Daniel Martins

Neuroprotective and neuroregenerative effects of low-intensity aerobic exercise on sciatic nerve crush injury in mice.

Here, we established a program of low-intensity aerobic exercise and compared the effects of exercise preoperative, postoperative, and a combination of both pre- and postoperative protocols on recovery from sciatic nerve crush injury in mice using behavioral, biochemical, and morphological assays. Sciatic nerve crush was performed in adult male mice. The animals were submitted to preoperative (for 2 weeks), postoperative (for 2 weeks), and a combination of preoperative-postoperative (for 4 weeks) training protocols. During the training period, functional recovery was monitored using the Sciatic Functional Index, the Sciatic Static Index, and mechanical and cold hypersensitivity analyses. Morphological and biochemical alterations were analyzed on the 14th day post-crushing. The functional recovery values of all of the exercised groups were significantly better than the nonexercised group. Biochemically, all of the exercise groups showed a reduction in the increase of interleukin-1β (IL-1β) in the sciatic nerve and in the IL-1β and interleukin-6 receptor (IL-6R) levels in the spinal cord. However, the levels of tumor necrosis factor alpha (TNF-α) decreased only in the postoperative group and in the combination exercise protocols. In the morphological analysis, the combination exercise subjects presented an increase in fiber and axon diameter, in the myelination degree and in the number of myelinated fibers. The present study showed that pre- and postoperative exercise achieved values for functional and morphological sciatic nerve regeneration that were significantly better than either the preoperative or postoperative protocols. This experimental study suggests that physical exercise can restore motor and nerve function to a substantial degree when performed using a prophylactic and therapeutic approach.

High-Intensity Extended Swimming Exercise Reduces Pain-Related Behavior in Mice: Involvement of Endogenous Opioids and the Serotonergic System

UNLABELLED 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.

Mechanisms involved in the antinociception caused by ethanolic extract obtained from the leaves of Melissa officinalis (lemon balm) in mice

The present study examined the antinociceptive effect of the ethanolic extract from Melissa officinalis L. and of the rosmarinic acid in chemical behavioral models of nociception and investigates some of the mechanisms underlying this effect. The extract (3-1000 mg/kg), given orally (p.o.) 1 h prior to testing, produced dose-dependent inhibition of acetic acid-induced visceral pain, with ID50 value of 241.9 mg/kg. In the formalin test, the extract (30-1000 mg/kg, p.o.) also caused significant inhibition of both, the early (neurogenic pain) and the late (inflammatory pain), phases of formalin-induced licking. The extract (10-1000 mg/kg, p.o.) also caused significant and dose-dependent inhibition of glutamate-induced pain, with ID50 value of 198.5 mg/kg. Furthermore, the rosmarinic acid (0.3-3 mg/kg), given p.o. 1 h prior, produced dose-related inhibition of glutamate-induced pain, with ID50 value of 2.64 mg/kg. The antinociception caused by the extract (100 mg/kg, p.o.) in the glutamate test was significantly attenuated by intraperitoneal (i.p.) treatment of mice with atropine (1 mg/kg), mecamylamine (2 mg/kg) or l-arginine (40 mg/kg). In contrast, the extract (100 mg/kg, p.o.) antinociception was not affected by i.p. treatment with naloxone (1 mg/kg) or D-arginine (40 mg/kg). It was also not associated with non-specific effects, such as muscle relaxation or sedation. Collectively, the present results suggest that the extract produced dose-related antinociception in several models of chemical pain through mechanisms that involved cholinergic systems (i.e. through muscarinic and nicotinic acetylcholine receptors) and the L-arginine-nitric oxide pathway. In addition, the rosmarinic acid contained in this plant appears to contribute for the antinociceptive property of the extract. Moreover, the antinociceptive action demonstrated in the present study supports, at least partly, the ethnomedical uses of this plant.

Inosine Reduces Pain-Related Behavior in Mice: Involvement of Adenosine A1 and A2A Receptor Subtypes and Protein Kinase C Pathways

Inosine, an endogenous purine, is the first metabolite of adenosine in a reaction catalyzed by adenosine deaminase. This study aimed to investigate the antinociceptive effects of inosine against several models of pain in mice and rats. In mice, inosine given by systemic or central routes inhibited acetic acid-induced nociception. Furthermore, inosine also decreased the late phase of formalin-induced licking and the nociception induced by glutamate. Inosine produced inhibition (for up to 4 h) of mechanical allodynia induced by complete Freunds adjuvant (CFA) injected into the mouses paw. Given chronically for 21 days, inosine reversed the mechanical allodynia caused by CFA. Moreover, inosine also reduced the thermal (cold stimuli) and mechanical allodynia caused by partial sciatic nerve ligation (PSNL) for 4 h; when inosine was chronically administered, it decreased the mechanical allodynia induced by PSNL for 22 days. Antinociception caused by inosine in the acetic acid test was attenuated by treatment of mice with 1,3-dipropyl-8-cyclopentylxanthine (DPCPX; a selective adenosine A1 receptor antagonist), 8-phenyltheophylline (8-PT; a nonselective adenosine A1 receptor antagonist), and 4-{2- [7-amino-2-(2-furyl)[1,2,4]triazolo-[2,3-a][1,3,5]triazin-5-yl- amino]ethyl}phenol (ZM241385; a selective adenosine A2A receptor antagonist). In rats, inosine inhibited the mechanical and heat hyperalgesia induced by bradykinin and phorbol 12-myristate 13-acetate, without affecting similar responses caused by prostaglandin E2 or forskolin. These results indicate that inosine induces antinociceptive, antiallodynic, and antihyperalgesic effects in rodents. The precise mechanisms through which inosine produces antinociception are currently under investigation, but involvement of adenosine A1 and A2A receptors and blockade of the protein kinase C pathway seem to largely account for inosines antinociceptive effect.

The Antinociceptive Effects of AR-A014418, a Selective Inhibitor of Glycogen Synthase Kinase-3 Beta, in Mice

UNLABELLED 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.

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

Summary Ankle joint mobilization suppressed pain behavior and attenuated astroglial activation, as well as accelerated motor functional recovery after sciatic nerve crush in rat. ABSTRACT 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.

Ankle Joint Mobilization Decreases Hypersensitivity by Activation of Peripheral Opioid Receptors in a Mouse Model of Postoperative Pain

OBJECTIVE Investigate whether ankle joint mobilization (AJM) decreases hypersensitivity in the mouse plantar incision (PI) model of postoperative pain as well as to analyze the possible mechanisms involved in this effect. DESIGN Experiment 1: PI male Swiss mice (25-35 g, N = eight animals per group) were subjected to five sessions of AJM, each lasting either 9 or 3 minutes. AJM movement was applied at a grade III as defined by Maitland. Paw withdrawal frequency to mechanical stimuli was assessed before realization of PI and before and after daily AJM sessions. Mechanical hypersensitivity was also assessed following systemic (intraperitoneal [i.p.]) and local (intraplantar) injection of naloxone (a nonselective opioid receptor antagonist; 1 mg/kg, i.p.; 5 µg/paw, respectively, experiment 2); and systemic injection of fucoidin (100 µg/mouse, i.p., an inhibitor of leukocyte rolling, experiment 3) in different groups of mice. RESULTS Nine but not 3 minutes of AJM reduced mechanical hypersensitivity caused by PI, an effect that was prevented by systemic and local administrations of naloxone but not by fucoidin. CONCLUSIONS Our results indicate that joint mobilization reduces postoperative pain by activation of the peripheral opioid pathway. However, antihypersensitivity induced by AJM is apparently not limited by the number of opioid-containing leukocytes but by opioid receptors availability in sensory neurons. A better understanding of the peripheral mechanisms of AJM could stimulate therapists to integrate joint mobilization with strategies also known to influence endogenous pain control, such as exercise, acupuncture, and transcutaneous electrical nerve stimulation to potentiate endogenous analgesia.

High-intensity swimming exercise reduces neuropathic pain in an animal model of complex regional pain syndrome type I: Evidence for a role of the adenosinergic system

This study investigated the involvement of the adenosinergic system in antiallodynia induced by exercise in an animal model of complex regional pain syndrome type I (CRPS-I). Furthermore, we analyzed the role of the opioid receptors on exercise-induced analgesia. Ischemia/reperfusion (IR) mice, nonexercised and exercised, received intraperitoneal injections of caffeine (10mg/kg, a non selective adenosine receptor antagonist), 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) (0.1mg/kg, a selective adenosine A receptor antagonist), ZM241385 (3mg/kg, a selective adenosine A receptor antagonist), adenosine deaminase inhibitor erythro-9-(2-hydroxy-3nonyl) adenine [(EHNA), 5mg/kg, an adenosine deaminase inhibitor] or naloxone (1mg/kg, a nonselective opioid receptor antagonist). The results showed that high-intensity swimming exercise reduced mechanical allodynia in an animal model of CRPS-I in mice. The antiallodynic effect caused by exercise was reversed by pretreatment with caffeine, naloxone, DPCPX but it was not modified by ZM241385 treatment. In addition, treatment with EHNA, which suppresses the breakdown of adenosine to inosine, enhanced the pain-relieving effects of the high-intensity swimming exercise. This is the first report demonstrating that repeated sessions of high-intensity swimming exercise attenuate mechanical allodynia in an animal model of CRPS-I and that the mechanism involves endogenous adenosine and adenosine A receptors. This study supports the use of high-intensity exercise as an adjunct therapy for CRPS-I treatment.

Glycogen synthase kinase 3-specific inhibitor AR-A014418 decreases neuropathic pain in mice: evidence for the mechanisms of action.

The present study examined the antihyperalgesic effect of a specific inhibitor of Glycogen Synthase Kinase 3 (GSK3), AR-A014418, on the partial ligation of the sciatic nerve (PSNL), a neuropathic pain model in mice and investigated some mechanisms of action. AR-A014418 (0.01-1 mg/kg) administered by intraperitoneal route (i.p.) inhibited mechanical hyperalgesia. This action started 30 min after i.p. administration and remained significant up to 2 h. When administered daily for 5 days, AR-A014418 (0.3 mg/kg, i.p.) significantly reduced the mechanical hyperalgesia caused by PSNL. Intraperitoneal (i.p.) treatment with AR-A014418 (0.3 mg/kg) also significantly inhibited cold hyperalgesia induced by PSNL. Pre-administration of PCPA (100 mg/kg, i.p., inhibitor of serotonin synthesis) and AMPT (100 mg/kg, i.p., inhibitor of tyrosine hydroxylase), but not l-arginine (600 mg/kg, i.p., a nitric oxide precursor), significantly reduced the mechanical hyperalgesia elicited by AR-A014418. Furthermore, the administration of AR-A014418 significantly prevented the increase of TNF-α (inhibition of 76±8%) and IL-1β (inhibition of 62±10%), but did not alter lumbar spinal cord IL1-ra and IL-10 levels. Finally, intraperitoneal administration of AR-A014418 did not affect locomotor activity in the open-field test. Taken together, these results provide experimental evidence indicating that AR-A014418 produces marked antihyperalgesic effects in neuropathic pain in mice, possibly due to mechanisms that reduce proinflammatory cytokines, as well as increases in serotonergic and catecholaminergic pathways. The present study suggests that GSK3 may be a novel pharmacological target for the treatment of neuropathic pain and AR-A014418 might be a potential molecule of interest for chronic pain relief.

Citral: A monoterpene with prophylactic and therapeutic anti-nociceptive effects in experimental models of acute and chronic pain

Citral (3,7-dimethyl-2,6-octadienal) is an open-chain monoterpenoid present in the essential oils of several medicinal plants. The aim of this work was to evaluate the effects of orally administered citral in experimental models of acute and chronic nociception, inflammation, and gastric ulcers caused by non-steroidal anti-inflammatory drugs (NSAIDs). Oral treatment with citral significantly inhibited the neurogenic and inflammatory pain responses induced by intra-plantar injection of formalin. Citral also had prophylactic and therapeutic anti-nociceptive effects against mechanical hyperalgesia in plantar incision surgery, chronic regional pain syndrome, and partial ligation of sciatic nerve models, without producing any significant motor dysfunction. In addition, citral markedly attenuated the pain response induced by intra-plantar injection of glutamate and phorbol 12-myristate 13-acetate (PMA, a protein kinase C activator), as well as by intrathecal (i.t.) injection of ionotropic and metabotropic glutamate receptor agonists (N-methyl-D-aspartic acid [NMDA] and 1-amino-1,3-dicarboxycyclopentane [trans-ACPD], respectively), substance P, and cytokine tumour necrosis factor-α. However, citral potentiated behaviours indicative of pain caused by i.t., but not intra-plantar, injection of a transient receptor potential vanilloid receptor type 1 (TRPV1) agonist. Finally, the anti-nociceptive action of citral was found to involve significant activation of the 5-HT2A serotonin receptor. The effect of citral was accompanied by a gastro-protective effect against NSAID-induced ulcers. Together, these results show the potential of citral as a new drug for the treatment of pain.