Project Summary. 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.