Acute Nociception Research Articles

Is the orofacial antinociceptive effect of lectins intrinsically related to their specificity to monosaccharides?

Lectins are proteins of non-immunological origin that may play several biological applications, of which we can highlight the anti-inflammatory and antinociceptive activities. In this work, we evaluated the possible effect of orofacial antinociceptive activity of three plant lectins, Dioclea violacea (DVL - Man/Glc-binding), Vatairea macrocarpa (VML - Gal-binding) and PPL (Parkia platycephala - Man/Glc-binding) in adult zebrafish. Acute nociception was induced by menthol (1.2 μM), or capsaicin (4.93 μM) applied into in the upper lip (5.0 μL) of adult wild zebrafish. Zebrafish were pretreated by intraperitoneal injection (20 μL) with vehicle (Control) or lectins (0.025; 0.05 or 0.1 mg/mL) 30 min before induction. The effect of lectins on zebrafish locomotor behavior was evaluated with the open field test. Naive groups (n = 8) were included in all tests. Our results indicate that only PPL presented antinociceptive induced by capsaicin, suggesting the potential clinical application of PPL as inhibitor of orofacial nociception and that this effect may be due to the modulation of TRPV1 channel. In conclusion, lectins that exhibit affinity to the same or different carbohydrates do not necessarily have an antinociceptive effect on the orofacial nociception model, indicating that the glycan carbohydrate binding pattern may be related to the effect on nociception inhibition.

Macrophages and Schwann cell TRPA1 mediate chronic allodynia in a mouse model of complex regional pain syndrome type I

Complex regional pain syndrome type I (CRPS-I) is characterized by intractable chronic pain. Poor understanding of the underlying mechanisms of CRPS-I accounts for the current unsatisfactory treatment. Antioxidants and antagonists of the oxidative stress-sensitive channel, the transient receptor potential ankyrin 1 (TRPA1), have been found to attenuate acute nociception and delayed allodynia in models of CRPS-I, evoked by ischemia and reperfusion (I/R) of rodent hind limb (chronic post ischemia pain, CPIP). However, it is unknown how I/R may lead to chronic pain mediated by TRPA1. Here, we report that the prolonged (day 1–15) mechanical and cold allodynia in the hind limb of CPIP mice was attenuated permanently in Trpa1−/− mice and transiently after administration of TRPA1 antagonists (A-967079 and HC-030031) or an antioxidant (α-lipoic acid). Indomethacin treatment was, however, ineffective. We also found that I/R increased macrophage (F4/80+ cell) number and oxidative stress markers, including 4-hydroxynonenal (4-HNE), in the injured tibial nerve. Macrophage-deleted MaFIA (Macrophage Fas-Induced Apoptosis) mice did not show I/R-evoked endoneurial cell infiltration, increased 4-HNE and mechanical and cold allodynia. Furthermore, Trpa1−/− mice did not show any increase in macrophage number and 4-HNE in the injured nerve trunk. Notably, in mice with selective deletion of Schwann cell TRPA1 (Plp1-CreERT;Trpa1fl/fl mice), increases in macrophage infiltration, 4-HNE and mechanical and cold allodynia were attenuated. In the present mouse model of CRPS-I, we propose that the initial oxidative stress burst that follows reperfusion activates a feed forward mechanism that entails resident macrophages and Schwann cell TRPA1 of the injured tibial nerve to sustain chronic neuroinflammation and allodynia. Repeated treatment one hour before and for 3 days after I/R with a TRPA1 antagonist permanently protected CPIP mice against neuroinflammation and allodynia, indicating possible novel therapeutic strategies for CRPS-I.

Antinociceptive Effect of the Citrus Flavonoid Eriocitrinon Postoperative Pain Conditions.

BackgroundPostoperative pain remains a major clinical problem as there are limited analgesic strategies that have been proven to be effective in preventing and relieving this type of pain. Natural products, including flavonoids, have distinct pharmacological properties and play an important role in the discovery of analgesic drugs.Materials and MethodsIn this study, the flavonoid eriocitrin (eriodictyol 7-O-rutinoside), which is the main flavonoid in lemon fruit (Citrus limon), was mechanistically investigated for its prospective antinociceptive effect in a mouse model of postoperative pain. The antinociceptive property was evaluated by utilizing both tonic (acetic acid-induced writhing behavior) and phasic (hot-plate) nociception modalities. The hindpaw incisional surgery was performed and hyperalgesia was assessed using von Frey filaments.ResultsThe tested doses of eriocitrin significantly attenuated (P<0.01, P<0.001) the chemically-induced tonic visceral nociception (5, 10, 15, and 30 mg/kg) and acute phasic thermal nociception (10, 15, and 30 mg/kg). A significant dose-dependent reduction in the incisional nociceptive hyperalgesia was exhibited by eriocitrin, with a marked antinociception observed at doses of 15 mg/kg (P<0.05 during 30–60 minutes) and 30 mg/kg (P<0.05, P<0.01 during 30–120 minutes).ConclusionThe antinociceptive effect of eriocitrin (30 mg/kg) was strongly blocked by the antagonists of the opioid receptor, naltrexone, and GABAA receptor, bicuculline, thereby suggesting the involvement of opioidergic and GABAergic mechanisms in the nociception, reducing proclivity of eriocitrin during transmission of incisional nociception. These results concluded that eriocitrin has a potent antinociceptive effect in postoperative pain conditions, probably mediated through opioid and GABAA receptors.

Analysis of Acute and Chronic Inflammatory Pain‐Depressed Wheel Running in the Rat

Traditional pain‐evoked tests (e.g., hot plate and tail withdrawal tests) do not mimic the disruptive effects of pain on daily life, a primary outcome measure used for pain in humans. This mismatch may contribute to the lack of translation of analgesics from the laboratory to the clinic. To solve this problem, we have previously demonstrated that pain‐depressed home cage wheel running is an objective and clinically relevant measure of the functional consequences of chronic inflammatory pain in the rat (Kandasamy et al., 2016, J. Neurosci. Methods). In this study, we extend this approach by assessing the extent to which acute formalin‐induced inflammatory pain depresses wheel running in the rat. The formalin test is a widely used test of acute nociception where animals are monitored for pain‐like behaviors (i.e., guarding or licking the paw) approximately one hour following formalin injection into the hindpaw. Few studies have examined the functional consequences of acute pain; thus, the aim of this study was to examine the effects of formalin‐induced inflammatory pain on function as measured by home cage wheel running. Rats were housed in individual cages containing a computerized running wheel where they remained for the rest of the experiment. Rats were allowed free access to the wheel 23 hours/day for 7 days prior to the induction of hindpaw inflammation to acquire stable running levels. Wheel running during the 23 hours immediately prior to induction of inflammation was used as the baseline. Inflammation was induced with an intraplantar injection of Complete Freund’s Adjuvant (CFA; 0.1 mL) or formalin (5%, 0.05 mL) into the right hindpaw. As expected, CFA almost completely inhibited wheel running in rats in the 23 hours following administration. Mechanical withdrawal thresholds, as measured by the von Frey test, remained low across the entire testing period. In contrast, the functional effects of a single formalin injection were apparent as indicated by decreased wheel running after the first hour following injection. Wheel running was depressed in the absence of mechanical allodynia, suggesting that inflammatory pain‐induced mechanical allodynia and decreased function are independent of each other. Importantly, these results indicate that continuous monitoring of the functional consequences of pain using home cage wheel running reveal insights into changes in behavior resulting from both acute and chronic pain.Support or Funding InformationSupport for this project was provided by a 2019–20 Faculty Support Grant from the California State University Division of Academic Affairs (RK) and funds from the College of Science at California State University, East Bay (RK).

Antinociceptive effects of potent, selective and brain penetrant muscarinic M4 positive allosteric modulators in rodent pain models

Analgesic properties of orthosteric agonists of the muscarinic M4 receptor subtype have been documented in literature reports, with evidence from pharmacological and in vivo receptor knock out (KO) studies. Constitutive M4 receptor KO mice demonstrated an increased response in the formalin pain model, supporting this hypothesis. Two novel positive allosteric modulators (PAM) of the M4 receptor, Compounds 1 and 2, were characterized in rodent models of acute nociception. Results indicated decreased time spent on nociceptive behaviors in the mouse formalin model, and efficacy in the mouse tail flick assay. The analgesic-like effects of Compounds 1 and 2 were shown to be on target, as the compounds lacked any activity in constitutive M4 KO mice, while retaining activity in wild type control littermates. The analgesic-like effects of Compounds 1 and 2 were significantly diminished in KO mice that have selective deletion of the M4 receptor in neurons that co-express the dopaminergic D1 receptor subtype, suggesting a centrally-mediated effect on nociception. The opioid antagonist naloxone did not diminish the effect of Compound 1, indicating the effects of Compound 1 are not secondarily linked to opioid pathways. Compound 1 was evaluated in the rat, where it demonstrated analgesic-like effects in tail flick and a subpopulation of spinal nociceptive sensitive neurons, suggesting some involvement of spinal mechanisms of nociceptive modulation. These studies indicate that M4 PAMs may be a tractable target for pain management assuming an appropriate safety profile, and it appears likely that both spinal and supraspinal pathways may mediate the antinociceptive-like effects.

Evaluation of two medicinal plants used for arthritis in northern Nigeria with focus on Terminalia avicennioides Guill. & Perr. and its mechanism of action

Chronic inflammation underlying non-communicable diseases continues to impose serious economic and public health burden globally. Exploring medicinal plants presents a valid approach to sourcing new anti-inflammatory therapies. This study was performed to evaluate Cassia sieberiana root and Terminalia avicennioides stem bark extracts in pain and inflammation, in order to identify an active extract and its mechanism of action. Aqueous and 70% v/v ethanol extracts of C. sieberiana root (CSA and CSE) and T. avicennioides stem bark extracts (TAA and TAE) were prepared. Acute toxicity, phenolic content and antioxidant activity of the extracts were determined. Graded doses of each extract were tested against acetic acid-induced nociception and acute formalin-induced paw inflammation. T. avicennioides stem bark ethanol extract was further tested in chronic paw inflammation and its effects on edematous response and nitric oxide in inflammed tissue were measured. All the extracts were acutely safe following oral administration of doses up to 2000 mg/kg. Comparatively, T. avicennioides aqueous extract (TAA) showed the highest phenolic content and displayed the highest antioxidant potency among the extracts. T. avicennioides and C. sieberiana ethanol extracts produced comparable inhibition of acetic acid-induced pain. Only T. avicennioides ethanol extract significantly (p < 0.001) ameliorated acute formalin-induced nociception in phase 1 of the test compared with other extracts. It was also the most effective in inhibiting edema formation during the inflammatory phase. In chronic paw inflammation, 300 and 900 mg/kg TAE significantly (p < 0.01) lowered post-treatment edema and reduced the relative paw index of the inflammed paw. At these doses, nitric oxide levels were also reduced compared to the control group. T. avicennioides and C. sieberiana extracts possess beneficial effects against pain, but T. avicennioides has a comparatively higher acute anti-inflammatory effect, concentrated in its ethanol extract. Inhibition of nitric oxide and prostaglandin activity may contribute to the anti-inflammatory effect of T. avicennioides ethanol extract in chronic inflammation.

Lemairamin, isolated from the Zanthoxylum plants, alleviates pain hypersensitivity via spinal α7 nicotinic acetylcholine receptors

Lemairamin (also known as wgx-50), is isolated from the pericarps of the Zanthoxylum plants. As an agonist of α7 nicotinic acetylcholine receptors (α7nAChRs), it can reduce neuroinflammation in Alzheimer’s disease. This study evaluated its antinociceptive effects in pain hypersensitivity and explored the underlying mechanisms. The data showed that subcutaneous lemairamin injection dose-dependently inhibited formalin-induced tonic pain but not acute nociception in mice and rats, while intrathecal lemairamin injection also dose-dependently produced mechanical antiallodynia in the ipsilateral hindpaws of neuropathic and bone cancer pain rats without affecting mechanical thresholds in the contralateral hindpaws. Multiple bi-daily lemairamin injections for 7 days did not induce mechanical antiallodynic tolerance in neuropathic rats. Moreover, the antinociceptive effects of lemairamin in formalin-induced tonic pain and mechanical antiallodynia in neuropathic pain were suppressed by the α7nAChR antagonist methyllycaconitine. In an α7nAChR antagonist-reversible manner, intrathecal lemairamin also stimulated spinal expression of IL-10 and β-endorphin, while lemairamin treatment induced IL-10 and β-endorphin expression in primary spinal microglial cells. In addition, intrathecal injection of a microglial activation inhibitor minocycline, anti-IL-10 antibody, anti-β-endorphin antiserum or μ-opioid receptor-preferred antagonist naloxone was all able to block lemairamin-induced mechanical antiallodynia in neuropathic pain. These data demonstrated that lemairamin could produce antinociception in pain hypersensitivity through the spinal IL-10/β-endorphin pathway following α7nAChR activation.

Functional Selectivity and Antinociceptive Effects of a Novel KOPr Agonist.

Kappa opioid receptor (KOPr) agonists represent alternative analgesics for their low abuse potential, although relevant adverse effects have limited their clinical use. Functionally selective KOPr agonists may activate, in a pathway-specific manner, G protein-mediated signaling, that produces antinociception, over β-arrestin 2-dependent induction of p38MAPK, which preferentially contributes to adverse effects. Thus, functionally selective KOPr agonists biased toward G protein-coupled intracellular signaling over β-arrestin-2-mediated pathways may be considered candidate therapeutics possibly devoid of many of the typical adverse effects elicited by classic KOPr agonists. Nonetheless, the potential utility of functionally selective agonists at opioid receptors is still highly debated; therefore, further studies are necessary to fully understand whether it will be possible to develop more effective and safer analgesics by exploiting functional selectivity at KOPr. In the present study we investigated in vitro functional selectivity and in vivo antinociceptive effects of LOR17, a novel KOPr selective peptidic agonist that we synthesized. LOR17-mediated effects on adenylyl cyclase inhibition, ERK1/2, p38MAPK phosphorylation, and astrocyte cell proliferation were studied in HEK-293 cells expressing hKOPr, U87-MG glioblastoma cells, and primary human astrocytes; biased agonism was investigated via cAMP ELISA and β-arrestin 2 recruitment assays. Antinociception and antihypersensitivity were assessed in mice via warm-water tail-withdrawal test, intraperitoneal acid-induced writhing, and a model of oxaliplatin-induced neuropathic cold hypersensitivity. Effects of LOR17 on locomotor activity, exploratory activity, and forced-swim behavior were also assayed. We found that LOR17 is a selective, G protein biased KOPr agonist that inhibits adenylyl cyclase and activates early-phase ERK1/2 phosphorylation. Conversely to classic KOPr agonists as U50,488, LOR17 neither induces p38MAPK phosphorylation nor increases KOPr-dependent, p38MAPK-mediated cell proliferation in astrocytes. Moreover, LOR17 counteracts, in a concentration-dependent manner, U50,488-induced p38MAPK phosphorylation and astrocyte cell proliferation. Both U50,488 and LOR17 display potent antinociception in models of acute nociception, whereas LOR17 counteracts oxaliplatin-induced thermal hypersensitivity better than U50,488, and it is effective after single or repeated s.c. administration. LOR17 administered at a dose that fully alleviated oxaliplatin-induced thermal hypersensitivity did not alter motor coordination, locomotor and exploratory activities nor induced pro-depressant-like behavior. LOR17, therefore, may emerge as a novel KOPr agonist displaying functional selectivity toward G protein signaling and eliciting antinociceptive/antihypersensitivity effects in different animal models, including oxaliplatin-induced neuropathy.

Adjunctive effect of the serotonin 5-HT2C receptor agonist lorcaserin on opioid-induced antinociception in mice

Opioid-sparing adjuncts are treatments that aim to reduce the overall dose of opioids needed to achieve analgesia, hence decreasing the burden of side effects through alternative mechanisms of action. Lorcaserin is a serotonin 5-HT2C receptor (5-HT2CR) agonist that has recently been reported to reduce abuse-related effects of the opioid analgesic oxycodone. The goal of our studies was to evaluate the effects of adjunctive lorcaserin on opioid-induced analgesic-like behavior using the tail-flick reflex (TFR) test as a mouse model of acute thermal nociception. We show that whereas subcutaneous (s.c.) administration of lorcaserin alone was inactive on the TFR test, adjunctive lorcaserin (s.c.) significantly increased the potency of oxycodone as an antinociceptive drug. This effect was prevented by the 5-HT2CR antagonist SB242084. A similar lorcaserin (s.c.)-induced adjunctive phenotype was observed upon administration of the opioid analgesics morphine and fentanyl. Remarkably, we also show that, opposite to the effects observed via s.c. administration, intrathecal (i.t.) administration of lorcaserin alone induced antinociceptive TFR behavior, an effect that was not prevented by the opioid receptor antagonist naloxone. This route of administration (i.t.) also led to a significant augmentation of oxycodone-induced antinociception. Lorcaserin (s.c.) did not alter the brain or blood concentrations of oxycodone, which suggests that its adjunctive effects on opioid-induced antinociception do not depend upon changes in opioid metabolism. Together, these data indicate that lorcaserin-mediated activation of the 5-HT2CR may represent a new pharmacological approach to augment opioid-induced antinociception.This article is part of the special issue entitled ‘Serotonin Research: Crossing Scales and Boundaries’.

Behavioral pharmacology of the mixed-action delta-selective opioid receptor agonist BBI-11008: studies on acute, inflammatory and neuropathic pain, respiration, and drug self-administration.

The present study characterized the behavioral pharmacology of a novel, mixed-action delta-selective (78:1) opioid receptor agonist, BBI-11008. This glycopeptide drug candidate was tested in assays assessing antinociception (acute, inflammatory, and neuropathic pain-like conditions) and side-effect endpoints (respiratory depression and drug self-administration). BBI-11008 had a 78-fold greater affinity for the delta opioid receptor than the mu receptor, and there was no binding to the kappa opioid receptor. BBI-11008 (3.2-100; 10-32mgkg-1, i.v.) and morphine (1-10; 1-3.2mgkg-1, i.v.) produced antinociceptive and anti-allodynic effects in assays of acute thermal nociception and complete Freund's adjuvant (CFA)-induced inflammatory pain, with BBI-11008 being less potent than morphine in both assays. BBI-11008 (1-18mgkg-1, i.v.) had similar efficacy to gabapentin (10-56mgkg-1, i.v.) in a spinal nerve ligation (SNL) model of neuropathic pain. In the respiration assay, with increasing %CO2 exposure, BBI-11008 produced an initial increase (32mgkg-1, s.c.) and then decrease (56mgkg-1, s.c.) in minute volume (MV) whereas morphine (3.2-32mgkg-1, s.c.) produced dose-dependent decreases in MV. In the drug self-administration procedure, BBI-11008 did not maintain self-administration at any dose tested. These results suggest that the glycopeptide drug candidate possesses broad-spectrum antinociceptive and anti-allodynic activity across a range of pain-like conditions. Relative to morphine or fentanyl, the profile for BBI-11008 in the respiration and drug self-administration assays suggests that BBI-11008 may have less pronounced deleterious side effects. Continued assessment of this compound is warranted.

Presynaptic glutamatergic transmission and feedback system of oxytocinergic neurons in the hypothalamus of a rat model of adjuvant arthritis.

The neurohypophysial hormone oxytocin (OXT) is synthesized in the hypothalamic paraventricular and supraoptic nuclei. Recently, some studies have considered OXT to be important in sensory modulation and that the OXT protein is upregulated by acute and chronic nociception. However, the mechanism by which OXT is upregulated in neurons is unknown. In this study, we examined the resting membrane potentials and excitatory postsynaptic currents in OXT-ergic neurons in the paraventricular nucleus in adjuvant arthritis rat model, a model of chronic inflammation, using whole-cell patch-clamping. Transgenic rats expressing OXT and monomeric red fluorescent protein 1 (mRFP1) fusion protein to visualize the OXT-ergic neurons were used, and the OXT-mRFP1 transgenic rat model of adjuvant arthritis was developed by injection of heat-killed Mycobacterium butyricum. Furthermore, the feedback system of synthesized OXT was also examined using the OXT receptor antagonist L-368,899. We found that the resting membrane potentials and frequency of miniature excitatory postsynaptic currents and spontaneous excitatory postsynaptic currents in OXT-monomeric red fluorescent protein 1 neurons in the paraventricular nucleus were significantly increased in adjuvant arthritis rats. Furthermore, L-368,899 dose-dependently increased the frequency of miniature excitatory postsynaptic currents and spontaneous excitatory postsynaptic currents in OXT-ergic neurons. Following bath application of the GABAA receptor antagonist picrotoxin and the cannabinoid receptor 1 antagonist AM 251, L-368,899 still increased the frequency of miniature excitatory postsynaptic currents. However, following bath application of the nitric oxide synthase inhibitor Nω-Nitro-L-arginine methyl ester hydrochloride, L-368,899 did not alter the miniature excitatory postsynaptic current frequency. Thus, it is suggested that OXT-ergic neuron activity is upregulated via an increase in glutamate release, and that the upregulated OXT neurons have a feedback system with released endogenous OXT. It is possible that nitric oxide, but not GABA, may contribute to the feedback system of OXT neurons in chronic inflammation.

NADPH oxidase1 inhibition leads to regression of central sensitization during formalin induced acute nociception via attenuation of ERK1/2-NFκB signaling and glial activation

Role of NADPH oxidase1 in the development of inflammatory pain has been demonstrated by gene knockout studies. Nevertheless, pharmacological inhibition of NOX1 is a requisite approach for therapeutic utility. Recently, we have reported the anti-nociceptive effect of newly identified NOX1 specific inhibitor ML171 (2-acetylphenothiazine). Inhibition of NOX1 resulted in attenuation of nociceptive sensitization during acute inflammatory pain via inhibition of ROS generation and its downstream ERK1/2 activation. However, glial activation accompanying inflammation is closely related to the initiation and maintenance of pain. Peripheral nociceptive inputs activate the primary afferents via release of various chemical mediators which are potentially capable of mediating signals from neuron to glia in DRG and subsequently in spinal cord dorsal horn. The subsequent interactions between neuron and glia contribute to pain hypersensitivity. Thus, the present study was focused to investigate the effect of ML171 on ERK1/2 signaling, glial activation, and crosstalk between neuron and glia in a mouse model of formalin induced acute nociception. Thus, the present study was focused to investigate the effect of ML171 on ERK1/2 signaling, glial activation, and crosstalk between neuron and glia in DRG and dorsal horn of the spinal cord of lumbar region (L3-L5) in a mouse model of formalin induced acute nociception.Intraperitoneal administration of ML171 decreased nociceptive behavioral responses, i.e. the flinch and lick counts, in formalin induced nociceptive mice. Immunofluorescence and Western blot analysis demonstrated decreased levels of nociceptive mediators like p-ERK1/2, p-NFκB p65, Iba1 and GFAP in DRG as well as in spinal cord dorsal horn; supporting anti-nociceptive potential of ML171. Further, co-localization studies showed the neuron-glia crosstalk in tissue dependent manner. ERK1/2 was found to be activated in glia and NFκB in neurons in DRG; whereas in case of spinal cord ERK1/2 was activated in neurons and NFκB in astrocytes. Decrease in nociceptive behavioral response and activation of nociceptive mediators after intraperitoneal administration of ML171 strongly advocate anti-nociceptive potential of ML171.This is the first report demonstrating modulation of ERK1/2-NFκB signaling pathway, glial activation and regulation of neuron-glia crosstalk by NADPH oxidase1 inhibition towards its anti-nociceptive action.

Pain condition and sex differences in the descending noradrenergic system following lateral hypothalamic stimulation

The lateral hypothalamus (LH) is known to modulate nociception via the descending noradrenergic system in acute nociception, but less is known about its role in neuropathic pain states. In naïve females, LH stimulation produces opposing effects of α-adrenoceptors, with α2-adrenoceptors mediating antinociception, while pronociceptive α1-adrenoceptors attenuate the effect. Whether this opposing response is seen in neuropathic conditions or in naïve males is unknown. We used a mixed factorial design to compare male and female rats with chronic constriction injury (CCI) to naïve rats, measured by Total Paw Withdrawal (TPW) responses to a thermal stimulus. Rats received one of three doses of carbachol to stimulate the LH followed by intrathecal injection of either an α1- or an α2-adrenoceptor antagonist (WB4101 or yohimbine, resp.) or saline for control. Overall, naïve rats showed a more pronounced opposing alpha-adrenergic response than CCI rats (p<0.04). Naïve male and female rats demonstrated antinociception following α1-adrenoceptor blockade and hyperalgesia following α2-adrenoceptor blockade. Male CCI rats also showed dose dependent effects from either WB4101 or yohimbine (p<0.05), while female CCI rats had significant antinociception from WB4101 (p<0.05), but no effect from yohimbine. These results support the idea that peripheral nerve damage differentially alters the descending noradrenergic modulatory system in male and female rats, and notably, that female CCI rats do not show antinociception from descending noradrenergic input. These findings are suggestive that clinical therapies that recruit the descending noradrenergic system may require a different approach based on patient gender.

Antinociceptive activity of the Psidium brownianum Mart ex DC. leaf essential oil in mice

Chronic pain management has several adverse effects and research looking for new and effective pain management drugs posing lower undesirable effects is necessary. Given the above, the pharmacological investigation of medicinal plants significantly contributes to the dissemination of plant-derived therapeutics. The aim of this study was to evaluate the antinociceptive activity of the Psidium brownianum Mart ex DC. leaf essential oil (PBEO) and the participation of the opioid pathway in this effect in mice. Swiss Mus musculus male mice were tested using acute nociception models (acetic acid induced abdominal contortions, formalin, capsaicin and hot plate tests). The possible myorelaxant action of the PBEO was tested using the rotarod test. The essential oil reduced animal nociception in chemical and heat models, with this action being devoid of a myorelaxant effect. Naloxone (2 mg/kg, intraperitoneally – i.p.) partially antagonized the PBEO activity, possibly acting via opioid receptors. The results obtained provide evidence that the traditional Psidium brownianum use may be effective for pain treatment.

P.548 New approaches for binge- eating disorder psychopharmacological treatment. lisdexamfetamine versus fluoxetine

Although it is well established that bulbo-spinal serotonergic projections contribute to pain control mechanisms, whether they exert anti- or pro-nociceptive modulations is still a matter of debate. In order to reappraise the role of 5-HT in descending controls, we used RNA interference to selectively inhibit 5-HT synthesis in B3 neurons and assess resulting changes in nociception.Rats were injected into the bulbar B3 group with a recombinant lentiviral vector, LV-shTPH2, encoding RNA interfering with tryptophan hydroxylase 2 expression. Together with the long term disappearance of this enzyme in the whole rostro-caudal extent of B3 group, 5-HT was markedly depleted selectively in the dorsal horn at all levels of the spinal cord. In contrast, immunolabeling of the 5-HT transporter was unaffected by LV-shTPH2 injection, indicating the preservation of serotonergic fibers integrity.Whereas mechanical and thermal nociceptive thresholds were unchanged by 5-HT depletion, marked reductions in intraplantar formalin (but not carrageenin)-evoked nocifensive responses, and, in contrast, significant increases in mechanical and thermal hyperalgesia evoked by sciatic nerve ligation were noted in LV-shTPH2-injected rats versus controls. Parallel changes in c-Fos immunolabeling within the dorsal horn confirmed that bulbo-spinal serotonergic projections modulate pain signaling under these various conditions.These results suggest that serotonergic neurons of the B3 group are only moderately concerned, if any, by acute nociception but exert modulatory influences under pain sensitizing conditions. The opposite changes in formalin injected- versus sciatic nerve ligated rats might be related to the implication of different receptors in 5-HT-mediated modulation of inflammatory versus neuropathic pain.

Involvement of the PKA pathway and inhibition of voltage gated Ca2+ channels in antihyperalgesic activity of Lippia grata/β-cyclodextrin

Neuropathic pain (NP) is a difficult condition to treat because of the modest efficacy of available drugs. New treatments are required. In the study we aimed to investigate the effects of the essential oil from Lippia grata alone or complexed in β-cyclodextrin (LG or LG-βCD) on persistent inflammatory and neuropathic pain in a mouse model. We also investigated Ca2+ currents in rat dorsal root ganglion (DRG) neurons. Male Swiss mice were treated with LG or LG/β-CD (24 mg/kg, i.g.) and their effect was evaluated using an acute inflammatory pleurisy model and nociception triggered by intraplantar injection of an agonist of the TRPs channels. We also tested their effect in chronic pain models: injection of Freund's Complete Adjuvant and partial sciatic nerve ligation (PSNL). In the pleurisy model, LG reduced the number of leukocytes and the levels of TNF-α and IL-1β. It also inhibited cinnamaldehyde and menthol-induced nociceptive behavior. The pain threshold in mechanical and thermal hyperalgesia was increased and paw edema was decreased in models of inflammatory and neuropathic pain. PSNL increased inflammatory protein contents and LG and LG-βCD restored the protein contents of TNF-α, NF-κB, and PKA, but not IL-1β and IL-10. LG inhibited voltage gated Ca2+ channels from DRG neurons. Our results suggested that LG or LG-βCD produce anti-hyperalgesic effect in chronic pain models through reductions in TNF-α levels and PKA, and inhibited voltage-gated calcium channels and may be innovative therapeutic agents for the management of NP.

Graviola Fruit Bar Added Acerola By-Product Extract Protects Against Inflammation and Nociception in Adult Zebrafish (Danio rerio).

Studies involving foods associated with pain reversal and anti-inflammatory effects using zebrafish are rarely reported in the literature. This study aimed to evaluate the effect of graviola (Annona muricata L.) fruit bar (GFB) and GFB added with acerola (Malpighia glabra L) seed extract (ASE) on acute nociception and abdominal inflammation in adult zebrafish (Danio rerio). Acute nociception was induced by formalin, capsaicin, cinnamaldehyde, acidic saline, glutamate (cutaneous models), and hypertonic saline (corneal model), and inflammation was induced by carrageenan. Both GFB and ASE exhibited antinociceptive effect modulated by the nitrergic system, guanylate cyclase, and transient receptor potential ankyrin 1 and acid-sensing ion channels. The antinociceptive effect of GFB also appears to be modulated by the opioid system and glutamatergic receptors (N-methyl-D-aspartate receptor). Only ASE presented corneal antinociceptive effect. Both samples showed anti-inflammatory effect, being more significant the effect of GFB. The addition of acerola by-product extract in GFB results in a product with greater biological potential.

The Presence of High Levels of Circulating Trimethylamine N-Oxide Exacerbates Central and Peripheral Inflammation and Inflammatory Hyperalgesia in Rats Following Carrageenan Injection.

Gut microbiota-derived metabolite trimethylamine N-oxide (TMAO) has recently been shown to promote inflammation in peripheral tissues and the central nervous system (CNS), contributing to the pathogenesis of various human diseases. Here, we examined whether the presence of high levels of circulating TMAO would influence central and peripheral inflammation and inflammatory hyperalgesia in a carrageenan (CG)-induced rat model of inflammation. Rats were treated with vehicle or TMAO in drinking water. After 2weeks of treatment, rats received intraplantar injection of saline or CG into the hind paw. Acute nociception was unaltered in TMAO-treated rats that had elevated plasma TMAO. Following CG injection, TMAO-treated rats were significantly more sensitive to thermal and mechanical stimulation of the inflamed paw and displayed greater paw edema. Molecular studies revealed that CG injection induced increases in recruitment of neutrophils/macrophages in the paw and activation of microglia in the spinal cord, along with increased activation of nuclear factor (NF)-kB and production of proinflammatory mediators in both vehicle-treated rats and TMAO-treated rats. However, the increases in the above parameters were more pronounced in TMAO-treated rats. Moreover, TMAO treatment decreased protein levels of anti-inflammatory mediator regulator of G protein signaling (RGS)-10 in both saline-injected rats and CG-injected rats. These findings suggest that the presence of high levels of circulating TMAO downregulates anti-inflammatory mediator RGS10 in both peripheral tissues and the CNS, which may increase the susceptibility to inflammatory challenge-induced NF-kB activity, leading to greater increase in production of inflammatory mediators and consequent exacerbation of peripheral inflammation and inflammatory hyperalgesia.

Nuclear Factor-kappaB Gates Nav1.7 Channels in DRG Neurons via Protein-Protein Interaction.

SummaryIt is well known that nuclear factor-kappaB (NF-κB) regulates neuronal structures and functions by nuclear transcription. Here, we showed that phospho-p65 (p-p65), an active form of NF-κB subunit, reversibly interacted with Nav1.7 channels in the membrane of dorsal root ganglion (DRG) neurons of rats. The interaction increased Nav1.7 currents by slowing inactivation of Nav1.7 channels and facilitating their recovery from inactivation, which may increase the resting state of the channels ready for activation. In cultured DRG neurons TNF-α upregulated the membrane p-p65 and enhanced Nav1.7 currents within 5 min but did not affect nuclear NF-κB within 40 min. This non-transcriptional effect on Nav1.7 may underlie a rapid regulation of the sensibility of the somatosensory system. Both NF-κB and Nav1.7 channels are critically implicated in many physiological functions and diseases. Our finding may shed new light on the investigation into the underlying mechanisms.

Improved efficacy of naproxen-loaded NLC for temporomandibular joint administration

Inflammatory conditions of the temporomandibular joint (TMJ) and peripheral tissues affect many people around the world and are commonly treated with non-steroidal anti-inflammatory drugs (NSAIDs). However, in order to get desirable results, treatments with NSAIDs may take weeks, causing undesirable side effects and requiring repeated administration. In this sense, this work describes the development of an optimized nanostructured lipid carrier (NLC) formulation for intra-articular administration of naproxen (NPX). An experimental design (23) selected the best formulation in terms of its physicochemical and structural properties, elucidated by different methods (DLS, NTA, TEM, DSC, and ATR-FTIR). The chosen formulation (NLC-NPX) was tested on acute inflammatory TMJ nociception, in a rat model. The optimized excipients composition provided higher NPX encapsulation efficiency (99.8%) and the nanoparticles were found stable during 1 year of storage at 25 °C. In vivo results demonstrated that the sustained delivery of NPX directly in the TMJ significantly reduced leukocytes migration and levels of pro-inflammatory cytokines (IL-1β and TNF-α), for more than a week. These results point out the NLC-NPX formulation as a promising candidate for the safe treatment of inflammatory pain conditions of TMJ or other joints.