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Postoperative pain management is challenging. We used mice with a transverse laparotomy to study tactile allodynia measured by the von Frey test, pain at rest measured by facial pain expressions detected by an artificial intelligence algorithm, and movement-induced pain measured by reductions in exploratory activity. The standard analgesics morphine and ibuprofen induced distinct patterns of outcome-dependent effects. Whereas morphine was more effective in reversing pain at rest compared to tactile allodynia, it was unable to alter movement-induced pain. Ibuprofen showed comparable effects across the three outcomes. Administered together, the compounds induced synergistic effects in the three aspects of postoperative pain, mirroring the known advantages of multimodal analgesia used in clinical practice. We explored the impact of neuroimmune interactions using a neutrophil depletion strategy. This reversed pain at rest and movement-induced pain, but did not alter cutaneous sensitivity. Non-peptidergic (IB4+) and peptidergic (CGRP+) nociceptors are segregated neuronal populations in the mouse. We tested the effects of gefapixant, an antitussive drug targeting non-peptidergic nociceptors through P2X3 antagonism, and olcegepant, an antimigraine drug acting as a CGRP antagonist. Both compounds reversed tactile allodynia, while only gefapixant reversed pain at rest, and none of them reversed movement-induced pain. In conclusion, tactile allodynia, pain at rest, and movement-induced pain after surgery have different pharmacological profiles, and none of the three aspects of postoperative pain can predict the effects of a given intervention on the other two. Combining these measures provides a more realistic view of postoperative pain and has the potential to benefit analgesic development., Competing Interests: Declaration of Competing Interest The authors declare no competing interests., (Copyright © 2024 The Authors. Published by Elsevier Masson SAS.. All rights reserved.)

The mechanisms for neuropathic pain amelioration by sigma-1 receptor inhibition are not fully understood. We studied genome-wide transcriptomic changes (RNAseq) in the dorsal root ganglia (DRG) from wild-type and sigma-1 receptor knockout mice prior to and following Spared Nerve Injury (SNI). In wildtype mice, most of the transcriptomic changes following SNI are related to the immune function or neurotransmission. Immune function transcripts contain cytokines and markers for immune cells, including macrophages/monocytes and CD4 + T cells. Many of these immune transcripts were attenuated by sigma-1 knockout in response to SNI. Consistent with this we found, using flow cytometry, that sigma-1 knockout mice showed a reduction in macrophage/monocyte recruitment as well as an absence of CD4 + T cell recruitment in the DRG after nerve injury. Sigma-1 knockout mice showed a reduction of neuropathic (mechanical and cold) allodynia and spontaneous pain-like responses (licking of the injured paw) which accompany the decreased peripheral neuroinflammatory response after nerve injury. Treatment with maraviroc (a CCR5 antagonist which preferentially inhibits CD4 + T cells in the periphery) of neuropathic wild-type mice only partially replicated the sigma-1 knockout phenotype, as it did not alter cold allodynia but attenuated spontaneous pain-like responses and mechanical hypersensitivity. Therefore, modulation of peripheral CD4 + T cell activity might contribute to the amelioration of spontaneous pain and neuropathic tactile allodynia seen in the sigma-1 receptor knockout mice, but not to the effect on cold allodynia. We conclude that sigma-1 receptor inhibition decreases DRG neuroinflammation which might partially explain its anti-neuropathic effect., (© 2024. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Most of the previous studies on the genetic variability in Spanish "Berrenda" breeds have been carried out using DNA microsatellites. The present work aimed to estimate the genetic diversity, population structure, and potential genetic differences among individuals of both Berrenda breeds and groups based on the presence of the Robertsonian chromosomal translocation, rob (1;29). A total of 373 samples from animals belonging to the two breeds, including 169 cases diagnosed as rob (1;29)-positive, were genotyped using an SNP50K chip. The genetic diversity at the breed level did not show significant differences, but it was significantly lower in those subpopulations containing the rob (1;29). Runs of homozygosity identified a region of homozygosity on chromosome 6, where the KIT ( KIT proto-oncogene, receptor tyrosine kinase) gene, which determines the typical spotted coat pattern in both breeds, is located. The four subpopulations considered showed minor genetic differences. The regions of the genome that most determined the differences between the breeds were observed on chromosomes 4, 6, 18, and 22. The presence of this Robertsonian translocation did not result in sub-structuring within each of the breeds considered. To improve the reproductive performance of Berrenda breeds, it would be necessary to implement strategies considering the involvement of potential breeding stock carrying rob (1;29).

Chronic pain occurs at epidemic levels throughout the population. Hypersensitivity to touch, is a cardinal symptom of chronic pain. Despite dedicated research for over a century, quantifying this hypersensitivity has remained impossible at scale. To address these issues, we developed the Chainmail Sensitivity Test (CST). Our results show that control mice spend significantly more time on the chainmail portion of the device than mice subject to neuropathy. Treatment with gabapentin abolishes this difference. CST-derived data correlate well with von Frey measurements and quantify hypersensitivity due to inflammation. Our study demonstrates the potential of the CST as a standardized tool for assessing mechanical hypersensitivity in mice with minimal operator input., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Ozdemir, Nakamoto, Boivin, Bullock, Andrews, González-Cano and Costigan.)

The design and synthesis of a series of 2,7-diazaspiro[4.4]nonane derivatives as potent sigma receptor (SR) ligands, associated with analgesic activity, are the focus of this work. In this study, affinities at S1R and S2R were measured, and molecular modeling studies were performed to investigate the binding pose characteristics. The most promising compounds were subjected to in vitro toxicity testing and subsequently screened for in vivo analgesic properties. Compound 9d ( AD258 ) exhibited negligible in vitro cellular toxicity and a high binding affinity to both SRs ( K i S1R = 3.5 nM, K i S2R = 2.6 nM), but not for other pain-related targets, and exerted high potency in a model of capsaicin-induced allodynia, reaching the maximum antiallodynic effect at very low doses (0.6-1.25 mg/kg). Functional activity experiments showed that S1R antagonism is needed for the effects of 9d and that it did not induce motor impairment. In addition, 9d exhibited a favorable pharmacokinetic profile.

The development of diazabicyclo[4.3.0]nonane and 2,7-diazaspiro[3.5]nonane derivatives as sigma receptors (SRs) ligands is reported. The compounds were evaluated in S1R and S2R binding assays, and modeling studies were carried out to analyze the binding mode. The most notable compounds, 4b (AD186, K i S1R = 2.7 nM, K i S2R = 27 nM), 5b (AB21, K i S1R = 13 nM, K i S2R = 102 nM), and 8f (AB10, K i S1R = 10 nM, K i S2R = 165 nM), have been screened for analgesic effects in vivo , and their functional profile was determined through in vivo and in vitro models. Compounds 5b and 8f reached the maximum antiallodynic effect at 20 mg/kg. The selective S1R agonist PRE-084 completely reversed their action, indicating that the effects are entirely dependent on the S1R antagonism. Conversely, compound 4b sharing the 2,7-diazaspiro[3.5]nonane core as 5b was completely devoid of antiallodynic effect. Interestingly, compound 4b fully reversed the antiallodynic effect of BD-1063, indicating that 4b induces an S1R agonistic in vivo effect. The functional profiles were confirmed by the phenytoin assay. Our study might establish the importance of 2,7-diazaspiro[3.5]nonane core for the development of S1R compounds with specific agonist or antagonist profile and the role of the diazabicyclo[4.3.0]nonane in the development of novel SR ligands.

Antagonists at σ 1 receptors have great potential for the treatment of neuropathic pain. Starting from monoterpene (-)-isopulegol ( 1 ), aminodiols 8-11 were obtained and transformed into bicyclic 13-16 and tricyclic ligands 19-22 . Aminodiols 8-11 showed higher σ 1 affinity than the corresponding bicyclic 13-16 and tricyclic derivatives 19-22 . ( R )-configuration in the side chain of aminodiols ( 8 and 10 ) led to higher σ 1 affinity than ( S )-configuration ( 9 and 11 ). 4-Benzylpiperidines ( b -series) revealed higher σ 1 affinity than 4-phenylbutylamines ( a -series). Aminodiol 8b showed very high σ 1 affinity ( K i = 1.2 nM), excellent selectivity over σ 2 receptors, and promising log D 7.4 (3.05) and lipophilic ligand efficiency (5.87) values. Molecular dynamics simulations were conducted to analyze the σ 1 affinity and selectivity on an atomistic level. In the capsaicin assay, 8b exhibited similar antiallodynic activity to the prototypical σ 1 antagonist S1RA. The antiallodynic activity of 8b was removed by co-application of the σ 1 agonist PRE-084, proving σ 1 antagonism being involved in the antiallodynic effect.

Abdominal pain is a common feature in inflammatory bowel disease (IBD) patients, and greatly compromises their quality of life. Therefore, the identification of new therapeutic tools to reduce visceral pain is one of the main goals for IBD therapy. Minocycline, a broad-spectrum tetracycline antibiotic, has gained attention in the scientific community because of its immunomodulatory and anti-inflammatory properties. The aim of this study was to evaluate the potential of this antibiotic as a therapy for the management of visceral pain in dextran sodium sulfate (DSS)-induced colitis in mice. Preemptive treatment with minocycline markedly reduced histological features of intestinal inflammation and the expression of inflammatory markers (Tlr4, Tnfα, Il1ß, Ptgs2, Inos, Cxcl2, and Icam1), and attenuated the decrease of markers of epithelial integrity (Tjp1, Ocln, Muc2, and Muc3). In fact, minocycline restored normal epithelial permeability in colitic mice. Treatment with the antibiotic also reversed the changes in the gut microbiota profile induced by colitis. All these ameliorative effects of minocycline on both inflammation and dysbiosis correlated with a decrease in ongoing pain and referred hyperalgesia, and with the improvement of physical activity induced by the antibiotic in colitic mice. Minocycline might constitute a new therapeutic approach for the treatment of IBD-induced pain. PERSPECTIVE: This study found that the intestinal anti-inflammatory effects of minocycline ameliorate DSS-associated pain in mice. Therefore, minocycline might constitute a novel therapeutic strategy for the treatment of IBD-induced pain., (Copyright © 2022 United States Association for the Study of Pain, Inc. Published by Elsevier Inc. All rights reserved.)

Abstract: The lack of sensitive and robust behavioral assessments of pain in preclinical models has been a major limitation for both pain research and the development of novel analgesics. Here, we demonstrate a novel data acquisition and analysis platform that provides automated, quantitative, and objective measures of naturalistic rodent behavior in an observer-independent and unbiased fashion. The technology records freely behaving mice, in the dark, over extended periods for continuous acquisition of 2 parallel video data streams: (1) near-infrared frustrated total internal reflection for detecting the degree, force, and timing of surface contact and (2) simultaneous ongoing video graphing of whole-body pose. Using machine vision and machine learning, we automatically extract and quantify behavioral features from these data to reveal moment-by-moment changes that capture the internal pain state of rodents in multiple pain models. We show that these voluntary pain-related behaviors are reversible by analgesics and that analgesia can be automatically and objectively differentiated from sedation. Finally, we used this approach to generate a paw luminance ratio measure that is sensitive in capturing dynamic mechanical hypersensitivity over a period and scalable for high-throughput preclinical analgesic efficacy assessment., (Copyright © 2022 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the International Association for the Study of Pain.)

The soluble epoxide hydrolase (sEH) has been suggested as a pharmacological target for the treatment of several diseases, including pain-related disorders. Herein, we report further medicinal chemistry around new benzohomoadamantane-based sEH inhibitors (sEHI) in order to improve the drug metabolism and pharmacokinetics properties of a previous hit. After an extensive in vitro screening cascade, molecular modeling, and in vivo pharmacokinetics studies, two candidates were evaluated in vivo in a murine model of capsaicin-induced allodynia. The two compounds showed an anti-allodynic effect in a dose-dependent manner. Moreover, the most potent compound presented robust analgesic efficacy in the cyclophosphamide-induced murine model of cystitis, a well-established model of visceral pain. Overall, these results suggest painful bladder syndrome as a new possible indication for sEHI, opening a new range of applications for them in the visceral pain field.

The first goal of this work was the description of a model addressed to quantify the carbon footprint in Spanish autochthonous dairy sheep farms (Manchega group), foreign dairy sheep farms (foreigners group: Lacaune and Assaf breeds), and Spanish autochthonous dairy goat farms (Florida group). The second objective was to analyze the GHG emission mitigation potential of 17 different livestock farming practices that were implemented by 36 different livestock farms, in terms of CO 2 e per hectare (ha), CO 2 e per livestock unit (LU), and CO 2 e per liter of fat- and protein-corrected milk (FPCM). The study showed the following results: 1.655 kg CO 2 e per ha, 6.397 kg CO 2 e per LU, and 3.78 kg CO 2 e per liter of FPCM in the Manchega group; 12.634 kg CO 2 e per ha, 7.810 CO 2 e kg per LU, and 2.77 kg CO 2 e per liter of FPCM in the Foreigners group and 1.198 kg CO 2 e per ha, 6.507 kg CO 2 e per LU, and 3.06 kg CO 2 e per liter of FPCM in Florida group. In summary, purchasing off-farm animal feed would increase emissions by up to 3.86%. Conversely, forage management, livestock inventory, electrical supply, and animal genetic improvement would reduce emissions by up to 6.29%, 4.3%, 3.52%, and 0.8%, respectively; finally, an average rise of 2 °C in room temperature would increase emissions by up to 0.62%.

The development of σ 1 receptor antagonists hybridized with a H 2 S-donor is here reported. We aimed to obtain improved analgesic effects when compared to σ 1 receptor antagonists or H 2 S-donors alone. In an in vivo model of sensory hypersensitivity, thioamide 1a induced analgesia which was synergistically enhanced when associated with the σ 1 receptor antagonist BD-1063. The selective σ 1 receptor agonist PRE-084 completely reversed this effect. Four thioamide H 2 S-σ 1 receptor hybrids (5a-8a) and their amide derivatives (5b-8b) were synthesized. Compound 7a (AD164) robustly released H 2 S and showed selectivity for σ 1 receptor over σ 2 and opioid receptors. This compound induced marked analgesia that was reversed by PRE-084. The amide analogue 7b (AD163) showed only minimal analgesia. Further studies showed that 7a exhibited negligible acute toxicity, together with a favorable pharmacokinetic profile. To the best of our knowledge, compound 7a is the first dual-acting ligand with simultaneous H 2 S-release and σ 1 antagonistic activities., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Masson SAS. All rights reserved.)

Following the concept of conformational restriction to obtain high affinity σ 1 ligands, the piperidine ring of eliprodil was replaced by the bicyclic tropane system and an exocyclic double bond was introduced. The envisaged benzylidenetropanes 9 were prepared by conversion of tropanone 10 into the racemic mixture of (Z)-14 and (E)-14. Reaction of racemate (Z)-14/(E)-14 with enantiomerically pure (R)- or (S)-configured 2-phenyloxirane provided mixtures of diastereomeric β-aminoalcohols (R,Z)-9 and (R,E)-9 as well as (S,Z)-9 and (S,E)-9, which were separated by chiral HPLC, respectively. X-ray crystal structure analysis of (S,Z)-9 allowed the unequivocal assignment of the configuration of all four stereoisomers. In receptor binding studies with radioligands, (R,E)-9 and (S,Z)-9 showed subnanomolar σ 1 affinity with eudismic ratios of 8.3 and 40. In both compounds the 4-fluorophenyl moiety is oriented towards (S)-configured C-5 of the tropane system. Both compounds display high selectivity for the σ 1 receptor over the σ 2 subtype but moderate selectivity over GluN2B NMDA receptors. In vivo, (R,E)-9 (K i (σ 1 ) = 0.80 nM) showed high antiallodynic activity in the capsaicin assay. The effect of (R,E)-9 could be reversed by pre-administration of the σ 1 agonist PRE-084 confirming the σ 1 antagonistic activity of (R,E)-9., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Masson SAS. All rights reserved.)

Pedigree analyses of two endangered cattle breeds were performed in order to study the structure and the genetic variability in their populations. Pedigree data were analyzed from 12,057 individuals belonging to the "Berrenda en Negro" cattle breed (BN) and 20,389 individuals belonging to the "Berrenda en Colorado" cattle breed (BC) that were born between 1983 and 2020. BN and BC reference populations (RP) were set up by 2300 and 3988 animals, respectively. The generation interval in BN and BC reference populations was equal to 6.50 and 6.92 years, respectively. The pedigree completeness level was 82.76% in BN and 79.57% in BC. The inbreeding rates were 4.5% in BN and 3.4% in BC, respectively. The relationship among animals when they were born in different herds was 1.8% in BN and 5% in BC; these values increased to 8.5% and 7.7%, respectively when comparing animals that were born in the same herd. The effective number of founding herds was 23.9 in BN and 60.9 in BC. Number of ancestors needed to explain 50% of genes pool in the whole population was 50 and 101, in BN and in BC, respectively. The effective population size based on co-ancestries was 92.28 in BN and 169.92 in BC. The genetic variability has been maintained in both populations over time and the results of this study suggest that measures to promote the conservation of the genetic variability in these two breeds would go through for the exchange of breeding animals among farms and for monitoring the genetic contributions before implementing any selective action.

Tetrodotoxin (TTX) is a potent neurotoxin found mainly in puffer fish and other marine and terrestrial animals. TTX blocks voltage-gated sodium channels (VGSCs) which are typically classified as TTX-sensitive or TTX-resistant channels. VGSCs play a key role in pain signaling and some TTX-sensitive VGSCs are highly expressed by adult primary sensory neurons. During pathological pain conditions, such as neuropathic pain, upregulation of some TTX-sensitive VGSCs, including the massive re-expression of the embryonic VGSC subtype Na V 1.3 in adult primary sensory neurons, contribute to painful hypersensitization. In addition, people with loss-of-function mutations in the VGSC subtype Na V 1.7 present congenital insensitive to pain. TTX displays a prominent analgesic effect in several models of neuropathic pain in rodents. According to this promising preclinical evidence, TTX is currently under clinical development for chemo-therapy-induced neuropathic pain and cancer-related pain. This review focuses primarily on the preclinical and clinical evidence that support a potential analgesic role for TTX in these pain states. In addition, we also analyze the main toxic effects that this neurotoxin produces when it is administered at therapeutic doses, and the therapeutic potential to alleviate neuropathic pain of other natural toxins that selectively block TTX-sensitive VGSCs.

Immune and glial cells play a pivotal role in chronic pain. Therefore, it is possible that the pharmacological modulation of neurotransmission from an exclusively neuronal perspective may not be enough for adequate pain management, and the modulation of complex interactions between neurons and other cell types might be needed for successful pain relief. In this article, we review the current scientific evidence for the modulatory effects of sigma-1 receptors on communication between the immune and nervous systems during inflammation, as well as the influence of this receptor on peripheral and central neuroinflammation. Several experimental models of pathological pain are considered, including peripheral and central neuropathic pain, osteoarthritic, and cancer pain. Sigma-1 receptor inhibition prevents peripheral (macrophage infiltration into the dorsal root ganglion) and central (activation of microglia and astrocytes) neuroinflammation in several pain models, and enhances immune-driven peripheral opioid analgesia during painful inflammation, maximizing the analgesic potential of peripheral immune cells. Therefore, sigma-1 antagonists may constitute a new class of analgesics with an unprecedented mechanism of action and potential utility in several painful disorders., (Copyright © 2020 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Pain measures traditionally used in rodents record mere reflexes evoked by sensory stimuli; the results thus may not fully reflect the human pain phenotype. Alterations in physical and emotional functioning, pain-depressed behaviors and facial pain expressions were recently proposed as additional pain outcomes to provide a more accurate measure of clinical pain in rodents, and hence to potentially enhance analgesic drug development. We aimed to review how preclinical pain assessment has evolved since the development of the tail flick test in 1941, with a particular focus on a critical analysis of some nonstandard pain outcomes, and a consideration of how sex differences may affect the performance of these pain surrogates. We tracked original research articles in Medline for the following periods: 1973-1977, 1983-1987, 1993-1997, 2003-2007, and 2014-2018. We identified 606 research articles about alternative surrogate pain measures, 473 of which were published between 2014 and 2018. This indicates that preclinical pain assessment is moving toward the use of these measures, which may soon become standard procedures in preclinical pain laboratories., (Copyright © 2020 The Authors. Published by Elsevier Ltd.. All rights reserved.)

No adequate treatment is available for painful urinary bladder disorders such as interstitial cystitis/bladder pain syndrome, and the identification of new urological therapeutic targets is an unmet need. The sigma-1 receptor (σ 1 -R) modulates somatic pain, but its role in painful urological disorders is unexplored. The urothelium expresses many receptors typical of primary sensory neurons (e.g. TRPV1, TRPA1 and P2X3) and high levels of σ 1 -R have been found in these neurons; we therefore hypothesized that σ 1 -R may also be expressed in the urothelium and may have functional relevance in this tissue. With western blotting and immunohistochemical methods, we detected σ 1 -R in the urinary bladder in wild-type (WT) but not in σ 1 -R-knockout (σ 1 -KO) mice. Interestingly, σ 1 -R was located in the bladder urothelium not only in mouse, but also in human bladder sections. The severity of histopathological (edema, hemorrhage and urothelial desquamation) and biochemical alterations (enhanced myeloperoxidase activity and phosphorylation of extracellular regulated kinases 1/2 [pERK1/2]) that characterize cyclophosphamide-induced cystitis was lower in σ 1 -KO than in WT mice. Moreover, cyclophosphamide-induced pain behaviors and referred mechanical hyperalgesia were dose-dependently reduced by σ 1 -R antagonists (BD-1063, NE-100 and S1RA) in WT but not in σ1-KO mice. In contrast, the analgesic effect of morphine was greater in σ 1 -KO than in WT mice. Together these findings suggest that σ 1 -R plays a functional role in the mechanisms underlying cyclophosphamide-induced cystitis, and modulates morphine analgesia against urological pain. Therefore, σ 1 -R may represent a new drug target for urinary bladder disorders., Competing Interests: Declaration of Competing Interest M.M. is an employee of Esteve Pharmaceuticals. None of the authors have conflicts of interest., (Copyright © 2020 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Morphine induces peripherally μ-opioid-mediated antinociception to heat but not to mechanical stimulation. Peripheral sigma-1 receptors tonically inhibit μ-opioid antinociception to mechanical stimuli, but it is unknown whether they modulate μ-opioid heat antinociception. We hypothesized that sigma-1 receptors might play a role in the modality-specific peripheral antinociceptive effects of morphine and other clinically relevant μ-opioid agonists. Mechanical nociception was assessed in mice with the paw pressure test (450 g), and heat nociception with the unilateral hot plate (55 °C) test. Local peripheral (intraplantar) administration of morphine, buprenorphine or oxycodone did not induce antinociception to mechanical stimulation but had dose-dependent antinociceptive effects on heat stimuli. Local sigma-1 antagonism unmasked peripheral antinociception by μ-opioid agonists to mechanical stimuli, but did not modify their effects on heat stimulation. TRPV1+ and IB4+ cells are segregated populations of small neurons in the dorsal root ganglia (DRG) and the density of sigma-1 receptors was higher in IB4+ cells than in the rest of small nociceptive neurons. The in vivo ablation of TRPV1-expressing neurons with resiniferatoxin did not alter IB4+ neurons in the DRG, mechanical nociception, or the effects of sigma-1 antagonism on local morphine antinociception in this type of stimulus. However, it impaired the responses to heat stimuli and the effect of local morphine on heat nociception. In conclusion, peripheral opioid antinociception to mechanical stimuli is limited by sigma-1 tonic inhibitory actions, whereas peripheral opioid antinociception to heat stimuli (produced in TRPV1-expressing neurons) is not. Therefore, sigma-1 receptors contribute to the modality-specific peripheral effects of opioid analgesics., (Copyright © 2018 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Immune cells have a known role in pronociception, since they release a myriad of inflammatory algogens which interact with neurons to facilitate pain signaling. However, these cells also produce endogenous opioid peptides with analgesic potential. The sigma-1 receptor is a ligand-operated chaperone that modulates neurotransmission by interacting with multiple protein partners, including the μ-opioid receptor. We recently found that sigma-1 antagonists are able to induce opioid analgesia by enhancing the action of endogenous opioid peptides of immune origin during inflammation. This opioid analgesia is seen only at the inflamed site, where immune cells naturally accumulate. In this article we review the difficulties of targeting the opioid system for selective pain relief, and discuss the dual role of immune cells in pain and analgesia. Our discussion creates perspectives for possible novel therapeutic uses of sigma-1 antagonists as agents able to maximize the analgesic potential of the immune system., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Chronic neuropathic pain is a major morbidity of neural injury, yet its mechanisms are incompletely understood. Hypersensitivity to previously non-noxious stimuli (allodynia) is a common symptom. Here, we demonstrate that the onset of cold hypersensitivity precedes tactile allodynia in a model of partial nerve injury, and this temporal divergence was associated with major differences in global gene expression in innervating dorsal root ganglia. Transcripts whose expression change correlates with the onset of cold allodynia were nociceptor related, whereas those correlating with tactile hypersensitivity were immune cell centric. Ablation of TrpV1 lineage nociceptors resulted in mice that did not acquire cold allodynia but developed normal tactile hypersensitivity, whereas depletion of macrophages or T cells reduced neuropathic tactile allodynia but not cold hypersensitivity. We conclude that neuropathic pain incorporates reactive processes of sensory neurons and immune cells, each leading to distinct forms of hypersensitivity, potentially allowing drug development targeted to each pain type., (Copyright © 2018 The Authors. Published by Elsevier Inc. All rights reserved.)

Sigma-1 antagonism potentiates the antinociceptive effects of opioid drugs, so sigma-1 receptors constitute a biological brake to opioid drug-induced analgesia. The pathophysiological role of this process is unknown. We aimed to investigate whether sigma-1 antagonism reduces inflammatory pain through the disinhibition of the endogenous opioidergic system in mice. The selective sigma-1 antagonists BD-1063 and S1RA abolished mechanical and thermal hyperalgesia in mice with carrageenan-induced acute (3 h) inflammation. Sigma-1-mediated antihyperalgesia was reversed by the opioid antagonists naloxone and naloxone methiodide (a peripherally restricted naloxone analog) and by local administration at the inflamed site of monoclonal antibody 3-E7, which recognizes the pan-opioid sequence Tyr-Gly-Gly-Phe at the N terminus of most endogenous opioid peptides (EOPs). Neutrophils expressed pro-opiomelanocortin, the precursor of β-endorphin (a known EOP), and constituted the majority of the acute immune infiltrate. β-endorphin levels increased in the inflamed paw, and this increase and the antihyperalgesic effects of sigma-1 antagonism were abolished by reducing the neutrophil load with in vivo administration of an anti-Ly6G antibody. The opioid-dependent sigma-1 antihyperalgesic effects were preserved 5 d after carrageenan administration, where macrophages/monocytes were found to express pro-opiomelanocortin and to now constitute the majority of the immune infiltrate. These results suggest that immune cells harboring EOPs are needed for the antihyperalgesic effects of sigma-1 antagonism during inflammation. In conclusion, sigma-1 receptors curtail immune-driven peripheral opioid analgesia, and sigma-1 antagonism produces local opioid analgesia by enhancing the action of EOPs of immune origin, maximizing the analgesic potential of immune cells that naturally accumulate in painful inflamed areas., Competing Interests: The authors declare no conflict of interest.

Visceral pain is very common and represents a major unmet clinical need for which current pharmacological treatments are often insufficient. Tetrodotoxin (TTX) is a potent neurotoxin that exerts analgesic actions in both humans and rodents under different somatic pain conditions, but its effect has been unexplored in visceral pain. Therefore, we tested the effects of systemic TTX in viscero-specific mouse models of chemical stimulation of the colon (intracolonic instillation of capsaicin and mustard oil) and intraperitoneal cyclophosphamide-induced cystitis. The subcutaneous administration of TTX dose-dependently inhibited the number of pain-related behaviors in all evaluated pain models and reversed the referred mechanical hyperalgesia (examined by stimulation of the abdomen with von Frey filaments) induced by capsaicin and cyclophosphamide, but not that induced by mustard oil. Morphine inhibited both pain responses and the referred mechanical hyperalgesia in all tests. Conditional nociceptor‑specific Na v 1.7 knockout mice treated with TTX showed the same responses as littermate controls after the administration of the algogens. No motor incoordination after the administration of TTX was observed. These results suggest that blockade of TTX-sensitive sodium channels, but not Na v 1.7 subtype alone, by systemic administration of TTX might be a potential therapeutic strategy for the treatment of visceral pain., Competing Interests: The authors declare no conflict of interest.

Key Points: Voltage-gated sodium channels play a fundamental role in determining neuronal excitability. Specifically, voltage-gated sodium channel subtype Na V 1.7 is required for sensing acute and inflammatory somatic pain in mice and humans but its significance in pain originating from the viscera is unknown. Using comparative behavioural models evoking somatic and visceral pain pathways, we identify the requirement for Na V 1.7 in regulating somatic (noxious heat pain threshold) but not in visceral pain signalling. These results enable us to better understand the mechanisms underlying the transduction of noxious stimuli from the viscera, suggest that the investigation of pain pathways should be undertaken in a modality-specific manner and help to direct drug discovery efforts towards novel visceral analgesics., Abstract: Voltage-gated sodium channel Na V 1.7 is required for acute and inflammatory pain in mice and humans but its significance for visceral pain is unknown. Here we examine the role of Na V 1.7 in visceral pain processing and the development of referred hyperalgesia using a conditional nociceptor-specific Na V 1.7 knockout mouse (Na V 1.7 Nav1.8 ) and selective small-molecule Na V 1.7 antagonist PF-5198007. Na V 1.7 Nav1.8 mice showed normal nociceptive behaviours in response to intracolonic application of either capsaicin or mustard oil, stimuli known to evoke sustained nociceptor activity and sensitization following tissue damage, respectively. Normal responses following induction of cystitis by cyclophosphamide were also observed in both Na V 1.7 Nav1.8 and littermate controls. Loss, or blockade, of Na V 1.7 did not affect afferent responses to noxious mechanical and chemical stimuli in nerve-gut preparations in mouse, or following antagonism of Na V 1.7 in resected human appendix stimulated by noxious distending pressures. However, expression analysis of voltage-gated sodium channel α subunits revealed Na V 1.7 mRNA transcripts in nearly all retrogradely labelled colonic neurons, suggesting redundancy in function. By contrast, using comparative somatic behavioural models we identify that genetic deletion of Na V 1.7 (in Na V 1.8-expressing neurons) regulates noxious heat pain threshold and that this can be recapitulated by the selective Na V 1.7 antagonist PF-5198007. Our data demonstrate that Na V 1.7 (in Na V 1.8-expressing neurons) contributes to defined pain pathways in a modality-dependent manner, modulating somatic noxious heat pain, but is not required for visceral pain processing, and advocate that pharmacological block of Na V 1.7 alone in the viscera may be insufficient in targeting chronic visceral pain., (© 2017 The Authors. The Journal of Physiology © 2017 The Physiological Society.)

We evaluated the effects of σ1-receptor inhibition on μ-opioid-induced mechanical antinociception and constipation. σ1-Knockout mice exhibited marked mechanical antinociception in response to several μ-opioid analgesics (fentanyl, oxycodone, morphine, buprenorphine, and tramadol) at systemic (subcutaneous) doses that were inactive in wild-type mice and even unmasked the antinociceptive effects of the peripheral μ-opioid agonist loperamide. Likewise, systemic (subcutaneous) or local (intraplantar) treatment of wild-type mice with the selective σ1 antagonists BD-1063 [1-[2-(3,4-dichlorophenyl)ethyl]-4-methylpiperazine dihydrochloride] or S1RA [4-[2-[[5-methyl-1-(2-naphthalenyl)1H-pyrazol-3-yl]oxy]ethyl] morpholine hydrochloride] potentiated μ-opioid antinociception; these effects were fully reversed by the σ1 agonist PRE-084 [2-(4-morpholinethyl)1-phenylcyclohexanecarboxylate) hydrochloride], showing the selectivity of the pharmacological approach. The μ-opioid antinociception potentiated by σ1 inhibition (by σ1-receptor knockout or σ1-pharmacological antagonism) was more sensitive to the peripherally restricted opioid antagonist naloxone methiodide than opioid antinociception under normal conditions, indicating a key role for peripheral opioid receptors in the enhanced antinociception. Direct interaction between the opioid drugs and σ1 receptor cannot account for our results, since the former lacked affinity for σ1 receptors (labeled with [(3)H](+)-pentazocine). A peripheral role for σ1 receptors was also supported by their higher density (Western blot results) in peripheral nervous tissue (dorsal root ganglia) than in several central areas involved in opioid antinociception (dorsal spinal cord, basolateral amygdala, periaqueductal gray, and rostroventral medulla). In contrast to its effects on nociception, σ1-receptor inhibition did not alter fentanyl- or loperamide-induced constipation, a peripherally mediated nonanalgesic opioid effect. Therefore, σ1-receptor inhibition may be used as a systemic or local adjuvant to enhance peripheral μ-opioid analgesia without affecting opioid-induced constipation.

We studied the modulation of morphine-induced mechanical antinociception and side effects by σ₁ receptor inhibition. Both wild-type (WT) and σ₁ receptor knockout (σ₁-KO) mice showed similar responses to paw pressure (100-600 g). The systemic (subcutaneous) or local (intraplantar) administration of σ₁ antagonists (BD-1063, BD-1047, NE-100 and S1RA) was devoid of antinociceptive effects in WT mice. However, σ₁-KO mice exhibited an enhanced mechanical antinociception in response to systemic morphine (1-16 mg/kg). Similarly, systemic treatment of WT mice with σ₁ antagonists markedly potentiated morphine-induced antinociception, and its effects were reversed by the selective σ₁ agonist PRE-084. Although the local administration of morphine (50-200 μg) was devoid of antinociceptive effects in WT mice, it induced dose-dependent antinociception in σ₁-KO mice. This effect was limited to the injected paw. Enhancement of peripheral morphine antinociception was replicated in WT mice locally co-administered with σ₁ antagonists and the opioid. None of the σ₁ antagonists tested enhanced morphine-antinociception in σ₁-KO mice, confirming a σ₁-mediated action. Morphine-induced side-effects (hyperlocomotion and inhibition of gastrointestinal transit) were unaltered in σ₁-KO mice. These results cannot be explained by a direct interaction of σ₁ ligands with μ-opioid receptors or adaptive changes of μ-receptors in σ₁-KO mice, given that [(3)H]DAMGO binding in forebrain, spinal cord, and hind-paw skin membranes was unaltered in mutant mice, and none of the σ₁ drugs tested bound to μ-opioid receptors. These results show that σ₁ receptor inhibition potentiates morphine-induced mechanical analgesia but not its acute side effects, and that this enhanced analgesia can be induced at peripheral level., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Background: Visceral pain is an important and prevalent clinical condition whose treatment is challenging. Sigma-1 (σ1) receptors modulate somatic pain, but their involvement in pure visceral pain is unexplored., Methods: The authors evaluated the role of σ1 receptors in intracolonic capsaicin-induced visceral pain (pain-related behaviors and referred mechanical hyperalgesia to the abdominal wall) using wild-type (WT) (n = 12 per group) and σ1 receptor knockout (σ1-KO) (n = 10 per group) mice, selective σ1 receptor antagonists (BD-1063, S1RA, and NE-100), and control drugs (morphine and ketoprofen)., Results: The intracolonic administration of capsaicin (0.01-1%) induced concentration-dependent visceral pain-related behaviors and referred hyperalgesia in both WT and σ1-KO mice. However, the maximum number of pain-related behaviors induced by 1% capsaicin in σ1-KO mice (mean ± SEM, 22 ± 2.9) was 48% of that observed in WT animals (46 ± 4.2). Subcutaneous administration of the σ1 receptor antagonists BD-1063 (16-64 mg/kg), S1RA (32-128 mg/kg), and NE-100 (8-64 mg/kg) dose-dependently reduced the number of behavioral responses (by 53, 62, and 58%, respectively) and reversed the referred hyperalgesia to mechanical control threshold (0.53 ± 0.05 g) in WT mice. In contrast, these drugs produced no change in σ1-KO mice. Thus, the effects of these drugs are specifically mediated by σ1 receptors. Morphine produced an inhibition of capsaicin-induced visceral pain in WT and σ1-KO mice, whereas ketoprofen had no effect in either mouse type., Conclusion: These results suggest that σ1 receptors play a role in the mechanisms underlying capsaicin-induced visceral pain and raise novel perspectives for their potential therapeutic value.

Tetrodotoxin (TTX) is a potent neurotoxin that blocks voltage-gated sodium channels (VGSCs). VGSCs play a critical role in neuronal function under both physiological and pathological conditions. TTX has been extensively used to functionally characterize VGSCs, which can be classified as TTX-sensitive or TTX-resistant channels according to their sensitivity to this toxin. Alterations in the expression and/or function of some specific TTX-sensitive VGSCs have been implicated in a number of chronic pain conditions. The administration of TTX at doses below those that interfere with the generation and conduction of action potentials in normal (non-injured) nerves has been used in humans and experimental animals under different pain conditions. These data indicate a role for TTX as a potential therapeutic agent for pain. This review focuses on the preclinical and clinical evidence supporting a potential analgesic role for TTX. In addition, the contribution of specific TTX-sensitive VGSCs to pain is reviewed.