Intrathecal clonidine decreases spinal nitric oxide release in a rat model of complete Freund's adjuvant induced inflammatory pain

Antinociceptive, anti-inflammatory and antioxidant effects of Boerhavia coccinea extracts and fractions on acute and persistent inflammatory pain models

Background Boerhavia coccinea (Nyctaginaceae) is an herbaceous plant used for the treatment of pain. The aim of this study was to evaluate the antinociceptive and anti-inflammatory activities of the aqueous (AEBC) and ethanol (EEBC) extracts of Boerhavia coccinea as well as the major fractions (F1, F2 and F3) from EEBC. Methods The antinociceptive effect of the extracts and fractions was evaluated using formalin test. AEBC, EEBC and F1 were selected and further evaluated acutely (24 h) and chronically (16 days) in Complete Freund's Adjuvant (CFA)-induced persistent inflammatory pain for their antihyperalgesic and anti-inflammatory effects. They were administered orally (100 and 200 mg/kg/day) from 48 h following the intraplantar injection of 100 µL of CFA. After the 16 days of chronic treatment, rats' spinal cord and brain were collected for the evaluation of oxidative stress parameters namely nitric oxide (NO), malondialdehyde (MDA), superoxide dismutase (SOD) and catalase (CAT). Results AEBC, EEBC and F1 significantly inhibited the first and second phases of the formalin-induced pain. They significantly reduced the hyperalgesia both in acute and chronic treatments. These extracts showed no acute anti-inflammatory effect. AEBC and EEBC exhibited anti-inflammatory activities after repeated administration. AEBC, EEBC and F1 significantly reduced MDA level and significantly increased SOD and catalase activities, mainly in the spinal cord. AEBC and EEBC also reduced the NO production in the spinal cord. Conclusions Boerhavia coccinea extracts and F1 possess potent antinociceptive activity which is not related to their anti-inflammatory properties. Their antioxidant effects may contribute to these activities in chronic treatment.

Antihypernociceptive activity of anethole in experimental inflammatory pain

Anethole has been reported to have antioxidant, antibacterial, antifungal, antiinflammatory, and anesthetic properties. In the present study, we evaluated the effects of anethole in two pain models of inflammatory origin: acute inflammation induced by carrageenan and persistent inflammation induced by Complete Freund's adjuvant. We evaluated the effects of anethole (125, 250, and 500 mg/kg) on the development of paw oedema and mechanical hypernociception. The liver was collected for histological analysis. Paw skin was collected to determine the levels of the cytokines tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), interleukin-17 (IL-17), and myeloperoxidase activity. Blood was collected to assess alanine transaminase (ALT) and aspartate transaminase (AST). The chemical composition of star anise oil was determined by gas chromatography/mass spectrometry (GC/MS), showing a presence of anethole of 98.1%. Oral pretreatment with anethole in mice inhibited paw oedema, mechanical pernociception, myelopewroxidase activity, TNF-α, IL-1β and IL-17 levels in acute and persistent inflammation models. Additionally, anethole treatment did not alter prostaglandin E2-induced mechanical hypernociception. Possible side effects were also examined. Seven-day anethole treatment did not alter plasma AST and ALT levels, and the histological profile of liver tissue was normal. The present study provides evidence of the antiinflammatory and analgesic activities of anethole in acute and persistent inflammation models.

Analgesic effect of electroacupuncture on inflammatory pain in collagen-induced arthritis rats: mediation by alpha2- and beta-adrenoceptors

This study was designed to investigate whether alpha- and beta-adrenergic systems mediate the analgesic effect of electroacupucture (EA) on inflammatory pain in a rat model of collagen-induced arthritis (CIA). To induce CIA, male Sprague-Dawley rats were immunized with bovine type II collagen emulsified in Freund's incomplete adjuvant, followed by a booster injection 14 days later. After induction of arthritis, the inflammatory pain threshold by the tail flick latency decreased as time passed and reached the minimum value at 4th week. Four weeks after the first immunization, low-frequency EA stimulation (2 Hz, 0.07 mA, 0.3 ms) delivered to Zusanli (ST(36)) for 30 min showed the analgesic effect. And also, the analgesic effect of EA was blocked by pretreatment with yohimbine (alpha2-adrenoceptor antagonist, 2 mg/kg, i.p.), but not by pretreatment with prazosin (alpha1-adrenoceptor antagonist, 1 mg/kg, i.p.) and propranolol (non-selective beta-adrenoceptor antagonist, 10 mg/kg, i.p.). These results suggest that the low-frequency EA can relieve the inflammatory pain in CIA, and the analgesic effect of EA can be mediated by alpha2- and beta-adrenoceptor, but not by alpha1-adrenoceptor.

Mechanisms of analgesic action of pulsed radiofrequency on adjuvant-induced pain in the rat: roles of descending adrenergic and serotonergic systems

Pulsed radiofrequency (PRF) has been reported to be effective in the treatment of several types of pain. The mechanism of action, however, is not well known. In a recent study, the antinociceptive effects of acute thermal pain were shown to be mediated via descending pain inhibitory pathways. In this study we observed an analgesic effect of PRF treatment in an adjuvant induced inflammatory pain model in rats. In this model, sciatic nerves were treated with PRF at 37 degrees and 42 degrees , which inhibited hyperalgesia in the inflammatory groups when compared to RF and sham treatment. This effect was attenuated after intrathecal administration of the alpha2-adrenoceptor antagonist yohimbine, the selective 5-HT3 serotonin receptor antagonist MDL72222, and the non-selective serotonin receptor antagonist methysergide. All three drugs were found to significantly inhibit the analgesic effect of PRF. The results suggest that the analgesic action of PRF involves the enhancement of noradrenergic and serotonergic descending pain inhibitory pathways.

Cerebrospinal fluid sampling by lumbar puncture in rats – repeated measurements of nitric oxide metabolites

The ability to measure nitric oxide (NO) metabolites (NO2- plus NO3-: NOx) in cerebrospinal fluid (CSF) will facilitate understanding the involvement of NO in neurogenic or inflammatory diseases. The purposes of this study were to develop a reliable method for CSF sampling from the lumbar region, and to repeatedly measure NOx in naive rats. NOx in CSF were measured using the Griess method. Twelve young (13-week-old) and seven middle-aged (40-week-old) male Wistar rats were used. CSF (50-70 microl) was collected four times at 1-week intervals. The success rate of CSF collection was 96% and average surgery time was 21 min. The blood contamination rate was 11% on macroscopic inspection. NOx in the CSF ranged from 3.8 to 10.6 microM. The NOx in clear CSF were not significantly different from those with blood contamination on macroscopic inspection. There was, however, a linear correlation between the increase in NOx and the volume of venous blood added experimentally. NOx levels were significantly higher (P < 0.05) in young rats (6.5+/-0.2 microM) than in middle-aged rats (5.6+/-0.3 microM). There was no significant difference in CSF NOx among the four samples collected at 1-week intervals in 13-week-old rats. These results indicate that our CSF sampling technique can be used to reliably obtain a small amount of CSF for NOx measurement. This technique will facilitate further experimental studies of the involvement of CSF NO in neurogenic or inflammatory diseases.

Role of the NO-cGMP pathway in the systemic antinociceptive effect of clonidine in rats and mice

The mechanism underlying the analgesic effect of clonidine, an alpha(2)-adrenoceptor agonist, remains uncertain. Activation of alpha(2)-adrenoceptor induces the release of nitric oxide (NO) from endothelial cells, which has led us to test the hypothesis that the observed antinociceptive effect induced by the systemic administration of clonidine depends on the NO-cGMP pathway. The possible involvement of an opioid link in the antinociceptive effect of clonidine was also evaluated. The antinociceptive effect induced by systemic administration (intravenous or intraperitoneal) of clonidine was evaluated using the rat paw formalin, mice tail-flick and writhing tests. Clonidine (3-120 microg/kg) induces a dose-dependent antinociceptive effect in the formalin, tail-flick and writhing tests. The antinociceptive effect of clonidine in a dose that had no sedative effect assessed by rota rod test, was significantly reduced by NO-synthase and guanylyl cyclase inhibition. The antinociceptive effect of morphine, but not clonidine, was inhibited by naloxone. Our current results suggest that the antinociceptive effect of systemic clonidine does not involve the opioid receptor and is modulated by the NO-cGMP pathway.

Mechanisms of Analgesic Action of Neurotropin on Chronic Pain in Adjuvant-Induced Arthritic Rat: Roles of Descending Noradrenergic and Serotonergic Systems

Neurotropin((R)), a non-protein extract from the inflamed skin of rabbits inoculated with vaccinia virus, has been clinically used as an analgesic drug for treatment of chronic pain. In this study, we investigated the analgesic mechanisms of Neurotropin in the adjuvant-induced arthritic rat, a chronic pain model with inflammation. Neurotropin caused dose-dependent inhibition of hyperalgesia in the adjuvant-induced arthritic rat after single intravenous (10 - 100 NU/kg) and oral (30 - 200 NU/kg) administration. The analgesic effect of Neurotropin (intravenous 100 NU/kg and oral 200 NU/kg) was significantly inhibited by intrathecal injections of the alpha(2)-adrenoceptor antagonist yohimbine (30 nmol/animal) and the selective 5-HT(3) serotonin receptor antagonist MDL72222 (30 nmol/animal), and slightly inhibited by the non-selective serotonin receptor antagonist methysergide (100 nmol/animal). The results suggest that the analgesic action of Neurotropin is at least in part due to the enhancement of noradrenergic and serotonergic descending pain inhibitory pathways. Neurotropin may be useful for the clinical management of chronic pain diseases such as a rheumatoid arthritis and osteoarthritis.