Immediate inhibition of spinal secretory phospholipase A2 prevents the pain and elevated spinal neuronal hyperexcitability and neuroimmune regulatory genes that develop with nerve root compression.

Cervical nerve root injury induces a host of inflammatory mediators in the spinal cord that initiate and maintain neuronal hyperexcitability and pain. Secretory phospholipase A2 (sPLA2) is an enzyme that has been implicated as a mediator of pain onset and maintenance in inflammation and neural injury. Although sPLA2 modulates nociception and excitatory neuronal signaling in vitro, its effects on neuronal activity and central sensitization early after painful nerve root injury are unknown. This study investigated whether inhibiting spinal sPLA2 at the time of nerve root compression (NRC) modulates the pain, dorsal horn hyperexcitability, and spinal genes involved in glutamate signaling, nociception, and inflammation that are seen early after injury. Rats underwent a painful C7 NRC injury with immediate intrathecal administration of the sPLA2 inhibitor thioetheramide-phosphorlycholine. Additional groups underwent either injury alone or sham surgery. One day after injury, behavioral sensitivity, spinal neuronal excitability, and spinal cord gene expression for glutamate receptors (mGluR5 and NR1) and transporters (GLT1 and EAAC1), the neuropeptide substance P, and pro-inflammatory cytokines (TNFα, IL1α, and IL1ß) were assessed. Treatment with the sPLA2 inhibitor prevented mechanical allodynia, attenuated neuronal hyperexcitability in the spinal dorsal horn, restored the proportion of spinal neurons classified as wide dynamic range, and reduced genes for mGluR5, substance P, IL1α, and IL1ß to sham levels. These findings indicate spinal regulation of central sensitization after painful neuropathy and suggest that spinal sPLA2 is implicated in those early spinal mechanisms of neuronal excitability, perhaps via glutamate signaling, neurotransmitters, or inflammatory cascades.

p38 mitogen-activated protein kinase and pain.

Inflammatory and neuropathic pain is initiated by tissue inflammation and nerve injury, respectively. Both are characterized by increased activity in the peripheral and central nervous system, where multiple inflammatory cytokines and other active molecules activate different signaling pathways that involve in the development and/or maintenance of pain. P38 mitogen-activated protein kinase (MAPK) is one member of the MAPK family, which is activated in neurons and glia and contributes importantly to inflammatory and neuropathic pain. The aim of this review is to summarize the latest advances made about the implication of p38 MAPK signaling cascade in pain. It can deepen our understanding of the molecular mechanisms of pain and may help to offer new targets for pain treatment.

The isoform-specific functions of the c-Jun N-terminal kinase (JNK) in a mouse model of antiretroviral-induced painful peripheral neuropathy.

Nucleoside reverse transcriptase inhibitors (NRTIs) are associated with the development of painful neuropathies and may further aggravate sensory neuropathy produced by HIV-1 infection, leading to discontinuation of NRTI therapy by HIV patients. Following antiretroviral-induced peripheral neuropathy, c-Jun N-terminal kinase (JNK) is activated in the dorsal root ganglia (DRG) and spinal cord. However, the contribution of individual JNK genes remains unknown. Here, we have tested the behavioural mechanical sensitivity of JNK1, JNK2 and JNK3 knockout (KO) mice in the von Frey test after treatment with 2',3'-dideoxycytidine (ddC). Protein expression was investigated in the spinal cord of wild type (wt) and KO mice by western blotting. The onset of neuropathic pain was prevented by the deletion of JNK3, leading us to hypothesize that JNK3 protein plays a major role in the regulation of pain threshold in antiretroviral neuropathy. The growth-associated protein 43 (GAP-43) and the transcription factor c-Jun are involved in regeneration processes. This study revealed an up-regulation of GAP-43 and c-Jun protein, 14 days after ddC administration. JNK1 deletion induced a significant reduction in c-Jun phosphorylation and GAP-43 protein contents. In contrast, there was no difference in ddC-induced reduction of hind paw intraepidermal nerve fibre density in all JNK KO mice. Overall, these findings indicate that JNK3 plays a critical role in regulating ddC neurotoxicity-induced mechanical pain hypersensitivity, while JNK1 is important for activation of c-Jun and GAP-43 as a critical pathway of a regeneration program. These data highlight the impact of individual JNK isoforms on antiretroviral neurotoxicity and neuro-regeneration processes.

Redox regulation of soluble epoxide hydrolase does not affect pain behavior in mice.

Signaling mediated by soluble epoxide hydrolase (sEH) has been reported to play an important role in pain processing. Previous studies revealed that sEH activity is inhibited by specific binding of electrophiles to a redox-sensitive thiol (Cys521) adjacent to the catalytic center of the hydrolase. Here, we investigated if this redox-dependent modification of sEH is involved in pain processing using "redox-dead" knockin-mice (sEH-KI), in which the redox-sensitive cysteine is replaced by serine. However, behavioral characterization of sEH-KI mice in various animal models revealed that acute nociceptive, inflammatory, neuropathic, and visceral pain processing is not altered in sEH-KI mice. Thus, our results suggest that redox-dependent modifications of sEH are not critically involved in endogenous pain signaling in mice.

Electroacupuncture Attenuates CFA-Induced Inflammatory Pain by Regulating CaMKII.

Ca2+/calmodulin-dependent protein kinase II (CaMKII) is a multifunctional serine/threonine kinase that is ubiquitously distributed in the central and peripheral nervous systems. Moreover, its phosphorylated protein (P-CaMKII) is involved in memory, mood, and pain regulation in the anterior cingulate cortex (ACC). Electroacupuncture (EA) is a traditional Chinese therapeutic technique that can effectively treat chronic inflammatory pain. However, the CaMKII-GluA1 role in EA analgesia in the ACC remains unclear. This study investigated the role of P-CaMKII and P-GluA1 in a mouse model of inflammatory pain induced by complete Freund's adjuvant (CFA). There were increased P-CaMKII and P-GluA1 levels in the ACC. We found that intracerebroventricular injection of KN93, a CaMKII inhibitor, as well as EA stimulation, attenuated complete Freund's adjuvant-induced pain behavior. Further, EA increased pCaMKII-PICK1 complex (abbreviated as C-P complex) levels. Our findings demonstrate that EA inhibits inflammatory pain by inhibiting CaMKII-GluA1 phosphorylation. P-CaMKII is involved in EA analgesia as the pCaMKII-PICK1 complex.

Enhanced histamine-induced itch in diacylglycerol kinase iota knockout mice.

Subsets of small-diameter dorsal root ganglia (DRG) neurons detect pruritogenic (itch-causing) and algogenic (pain-causing) stimuli and can be activated or sensitized by chemical mediators. Many of these chemical mediators activate receptors that are coupled to lipid hydrolysis and diacylglycerol (DAG) production. Diacylglycerol kinase iota (DGKI) can phosphorylate DAG and is expressed at high levels in small-diameter mouse DRG neurons. Given the importance of these neurons in sensing pruritogenic and algogenic chemicals, we sought to determine if loss of DGKI impaired responses to itch- or pain-producing stimuli. Using male and female Dgki-knockout mice, we found that in vivo sensitivity to histamine-but not other pruritogens-was enhanced. In contrast, baseline pain sensitivity and pain sensitization following inflammatory or neuropathic injury were equivalent between wild type and Dgki-/- mice. In vitro calcium responses in DRG neurons to histamine was enhanced, while responses to algogenic ligands were unaffected by Dgki deletion. These data suggest Dgki regulates sensory neuron and behavioral responses to histamine, without affecting responses to other pruritogenic or algogenic agents.

Dual role of D-amino acid oxidase in experimental pain models.

D-amino acid oxidase (DAAO) is an astroglial enzyme abundantly present in the pain sensing regions including brain and spinal cord. There have been studies indicating an upregulation and increased activity of DAAO in different pain models. Furthermore, the upregulation of DAAO also results in the development of morphine tolerance as well as morphine-induced hyperalgesia. Accordingly, the knockdown of DAAO gene or pharmacological inhibition of DAAO reduces pain, reverses tolerance to morphine and hyperalgesia. The pain inducing actions of DAAO are related to augmented production of (hydrogen peroxide) H2O2, pro-inflammatory cytokines and activation of (Transient receptor protein Ankyrin-1) TRPA1 channels. On the other hand, exogenously administrated DAAO has also been shown to attenuate the pain in different pain models. The pain attenuating actions of DAAO enzyme has been linked to extensive metabolism of D-serine, which may not be able to activate NMDA receptor and trigger pain. The current review highlights the pain attenuating and pain inducing role of DAAO in experimental studies.

AMP-Activated Protein Kinase Activation in Dorsal Root Ganglion Suppresses mTOR/p70S6K Signaling and Alleviates Painful Radiculopathies in Lumbar Disc Herniation Rat Model.

STUDY DESIGN: Animal experiment: a rat model of lumbar disc herniation (LDH) induced painful radiculopathies. OBJECTIVE: To investigate the role and mechanism of AMP-activated protein kinase (AMPK) in dorsal root ganglia (DRG) neurons in LDH-induced painful radiculopathies. SUMMARY OF BACKGROUND DATA: Overactivation of multiple pain signals in DRG neurons triggered by LDH is crucial to the development of radicular pain. AMPK is recognized as a cellular energy sensor, as well as a pain sensation modulator, but its function in LDH-induced pain hypersensitivity remains largely unknown. METHODS: The LDH rat model was established by autologous nucleus pulposus transplantation into the right lumbar 5 (L5) nerve root. At different time points after AMPK agonist metformin (250 mg/kg/d) or mammalian target of rapamycin (mTOR) inhibitor rapamycin (5 mg/kg) intraperitoneal administration, thermal and mechanical sensitivity were evaluated by measuring paw withdrawal latency (PWL) and 50% paw withdrawal thresholds (PWT). The levels of AMPK, mTOR, and p70S6K phosphorylation were determined by Western blot. We also investigated the proportion of p-AMPK positive neurons in the right L5 DRG neurons using immunofluorescence. RESULTS: LDH evoked persistent thermal hyperalgesia and mechanical allodynia on the ipsilateral paw, as indicated by the decreased PWL and 50% PWT. These pain hypersensitive behaviors were accompanied with significant inhibition of AMPK and activation of mTOR in the associated DRG neurons. Pharmacological activation of AMPK in the DRG neurons not only suppressed mTOR/p70S6K signaling, but also alleviated LDH-induced pain hypersensitive behaviors. CONCLUSION: We provide a molecular mechanism for the activation of pain signals based on AMPK-mTOR axis, as well as an intervention strategy by targeting AMPK-mTOR axis in LDH-induced painful radiculopathies. LEVEL OF EVIDENCE: N/A.

Does vibration benefit delayed-onset muscle soreness?: a meta-analysis and systematic review.

OBJECTIVE: Delayed-onset muscle soreness (DOMS) is a symptom of exercise-induced muscle injury that is commonly encountered in athletes and fitness enthusiasts. Vibration is being increasingly used to prevent or treat DOMS. We therefore carried out a meta-analysis to evaluate the effectiveness of vibration in patients with DOMS. METHOD: We searched nine databases for randomized controlled trials of vibration in DOMS, from the earliest date available to 30 May 2018. Visual analogue scale (VAS) and creatine kinase (CK) levels were set as outcome measures. RESULTS: The review included 10 identified studies with 258 participants. The meta-analysis indicated that vibration significantly improved the VAS at 24, 48, and 72 hours after exercise, and significantly improved CK levels at 24 and 48 hours, but not at 72 hours. CONCLUSION: Vibration is a beneficial and useful form of physiotherapy for alleviating DOMS. However, further studies are needed to clarify the role and mechanism of vibration in DOMS.

A Promising New Approach for the Treatment of Inflammatory Pain: Transfer of Stem Cell-Derived Tyrosine Hydroxylase-Positive Cells.

OBJECTIVES: The appearance of endogenous tyrosine hydroxylase-positive cells (TH+ cells) in collagen-induced arthritis was associated with an anti-inflammatory effect. Here we investigated putative anti-inflammatory and antinociceptive effects of the transfer of induced, bone marrow stem cell-derived TH+ cells (iTH+ cells) on murine antigen-induced arthritis (AIA). METHODS: Bone marrow-derived stem cells were differentiated into iTH+ cells. These cells were transferred to mice immunized against methylated bovine serum albumin (mBSA) 2 days before AIA was induced by injection of mBSA into one knee joint. In AIA control mice and iTH+-treated mice the severity of AIA, pain-related behavior, humoral and cellular responses, and the invasion of macrophages into the dorsal root ganglia were assessed. RESULTS: The intravenous transfer of iTH+ cells before AIA induction did not cause a sustained suppression of AIA severity but significantly reduced inflammation-evoked pain-related behavior. The iTH+ cells used for transfer exhibited enormous production of interleukin-4. A major difference between AIA control mice and iTH+-treated AIA mice was a massive invasion of the dorsal root ganglia by iNOS-negative, arginine 1-positive macrophages corresponding to an M2 phenotype. The differences in other cellular and humoral immune parameters such as release of cytokines from stimulated lymphocytes between AIA control mice and iTH+-treated mice were small. CONCLUSIONS: The transfer of iTH+ cells may cause a long-lasting reduction of arthritis-induced pain even if it does not ameliorate inflammation. The invasion of M2 macrophages into the dorsal root ganglia is likely to be an important mechanism of antinociception.

Tailoring the Substitution Pattern on 1,3,5-Triazine for Targeting Cyclooxygenase-2: Discovery and Structure-Activity Relationship of Triazine-4-Aminophenylmorpholin-3-one Hybrids that Reverse Algesia and Inflammation in Swiss Albino Mice.

Here, we report analgesic and anti-inflammatory activity of a series of compounds obtained by appending 4-aminophenylmorpholin-3-one and acyclic, cyclic, or heterocyclic moieties on 1,3,5-triazine. The structures of compounds 4b and 6b are optimized for the best inhibition of COX-2 with IC50 values of 0.06 and 0.08 µM, respectively, and selectivity over COX-1 of 166 and >125, respectively. At the dose of 5 mg kg-1, these compounds significantly reduced acetic acid induced writhings, and their ED50 values were found to be 2.2 and 1.9 mg kg-1, respectively. Besides the cell-based and animal-based experiments showing the modes of action of these compounds targeting COX-2, the interaction behavior of 4b with COX-2 was also characterized, with physicochemical experiments including ITC, NMR, UV-vis, and molecular-modeling studies. Characteristically, these compounds interact with R120, Y355, and W385, the residues responsible for holding the substrate and mediating the process of electron transfer during the metabolic phase of the enzyme.

Identification of ABX-1431, a Selective Inhibitor of Monoacylglycerol Lipase and Clinical Candidate for Treatment of Neurological Disorders.

The serine hydrolase monoacylglycerol lipase (MGLL) converts the endogenous cannabinoid receptor agonist 2-arachidonoylglycerol (2-AG) and other monoacylglycerols into fatty acids and glycerol. Genetic or pharmacological inactivation of MGLL leads to elevation in 2-AG in the central nervous system and corresponding reductions in arachidonic acid and eicosanoids, producing antinociceptive, anxiolytic, and antineuroinflammatory effects without inducing the full spectrum of psychoactive effects of direct cannabinoid receptor agonists. Here, we report the optimization of hexafluoroisopropyl carbamate-based irreversible inhibitors of MGLL, culminating in a highly potent, selective, and orally available, CNS-penetrant MGLL inhibitor, 28 (ABX-1431). Activity-based protein profiling experiments verify the exquisite selectivity of 28 for MGLL versus other members of the serine hydrolase class. In vivo, 28 inhibits MGLL activity in rodent brain (ED50 = 0.5-1.4 mg/kg), increases brain 2-AG concentrations, and suppresses pain behavior in the rat formalin pain model. ABX-1431 (28) is currently under evaluation in human clinical trials.

Salivary alpha-amylase activity and cortisol in horses with acute abdominal disease: a pilot study.

BACKGROUND: The aim of this study was to evaluate salivary alpha-amylase (sAA), considered a non-invasive biomarker for sympathetic nervous system (SNS) activity, and salivary cortisol as possible pain-induced stress biomarker, in horses with acute abdominal disease. Therefore, a prospective observational study was performed in which both biomarkers were analyzed in a group of horses with acute abdomen syndrome, and compared with a group of healthy control horses by an unpaired Student's t-test. In addition, the possible relationship between both biomarkers, the score in Equine Acute Abdominal Pain scales version 1 (EAAPS-1 scale), Heart Rate (HR) and Respiratory Rate (RR), plasma lactate, the systemic inflammatory response syndrome (SIRS) score and serum amyloid A (SAA) concentration was assessed by a Spearman correlation test. RESULTS: A total of 30 horses were included in the study, 19 with acute abdominal disease diagnosed as large colon displacements, simple impactions of the pelvic flexure, spasmodic colics and enteritis and 11 healthy ones. sAA activity (24.5 median-fold, P <  0.0001) and salivary cortisol (1.7 median-fold, P <  0.01) were significantly higher in horses with acute abdomen than in healthy horses. sAA activity was significantly correlated with EAAPS-1 scale (r = 0.78, 95% confidence interval [CI] 0.38-0.89, P < 0.001) and SIRS score (r = 0.49, 95% CI 0.03-0.78, P < 0.05). Neither sAA nor salivary cortisol correlated with HR, RR, plasma lactate and SAA. CONCLUSIONS: Although this study should be considered as preliminary one, alpha-amylase measurements in saliva could be a biomarker of pain-induced stress in horses with acute abdominal disease.

Synergistic activation of ERK1/2 between A-fiber neurons and glial cells in the DRG contributes to pain hypersensitivity after tissue injury.

Background Intense nociceptive signaling arising from ongoing injury activates primary afferent nociceptive systems to generate peripheral sensitization. ERK1/2 phosphorylation in dorsal root ganglion can be used to visualize intracellular signal activity immediately after noxious stimulation. The aim of this study was to investigate spatiotemporal characteristics of ERK1/2 phosphorylation against tissue injury in the primary afferent neurons. Methods Plantar incisions were made in the hind paws of Sprague-Dawley rats (n =150). Levobupivacaine was injected into the plantar aspect of the paws and ankles, Mitogen-activated protein kinase kinase (MEK) inhibitor was injected into the paw, and carbenoxolone, dual inhibitor of the gap junction and pannexin channel, was intraperitoneally injected. Pain hypersensitivity was investigated by a behavioral study, while phosphorylated ERK1/2 was detected in dorsal root ganglion and hind paw using immunohistochemistry and Western blot. Results Phosphorylated ERK1/2 was induced in dorsal root ganglion (26.8 ± 2.9% at baseline, 65.6 ± 3.6% at 2 min, and 26.3 ± 3.4% at 2 h) after the incision. NF-200 positive A-fiber neurons and satellite glial cells were positive for phosphorylated ERK1/2. Injury-induced pain hypersensitivity was abolished by MEK inhibitor. Levobupivacaine treatment inhibited phosphorylated ERK1/2 induction, carbenoxolone treatment inhibited glial phosphorylated ERK1/2 at 2 min after the injury, and carbenoxolone inhibited pain hypersensitivity and neuronal phosphorylated ERK1/2 at 1 h after the injury. Conclusion ERK1/2 phosphorylation in A-fiber neurons and satellite glial cells immediately after injury contributes to the generation of pain hypersensitivity. Signal communication between neurons and satellite glial cells expands the duration of neuronal ERK1/2 phosphorylation and pain hypersensitivity at 1 h after tissue injury.

Emotion regulation and positive affect in the context of salivary alpha-amylase response to pain in children with cancer.

BACKGROUND: Children with cancer routinely undergo painful medical procedures invoking strong physiological stress responses. Resilience to this pain may be conferred through resources such as emotion regulation strategies and positive affect. PROCEDURE: This study measured dispositional positive affect in children with cancer (N = 73) and randomly assigned participants to one of three emotion regulation strategy conditions (distraction, reappraisal, or reassurance). Children applied their assigned strategy during an experimental pain procedure (the cold pressor task [CPT]) and provided saliva samples before, immediately after, and 15 min after the CPT. Saliva samples were later assayed for salivary alpha amylase (sAA)-a surrogate marker for autonomic/sympathetic nervous system activity and regulation. RESULTS: Children in the reassurance group had sAA levels that continued to rise after completion of the CPT compared to children in the distraction (b = -1.68, P = 0.021) and reappraisal conditions (b = -1.24, P = 0.084). Furthermore, dispositional positive affect moderated the effect of condition such that children in the reassurance group with lower levels of positive affect had sAA levels that continued to rise after completion of the CPT (dy/dx = 1.56, P = 0.027), whereas children in the reassurance condition with higher levels of positive affect did not exhibit this rise (P > 0.05). CONCLUSIONS: Specific emotion regulation strategies, such as distraction and reappraisal, may attenuate the stress response to pain in pediatric patients with cancer, and positive affect may confer resilience in response to pain even with use of less effective coping strategies such as reassurance.

Teriparatide rapidly improves pain-like behavior in ovariectomized mice in association with the downregulation of inflammatory cytokine expression.

Recent studies have indicated that teriparatide, an anti-osteoporosis agent, significantly improves back pain regardless of the presence of vertebral fracture in osteoporosis patients. The aims of this study were to examine whether teriparatide improves pain-like behavior in an ovariectomized (OVX) mouse model, and to evaluate changes in osteoclast marker levels and inflammatory cytokine expression levels induced by teriparatide treatment in bone tissue in association with improvements in pain-like behavior. OVX and sham operations were performed in 8-week-old mice, followed by teriparatide treatment for 2 weeks. Pain-like behavior tests (von Frey, paw flick and spontaneous pain test), and the measurement of serum tartrate-resistant acid phosphatase 5b (TRAP5b) level and inflammatory cytokine (interleukin [IL]-1ß, IL-6 and tumor necrosis factor [TNF]-α) expression levels in the bone tissue were conducted after teriparatide treatment in OVX mice. Pain-like behavior in the von Frey test was significantly improved by teriparatide treatment in OVX mice. With regard to the early phase (within the first 7 days of treatment), teriparatide significantly improved pain-like behavior in the von Frey test, the paw flick test and the spontaneous pain test. Teriparatide significantly inhibited the expression of IL-1ß, IL-6 and TNF-α in OVX mice in the early phase of the treatment, while the TRAP5b level in OVX mice was not significantly affected. We demonstrated that the teriparatide-induced rapid improvement effect on pain-like behavior in OVX mice was associated with the downregulation of inflammatory cytokine expression, including IL-1ß, IL-6 and TNF-α.

Involvement of NF-κB in the upregulation of cystathionine-γ-lyase, a hydrogen sulfide-forming enzyme, and bladder pain accompanying cystitis in mice.

Hydrogen sulfide (H2 S) is generated from l-cysteine by multiple enzymes including cystathionine-γ-lyase (CSE), and promotes nociception by targeting multiple molecules such as Cav 3.2 T-type Ca2+ channels. Bladder pain accompanying cyclophosphamide (CPA)-induced cystitis in mice has been shown to involve the functional upregulation of the CSE/H2 S/Cav 3.2 pathway. Therefore, we investigated whether NF-κB, as an upstream signal of the CSE/H2 S system, contributes to bladder pain in mice with CPA-induced cystitis. Bladder pain-like nociceptive behaviour was observed in CPA-treated mice, and referred hyperalgesia was evaluated by the von Frey test. Isolated bladder weights were assessed to estimate bladder swelling, and protein levels were measured by Western blotting. CPA, administered intraperitoneally, induced nociceptive behaviour, referred hyperalgesia and increased bladder weights in mice. ß-Cyano-l-alanine, a reversible selective CSE inhibitor, prevented CPA-induced nociceptive behaviour, referred hyperalgesia, and, in part, increases in bladder weight. CPA markedly increased phosphorylated NF-κB p65 levels in the bladder, an effect that was prevented by pyrrolidine dithiocarbamate (PDTC), an NF-κB inhibitor. PDTC and curcumin, which inhibits NF-κB signals, abolished CPA-induced nociceptive behaviour, referred hyperalgesia and, in part, increases in bladder weight. CPA caused the overexpression of CSE in the bladder, and this was prevented by PDTC or curcumin. The CPA-induced activation of NF-κB signals appeared to cause CSE overexpression in the bladder, contributing to bladder pain and in part swelling, possibly through H2 S/Cav 3.2 signaling. Therefore, NF-κB-inhibiting compounds including curcumin may be useful for the treatment of cystitis-related bladder pain.

Laser acupuncture-induced analgesic effect and molecular alterations in an incision pain model: a comparison with electroacupuncture-induced effects.

Low-level laser acupuncture (LLLA) produces photobiomodulation through acupuncture point and is an alternative to low-level laser therapy. Although the analgesic effect of LLLA on chronic pain has been proven, its effect on acute postincisional pain has yet to be investigated. A plantar incision (PI) model was used to mimic human postsurgical pain. Male adult rats received GaAlAs laser irradiation at the right ST36 acupoint immediately after operation and on the following 4 days. Three laser treatment groups (two red laser groups with a 30- or 15-min treatment duration and one 30-min near-infrared laser group) were compared with sham LLLA and naive groups and an electroacupuncture (EA) group (separate study). Behavioral withdrawal thresholds of both hind paws were measured before and after incision. Expression of mitogen-activated protein kinases (p-ERK and p-p38), inducible nitric oxide synthase (iNOS), and tumor necrosis factor (TNF) in the spinal cord was analyzed. All three LLLA treatments attenuated post-PI tactile allodynia in the ipsilateral paw, but only the 30-min red laser treatment affected the contralateral paw and had similar efficacy to that of EA. All laser treatments barely reduced heat hyperalgesia in both hind paws. At 3 days after PI, the 30-min red laser group showed reversed increases of PI-induced p-ERK, p-p38, and iNOS but not TNF expression in the spinal cord. Repetitive LLLA treatments ameliorated PI-induced mechanical pain. The inhibition of multiple sensitization signals highlights the unique clinical role of LLLA. Thus, LLLA is an alternative to EA as an adjuvant for postoperative pain control.

Investigation of Diacylglycerol Lipase Alpha Inhibition in the Mouse Lipopolysaccharide Inflammatory Pain Model.

Diacylglycerol lipase (DAGL) α and ß, the major biosynthetic enzymes of the endogenous cannabinoid (endocannabinoid) 2-arachidonylglycerol (2-AG), are highly expressed in the nervous system and immune system, respectively. Genetic deletion or pharmacological inhibition of DAGL-ß protects against lipopolysaccharide (LPS)-induced inflammatory responses in mouse peritoneal macrophages and reverses LPS-induced allodynia in mice. To gain insight into the contribution of DAGL-α in LPS-induced allodynia, we tested global knockout mice as well as DO34, a dual DAGL-α/ß inhibitor. Intraperitoneal administration of DO34 (30 mg/kg) significantly decreased whole-brain levels of 2-AG (∼83%), anandamide (∼42%), and arachidonic acid (∼58%). DO34 dose-dependently reversed mechanical and cold allodynia, and these antinociceptive effects did not undergo tolerance after 6 days of repeated administration. In contrast, DO34 lacked acute thermal antinociceptive, motor, and hypothermal pharmacological effects in naive mice. As previously reported, DAGL-ß (-/-) mice displayed a protective phenotype from LPS-induced allodynia. However, DAGL-α (-/-) mice showed full allodynic responses, similar to their wild-type littermates. Interestingly, DO34 (30 mg/kg) fully reversed LPS-induced allodynia in DAGL-α (+/+) and (-/-) mice, but did not affect the antinociceptive phenotype of DAGL-ß (-/-) mice in this model, indicating a DAGL-α-independent site of action. These findings suggest that DAGL-α and DAGL-ß play distinct roles in LPS-induced nociception. Whereas DAGL-α appears to be dispensable for the development and expression of LPS-induced nociception, DAGL-ß inhibition represents a promising strategy to treat inflammatory pain.