Grip strength in mice with joint inflammation: A rheumatology function test sensitive to pain and analgesia

Grip strength deficit is a measure of pain-induced functional disability in rheumatic disease. We tested whether this parameter and tactile allodynia, the standard pain measure in preclinical studies, show parallels in their response to analgesics and basic mechanisms. Mice with periarticular injections of complete Freund's adjuvant (CFA) in the ankles showed periarticular immune infiltration and synovial membrane alterations, together with pronounced grip strength deficits and tactile allodynia measured with von Frey hairs. However, inflammation-induced tactile allodynia lasted longer than grip strength alterations, and therefore did not drive the functional deficits. Oral administration of the opioid drugs oxycodone (1–8 mg/kg) and tramadol (10–80 mg/kg) induced a better recovery of grip strength than acetaminophen (40–320 mg/kg) or the nonsteroidal antiinflammatory drugs ibuprofen (10–80 mg/kg) or celecoxib (40–160 mg/kg); these results are consistent with their analgesic efficacy in humans. Functional impairment was generally a more sensitive indicator of drug-induced analgesia than tactile allodynia, as drug doses that attenuated grip strength deficits showed little or no effect on von Frey thresholds. Finally, ruthenium red (a nonselective TRP antagonist) or the in vivo ablation of TRPV1-expressing neurons with resiniferatoxin abolished tactile allodynia without altering grip strength deficits, indicating that the neurobiology of tactile allodynia and grip strength deficits differ. In conclusion, grip strength deficits are due to a distinct type of pain that reflects an important aspect of the human pain experience, and therefore merits further exploration in preclinical studies to improve the translation of new analgesics from bench to bedside.This study was partially supported by the Spanish Ministry of Economy and Competitiveness (MINECO, grant SAF2013-47481P), the Junta de Andalucía (grant CTS 109), and funding from Esteve and the European Regional Development Fund (FEDER)

Formalin-induced pain is reduced in σ1 receptor knockout mice

2 pages, 1 figure.-- PMID: 15777781 [PubMed]The role of σ1 receptors in non-acute pain has not been explored. In this study we show that both phases of formalin-induced pain were reduced by approximately 55% in σ1 receptor knockout mice in comparison to wild-type animals. These results suggest that the tonic pain induced by formalin is altered in mice lacking σ1 receptors, and highlight the potential usefulness of further studies of the role of σ1 receptors in models of non-acute pain.The experiments performed in the laboratory headed by José M. Baeyens are supported in part by a grant from Junta de Andalucía (CTS 109).Peer reviewe

Formalin-induced pain is reduced in σ1 receptor knockout mice

2 pages, 1 figure.-- PMID: 15777781 [PubMed]The role of σ1 receptors in non-acute pain has not been explored. In this study we show that both phases of formalin-induced pain were reduced by approximately 55% in σ1 receptor knockout mice in comparison to wild-type animals. These results suggest that the tonic pain induced by formalin is altered in mice lacking σ1 receptors, and highlight the potential usefulness of further studies of the role of σ1 receptors in models of non-acute pain.The experiments performed in the laboratory headed by José M. Baeyens are supported in part by a grant from Junta de Andalucía (CTS 109).Peer reviewe

Sigma-1 antagonism inhibits binge ethanol drinking at adolescence

Ethanol use during adolescence is a significant health problem, yet the pharmacological treatments to reduce adolescent binge drinking are scarce. The present study assessed, in male and female adolescent Wistar rats, if the sigma-1 receptor (S1-R) antagonists S1RA or BD-1063 disrupted ethanol drinking. Methods: Three times a week, for two weeks, the rats received the S1-R antagonists. Thirty min later they were exposed, for 2 h, to a bottle of 8% or 10 % v/v ethanol. A 24 h, two-bottle, ethanol intake test was conducted after termination of these procedures. A subset of these rats was tested for recognition memory via the novel object recognition test. Results: The rats given 64 mg/kg S1RA drank, in each binge session, significantly less than vehicle counterparts. Male rats given 4 or 16 mg/kg S1RA drank significantly less than those given 0 mg/kg in session 3 or in session 1 and 2, respectively; whereas female rats given 4 or 16 mg/kg drank significantly less than females given 0 mg/kg in session 2–5 or in sessions 2–6, respectively. Administration of 32 mg/kg, but not of 2 or 8 mg/kg, BD-1063 suppressed, across sessions, ethanol drinking. S1-R antagonism reduced absolute ethanol drinking at the two-bottle choice post-test. Recognition memory was not affected by the ethanol exposure. Conclusions: The results indicate that S1-R antagonists may be promising targets to prevent increases in ethanol intake at adolescence. The persistent effect of S1-R antagonism in free-choice drinking suggests that modulation of the S1-R is altering plastic effects associated with ethanol exposure.Fil: Ruiz Leyva, Leandro. Universidad de Granada; España. Instituto de Investigación Biosanitaria (IBS); EspañaFil: Salguero, Juan Agustín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigación Médica Mercedes y Martín Ferreyra. Universidad Nacional de Córdoba. Instituto de Investigación Médica Mercedes y Martín Ferreyra; ArgentinaFil: Morón, Ignacio. Universidad de Granada; España. Instituto de Investigación Biosanitaria (IBS); EspañaFil: Portillo-Salido, Enrique. Parc Científic de Barcelona; EspañaFil: Cendán, Cruz Miguel. Instituto de Investigación Biosanitaria (IBS); España. Universidad de Granada; EspañaFil: Pautassi, Ricardo Marcos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigación Médica Mercedes y Martín Ferreyra. Universidad Nacional de Córdoba. Instituto de Investigación Médica Mercedes y Martín Ferreyra; Argentin

The selective sigma-1 receptor antagonist E-52862 attenuates neuropathic pain of different aetiology in rats

E-52862 is a selective σ(1)R antagonist currently undergoing phase II clinical trials for neuropathic pain and represents a potential first-in-class analgesic. Here, we investigated the effect of single and repeated administration of E-52862 on different pain-related behaviours in several neuropathic pain models in rats: mechanical allodynia in cephalic (trigeminal) neuropathic pain following chronic constriction injury of the infraorbital nerve (IoN), mechanical hyperalgesia in streptozotocin (STZ)-induced diabetic polyneuropathy, and cold allodynia in oxaliplatin (OX)-induced polyneuropathy. Mechanical hypersensitivity induced after IoN surgery or STZ administration was reduced by acute treatment with E-52862 and morphine, but not by pregabalin. In the OX model, single administration of E-52862 reversed the hypersensitivity to cold stimuli similarly to 100 mg/kg of gabapentin. Interestingly, repeated E-52862 administration twice daily over 7 days did not induce pharmacodynamic tolerance but an increased antinociceptive effect in all three models. Additionally, as shown in the STZ and OX models, repeated daily treatment with E-52862 attenuated baseline pain behaviours, which supports a sustained modifying effect on underlying pain-generating mechanisms. These preclinical findings support a role for σ(1)R in neuropathic pain and extend the potential for the use of selective σ(1)R antagonists (e.g., E-52862) to the chronic treatment of cephalic and extra-cephalic neuropathic pain

Resilience to Pain-Related Depression in σ₁ Receptor Knockout Mice Is Associated with the Reversal of Pain-Induced Brain Changes in Affect-Related Genes

Mice lacking the σ1 receptor chaperone (σ1R–/–) are resilient to depressive-like behaviors secondary to neuropathic pain. Examining the resilience’s brain mechanisms could help develop conceptually novel therapeutic strategies. We explored the diminished motivation for a natural reinforcer (white chocolate) in the partial sciatic nerve ligation (PSNL) model in wild-type (WT) and σ1R–/– mice. In the same mice, we performed a comprehensive reverse transcription quantitative PCR (qPCR) analysis across ten brain regions of seven genes implicated in pain regulation and associated affective disorders, such as anxiety and depression. PSNL induced anhedonic-like behavior in WT but not in σ1R–/– mice. In WT mice, PSNL up-regulated dopamine transporter (DAT) and its rate-limiting enzyme, tyrosine hydroxylase (Th), in the ventral tegmental area (VTA) and periaqueductal gray (PAG) as well as the serotonin transporters (SERT) and its rate-limiting enzyme tryptophan hydroxylase 2 (Tph2) in VTA. In addition, μ-opioid receptor (MOR) and σ1R were up-regulated in PAG, and MOR was also elevated in the somatosensory cortex (SS) but down-regulated in the striatum (STR). Finally, increased BDNF was found in the medial prefrontal cortex (mPFC) and hypothalamus (HPT). Sham surgery also produced PSNL-like expression changes in VTA, HPT, and STR. Genetic deletion of the σ1R in mice submitted to PSNL or sham surgery prevented changes in the expression of most of these genes. σ1R is critically involved in the supraspinal gene expression changes produced by PSNL and sham surgery. The changes in gene expression observed in WT mice may be related to pain-related depression, and the absence of these changes observed in σ1R–/– mice may be related to resilience

Predicting the Antinociceptive Efficacy of σ₁ Receptor Ligands by a Novel Receptor Fluorescence Resonance Energy Transfer (FRET) Based Biosensor

We have developed a novel methodology for monitoring the σ₁ receptor activation switch in living cells. Our assay uncovered the intrinsic nature of σ₁ receptor ligands by recording the ligand-mediated conformational changes of this chaperone protein. The change triggered by each ligand correlated well with its ability to attenuate formalin induced nociception in an animal model of pain. This tool may assist in predicting the antinociceptive efficacy of σ₁ receptor ligands