Spinal cord injury (SCI) can result in profound loss of function the majority of patients experience persistent pain that is difficult to manage. Most of what is known about the mechanisms underlying pain following SCI has focused on changes occurring within the spinal cord. However, recent work has shown that primary afferents also contribute to the initiation and maintenance of SCI-induced chronic pain. Of particular significance is the finding that afferents exhibit spontaneous activity (SA) following SCI, and fire independent of peripheral stimulation. SA has also been shown to contribute to behavioral indices of SCI-induced chronic pain. The mechanisms underlying the emergence of SA in sensory neurons have not been clearly elucidated, but a population of afferents that express the sodium channel, Nav1.8, and the TRPV1 receptor appear to be vulnerable to the effects of SCI. These afferents are thought to be peptidergic, suggesting that this population of nociceptors is primarily responsible for the emergence of pain following SCI. However, recent work from our laboratory has shown that the SCI impacts both peptidergic and nonpeptidergic afferents. Using single cell qPCR, we have shown that the expression of a number of pain-relevant genes is increased in both populations of afferents within 24 hr of SCI, and that increased gene expression corresponds to the onset of SA. Of these targets, Acid Sensing Ion Channel Subunit 3 (ASIC3) exhibits the largest increase in expression following SCI. Given that ASIC3 shows a rapid increase in expression following SCI in both populations of afferents, we hypothesize that ASIC3 functions to relay the onset of SCI and initiates afferent sensitization and subsequent behavioral sensitivity. To examine the role of ASIC3 in afferent sensitization and behavioral sensitivity following injury, SCI, sham, and nave mice will receive injections of targeting or nontargeting antisense oligonucleotides (ASOs) at the time of SCI (Aim 1) or 6 days following injury (Aim 2). We will then assess behavioral sensitivity to mechanical stimulation of the hindpaw, followed by ex vivo characterization of neuronal responses to mechanical, heat, and cold stimulation 1, 7, 14, and 28 days following SCI. Recorded cells will then be collected and levels of ASIC3 mRNA expression will be evaluated using single cell qPCR. We predict that administration of ASIC3 targeting siRNA will attenuate the development of SCI-induced mechanical sensitivity and afferent sensitization. We further propose that given the nature of SCI and the potential for early intervention, targeting ASIC3 at the time of injury may be effective at disrupting the processes underlying the development of persistent pain following SCI.
A majority of patients with spinal cord injury experience persistent pain that is difficult to manage and significantly impairs quality of life. The proposed application will employ a mouse model of spinal cord injury to explore the role of Acid Sensing Ion Channel Subunit 3 (ASIC3) in the initiation and maintenance of afferent sensitization and behavioral hypersensitivity. The results from this study may advance the development of new therapies for treating chronic pain following spinal cord injury by providing a novel target for therapeutic intervention at the time of injury.
