Effects of dorsal root transection on morphology and chemical composition of degenerating nerve fibers and reactive astrocytes in the dorsal funiculus

S100A4 in the Physiology and Pathology of the Central and Peripheral Nervous System

S100A4 is a member of the large family of S100 proteins, exerting a broad range of intracellular and extracellular functions that vary upon different cellular contexts. While S100A4 has long been implicated mainly in tumorigenesis and metastatization, mounting evidence shows that S100A4 is a key player in promoting pro-inflammatory phenotypes and organ pro-fibrotic pathways in the liver, kidney, lung, heart, tendons, and synovial tissues. Regarding the nervous system, there is still limited information concerning S100A4 presence and function. It was observed that S100A4 exerts physiological roles contributing to neurogenesis, cellular motility and chemotaxis, cell differentiation, and cell-to cell communication. Furthermore, S100A4 is likely to participate to numerous pathological processes of the nervous system by affecting the functions of astrocytes, microglia, infiltrating cells and neurons and thereby modulating inflammation and immune reactions, fibrosis as well as neuronal plasticity and survival. This review summarizes the current state of knowledge concerning the localization, deregulation, and possible functions of S100A4 in the physiology of the central and peripheral nervous system. Furthermore, we highlight S100A4 as a gene involved in the pathogenesis of neurological disorders such as brain tumors, neurodegenerative diseases, and acute injuries.

New insights into mitochondrial structure during cell death

Mitochondria play a pivotal role in the cascade of events associated with cell death pathways that are involved with several forms of neurodegeneration. Recent findings show that in the Bax/Bak-dependent pathway of apoptosis, the release of cytochrome c from mitochondria is a consequence of two carefully coordinated events: opening of crista junctions triggered by OPA1 oligomer disassembly and formation of outer membrane pores. Both steps are necessary for the complete release of pro-apoptotic proteins. The remodeling of mitochondrial structure accompanies this pathway, including mitochondrial fission, and cristae and crista junction alterations. Yet, there is controversy surrounding the timing of certain remodeling events and whether they are necessary early events required for the release of pro-apoptotic factors or are simply a downstream after-effect. Here, we analyze the current knowledge of mitochondrial remodeling during cell death and discuss what structural alterations occur to this organelle during neurodegeneration, focusing on the higher resolution structural correlates obtained by electron microscopy and electron tomography.

Reimplantation of avulsed lumbosacral ventral roots in the rat ameliorates injury-induced degeneration of primary afferent axon collaterals in the spinal dorsal columns

Injuries to the cauda equina/conus medullaris portion of the spinal cord can result in motor, sensory, and autonomic dysfunction, and neuropathic pain. In rats, unilateral avulsion of the motor efferents from the lumbosacral spinal cord results in at-level allodynia, along with a corresponding glial and inflammatory response in the dorsal horn of the spinal cord segments immediately rostral to the lesion. Here, we investigated the fate of intramedullary primary sensory projections following a motor efferent lesion. The lumbosacral (L6 and S1) ventral roots were unilaterally avulsed from the rat spinal cord (VRA; n=9). A second experimental group had the avulsed roots acutely reimplanted into the lateral funiculus (Imp; n=5), as this neural repair strategy is neuroprotective, and promotes the functional reinnervation of peripheral targets. A laminectomy-only group served as controls (Lam; n=7). At 8 weeks post-lesion, immunohistochemical examination showed a 42% reduction (P<0.001) in the number of RT97-positive axons in the ascending tracts of the dorsal funiculus of the L4-5 spinal segment in VRA rats. Evidence for degenerating myelin was also present. Reimplantation of the avulsed roots ameliorated axon and myelin degeneration. Axons in the descending dorsal corticospinal tract were unaffected in all groups, suggesting a specificity of this lesion for spinal primary sensory afferents. These results show for the first time that a lesion restricted to motor roots can induce the degeneration of intramedullary sensory afferents. Importantly, reimplantation of the lesioned motor roots ameliorated sensory axon degeneration. These data further support the therapeutic potential for reimplantation of avulsed ventral roots following trauma to the cauda equina/conus medullaris.

Tissue type plasminogen activator induced in rat dorsal horn astrocytes contributes to mechanical hypersensitivity following dorsal root injury

Dorsal root injury is known to induce alteration of the extracellular environment in the spinal cord and synaptic reorganization with degradation of injured primary afferent and sprouting of spared terminal. These changes affect behavioral sensitivity and sometimes lead to neuropathic pain. We have hypothesized that changes in extracellular proteolysis in the dorsal horn is involved in neuroplastic changes in the dorsal horn after nerve injury. Tissue type plasminogen activator (tPA) is a well-known extracellular serine protease and is involved in the modification of the extracellular matrix, which leads to neuroplastic changes such as long-term potentiation in the hippocampus. In the present study, we found a marked induction of tPA in activated astrocytes following L4/5 root injury and a resultant increase of proteolytic enzymatic activity in the dorsal horn. We also examined the involvement of tPA activity on mechanical hypersensitivity using a root ligation model which has been used for investigating radiculopathy pain behavior. Intrathecal and continuous administration of tPA inhibitor, tPA-STOP, suppressed root ligation-induced mechanical allodynia in a dose-dependent manner during an early stage of injury (0-4 days). In contrast, the delayed administration of tPA-STOP during the chronic stage of injury (10 days) did not affect pain behavior. These data suggest an important contribution of astrocytes in the dorsal horn to the pathophysiology of radiculopathy pain, and astrocyte-derived tPA and the proteolytic activity in the dorsal horn may be one of the essential factors involved in pain following root injury.

Sequential loss of myelin proteins during Wallerian degeneration in the rat spinal cord

Axotomy of nerve fibers leads to the subsequent degeneration of their distal part, a process termed Wallerian degeneration (WD). While WD in the peripheral nervous system is usually followed by regeneration of the lesioned axons, central nervous system (CNS) neurons are generally unable to regrow. In this study, we investigated the process of WD in the dorsal columns of the rat spinal cord rostral to a mid-thoracic lesion. We confirm earlier studies describing a very delayed microglial and an early and sustained astroglial reaction finally leading to scar formation. Interestingly, we found a differential time course in the loss of myelin proteins depending on their location. Proteins situated on the periaxonal myelin membrane such as myelin associated glycoprotein disappeared early, within a few days after lesion, concomitantly with cytoskeletal axonal proteins, whereas compact myelin and outer myelin membrane proteins such as MBP and Nogo-A remained for long intervals in the degenerating tracts. Two distinct mechanisms are probably responsible for this difference: processes of protein destruction emanating from and initially probably located in the axon act on a time scale of 1-3 days. In contrast, the bulk of myelin destruction is due to phagocytosis known to be slow, prolonged, and inefficient in the CNS. These results may also have implications for future intervention strategies aiming at enhancing CNS regeneration.

Changes in intracellular sodium, potassium, and calcium concentrations in transplanted mouse pancreatic islets

BACKGROUND

Our previous studies have suggested a chronically low oxygen tension in transplanted pancreatic islets. The present study tested the hypothesis that this may be coupled to changes in intracellular concentrations of crucial ions within the transplanted islet cells and, thus, their function.

METHODS

X-ray microanalysis was used for studies of native islet cells and islet grafts residing for 1 day or 1 month in nondiabetic or diabetic recipients.

RESULTS

Markedly increased sodium concentrations and decreased potassium concentrations were recorded in all transplanted islet cells, irrespective of whether the grafts had been implanted into nondiabetic or diabetic recipients or whether they were investigated 1 day or 1 month after transplantation. The calcium concentration in 1-day-old islet grafts was similar to that in native islet cells, but it decreased markedly between 1 day and 1 month after transplantation. Again this was seen in both nondiabetic and diabetic recipients.

CONCLUSIONS

Most probably, the disturbances in graft sodium and potassium concentrations reflect ATP depletion and inhibition of the Na/K-ATPase in the plasma membrane as a result of impeded oxygen supply. The decreased calcium concentrations developing over time in the transplanted islet cells might be potentially detrimental, because calcium plays a fundamental role in the control of a variety of cellular functions, including insulin secretion, in beta cells.

Preservation of neurologic function during inflammatory demyelination correlates with axon sparing in a mouse model of multiple sclerosis

Axonal injury has been proposed as the basis of permanent deficits in the inflammatory, demyelinating disease, multiple sclerosis. However, reports on the degree of injury are highly variable, and the responsible mechanisms are poorly understood. We examined the relationships among long-term demyelination, inflammation, axonal injury, and motor function in a model of multiple sclerosis, in which mice develop chronic, immune-mediated demyelination of the spinal cord resulting from persistent infection with Theiler's virus. We studied two strains of mice, inbred SJL/J and C57BL/6x129 mice deficient in beta(2)-microglobulin and therefore CD8 lymphocytes. After 8 months of disease, SJL mice had considerably worse motor function than beta(2)-microglobulin-deficient mice. Motor dysfunction correlated linearly with the extent of demyelinated lesions in the spinal cord (lesion load) within each strain, but no difference in lesion load was present between strains. Also, the extent of remyelination did not differ between strains. Instead, the disparity in motor deficits reflected differences in the integrity of descending neurons. That is, retrograde labeling of reticulospinal, vestibulospinal, and rubrospinal neurons, although reduced in all chronically diseased mice, was two to seven times higher in beta(2)-microglobulin-deficient mice. The labeling was superior in beta(2)-microglobulin-deficient mice despite the fact that lesion expanse and therefore the number of axons traversing lesions were similar in both strains. Thus, by all criteria axons were equivalently demyelinated in SJL and beta(2)-microglobulin-deficient mice, but the extent of axonal injury differed significantly. These results indicate that mechanisms of demyelination and axonal injury are at least partly separable, and are consistent with the hypothesis that cytotoxic CD8 lymphocytes may selectively injure demyelinated axons. Additionally, the data suggest that axonal injury obligatorily results from chronic inflammatory demyelination and significantly contributes to neurological deficits.