Models of nociception: hot-plate, tail-flick, and formalin tests in rodents

Molecular assessment of NMDAR subunits and neuronal apoptosis in the trigeminal ganglion in a model of male migraine-induced rats following Moringa oleifera alcoholic extract administration

INTRODUCTION

Migraine, a common disorder marked by severe and repetitive headaches, has been linked to the involvement of the NMDA receptor (NMDAR), a receptor responsible for glutamate signaling. Moringa oleifera (M. oleifera), recognized for its anti-inflammatory properties and therapeutic potential in various conditions, has been investigated. This study aims to assess the efficacy and precise mechanisms of M. oleifera for the treatment of migraine, for which evidence is limited.

METHODS

Rats were stratified into four distinct groups. The control group did not undergo the migraine-induction protocol. Post-induction, the "sumatriptan" group was administered sumatriptan injections, the "treatment" group received oral M. oleifera extract, and the "vehicle" group was provided with oral solvent treatment. Behavioral evaluations encompassing Von Frey's and hot plate assessments, in addition to qPCR analysis targeting Nr2a, Nr2b, Bax, Bcl-2, and Caspase-3, were conducted.

RESULTS

Von Fery's and hot plate tests revealed a notable decrease in triggering pressure and temperature within the vehicle group when compared to the other groups (both ps < 0.001). The Nr2a expression levels in both the vehicle and treatment cohorts exhibited significantly higher values than those observed in the control group (p < 0.001, p = 0.001) and the sumatriptan group (p < 0.001, p = 0.002). Conversely, no substantial alterations in Nr2b or Bcl-2 expression levels were observed across the study groups (p = 0.404, p = 0.976). Notably, heightened expressions of Caspase-3 and Bax were evident in the vehicle group relative to the other groups (p = 0.013, p = 0.010).

CONCLUSIONS

Moringa oleifera extract appears to mitigate symptoms of migraine by inhibiting apoptosis, suggesting potential efficacy in migraine treatment; however, additional research investigating a wider range of pathways is necessary.

CLINICAL TRIAL NUMBER

Not applicable.

Backbone breakthroughs: How rodent models are shaping intervertebral disc disease treatment

Intervertebral disc degeneration (IVDD) is a widespread, disabling condition that significantly contributes to the global burden of musculoskeletal disorders. To better understand its underlying mechanisms and explore potential therapeutic strategies, animal models serve as valuable tools for simulating the complicated pathophysiology of IVDD. Rodent models are extensively used due to their genetic similarities to humans, cost-effectiveness, and rapid attainment of maturity. These models enable the study of specific molecular pathways involved in IVDD, such as inflammation, matrix degradation, tissue repair, and disc microenvironment homeostasis. This review provides a comprehensive overview of the current status of rodent models used in IVDD research, highlighting their advantages, limitations, and contributions to our understanding of the disease. Specifically, we discussed various rodent models, including traumatic (such as needle puncture in the lumbar and coccygeal region, nucleotomy, and annulus fibrosus defect), non-traumatic (including compression models, lumbar spine instability, and bipedalism), chemically induced models (chymopapain, chondroitinase ABC), and genetically modified models. These models offer insights into the severity of IVDD under different conditions, such as trauma, aging, and genetics. In conclusion, rodent models remain indispensable tools for advancing our understanding of IVDD mechanisms and therapeutic interventions. Carefully selecting animal species and models can provide valuable insights that guide future clinical research and treatment approaches. Our review aims to leverage these models to identify therapeutic targets and strategies that may ultimately reduce the impact of IVDD on human health. PERSPECTIVE: This review describes the role of rodent models in IVDD, highlighting their utility in unraveling disease mechanisms and evaluating therapeutics. By replicating the complex molecular pathways and conditions of disc disease, like trauma, aging, and genetics, these models aid in identifying future advancements in managing lower back pain.

Antinociceptive in vivo activity and chemical profiling by UHPLC-MS/MS of stem bark and leaves extracts of Ficus maxima Mill. (Moraceae)

ETHNOPHARMACOLOGICAL RELEVANCE

Ficus maxima is a medicinal plant extensively used in traditional medicine by Indigenous peoples across Central and South America. It is a member of the family Moraceae, subgenus Pharmacosycea, employed in treating various conditions, including intestinal parasites, gingivitis, internal inflammations, and snake bites. Despite its significant pharmacological potential, the species remains underrepresented in scientific literature.

AIM OF THE STUDY

This study aimed to evaluate the in vivo antinociceptive properties of leaf (ELFM) and stem bark (EBFM) extracts from Ficus maxima. Additionally, the chemical composition of these extracts was determined using ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS).

MATERIALS AND METHODS

Plant material was collected in Abaetetuba, Pará, Brazil, in October 2013 and subjected to static maceration to obtain crude ELFM and EBFM. Bio-guided fractionation was performed by sequential liquid-liquid partitioning with hexane (Hex), dichloromethane (DCM), and ethyl acetate (EtOAc), yielding the following fractions: ELFM-Hex and EBFM-Hex, ELFM-DCM and EBFM-DCM, and ELFM-EtOAc and EBFM-EtOAc. The biological activity of EBFM, ELFM, and their respective fractions were evaluated using the formalin-induced pain test and the hot plate test, followed by an assessment of their mechanisms of action. The UHPLC-MS/MS analysis was conducted using electrospray ionization (ESI) in both positive and negative modes. Metabolite annotation was facilitated by MS/MS libraries and molecular networks constructed on the GNPS platform.

RESULTS

The reactivity time to formalin in the neurogenic phase was reduced from 84.7 ± 7.6 s (100%) to 37.3 ± 4.7 s (44%), 33.1 ± 6.3 s (39%), 40.7 ± 7.4 s (48%), 57.2 ± 2.6 s (77%), 49.7 ± 4.1 s (58%), 46.8 ± 8.1 s (55%), and 52.4 ± 5.3 s (61%) after treatment with ASA, morphine, EBFM, ELFM, ELFM-Hex, ELFM-DCM, and ELFM-EtOAc at doses of 30 mg/kg, respectively. In the inflammatory phase, the reactivity time to formalin was reduced from 124.3 ± 25.9 s (100%) to 49.7 ± 4.7 s (40%), 9.8 ± 4.3 s (8%), 32.5 ± 8.5 s (26%), 59.8 ± 16.8 s (48%), and 54.4 ± 7.3 s (44%) after treatment with ASA, morphine, EBFM, ELFM, and ELFM-Hex at doses of 30 mg/kg, respectively. A reversal of the antinociceptive action of EBFM and ELFM was observed in the inflammatory phase after treatment with atropine, a muscarinic antagonist, and naloxone, an opioid antagonist, respectively. In the hot plate test, EBFM showed Antinociceptive Activity (AA) of 62.6 ± 9.2% after 90 min; however, there was a reversal of AA to 8.6 ± 2.8% when naloxone was used. The UHPLC-MS/MS metabolite analysis revealed the presence of loliolide (3), luteolin (13), lupeol (14), gallic acid (15), chlorogenic acid (16), pygenic acid A (17), and other metabolites from the alkaloids and fatty acids classes.

Synthesis and biological evaluation of new dual APN/NEP inhibitors as potent analgesics

An alternative approach for the management of acute and chronic pains involves prolonging the half-life of endogenous opiates, such as enkephalins that are released in response to nociceptive stimuli. This can be achieved through the inhibition of enzymatic pathways responsible for the hydrolysis of these peptides, particularly targeting Aminopeptidase N (APN) and Neutral Endopeptidase (NEP). In this study, we designed and synthesized a series of dual enkephalinase inhibitors (DENKIs) targeting both APN and NEP as novel analgesic treatments. Notably, SDUY812, SDUY816 and SDUY817 exhibited potent inhibition of APN activity with IC50 values of 0.38 µM, 0.68 µM and 0.29 µM, respectively, whereas their IC50 values against NEP were 6.9 µM, 6.9 µM and 7.4 µM, separately. In in-vivo antinociceptive assays, SDUY816 and SDUY817 demonstrated superior analgesic efficacy compared to Thiorphan and Bestatin in mice models of acute, inflammatory and neuropathic pains with jumping latencies exceeding 100 s and withdrawal thresholds more than 0.13 g. Moreover, the analgesic activity of these inhibitors was significantly diminished by a potent opioid antagonist, naloxone, indicating the contribution of opioid receptors to the robust analgesic properties of these newly developed DENKIs. In addition, SDUY816 and SDUY817 exerted the analgesic activity in a concentration- and time-dependent manner with SDUY816 possessing acceptable pharmacokinetic properties (t1/2 = 4.02 h and F = 27 %) and low toxicity. These findings provide alternative analgesic therapeutics that are potentially devoid of opioid-associated side effects.

Synergistic Pain-Reducing Effects of Bixa orellana (Chronic® and Chronic In®) and Cannabidiol-Rich Cannabis sativa Extracts in Experimental Pain Models

Background: The present study aimed to evaluate the potential synergy between pharmaceutical formulations containing Bixa orellana L. (granulated-CHR OR and injectable nanodispersion-CHR IN) in conjunction with a cannabidiol (CBD)-rich extract of Cannabis sativa L. (CSE) on experimental pain models in Wistar rats. Methods: Chemical analysis was performed using gas chromatography (GC-MS). The pain tests employed were acetic acid-induced writhing (injection i.p. of 0.9% acetic acid), formalin (solution 1%), hot plate (55 ± 0.5 °C), and cold-water tail withdrawal tests. Results: Chemical analyses by chromatography confirmed that the oil from B. orellana is rich in δ-tocotrienol (72.0 ± 1.0%), while the oil from Cannabis sativa highlighted the presence of cannabidiol (CBD). The results from the experimental pain tests indicated that the combined administration of formulations containing Bixa orellana and C. sativa, such as the granulated CHR OR (400 mg/kg, orally) with CSE (40 mg/kg, orally) or the nanodispersion CHR IN (10 mg/kg, intramuscularly) with CSE (40 mg/kg, orally), demonstrated significant results (p < 0.001) in pain reduction. Although the formulations containing Bixa orellana extract showed statistical significance in the tests when used in isolation, their effects were inferior compared to the combined use with CSE or the isolated use of CSE. These findings suggest that combining formulations containing extracts of these plant species may represent a viable therapeutic option, considering the synergistic action in reducing pain under the experimental conditions employed. Conclusions: these results imply that combining the phytocomplexes present in B. orellana and C. sativa may be a promising approach for pain treatment.

Antinociceptive Potential of Ximenia americana L. Bark Extract and Caffeic Acid: Insights into Pain Modulation Pathways

Background/Objectives: This study evaluated the antinociceptive effect of the Ximenia americana L. bark extract (HEXA) and its primary component, caffeic acid (CA), through in vivo assays. Methods: The antinociceptive properties were assessed using abdominal writhing, hot plate, and Von Frey tests. Additionally, the study investigated the modulation of various pain signaling pathways using a pharmacological approach. Results: The results demonstrated that all doses of the HEXA significantly increased latency in the hot plate test, decreased the number of abdominal contortions, reduced hyperalgesia in the Von Frey test, and reduced both phases of the formalin test. Caffeic acid reduced licking time in the first phase of the formalin test at all doses, with the highest dose showing significant effects in the second phase. The HEXA potentially modulated α2-adrenergic (52.99%), nitric oxide (57.77%), glutamatergic (33.66%), vanilloid (39.84%), cyclic guanosine monophosphate (56.11%), and K+ATP channel-dependent pathways (38.70%). Conversely, CA influenced the opioid, glutamatergic (53.60%), and vanilloid (34.42%) pathways while inhibiting nitric oxide (52.99%) and cyclic guanosine monophosphate (38.98%). Conclusions: HEXA and CA exhibit significant antinociceptive effects due to their potential interference in multiple pain signaling pathways. While the molecular targets remain to be fully investigated, HEXA and CA demonstrate significant potential for the development of new analgesic drugs.

Ultrasound-assisted extraction, optimization, and purification of total flavonoids from Daphnegenkwa and analysis of their antioxidant, anti-inflammatory, and analgesic activities

Daphne genkwa (D. genkwa) is the dried flower buds of a Chinese medicinal plant with multiple biological activities. Response surface methodology (RSM) combined with artificial neural network (ANN) techniques were utilized to optimize ultrasound-assisted extraction conditions for D. genkwa. Antioxidant activity and anti-inflammatory and analgesic properties of total flavonoids from D. genkwa (TFDG) were assessed. Optimal conditions involving ultrasonic power of 225 W, 30 min extraction time, 30 mL/g liquid-solid ratio, 60 °C extraction temperature, and 70% ethanol concentration yielded a maximum total flavonoids content (TFC) of 5.41 mg/g. After microporous resin purification, four specific flavonoids in D. genkwa were identified and quantified using high-performance liquid chromatography (HPLC). The TFDG demonstrated potent antioxidant activity, with a 94% rate of scavenging the 2, 2-diphenyl-1-picrylhydrazyl (DPPH). Furthermore, TFDG exhibited pain-alleviating properties in hot plate and acetic acid-induced writhing tests and noteworthy inhibitory effects on xylene-induced ear swelling in mice. The total flavonoids extracted by ultrasound had excellent biological activity. This establishes a foundation for further investigation into the potential medical value of D. genkwa.

Morphine-induced hyperalgesia impacts small extracellular vesicle miRNA composition and function

Morphine and other synthetic opioids are widely prescribed to treat pain. Prolonged morphine exposure can paradoxically enhance pain sensitivity in humans and nociceptive behavior in rodents. To better understand the molecular mechanisms underlying opioid-induced hyperalgesia, we investigated changes in miRNA composition of small extracellular vesicles (sEVs) from the serum of mice after a morphine treatment paradigm that induces hyperalgesia. We observed significant differential expression of 18 miRNAs in sEVs from morphine-treated mice of both sexes compared to controls. Several of these miRNAs were bioinformatically predicted to regulate cyclic AMP response element binding protein (CREB), a well-characterized transcription factor implicated in pain and drug addiction. We confirmed the binding and repression of Creb mRNA by miR-155 and miR-10a. We tested if serum-derived sEVs from morphine-treated mice could elicit nociceptive behavior in naïve recipient mice. Intrathecal injection of 1 μg sEVs did not significantly impact basal mechanical and thermal threshold in naïve recipient mice. However, prophylactic 1 μg sEV administration in recipient mice resulted in faster resolution of complete Freund's adjuvant-induced mechanical and thermal inflammatory hypersensitivity. Other behaviors assayed following administration of these sEVs were not impacted including sEV conditioned place preference and locomotor sensitization. These results indicate that morphine regulation of serum sEV composition can contribute to analgesia and suggest a potential for sEVs to be a non-opioid therapeutic intervention strategy to treat pain.

The PIEZO1/miR-155-5p/GDF6/SMAD2/3 signaling axis is involved in inducing the occurrence and progression of osteoarthritis under excessive mechanical stress

OBJECTIVE

To elucidate the molecular mechanism of overloading-induced osteoarthritis (OA) and to find a novel therapeutic target.

METHODS

We utilized human cartilage specimens, mouse chondrocytes, a destabilization of the medial meniscus (DMM) mouse model, and a mouse hindlimb weight-bearing model to validate the role of overloading on chondrocyte senescence and OA development. Then, we observed the effect of PIEZO1-miR-155-5p-GDF6-SMAD2/3 signaling axis on the preservation of joint metabolic homeostasis under overloading in vivo, in vitro and ex vivo by qPCR, Western blot, enzyme-linked immunosorbent assay (ELISA), immunohistochemistry, immunofluorescence, SA-β-gal staining, CCK8 assay, et al. Finally, we verified the therapeutic effects of intra-articular injection of miR-155-5p inhibitor or recombinant GDF6 on the murine overloading-induced OA models.

RESULTS

Chondrocytes sensesed the mechanical overloading through PIEZO1 and up-regulated miR-155-5p expression. MiR-155-5p mimics could copy the effects of overloading-induced chondrocyte senescence and OA. Additionally, miR-155-5p could suppress the mRNA expression of Gdf6-Smad2/3 in various tissues within the joint. Overloading could disrupt joint metabolic homeostasis by downregulating the expression of anabolism indicators and upregulating the expression of catabolism indicators in the chondrocytes and synoviocytes, while miR-155-5p inhibition or GDF6 supplementation could exert an antagonistic effect by preserving the joint homeostasis. Finally, in the in vivo overloading models, intra-articular injection of miR-155-5p inhibitor or recombinant GDF6 could significantly mitigate the severity of impending OA and lessened the progression of existing OA.

CONCLUSION

GDF6 overexpression or miR-155-5p inhibition could attenuate overloading-induced chondrocyte senescence and OA through the PIEZO1-miR-155-5p-GDF6-SMAD2/3 signaling pathway. Our study provides a new therapeutic target for the treatment of overloading-induced OA.

The development and characterization of a CRISPR/Cas9-mediated PD-1 functional knockout rat as a tool to study idiosyncratic drug reactions

Idiosyncratic drug reactions are rare but serious adverse drug reactions unrelated to the known therapeutic properties of the drug and manifest in only a small percentage of the treated population. Animal models play an important role in advancing mechanistic studies examining idiosyncratic drug reactions. However, to be useful, they must possess similarities to those seen clinically. Although mice currently represent the dominant mammalian genetic model, rats are advantageous in many areas of pharmacologic study where their physiology can be examined in greater detail and is more akin to that seen in humans. In the area of immunology, this includes autoimmune responses and susceptibility to diabetes, in which rats more accurately mimic disease states in humans compared with mice. For example, oral nevirapine treatment can induce an immune-mediated skin rash in humans and rats, but not in mice due to the absence of the sulfotransferase required to form reactive metabolites of nevirapine within the skin. Using CRISPR-mediated gene editing, we developed a modified line of transgenic rats in which a segment of IgG-like ectodomain containing the core PD-1 interaction motif containing the native ligand and therapeutic antibody domain in exon 2 was deleted. Removal of this region critical for mediating PD-1/PD-L1 interactions resulted in animals with an increased immune response resulting in liver injury when treated with amodiaquine.

Mentha rotundifolia (L.) Huds. and Salvia officinalis L. hydrosols mitigate aging related comorbidities in rats

Introduction

Aging is often linked to oxidative stress, where the body experiences increased damage from free radicals. Plants are rich sources of antioxidants, playing a role in slowing down aging and supporting the proper functioning and longevity of cells. Our study focuses on exploring the impact of Mentha rotundifolia (MR) and Salvia officinalis (SO) hydrosols on aging-related comorbidities.

Methods

The chemical composition of MR and SO hydrosols was analyzed by gas chromatography coupled to mass spectrometry. 2,2-Diphenyl 1-picrylhydrazyl and 2,20-azino-bis 3-ethylbenzothiazoline-6-sulfonic acid radicals scavenging assays were used to assess their in vitro antioxidant activity, and heat induced albumin denaturation test was used to evaluate their anti-inflammatory activity. Subsequently, we administered 5% of each plant hydrosol in the drinking water of 18-month-old rats for six months. We then conducted behavioral tests, including open field, dark/light box, rotarod, and Y-maze assessments, and measured biochemical parameters in plasma, liver and brain tissues.

Results and discussion

At two years old, animals treated with MR and SO hydrosols displayed fewer physical and behavioral impairments, along with well-preserved redox homeostasis in comparison with animals in the control group. These results highlighted the significance of MR and SO hydrosols in addressing various aspects of age-related comorbidities. The study suggests that these plant-derived hydrosols may have potential applications in promoting healthy aging and mitigating associated health challenges.

Prolonged testosterone 17β-cyclopentylpropionate exposition induces behavioral, ovarian, oviductal, uterine and reproductive disturbances in female mice

Anabolic-androgenic steroids (AAS) abuse is often associated with metabolic disorders and infertility. However, the current evidence on AAS-induced reproductive toxicity is mainly based on male studies. Thus, AAS repercussions on female reproductive capacity remain poorly understood, despite scarce evidence that fertility determinants may be more severely impaired in females than males exposed to these drugs. Accordingly, this study used an integrated framework to investigate the impact of different testosterone 17β-cyclopentylpropionate (TC) doses on pain sensitivity, aggressiveness, anxiety, sexual behavior, ovarian, oviductal, uterine and reproductive morphofunctional and molecular outcomes. These parameters were used to explore the reproductive capacity in female mice exposed to this synthetic testosterone ester. The animals were untreated or intraperitoneally treated with 5, 10 and 20 mg/kg TC every 48 h for 12 weeks. Our findings indicated that testosterone was upregulated while the hormones luteinizing, follicle-stimulating, estrogen and progesterone were down-regulated by TC. This AAS also exerted deleterious effects on anxiety, aggressivity, nociception, exploratory and sexual behavior in female mice. Concurrently, TC attenuated ovarian follicle maturation, interrupted the estrous cycle, induced oviductal and uterine hypotrophy. Estrous cyclicity was reestablished 60 days after AAS treatment. However, TC-treated mice still exhibited impaired reproductive capacity, a disturbance potentially related to deficiency in folliculogenesis, sex hormones production, and endometrial receptivity mediate by ER-α, PR, HOXA-10 and LIF down-regulation. Taken together, our findings indicated that in addition to female behavior, reproductive organs microstructure and function are markedly impaired by TC in a dose-dependent manner, whose time-dependent reversibility remains to be clarified.

Assessing cognitive biases induced by acute formalin or hotplate treatment: an animal study using affective bias test

Pain, a universal and burdensome condition, influences numerous individuals worldwide. It encompasses sensory, emotional, and cognitive facets, with recent research placing a heightened emphasis on comprehending pain's impact on emotion and cognition. Cognitive bias, which encompasses attentional bias, interpretation bias, and memory bias, signifies the presence of cognitive distortions influenced by emotional factors. It has gained significant prominence in pain-related research. Human studies have shown that individuals experiencing pain exhibit cognitive bias. Similarly, animal studies have demonstrated cognitive bias in pain-induced states across various species and disease models. In this study, we aimed to investigate the memory bias displayed by rats experiencing acute pain, using the affective bias test (ABT) as a tool and administering either hotplate or formalin to induce acute pain. Our data showed that rats demonstrated a significant preference for the control treatment-related substrate over the substrate associated with formalin treatment (p < 0.001), an indication of the prominent memory bias stimulated by acute formalin injections. However, when exposed to substrates related to hotplate treatment and control treatment, the acute pain induced by the hotplate treatment failed to generate a statistically significant choice bias in rats (p = 0.674). Our study demonstrates that the negative emotions associated with acute pain can be reflected by memory bias in ABT, at least for formalin-induced acute pain. This finding will augment our comprehension of the emotional and cognitive aspects of acute pain.

Prevention of vincristine-induced peripheral neuropathy by protecting the endothelial glycocalyx shedding

Vincristine-induced peripheral neuropathy (VIPN) adversely affects the quality of life and treatment continuity of patients. The endothelial glycocalyx (eGCX) protects nerves from harmful substances released from the capillary vessels, but its role in peripheral neuropathy remains unclear. We investigated the impact of eGCX protection on VIPN. Using a murine model of VIPN, we administered nafamostat mesylate to protect the eGCX shedding, and analyzed the eGCX integrity and manifestation of peripheral neuropathy. Nafamostat treatment suppressed allodynia associated with neuropathy. Additionally, nafamostat administration resulted in the suppression of increased vascular permeability in capillaries of peripheral nerves, further indicating its positive influence on eGCX in VIPN model mice. This study provided the importance of eGCX in VIPN. With the potential for rapid clinical translation through drug repositioning, nafamostat may be a new promising treatment for the prevention of VIPN.

Differential Roles of the D1- and D2-Like Dopamine Receptors Within the Ventral Tegmental Area in Modulating the Antinociception Induced by Forced Swim Stress in the Rat

Several preclinical and clinical studies indicate that exposure to acute stress may decrease pain perception and increases pain tolerance. This phenomenon is called stress-induced analgesia (SIA). A variety of neurotransmitters, including dopamine, is involved in the SIA. Dopaminergic neurons in the mesolimbic circuits, originating from the ventral tegmental area (VTA), play a crucial role in various motivational, rewarding, and pain events. The present study aimed to investigate the modulatory role of VTA dopaminergic receptors in the antinociceptive responses evoked by forced swim stress (FSS) in a model of acute pain. One hundred-five adult male albino Wistar rats were subjected to stereotaxic surgery for implanting a unilateral cannula into the VTA. After one week of recovery, separate groups of animals were given different doses of SCH23390 and Sulpiride (0.25, 1, and 4 µg/0.3 µl) as D1- and D2-like receptor antagonists into the VTA, respectively. Then, the animals were exposed to FSS for a 6-min period, and the pain threshold was measured using the tail-flick test over a 60-min time set intervals. Results indicated that exposure to FSS produces a prominent antinociceptive response, diminishing by blocking both dopamine receptors in the VTA. Nonetheless, the effect of a D1-like dopamine receptor antagonist on FSS-induced analgesia was more prominent than that of a D2-like dopamine receptor antagonist. The results demonstrated that VTA dopaminergic receptors contribute to the pain process in stressful situations, and it might be provided a practical approach to designing new therapeutic agents for pain management.

A cholinergic circuit that relieves pain despite opioid tolerance

Chronic pain is a tremendous burden for afflicted individuals and society. Although opioids effectively relieve pain, significant adverse outcomes limit their utility and efficacy. To investigate alternate pain control mechanisms, we explored cholinergic signaling in the ventrolateral periaqueductal gray (vlPAG), a critical nexus for descending pain modulation. Biosensor assays revealed that pain states decreased acetylcholine release in vlPAG. Activation of cholinergic projections from the pedunculopontine tegmentum to vlPAG relieved pain, even in opioid-tolerant conditions, through ⍺7 nicotinic acetylcholine receptors (nAChRs). Activating ⍺7 nAChRs with agonists or stimulating endogenous acetylcholine inhibited vlPAG neuronal activity through Ca2+ and peroxisome proliferator-activated receptor α (PPAR⍺)-dependent signaling. In vivo 2-photon imaging revealed that chronic pain induces aberrant excitability of vlPAG neuronal ensembles and that ⍺7 nAChR-mediated inhibition of these cells relieves pain, even after opioid tolerance. Finally, pain relief through these cholinergic mechanisms was not associated with tolerance, reward, or withdrawal symptoms, highlighting its potential clinical relevance.

Impact of early-life lead exposure on adult delta-9-tetrahydrocannabinol sensitivity in male and female C57BL6/J mice

Environmental exposure to lead (Pb) and cannabis use are two of the largest public health issues facing modern society in the United States and around the world. Exposure to Pb in early life has been unequivocally shown to have negative impacts on development, and recent research is mounting showing that it may also predispose individuals for risk of developing substance use disorders (SUD). At the same time, societal and legal attitudes towards cannabis (the main psychoactive component of which is delta-9-tetrahydrocannabinol) have been shifting, and many American states have legalized the recreational use of cannabis. It is also the 3rd most widely used drug of abuse in the US, and rates of cannabis use disorder are on the rise. Here we establish a link between early life Pb exposure and later THC-related behavior in C57BL6/J mice, as has been demonstrated for other drugs of abuse. The study seeks to answer whether Pb exposure affects physiological/behavioral THC sensitivity (as measured by the cannabinoid-induced tetrad). It was hypothesized that Pb exposure would decrease THC sensitivity and that sex-dependent effects of Pb-exposure and THC would be observed. Interestingly, results showed that THC sensitivity was increased by Pb exposure, but only in female mice. Future research will fully explore the implications of these findings, namely how these effects impact THC self-administration and the mechanism(s) by which developmental Pb exposure produces these effects.

Efficacy of the Multi-Target Compound E153 in Relieving Pain and Pruritus of Different Origins

Itch and pain are closely related but distinct sensations that share largely overlapping mediators and receptors. We hypothesized that the novel, multi-target compound E153 has the potential to attenuate pain and pruritus of different origins. After the evaluation of sigma receptor affinity and pharmacokinetic studies, we tested the compound using different procedures and models of pain and pruritus. Additionally, we used pharmacological tools, such as PRE-084, RAMH, JNJ 5207852, and S1RA, to precisely determine the role of histamine H3 and sigma 1 receptors in the analgesic and antipruritic effects of the compound. In vitro studies revealed that the test compound had potent affinity for sigma 1 and sigma 2 receptors, moderate affinity for opioid kappa receptors, and no affinity for delta or μ receptors. Pharmacokinetic studies showed that after intraperitoneal administration, the compound was present at high concentrations in both the peripheral tissues and the central nervous system. The blood-brain barrier-penetrating properties indicate its ability to act centrally at the levels of the brain and spinal cord. Furthermore, the test compound attenuated different types of pain, including acute, inflammatory, and neuropathic. It also showed a broad spectrum of antipruritic activity, attenuating histamine-dependent and histamine-independent itching. Finally, we proved that antagonism of both sigma 1 and histamine H3 receptors is involved in the analgesic activity of the compound, while the antipruritic effect to a greater extent depends on sigma 1 antagonism.

Simultaneous Administration of Hyperbaric Oxygen Therapy and Antioxidant Supplementation with Filipendula ulmaria Extract in the Treatment of Thermal Skin Injuries Alters Nociceptive Signalling and Wound Healing

Background and Objectives: Thermal skin injuries are a prevalent cause of skin damage, potentially leading to severe morbidity and significant mortality. In this study, we intended to estimate the effects of HBO (hyperbaric oxygen treatment) and antioxidant supplementation with Filipendula ulmaria extract, individually and simultaneously, in the treatment of thermal skin injuries. Materials and Methods: As a thermal skin injury experimental model, we used two-month-old male Wistar albino rats. Thermal injuries were made with a solid aluminium bar at a constant temperature of 75 °C for 15 s. Hyperbaric oxygen treatment was performed in a specially constructed hyperbaric chamber for rats (HYB-C 300) for seven consecutive days (100% O2 at 2.5 ATA for 60 min). Antioxidant supplementation was performed with oral administration of Filipendula ulmaria extract dissolved in tap water to reach a final concentration of 100 mg/kg b.w. for seven consecutive days. Results: Simultaneous administration of hyperbaric oxygen therapy and antioxidant supplementation with Filipendula ulmaria extract significantly ameliorated the macroscopic and histopathological characteristics of the wound area and healing. Also, this therapeutic approach decreased the local expression of genes for proinflammatory mediators and increased the expression of the μ-opioid receptor and the MT1 and MT2 receptors in the wound area and spinal cord, with a consequent increase in reaction times in behavioural testing. Conclusions: In conclusion, the presented results of our study allow evidence for the advantages of the simultaneous employment of HBO and antioxidant supplementation in the treatment of thermal skin injuries, with special reference to the attenuation of painful sensations accompanied by this type of trauma.

Microglial Depletion does not Affect the Laterality of Mechanical Allodynia in Mice

Mechanical allodynia (MA), including punctate and dynamic forms, is a common and debilitating symptom suffered by millions of chronic pain patients. Some peripheral injuries result in the development of bilateral MA, while most injuries usually led to unilateral MA. To date, the control of such laterality remains poorly understood. Here, to study the role of microglia in the control of MA laterality, we used genetic strategies to deplete microglia and tested both dynamic and punctate forms of MA in mice. Surprisingly, the depletion of central microglia did not prevent the induction of bilateral dynamic and punctate MA. Moreover, in dorsal root ganglion-dorsal root-sagittal spinal cord slice preparations we recorded the low-threshold Aβ-fiber stimulation-evoked inputs and outputs of superficial dorsal horn neurons. Consistent with behavioral results, microglial depletion did not prevent the opening of bilateral gates for Aβ pathways in the superficial dorsal horn. This study challenges the role of microglia in the control of MA laterality in mice. Future studies are needed to further understand whether the role of microglia in the control of MA laterality is etiology-or species-specific.

Geometric Isomer of Guanabenz Confers Hepatoprotection to a Murine Model of Acetaminophen Toxicity

Overdose of acetaminophen, a widely used antipyretic and analgesic drug, is one of the leading causes of drug-induced acute liver injury in the United States and worldwide. Phase-I metabolism of acetaminophen generates the toxic N-acetyl-p-benzoquinone imine (NAPQI) intermediate. Reactions of NAPQI with a wide range of biomolecules cause increased oxidative stress, endoplasmic reticulum (ER) stress, inflammation, and mitochondrial dysfunction, some of the cellular events contributing toward liver toxicity. Previously, we evaluated the potential of an FDA-approved, ER stress-modulating antihypertensive drug, Wytensin (trans-guanabenz, E-GA), as an antidote for acetaminophen hepatotoxicity. E-GA prevented elevation of the liver enzyme alanine aminotransferase (ALT), even when administered up to 6 h after acetaminophen overdose, and exhibited synergistic analgesic interactions. However, the commercially available guanabenz exists solely as a trans-isomer and suffers from sedative side effects resulting from the inhibition of central α2A-adrenergic receptors in locus coeruleus. Here, we studied the utility of the relatively unexplored cis-isomer of guanabenz as a treatment option for acetaminophen-induced liver toxicity. cis(Z)-Guanabenz acetate (Z-GA) lacks interaction with α2A-adrenoreceptors and is thus devoid of sedative, blood-pressure-lowering side effects of E-GA. Treatment of mice with Z-GA (10 mg/kg) before acetaminophen overdose and up to 6 h post APAP administration prevented liver injury and suppressed the elevation of serum ALT levels. Mechanistically, hepatoprotective effects of both isomers are similar and partly attributed to attenuation of the ER stress and oxidative stress in the liver. The results of this study suggest that Z-GA may be a safer, effective antidote for the clinical management of acute liver injury resulting from acetaminophen overdose. It also raises a tantalizing possibility of a prophylactic combination of the geometric isomer of the approved drug guanabenz with acetaminophen in a clinical setting.

A Novel Molecular Reservoir Based on Reverse Self-Assembled Liquid Crystals - A New Strategy for Prolonging the Duration in Action of Analgesics

PURPOSE

The aim of this study was to develop liquid crystal (LC) precursors to obtain novel long-acting analgesics for injection based on depot systems and compare the difference between the cubic and hexagonal precursors in delivering Diclofenac sodium (DS).

METHODS

Diclofenac sodium liquid crystal precursor injections were prepared and characterized, followed by in vitro release, pharmacodynamic, and pharmacokinetic studies.

RESULTS

The optimal formulations were prepared with a ratio of Phytantriol/ethanol/water as 76:19:5 for cubic LC precursors, and a ratio of Phytantriol/ethanol/water/Vitamine-E acetate as 72:18:5:5 for hexagonal, both loading various drug dosages (2.5%, 3.75% and 5%), respectively. Polarized light microscopy and small angle diffraction confirmed that the precursors were isotropic fluids and transformed into gels with Pn3m or HII framework in water. Rheological studies have shown that precursors belong to Newtonian fluids and gels to pseudoplastic fluids. The release showed that the DS in the commercial injection (DS-inj) was completely liberated within 6 h, whereas only 46.55% and 49.73% of the DS in 2.5% cubic precursors and 2.5% hexagonal precursors were freed, respectively. Pharmacodynamic studies have shown that cubic, hexagonal and DS-inj raised the pain threshold in mice by 169.4%, 157.3% and 113.79%, respectively. The mean retention times of DS in cubic and hexagonal were 3.16 and 2.67 times longer than DS-inj, respectively, according to pharmacokinetic results.

CONCLUSION

In conclusion, cubic and hexagonal are both promising analgesic sustained release formulations. In addition, based only on the current comparison, cubic seems to have a better long-acting effect.

Reduced pain sensitivity of episodic pain syndrome model mice carrying a Nav1.9 mutation by ANP-230, a novel sodium channel blocker

The sodium channel Nav1.9 is expressed in the sensory neurons of small diameter dorsal root ganglia that transmit pain signals, and gain-of-function Nav1.9 mutations have been associated with both painful and painless disorders. We initially determined that some Nav1.9 mutations are responsible for familial episodic pain syndrome observed in the Japanese population. We therefore generated model mice harboring one of the more painful Japanese mutations, R222S, and determined that dorsal root ganglia hyperexcitability was the cause of the associated pain. ANP-230 is a novel non-opioid drug with strong inhibitory effects on Nav1.7, 1.8 and 1.9, and is currently under clinical trials for patients suffering from familial episodic pain syndrome. However, little is known about its mechanism of action and effects on pain sensitivity. In this study, we therefore investigated the inhibitory effects of ANP-230 on the hypersensitivity of Nav1.9 p.R222S mutant model mouse to pain. In behavioral tests, ANP-230 reduced the pain response of the mice, particularly to heat or mechanical stimuli, in a concentration- and time-dependent manner. Furthermore, ANP-230 suppressed the repetitive firing of dorsal root ganglion neurons of these mutant mice. Our results clearly demonstrate that ANP-230 is an effective analgesic for familial episodic pain syndrome resulting from DRG neuron hyperexcitability, and that such analgesic effects are likely to be of clinical significance.

Intermittent systemic exposure to lipopolysaccharide-induced inflammation disrupts hippocampal long-term potentiation and impairs cognition in aging male mice

Age-related cognitive decline, a common component of the brain aging process, is associated with significant impairment in daily functioning and quality of life among geriatric adults. While the complexity of mechanisms underlying cognitive aging are still being elucidated, microbial exposure and the multifactorial inflammatory cascades associated with systemic infections are emerging as potential drivers of neurological senescence. The negative cognitive and neurobiological consequences of a single pathogen-associated inflammatory experience, such as that modeled through treatment with lipopolysaccharide (LPS), are well documented. Yet, the brain aging impacts of repeated, intermittent inflammatory challenges are less well studied. To extend the emerging literature assessing the impact of infection burden on cognitive function among normally aging mice, here, we repeatedly exposed adult mice to intermittent LPS challenges during the aging period. Male 10-month-old C57BL6 mice were systemically administered escalating doses of LPS once every two weeks for 2.5 months. We evaluated cognitive consequences using the non-spatial step-through inhibitory avoidance task, and both spatial working and reference memory versions of the Morris water maze. We also probed several potential mechanisms, including cortical and hippocampal cytokine/chemokine gene expression, as well as hippocampal neuronal function via extracellular field potential recordings. Though there was limited evidence for an ongoing inflammatory state in cortex and hippocampus, we observed impaired learning and memory and a disruption of hippocampal long-term potentiation. These data suggest that a history of intermittent exposure to LPS-induced inflammation is associated with subtle but significantly impaired cognition among normally aging mice. The broader impact of these findings may have important implications for standard of care involving infections in aging individuals or populations at-risk for dementia.

Increased Heat Pain Tolerance but Hyperalgesia to Tonic Inflammatory Pain in the CRND8 Mouse Model of Alzheimer's Disease

BACKGROUND

The effects of Alzheimer's disease (AD) pathology on the experience of pain are poorly understood.

OBJECTIVE

To understand the pathophysiological mechanisms underlying pain sensory transmission in the transgenic mouse model of AD, CRND8.

METHODS

We explored AD-related pathology in the spinal cord and dorsal root ganglia of 18-week-old female CRND8 mice. We assessed nociceptive responses to both acute heat stimuli and persistent inflammatory pain in CRND8 mice and non-transgenic (non-Tg) littermates. In addition, we searched for differences in biochemical correlates of inflammatory pain between CRND8 and non-Tg mice. Finally, we investigated the excitability of dorsal horn noc iceptive neurons in spinal cord slices from CRND8 and non-Tg mice.

RESULTS

We demonstrated the presence of intracellular AD-like pathology in the spinal cord and in the dorsal root ganglia nociceptive sensory neurons of CRND8 mice. We found that CRND8 mice had a reduced susceptibility to acute noxious heat stimuli and an increased sensitivity to tonic inflammatory pain. Tonic inflammatory pain correlated with a lack of induction of pro-opiomelanocortin in the spinal cord of CRND8 mice as compared to non-Tg mice. Electrophysiological recording in acute spinal cord slice preparations indicated an increased probability of glutamate release at the membrane of dorsal horn nociceptive neurons in CRND8 mice.

CONCLUSION

This study suggests that an increased thermal tolerance and a facilitation of nociception by peripheral inflammation can coexist in AD.

Mentha rotundifolia (L.) Huds. aqueous extract attenuates H2O2 induced oxidative stress and neurotoxicity

Introduction

Oxidative stress plays a causal role in neurodegenerative diseases. The aim of this study is to evaluate the antioxidant and neuroprotective effects of Mentha rotundifolia (L.) Huds (M. rotundifolia), a widely used Moroccan plant in traditional medicine.

Methods

The chemical composition of M. rotundifolia aqueous extract was analyzed by liquid chromatography coupled to mass spectrometry (LC-MS). 2,2-diphenyl 1-picrylhydrazyl (DPPH) and 2,2'-azino-bis 3-ethylbenzothiazoline-6-sulfonic acid (ABTS⁺) assays were used to assess its in vitro antioxidant activity. H₂O₂ was utilized to induce oxidative stress and neurotoxicity in vivo. Behavioral changes were evaluated using Open Field, Y-maze and Rotarod tests. Hyperalgesia was assessed using the tail immersion test.

Results and discussion

The LC-MS/MS analysis revealed high content of kaempferol glucuronide (85%) at the extract. IC₅₀ values of the DPPH and ABTS were 26.47 and 41.21 μg/mL, respectively. Pre-treatments with M. rotundifolia extract attenuated the behavioral changes induced by H₂O₂. In addition, the latency of tail withdrawal increased significantly in the treated groups suggesting central analgesic effect of M. rotundifolia extract. Moreover, the extract attenuated the deleterious effects of H₂O₂ and improved all liver biomarkers. The obtained results suggested that M. rotundifolia had remarkable antioxidant and neuroprotective effects and may prevent oxidative stress related disorders.

Analysis of the Involvement of NMDA Receptors in Analgesia and Hypothermia Induced by the Activation of TRPV1 Ion Channels

NMDA glutamate receptors play an important role in normal and pathophysiological nociception. At the periphery, they can interact with TRPV1 ion channels. The blockade of TRPV1 ion channels decreases NMDA-induced hyperalgesia, and NMDA receptor antagonists suppress the pain response to the TRPV1 agonist capsaicin. Since TRPV1 ion channels and NMDA receptors can functionally interact at the periphery, it would be interesting to investigate the possibility that they interact in the CNS. A single subcutaneous injection of 1 mg/kg of capsaicin was found to raise the thermal pain threshold in the tail flick test in mice, which reproduces the spinal flexion reflex, owing to the ability of capsaicin to cause long-term desensitization of nociceptors. Preventive administration of either noncompetitive NMDA receptor antagonists (high-affinity MK-801 20 μg/kg and 0.5 mg/kg subcutaneously; low-affinity hemantane 40 mg/kg intraperitoneally) or the selective TRPV1 antagonist BCTC (20 mg/kg intraperitoneally) inhibit the capsaicin-induced increase in the pain threshold. Capsaicin (1 mg/kg, subcutaneous injection) induces transient hypothermia in mice, which is brought about by hypothalamus-triggered vegetative reactions. This effect is prevented by BCTC but not by the noncompetitive NMDA receptor antagonists.

Body size and brain volumetry in the rat following prolonged morphine administration in infancy and adulthood

Background

Prolonged morphine treatment in infancy is associated with a high incidence of opioid tolerance and dependence, but our knowledge of the long-term consequences of this treatment is sparse. Using a rodent model, we examined the (1) short- and (2) long-term effects of prolonged morphine administration in infancy on body weight and brain volume, and (3) we evaluated if subsequent dosing in adulthood poses an increased brain vulnerability.

Methods

Newborn rats received subcutaneous injections of either morphine or equal volume of saline twice daily for the first two weeks of life. In adulthood, animals received an additional two weeks of saline or morphine injections before undergoing structural brain MRI. After completion of treatment, structural T2-weigthed MRI images were acquired on a 7 T preclinical scanner (Bruker) using a RARE FSE sequence. Total and regional brain volumes were manually extracted from the MRI images using ITK-SNAP (v.3.6). Regions of interest included the brainstem, the cerebellum, as well as the forebrain and its components: the cerebral cortex, hippocampus, and deep gray matter (including basal ganglia, thalamus, hypothalamus, ventral tegmental area). Absolute (cm³) and normalized (as % total brain volume) values were compared using a one-way ANOVA with Tukey HSD post-hoc test.

Results

Prolonged morphine administration in infancy was associated with lower body weight and globally smaller brain volumes, which was not different between the sexes. In adulthood, females had lower body weights than males, but no difference was observed in brain volumes between treatment groups. Our results are suggestive of no long-term effect of prolonged morphine treatment in infancy with respect to body weight and brain size in either sex. Interestingly, prolonged morphine administration in adulthood was associated with smaller brain volumes that differed by sex only in case of previous exposure to morphine in infancy. Specifically, we report significantly smaller total brain volume of female rats on account of decreased volumes of forebrain and cortex.

Conclusions

Our study provides insight into the short- and long-term consequences of prolonged morphine administration in an infant rat model and suggests brain vulnerability to subsequent exposure in adulthood that might differ with sex.

LQM10, a guanylhydrazone derivative, reduces nociceptive and inflammatory responses in mice

In the present study, we examined the antinociceptive and anti-inflammatory activities of a guanylhydrazone derivative, (E)-(3,5-di-tert-butyl-4-hydroxybenzylidene)-2-guanylhydrazone hydrochloride (LQM10), in mice. The antinociceptive effect was determined by assessing behavioural responses in different pain models, while anti-inflammatory activity was examined in carrageenan-induced pleurisy. Intraperitoneal LQM10 administration reduced the acetic acid-induced nociceptive behaviour, a phenomenon that was unaltered by pretreatment with yohimbine, atropine, naloxone or glibenclamide. In the formalin assay, LQM10 reduced nociceptive behaviour only in the second phase, indicating an inhibitory effect on inflammatory pain. LQM10 did not alter the pain latency in the hot plate assay and did not impact the locomotor activity of mice in the rotarod assay. In the carrageenan-induced pleurisy assay, LQM10 treatment inhibited critical events involved in inflammatory responses, namely, leucocyte recruitment, plasma leakage and increased inflammatory mediators (tumour necrosis factor Like Properties of Chalchones and Flavonoid Derivatives [TNF]-α and interleukin [IL]-1β) in the pleural exudate. Overall, these results indicate that LQM10 exhibits antinociceptive effects associated with peripheral mechanisms and anti-inflammatory activity mediated via a reduction in leucocyte migration and proinflammatory mediators, rendering this compound a promising candidate for treating pain and inflammatory process.

The YTHDF1-TRAF6 pathway regulates the neuroinflammatory response and contributes to morphine tolerance and hyperalgesia in the periaqueductal gray

Long-term use of opioids such as morphine has negative side effects, such as morphine analgesic tolerance and morphine-induced hyperalgesia (MIH). These side effects limit the clinical use and analgesic efficacy of morphine. Elucidation of the mechanisms and identification of feasible and effective methods or treatment targets to solve this clinical phenomenon are important. Here, we discovered that YTHDF1 and TNF receptor-associated factor 6 (TRAF6) are crucial for morphine analgesic tolerance and MIH. The m6A reader YTHDF1 positively regulated the translation of TRAF6 mRNA, and chronic morphine treatments enhanced the m6A modification of TRAF6 mRNA. TRAF6 protein expression was drastically reduced by YTHDF1 knockdown, although TRAF6 mRNA levels were unaffected. By reducing inflammatory markers such as IL-1β, IL-6, TNF-α and NF-κB, targeted reduction of YTHDF1 or suppression of TRAF6 activity in ventrolateral periaqueductal gray (vlPAG) slows the development of morphine analgesic tolerance and MIH. Our findings provide new insights into the mechanism of morphine analgesic tolerance and MIH indicating that YTHDF1 regulates inflammatory factors such as IL-1β, IL-6, TNF-α and NF-κB by enhancing TRAF6 protein expression.

Oral Administration of Glutathione Trisulfide Increases Reactive Sulfur Levels in Dorsal Root Ganglion and Ameliorates Paclitaxel-Induced Peripheral Neuropathy in Mice

Peripheral neuropathy is a dose-limiting side effect of chemotherapy with paclitaxel. Paclitaxel-induced peripheral neuropathy (PIPN) is typically characterized by a predominantly sensory neuropathy presenting with allodynia, hyperalgesia and spontaneous pain. Oxidative mitochondrial damage in peripheral sensory neurons is implicated in the pathogenesis of PIPN. Reactive sulfur species, including persulfides (RSSH) and polysulfides (RSnH), are strong nucleophilic and electrophilic compounds that exert antioxidant effects and protect mitochondria. Here, we examined the potential neuroprotective effects of glutathione trisulfide (GSSSG) in a mouse model of PIPN. Intraperitoneal administration of paclitaxel at 4 mg/kg/day for 4 days induced mechanical allodynia and thermal hyperalgesia in mice. Oral administration of GSSSG at 50 mg/kg/day for 28 days ameliorated mechanical allodynia, but not thermal hyperalgesia. Two hours after oral administration, 34S-labeled GSSSG was detected in lumber dorsal root ganglia (DRG) and in the lumber spinal cord. In mice treated with paclitaxel, GSSSG upregulated expression of genes encoding antioxidant proteins in lumber DRG, prevented loss of unmyelinated axons and inhibited degeneration of mitochondria in the sciatic nerve. In cultured primary neurons from cortex and DRG, GSSSG mitigated paclitaxel-induced superoxide production, loss of axonal mitochondria, and axonal degeneration. These results indicate that oral administration of GSSSG mitigates PIPN by preventing axonal degeneration and mitochondria damage in peripheral sensory nerves. The findings suggest that administration of GSSSG may be an approach to the treatment or prevention of PIPN and other peripheral neuropathies.

Next generation behavioral sequencing for advancing pain quantification

With symptoms such as spontaneous pain and pathologically heightened sensitivity to stimuli, chronic pain accounts for about 20% of physician visits and up to 2/3 of patients are dissatisfied with current treatments. Much of our knowledge on pain processing and analgesics has emerged from behavioral studies performed on animals presenting the same symptoms under pathological conditions. While humans can verbally describe their pain, studies on rodents have relied on behavioral assays providing non-exhaustive characterization or altering animals' original sensitivity through repetitive stimulations. The emergence of what we term "next-generation behavioral sequencing" is now permitting us to quantitatively describe behavioral features on millisecond to minutes long timescales that lie beyond easy detection with the unaided eye. Here, we summarize emerging videography and computational based behavioral approaches that have the potential to significantly improve pain research.

Discovery of Potent and Selective Transient Receptor Potential Vanilloid 1 (TRPV1) Agonists with Analgesic Effects In Vivo Based on the Functional Conversion Induced by Altering the Orientation of the Indazole Core

Transient receptor potential vanilloid 1 (TRPV1) is a promising target for developing antinociceptive agents. Here, we report the synthesis of N-indazole-4-aryl piperazine carboxamide analogues as TRPV1 modulators. The structure-activity relationship (SAR) reveals that substituting indazole at the 5-/6-position leads to TRPV1 agonism, whereas the 4- and 7-positions of indazole obtain mild antagonism and loss of activity, respectively. The whole-cell clamp patch assay shows that 28 is a potent and selective TRPV1 agonist and it relieves inflammatory and thermal pain by desensitizing the native TRPV1 current in the dorsal root ganglion (DRG) in mice. Additionally, site-directed mutagenesis combined with molecular docking shows an important hydrogen interaction between Arg557 and the indazole of 28. Taken together, our findings provide insight into TRPV1 agonism-antagonism conversion based on the interaction between indazole and Arg557, which provides a strategy to obtain new TRPV1 agonists by structural modification of antagonists. Compound 28 may be used as a lead compound for further optimization.

Etv4 regulates nociception by controlling peptidergic sensory neuron development and peripheral tissue innervation

The perception of noxious environmental stimuli by nociceptive sensory neurons is an essential mechanism for the prevention of tissue damage. Etv4 is a transcriptional factor expressed in most nociceptors in dorsal root ganglia (DRG) during the embryonic development. However, its physiological role remains unclear. Here, we show that Etv4 ablation results in defects in the development of the peripheral peptidergic projections in vivo, and in deficits in axonal elongation and growth cone morphology in cultured sensory neurons in response to NGF. From a mechanistic point of view, our findings reveal that NGF regulates Etv4-dependent gene expression of molecules involved in extracellular matrix (ECM) remodeling. Etv4-null mice were less sensitive to noxious heat stimuli and chemical pain, and this behavioral phenotype correlates with a significant reduction in the expression of the pain-transducing ion channel TRPV1 in mutant mice. Together, our data demonstrate that Etv4 is required for the correct innervation and function of peptidergic sensory neurons, regulating a transcriptional program that involves molecules associated with axonal growth and pain transduction.

In Vivo and In Silico Study of the Antinociceptive and Toxicological Effect of the Extracts of Petiveria alliacea L. Leaves

Petiveria alliacea L. is an herb used in traditional medicine in Mexico and its roots have been studied to treat pain. However, until now, the antinociceptive properties of the leaves have not been investigated, being the main section used empirically for the treatment of diseases. For this reason, this study aimed to evaluate the antinociceptive and toxoicological activity of various extracts (aqueous, hexanic, and methanolic) from P. alliacea L. leaves in NIH mice and to perform an in silico analysis of the phytochemical compounds. Firstly, the antinociceptive effect was analyzed using the formalin model and the different doses of each of the extracts that were administered orally to obtain the dose–response curves. In addition, acute toxicity was determined by the up and down method and serum biochemical analysis. Later, the phytochemical study of extracts was carried out by thin layer chromatography (TLC) and visible light spectroscopy, and the volatile chemical components were analyzed by gas chromatography-mass spectrometry (GC/MS). Moreover, the most abundant compounds identified in the phytochemical study were analyzed in silico to predict their biological activity (PASSonline) and toxicology (OSIRIS Property Explorer). As a result, it was known that all extracts at doses from 10 to 316 mg/kg significantly reduced the pain response in both phases of the formalin model, with values of 50–60% for the inflammatory response. The toxicological studies (DL50) exhibited that all extracts did not cause any mortality up to the 2000 mg/kg dose level. This was corroborated by the values in the normal range of the biochemical parameters in the serum. Finally, the phytochemical screening of the presence of phenolic structures (coumarins, flavonoids) and terpenes (saponins and terpenes) was verified, and the highest content was of a lipid nature, 1.65 ± 0.54 meq diosgenin/mL in the methanolic extract. A total of 54 components were identified, 11 were the most abundant, and only four (Eicosane, Methyl oleate, 4-bis(1-phenylethyl) phenol, and Ethyl linolenate) of them showed a probability towards active antinociceptive activity in silico greater than 0.5. These results showed that the P. alliacea L. leaf extract possesses molecules with antinociceptive activity.

Thrombin Activity in Rodent and Human Skin: Modified by Inflammation and Correlates with Innervation

Thrombin is present in peripheral nerves and is involved in the pathogenesis of neuropathy. We evaluated thrombin activity in skin punch biopsies taken from the paws of male mice and rats and from the legs of patients with suspected small-fiber neuropathy (SFN). In mice, inflammation was induced focally by subcutaneous adjuvant injection to one paw and systemically by intraperitoneal lipopolysaccharides (LPS) administration. One day following injection, thrombin activity increased in the skin of the injected compared with the contralateral and non-injected control paws (p = 0.0009). One week following injection, thrombin increased in both injected and contralateral paws compared with the controls (p = 0.026), coupled with increased heat-sensitivity (p = 0.009). Thrombin activity in the footpad skin was significantly increased one week after systemic administration of LPS compared with the controls (p = 0.023). This was not accompanied by increased heat sensitivity. In human skin, a correlation was found between nerve fiber density and thrombin activity. In addition, a lower thrombin activity was measured in patients with evidence of systemic inflammation compared with the controls (p = 0.0035). These results support the modification of skin thrombin activity by regional and systemic inflammation as well as a correlation with nerve fiber density. Skin thrombin activity measurments may aid in the diagnosis and treatment of SFN.

Venlafaxine HCl Encapsulated in Niosome: Green and Eco-friendly Formulation for the Management of Pain

The goal of this experimentation was to increase the cutaneous absorption of venlafaxine HCl (VFX) encapsulated in a niosome (venlasosme) produced by an ultrasonic approach. The impact of the cholesterol:surfactant (Chol:Surf) proportion was examined to modify the venlasosme properties. Photon correlation spectroscopy, powder X-ray diffraction (PXRD), SEM, DSC, and ATR-FTIR spectroscopy were utilized to investigate the solid-state and morphology of VFX in the venlasosme. The studies revealed that increasing the level of Chol in the venlasosme increased the size of the particles. Alterations in the Chol to surfactant ratios (when Chol decreased from 2.5 to 0%) caused the zeta potential enhancement from 7.37 ± 0.67 to 15.53 ± 1.47 mV. The venlasosme with the highest cholesterol concentration (2.5%) had the highest encapsulation efficiency (approximately 63%). PXRD results revealed that VFX in venlasosme was in the amorphous form. The levels of VFX in the cutaneous layers and the receiver compartment were higher for the venlasosme gel than for VFX simple gel in the cutaneous permeability study and showed no cutaneous irritancy in rats. Furthermore, the venlasosme gel demonstrated significant antinociceptive and anti-inflammatory responses when compared to the control groups (VFX simple gel and diclofenac gel). The topical administration of the venlasosme gel also considerably increased the tail-flick and hot-plate response time when compared to the VFX simple gel, control groups, and diclofenac gel (p < 0.05). These findings suggest that niosomes can improve VFX efficacy as an antinociceptive and anti-inflammatory substance by improving the medicaments delivery to the specified site.

Transmembrane protein TMEM184B is necessary for interleukin-31-induced itch

ABSTRACT

Nociceptive and pruriceptive neurons in the dorsal root ganglia (DRG) convey sensations of pain and itch to the spinal cord, respectively. One subtype of mature DRG neurons, comprising 6% to 8% of neurons in the ganglia, is responsible for sensing mediators of acute itch and atopic dermatitis, including the cytokine IL-31. How itch-sensitive (pruriceptive) neurons are specified is unclear. Here, we show that transmembrane protein 184B (TMEM184B), a protein with roles in axon degeneration and nerve terminal maintenance, is required for the expression of a large cohort of itch receptors, including those for interleukin 31 (IL-31), leukotriene C4, and histamine. Male and female mice lacking TMEM184B show reduced responses to IL-31 but maintain normal responses to pain and mechanical force, indicating a specific behavioral defect in IL-31-induced pruriception. Calcium imaging experiments indicate that a reduction in IL-31-induced calcium entry is a likely contributor to this phenotype. We identified an early failure of proper Wnt-dependent transcriptional signatures and signaling components in Tmem184b mutant mice that may explain the improper DRG neuronal subtype specification. Accordingly, lentiviral re-expression of TMEM184B in mutant embryonic neurons restores Wnt signatures. Together, these data demonstrate that TMEM184B promotes adult somatosensation through developmental Wnt signaling and promotion of proper pruriceptive gene expression. Our data illuminate a new key regulatory step in the processes controlling the establishment of diversity in the somatosensory system.

The memory modulatory effect of agmatine in passive avoidance task coincides with alterations of hippocampal CaMKII-α and ERK signaling in mice

Agmatine is a polyamine suggested to act as a supposed neurotransmitter in the brain. Evidence has indicated that acute agmatine administration might modulate memory. The present study aimed to investigate the effect of repeated agmatine treatment on passive avoidance memory, hippocampal calcium-calmodulin-dependent protein kinase II-alpha (CaMKII-α), and Extracellular Signal-Regulated Kinase (ERK) signaling pathways in naive mice. Adult male NMRI mice were treated with agmatine (10, 20, 30, 40, and 80 mg/kg/ip) or saline for 11 days. Acquisition and retention tests of passive avoidance memory were performed on days 10 and 11, respectively. Following the memory retention test, the hippocampi were assessed for the levels of CaMKII-α and ERK using the western blotting technique. The results revealed the dose-dependent effect of agmatine on the passive avoidance memory. Accordingly, the memory was impaired in lower doses, but was improved in higher ones. Agmatine in none of the doses affected the nociception of the mice in tail-flick test. Furthermore, agmatine increased the phosphorylation of CaMKII-α and ERK in the hippocampus at memory enhancing doses, while ERK phosphorylation decreased following the impairing doses of agmatine. Thus, the dose-dependent effect of agmatine on memory might be related to its modulatory effect on CaMKII-α and ERK signal transduction, eventually regulating the memory process.

Modestly increasing systemic interleukin-6 perinatally disturbs secondary germinal zone neurogenesis and gliogenesis and produces sociability deficits

Epidemiologic studies have demonstrated that infections during pregnancy increase the risk of offspring developing Schizophrenia, Autism, Depression and Bipolar Disorder and have implicated interleukin-6 (IL-6) as a causal agent. However, other cytokines have been associated with the developmental origins of psychiatric disorders; therefore, it remains to be established whether elevating IL-6 is sufficient to alter the trajectory of neural development. Furthermore, most rodent studies have manipulated the maternal immune system at mid-gestation, which affects the stem cells and progenitors in both the primary and secondary germinal matrices. Therefore, a question that remains to be addressed is whether elevating IL-6 when the secondary germinal matrices are most active will affect brain development. Here, we have increased IL-6 from postnatal days 3-6 when the secondary germinal matrices are rapidly expanding. Using Nestin-Cre^ERT2 fate mapping we show that this transient increase in IL-6 decreased neurogenesis in the dentate gyrus of the dorsal hippocampus, reduced astrogliogenesis in the amygdala and decreased oligodendrogenesis in the body and splenium of the corpus callosum all by ∼ 50%. Moreover, the IL-6 treatment elicited behavioral changes classically associated with neurodevelopmental disorders. As adults, IL-6 injected male mice lost social preference in the social approach test, spent ∼ 30% less time socially engaging with sexually receptive females and produced ∼ 50% fewer ultrasonic vocalizations during mating. They also engaged ∼ 50% more time in self-grooming behavior and had an increase in inhibitory avoidance. Altogether, these data provide new insights into the biological mechanisms linking perinatal immune activation to complex neurodevelopmental brain disorders.

Selected Thiadiazine-Thione Derivatives Attenuate Neuroinflammation in Chronic Constriction Injury Induced Neuropathy

Neuropathic pain refers to a lesion or disease of peripheral and/or central somatosensory neurons and is an important body response to actual or potential nerve damage. We investigated the therapeutic potential of two thiadiazine-thione [TDT] derivatives, 2-(5-propyl-6-thioxo-1, 3, 5-thiadiazinan-3-yl) acetic acid [TDT1] and 2-(5-propyl-2-thioxo-1, 3, 5-thiadiazinan-3-yl) acetic acid [TDT2] against CCI (chronic constriction injury)-induced neuroinflammation and neuropathic pain. Mice were used for assessment of acute toxicity of TDT derivatives and no major toxic/bizarre responses were observed. Anti-inflammatory activity was assessed using the carrageenan test, and both TDT1 and TDT2 significantly reduced carrageenan-induced inflammation. We also used rats for the induction of CCI and performed allodynia and hyperalgesia-related behavioral tests followed by biochemical and morphological analysis using RT-qPCR, immunoblotting, immunohistochemistry and immunofluorescence. Our findings revealed that CCI induced clear-cut allodynia and hyperalgesia which was reversed by TDT1 and TDT2. To determine the function of TDT1 and TDT2 in glia-mediated neuroinflammation, Iba1 mRNA and protein levels were measured in spinal cord tissue sections from various experimental groups. Interestingly, TDT1 and TDT2 substantially reduced the mRNA expression and protein level of Iba1, implying that TDT1 and TDT2 may mitigate CCI-induced astrogliosis. In silico molecular docking studies predicted that both compounds had an effective binding affinity for TNF-α and COX-2. The compounds interactions with the proteins were dominated by both hydrogen bonding and van der Waals interactions. Overall, these results suggest that TDT1 and TDT2 exert their neuroprotective and analgesic potentials by ameliorating CCI-induced allodynia, hyperalgesia, neuroinflammation and neuronal degeneration in a dose-dependent manner.

Bivalent Conjugate Vaccine Induces Dual Immunogenic Response That Attenuates Heroin and Fentanyl Effects in Mice

Opioid use disorders and fatal overdose due to consumption of fentanyl-laced heroin remain a major public health menace in the United States. Vaccination may serve as a promising potential remedy to combat accidental overdose and to mitigate the abuse potential of opioids. We previously reported the heroin and fentanyl monovalent vaccines carrying, respectively, a heroin hapten, 6-AmHap, and a fentanyl hapten, para-AmFenHap, conjugated to tetanus toxoid (TT). Herein, we describe the mixing of these antigens to formulate a bivalent vaccine adjuvanted with liposomes containing monophosphoryl lipid A (MPLA) adsorbed on aluminum hydroxide. Immunization of mice with the bivalent vaccine resulted in IgG titers of >105 against both haptens. The polyclonal sera bound heroin, 6-acetylmorphine, morphine, and fentanyl with dissociation constants (Kd) of 0.25 to 0.50 nM. Mice were protected from the anti-nociceptive effects of heroin, fentanyl, and heroin +9% (w/w) fentanyl. No cross-reactivity to methadone and buprenorphine was observed in vivo. Naloxone remained efficacious in immunized mice. These results highlighted the potential of combining TT-6-AmHap and TT-para-AmFenHap to yield an efficacious bivalent vaccine that could ablate heroin and fentanyl effects. This vaccine warrants further testing to establish its potential translatability to humans.

Baccharis trimera aqueous extract modulates inflammation and nociception in mice

Background

The aerial parts of Baccharis trimera (Less.) are frequently used as a tea to treat several diseases. Therefore, the aim of this study was to identify the constituents of an aqueous extract of B. trimera, focusing on their antioxidant, anti-inflammation, and antinociception activities and properties. For that, the researchers performed in vivo assays using the formalin test and Freund’s Complete Adjuvant (FCA) to measure the acute and chronic inflammatory pain in mice. Moreover, the myeloperoxidase enzyme (MPO) was analyzed in the subcutaneous tissue after the FCA injection, together with the counting of lymphocytes in the peripheral blood of the mice.

Results

The qualitative phytochemical analysis indicated the presence of flavonoids and saponins in the B. trimera aqueous extract. The high-performance liquid chromatography (HPLC) analyses showed the presence of phenolic compounds, such as chlorogenic acid, ellagic acid, rosmarinic acid, as well as flavonoids, such as rutin, quercetin, and luteolin. The DPPH assay was used in order to measure the antioxidant activity of the aqueous extract of B. trimera and this showed an IC50 of 118.18 ± 1.02 μg/mg. The data from the formalin test demonstrated that a single dose of the aqueous extract of B. trimera was not able to decrease the nociceptive behavior during the neurogenic phase, at any of the tested doses (20, 40, or 80 mg/kg p.o.). However, during the inflammatory phase of this test, the aqueous extract of B. trimera at 80 mg/kg (p.o.) significantly decreased the nociceptive behavior, showing more effectiveness when compared to the other tested doses (p < 0.05). Importantly, in the chronic inflammatory model on the 5th day of treatment, the aqueous extract of B. trimera (80 mg/kg p.o.) significantly reduced mechanical allodynia (p < 0.01), heat thermal hyperalgesia (p < 0.001), and paw edema (p < 0.05). There were no changes in the MPO activity, but the data exhibited an equivalent decrease in the number of lymphocytes in the blood of the mice that were treated with B. trimera (80 mg.kg− 1 p.o.) and diclofenac sodium.

Conclusion

Taken together, the present data reinforces the potential of the B. trimera aqueous extract as an anti-inflammatory and analgesic compound.

Antinociceptive and Anti-Inflammatory Effects of Recombinant Crotamine in Mouse Models of Pain

Crotamine, a toxin found in the venom of the South American rattlesnake Crotalus durissus terrificus, has been reported to have antinociceptive effects. We purified recombinant crotamine expressed in Escherichia coli and investigated its antinociceptive and anti-inflammatory effects using the hot-plate test, acetic-acid-induced writhing method, and formalin test in mice. Recombinant crotamine was administered intraperitoneally (0.04–1.2 mg kg⁻¹) or intraplantarly (0.9–7.5 μg 10 μL⁻¹) before the tests. The paw volume was measured with a plethysmometer. To evaluate the antagonistic and anti-inflammatory effects of naloxone, subcutaneous naloxone (4 mg kg⁻¹) or intraplantar naloxone (5 μg 10 μL⁻¹) was administered before recombinant crotamine. For tumor necrosis factor (TNF)-α assays, blood was drawn 3 h after formalin injection and measured using enzyme-linked immunosorbent assay. Intraperitoneal and intraplantar recombinant crotamine had antinociceptive and anti-inflammatory effects, neither of which were affected by pre-treatment with naloxone. The mean serum TNF-α levels were significantly lower in the intraperitoneal recombinant crotamine (0.4 and 1.2 mg kg⁻¹) or intraplantar (2.5 and 7.5 μg 10 μL⁻¹) recombinant crotamine groups than in the saline group and were not affected by naloxone pre-treatment. In conclusion, recombinant crotamine possesses significant antinociceptive and anti-inflammatory effects that do not appear to be related to the opioid receptor. The antinociceptive and anti-inflammatory effects of intraperitoneal or intraplantar recombinant crotamine are related to TNF-α.

Docetaxel and Lidocaine Co-Loaded (NLC-in-Hydrogel) Hybrid System Designed for the Treatment of Melanoma

Melanoma is the most aggressive skin carcinoma and nanotechnology can bring new options for its pharmacological treatment. Nanostructured lipid carriers (NLC) are ideal drug-delivery carriers for hydrophobic drugs, such as the antineoplastic docetaxel (DTX), and hybrid (NLC-in-hydrogel) systems are suitable for topical application. This work describes a formulation of NLC_DTX in xanthan-chitosan hydrogel containing lidocaine (LDC) with anticancer and analgesia effects. The optimized nanoparticles encapsulated 96% DTX and rheological analysis revealed inherent viscoelastic properties of the hydrogel. In vitro assays over murine fibroblasts (NIH/3T3) and melanoma cells (B16-F10), human keratinocytes (HaCaT) and melanoma cells (SK-MEL-103) showed reduction of docetaxel cytotoxicity after encapsulation in NLC_DTX and HGel-NLC_DTX. Addition of LDC to the hybrid system (HGel-NLC_DTX-LDC) increased cell death in tumor and normal cells. In vivo tests on C57BL/6J mice with B16-F10-induced melanoma indicated that LDC, NLC_DTX, HGel-NLC_DTX-LDC and NLC_DTX + HGel-LDC significantly inhibited tumor growth while microPET/SPECT/CT data suggest better prognosis with the hybrid treatment. No adverse effects were observed in cell survival, weight/feed-consumption or serum biochemical markers (ALT, AST, creatinine, urea) of animals treated with NLC_DTX or the hybrid system. These results confirm the adjuvant antitumor effect of lidocaine and endorse HGel-NLC_DTX-LDC as a promising formulation for the topical treatment of melanoma.

Effects of fadolmidine, an α2 -adrenoceptor agonist, as an adjuvant to spinal bupivacaine on antinociception and motor function in rats and dogs

α2 -Adrenoceptor agonists such as clonidine and dexmedetomidine are used as adjuvants to local anesthetics in regional anesthesia. Fadolmidine is an α2 -adrenoceptor agonist developed especially as a spinal analgesic. The current studies investigate the effects of intrathecally administered fadolmidine with a local anesthetic, bupivacaine, on antinociception and motor block in conscious rats and dogs. The antinociceptive effects of intrathecal fadolmidine and bupivacaine alone or in combination were tested in the rat tail-flick and the dog's skin twitch models. The durations of motor block in rats and in dogs were also assessed. In addition, the effects on sedation, mean arterial blood pressure, heart rate, respiratory rate and body temperature were evaluated in telemetrized dogs. Concentrations of fadolmidine in plasma and spinal cord were determined after intrathecal and intravenous administration in rats. Co-administration of intrathecal fadolmidine with bupivacaine increased the magnitude and duration of the antinociceptive effects and prolonged motor block without hypotension. The interaction of the antinociceptive effect was synergistic in its nature in rats. Concentration of fadolmidine in plasma was very low after intrathecal dosing. Taken together, these studies show that fadolmidine as an adjuvant to intrathecal bupivacaine provides enhanced sensory-motor block and enables a reduction of the doses of both drugs. The results indicate that co-administration of fadolmidine with intrathecal bupivacaine was able to achieve an enhanced antinociceptive effect without hypotension and could thus represent a suitable combination for spinal anesthesia.

Effect of Preexisting Immunity to Tetanus Toxoid on the Efficacy of Tetanus Toxoid-Conjugated Heroin Vaccine in Mice

Opioid use disorder (OUD) is a serious health problem that has dramatically increased over the last decade. Although current therapies for the management of OUD can be effective, they have limitations. The complementary strategy to combat the opioid crisis is the development of a conjugate vaccine to generate high affinity antibodies in order to neutralize opioids in circulation before reaching the brain. The components of an opioid vaccine include an opioid hapten (6-AmHap) that is conjugated to a carrier protein (tetanus toxoid) with the addition of adjuvants (Army Liposome Formulation adsorbed to aluminum hydroxide-ALFA). There is no consensus in the literature as to whether preexisting immunity to the carrier protein may impact the immunogenicity of the conjugate vaccine by inducing an enhanced or suppressed immune response to the hapten. Here, we investigated whether pre-exposure to tetanus toxoid would affect the immunogenicity and efficacy of the heroin vaccine, TT-6-AmHap. Mice were primed with diphtheria, tetanus, and acellular pertussis (DTaP) vaccine at weeks -4 and -2, then immunized with TT-6-AmHap vaccine at weeks 0, 3, and 6. Using ELISA and behavioral assays, we found that preexisting immunity to tetanus toxoid had no influence on the immunogenicity and efficacy of the TT-6-AmHap vaccine.

The Analgesic Effect of Aconitum Sinomontanum Nakai Pharmacopuncture in Sprague-Dawley Rats

Background: Aconitum sinomontanum Nakai (ASN) has been reported to have analgesic effects. In this study an animal model of pharmacopuncture using ASN (100-500 mg/kg) was examined.Methods: Sprague-Dawley (SD) rats (<i>n</i> = 40) were randomly assigned to ASN-Low (1 mg/mL, 1.8 mL, ASN-L), ASN-Intermediate (5 mg/mL, 1.8 mL, ASN-M), ASN-High (10 mg/mL, 1.8 mL, ASN-H), negative control (0.2 mL normal saline), and positive control (0.2 mL 0.5% lidocaine) groups. All experiments were administered to the rats’ left hind leg. The analgesic response was assessed by monitoring the physical (hot plate, and von Frey test) and chemical (formalin) responses to pain.Results: All ASN pharmacopuncture groups demonstrated significant differences in pain response to the hot plate test, von Frey test, and formalin test, compared to the control group (<i>p</i> < 0.05). The response of the ASN-M group and ASN-H groups to the hot plate, the formalin, and the von Frey tests were significantly different, compared to the lidocaine group (<i>p</i> < 0.05).Conclusion: ASN pharmacopuncture had a significant analgesic effect on SD rats in response to physical and chemical models of pain.