Sex Differences in Protein Kinase A Signaling of the Latent Postoperative Pain Sensitization That Is Masked by Kappa Opioid Receptors in the Spinal Cord

Abstract

Latent sensitization (LS) of pain engages pronociceptive signaling pathways in the dorsal horn that include NMDA receptor (NMDAR)fiadenylyl cyclase-1 (AC1)fiprotein kinase A (PKA), and exchange proteins directly activated by cyclic AMP (Epacs). To determine whether these pathways operate similarly between males and females or are under the inhibitory control of spinal j opioid receptors (KOR), we allowed hyperalgesia to resolve after plantar incision and then blocked KOR with intrathecal administration of LY2456302, which reinstated hyperalgesia and facilitated touch-evoked immunoreactivity of phosphorylated extracellular signal-regulated kinase (pERK) in neurons (NeuN) but not astrocytes (GFAPs) nor microglia (Iba1). LY2456302 reinstated hyperalgesia even when administered 13 months later, indicating that chronic postoperative pain vulnerability persists for over a year in a latent state of remission. In both sexes, intrathecal MK-801 (an NMDAR competitive antagonist) prevented LY2456302-evoked reinstatement of hyperalgesia as did AC1 gene deletion or the AC1 inhibitor NB001. NB001 also prevented stimulus-evoked pERK. In both sexes, the Epac inhibitor ESI-09 prevented reinstatement, whereas the Epac activator 8-CPT reinstated hyperalgesia. By contrast, the PKA inhibitor H89 prevented reinstatement only in male mice, whereas the PKA activator 6-bnz-cAMP itself evoked reinstatement at all doses tested (3-30 nmol, i.t.). In neither sex did incision change gene expression of KOR, GluN1, PKA, or Epac1 in dorsal horn. We conclude that sustained KOR signaling inhibits spinal PKA-dependent mechanisms that drive postoperative LS in a sex-dependent manner. Our findings support the development of AC1, PKA, and Epac inhibitors toward a new pharmacotherapy for chronic postoperative pain.

Contribution of µ Opioid Receptor–expressing Dorsal Horn Interneurons to Neuropathic Pain–like Behavior in Mice

“…Quantitative polymerase chain reaction was performed as previously described. 19 Briefly, after the decapitation of unanesthetized animals, the spinal cord was extruded by pressure ejection with a blunt 20- to 22-gauge needle attached to a 10-ml syringe filled with cold saline. The lumbar enlargement (L3–L5) was removed rapidly.…”

Postsurgical Latent Pain Sensitization Is Driven by Descending Serotonergic Facilitation and Masked by µ-Opioid Receptor Constitutive Activity in the Rostral Ventromedial Medulla

“…Plantar incision was performed as previously described (Pogatzki and Raja, 2003;Basu et al, 2021). Anesthesia was induced with 5% isoflurane (Abbott Laboratories, USA) and then maintained at 2% isoflurane.…”

“…Chronic post-surgical pain impacts approximately 10% of patients and is often resistant to treatment (Glare et al, 2019). After an incision heals, a state of latent sensitization (LS) continues, whereby spinal nociceptive transmission in the dorsal horn (DH) remains within a state of heightened responsivity (Basu et al, 2021), kept in remission by compensatory signaling through inhibitory GPCRs including the neuropeptide Y Y1 receptor (Fu et al, 2019, kappa opioid receptor (Custodio-Patsey et al, 2020;Basu et al, 2021), and μ-opioid receptor (MOR) (Corder et al, 2013;Walwyn et al, 2016;Cooper et al, 2021). This endogenous analgesia lasts for long durations, in part due to MOR constitutive activity (MOR CA ).…”

Endogenous μ-opioid – neuropeptide Y Y1 receptor synergy silences chronic postoperative pain

“…Plantar Incision Model Post-operative hyperalgesia was induced by longitudinal incision of the plantaris muscle as previously described (Basu et al, 2021;Pogatzki and Raja, 2003). Following antisepsis of the left hind paw with Chlorascrub® and 70% ethanol, a #11 scalpel blade was used to make a 5mm incision through the skin and fascia, beginning 2mm from the proximal edge of the heel and extending towards the digits.…”

“…Following tissue injury and the subsequent resolution of hyperalgesia, intrathecal administration (i.t.) of selective antagonists at inhibitory Gαi/o G protein-coupled receptors (GPCRs), including μ-opioid receptors (MOR), kappa opioid receptors (KOR), neuropeptide Y Y1 receptors (Y1R), or several other receptors, unmask LS and reinstate hyperalgesia (Basu et al, 2021;Corder et al, 2013;Fu et al, 2019Fu et al, , 2020Solway et al, 2011;Walwyn et al, 2016). Remarkably, each antagonist was sufficient to produce a complete, not partial, reinstatement of was not certified by peer review) is the author/funder.…”