Targeted stimulation of the spinal cord to restore locomotor activity

Corticospinal circuit neuroplasticity may involve silent synapses: Implications for functional recovery facilitated by neuromodulation after spinal cord injury

Spinal cord injury (SCI) leads to devastating physical consequences, such as severe sensorimotor dysfunction even lifetime disability, by damaging the corticospinal system. The conventional opinion that SCI is intractable due to the poor regeneration of neurons in the adult central nervous system (CNS) needs to be revisited as the CNS is capable of considerable plasticity, which underlie recovery from neural injury. Substantial spontaneous neuroplasticity has been demonstrated in the corticospinal motor circuitry following SCI. Some of these plastic changes appear to be beneficial while others are detrimental toward locomotor function recovery after SCI. The beneficial corticospinal plasticity in the spared corticospinal circuits can be harnessed therapeutically by multiple contemporary neuromodulatory approaches, especially the electrical stimulation-based modalities, in an activity-dependent manner to improve functional outcomes in post-SCI rehabilitation. Silent synapse generation and unsilencing contribute to profound neuroplasticity that is implicated in a variety of neurological disorders, thus they may be involved in the corticospinal motor circuit neuroplasticity following SCI. Exploring the underlying mechanisms of silent synapse-mediated neuroplasticity in the corticospinal motor circuitry that may be exploited by neuromodulation will inform a novel direction for optimizing therapeutic repair strategies and rehabilitative interventions in SCI patients.

The Neuroprotective Role of Polydatin: Neuropharmacological Mechanisms, Molecular Targets, Therapeutic Potentials, and Clinical Perspective

Neurodegenerative diseases (NDDs) are one of the leading causes of death and disability in humans. From a mechanistic perspective, the complexity of pathophysiological mechanisms contributes to NDDs. Therefore, there is an urgency to provide novel multi-target agents towards the simultaneous modulation of dysregulated pathways against NDDs. Besides, their lack of effectiveness and associated side effects have contributed to the lack of conventional therapies as suitable therapeutic agents. Prevailing reports have introduced plant secondary metabolites as promising multi-target agents in combating NDDs. Polydatin is a natural phenolic compound, employing potential mechanisms in fighting NDDs. It is considered an auspicious phytochemical in modulating neuroinflammatory/apoptotic/autophagy/oxidative stress signaling mediators such as nuclear factor-κB (NF-κB), NF-E2–related factor 2 (Nrf2)/antioxidant response elements (ARE), matrix metalloproteinase (MMPs), interleukins (ILs), phosphoinositide 3-kinases (PI3K)/protein kinase B (Akt), and the extracellular regulated kinase (ERK)/mitogen-activated protein kinase (MAPK). Accordingly, polydatin potentially counteracts Alzheimer’s disease, cognition/memory dysfunction, Parkinson’s disease, brain/spinal cord injuries, ischemic stroke, and miscellaneous neuronal dysfunctionalities. The present study provides all of the neuroprotective mechanisms of polydatin in various NDDs. Additionally, the novel delivery systems of polydatin are provided regarding increasing its safety, solubility, bioavailability, and efficacy, as well as developing a long-lasting therapeutic concentration of polydatin in the central nervous system, possessing fewer side effects.

Interactions Between Baclofen and DC-induced Plasticity of Afferent Fibers within the Spinal Cord

The aims of the study were to compare effects of baclofen, a GABA_B receptor agonist commonly used as an antispastic drug, on direct current (DC) evoked long-lasting changes in the excitability of afferent fibers traversing the dorsal columns and their terminal branches in the spinal cord, and to examine whether baclofen interferes with the development and expression of these changes. The experiments were performed on deeply anesthetized rats by analyzing the effects of DC before, during and following baclofen administration. Muscle and skin afferent fibers within the dorsal columns were stimulated epidurally and changes in their excitability were investigated following epidural polarization by 1.0-1.1 μA subsequent to i.v. administration of baclofen. Epidural polarization increased the excitability of these fibers during post-polarization periods of at least 1 h. The facilitation was as potent as in preparations that were not pretreated with baclofen, indicating that the advantages of combining epidural polarization with epidural stimulation would not be endangered by pharmacological antispastic treatment with baclofen. In contrast, baclofen-reduced effects of intraspinal stimulation combined with intraspinal polarization (0.3 μA) of terminal axonal branches of the afferents within the dorsal horn or in motor nuclei, whether administered ionophoretically or intravenously. Effects of DC on monosynaptically evoked synaptic actions of these fibers (extracellular field potentials) were likewise reduced by baclofen. The study thus provides further evidence for differential effects of DC on afferent fibers in the dorsal columns and the preterminal branches of these fibers and their involvement in spinal plasticity.

Balance, gait, and falls in spinal cord injury

This chapter covers balance, gait, and falls in individuals with spinal cord injury (SCI) from a clinical perspective. First, the consequences of an SCI on functioning are explained, including etiology, clinical presentation, classification, and epidemiologic data. Then, the specific aspects of balance disorders, gait disorders, and falls are discussed with respect to motor complete (cSCI) and incomplete (iSCI) SCI. Typically, these activities are affected by impaired afferent and efferent nerves, but not by central nervous processing. Performance of daily life activities in cSCI depends on the ability to control the interaction between the center of mass and the base of support or limits of stability. In iSCI, impaired proprioception and muscle strength are important factors for completing balancing tasks and for walking. Falls are common in patients with SCI. Subsequent sections describe therapy approaches aimed at modifying balance, gait, and the risk for falls by means of therapeutic exercises, assistive devices like robots or functional electric stimulation, and environmental adaptations. The last part covers recent developments and future directions. These encompass interventions for maximizing residual neural function and regeneration of axons, as well as technical solutions like epidural or intraspinal electric stimulation, powered exoskeletons, and brain computer interfaces.

Spinal control of motor outputs by intrinsic and externally induced electric field potentials

Despite numerous studies on spinal neuronal systems, several issues regarding their role in motor behavior remain unresolved. One of these issues is how electric fields associated with the activity of spinal neurons influence the operation of spinal neuronal networks and how effects of these field potentials are combined with other means of modulating neuronal activity. Another closely related issue is how external electric field potentials affect spinal neurons and how they can be used for therapeutic purposes such as pain relief or recovery of motor functions by transspinal direct current stimulation. Nevertheless, progress in our understanding of the spinal effects of electric fields and their mechanisms has been made over the last years, and the aim of the present review is to summarize the recent findings in this field.

Enhancing Nervous System Recovery through Neurobiologics, Neural Interface Training, and Neurorehabilitation

After an initial period of recovery, human neurological injury has long been thought to be static. In order to improve quality of life for those suffering from stroke, spinal cord injury, or traumatic brain injury, researchers have been working to restore the nervous system and reduce neurological deficits through a number of mechanisms. For example, neurobiologists have been identifying and manipulating components of the intra- and extracellular milieu to alter the regenerative potential of neurons, neuro-engineers have been producing brain-machine and neural interfaces that circumvent lesions to restore functionality, and neurorehabilitation experts have been developing new ways to revitalize the nervous system even in chronic disease. While each of these areas holds promise, their individual paths to clinical relevance remain difficult. Nonetheless, these methods are now able to synergistically enhance recovery of native motor function to levels which were previously believed to be impossible. Furthermore, such recovery can even persist after training, and for the first time there is evidence of functional axonal regrowth and rewiring in the central nervous system of animal models. To attain this type of regeneration, rehabilitation paradigms that pair cortically-based intent with activation of affected circuits and positive neurofeedback appear to be required-a phenomenon which raises new and far reaching questions about the underlying relationship between conscious action and neural repair. For this reason, we argue that multi-modal therapy will be necessary to facilitate a truly robust recovery, and that the success of investigational microscopic techniques may depend on their integration into macroscopic frameworks that include task-based neurorehabilitation. We further identify critical components of future neural repair strategies and explore the most updated knowledge, progress, and challenges in the fields of cellular neuronal repair, neural interfacing, and neurorehabilitation, all with the goal of better understanding neurological injury and how to improve recovery.