Dorsal White Columns Research Articles

Age-related NADPH-diaphorase positive bodies in the lumbosacral spinal cord of aged rats

In the course of a morphological investigation of age-related changes in the rat spinal cord, using nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemistry, we found abundant NADPH-d positive bodies, which were characteristically expressed in the aged lumbosacral spinal cord. Together with a normally stained fiber network and a few neurons, the dense, spheroidal NADPH-d positive bodies occurred in portions of the sacral dorsal spinal cords, such as the dorsal commissural nucleus, intermediolateral nuclei, and superficial dorsal horn, and were scattered throughout the dorsal white column. These NADPH-d positive bodies were occasionally observed in a fibrous structure. Two morphologically distinctive subsets of NADPH-d positive bodies were noted in the spinal cord of rats aged 8 to 36 months: 1) highly-dense spheroidal shapes with sharp edges; 2) moderately-dense spheroidal or multiangular shapes with a central "core" and a peripheral "halo". The quantitative analysis, particularly the stereological measurement, confirmed a gradual increase in the incidence and size of NADPH-d positive bodies with increasing age. With nNOS immunohistochemistry, no corresponding structures to NADPH-d positive bodies were detected in aged rats; thus NADPH-d activity is not always specific to the NO-containing neural structures. The major distribution of the NADPH-d positive bodies in the aged lumbosacral spinal cord indicates some anomalous changes in the neurite, which might account for a disturbance in the aging pathway of the autonomic and sensory nerve in the pelvic visceral organs.

Axonal sprouting in the hemisected adult rat spinal cord

The morphological and biochemical changes were studied in adult Sprague-Dawley rats after hemisection at the L 3 spinal cord level. After survival periods of one, two and three months, fluorescent tracers, FluoroGold or rhodamine B, were implanted into the dorsal white columns of these rats at the positions of the corticospinal tract below the lesion. Following uptake of the tracer, the rats were killed and the motor cortices and spinal cords of both control and hemisected rats were analysed for positively labelled neurons. The highest number of labelled cells were found two months after hemisection. They were present in both sides of the cortices, particularly in the contralateral cortex, and also in the gray matter of the spinal cord above the hemisection. A few rats which were subjected to complete transection of the spinal cord also showed labelling of neurons in the motor cortex two months after lesion. The Protargol silver technique and the [ 3H]choline uptake study confirmed the presence of nerve fibres traversing the lesion site in the hemisected spinal cord. Furthermore, when the rats that had been hemisected two months earlier were subjected to a second cut at the same site, chromatolytic neurons were observed in the spinal cord as well as in the motor cortices of both sides. The hemisected rats demonstrated limited recovery in limb movement. The evidence in this study clearly shows that sprouting of nerve fibres has occurred in the lesioned adult rat spinal cord.

Spinal somatosensory evoked potentials in mice and their developmental changes

Spinal somatosensory evoked potentials (SEP) were recorded in 58 normal mice (C3H strain) divided into 4 groups according to age (3-, 6-, 9- and 12 weeks). Monopolar recordings of spinal SEP were made by subdermal needle electrodes from 3 vertebral levels, ‘low-lumbar’, ‘high-lumbar’ and ‘mid-thoracic’, by stimulating the tibial nerve bilaterally at the ankle. Three negative peaks, NI, NII and NIII, presumably due to conduction through muscle afferents, cutaneous afferents (in the dorsal root or dorsal white column) and spinocerebellar tract, respectively, were recorded at the high-lumbar level in the 12-week-old mouse. Besides the NI and NII peaks, a small ventral root potential was also occasionally recorded at the low-lumbar level. At the mid-thoracic level, only NI and NIII were recordable. At both the high-lumbar and mid-thoracic levels, the negative peaks were superimposed over long duration ‘summation potentials’ of opposite polarities. Well-defined standing potentials were also recorded at these two levels. The standing potentials could be the ‘entry point potential’ due to the entry of S1 root into the spinal cord at the T13 vertebral level. The summation potential presumably is due to a fixed generator located between the T7 and T12 vertebral levels resulting from intense synaptic activity at this level. In 3- and 6-week-old mice, the entry point potential was recorded in the low-lumbar SEP also, possibly due to less axial growth of the vertebral column at this stage of development. The summation potential and NIII peak were reduced in size in these young mice, possibly due to less developed collaterals and synaptic activity. The somatosensory conduction velocity, measured between the low-lumbar and mid-thoracic recording sites, showed a highly significant increase during the 3–6 and 6–9 week periods, suggesting that a significant amount of myelination occurs in proprioceptive fibres postnatally in mice.

Distribution of a novel 57 kDa intermediate filament (IF) protein in the nervous system

A 57 kDa protein, that is not vimentin, is the major component of intermediate filaments (IF) obtained after 2 cycles of in vitro assembly from PC12 cells (Parysek and Goldman, 1987). By use of an antiserum to the 57 kDa protein, a cross-reacting antigen (of identical molecular weight) was detected on immunoblots of IF preparations and by immunofluorescence of various rat tissues. Immunolocalization studies on 3-4 micron frozen sections of tongue, small intestine, and adrenal gland showed bright labeling of nerve bundles and fine-caliber nerve fibers. The chromaffin cells and ganglion cells of the adrenal medulla also were labeled. In the nervous system, intense labeling was seen in small-caliber nerve fibers in sciatic nerve and spinal cord dorsal roots, as well as in the dorsal white columns and dorsal root ganglia. Of the ganglion cells, preferential labeling was seen in small-sized ganglion cells, whereas a monoclonal antibody to the 150 and 200 kDa neurofilament triplet (NFT) components labeled the large-sized ganglion cells. In the areas of the brain thus far examined with 57 kDa antiserum, there was labeling of components of cranial nerves and labeling of thin fibers in several areas, including the granular layer of the cerebellum and the corticospinal tract in the brain stem. For each tissue, adjacent sections treated with vimentin or glial fibrillary acidic protein antibody revealed labeling patterns distinct from that seen with either the 57 kDa or NFT antibodies. These results indicate that the 57 kDa IF protein is a neural IF component. Furthermore, this protein is distributed in only certain neuronal elements; these elements may be unified by an as yet unrecognized pattern of function in the nervous system.

Relationship between posttraumatic ischemia and hemorrhage in the injured rat spinal cord as shown by colloidal carbon angiography.

Adult female Wistar rats underwent extradural clip compression injury of the spinal cord at T-1. A force of 40 g was applied for 1 minute; this moderately severe injury renders animals paraparetic. We performed colloidal carbon angiography with Aquablak on four animals at 15 minutes, 2 hours, and 24 hours after injury. The entire spinal cord was then removed, frozen, and sectioned serially at 250 micron. The sections were examined microscopically for patterns of ischemia and hemorrhage at the site of compression injury and at adjacent and remote sites in the spinal cord. There was a marked lack of filling of the arterioles, capillaries, and venules at the injury site. In addition, there was a specific anatomical distribution of the ischemic areas in that ischemia of the white matter occurred in areas supplied by arteries that traversed adjacent hemorrhagic gray matter. For example, ischemia of the ventral funiculus was consistently seen adjacent to hemorrhage in the ventral gray matter. Similarly, ischemia of the dorsal white columns was related to hemorrhagic lesions surrounding the feeding vessels in the dorsal gray matter. This study also demonstrates the usefulness of a new colloidal carbon suspension (Aquablak) for documenting the pathophysiology of posttraumatic ischemia of the spinal cord. The results suggest that ischemic lesions in the white matter are anatomically related to hemorrhagic lesions in the gray matter. The pathophysiology of this relationship is unknown, but may include thrombosis, vasospasm, or direct injury of the feeding vessels.

The dorsal column nuclei of the frog

Surface potentials and field potentials recorded from the medulla in response to cutaneous and mixed nerve stimulation revealed that fibers of the dorsal white column project onto two separate neuron groups in the medulla representing the dorsal column nuclei. The hind-limb was represented in the medial group and the fore-limb in the lateral group in the projection. The fore-limb nerves projected to a region extending from the medulla to the 4th segment of the spinal cord. Primary afferent depolarization and depression of synaptic activities were shown by direct and indirect stimulation of dorsal column fiber terminals in the dorsal column nuclei. Conditioning volleys set up in hind-limb nerves had no effect on test responses evoked by stimulation of forelimb nerves, and vice versa. Slow negative potentials with decreasing latencies were recorded from the posterocentral nucleus of the thalamus in response to stimulation of the 2nd dorsal root, the dorsal column and the dorsal column nuclei, respectively. The physiological results were correlated with histological observations using the cobalt labelling method. It was concluded that the amphibian dorsal column-medial lemniscus system is closely comparable with that found in the mammalian brain.

Longitudinal extent of dorsal root fibres in the spinal cord and brain stem of the frog

The longitudinal arrangement of dorsal root fibres was investigated with a modified cobalt labelling technique in the spinal cord and brain stem of frogs. The topographical order of dorsal root fibres in the dorsal white column closely resembles the well-known scheme of the mammalian spinal cord. A significant difference between frogs and mammals is the extension of fibres up to the cerebellar plate. The ascending fibres of different origin are organized in concentric rings in the medulla. An oval-shaped area and a triangular area in the dorsal horn, and the motor horn, receive fibre collaterals in the spinal cord. Thoracic dorsal root fibres terminate exclusively in the oval-shaped area. Fibre terminations clearly outline the dorsal column nuclei which begin in the obex region and end at the level of the glossopharyngeal nucleus. The spinal nucleus of the trigeminus is richly supplied by both thin and thick calibre dorsal root fibres in its entire rostrocaudal extension. Two parts of the reticular formation receive dorsal root fibres; the first is in the dorsal gray matter ventral and lateral to the solitary fascicle in the medulla, the second is the lateral reticular zone. In the vestibular region, the medial, lateral and superior vestibular nuclei are innervated by dorsal root fibres. The granular layer of the cerebellum receives a significant contingent of dorsal root fibres. Fibres terminating in the vestibular region and in the cerebellum arise from limb-innervating spinal ganglia. The results indicate a close similarity in the longitudinal arrangement of dorsal root fibres in frogs and in higher vertebrates. The several collaterals that terminate in the hindbrain may modulate the function of the receiving structures. On the basis of present and previous findings the aggregation of primary sensory fibres and the convergence of their terminations are surveyed in the hindbrain.

AXON SPROUTING INTO SEGMENTS OF RAT SPINAL CORD ADJACENT TO THE SITE OF A PREVIOUS TRANSECTION

Transection of the spinal cord is adult Long-Evans Hooded rats is followed by the formation of a connective tissue matrix in the lesion site and the rapid erosion of the neural elements above and below this zone particularly within the dorsal white columns. In the period between 15--45 days after operation two significant events begin to occur. First the injured surfaces of the divided cord become invested by a glial limiting membrane (glia limitans) and, concomitantly, large numbers of axons ensheathed by Schwann cells sprout into the scar matrix and along the eroded dorsal column region. The injured surface of the spinal cord is highly irregular with deep, collagen-filled rifts into which the sprouting axons may probe and penetrate into the adjacent normal neuropil. Electron microscopic examination generally reveals the interposed glia limitans and that these fibres are usually restricted to the peripheral environment. However, as some axons approach the reconstituting glia limitans, they are enveloped by an astrocytic cytoplasmic process which may either displace the Schwann cell or encompass it together with the enclosed axons. This last phenomenon appears to precede the entry of some axons into the neuropil and suggests that the glia limitans may not necessarily represent an impenetrable barrier to the passage of regenerating axons into the CNS. Apparent maintenance of most of these fibres for periods of up to 3 months may suggest that viable, functional synapses were established upon available neuronal elements, but clear evidence of this could not be documented.

Conduction in the dorsal white columns of the tortoise

1. 1. Nervous conduction along the dorsal white columns of the spinal cord has been examined in T. graeca. 2. 2. Volleys were elicited either by electrical stimulation of primary afferents in dorsal roots, or by direct stimulation of the columns. 3. 3. The volley in the columns was characterized by two principle components having conduction velocities, in the lumbar region, of 9 m/sec and 4 m/sec respectively, at 22–25°C. 4. 4. The more slowly conducting component was identified with sensory projections to segments close to the root of inflow while the other component probably represents direct connections with brain stem nuclei.

Alterations of spatio-tactile discrimination after lesions of primate spinal cord

Macaca speciosa monkeys were trained to produce psychophysical thresholds for tactile size discrimination. The stimuli were Plexiglass discs of varying sizes that were impressed onto the sole of either foot. The monkeys learned to make one response when touched with the smallest (standard) stimulus and to respond differently when contacted by any of the larger (comparison) stimuli. Thoracic dorsal column lesions produced large, ipsilateral deficits that endured more than 2 months, and then gradual recovery to preoperative levels was observed over succeeding months of testing. Subsequent addition of homolateral-dorsolateral column lesions returned the large deficits for several months. Another gradual recovery period followed, but thresholds did not reach normal values after nearly a year of testing. Although the impairments after dorsal column lesions were not permanent, these results are interpreted to mean that certain forms of information leading to distinct somesthetic sensations have their spinal conduction restricted exclusively to the dorsal white columns.