Nociceptor Overexpression of Na1.7 Contributes to Chronic Muscle Pain Induced by Early-Life Stress.

Adult rats previously submitted to neonatal limited bedding (NLB), a model of early-life stress, display muscle mechanical hyperalgesia and nociceptor hyperexcitability, the underlying mechanism for which is unknown. Since voltage-gated sodium channel subtype 7 (Na1.7) contributes to mechanical hyperalgesia in several preclinical pain models and is critical for nociceptor excitability, we explored its role in the muscle hyperalgesia exhibited by adult NLB rats. Western blot analyses demonstrated increased Na1.7 protein expression in L4-L5 dorsal root ganglia (DRG) from adult NLB rats, and antisense oligodeoxynucleotide (AS ODN) targeting Na1.7 alpha subunit mRNA attenuated the expression of Na1.7 in DRG extracts. While this AS ODN did not affect nociceptive threshold in normal rats it significantly attenuated hyperalgesia in NLB rats. The selective Na1.7 activator OD1 produced dose-dependent mechanical hyperalgesia that was enhanced in NLB rats, whereas the Na1.7 blocker ProTx-II prevented OD1-induced hyperalgesia in control rats and ongoing hyperalgesia in NLB rats. AS ODN knockdown of extracellular signal-regulated kinase 1/2, which enhances Na1.7 function, also inhibited mechanical hyperalgesia in NLB rats. Our results support the hypothesis that overexpression of Na1.7 in muscle nociceptors play a role in chronic muscle pain induced by early-life stress, suggesting that Na1.7 is a target for the treatment of chronic muscle pain. PERSPECTIVE: We demonstrate that early-life adversity, induced by exposure to inconsistent maternal care, produces chronic muscle hyperalgesia, which depends, at least in part, on increased expression of Na1.7 in nociceptors.