The overall goal is to develop effective, clinically applicable, approaches to restore upper limb function (reach-and-grasp) after chronic contusive cervical spinal cord injury (cSCI). Impairments in upper limb function significantly reduce the quality of life for people with cSCI. Reach-and-grasp actions in animals and humans are largely controlled by the corticospinal tract (CST). The investigators argue that promoting plasticity within the CST may support the recovery of upper limb function after cSCI. Repetitive exposure to acute intermittent hypoxia (rAIH) combined with motor training is a safe, minimally invasive, treatment that elicits neuroplasticity resulting in improved recovery after cSCI, but its overall effects remain limited. The main goals are to: 1) enhance rAIH/training-induced aftereffects on forelimb function and increase the understanding of the neuronal substrates in an adult rat model of chronic contusive cSCI, and 2) use this knowledge to guide the development of more effective rAIH/training approaches to improve upper limb function in humans with chronic contusive cSCI.~In Specific Aim 1, using an adult rat model of chronic contusive cSCI, the investigators will investigate the effects of rAIH frequency and dose on rAIH/training-mediated functional recovery of the impaired forelimb. Also, the investigators will combine rAIH/training with N-methyl-D-aspartate receptor (NMDA)-mediated synaptic plasticity through D-cycloserine treatment and study the effects on recovery of forelimb function. Immunocytochemistry with imaging techniques will be used to assess structural neuronal plasticity in the CST after rAIH/training. In Specific Aim 2, in people with chronic incomplete cSCI, guided by the findings in Specific Aim 1, the investigators will study the effects of rAIH frequency and concurrent D-cycloserine treatment on rAIH/training-mediated upper limb function recovery. The investigators will comprehensively analyze the effects of rAIH on the strength of electrophysiological and functional aftereffects in the upper limb.~The proposed research will provide new knowledge on rAIH/training-mediated functional and anatomical aftereffects (Specific Aim 1), which will be used to develop effective rAIH/training protocols for people with contusive, functionally incomplete, cSCI (Specific Aim 2). The data from the investigators' experiments may lead to clinically applicable approaches that improve arm and hand function recovery after chronic contusive cSCI, which would positively impact the quality of life of Veterans with cSCI. The relevance of this proposal is emphasized by the limited efficacy of current strategies to improve upper limb function after cSCI.
Contusive cervical spinal cord injury (cSCI) impairs upper limb function (reach-and-grasp) which limits daily-life activities and thus decreases the quality of life. Promoting neuroplasticity may support upper limb recovery after SCI. Repetitive exposure to acute intermittent hypoxia (rAIH) combined with motor training promotes recovery of motor function after SCI; however, the overall effects of rAIH/training are limited. The investigators will use an adult rat model of long-term contusive cSCI to study novel approaches to enhance the effect of rAIH/training on forelimb function and study the neuronal substrate underlying the effects. The findings will be used to direct the development of more effective rAIH/training approaches for people with contusive, functionally incomplete, cSCI. Because deficits in upper limb function are a major problem after stroke, amyotrophic lateral sclerosis, multiple sclerosis, and other motor disorders, this work may also be relevant for patients with other types of central nervous system (CNS) lesions.