Some pharmacologic and toxicologic studies on rhazya stricta decne in rats,mice and rabbits

• 1.1. This work examines some in vivo and in vitro pharmacologic and toxicologic effects of extracts of Rhazya stricta, a medicinal plant in the United Arab Emirates.
• 2.2.R. stricta extracts at doses of 0.1–10 mg reduced the mean arterial blood pressure (MBP) of anesthetized rats in a dose-dependent manner. The depressor effect was partially sensitive to atropine (5 μM). Although the MBP was reduced by 50% by both doses of extracts, the normal electrocardiogram pattern and the heart rate remained unaltered.
• 3.3. Acute treatment of rats with the lyophilized extract at doses of 4 g/kg produced a significant rise in insulin concentration. In streptozotocin-diabetic rats loaded orally with glucose (1 g/kg), R. stricta at doses of 8 g/kg produced significant decreases in plasma glucose concentration at 0.5 and 1 h after treatment.
• 4.4. Chronic treatment of rats and mice for 28 days with the lyophilized extract of R. stricta did not affect the plasma glucose or insulin concentration or any of the hematological or biochemical indices measured.
• 5.5. The extracts of R. stricta (0.5–4 g/kg) dose-dependently decreased the gastrointestinal transit time in mice by 4–50%.
• 6.6. The butanolic extract of R. stricta (1 and 2 g/kg) significantly reduced the carrageenan-induced increase in raw paw edema 3 and 4 h after the extract administration.
• 7.7. The rectal temperatures of normothermic and pyrexic rats were reduced significantly 0.5 and 1 h after administration of butanolic R. stricta at doses of 1 and 2 g/kg.
• 8.8. The butanolic extract of R. stricta at doses of 1 and 2 g/kg significantly increased the reaction time on the hot plate 30 and 60 min after administration to rats.
• 9.9. At concentrations <0.05 mg/ml (bath concentration), lyophilized water and butanol extracts of R. stricta potentiated the twitch responses induced by indirect electrical stimulation in the rat phrenic nerve diaphragm preparation. The responses were inhibited by concentrations >0.05 mg/ml. Neostigmine (2 × 10⁻⁴M) did not alter these effects of the extracts.
• 10.10. R. stricta extracts dose-dependently decreased the force of contraction and heart rate of the isolated rabbit heart. Atropine (1×10⁻⁵M) had no effect on the inhibitory activity of these extracts. The lyophilized water extract (> 10 mg) and butanol extract (>5 mg) produced irreversible inhibition and disturbances in the force of contraction and heart rate.

     

Corrigendum to ‘Antinociceptive effects of the selective non-peptide δ-opioid receptor agonist TAN-67 in diabetic mice’ [Eur. J. Pharmacol. 276 (1995) 131–135]

The antinociceptive potencies of 2-methyl-4aα-(3-hydroxyphenyl)-1,2,3,4,4a,5,12,12aα-octahydro-quinolino[2,3,3-g]isoquinoline (TAN-67), a non-peptidic δ-opioid receptor agonist, were examined using the acetic acid abdominal constriction test and the tail-flick test in diabetic mice. TAN-67, at doses of 3–100 mg/kg, i.p., produced a marked and dose-dependent inhibition of the number of acetic acid-induced abdominal constrictions in both non-diabetic and diabetic mice. The antinociceptive effect of TAN-67 in the acetic acid abdominal constriction test in diabetic mice was greater than that in non-diabetic mice. Indeed, the ED₅₀ (95% confidence limits) value of TAN-67 for the inhibition of acetic acid-induced abdominal constrictions in diabetic mice (6.0 (3.5–10.5) mg/kg) was significantly lower than that in non-diabetic mice (31.4 (14.2–69.4) mg/kg). The antinociceptive effect of TAN-67 was not antagonized by pretreatment with either β-funaltrexamine, a selective μ-opioid receptor antagonist, or nor-binaltorphimine, a selective κ-opioid receptor antagonist. When 7-benzylidenenaltrexone (0.3 mg/kg, s.c.), a selective δ₁-opioid receptor antagonist, was administered 10 min before treatment with TAN-67, the antinociceptive effect of TAN-67 was significantly antagonized. However, naltriben, a selective δ₂-opioid receptor antagonist, had no significant effect on the antinociceptive effect of TAN-67. Furthermore, in the tail-flick test, TAN-67 at doses of 3–30 mg/kg, i.p., also produced a marked and dose-dependent antinociceptive effect in diabetic mice, but not in non-diabetic mice. In conclusion, TAN-67 produced an antinociceptive effect through the activation of δ₁-opioid receptors. Furthermore, the results of this study support our hypothesis that mice with diabetes are selectively hyperresponsive to δ₁-opioid receptor-mediated antinociception.     

Some Effects of Cassia italica on the Central Nervous System in Mice

This work examines some effects of the crude ethanolic extract of the medicinal plant Cassia italica, given at single oral doses of 0.25, 0.5 or 1 g kg^?1, on the central nervous system in mice. Several models of nociception have been used to examine the analgesic effect of the extract. HPLC fingerprinting of the extract was performed to ensure uniformity of the extract material used. In treated mice, the extract caused dose-related inhibition of acetic acid-induced abdominal constriction, and in the formalin test of antinociception the extract reduced formalin-induced pain in the second (late) but not in the first (early) phase of the pain. Treatment with the extract at doses of 0.5 and 1 g kg^?1 significantly increased the reaction time in the hot-plate and warm-water tail-flick tests. Naloxone was ineffective in antagonizing the analgesic effect of C. italica on tail-flick and abdominal constriction tests, possibly indicating that the effect occurs via non-opiate pathways. The C. italica extract caused slight dose-related impairment of motor control which was significant only at a dose of 1 g kg^?1. Treatment at the three doses used did not affect the rectal temperature of normothermic mice, but was effective in significantly reducing the rectal temperature of hyperthermic rats, 0.5 and 1 h (but not 6 h) after administration of the extract at doses of 0.5 and 1 g kg^?1. The extract also produced progressive diminution in the ambulatory and total activity of treated mice for up to 2 h after administration. It is concluded that the crude ethanolic extract of C. italica has CNS depressant properties, manifested as antinociception and sedation.     

Antinociceptive and anti-inflammatory activities of the aqueous extract of <Emphasis Type="Italic">Kaempferia galanga</Emphasis> leaves in animal models

This study was performed to determine the antinociceptive and anti-inflammatory activities of aqueous extract of Kaempferia galanga leaves using various animal models. The extract, in the doses of 30, 100, and 300 mg/kg, was prepared by soaking (1:10; w/v) the air-dried powdered leaves (40 g) in distilled water (dH₂O) for 72 h and administered subcutaneously in mice/rats 30 min prior to the tests. The extract exhibited significant (P < 0.05) antinociceptive activity when assessed using the abdominal constriction, hot-plate and formalin tests, with activity observed in all tests occurring in a dose-dependent manner. Furthermore, the antinociceptive activity of K. galanga extract was significantly (P < 0.05) reversed when prechallenged with 10 mg/kg naloxone. The extract also produced a significantly (P < 0.05) dose-dependent anti-inflammatory activity when assessed using the carrageenan-induced paw-edema test. In conclusion, this study demonstrated that K. galanga leaves possessed antinociceptive and anti-inflammatory activities and thus supports the Malay’s traditional uses of the plant for treatments of mouth ulcer, headache, sore throat, etc.     

The effects of systemic procaine,lidocaine and dimethocaine on nociception in mice

• 1.1. Different local anesthetics were tested for analgesic activity in three antinociceptive models, the acetic acid-induced abdominal constriction, tail-flick and hot plate tests in the mouse.
• 2.2. In the abdominal constriction test, subcutaneous, SC, injection of lidocaine (10, 20 or 30 mg/kg) and dimethocaine (5, 10 or 20 mg/kg) induced dose-dependent antinociceptive responses. Procaine (20, 30 or 50 mg/kg) was also able to reduce the response to noxious chemical stimuli.
• 3.3. The IP injection of lidocaine and dimethocaine significantly inhibited the tail-flick and paw-licking hot plate responses; procaine was weak or inactive in these tests, in which heat was the noxious stimulus
• 4.4. Taken together, these results suggest that antinociception produced by systemically administered lidocaine and dimethocaine at nontoxic doses in mice is due, at least in part, to their central effects.

     

Corrigendum to ‘Antinociceptive effects of the selective non-peptide δ-opioid receptor agonist TAN-67 in diabetic mice’ [Eur. J. Pharmacol. 276 (1995) 131–135]

The antinociceptive potencies of 2-methyl-4a-(3-hydroxyphenyl)-1,2,3,4,4a,5,12,12a-octahydro-quinolino[2,3,3-g]isoquinoline (TAN-67), a non-peptidic δ-opioid receptor agonist, were examined using the acetic acid abdominal constriction test and the tail-flick test in diabetic mice. TAN-67, at doses of 3–100 mg/kg, i.p., produced a marked and dose-dependent inhibition of the number of acetic acid-induced abdominal constrictions in both non-diabetic and diabetic mice. The antinociceptive effect of TAN-67 in the acetic acid abdominal constriction test in diabetic mice was greater than that in non-diabetic mice. Indeed, the ED₅₀ (95% confidence limits) value of TAN-67 for the inhibition of acetic acid-induced abdominal constrictions in diabetic mice (6.0 (3.5–10.5) mg/kg) was significantly lower than that in non-diabetic mice (31.4 (14.2–69.4) mg/kg). The antinociceptive effect of TAN-67 was not antagonized by pretreatment with either β-funaltrexamine, a selective μ-opioid receptor antagonist, or nor-binaltorphimine, a selective κ-opioid receptor antagonist. When 7-benzylidenenaltrexone (0.3 mg/kg, s.c.), a selective δ₁-opioid receptor antagonist, was administered 10 min before treatment with TAN-67, the antinociceptive effect of TAN-67 was significantly antagonized. However, naltriben, a selective δ₂-opioid receptor antagonist, had no significant effect on the antinociceptive effect of TAN-67. Furthermore, in the tail-flick test, TAN-67 at doses of 3–30 mg/kg, i.p., also produced a marked and dose-dependent antinociceptive effect in diabetic mice, but not in non-diabetic mice. In conclusion, TAN-67 produced an antinociceptive effect through the activation of δ₁-opioid receptors. Furthermore, the results of this study support our hypothesis that mice with diabetes are selectively hyperresponsive to δ₁-opioid receptor-mediated antinociception.     

Antinociceptive and anti-inflammatory activities of Viburnum opulus

Water extract of Viburnum opulus L. (Caprifoliaceae) (VO) leaf was investigated for antinociceptive and anti-inflammatory activities in mice and rats. The tail flick test, acetic acid-induced writhing test, and the carrageenan-induced rat paw edema test were used to determine these effects. Our findings show that VO causes dose related inhibition in acetic acid-induced abdominal stretching in mice. VO inhibited abdominal stretching at 100 and 200?mg/kg. VO showed antinociceptive activity, which was quantified by the tail-flick test at doses of 100 and 200?mg/kg. However, VO did not have an anti-inflammatory effect at these doses. The LD₅₀ of VO was determined as 5.447?g/kg.     

Effect of diazepam and midazolam on the antinociceptive effect of morphine, metamizol and indomethacin in mice

The influence of midazolam and diazepam on antinociceptive effect of morphine (10 mg/kg), metamizol (500 mg/kg) and indomethacin (10 mg/kg) was investigated in a mouse model using the tail-flick and hot-plate tests. All drugs were injected intraperitoneally. Benzodiazepines were administered to mice 30 min before applying the analgesic drugs. Measurement of nociception was performed within 2 h after benzodiazepine administration. Diazepam at doses of 0.25 mg/kg and 2.5 mg/kg injected with morphine was found to decrease the antinociceptive effect of morphine. Similarly, diazepam decreased the antinociceptive effect of metamizol (only in the tail-flick test) and indomethacin. Midazolam used at doses of 1.25 mg/kg and 2.5 mg/kg decreased the antinociceptive effect of morphine, metamizol (only in the tail-flick test) and indomethacin.     

Socio-psychological stress-induced antinociception in diabetic mice

Rationale: Although it is well established that different forms of stress produce a pronounced antinociception, the effect of diabetes on psychological stress-induced antinociception is not yet clear. Objectives: The effect of diabetes on psychological stress-induced antinociceptive effect was assessed in mice. Methods: Animals were rendered diabetic by an injection of streptozotocin (200 mg/kg, IV). Mice were exposed to psychological stress in the compartment of a communication box. The antinociceptive response was evaluated by the tail-flick test, using radiant heat as a stimulus, which was performed before stress (pre-stress latency) and 0, 30 and 60 min after stress. Results: Exposure to socio-psychological stress for 5, 10 and 15 min produced duration-dependent antinociception in diabetic mice. However, in non-diabetic mice, no appreciable antinociception was found even in the case of socio-psychological stress for 15 min. Pretreatment with diazepam (0.3 mg/kg, IP) significantly attenuated socio-psychological stress-induced antinociception in diabetic mice (vehicle: 62.9±5.5%, n=10; diazepam: 22±1%, n=10). Furthermore, pretreatment with flumazenil (1 mg/kg, IV), a benzodiazepine receptor antagonist, also significantly reduced socio-psychological stress-induced antinociception in diabetic mice (vehicle: 77.9±5.0%, n=10; flumazenil: 5.8±1.2%, n=10). In contrast, pretreatment with methyl β-carboline-3-carboxylate (β-CCM, 2 mg/kg, IV), a benzodiazepine receptor inverse agonist, significantly enhanced socio-psychological stress-induced antinociception in non-diabetic mice (vehicle: 4.9±0.6%, n=10; β-CCM: 61.5±5.9%, n=10), but not in diabetic mice (vehicle: 50.7±4.5%, n=10; β-CCM: 64.4±7.2%, n=10). Conclusions: These results indicate that emotional stress can readily induce antinociception in diabetic mice. Furthermore, this enhanced emotional stress-induced antinociception might be attributable to an increase in the production and/or release of endogenous ligands for benzodiazepine receptors, such as diazepam binding inhibitor, which act as inverse benzodiazepine receptor agonists. Received: 1 September 1999 / Final version: 12 January 2000     

Antinociception Effect and Mechanisms of Campanula Punctata Extract in the Mouse

In the present study, the antinociceptive profiles of Campanula punctata extract were examined in ICR mice. The Campanula punctata contain a large dose of saponin. Campanula punctata extract administered orally (200 mg/kg) showed an antinociceptive effect as measured by the tail-flick and hot-plate tests. In addition, Campanula punctata extract attenuated the writhing numbers in the acetic acid-induced writhing test. Furthermore, the cumulative nociceptive response time for intrathecal (i.t.) injection of substance P (0.7 µg) was diminished by Campanula punctata extract. Intraperitoneal (i.p.) pretreatment with yohimbine (α₂-adrenergic receptor antagonist) attenuated antinociceptive effect induced by Campanula punctata extract in the writhing test. However, naloxone (opioid receptor antagonist) or methysergide (5-HT serotonergic receptor antagonist) did not affect antinociception induced by Campanula punctata extract in the writhing test. Our results suggest that Campanula punctata extract shows an antinociceptive property in various pain models. Furthermore, this antinociceptive effect of Campanula punctata extract may be mediated by α₂-adrenergic receptor, but not opioidergic and serotonergic receptors.     

PROSTAGLANDINS: ANTINOCICEPTIVE EFFECT OF PROSTAGLANDIN E1 IN THE RAT

1. The antinociceptive effect of prostaglandins E₁, E₂ and F_2α was studied in albino rats. Though all three prostaglandins produced similar degrees of sedation, only prostaglandin E₁ (PGE₁) produced a dose-related antinociceptive activity. 2. The antinociceptive activities of equi-analgesic doses of morphine (7.5 mg/kg, i.p.) and PGE₁ (2.0 mg/kg, i.p.) were inhibited to almost similar extents after pretreatment with drugs known to reduce central turnover of serotonin receptors, namely reserpine, fenclonine (p-chlorophenylalanine), methysergide and 5,6-dihydroxytryptamine. 3. Prostaglandin F_2α (2.0 mg/kg, i.p.) significantly inhibited the antinociceptive effects of both morphine and PGE₁. 4. The prostaglandin synthesis inhibitors, indomethacin and diclofenac, significantly inhibited morphine analgesia. 5. Probenecid markedly prolonged the duration of antinociceptive effect of morphine and the duration of PGE₁-induced potentiation of subanalgesic dose of morphine. 6. The results suggest that, in albino rats, PGE₁-induced antinociceptive activity is serotonin mediated and that morphine analgesia is not only mediated through serotonin but also through prostaglandins (PGE₁?) and 5-hydroxyindole acetic acid, the serotonin metabolite.     

Inhibitory effects of MPEP,an mGluR5 antagonist,and memantine,an <Emphasis Type="Italic">N</Emphasis>-methyl-<Emphasis Type="SmallCaps">D</Emphasis>-aspartate receptor antagonist,on morphine antinociceptive tolerance in mice

Abstract Rationale. Inhibition of N-methyl-D-aspartate (NMDA) receptors by memantine, an NMDA-receptor antagonist, and other antagonists of ionotropic receptors for glutamate inhibit the development of opiate antinociceptive tolerance. The role of metabotropic receptors for glutamate (mGluR) in opiate tolerance is less known. Objective. In the present study, we examined the effect of 2-methyl-6-(phenylethynyl)-pyridine (MPEP), the mGluR type-I (subtype mGluR5) antagonist, as well as the effect of co-administration of low doses of memantine and MPEP on morphine antinociceptive tolerance in mice. Methods. Morphine antinociceptive activity was tested twice, before and after chronic morphine administration, in the tail-flick test using a cumulative dose–response protocol. Tolerance was induced by six consecutive days of b.i.d. administration of morphine (10 mg/kg, s.c.). Saline, memantine (7.5 mg/kg and 2.5 mg/kg, s.c.), MPEP (30 mg/kg and 10 mg/kg, i.p.) and the combination of both antagonists at low doses was given 30 min prior to each morphine injection during its chronic administration. A separate experiment assessed the effects of memantine, MPEP and their combination on acute morphine antinociception using a tail-flick test. Results. MPEP (30 mg/kg but not 10 mg/kg) as well as memantine (7.5 mg/kg but not 2.5 mg/kg) attenuated the development of tolerance to morphine-induced antinociception. When given together, the low doses of MPEP (10 mg/kg) and memantine (2.5 mg/kg) also significantly attenuated opiate tolerance. None of the treatments with glutamate antagonists produced antinociceptive effects or significantly affected morphine-induced antinociception. Conclusions. The data suggest that both mGluR5 and NMDA receptors may be involved in the development of morphine antinociceptive tolerance. Electronic Publication     

The effect of Rhazya stricta Decne, a traditional medicinal plant, on spontaneous and drug-induced alterations in activity of rats.

The effect of acute and chronic treatment of rats with a lyophilized extract of the leaves of the medicinal plant Rhazya stricta on total and ambulatory activity was studied. Given acutely at single oral doses of 1, 2, 4, and 8 g/kg, the extract produced dose-dependent decreases in total activity and ambulatory activity. Diazepam (20 mg/kg, orally) produced a decrease in rat activity comparable to that produced by a dose of 1 g/kg of the extract. When given daily at an oral dose of 2 g/kg for 21 consecutive days, the extract produced, on the last day of treatment, significant decrease in activity amounting to about 30% of control activity levels. Subcutaneous (SC) treatment of rats with caffeine (7.5, 15, and 30 mg/kg), dose-dependently and significantly increased total activity and ambulatory activity. These effects were dose-dependently attenuated when the extract was given concomitantly with caffeine at oral doses of 1, 2, and 4 mg/kg. Treatment of rats with zoxazolamine alone (10, 20, or 40 mg/kg, SC) or R. Stricta (1 and 4 g/kg orally) alone significantly decreased total and ambulatory activities. Concomitant treatment with zoxazolamine and R. Stricta decreased the rats activity to a greater degree than with either treatment given alone.     

Analysis of the antinociceptive effect of systemic administration of tramadol and dexmedetomidine combination on rat models of acute and neuropathic pain

The aim of the present study was to investigate the possible antinociceptive effect of systemic administration of tramadol and dexmedetomidine either alone or in combination on acute and neuropathic pain models in rats. The antinociceptive effects of intraperitoneal (i.p.) tramadol (5-20 mg/kg) and dexmedetomidine (5-20 microg/kg) and three different combinations of tramadol+dexmedetomidine (5+5, 5+10 and 10+5, mg/kg+microg/kg, respectively) were measured by tail-flick and hot-plate methods in acute pain. The effects on the sciatic nerve ligation-induced neuropathic pain was tested by i.p. administration of tramadol (5 mg/kg), dexmedetomidine (5 microg/kg) and tramadol+dexmedetomidine combination (5+5) using a thermal plantar test. Sedation/motor-incoordination was assessed on rotarod. Tramadol and dexmedetomidine produced dose-related antinociception in tail-flick and hot-plate tests. In both tests, combination of these drugs produced an antinociceptive effect that is greater than that produced by tramadol or dexmedetomidine alone at several time points. In hot-plate test, tramadol+dexmedetomidine combination (5+10) exerted the strongest antinociceptive effect, while tramadol+dexmedetomidine combination (10+5) was significantly most effective in tail-flick test. In the neuropathic pain, the antinociceptive effect exerted by tramadol+dexmedetomidine combination (5+5) was also significantly greater than their applications alone. In rotarod test, tramadol (30 and 40 mg/kg), dexmedetomidine (30 and 40 microg/kg), tramadol+dexmedetomidine combination (10+10, 20+20) produced sedation/motor-incoordination, whereas tramadol (5-20 mg/kg), dexmedetomidine (5-20 microg/kg) and tramadol+dexmedetomidine combination (5+5, 5+10 and 10+5) did not produce any effect on sedation/motor-incoordination. The combination of tramadol and dexmedetomidine was more effective in increasing the pain threshold in acute and neuropathic pain when compared with the administration of either of these drugs alone.     

Antinociceptive Properties of the Hydroalcoholic Extract and the Flavonoid Rutin Obtained from Polygala paniculata L. in Mice

Abstract: The present study examined the antinociceptive effects of a hydroalcoholic extract of Polygala paniculata in chemical and thermal behavioural models of pain in mice. The antinociceptive effects of hydroalcoholic extract was evaluated in chemical (acetic‐acid, formalin, capsaicin, cinnamaldehyde and glutamate tests) and thermal (tail‐flick and hot‐plate test) models of pain or by biting behaviour following intratecal administration of both ionotropic and metabotropic agonists of excitatory amino acids receptors glutamate and cytokines such as interleukin‐1β (IL‐1β) and tumour necrosis factor‐α (TNF‐α) in mice. When given orally, hydroalcoholic extract (0.001–10 mg/kg), produced potent and dose‐dependent inhibition of acetic acid‐induced visceral pain. In the formalin test, the hydroalcoholic extract (0.0001–0.1 mg/kg orally) also caused significant inhibition of both the early (neurogenic pain) and the late (inflammatory pain) phases of formalin‐induced licking. However, it was more potent and efficacious in relation to the late phase of the formalin test. The capsaicin‐induced nociception was also reduced at a dose of only 1.0 mg/kg orally. The hydroalcoholic extract significantly reduced the cinnamaldehyde‐induced nociception at doses of 0.01, 0.1 and 1.0 mg/kg orally. Moreover, the hydroalcoholic extract (0.001–1.0 mg/kg orally) caused significant and dose‐dependent inhibition of glutamate‐induced pain. However, only rutin, but not phebalosin or aurapten, isolated from P. paniculata, administered intraperitoneally to mice, produced dose‐related inhibition of glutamate‐induced pain. Furthermore, the hydroalcoholic extract (0.1–100 mg/kg orally) had no effect in the tail‐flick test. On the other hand, the hydroalcoholic extract caused a significant increase in the latency to response at a dose of 10 mg/kg orally, in the hot‐plate test. The hydroalcoholic extract (0.1 mg/kg orally) antinociception, in the glutamate test, was neither affected by intraperitoenal treatment of animals with l ‐arginine (precursor of nitric oxide, 600 mg/kg) and naloxone (opioid receptor antagonist, 1 mg/kg.) nor associated with non‐specific effects such as muscle relaxation or sedation. In addition, oral administration of hydroalcoholic extract produced a great inhibition of the pain‐related behaviours induced by intrathecal injection of glutamate, N‐methyl‐d ‐aspartate (NMDA), IL‐1β and TNF‐α, but not by α‐amino‐3‐hydroxy‐5‐methyl‐isoxazole‐4‐propionic acid (AMPA), kainate or trans‐1‐amino‐1.3‐cyclopentanediocarboxylic acid (trans‐ACPD). Together, our results suggest that inhibition of glutamatergic ionotropic receptors, may account for the antinociceptive action reported for the hydroalcoholic extract from P. paniculata in models of chemical pain used in this study.     

Effects of diazepam on nociception in rats

Summary Acute i.p. injection of diazepam (1 mg/kg) resulted in a moderate increase in the tail-flick latency in rats. Tolerance to this diazepam effect developed after 10 days of diazepam treatment (1 mg kg^–1 day^–1). The benzodiazepine antagonist Ro 15-3505 only partially reversed the effect of diazepam on nociception. Naloxone (5 mg/kg i.p.) failed to affect the effect of diazepam on nociception, while the kappa antagonist MR 2266 fully antagonized the diazepam-induced increase of the tail-flick latency.Diazepam injected intracerebroventricularly (1, 5, 20 g/rat) did not alter basal nociceptive threshold, however, diazepam injected intrathecally (20 g/rat) prolonged the tail-flick latency. Furthermore, intracerebroventricular injection of muscimol partially antagonized the i.p. diazepam-induced increase of the tail-flick latency.These results suggest that benzodiazepine receptor sites are partially involved in the effect of diazepam on nociception and indicate that an indirect kappa-opioid-receptor-mediated mechanism may be involved. The anatomical site of diazepam action on tail-flick latency seems to be at the spinal level. Descending axons to the spinal cord from brain areas reached by intracerebroventricular injection of muscimol seem to modulate the effect of diazepam effect on nociception.This work was supported by MPI grant Send offprint requests to N. Zonta at the above address     

Phytotherapeutic activity of curcumol: Isolation,GC–MS identification,and assessing potentials against acute and subchronic hyperglycemia,tactile allodynia,and hyperalgesia

Context: Curcumol has recently attracted special attention due to its potential activities in many chronic disorders. Moreover, the traditional role of turmeric [Curcuma longa L. (Zingiberaceae)] in suppression of hyperglycemia is of great interest.

Objectives: The present work explores the potential acute and subchronic antihyperglycemic, antinociceptive, and in vivo antioxidant effects of curcumol in alloxan-diabetic mice.

Materials and methods: Bio-guided fractionation, column-chromatography, and GC–MS were utilized to identify the most active compound of turmeric (curcumol). Turmeric (25, 50, and 100?mg/kg), the curcumol rich fraction (CRF) (7?mg/kg), and curcumol (20, 30, and 40?mg/kg) were assessed for their acute (6 h) and subchronic (8 d) antihyperglycemic potentials and antinociceptive effects (8 weeks) were measured, using hot-plate and tail-flick latencies and von-Frey filaments method and in vivo antioxidant effects in alloxan-diabetic mice.

Results: The most-active turmeric fraction was found to be rich in curcumol (45.5%) using GC–MS analysis method. The results proved that the highest dose levels of turmeric extract and curcumol exerted remarkable hypoglycemic activity with 41.4 and 39.3% drop in the mice glucose levels after 6 h, respectively. Curcumol (40?mg/kg) was found to be 9.4% more potent than turmeric extract (100?mg/kg) in subchronic management of diabetes. Curcumol also showed a significant improvement of peripheral nerve function as observed from the latency and tactile tests.

Discussion: The antioxidant potential of curcumol may cause its ability to ameliorate diabetes and diabetes-related complications.

Conclusions: Curcumol, a natural metabolite with a good safety-profile, showed results comparable with tramadol in reversing diabetes-induced tactile allodynia and hyperalgesia.     

Antinociceptive effect of oxycodone in diabetic mice

The effect of oxycodone on thermal hyperalgesia in streptozotocin-induced diabetic mice was examined. The antinociceptive response was assessed by recording the latency in the tail-flick test using the radiant heat from a 50-W projection bulb on the tail. The tail-flick latency in diabetic mice was significantly shorter than that in non-diabetic mice. When diabetic mice were treated with oxycodone (5 mg/kg, s.c.), the tail-flick latency in diabetic mice was prolonged to the level considerably longer than the baseline latencies of non-diabetic mice. However, s.c. administration of morphine (5 mg/kg) did not produce a significant inhibition of the tail-flick response in diabetic mice. Oxycodone, at doses of 1.25-5.0 mg/kg administered s.c., produced a dose-dependent increase in the tail-flick latencies in both diabetic and non-diabetic mice. The antinociceptive effect of oxycodone was antagonized by pretreatment with a selective delta-opioid receptor antagonist, beta-funaltrexamine (20 mg/kg, s.c.), in both non-diabetic and diabetic mice. In non-diabetic mice, pretreatment with a selective kappa-opioid receptor antagonist, nor-binaltorphimine (20 mg/kg, s.c.) had no effect on the peak antinociceptive effect of oxycodone observed 30 min after administration, however, it slightly but significantly reduced oxycodone-induced antinociception observed 60 and 90 min after administration. On the other hand, pretreatment with nor-binaltorphimine practically abolished the peak (30 min) and persistent (60 and 90 min) antinociceptive effects of oxycodone in diabetic mice. Naltrindole (35 mg/kg, s.c.), a selective delta-opioid receptor antagonist, had no effects on the antinociceptive effect of oxycodone in both non-diabetic and diabetic mice. These results suggest that the antinociceptive effects of oxycodone may be mediated by mu- and kappa-opioid receptors in diabetic mice, whereas it may interact primarily with mu-opioid receptors in non-diabetic mice.     

Morphine Antinociception Is Enhanced in mdr1a Gene-Deficient Mice

Purpose. Previous studies have suggested that P-glycoprotein (P-gp)modulates opioid antinociception for selected -and -agonists. Thisstudy was undertaken to assess morphine antinociception in micelacking the mdr1a gene for expression of P-gp in the CNS. Methods. Morphine (n = 4–5/group) was administered as a single s.c.dose to mdr1a(–/–) mice (3–5 mg/kg) or wild-type FVB controls(8–10 mg/kg). Tail-flick response to radiant heat, expressed as percentof maximum response (%MPR), was used to determine theantinociceptive effect of morphine. Concentrations in serum, brain tissue, andspinal cord samples obtained immediately after the tail-flick test weredetermined by HPLC with fluorescence detection. Parallel experimentswith R(+)-verapamil, a chemical inhibitor of P-gp, also were performedto further investigate the effect of P-gp on morphine-associatedantinociception. Results. Morphine-associated antinociception was increasedsignificantly in the mdr1a(–/–) mice. The ED₅₀ for morphine was > 2-foldlower in mdr1a(–/–) (3.8 ± 0.2 mg/kg) compared to FVB (8.8 ±0.2 mg/kg) mice. However, the EC;i5;i0 derived from the brain tissuewas similar between the two mouse strains (295 ng/g vs. 371 ng/g).Pretreatment with R(+)-verapamil produced changes similar to thoseobserved in gene-deficient mice. P-gp does not appear to affectmorphine distribution between spinal cord and blood, as the spinalcord:serum morphine concentration ratio was similar betweengene-deficient and wild-type mice (0.47 ± 0.03 vs. 0.56 ± 0.04, p > 0.05). Conclusions. The results of this study are consistent with thehypothesis that P-gp attenuates the antinociceptive action of morphine bylimiting the brain:blood partitioning of the opioid.     

Antinociceptive and anti-inflammatory effects of the ethyl acetate stem bark extract of Bridelia scleroneura (Euphorbiaceae)

Bridelia scleroneura is a member of the Euphorbiaceae family. In folk medicine in Cameroon, the stem bark of this plant is used for relieving abdominal pain, contortion, arthritis and inflammation. In this study, the antinociceptive and anti-inflammatory activities of the ethyl acetate stem bark extract have been evaluated. The putative analgesic effect of the plant extract was examined in abdominal constriction, hot plate, formalin and on pain using tail immersion mouse models and in carrageenan-induced paw edema in rats. The extract (150–600 mg/kg) exhibited a dose-dependent analgesic effect (46.27–78.97%) in acetic acid-induced abdominal constriction in mice. B. scleroneura extract increased the pain latency of nociceptive response to thermal stimuli at the higher dose of 600 mg/kg. B. scleroneuna induced significant dose-dependent reduction of the nociception in both early and late phases of the formalin test. The extract at the dose of 300 mg/kg, increased significantly, by 63.70% and 52.01% the tail-immersion latency time, 1 and 2 h post-dosing. In the carrageenan test, B. scleroneura (150–600 mg/kg, p.o) had dose-dependent and significant effects at different time intervals. This behaviour was similar to indometacin (10 mg/kg) used as a standard drug. These results show that the ethyl acetate stem bark extract of B. scleroneura possesses peripheral and central analgesic properties as well as anti-inflammatory activity against acute inflammation processes, in support of the folk medicinal use of the plant.