChE and choline acetyltransferase (ChAT) activities were measured biochemically in axons of developing hindlimb motoneurons. At early larval stages, only spinal neurons born during embryonic life (primary neurons) showed histochemical evidence of AChE activity. Hindlimb motoneuron somata did not show AChE activity until mid-larval stages. AChE and ChAT activities were found in hindlimb motoneuron axons at the earliest stages examined, when the hindlimb consists of a small bud of undifferentiated mesenchyme. Activities of both enzymes show steady increases over the course of development until climax, when activities maintain a plateau until metamorphosis is complete. Total activities of both enzymes increase as the adult frog grows, although ChAT activity shows a much greater proportional increase than AChE activity.

The development of the spinal motor column in relation to the myotomal muscle fibers in the zebrafish (Brachydanio rerio)

The neuromuscular system in the trunk of larval and adult zebrafishes was studied by means of light and electronmicroscopical methods. Spinal motoneurons were identified with the horseradish peroxidase retrograde transport method. We correlated the differentiation and growth of the myotomal muscle with the number of motoneurons per spinal cord segment and the size of the motoneuron somata. The adult number of motoneurons is reached in an early larval stage, before the muscle fiber type differentiation in the myotomes is completed. The mean motoneuron size does not bear a clear correlation with the size of the myotomal muscle. In adult zebrafishes we could distinguish the motoneurons which innervate the superficial slow red and the deep fast white muscle fibers on the basis of soma size and position in the motor column. The motoneurons of the red muscle part are small; they are located in the ventrolateral part of the motor column. The motoneurons of the deep fast white fibers are large; they lie near the central canal.

Location and distribution of tracheosyringeal motorneuron somata in the fowl.

Injection of horseradish peroxidase solution (HRP) into the tracheosyringeal musculature and tongue of the domestic chick labeled their motorneuron somata in the medulla. Those of tracheosyringeal motor neurons occupied the caudal portions of the nucleus nervi hypoglossi (n. XII), whereas those for motor neurons supplying the tongue occupied the rostral part. The rostrocaudal representations of tracheolateralis, sternotrachealis, and ypsilotrachealis muscles were roughly mapped by the rostrocaudal distribution of labeled somata in n. XII. Except for sparse labeling found in the caudal part of the dorsal vagal nucleus of a few animals, no labeled cells were found outside of n. XII. Most tracheosyringeal injections labeled contralateral n. XII, but section of the contralateral tracheosyringeal nerve high on the neck prior to HRP injection abolished this labeling.

Axotomy increases excitability in crayfish fast flexor motoneuron somata

Somata of crayfish fast flexor motoneurons whose axons had been cut several days previously were found to display much greater electrical excitability than intact contralateral controls. This increased excitability was evidenced by the consistent appearance in intracellular (soma) recordings of overshooting action potentials during antidromic stimulation, in contrast to the decremented passive antidromic potentials usually seen in control cells. The excitability increase was apparently shared by all fast flexor motoneurons whose axons pass out through the severed (main third) root (arising from three major clusters of somata in two ganglia); it also occurred when only one of the first two major branches of the root was cut. These findings corroborate and extend similar results from crayfish and other arthropods, and may find application in the study of central motoneuron circuitry.

The crayfish second antennae. II—motoneuron structure as revealed by cobalt chloride backfilling

1. 1. The location of both the crayfish antennal motoneuron somata, and dendrites were determined using a cobalt chloride backfilling technique. The cobalt technique is especially useful in analysing unstructured neuropile. 2. 2. The antennal motoneuron somata (AMS) occur in several distinct regions of the brain. A majority of the somata belong to the angular cell group (Helm, 1928) located posterio-laterally in the tritocerebrum. Another prominent group of AMS form an extension of Helm's superior, lateral cell group. 3. 3. Most of these cells occur over the posterio-medial portion of the accessory neuropile, with a few cells located along the medial edge of the accessory neuropile. One cell body is located between the circumesophageal connectives. 4. 4. All the motoneurons are unipolar, with the somata being located ipsilaterally and dorsally in the brain. Most of the somata are 40 μm long by 30 μm wide. 5. 5. The antennal motoneuron dendrites form a dorsal, diffuse motoneuron neuropile that overlies the medial portion of the antennal neuropile and the lateral part of the tegumentary neuropile. 6. 6. The dendritic structure of individual motoneurons is highly complex. The motoneurons exhibit profuse branching, with primary, secondary and higher order branches being easily distinguished. 7. 7. In addition, there are alternating thick and thin diameter segments along the larger individual dendritic branches. 8. 8. The potential effects of this structural complexity on integration are discussed.

Direct observations on the contacts made between Ia afferent fibres and alpha-motoneurones in the cat's lumbosacral spinal cord.

1. The enzyme horseradish peroxidase was injected into identified lumbosacral alpha-motoneurones and Group Ia afferent fibres in cats anaesthetized with chloralose and paralysed with gallamine triethiodide. Subsequent histological examination allowed the determination of (a) the extent of the motoneuronal dendritic trees, (b) the number and location of Ia synapses upon the motoneurones. 2. alpha-motoneurones had seven to eighteen primary dendrites and each produced daughter branches up to the fourth to the sixth order. At dendritic bifurcations Rall's 3/2 Power Law was obeyed. There was little or no dendritic tapering up to about 800 micrometers from the soma. Beyond this distance, however, there was considerable tapering. 3. Horseradish peroxidase injections revealed that motoneuronal dendrites are much longer than previously thought. Individual dendrites could be traced for up to 1600 micrometers from the soma and dendritic trees were usually 2-3 mm from tip to tip. Nearly all the motoneurones had dendrites that entered the white matter of the cord. Dendrites could also reach as far dorsally as laminae V and VI. 4. Ia synapses upon motoneuronal somata were examined in cords counterstained with cresyl violet or methylene green. About 10% of Ia boutons in lamina IX were on somata and each Ia collateral terminated on 3.66 motoneuronal somata or the most proximal (30 micrometer) dendrites, with on average about two contacts per motoneurone. 5. Ten Ia afferent fibre-motoneurone pairs were injected with horseradish peroxidase. The following conclusions were drawn: (i) only one collateral of any given Ia axon makes contact with a motoneurone even though other collaterals from the same axon might pass through the dendritic tree, (ii) usually all contacts made between a Ia fibre and a motoneurone are at about the same geometrical distance from the soma, even when on different dendrites, (iii) between two and five contacts are made upon the dendritic tree (average 3.4) at distances of between 20 and 820 micrometers from the soma. 6. The results are discussed in relation to previous anatomical and electrophysiological work.

Interactions among lumbar motoneurons on opposite sides of the frog spinal cord: morphological and electrophysiological studies.

Light and electron microscopy have been used to study the projections of dendrites from motoneurons in lumbar segments of the spinal cord of the frog following administration of horseradish peroxidase to cut ventral roots. Processes originating from motoneurons crossed to the opposite side of the spinal cord via the anterior commissure and made contact with dendrites and motoneuronal somata. Typically, in segments 6 to 8 the crossing dendrites showed irregular enlargements in diameter. Electrophysiological recordings were obtained both extracellularly from ventral roots and intracellularly from motoneuronal somata. In Ringer's solution containing 1 mM calcium, stimulation of a lumbar ventral root, elicited population responses with early and late components in the ventral root of the opposite side of the same segment. Only the early, short latency component remained in calcium-deficient Ringer's solution. In calcium-containing Ringer's solution, intracellular recording from an antidromically activated motoneuron showed an action potential with a short latency; this response was followed by excitatory postsynaptic potentials (epsps) from which action potentials could be generated. Contralateral ventral root stimulation also elicited in the same motoneuron a short latency action potential that was rarely followed by epsps. The short latency responses, that were elicited by stimulation of ventral roots of either side persisted in calcium-deficient Ringer's solution, but the epsps were abolished. Contralaterally elicited short latency responses were eliminated by section of the anterior commissure. We believe that electrically mediated crossed interactions among lumbar motoneurons may serve as a means of coordinating muscle groups of opposite sides that are used in movements that require bilateral synchronization, such as jumping and swimming.

Localization and morphology of cat retractor bulbi motoneurons.

1. Motoneurons innervating the cat retractor bulbi muscle have been identified by retrograde axonal transport of horseradish peroxidase (HRP). Following injections of the four slips of the retractor bulbi muscle, labeled motoneurons were found in the abducens nucleus overlapping the distribution of lateral rectus motoneurons and in the oculomotor nucleus partially overlapping the distribution of medial rectus motoneurons. Retractor bulbi motoneurons also were found in the accessory abducens nucleus situated ventral and lateral to the abducens nucleus. 2. Retractor bulbi motoneurons varied considerably in shape and size, but in all instances contained similar cytoplasmic organelles. Quantitative analyses of mean soma diameter indicated that the average size of retractor bulbi motoneurons was larger than the average size of lateral rectus and medial rectus motoneurons. 3. Retractor bulbi motoneurons in the accessory abducens nucleus were identified electrophysically and stained by intracellular injection of HRP. Neuronal reconstructions demonstrated a dorsomedial axonal trajectory directed toward the abducens nucleus and elongated dendritic fields oriented in a dorsomedial-ventrolateral axis. Another major dendritic extension was directed toward the magnocellular division of the spinal trigeminal nucleus, a major source of excitatory input to these motoneurons. 4. Quantitative analyses of synaptic density indicated that the somata of retractor bulbi motoneurons were contacted by significantly fewer synaptic endings than the somata of motoneurons in the abducens nucleus. Retractor bulbi motoneurons in the abducens nucleus exhibited variations in synaptic density that were similar to the densities on lateral rectus motoneurons. 5. Given the morphological differences in location, size, and somadendritic extent between motoneurons in the accessory abducens, abducens and oculomotor nuclei, it is suggested that such features reflect functional differences between the motoneurons with respect to fiber composition of the muscles they innervate, and subsequently to the role each muscle plays in eye movement. 6. Since the morphological features of retractor bulbi motoneurons in the accessory abducens nucleus are quite different from those in either the abducens or oculomotor nuclei, it appears that each motoneuronal population may perform unique oculomotor functions.

Mixed (chemical and electrical) synapses on frog spinal motoneurons.

Freeze-fracture replicas and ultrathin sections were used to characterize the gap junctions on the somata and large dendrites of frog motoneurons found earlier by Sonnhof et al. (1977). In freeze-fracture replicas one of the specific features of these relatively frequent gap junctions is the presence of circular regions of non-junctional membrane ("fenestrae") within areas of typical gap junction appearance displaying P-face particles or E-face pits. Such "fenestrated" gap junctions are mostly associated with membrane specializations indicative of the active zone of a chemical synapse (including vesicle attachment sites in non anaesthetized animals) to constitute mixed synapses. These findings could be verified in ultrathin sections, which revealed that the vesicles of the chemical component of the mixed synapses were spherical and agranular. Our results suggest that the mixed synapses are predominantly axo-somatic and axo-dendritic. The existence of dendro-dendritic gap junctions in the ventral horn region as described by Sotelo and Taxi (1970) was verified in ultrathin sections; they were rare, solely electrotonic in character, and probably represent the morphological basis for the VR-EPSP (Katz and Miledi, 1963; Kubota and Brookhart, 1963), i.e. electrotonic coupling between motoneurons of different spinal segments (Washizu, 1960). Electrotonic coupling can also be demonstrated between motoneurons and afferent fibers of the dorsal root and the lateral column. Electrotonic potentials recorded within motoneurons during electrical stimulation of dorsal root or lateral column precede the chemical postsynaptic potentials; after Mn2+-blockade of chemical synaptic transmission, the electrotonic component persists. Some fibers of these afferent pathways are therefore assumed to act monosynaptic on the motoneuron via mixed axo-somatic and axo-dendritic synapses.

Motoneuron interactions in crayfish claw control: Evidence from intracellular recording

1. Intracellular recordings from crayfish claw motoneuron somata revealed synaptic potentials concurrent with spikes in other specific claw motoneurons when the latter were activated by: a) sensory stimulation; b) antidromic axon stimulation; or c) current injection. 2. These synaptic potentials were studied mainly by signal-averaging one cell's recorded response to antidromic stimulation of another. The interactions thus revealed were: a) central inhibition of the opener excitor (OE) by the opener inhibitor (OI); b) excitation of OI by OE; and c) mutual excitation among all of OI, SCE, and FCE (the slow and fast closer excitors). 3. Central latencies of the connecting pathways lie between 0.5 and 2.0 ms, suggesting monosynaptic cross-connections among these motoneurons. 4. These conclusions are consistent both with earlier data from spike-train analysis (Wiens and Gerstein, 1975) and with the requirements of the control system.

Electrotonic coupling between frog spinal motoneurons. An electrophysiological and morphological study

Summary In motoneurons of the isolated spinal cord of frogs ( Rana esculenta ) short latency depolarizations (‘VR-EPSPs’), produced by stimulation of different ventral roots, were investigated. During increased extracellular magnesium ion concentration, postsynaptic potentials were reversibly suppressed. In addition, the antidromic spike invasion of the somatodendritic membrane of motoneurons was blocked because of membrane hyperpolarization and the subsequent increment in threshold depolarization. Consequently, the antidromic focal potential diminished in amplitude and the VR-EPSPs disappeared to a similar extent. At the same time, the neuron input resistance increased and the extracellular concentration of potassium ions, [K + ] e , decreased below control levels. However, antidromic spikes again invaded the somatodendritic membrane of motoneurons, despite the maintained action of magnesium ions, whenever the bulk of motoneurons were depolarized by increasing [K + ] e . As a result, the VR-EPSPs reappeared, whereas all chemical PSPs remained blocked. PSPs were also blocked reversibly by application of manganese ions. No effects were seen either in [K + ] e , membrane potential, passive membrane properties, or in antidromic spike invasion of motoneurons, and VR-EPSPs remained unchanged. On the basis of these results, it was concluded that the VR-EPSP is electronically propagated between different motoneurons. Electron microscopic inspection of the membranes of frog motoneuron somata and dendrites, as exposed by freeze-fracturing, revealed numerous membrane specializations of gap junction character. As a typical feature of these gap junctions, regions of densely packed particles surrounded small particle free regions. As a consequence of these findings the term VR-EPSP, as employed by Kubota and Brookhart, should be used with some reservation. If the proposed interpretation of the signal should prove to be correct, the designation ‘ventral root electrotonic junction potential’ (VR-EJP) would, in our opinion, be more appropriate.

An electron microscope study of motoneurones and interneurones in the cat abducens nucleus identified by retrograde intraaxonal transport of horseradish peroxidase

AbstractAbducens motoneurones innervating the lateral rectus muscle and abducens interneurones projecting to the oculomotor nucleus have been studied in the cat by light and electron microscopy following labelling with horseradish peroxidase. Motoneurones ranged from 15–60 μm in diameter and typically contained circular nuclei with smooth or slightly irregular nuclear membranes and extensive cisternae of granular endoplasmic reticulum. Interneurones ranged from 25–50 μm in diameter and comprised two cytologically distinct cell types. One type was fusiform in profile and contained nuclei with fluted or deeply invaginated nuclear membranes and poorly developed granular endoplasmic reticulum. The other interneurone type resembled the motoneurones cytologically, having multipolar or circular profiles, smooth or slightly irregular nuclear membranes, and well developed cisternae of granular endoplasmic reticulum.The densities with which boutons were distributed on the somata of motoneurones and interneurones were similar, as were the ratios of boutons containing spheroidal or flattened synaptic vesicles. Motoneurones varied significantly in the density with which boutons were distributed on their somata, and had greater densities on their dendrites than on their somata. Density was, furthermore, not correlated with motoneurone soma diameter. The proportion of spheroidal or flattened vesicle boutons on the somata of motoneurones was almost equal, with comparatively little variation between individual motoneurones. Motoneurone dendrites, however, with the exception of lateral dendrites, had a relatively higher proportion of boutons containing spheroidal synaptic vesicles. The lateral dendrites, which extend toward the medial vestibular nucleus, a known source of inhibitory afferents to the abducens motoneurones, had a higher proportion of boutons containing flattened vesicles.The results indicate that abducens motoneurones and interneurones cannot be distinguished by any simple morphological criteria. The somadendritic distribution of boutons on motoneurones appears to be governed by certain broad rules.

Retrograde axonal transport of horseradish peroxidase for determining motor projection patterns to the developing limb in Xenopus

Horseradish peroxidase (HRP) injected into developing limb buds of Xenopus laevis tadpoles is carried by retrograde axonal transport to the somata of motoneurones in the ventral horn. Small injection of 10% HRP were found to remain well localised to specified sites in the limb bud. Two types of labelled cells were found: diffusely labelled and granular labelled. Diffusely labelled cells result from axonal damage in the presence of HRP. Granular labelled cells result only from uptake of HRP from the region of the axon endings. No gradular uptake was found from axon shafts. It is concluded that the distribution of granular labelled cells accurately reflects the region of the ventral horn projecting to the site of injection in the limb.

Ventral root elicited depression of the dorsal root evoked response in frog motoneurons.

Recurrent inhibition of the dorsal root (DR) evoked responses of frog motoneurons was studied by intracellular recording. Monosynaptic and early polysynaptic action potentials, as well as compound EPSPs initiated by a DR volley in motoneurons were depressed by an antidromic volley in motor axons. The depression had about 10 msec latency, reached maximum at 20-30 msec, and was maintained for 80 msec. The depression was associated with a slow, negative dorsal root potential (VR-DRP) of similar time course. No sign of recurrent postsynaptic inhibition of the motoneuron somata was found. Decrease in excitability of the motoneurons was also observed during the afterhyperpolarization (AHP) associated with either antidromic or direct spikes in the motoneurons. This excitability decrease was detectable at the time of recurrent depression of the DR-evoked responses. The data are explained by the assumption that two mechanisms are involved in the recurrent depression of the DR-evoked responses: the excitability decrease during the AHP in the motoneurons themselves, and the inhibition transmitted by a recurrent pathway which may depress the DR inputs to motoneurons presynaptically.

Ventral horn synaptology in the rat

The synaptology of the normal ventral horn of the rat was studied. Presynaptic boutons were classified as S (Spherical vesicles), F (flattened vesicles), and G (predominance of 700-1200 A granular vesicles). In addition, Cf, Cs, M, and T synaptic complexes were defined and quantitated. Synaptology was studied on alpha-motoneuron somata, alpha-motoneuron primary dendrites, peripheral dendrites and interneuron somata. In addition, organelles were quantified for the pre- and postsynaptic members of the synaptic complex. All counts were made on coded material and these data were analyzed statistically. Motoneuron somata had significantly more (P less than 0.01) F (58%) than S (33%) boutons. This was also the case for the motoneuron primary dendrite (P less than 0.01; F, 61%; S, 37%). The small dendrites had more (P less than 0.05) S (56%) than F (44%) boutons. More Cf bulbs (P less than 0.01) were found on motoneuron somata (9%) than on motoneuron primary dendrites (2%) or interneruon somata (3%). The C complex presynaptic bouton contained spherical (Cs) or flattened (Cf) synaptic vesicles which were attributed to the fixation employed. Cf bulbs were not observed on small dendrites. G bulbs were observed (less than 1%) only on small dendrites M bulbs were not observed on any postsynaptic structure. The boutons of the motoneuron primary dendrites (15% of total afferents) and peripheral dendrites (14% of total afferents) were frequently branched whereas there was significantly (P less than 0.01) less branching of boutons on motoneuron and interneuron somata. Small postsynaptic subsurface cisterns were associated with boutons of both the S and F type on all structures. In addition, these cisterns were observed in motoneuron somata (4%) and interneuron somata (2%) without an accompanying bouton. C postsynaptic organelles were observed in motoneuron somata (3%) and primary dendrites (1%) with an overlying neuroglial cell process and no presynaptic bouton. The synaptology of the rat ventral horn is comparable to that in the cat and monkey. However, M (R) and P bulbs were not observed in the rat. This could be due to the sampling method which indicated that synapses with less than 1% occurrence fall at the level of statistical resolution in quantitative electron microscopy. The presence of postsynaptic specialization usually associated with presynaptic boutons with no presynaptic component may be a reflection of the dynamics of normal bouton renewal in the rat ventral horn.

The morphology of motoneurons and dorsal root fibers in the frog's spinal cord

Ventral and dorsal roots of the frog's spinal cord were filled with cobaltous chloride, and the resulting cobaltous sulfide precipitate, following treatment with H2S-buffer solutions, was intensified with physical developers. A ventromedial and a dorsolateral motoneuron group could be discerned in the ventral horn. The ventromedial, motoneurons gave origin to a strong dendrite crossing to the contralateral side. In the dendritic arborization pattern of the dorsolateral motoneurons a dorsomedial, a dorsal and a lateral dendritic array were distinguished. They were regarded as representing three different input channels to the motoneurons. Intramedullary branching of motor axons and recurrent axon collaterals were never observed. The dorsal root could be divided into a medial and lateral division carrying small and large caliber fibers, respectively. The end-branches of the small caliber fibers were seen to terminate in the substantia gelatinosa. Fine collaterals of the large caliber fibers also terminated in the substantia gelatinosa; coarser collaterals penetrated deeper and terminated in a triangular-shaped area in the base of the dorsal horn and in the intermediate gray matter. From this area a tail was followed into the ventral horn and several synapses were seen on the proximal dendrites and on the somata of motoneurons. A few dorsal root fibers could be seen crossing to the contralateral side.

Immunocytochemical localization of glutamate decarboxylase in rat spinal cord.

The GABA synthesizing enzyme, glutamate decarboxylase (GAD), has been localized by light and electron microscopy in the rat lumbosacral spinal cord using a peroxidase-labeling antibody technique. The light microscopic localization shows heavy, punctate reaction product for GAD in the dorsal horn laminae I-III. Moderately heavy reaction product is also seen in the deeper dorsal horn laminae IV-VI, the medial aspect of the intermediate gray (lamina VII) and the region around the central canal (lamina X). A moderately light concentration of GAD reaction product is observed in the ventral horn, and punctate deposits of reaction product also are seen on motoneuron cell bodies. The punctate distribution of reaction product for GAD in both ventral and dorsal horns, as visualized by light microscopy, corresponds to GAD-containing synaptic terminals seen by electron microscopy in comparable regions of the spinal gray. Many more GAD-positive terminals are observed in dorsal horn laminae I-III than in deeper laminae IV-VI. GAD-containing terminals in the dorsal horn are presynpatic to dendrites and cell bodies. Gad-containing terminals presynaptic to other axon terminals are observed also, and they are more numerous in laminae II and III. In the ventral horn motor nuclei, GAD-positive knobs are presynaptic to large and small dendrites and motoneuror cell bodies. In addition, small GAD-containing terminals also are presynaptic to larger axonal terminals which are in turn presynaptic to motoneuron somata. The observation of GAD-containing terminals presynaptic to dendrites and cell bodies in both dorsal and ventral horns is compatible with the evidence suggesting that GABA terminals may mediate postsynaptic inhibition of spinal interneurons and motoneurons. The additional finding of GAD-positive terminals presynaptic to other axonal terminals in the dorsal horn and motor nuclei is consistent with the growing evidence that GABA also may be the transmises mediating presynaptic inhibition via axo-axond synapses in the spinal cord.

Origin of specific synaptic types in the motoneuron neuropil of the monkey.

An attempt has been made to establish, so far as possible, the specific types of synaptic bulbs on motoneurons which arise from extrinsic (descending and dorsal root) and intrinsic sources (interneurons). This has involved the laborious analysis of thousands of electron micrographs of material from normal motoneuron neuropil, and motoneuron neuropil of animals with lesions of spinal tracts, spinal roots, and motor cortex. Our studies have established that the large synaptic bulbs on dendrites, which are the only type in the spinal cord to possess pre-synaptic synapses (serial synapses), are derived from monosynaptic dorsal root fibers (R bulbs). The presynaptic component of the serial synapse appeared to degenerate at levels below spinal cord transections (P bulbs). By means of transections of spinal cord we have found that descending fibers in the spinal cord terminate as one of at least two distinct classes of synaptic bulbs, one with spheroid synaptic vesicles (S) and one with flattened vesicles (F). There is evidence from several sources that the first type may often be excitatory in function and the second type inhibitory. Only synaptic bulbs with spheroid vesicles show definite signs of degeneration after lesions of the opposite motor cortex. The large (L) synaptic bulbs on motoneuron somata, associated with subsynaptic cisterns, are clearly not derived from the descending systems, or from posterior root fibers.

The effects of 5,6-dihydroxytryptamine in the amphibian spinal cord using silver staining techniques

The lumbar area of the spinal cords of adult frogs administered single injections of the drug 5,6-dihydroxytryptamine were treated with silver staining techniques for axonal and terminal degeneration. At all doses, maximal fiber degeneration occurred in the lateral columns of the spinal cord. The degeneration followed discrete patterns entering the spinal gray in bundles and terminating on somata and dendrites of interneurons and motoneurons. Fiber degeneration was also seen in the dorsal columns, particularly the dorsolateral zone and in the ventrolateral and ventromedial fiber tracts. Terminal degeneration was always heaviest in the ventral gray; fewer terminals were located in more dorsal areas of the central gray.

Responses of cat spinal motoneuron somata and axons to linearly rising currents.

Responses of cat spinal motoneuron somata and axons to linearly rising currents.W R Schlue, D W Richter, K H Mauritz, and A C NacimientoW R Schlue, D W Richter, K H Mauritz, and A C NacimientoPublished Online:01 Mar 1974https://doi.org/10.1152/jn.1974.37.2.303MoreSectionsPDF (1 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformation Cited ByContribution of intrinsic motoneuron properties to discharge hysteresis and its estimation based on paired motor unit recordings: a simulation studyRandall K. Powers and C. J. Heckman10 July 2015 | Journal of Neurophysiology, Vol. 114, No. 1Effects of persistent inward currents, accommodation, and adaptation on motor unit behavior: a simulation studyAnn L. Revill, and Andrew J. Fuglevand1 September 2011 | Journal of Neurophysiology, Vol. 106, No. 3Persistent Sodium Currents and Repetitive Firing in Motoneurons of the Sacrocaudal Spinal Cord of Adult RatsP. J. Harvey, Y. Li, X. Li, and D. J. Bennett1 September 2006 | Journal of Neurophysiology, Vol. 96, No. 3Endogenous Monoamine Receptor Activation Is Essential for Enabling Persistent Sodium Currents and Repetitive Firing in Rat Spinal MotoneuronsP. J. Harvey, X. Li, Y. Li, and D. J. Bennett1 September 2006 | Journal of Neurophysiology, Vol. 96, No. 35-HT2 Receptor Activation Facilitates a Persistent Sodium Current and Repetitive Firing in Spinal Motoneurons of Rats With and Without Chronic Spinal Cord InjuryP. J. Harvey, X. Li, Y. Li, and D. J. Bennett1 September 2006 | Journal of Neurophysiology, Vol. 96, No. 3Spontaneous field potentials influence the activity of neocortical neurons during paroxysmal activities in vivoNeuroscience, Vol. 119, No. 1Responses to ramp current stimulation of the neurons in substantia nigra pars compacta in vitroBrain Research, Vol. 475, No. 1In vivo properties of neurons of the precruciate cortex of catsBrain Research Bulletin, Vol. 21, No. 3Two different mechanisms control inhibition of spike discharge in neurons of cat motor cortex after stimulation of the pyramidal tractBrain Research, Vol. 332, No. 2Electrophysiologic characterization of morphologically identified neurons in the cerebellar cortex of awake catsExperimental Neurology, Vol. 67, No. 2Hyperexcitability of cultured central nervous system neurons caused by tetanus toxinExperimental Neurology, Vol. 65, No. 1Characterization of electrophysiological properties of intracellularly recorded neurons in the neocortex of awake cats: A comparison of the response to injected current in spike overshoot and undershoot neuronsBrain Research, Vol. 158, No. 2Effects of acetylcholine and cyclic GMP on input resistance of cortical neurons in awake catsBrain Research, Vol. 158, No. 2Survey of intracellular recording in the cochlear nucleus of the catBrain Research, Vol. 148, No. 1Differential action of TEA on excitation threshold in sensory neurons of the leech central nervous systemComparative Biochemistry and Physiology Part C: Comparative Pharmacology, Vol. 57, No. 1Which elements are excited in electrical stimulation of mammalian central nervous system: A reviewBrain Research, Vol. 98, No. 3Generation of spike trains in CNS neuronsBrain Research, Vol. 84, No. 1 More from this issue > Volume 37Issue 2March 1974Pages 303-9 https://doi.org/10.1152/jn.1974.37.2.303PubMed4815207History Published online 1 March 1974 Published in print 1 March 1974 Metrics