Dual Modulation of Nociception and Cardiovascular Reflexes during Peripheral Ischemia through P2Y1 Receptor-Dependent Sensitization of Muscle Afferents

Abstract

Numerous musculoskeletal pain disorders are based in dysfunction of peripheral perfusion and are often comorbid with altered cardiovascular responses to muscle contraction/exercise. We have recently found in mice that 24 h peripheral ischemia induced by a surgical occlusion of the brachial artery (BAO) induces increased paw-guarding behaviors, mechanical hypersensitivity, and decreased grip strength. These behavioral changes corresponded to increased heat sensitivity as well as an increase in the numbers of chemosensitive group III/IV muscle afferents as assessed by an ex vivo forepaw muscles/median and ulnar nerves/dorsal root ganglion (DRG)/spinal cord (SC) recording preparation. Behaviors also corresponded to specific upregulation of the ADP-responsive P2Y1 receptor in the DRGs. Since group III/IV muscle afferents have separately been associated with regulating muscle nociception and exercise pressor reflexes (EPRs), and P2Y1 has been linked to heat responsiveness and phenotypic switching in cutaneous afferents, we sought to determine whether upregulation of P2Y1 was responsible for the observed alterations in muscle afferent function, leading to modulation of muscle pain-related behaviors and EPRs after BAO. Using an afferent-specific siRNA knockdown strategy, we found that inhibition of P2Y1 during BAO not only prevented the increased mean blood pressure after forced exercise, but also significantly reduced alterations in pain-related behaviors. Selective P2Y1 knockdown also prevented the increased firing to heat stimuli and the BAO-induced phenotypic switch in chemosensitive muscle afferents, potentially through regulating membrane expression of acid sensing ion channel 3. These results suggest that enhanced P2Y1 in muscle afferents during ischemic-like conditions may dually regulate muscle nociception and cardiovascular reflexes.

A dual role for peripheral GDNF signaling in nociception and cardiovascular reflexes

“…Ischemia also increases the response to muscle contractions of ~50% of group IV and ~12% of group III muscle afferents 14 . This correlates with observed changes in nociceptive behaviors, EPRs, and gene expression in the affected muscles and dorsal root ganglia (DRGs) 7,13,18 .…”

“…A common method to study the involvement of peripheral sensory neurons in both nociception and sympathetic reflexes is to use a skeletal muscle ischemic injury model 13,14,15,16,17 . After ischemic injuries, group III and IV muscle afferents display peripheral sensitization, including increased responsiveness to mechanical and chemical stimuli.…”

“…A common hallmark of these diseases is chronic musculoskeletal pain that is often observed alongside an exacerbation of the patient's EPR 36,37 . In clinical settings, the changes associated with muscle ischemia can cause pain and lead to exercise intolerance or further complicate underlying cardiovascular conditions 13,37,38,39 . While there is a plethora of knowledge regarding EPRs and the peripheral mechanisms of nociception from the skin 31,40,41 , there is a significant disparity in our understanding of afferent mechanisms of myalgia, especially in the context of ischemia.…”

Thin‐fibre receptors expressing acid‐sensing ion channel 3 contribute to muscular mechanical hypersensitivity after exercise

“…However, response behaviours of thinly myelinated Aδfibres supplying skeletal muscle have not been characterized in general (Kaufman, Iwamoto, Longhurst, & Mitchell, 1982;Paintal, 1960Paintal, , 1961Queme, Ross, Lu, Hudgins, & Jankowski, 2016), and their involvement in DOMS has not been explored. Mechanical sensitization of muscular Aδfibres, but not C-fibres, was induced by glial cell line-derived neurotrophic factor (GDNF), which was up-regulated in the muscle after LC (Hayashi et al, 2017;Murase, Kato, Taguchi, & Mizumura, 2014;Murase et al, 2013).…”

Mechanism and implications of hyperpnea exaggeration at the onset of exercise in mechanical hyperalgesia after eccentric exercise

“…Smith et al 52) revealed that the abolition of capsaicinsensitive fibers, which play a role in nociceptors, caused a significant abnormality in the cardiovascular response to both muscle contraction and stretching in rats. Queme et al 53) demonstrated that inhibition of ADP-responsive P2Y1 receptors, which are related to ischemic pain, not only prevented the increase in mean blood pressure after exercise, but also significantly reduced alterations in painrelated behavior in mice. Mizumura and Kumazawa 42) also showed that nociceptive chemical stimulations to thin muscle afferents, that are assumed to be polymodal receptors in dogs, induced a significant increase in ventilation.…”