Longitudinal peripheral tissue RNA-Seq transcriptomic profiling, hyperalgesia, and wound healing in the rat plantar surgical incision model

Widespread hyperexcitability of nociceptor somata outlasts enhanced avoidance behavior after incision injury

ABSTRACT

Nociceptors with somata in dorsal root ganglia (DRGs) readily switch from an electrically silent state to a hyperactive state of tonic, nonaccommodating, low-frequency, irregular discharge of action potentials (APs). Spontaneous activity (SA) during this state is present in vivo in rats months after spinal cord injury (SCI) and has been causally linked to SCI pain. Intrinsically generated SA and, more generally, ongoing activity (OA) are induced by various neuropathic conditions in rats, mice, and humans and are retained in nociceptor somata after dissociation and culturing, providing a powerful tool for investigating its mechanisms and functions. The present study shows that long-lasting hyperexcitability that can generate OA during modest depolarization in probable nociceptors dissociated from DRGs of male and female rats is induced by plantar incision injury. OA occurred when the soma was artificially depolarized to a level within the normal range of membrane potentials where large, transient depolarizing spontaneous fluctuations (DSFs) can approach AP threshold. This hyperexcitability persisted for at least 3 weeks, whereas behavioral indicators of affective pain-hind paw guarding and increased avoidance of a noxious substrate in an operant conflict test-persisted for 1 week or less. The most consistent electrophysiological alteration associated with OA was enhancement of DSFs. An unexpected discovery after plantar incisions was hyperexcitability in neurons from thoracic DRGs that innervate dermatomes distant from the injured tissue. Potential in vivo functions of widespread, low-frequency nociceptor OA consistent with these and other findings are to contribute to hyperalgesic priming and to drive anxiety-related hypervigilance.

Widespread latent hyperactivity of nociceptors outlasts enhanced avoidance behavior following incision injury

Nociceptors with somata in dorsal root ganglia (DRGs) exhibit an unusual readiness to switch from an electrically silent state to a hyperactive state of tonic, nonaccommodating, low-frequency, irregular discharge of action potentials (APs). Ongoing activity (OA) during this state is present in vivo in rats months after spinal cord injury (SCI), and has been causally linked to SCI pain. OA induced by various neuropathic conditions in rats, mice, and humans is retained in nociceptor somata after dissociation and culturing, providing a powerful tool for investigating its mechanisms and functions. An important question is whether similar nociceptor OA is induced by painful conditions other than neuropathy. The present study shows that probable nociceptors dissociated from DRGs of rats subjected to postsurgical pain (induced by plantar incision) exhibit OA. The OA was most apparent when the soma was artificially depolarized to a level within the normal range of membrane potentials where large, transient depolarizing spontaneous fluctuations (DSFs) can approach AP threshold. This latent hyperactivity persisted for at least 3 weeks, whereas behavioral indicators of affective pain - hindpaw guarding and increased avoidance of a noxious substrate in an operant conflict test - persisted for 1 week or less. An unexpected discovery was latent OA in neurons from thoracic DRGs that innervate dermatomes distant from the injured tissue. The most consistent electrophysiological alteration associated with OA was enhancement of DSFs. Potential in vivo functions of widespread, low-frequency nociceptor OA consistent with these and other findings are to amplify hyperalgesic priming and to drive anxiety-related hypervigilance.

STING-IFN-I pathway relieves incision induced acute postoperative pain via inhibiting the neuroinflammation in dorsal root ganglion of rats

BACKGROUND

The purpose of this study was to study the effect of STING-IFN-I pathway on incision induced postoperative pain in rats and its possible mechanisms.

METHODS

The pain thresholds were evaluated by measuring the mechanical withdrawal threshold and the thermal withdrawal latency. The satellite glial cell and macrophage of DRG were analyzed. The expression of STING, IFN-a, P-P65, iNOS, TNF-α, IL-1β and IL-6 in DRG was evaluated.

RESULTS

The activation of STING-IFN-I pathway can reduce the mechanical hyperalgesia, thermal hyperalgesia, down-regulate the expression of P-P65, iNOS, TNF-α, IL-1β and IL-6, and inhibit the activation of satellite glial cell and macrophage in DRG.

CONCLUSIONS

The activation of STING-IFN-I pathway can alleviate incision induced acute postoperative pain by inhibiting the activation of satellite glial cell and macrophage, which reducing the corresponding neuroinflammation in DRG.

The mechanisms and management of persistent postsurgical pain

An estimated 10%-50% of patients undergoing a surgical intervention will develop persistent postsurgical pain (PPP) lasting more than 3 months despite adequate acute pain management and the availability of minimally invasive procedures. The link between early and late pain outcomes for surgical procedures remains unclear-some patients improve while others develop persistent pain. The elective nature of a surgical procedure offers a unique opportunity for prophylactic or early intervention to prevent the development of PPP and improve our understanding of its associated risk factors, such as pre-operative anxiety and the duration of severe acute postoperative pain. Current perioperative pain management strategies often include opioids, but long-term consumption can lead to tolerance, addiction, opioid-induced hyperalgesia, and death. Pre-clinical models provide the opportunity to dissect mechanisms underpinning the transition from acute to chronic, or persistent, postsurgical pain. This review highlights putative mechanisms of PPP, including sensitisation of peripheral sensory neurons, neuroplasticity in the central nervous system and nociceptive signalling along the neuro-immune axis.

Expression levels of NPPB, ITGB6, CPNE4, EML5, and ITSN1 in fresh exudates swabbed from critically colonised and infected full-thickness wounds in rats

Pressure injury management requires reliable identification of critical colonisation due to lack of infection signs. Our research group previously proposed the mRNAs natriuretic peptide B (Nppb), integrin subunit beta 6 (Itgb6), copine 4 (Cpne4), echinoderm microtubule-associated protein like 5, and intersectin 1 as candidate markers in pooled exudates of critically colonised wounds. However, it is unclear whether mRNAs or proteins of the candidate genes would be suitable as biomarkers in fresh exudate. Therefore, this study aimed to evaluate the validity of the mRNAs and proteins as fresh exudate markers for critical colonisation. Three wound models of normal healing, critical colonisation, and infection were created in rats. Fresh swab-collected exudates were collected, and mRNA and protein expression levels were measured. In the fresh wound exudates, the detection frequency of Itgb6 tended to decrease in the critically colonised and infected wounds (P = .067), and those of Cpne4 and Nppb tended to be lower in the infected wounds than in the normal healing and critically colonised wounds (P = .006 and .067, respectively). In contrast, there was no difference in protein expression in the exudates. This study suggests that Itgb6 mRNA in fresh exudates is a promising biomarker for critical colonisation.

Effect of Matrix Metalloproteinase 23 Accelerating Wound Healing Induced by Hydroxybutyl Chitosan

Skin wounds may cause severe financial and social burden due to the difficulties in wound healing. Original inert dressings cannot meet multiple needs in the process of wound healing. Therefore, the development of materials to accelerate healing progress is essential and urgent. In the previous study, we found that the homogeneously synthesized hydroxybutyl chitosan (HBCS) had an effective performance in promoting wound healing. Proteomic analysis of the same specimen suggested that matrix metalloproteinase 23 (MMP23) may play a key role in HBCS expediting the progress of wound healing. In this work, we aim to reveal the underlying mechanism of MMP23 in the dynamic process of cutaneous proliferation and repair period. In order to regulate the expression level of MMP23 in the local wound area, we leaded in adeno-associated virus (AAV) to specifically decreased expression quantity of MMP23 in rat skin. In contrast to the negative control groups, we found that the wound closed faster and the collagen fibers and neovascularization were significantly increased in AAV groups. These findings highlighted that MMP23 was involved in wound healing after traumatic injury, and managing the expression of MMP23 could be a potential intervention target to accelerate wound healing.

Anti-nociceptive effects of magnolol via inhibition of TRPV1/P2Y and TLR4/NF-κB signaling in a postoperative pain model

AIMS

The current study explored the anti-nociceptive activity of magnolol in post-incisional inflammatory nociceptive pain.

MAIN METHODS

Preliminary, the anti-inflammatory, antioxidant, and cytoprotective potential of magnolol were confirmed against hydrogen peroxide (H₂O₂)-induced PC12 cells. Next, an in-vivo model of planter incision surgery was established in BALB/c mice. Tramadol 50 mg/kg intraperitoneal (i.p.) and magnolol (0.1, 1, 10 mg/kg i.p. + 10 mg/kg intra planter) were administered after plantar incision surgery and behavior parameters were measured.

KEY FINDINGS

The results indicate that magnolol significantly suppressed post-incision-induced mechanical allodynia, thermal hyperalgesia, and paw edema. Magnolol promisingly inhibited post-incision induces nitric oxide (NO), malondialdehyde (MDA), eosinophil peroxidase (EPO), and neutrophil infiltration. Magnolol strongly attenuated post-incision inducing the release of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and inhibited deoxyribonucleic acid (DNA) fragmentation. Magnolol markedly reverses post-incisional histopathological changes and biochemical composition of the incised paw. Magnolol markedly down-regulated post-incisional increase expression of transient receptor potential vanilloid 1 (TRPV1), purinergic (P2Y) nociceptors as well as toll-like receptor 4 (TLR4), nuclear factor kappa light chain enhancer of activated B cell (NF-κB), cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) while upregulating the expression of inhibitor of nuclear kappa B alpha (IκB-α).

SIGNIFICANCE

The present study strongly suggests that magnolol significantly suppressed post-incisional inflammatory nociceptive pain by targeting TRPV1/P2Y and TLR4/NF-κB signaling.