Dorsal Root Fibers Research Articles

Unexpected features of the interaction between individual primary afferents and spinal motoneurones

Simultaneous intracellular recording from spinal motoneurone and dorsal root fibres afferent to it in the isolated amphibian cord revealed a specific correlation between the slow spontaneous depolarizing activity in motoneurones and primary afferents.

Faseranalyse der vorderen und hinteren Rückenmarkswurzeln des Menschen auf Grund unterschiedlicher Acetylcholinesteraseaktivität

Marked differences in the AChE activity of myelinated nerve fibers of ventral and dorsal roots could be established in human post mortem material. After a fixation time of 3 h and a critical incubation period of 24 h, in the mean 96% of the myelinated ventral root but only 4% of dorsal root fibers showed reaction product, detectable by the light microscope. The percentage of stained fibres varies, to some extent, in the different segments. Groups of very thin myelinated fibres within the ventral roots between the segments C-8 and L-3, showing a conspicuous high enzyme activity, are interpreted as pre-ganglionic sympathetic fibres; similar elements in the sacral ventral roots may represent parasympathetic fibres. The method of Karnovsky, applied under conditions established in this study, can be used for analysis of fibre types in a given human peripheral nerve.

Routing of transported materials in the dorsal root and nerve fiber branches of the dorsal root ganglion

After injection of the L7 dorsal root ganglion with 3H-leucine, fast axoplasmic transport carries some 3--5 x more labeled materials down the sensory fibers branches entering the sciatic nerve as compared to the dorsal root fiber branches of the neurons. Freeze-substitution preparations taken from the two sides of the lumbar seventh dorsal root ganglia of cats and monkeys showed little difference in the histograms of nerve fiber diameters of the sensory nerve fiber branch of these neurons as compared to the dorsal root fiber branches. A similar density of microtubules and of neurofilaments in the dorsal root and sensory nerve fiber branches over a wide range of fiber diameters was found in electron micrograph preparations. In the absence of an anatomical difference in the fibers to account for the asymmetrical outflow, a functional explanation based on the transport filament model was advanced.

Some actions of catechol on synaptic transmission in the isolated spinal cord of the frog

The isolated frog spinal cord was used to investigate the synaptic effects of the convulsant agent catechol. Addition of the compound to the superfusate consistently enhanced orthodromic reflex activity recorded from ventral roots and augmented primary affarent depolarization. Concomitantly catechol altered the polarization changes produced in ventral and dorsal roots by putative neurotransmitter amino acids when these compounds were applied in Mg 2+-containing Ringer. Catechol reduced the hyperpolarizations induced in motoneurons by the neutral amino acids, GABA, β-alanine, taurine and glycine, but did not affect the depolarizations produced by the dicarboxylic amino acids, l-glutamate and l-aspartate. In contrast, catechol increased the dorsal root depolarizations elicited by both neutral and dicarboxylic amino acids and also the depolarizations produced by elevated potassium concentrations. Catechol did not bring about significant changes in the passive electrical properties of motoneurons or dorsal root fibers. In addition, it did not alter either the high affinity uptake or the depolarization-evoked release of tritiated GABA, glycine, l-glutamate and l-aspartate. It appears that the postsynaptic actions of catechol explain its ability to enhance spinal reflexes.

Intraspinal alumina injection: the relationship between epileptiform focus, root scarring and chronic pain.

Intramedullary or subarachnoid injections of alumina cream were made in the lumbar region of 38 adult cats. The animals were observed for 3 to 12 months and then subjected to acute neurophysiologic and histologic analysis. Neuronal hyperactivity in the dorsal horns was reliably produced by either subarachnoid or intramedullary alumina; behavioral abnormalities were not produced unless some of the alumina was present adjacent to dorsal root fibers in the subarachnoid space. Neuronal hyperactivity does not predict cutaneous hyperesthesia or motor abnormality; alumina produces scarring in the subarachnoid space and probably causes pain by making the dorsal root fibers mechanosensitive. Subarachnoid alumina may be a good model for human arachnoiditis.

Characterization of various nervous tissues of the chick embryos through responses to chronic application and immunocytochemistry of β‐bungarotoxin

beta-Bungarotoxin (beta-BT) was applied to chick embryos at 3-day intervals beginning on the fourth day of incubation to investigate ultrastructurally the effects of chronically and massively applied beta-BT on various nervous tissues and muscles. On the twenty-first day of incubation, spinal cords of beta-BT treated embryos were conspicuously decreased in size. Ventral root fibers dorsal root fibers, white matter, and motor neurons disappeared. Although spinal ganglia and sympathetic trunk ganglia were completely absent, Auerbach's and Meissner's ganglia nerve cells in the small intestine and adrenal medullary cells were not affected. In retinas of beta-BT treated animals ganglion cells and optic nerve fibers disappeared, but photoreceptor cells, bipolar cells and horizontal cells remained intact. Furthermore, olfactory nerve cells and their unmyelinated nerve fibers ensheathed by Schwann cells were quite undamaged. Skeletal muscles degenerated, whereas cardiac muscles were unaffected. In the present study various nervous tissues of the twenty-first day normal chick embryos were incubated with beta-BT and target cells of beta-BT were detected directly by the reaction with horseradish peroxidase labelled anti beta-BT guinea pig IgG. Motor nerve cells in the spinal cords, spinal and sympathetic ganglia nerve cells, ganglion cells and some nerve cells at the inner part of the inner nuclear layer in the retinas were positively stained, whereas Auerbach's and Meissner's ganglia nerve cells in the small intestine, adrenal medullary cells, photoreceptor cells, bipolar cells and horizontal cells in the retina and olfactory nerve cells were negative. Thus the present study shows the beta-BT has extensive destructive effects on various nerve cells which were revealed to be target neurons of beta-BT by immunocytochemistry. Those nerve cells, affected by beta-BT and positively stained with immunocytochemical reaction were supposed to have different characteristics from unaffected cells. One of the differences between these affected cells and unaffected cells may be whether there exist binding sites for beta-BT on the plasma membrane or not. The possibility of the use of beta-BT to characterize various nervous tissues is presented in the present study.

Evoked electrospinogram in spinal cord and peripheral nerve disorders.

Spinal cord evoked potentials have been studied by means of intrathecal application in 80 patients with various spinal cord and peripheral nerve disorders. The segmental spinal cord potentials are normal in acute motor polyneuropathy, generalized anterior horn cell disease and in discrete lesions of dorso-lumbar segments. On the other hand, the first component of the segmental response is delayed, reduced and sometimes dispersed or lost in chronic sensory-motor polyneuropathy and in hereditary spinocerebellar degeneration. the reduction in amplitude is also present in multiple sclerosis with clinical signs of dorsal funiculus involvement. In compressive lesions of the cauda-conus, recordings of lower thoracic intervertebral level show that the segmental responses are delayed with marked amplitude reduction. The potentials recorded from lumbo-sacral segments show a greater the amplitude of the second component proportionally to the first one as the duration of second component is longer in spastic paraplegia regardless of its etiology. The cervical tractus response is seen to be markedly slowed with a reduction of amplitude or is often absent in chronic polyneuropathy, spinocerebellar degeneration and in multiple sclerosis. The primary sensory neurones lying both in periphery and in the dorsal column are assumed to be responsible for the segmental evoked potentials especially for the first component. the late slow component is related to the activation of interneurones situated within the segmental gray matter and segmental collaterals of the dorsal root fibres carrying impulses to those cells. Cervical tractus responses are mostly formed by the dorsal column fibres and their physiological action upon demyelination is similar to that of the peripheral nerves.

Acetylcholinesterase activity of primary sensory neurons and dorsal root fibers in the cat.

Dorsal roots and spinal ganglion cells of adult cats were studied for acetylcholinesterase (AChE) content. An inverse correlation exists between cell size and AChE activity; large neurons are AChE-negative whereas small ones are intensely AChE-positive. A few AChE-positive fibers were demonstrated in the dorsal roots. A possible correlation between AChE activity and substance P content of primary sensory neurons is discussed.

Patterns of degeneration in the external cuneate nucleus after multiple dorsal rhizotomies.

Unilateral, intradural dorsal rhizotomies (C3-Cs) were performed on adult rats to study the patterns of synaptic organization of ascending dorsal root fibers in the external cuneate nucleus (ECN). Animals were permitted to survive for periods of time ranging from 3 hours to 12 days. Sham-operated animals presented a morphology indistinguishable from that of normal, unoperated animals. In rhizotomized animals, degeneration was observed ipsilaterally at all survival periods. After postoperative survivals of 3 to 14 hours some terminal boutons displayed clumping and diminution in numbers of synaptic vesicles and, in addition, degeneration myelinated axons were observed at this time. There was considerable degeneration in the neuropil between 24 and 48 hours postoperative. Two forms of degeneration occurred in axons and terminal boutons with comparable frequency: electron lucent degeneration and electron opaque degeneration. Reactive phagocytic glial cells contained degenerated masses, lipoid droplets, lysosome-like structures and myelin fragments. After postoperative survivals of four to six days, lucent and opaque degenerating terminals were less numerous. Neurofilamentous degeneration was observed only occasionally. Unaltered synaptic membrane specializations were present and were usually abutted by glia. At 12 days postoperative, synaptic glomeruli and serial synapses were not seen. Invaginating dendritic spines were rarely seen. Bouton populations that remained unualtered were: small (0.3-3.0 micron) boutons that contact dendritic shafts and somata, nodal synaptic boutons and boutons containing granular vesicles (80-100 nm).

Electron microscopic identification of postsynaptic dorsal root terminals: a possible substrate of dorsal root potentials in the frog spinal cord

Dorsal root fibers were labeled with cobaltous chloride iontophoresis for electron microscopic investigations. In the base of the dorsal horn, where most of the coarser collaterals of dorsal root fibers terminate, many dorsal root terminals were found in postsynaptic relation to synapsing profiles. According to their morphological characteristics, three kinds of presynaptic terminals could be discerned in these complex synapses: axon terminals with spheric vesicles, axon terminals with flattered vesicles and presynaptic dendrites. These latter terminals contained relatively few flattened vesicles accumulated adjacent to a short synaptic articulation surface, and they were rich in cytoplasmic organelles. The functional significance of these structural specializations in the mediation of dorsal root potentials and recurrent inhibition is discussed.

Staining of the dorsal root projection to the cat's dorsal horn by anterograde movement of horseradish peroxidase

A modification of the horseradish peroxidase method was used to stain selectively dorsal root fibers entering the spinal cord of the cat. This technique stains intact terminal arborizations. Using this method to examine the primary afferent supply to lamina II of the lumbosacral segments, we observed that both thick primary afferent collaterals (2–3 μm), entering by way of the dorsal column, and thinner primary afferent collaterals (<1 μm), entering by way of Lissauer's tract, form terminals in lamina II. The terminals derived from the thick primary afferent collaterals were concentrated in the ventral portion of lamina II.

The origin of spinocerebellar pathways. I. The nucleus cervicalis centralis of the cranial cervical spinal cord

AbstractThe origin of spinocerebellar projections from the cranial cervi cal spinal cord was studied in neonatal dogs following cerebellar ablations or the injection of horseradish peroxidase (HRP) into the cerebellum. Cerebellar ablations produced distinct retrograde changes of three types: type I response or cen tral chromatolysis; type II response or ghost cells; and type 111 response or neu ronal loss and gliosis. These ablation‐induced changes were evident in the cells of the nucleus cervicalis centralis. The results of hemicerebellectomy, unilateral cer ebellar pedunculotomy, and cordotomy established that the cells of this nucleus project contralaterally to the cerebellum. Cytoarchitectonic study revealed that this nucleus is composed of clustered medium‐sized, multipolar, chromatophilic neurons located in the zona intermedia of the C1‐C4 segments. The retrograde la beling of central cervical neurons following cerebellar injections of HRP con firmed the results obtained with the axonal reaction.Anterograde fiber degeneration was present in the central cervical nucleus following dorsal rhizotomy in the dog and cat. These experiments demonstrated dorsal root fibers among the somata of central cervical neurons rendered chromatolytic following cerebellectomy in the dog. Electron microscopic evidence is presented for the presence of degenerated dorsal root terminals upon the dendrites and somata of central cervical neurons.The nucleus cervicalis centralis forms a direct link between neck afferents and the cerebellum by way of a crossed cervicospinocerebellar pathway. Evidence could not be found for the presence of a spinocerebellar projection originating in the nucleus ceruicalis lateralis.

Spinal Neurons Project to the Dorsal Column Nuclei of Rhesus Monkeys

Cells of origin of ascending nonprimary afferents to the dorsal column nuclei of rhesus monkeys have been identified in the spinal cord by the retrograde transport of horseradish peroxidase. These neurons are mainly located in lamina IV and medially in more ventral laminae of the dorsal horn on the side ipsilateral to the medullary injection. Large neurons in the ventral horn ("spinal border cells") also appear to project to the ipsilateral dorsal medulla. The dorsal column nuclei of a primate thus are the recipient not only of ascending dorsal root fibers but also of a more complexly integrated spinal input.

Sensory fibres in ventral roots L7 and Si in the cat.

1. Receptive fields were determined for ninety-eight unmyelinated and 132 myelinated axons in the L7 and S1 cat ventral roots.2. Seventy of the ninety-eight unmyelinated axons had their receptive fields in somatic structures, the skin and deep tissues.3. Of the seventy unmyelinated axons with somatic receptive fields, thirty-five were mechanical nociceptors, fifteen were mechanical and thermal nociceptors, eleven were deep nociceptors, six were thermal receptors, and three were low threshold mechanoceptors.4. Twenty-four of the ninety-eight unmyelinated axons had their receptive fields in visceral structures: the intestine, bladder and vagina.5. We confirm the work of others that myelinated fibres attached to peripheral receptive fields can be found in ventral roots and that the receptive fields and functional qualities of these fibres are as one would expect of dorsal root fibres for the same segments.6. A previous study demonstrated that approximately 30% of the axons in the L7 and S1 cat ventral roots are unmyelinated and arise from dorsal root ganglion cells. The present study confirms that these axons are sensory and that the axons are predominantly cutaneous nociceptors and visceral afferents. Thus it is concluded that the L7 and S1 cat ventral roots have a major sensory component.

Glutamic acid as a synaptic transmitter candidate in the dorsal sensory neuron: Reconsiderations

Two primary reasons which are emerging to suggest that glutamate is not a dorsal root transmitter are: 1) that free glutamate levels in the dorsal root vs. the ventral root are not sufficiently different to warrant a transmitter function in the dorsal root, and 2) the spinal cord glutamate levels do not significantly change (per g tissue) after dorsal root input section. Recent analyses suggest, however, that there is a highly significant depression of glutamate in the dorsal root when related to total free amino acid concentration changes after root injury. This is not seen in the peripheral nerve. Thus the dorsal vs. ventral root free glutamate concentration difference is highly significant metabolically. The failure to see a decrease in spinal cord gray glutamate levels after dorsal root section would appear to be explained by the fact that the spinal cord satellite cells and neurons have a higher free glutamate concentration than the entering dorsal roots along with a considerable perikaryal free amino acid pool for protein synthesis. This will mask any changes due to dorsal root section. Comparisons of excess free glutamate and substance P (the two leading dorsal root transmitter candidates) in the dorsal root compared to the ventral root have shown that there is a much larger excess of free glutamate in the dorsal root. This is true, even when considering the excitatory potency differences of these two substances. Thus, a very large free glutamate excess in the dorsal root is present with a relatively small concentration difference compared to the ventral root (where a transmitter role is not entertained). This fact could be of considerable metabolic significance in the regulation of transmitter levels of glutamate. The data available, therefore, are supportive of a possible glutamate transmitter role in a population of dorsal root fibers.

Distribution of the tract of lissauer and the dorsal root fibers in the primate spinal cord

The tract of Lissauer receives small caliber dorsal root fibers in addition to axons arising from dorsal horn neurons. The termination of Lissauer's tract and dorsal root fibers was examined in the C7 segment of the rhesus monkey spinal cord. The distribution of normal dorsal root afferents was mapped by labelling the C7 dorsal root ganglion with tritiated amino acids, and then compared with the degeneration of C7 dorsal root fibers following an intradural dorsal rhizotomy. To focus on the distribution of the small afferents, the degeneration following a Lissauer tractotomy was compared with the degeneration following dorsal rhizotomy and following selected lesions involving the large afferents. The survival times following the lesions and rhizotomies were varied to facilitate identification of groups of fibers and terminals which might degenerate at different rates. Both large and small diameter dorsal root afferents were found to exhibit the same rostro-caudal topography within the dorsal horn. The C7 root axons and terminals distribute throughout the mid-C7 dorsal horn grey. Proceeding rostrally through C6, the majority of the C7 root fibers ending in laminae I-IV shift to a lateral position. Proceeding caudally through C8, the C7 root fibers shift medially. Few of the small diameter C7 afferents entering via Lissauer's tract extend above C6 or below C8. Large diameter C7 afferents, arising as dorsal column collaterals, can extend several segments above and below C7. Autoradiography revealed label in all dorsal horn laminae, the heaviest always occurring in the substantia gelatinosa. After one day, label was absent over dorsal column and Lissauer's tract axons, suggesting that the label was mainly associated with fine axonal branches or possibly terminals. After six to ten days many axons were labelled and could be traced into the dorsal and ventral horn. Degeneration from the rhizotomies and lesions, as demonstrated with Fink-Heimer and Nauta methods, depended on the survival time. No degeneration products were present before three days. The large afferents begin to degenerate within the dorsal horn after three to four days and mainly terminate in laminae IV-VI; by 12 days they can also be traced into the intermediate and ventral grey. The small afferents, which include those serving pain and temperature sensibility, arise from the tract of Lissauer and distribute to laminae I, II and III. The tract of Lissauer consists of two populations, each containing small afferents. One population degenerates at three to five days and distributes mainly to laminae II and III (substantia gelatinosa); the other degenerates around 12 days and distributes mainly to lamina I and the outer zone of II. It is suggested that the exclusive termination of the small afferents to laminae I, II and III may be correlated with certain unique histochemical properties (e.g., high substance P and high opiate receptor binding levels) of these same dorsal horn areas...

Oligodendroglial response to degeneration of dorsal root fibers in adult rat spinal cord

The cytology of oligodendrocytes in the unoperated adult rat spinal cord and after crush lesion of dorsal roots was studied by electron microscopy. The oligodendrocytes in the substantia gelatinosa of normal rat cord displayed a rather variable cytology. However, the more salient morphological features of these cells include a dense oval or circular nucleus and a small amount of cytoplasm especially rich in free ribosomes and polysomes interspersed with other organelles such as endoplasmic reticulum, mitochondria, and Golgi complex. In general, these cells corresponded to the light and medium oligodendrocytes described by Mori and Leblond (1970. J. Comp. Neurol. 139: 1–30). Oligodendrocytes in animals killed 4 days postlesion showed distinct evidence of cytoplasmic hypertrophy with accumulations of abundant polysomes, free ribosomes, endoplasmic reticulum, and Golgi complexes. Both nucleus and cytoplasm appeared to have increased background density. Several instances of oligodendrocytes enclosing degenerating myelin ovoids were observed in animals killed 3 weeks after lesion. However the astrocytes were the principal cellular elements picking up damaged myelin. In animals sacrificed 6, 10, and 16 weeks postlesion, regenerated dorsal root fibers were observed both in substantia gelatinosa and the adjacent posterior funiculus. Cytoplasm trapped in the region of the inner and outer mesaxons of these young fibers resembled oligodendrocytic cytoplasm, providing additional evidence as to the role of these cells in remyelination.

Reflex response to stretch of limb muscles in the Australian blue tongue lizard

1. 1. Stretch of hind limb muscles in decerebrate blue tongue lizards was shown to evoke autogenetic reflex contraction. 2. 2. Ventral root and intracellular recording demonstrated the presence of monosynaptic as well as polysynaptic pathways between dorsal root fibres and motoneurones. 3. 3. Monosynaptic excitation of motoneurones could be evoked by electrically or stretch-evoked afferent input from muscle, but not from skin, as in mammals. 4. 4. It is conjectured that acquisition of a stretch-reflex mechanism may have been significant in the colonisation of dry land by primitive reptiles, including the ancestors of mammals.

Astroglial response to degeneration of dorsal root fibers in adult rat spinal cord

The morphology of the astrocyte was studied with the electron microscope in the posterior gray and at the edge of the spinal cord, in both normal adult rats and after crush lesion of dorsal roots in adult rats. In general, the astrocyte was characterized by a pale, round nucleus surrounded by a cytoplasm containing small bundles of filaments and few organelles. However, the subpial astrocyte appeared to possess a larger amount of filaments. Within 4 days after injury, the astrocytes responded by accumulating glycogen particles within their cytoplasm even in the absence of morphological evidence of damage to nerve fibers. In addition, the astrocytic nucleus appeared reactive as evidenced by a tendency to increased nuclear irregularity, nuclear pores, and prominent nucleoli. The cytoplasm of several astrocytes also displayed hypertrophy resulting in accumulation of microfilaments, mitochondria, multiple Golgi complexes, and several electron-dense bodies. In animals killed 4 weeks after lesion, clear evidence of astrocytes functioning as macrophages in the removal of degenerating myelin was observed. These reactive astrocytes exhibited multiple Golgi complexes, large amounts of microfilaments, and numerous mitochondria. The subpial astrocytes especially possessed an abundance of microfilaments.

A light and electron microscopic examination of dorsal root afferent development in three species of anurans

Counts of afferent fibres in dorsal root III were undertaken in larval Rana temporaria using electron microscopy. There is a progressive increase in both myelinated and unmyelinated fibres from mid-larval stages to the completion of metamorphosis. A significant decrease in both fibre types occurs during the last two stages of metamorphosis, to roughly one-half earlier peak values. Light microscopic examinations of similar dorsal roots utilizing degeneration histology failed to corroborate the electron microscopic observations.