Walker JR, Ong A, Detloff MR (2019) Role of nociceptive afferent input on forelimb reaching and grasping behaviors in the spinal cord injured rat. Neuroscience 2019 Abstracts 572.09. Society for Neuroscience, Chicago, IL.
Summary: Individuals with spinal cord injury (SCI) suffer a loss of motor and sensory function. The current standard of care to recover fine motor control is rehabilitation focused on a combination of range of motion, aerobic, and strength training (ST). However, limited research has been conducted to determine the role of nociceptive afferent inputs from muscle on spinal plasticity and/or recovery of function. Using a rodent model of SCI strength training rehabilitation, we determined that motor training not only improves forelimb strength and fine motor function but also can modulate the development of neuropathic pain, suggesting that improvements in reaching and grasping may be due, in part, to plasticity of nociceptive afferents. To further explore this, Sprague-Dawley rats received injections of rIB4-conjugated saporin, mu p75-conjugated saporin or unconjugated (vehicle) into the cervical dorsal root ganglia unilaterally to eliminate non-peptidergic and peptidergic nociceptors. There is an uninjured cohort and a group with unilateral C5 SCI. Von Frey and Hargreaves’ tests were performed at baseline and several time points post-injection to assess the effcacy of the nociceptive elimination. Several measures of forelimb strength were recorded over time including the isometric pull task, a single pellet retrieval task and the Montoya staircase test. To confirm the depletion of peptidergic and non-peptidergic nociceptors following saporin injection and/or SCI, cervical DRGs and spinal cords were stained with antibodies against CGRP and isolectin-B4. An understanding of the role of nociceptors in spinal plasticity and functional motor and sensory recovery of SCI patients will guide future research and refine rehabilitation strategies to further improve their quality of life.