. The majority of human spinal cord injuries (SCI) are anatomically incomplete, potentially leaving propriospinal pathways, which may relay information past the injury epicenter, intact. Following SCI in rodents, descending motor tracts sprout and increasingly contact descending propriospinal neurons (DPNs), forming detour circuits to relay signals caudal to the injury. However, no studies have evaluated the potential for ascending PNs to form bottom-up detour circuits post-SCI. We previously found that silencing long ascending PNs (LAPNs), which directly connect the lumbar and cervical spinal enlargements, disrupted coordination at each limb girdle. Surprisingly, silencing this anatomically intact pathway post-SCI improved locomotor function. Thus, it is critical to evaluate LAPN plasticity, and determine how this plasticity might be refined by therapeutic interventions. To do so, LAPN somatic and dendritic morphology will be characterized using a dual-viral system to specifically label LAPNs. We will also use a multi-viral system with a highly modified rabies virus to identify the sources of direct synaptic input to LAPNs. Increased physical activity and rehabilitative training are known to improve locomotor function and anatomical outcomes post-SCI. To evaluate the impact of physical activity and rehabilitative training on LAPN plasticity and locomotor function post-SCI, we will alter activity levels by housing animals in tiny cages or in large cages to restrict or facilitate activity. Animals in large cages will also receive rehabilitative training, which mimics clinical rehabilitation. Further understanding SCI-induced neuroplasticity, and how physical activity and rehabilitative training impact this plasticity will further our understanding of SCI pathology and provide new therapeutic targets. Working closely with my mentors, we have developed a training plan that will broaden my scientific skills, facilitate independent scientific thought, and cultivate skills needed to be a productive postdoctoral fellow. The Kentucky Spinal Cord Injury Research Center provides clinical and scientific expertise in SCI and related fields, and has a history of successfully preparing trainees for current and next stages in their careers. Hypothesis. Pre-SCI we hypothesize that DPNs, reticulospinals, and sensory afferents will provide input to LAPNs. Post-SCI we anticipate 1) LAPN dendrite orientation change, 2) LAPNs will be increasingly contacted by sensory afferents to form bottom-up detour circuits, and 3) increased activity plus rehabilitative training post- SCI will improve locomotor function, impact dendrite reorganization, and refine detour circuits.
Aim 1. Characterize the somatic and dendritic morphology of LAPNs, and identify the sources of direct synaptic input onto LAPNs.
Aim 2. Evaluate the effects of activity and rehabilitative training on locomotor function, LAPN morphology, and the sources of direct synaptic inputs to LAPNs after T10 contusive spinal cord injury.
This project aims to evaluate spinal cord injury (SCI)-induced neuroplasticity, and how rehabilitative training alters this plasticity. By characterizing the morphology of and inputs to long ascending propriospinal neurons (LAPNs) before SCI, we will be able to assess SCI induced changes to LAPN morphology, determine the role of LAPNs in forming de novo spinal circuits post-SCI, and determine the potential for rehabilitative training to refine these newly formed spinal circuits. Elucidating this will enhance our understanding of SCI pathology and provide new targets for neuromodulatory and rehabilitative therapies.