Long-Distance Axonal Regeneration in the Filum Terminale of Adult Rats Is Regulated by Ependymal Cells

Development of a new surgical technique to infuse kynurenic acid to optic nerves in chickens for studying loss of myelination

Prolonged infusion of a high dose of kynurenic acid (KYNA) reduces the myelin content in the rat spinal cord with preservation of the axonal integrity and without inducing an inflammatory response. We hypothesized that subdural infusion of a high concentration of KYNA can induce myelin loss in the optic nerves (ONs) of chickens. However, existing methods to deliver agents to the ON are inefficient, unlocalized and provide only acute exposure. Thus, we developed a surgical approach for sustained delivery of KYNA to the chicken ON. In brief, the novel surgical technique, which does not include excision of the extraocular muscles, involves incision of the skin and underlying fascial sheath to access the optic nerve within the muscle cone, implantation of a catheter in the dura of the optic nerve, the other end of which exits the orbit under the skin. The catheter runs under the skin near the lateral canthus, over the ears to the back of the neck, where a second incision is made to both implant the osmotic pump and to attach the catheter to the osmotic pump. India ink was used to confirm prolonged sustained administration to the optic nerves and across the chiasm. This surgical model was used to investigate KYNA's effect(s) on myelin loss in the ON. ONs of 7-day old chickens were infused with 50 mM KYNA or phosphate buffered saline (PBS) for seven days. Analysis of KYNA-infused contralateral ON g-ratios and protein levels indicated a reduction in myelin. These findings demonstrate the utility of our surgical approach for sustained delivery of KYNA into the ON and suggest a role for KYNA in modulating CNS myelination.

Filum Terminale: A Comprehensive Review with Anatomical, Pathological, and Surgical Considerations

The conus medullaris is the distal tapering end of the spinal cord, and the filum terminale (FT) is regarded as a bundle of non-functional fibrous tissue; therefore, some scholars call it the spinal ligament, while others describe the human FT as "remnants of the spinal cord." It was later found that in the human spinal cord, the FT is composed of an intradural segment and an epidural segment, and the end of the FT is connected to the coccyx periosteum. Because some nerve tissue is also found in the FT, as research progresses, FT may have the potential for transplantation. A lack of exhaustive overviews on the FT in the present literature prompted us to conduct this review. Considering that a current comprehensive review seemed to be the need of the hour, herein, we attempted to summarize previous research and theories on the FT, elucidate its anatomy, and understand its pathological involvement in various diseases.

Prolonged inflammation leads to ongoing damage after spinal cord injury

The pathogenesis of spinal cord injury (SCI) remains poorly understood and treatment remains limited. Emerging evidence indicates that post-SCI inflammation is severe but the role of reactive astrogliosis not well understood given its implication in ongoing inflammation as damaging or neuroprotective. We have completed an extensive systematic study with MRI, histopathology, proteomics and ELISA analyses designed to further define the severe protracted and damaging inflammation after SCI in a rat model. We have identified 3 distinct phases of SCI: acute (first 2 days), inflammatory (starting day 3) and resolution (>3 months) in 16 weeks follow up. Actively phagocytizing, CD68+/CD163- macrophages infiltrate myelin-rich necrotic areas converting them into cavities of injury (COI) when deep in the spinal cord. Alternatively, superficial SCI areas are infiltrated by granulomatous tissue, or arachnoiditis where glial cells are obliterated. In the COI, CD68+/CD163- macrophage numbers reach a maximum in the first 4 weeks and then decline. Myelin phagocytosis is present at 16 weeks indicating ongoing inflammatory damage. The COI and arachnoiditis are defined by a wall of progressively hypertrophied astrocytes. MR imaging indicates persistent spinal cord edema that is linked to the severity of inflammation. Microhemorrhages in the spinal cord around the lesion are eliminated, presumably by reactive astrocytes within the first week post-injury. Acutely increased levels of TNF-alpha, IL-1beta, IFN-gamma and other pro-inflammatory cytokines, chemokines and proteases decrease and anti-inflammatory cytokines increase in later phases. In this study we elucidated a number of fundamental mechanisms in pathogenesis of SCI and have demonstrated a close association between progressive astrogliosis and reduction in the severity of inflammation.

Methods for Assessing Serpins as Neuroprotective Therapeutics

As the systematic work on the pathogenesis of the white matter injury in the spinal cord models progresses, it becomes obvious that a severe and extraordinarily protracted, destructive inflammation follows the initial injury. Appropriate anti-inflammatory therapies of sufficient duration should not only inhibit but also lead to the elimination of this destructive inflammation, thus resulting in neuroprotection of the spinal cord tissue and a greater preservation of the neurologic function. While dexamethasone, a powerful, anti-inflammatory steroid analog administered continuously by subdural infusion for 7 days inhibited severe macrophage infiltration in the cavity of injury, the dose used was remarkably toxic. A 2-week-long infusion of lower doses of dexamethasone resulted in dose-dependent inhibition of macrophage infiltration and was better tolerated by the rats, but it became evident that a much longer duration of subdural administration of a powerful anti-inflammatory drug is required to eliminate myelin-rich, necrotic debris from the cavity and synthetic steroids such as dexamethasone, and methylprednisolone may be too toxic for this application. Therefore, nontoxic but powerful anti-inflammatory compounds are required for neuroprotective treatment of the spinal cord injury (SCI) and also brain trauma and stroke where the massive injury to the white matter occurs. Serpins have been associated with neurological damage. The mammalian serpin neuroserpin (SERPINI1) is reported to act in a protective manner after cerebrospinal infarction. The serine protease, tissue-type plasminogen activator (tPA), and the serpin plasminogen activator inhibitor (PAI-1, SERPINE1) are both upregulated at sites of central nervous system damage. In preliminary studies, subdural infusion of the myxomaviral serpin, Serp-1, resulted in the powerful inhibition of the macrophage infiltration of the cavity of injury, comparable to the inhibition by high dose of dexamethasone that has proven to be unduly toxic. Nontoxic, yet powerful neuroprotective, anti-inflammatory effects of Serp-1 may indicate this serpin protein as a potential attractive compound to treat SCI and similar syndromes involving massive injury to the white matter such as brain trauma and stroke. Novel methods of drug delivery, chronic subdural infusion, and novel analytic methods to measure the effectiveness of the neuroprotective serpin treatments are discussed in this chapter.

Structures of filum terminale and characteristics of ependymal cells of its central canal in rats

The filum terminale (FT) is a potential source of ependymal cells for transplantation. The present study was performed to clarify the characteristics of ependymal cells of the central canal (CC) of the FT in rats. The FT was a thin strand continuous with the conus medullaris (CM), a caudal end of the main spinal cord, situated at the L3-4 level in adult rats. The border between the CM and FT was not visible, but could be defined as the site where the strand was as thin as its more caudal segment. While the CM contained an appreciable amount of white and grey matter associated with the CC at its center, the FT had no or only a negligible amount of such spinal cord parenchymal tissue. The FT was tracked ca. 4 cm from the site defined above to the level of S4-5 in adult rats. The rostral part of the FT (FTI) included within the cauda equina is exposed to cerebrospinal fluid, whereas the more caudal part (FTE) was surrounded by a dense layer of connective tissue. Almost all ependymal cells were immunostained for Sox2, Sox9, FoxJ1, and CD133, generally recognized immunochemical markers for ependymal cells of the CC in the spinal cord. Ependymal cells of the CC of FT exhibited almost the same structural and immunohistochemical characteristics as those of the CC of the main spinal cord. Ependymal cells of FTI covered by a thin layer of connective tissue are considered appropriate for transplantation.

Cancer pain and neuropathic pain are associated with A β sensory neuronal plasticity in dorsal root ganglia and abnormal sprouting in lumbar spinal cord

Evidence suggests that there are both nociceptive and neuropathic components of cancer-induced pain. We have observed that changes in intrinsic membrane properties and excitability of normally non-nociceptive Aβ sensory neurons are consistent in rat models of peripheral neuropathic pain and cancer-induced pain. This has prompted a comparative investigation of the intracellular electrophysiological characteristics of sensory neurons and of the ultrastructural morphology of the dorsal horn in rat models of neuropathic pain and cancer-induced pain. Neuropathic pain model rats were induced with a polyethylene cuff implanted around a sciatic nerve. Cancer-induced pain model rats were induced with mammary rat metastasis tumour-1 rat breast cancer or MATLyLu rat prostate cancer cells implanted into the distal epiphysis of a femur. Behavioural evidence of nociception was detected using von Frey tactile assessment. Aβ-fibre low threshold mechanoreceptor neurons in both cancer-induced pain and neuropathic pain models exhibited slower dynamics of action potential genesis, including a wider action potential duration and lower action potential amplitude compared to those in control animals. Enhanced excitability of Aβ-fibre low threshold mechanoreceptor neurons was also observed in cancer-induced pain and neuropathic pain models. Furthermore, both cancer-induced pain and neuropathic pain models showed abundant abnormal axonal sprouting in bundles of myelinated axons in the ipsilateral spinal laminae IV and V. The patterns of changes show consistency between rat models of cancer-induced pain and neuropathic pain. These findings add to the body of evidence that animal models of cancer-induced pain and neuropathic pain share features that may contribute to the peripheral and central sensitization and tactile hypersensitivity in both pain states.

Activated spinal cord ependymal stem cells rescue neurological function

Spinal cord injury (SCI) is a major cause of paralysis. Currently, there are no effective therapies to reverse this disabling condition. The presence of ependymal stem/progenitor cells (epSPCs) in the adult spinal cord suggests that endogenous stem cell-associated mechanisms might be exploited to repair spinal cord lesions. epSPC cells that proliferate after SCI are recruited by the injured zone, and can be modulated by innate and adaptive immune responses. Here we demonstrate that when epSPCs are cultured from rats with a SCI (ependymal stem/progenitor cells injury [epSPCi]), these cells proliferate 10 times faster in vitro than epSPC derived from control animals and display enhanced self renewal. Genetic profile analysis revealed an important influence of inflammation on signaling pathways in epSPCi after injury, including the upregulation of Jak/Stat and mitogen activated protein kinase pathways. Although neurospheres derived from either epSPCs or epSPCi differentiated efficiently to oligodendrocites and functional spinal motoneurons, a better yield of differentiated cells was consistently obtained from epSPCi cultures. Acute transplantation of undifferentiated epSPCi or the resulting oligodendrocyte precursor cells into a rat model of severe spinal cord contusion produced a significant recovery of motor activity 1 week after injury. These transplanted cells migrated long distances from the rostral and caudal regions of the transplant to the neurofilament-labeled axons in and around the lesion zone. Our findings demonstrate that modulation of endogenous epSPCs represents a viable cell-based strategy for restoring neuronal dysfunction in patients with spinal cord damage.

Robust axonal growth and a blunted macrophage response are associated with impaired functional recovery after spinal cord injury in the MRL/MpJ mouse

Spinal cord injury (SCI) in mammals leads to a robust inflammatory response followed by the formation of a glial and connective tissue scar that comprises a barrier to axonal regeneration. The inbred MRL/MpJ mouse strain exhibits reduced inflammation after peripheral injury and shows true regeneration without tissue scar formation following an ear punch wound. We hypothesized that following SCI, the unique genetic wound healing traits of this strain would result in reduced glial and connective tissue scar formation, increased axonal growth, and improved functional recovery. Adult MRL/MpJ and C57BL/6J mice were subjected to a mid-thoracic spinal contusion and the distribution of axon profiles and selected cellular and extracellular matrix components was compared at 1, 2, 4 and 6 weeks post-injury. Recovery of hind-limb locomotor function was assessed over the same time period. The MRL/MpJ mice exhibited robust axon growth within the lesion, beginning at 4 weeks post-injury. This growth was accompanied by reduced macrophage staining at 1, 2, 4 and 6 weeks post-injury, decreased chondroitin sulfate proteoglycan staining at 1-2 weeks and increased laminin staining throughout the lesion at 2-6 weeks post-injury. Paradoxically, the extent of locomotor recovery was impaired in the MRL/MpJ mice. Close examination of the chronic lesion site revealed evidence of ongoing degeneration both within and surrounding the lesion site. Thus, the regenerative genetic wound healing traits of the MRL/MpJ mice contribute to the evolution of a lesion environment that supports enhanced axon growth after SCI. However, this response occurs at the expense of meaningful functional recovery.