Electrical stimulation of the auricular branch of the vagus nerve potentiates analgesia induced by physical exercise in mice with peripheral inflammation

Objective

This study evaluated the antihyperalgesic and anti-inflammatory effects of percutaneous vagus nerve electrical stimulation (pVNS) associated with physical exercise, i.e., swimming, in mice with peripheral inflammation.

Methods

The pain model was induced by intraplantar (i.pl.) injection of Freund's complete adjuvant (CFA). Sixty-four male Swiss mice (35-40 g) received an i.pl. of CFA and underwent behavioral tests, i.e., mechanical hyperalgesia, edema, and paw temperature tests. Additionally, cytokine levels, specifically interleukin-6 (IL-6) and interleukin-10 (IL-10), were determined by enzyme-linked immunosorbent assay. Mice were treated with swimming exercise for 30 min alone or associated with different time protocols (10, 20, or 30 min) of stimulation in the left ear with random frequency during four consecutive days.

Results

pVNS for 20 min prolonged the antihyperalgesic effect for up to 2 h, 24 h after CFA injection. pVNS for 30 min prolonged the antihyperalgesic effect for up to 7 h, 96 h after CFA injection. However, it did not alter the edema or temperature at both analyzed times (24 and 96 h). Furthermore, the combination of pVNS plus swimming exercise, but not swimming exercise alone, reduced IL-6 levels in the paw and spinal cord, as well as IL-10 levels in the spinal cord.

Conclusion

pVNS potentiates the analgesic effect induced by swimming, which may be, at least in part, mediated by the modulation of inflammatory cytokines in the periphery (paw) and central nervous system (spinal cord). Therefore, the combination of these therapies may serve as an important adjunctive treatment for persistent inflammatory pain.

Antihyperalgesic effect of joint mobilization requires Cav3.2 calcium channels

The present study was undertaken to explore the relative contributions of Cav3.2 T-type channels to mediating the antihyperalgesic activity of joint manipulation (JM) therapy. We used the chronic constriction injury model (CCI) to induce peripheral neuropathy and chronic pain in male mice, followed by JM. We demonstrate that JM produces long-lasting mechanical anti-hyperalgesia that is abolished in Cav3.2 null mice. Moreover, we found that JM displays a similar analgesic profile as the fatty acid amide hydrolase inhibitor URB597, suggesting a possible converging mechanism of action involving endocannabinoids. Overall, our findings advance our understanding of the mechanisms through which JM produces analgesia.

Differential regulation of Cav 3.2 and Cav 2.2 calcium channels by CB1 receptors and cannabidiol

BACKGROUND AND PURPOSE

Cannabinoids are a promising therapeutic avenue for chronic pain. However, clinical trials often fail to report analgesic efficacy of cannabinoids. Inhibition of voltage gate calcium (Ca_v ) channels is one mechanism through which cannabinoids may produce analgesia. We hypothesized that cannabinoids and cannabinoid receptor agonists target different types of Ca_v channels through distinct mechanisms.

EXPERIMENTAL APPROACH

Electrophysiological recordings from tsA-201 cells expressing either Ca_v 3.2 or Ca_v 2.2 were used to assess inhibition by HU-210 or cannabidiol (CBD) in the absence and presence of the CB₁ receptor. Homology modelling assessed potential interaction sites for CBD in both Ca_v 2.2 and Ca_v 3.2. Analgesic effects of CBD were assessed in mouse models of inflammatory and neuropathic pain.

KEY RESULTS

HU-210 (1 μM) inhibited Ca_v 2.2 function in the presence of CB₁ receptor but had no effect on Ca_v 3.2 regardless of co-expression of CB₁ receptor. By contrast, CBD (3 μM) produced no inhibition of Ca_v 2.2 and instead inhibited Ca_v 3.2 independently of CB₁ receptors. Homology modelling supported these findings, indicating that CBD binds to and occludes the pore of Ca_v 3.2, but not Ca_v 2.2. Intrathecal CBD alleviated thermal and mechanical hypersensitivity in both male and female mice, and this effect was absent in Ca_v 3.2 null mice.

CONCLUSION AND IMPLICATIONS

Our findings reveal differential modulation of Ca_v 2.2 and Ca_v 3.2 channels by CB₁ receptors and CBD. This advances our understanding of how different cannabinoids produce analgesia through action at different voltage-gated calcium channels and could influence the development of novel cannabinoid-based therapeutics for treatment of chronic pain.

Ankle joint mobilization reduces axonotmesis-induced neuropathic pain and glial activation in the spinal cord and enhances nerve regeneration in rats

An important issue in physical rehabilitation is how to protect from or to reduce the effects of peripheral nerve injury. In the present study, we examined whether ankle joint mobilization (AJM) would reduce neuropathic pain and enhance motor functional recovery after nerve injury. In the axonotmesis model, AJM during 15 sessions every other day was conducted in rats. Mechanical and thermal hyperalgesia and motor performance deficit were measured for 5 weeks. After 5 weeks, we performed morphological analysis and quantified the immunoreactivity for CD11b/c and glial fibrillary acidic protein (GFAP), markers of glial activation, in the lumbar spinal cord. Mechanical and thermal hyperalgesia and motor performance deficit were found in the Crush+Anesthesia (Anes) group (P<0.001), which was significantly decreased after AJM (P<0.001). In the morphological analysis, the Crush+Anes group presented reduced myelin sheath thickness (P<0.05), but the AJM group presented enhanced myelin sheath thickness (P<0.05). Peripheral nerve injury increased the immunoreactivity for CD11b/c and GFAP in the spinal cord (P<0.05), and AJM markedly reduced CD11b/c and GFAP immunoreactivity (P<0.01). These results show that AJM in rats produces an antihyperalgesic effect and peripheral nerve regeneration through the inhibition of glial activation in the dorsal horn of the spinal cord. These findings suggest new approaches for physical rehabilitation to protect from or reduce the effects of nerve injury.

The antinociceptive effects of AR-A014418, a selective inhibitor of glycogen synthase kinase-3 beta, in mice

We investigated the antinociceptive effects of AR-A014418, a selective inhibitor of glycogen synthase kinase-3β (GSK-3β) in mice. A 30-minute pretreatment with AR-A014418 (.1 and 1 mg/kg, intraperitoneal [ip]) inhibited nociception induced by an ip injection of acetic acid. AR-A014418 pretreatment (.1 and .3 mg/kg, ip) also decreased the late (inflammatory) phase of formalin-induced licking, without affecting responses of the first (neurogenic) phase. In a different set of experiments, AR-A014418 (.1-10 μg/site) coinjected intraplantarly (ipl) with formalin inhibited the late phase of formalin-induced nociception. Furthermore, AR-A014418 administration (1 and 10 ng/site, intrathecal [it]) inhibited both phases of formalin-induced licking. In addition, AR-A014418 coinjection (10 ng/site, it) inhibited nociception induced by glutamate, N-methyl-D-aspartate (NMDA), (±)-1-aminocyclopentane-trans-1,3-dicarboxylic acid (trans-ACPD), tumor necrosis factor-alpha (TNF-α), and interleukin-1beta (IL-1β) by 47 ± 12%, 48 ± 11%, 31 ± 8%, 46 ± 13%, and 44 ± 11%, respectively. In addition, a 30-minute pretreatment with NP031115 (3 and 10 mg/kg, ip), a different GSK-3 β inhibitor, also attenuated the late phase of formalin-induced nociception. Collectively, these results provide convincing evidence that AR-A014418, given by local, systemic, and central routes, produces antinociception in several mouse models of nociception. The AR-A014418-dependent antinociceptive effects were induced by modulation of the glutamatergic system through metabotropic and ionotropic (NMDA) receptors and the inhibition of the cytokine (TNF-α and IL-1β) signaling.

PERSPECTIVE

These results suggest that GSK-3β may be a novel pharmacological target for the treatment of pain.

High-intensity extended swimming exercise reduces pain-related behavior in mice: involvement of endogenous opioids and the serotonergic system

The present study examined the hyponociceptive effect of swimming exercise in a chemical behavioral model of nociception and the mechanisms involved in this effect. Male mice were submitted to swimming sessions (30 min/d for 5 days). Twenty-four hours after the last session, we noticed that swimming exercise decreased the number of abdominal constriction responses caused by acetic acid compared with the nonexercised group. The hyponociception caused by exercise in the acetic acid test was significantly attenuated by intraperitoneal (i.p.) pretreatment of mice with naloxone (a nonselective opioid receptor antagonist, 1 mg/kg), ρ-chlorophenylalanine methyl ester (PCPA, an inhibitor of serotonin synthesis, 100 mg/kg once a day for 4 consecutive days), and by bilateral adrenalectomy. Collectively, the present results provide experimental evidences indicating for the first time that high-intensity extended swimming exercise reduces pain-related behavior in mice. The mechanisms involve an interaction with opioid and serotonin systems. Furthermore, endogenous opioids released by adrenal glands probably are involved in this effect.

PERSPECTIVE

Our results indicate that high-intensity extended exercise endogenously controls acute pain by activation of opioidergic and serotonergic pathways. Furthermore, these results support the use of exercise as a nonpharmacological approach for the management of acute pain.

Antinociceptive action of the extract and the flavonoid quercitrin isolated from Bauhinia microstachya leaves

This study examined the antinociceptive effect of Bauhinia microstachya (Leguminosae), a native plant widely distributed in the South of Brazil, in several chemical and mechanical models of pain. The methanolic extract (ME) from B. microstachya (3–30 mg kg−1, i.p.) and the isolated compound quercitrin (1–10 mg kg−1, i.p.), given 30 min earlier, produced a dose-dependent inhibition of acetic-acid-induced visceral pain in mice, with a mean ID50 value (dose necessary to reduce the nociceptive response by 50% relative to the control value) of 7.9 and 2.4 mg kg−1, respectively. The ME of B. microstachya (3–100 mg kg−1, i.p., 30 min earlier) also caused a dose-dependent inhibition of capsaicin-induced pain, with a mean ID50 value of 18.8 mg kg−1. Moreover, the ME (3–100 mg kg−1, i.p., 30 min earlier) produced marked inhibition of both phases of formalin-induced pain, with mean ID50 values for the neurogenic and the inflammatory phases of 30.3 and 17.2 mg kg−1, respectively. In addition, the ME of B. microstachya (3–300 mg kg −1, i.p., 30 min earlier) inhibited, in a graded manner, the hyperalgesia induced by bradykinin (3.2 μg/paw), substance P (13.5 μg/paw), carrageenan (300 μg/paw), capsaicin (100 μg/paw) and adrenaline (100ng/paw) in the rat paw, with mean ID50 values of 20.5, 17.9, 101.8, 54.2 and 99.7 mg kg−1, respectively. Taken together, these data demonstrate that ME of B. microstachya elicited a pronounced antinociceptive action against several chemical and mechanical models of pain in mice and rats. The precise mechanism responsible for the antinociceptive effect of the extract still remains unclear, but seems to be partly related to modulation of the release or action of pro-inflammatory mediators involved in the models of pain used. Finally, the flavonoid quercitrin isolated from this plant appears to contribute for the antinociceptive property of the methanolic extract.

Role of different types of potassium channels in the antidepressant-like effect of agmatine in the mouse forced swimming test

The administration of agmatine elicits an antidepressant-like effect in the mouse forced swimming test by a mechanism dependent on the inhibition of the NMDA receptors and the L-arginine-nitric oxide (NO) pathway. Since it has been reported that the NO can activate different types of potassium (K(+)) channels in several tissues, the present study investigates the possibility of synergistic interactions between different types of K(+) channel inhibitors and agmatine in the forced swimming test. Treatment of mice by i.c.v. route with subeffective doses of tetraethylammonium (a non specific inhibitor of K(+) channels, 25 pg/site), glibenclamide (an ATP-sensitive K(+) channels inhibitor, 0.5 pg/site), charybdotoxin (a large- and intermediate-conductance calcium-activated K(+) channel inhibitor, 25 pg/site) or apamin (a small-conductance calcium-activated K(+) channel inhibitor, 10 pg/site), augmented the effect of agmatine (0.001 mg/kg, i.p.) in the forced swimming test. Furthermore, the administration of agmatine and the K(+) channel inhibitors, alone or in combination, did not affect locomotion in the open-field test. Moreover, the reduction in the immobility time elicited by an active dose of agmatine (10 mg/kg, i.p.) in the forced swimming test was prevented by the pre-treatment of mice with the K(+) channel openers cromakalim (10 microg/site, i.c.v.) and minoxidil (10 microg/site, i.c.v.), without affecting locomotion. Together these data raise the possibility that the antidepressant-like effect of agmatine in the forced swimming test is related to its modulatory effects on neuronal excitability, via inhibition of K(+) channels.

Antinociceptive and anti-inflammatory properties from the bulbs of Cipura paludosa Aubl

This study examined the antinociceptive and anti-inflammatory actions of Cipura paludosa Aubl. in several models of inflammatory pain in mice and rats. The ethanolic extract (EE) from Cipura paludosa (1-300mg/kg) given by i.p. and p.o. routes, 30 or 60min earlier, produced a dose-dependent inhibition of the acetic acid-induced pain and Evans blue leakage in mice with ID(50) values of 2.8 and 17.6mg/kg and 17.2 and 176.1mg/kg, respectively. The EE (10mg/kg, i.p.) also inhibited the allodynia (39+/-6%)- and oedema (97+/-6%)-induced by the intraplantar injection of CFA. In addition, the EE (1-30mg/kg, i.p.) inhibited both mechanical and thermal hyperalgesia induced by prostaglandin E(2), PMA and bradykinin in the rat paw, with ID(50) values of 7.3, 12.1 and 4.7 and 13.9, 18.9 and 1.5mg/kg, respectively. These data demonstrate that EE of Cipura paludosa elicited pronounced antinociceptive and anti-inflammatory actions against some models of inflammatory pain in mice and rats. The mechanism by which the extract produced antinociception still remains unclear, but a great part of this effect seems to be related to modulation of the release or action of pro-inflammatory mediators. Moreover, the antinociceptive action demonstrated in the present study supports, at least partly, the ethnomedical uses of this plant.

Antidepressant-like and antinociceptive-like actions of 4-(4′-chlorophenyl)-6-(4″-methylphenyl)-2-hydrazinepyrimidine Mannich base in mice

This study investigated the possible antidepressant and antinociceptive action of CPMPH Mannich base, as well as the involvement of serotonergic, dopaminergic, noradrenergic and opioid systems and the L-arginine-nitric oxide pathway in the antidepressant-like effect of CPMPH in the forced swimming test (FST) in mice. The immobility time in the FST was significantly reduced by CPMPH (0.1-10 mg/kg, i.p.), without accompanying changes in the ambulation in an open-field. CPMPH at high doses (i.p. or s.c. routes) produced a significant inhibition of acetic acid-induced writhing. The antidepressant-like effect of CPMPH (1 mg/kg, i.p.) in the FST was prevented by pre-treatment of mice with methysergide (2 mg/kg, i.p., a non-selective serotonin receptor antagonist), sulpiride (32 mg/kg, i.p., a D2 receptor antagonist) or yohimbine (1 mg/kg, i.p., an alpha2-adrenoceptor antagonist). In contrast, the antidepressant-like effect of CPMPH was not affected by pre-treatment (i.p.) with naloxone (1 mg/kg, a non-selective opioid receptor antagonist) or L-arginine (750 mg/kg, a nitric oxide precursor). The results demonstrate that CPMPH had an antidepressant-like action that appears to be mediated through its interaction with serotonergic, dopaminergic and noradrenergic systems.

Phytochemical and pharmacological analysis of Bauhinia microstachya (Raddi) Macbr. (Leguminosae)

This paper describes the isolation of four phytoconstituents from the leaves of Bauhinia microstachya, a Brazilian medicinal plant used in folk medicine for the treatment of several ailments. Based on spectroscopic evidence, these compounds were identified as methyl gallate (1), kaempferol 3-O-rhamnosyl (2), quercitrin (3) and myricitrin (4). The crude methanolic extract and two compounds (3 and 4) were tested as analgesic using the writhing test in mice. The extract and compound 3 caused potent and dose-related analgesic effects, confirming the popular use of this plant for the treatment dolorous processes.