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An estimated 11,000 spinal cord injuries occur each year in the United States and more than 200,000 Americans suffer from maladies associated with spinal cord injury. This includes paralysis, bowel and bladder dysfunction, sexual dysfunction, respiratory impairment, temperature regulation problems, and chronic pain. During the last two decades, longstanding beliefs about the inability of the adult central nervous system to heal itself have been eroded by the flood of new information from research in the neurosciences and related fields. However, there are still no cures and the challenge of restoring function in the wake of spinal cord injuries remains extremely complex. Spinal Cord Injury examines the future directions for research with the goal to accelerate the development of cures for spinal cord injuries. While many of the recommendations are framed within the context of the specific needs articulated by the New York Spinal Cord Injury Research Board, the Institute of Medicine's panel of experts looked very broadly at research priorities relating to future directions for the field in general and make recommendations to strengthen and coordinate the existing infrastructure. Funders at federal and state agencies, academic organizations, pharmaceutical and device companies, and non-profit organizations will all find this book to be an essential resource as they examine their opportunities.

Spasms after spinal cord injury (SCI) are debilitating involuntary muscle contractions that have been associated with increased motor neuron excitability and decreased inhibition. However, whether spasms involve activation of premotor spinal excitatory neuronal circuits is unknown. Here we use mouse genetics, electrophysiology, imaging and optogenetics to directly target major classes of spinal interneurons as well as motor neurons during spasms in a mouse model of chronic SCI. We find that assemblies of excitatory spinal interneurons are recruited by sensory input into functional circuits to generate persistent neural activity, which interacts with both the graded expression of plateau potentials in motor neurons to generate spasms, and inhibitory interneurons to curtail them. Our study reveals hitherto unrecognized neuronal mechanisms for the generation of persistent neural activity under pathophysiological conditions, opening up new targets for treatment of muscle spasms after SCI.

Unsuccessful axonal regeneration in transected spinal cord injury (SCI) is mainly attributed to shortage of growth factors, inhibitory glial scar, and low intrinsic regenerating capacity of severely injured neurons. Previously, we constructed an axonal growth permissive pathway in a thoracic hemisected injury by transplantation of Schwann cells overexpressing glial-cell-derived neurotrophic factor (SCs-GDNF) into the lesion gap as well as the caudal cord and proved that this novel permissive bridge promoted the regeneration of descending propriospinal tract (dPST) axons across and beyond the lesion. In the current study, we subjected rats to complete thoracic (T11) spinal cord transections and examined whether these combinatorial treatments can support dPST axons’ regeneration beyond the transected injury. The results indicated that GDNF significantly improved graft–host interface by promoting integration between SCs and astrocytes, especially the migration of reactive astrocyte into SCs-GDNF territory. The glial response in the caudal graft area has been significantly attenuated. The astrocytes inside the grafted area were morphologically characterized by elongated and slim process and bipolar orientation accompanied by dramatically reduced expression of glial fibrillary acidic protein. Tremendous dPST axons have been found to regenerate across the lesion and back to the caudal spinal cord which were otherwise difficult to see in control groups. The caudal synaptic connections were formed, and regenerated axons were remyelinated. The hindlimb locomotor function has been improved.

Increasing evidence supports the notion that spinal cord microglia activation plays a causal role in the development of neuropathic pain after peripheral nerve injury; yet the mechanisms for microglia activation remain elusive. Here, we provide evidence that NADPH oxidase 2 (Nox2)-derived ROS production plays a critical role in nerve injury-induced spinal cord microglia activation and subsequent pain hypersensitivity. Nox2 expression was induced in dorsal horn microglia immediately after L5 spinal nerve transection (SNT). Studies using Nox2-deficient mice show that Nox2 is required for SNT-induced ROS generation, microglia activation, and proinflammatory cytokine expression in the spinal cord. SNT-induced mechanical allodynia and thermal hyperalgesia were similarly attenuated in Nox2-deficient mice. In addition, reducing microglial ROS level via intrathecal sulforaphane administration attenuated mechanical allodynia and thermal hyperalgesia in SNT-injured mice. Sulforaphane also inhibited SNT-induced proinflammatory gene expression in microglia, and studies using primary microglia indicate that ROS generation is required for proinflammatory gene expression in microglia. These studies delineate a pathway involving nerve damage leading to microglial Nox2-generated ROS, resulting in the expression of proinflammatory cytokines that are involved in the initiation of neuropathic pain.

In humans, spinal cord lesions induce not only major motor and neurovegetative deficits but also severe neuropathic pain which is mostly resistant to classical analgesics. Better treatments can be expected from precise characterization of underlying physiopathological mechanisms. This led us to thoroughly investigate (i) mechanical and thermal sensory alterations, (ii) responses to acute treatments with drugs having patent or potential anti-allodynic properties and (iii) the spinal/ganglion expression of transcripts encoding markers of neuronal injury, microglia and astrocyte activation in rats that underwent complete spinal cord transection (SCT). SCT was performed at thoracic T8-T9 level under deep isoflurane anaesthesia, and SCT rats were examined for up to two months post surgery. SCT induced a marked hyper-reflexia at hindpaws and strong mechanical and cold allodynia in a limited (6 cm2) cutaneous territory just rostral to the lesion site. At this level, pressure threshold value to trigger nocifensive reactions to locally applied von Frey filaments was 100-fold lower in SCT- versus sham-operated rats. A marked up-regulation of mRNAs encoding ATF3 (neuronal injury) and glial activation markers (OX-42, GFAP, P2×4, P2×7, TLR4) was observed in spinal cord and/or dorsal root ganglia at T6-T11 levels from day 2 up to day 60 post surgery. Transcripts encoding the proinflammatory cytokines IL-1β, IL-6 and TNF-α were also markedly but differentially up-regulated at T6-T11 levels in SCT rats. Acute treatment with ketamine (50 mg/kg i.p.), morphine (3-10 mg/kg s.c.) and tapentadol (10-20 mg/kg i.p.) significantly increased pressure threshold to trigger nocifensive reaction in the von Frey filaments test, whereas amitriptyline, pregabalin, gabapentin and clonazepam were ineffective. Because all SCT rats developed long lasting, reproducible and stable allodynia, which could be alleviated by drugs effective in humans, thoracic cord transection might be a reliable model for testing innovative therapies aimed at reducing spinal cord lesion-induced central neuropathic pain.

Spinal cord injuries result in the loss of motor and sensory functions controlled by neurons located at the site of the lesion and below. We hypothesized that experimentally enhanced remyelination supports axon preservation and/or growth in the total spinal cord transection in rats. Multifocal demyelination was induced by injection of ethidium bromide (EB), either at the time of transection or twice during transection and at 5 days post-injury. We demonstrated that the number of oligodendrocyte progenitor cells (OPCs) significantly increased 14 days after demyelination. Most OPCs differentiated into mature oligodendrocytes by 60–90 dpi in double-EB-injected rats; however, most axons were remyelinated by Schwann cells. A significant number of axons passed the injury epicenter and entered the distant segments of the spinal cord in the double-EB-injected rats. Moreover, some serotoninergic fibers, not detected in control animals, grew caudally through the injury site. Behavioral tests performed at 60–90 dpi revealed significant improvement in locomotor function recovery in double-EB-injected rats, which was impaired by the blockade of serotonin receptors, confirming the important role of restored serotonergic fibers in functional recovery. Our findings indicate that enhanced remyelination per se, without substantial inhibition of glial scar formation, is an important component of spinal cord injury regeneration.

Introduction Severe spinal cord injury results in the loss of neurons in the relatively intact spinal cord below the injury area and skeletal muscle atrophy in the paralyzed limbs. These pathological processes are significant obstacles for motor function reconstruction. Objective We performed tail nerve electrical stimulation (TNES) to activate the motor neural circuits below the injury site of the spinal cord to elucidate the regulatory mechanisms of the excitatory afferent neurons in promoting the reconstruction of locomotor function. Methods Eight days after T10 spinal cord transection in rats, TNES was performed for 7 weeks. Behavioral scores were assessed weekly. Electrophysiological tests and double retrograde tracings were performed at week 8. Results After 7 weeks of TNES treatment, there was restoration in innervation, the number of stem cells, and mitochondrial metabolism in the rats' hindlimb muscles. Double retrograde tracings of the tail nerve and sciatic nerve further confirmed the presence of synaptic connections between the tail nerve and central pattern generator (CPG) neurons in the lumbar spinal cord, as well as motor neurons innervating the hindlimb muscles. Conclusion The mechanisms of TNES induced by the stimulation of primary afferent nerve fibers involves efficient activation of the motor neural circuits in the lumbosacral segment, alterations of synaptic plasticity, and the improvement of muscle and nerve regeneration, which provides the structural and functional foundation for the future use of cutting‐edge biological treatment strategies to restore voluntary movement of paralyzed hindlimbs. The specific neural pathway and the mechanism of activation in the spinal cord CPG and effects on the motor neural circuits during TNES treatment.

Introduction Self‐repair of spinal cord injury (SCI) has been found in humans and experimental animals with partial recovery of neurological functions. However, the regulatory mechanisms underlying the spontaneous locomotion recovery after SCI are elusive. Aims This study was aimed at evaluating the pathological changes in injured spinal cord and exploring the possible mechanism related to the spontaneous recovery. Results Immunofluorescence staining was performed to detect GAP43 expression in lesion site after spinal cord transection (SCT) in rats. Then RNA sequencing and gene ontology (GO) analysis were employed to predict lncRNA that correlates with GAP43. LncRNA smart‐silencing was applied to verify the function of lncRNA vof16 in vitro, and knockout rats were used to evaluate its role in neurobehavioral functions after SCT. MicroRNA sequencing, target scan, and RNA22 prediction were performed to further explore the underlying regulatory mechanisms, and miR‐185‐5p stands out. A miR‐185‐5p site‐regulated relationship with GAP43 and vof16 was determined by luciferase activity analysis. GAP43‐silencing, miR‐185‐5p‐mimic/inhibitor, and miR‐185‐5p knockout rats were also applied to elucidate their effects on spinal cord neurite growth and neurobehavioral function after SCT. We found that a time‐dependent increase of GAP43 corresponded with the limited neurological recovery in rats with SCT. CRNA chip and GO analysis revealed lncRNA vof16 was the most functional in targeting GAP43 in SCT rats. Additionally, silencing vof16 suppressed neurite growth and attenuated the motor dysfunction in SCT rats. Luciferase reporter assay showed that miR‐185‐5p competitively bound the same regulatory region of vof16 and GAP43. Conclusions Our data indicated miR‐185‐5p could be a detrimental factor in SCT, and vof16 may function as a ceRNA by competitively binding miR‐185‐5p to modulate GAP43 in the process of self‐recovery after SCT. Our study revealed a novel vof16‐miR‐185‐5p‐GAP43 regulatory network in neurological self‐repair after SCT and may underlie the potential treatment target for SCI. Here, we found that vof16‐miR185‐5p‐GAP43 network is closely related to SCT self‐repair, and simultaneously enhances motor and sensory function after SCT. Knocking out vof16 or GAP43 could inhibit the self‐repair of spinal cord and neurite growth, while miR‐185‐5p knockout promoted the axonal growth after SCT. Furthermore, miR‐185‐5p can competitively bind the same regulatory region of vof16 and GAP43. Our study provides a novel regulatory network that functions via a miRNA competitive mechanism mediated by vof16 in SCT self‐repair and axonal growth.

Activity-based interventions such as locomotor training or passive cycling have a positive influence on the spinal circuitry and recovery following a spinal cord injury (SCI). The use of quipazine in combination with exercise training has demonstrated a greater functional recovery than has exercise training alone. However, the influence of exercise or training on the responsiveness of the spinal cord to quipazine has not been examined following a chronic spinal transection. The purpose of this study was to characterize the flexor and extensor monosynaptic reflex (MSR) response pre- and post-quipazine in chronic complete spinally transected rats that either underwent daily passive cycling for 3 months or did not receive passive cycling. Following a chronic spinal transection, the extensor MSR demonstrated a hyperreflexive response (fivefold increase) to afferent stimuli, and did not respond to quipazine injection. With daily passive cycling, the extensor MSR hyperexcitability was attenuated, and the MSR amplitude increased 72% following quipazine injection (p<0.004), which was comparable to the extensor MSR response (94%) in the control group. For both chronic spinal transection groups, the flexor MSR amplitudes were not altered following quipazine injection, whereas in the control group the flexor MSR amplitude increased 86% in response to quipazine (p<0.004). These results demonstrate that passive cycling attenuates the hyperreflexive response of the extensor MSR following a chronic SCI, and restores the MSR response to quipazine.

Background: Complete spinal cord injury (SCI) leads to a disconnection between the brain and the body below the injury level, resulting in the functional silencing, degeneration, and apoptosis of sensorimotor cortex (SMC) neurons, which is of crucial importance to the pathological process. Methods: In this study, a rat model of spinal cord transection was employed to explore the activation of neurons in the SMC and the reversal of neurodegeneration after the rats were treated with transcranial intermittent theta-burst stimulation (T-iTBS). Results: The results demonstrated that the expression of the immediate early gene c-Fos and the synaptic plasticity-associated activity-regulated cytoskeleton (Arc) gene in the neurons of the SMC was increased in the T-iTBS group 4 weeks after SCI. Transcriptome sequencing revealed that neuronal activation-, neuronal metabolism-, synaptic activity-, and neural regeneration-related genes were significantly upregulated in the T-iTBS group compared with those of the sham-iTBS group, but the expression was similar to that in the normal group. Western blot analysis indicated that the expression of Cle-caspase-3 (CC3) in the SMC was significantly reduced in the T-iTBS group, and the number of CD68-positive cells in the SMC was close to that of normal rats but significantly less than that in the sham-iTBS and SCI groups. These results are in line with those of the transcriptome sequencing. Correlation analysis of the expression rate between c-Fos and Arc, CC3, and CD68 further suggested that T-iTBS improved the immune microenvironment and prevented neurodegeneration by regulating the activation and synaptic plasticity of SMC neurons in the early stages of injury. Conclusions: Collectively, our findings offer support for the utilization of T-iTBS, a non-invasive neural stimulation treatment, to prevent SMC degeneration following severe SCI.