Role of ETA and ETB endothelin receptors on endothelin-1-induced potentiation of nociceptive and thermal hyperalgesic responses evoked by capsaicin in rats

Increasing evidence indicates that endothelin-1 (ET-1) activates nociceptive neurons and sensitizes them to different noxious stimuli, but involvement of TRPV1-dependent mechanisms in mediation of such effects is not yet fully understood. Here we report that intraplantar (i.pl.) injection of ET-1 (10 pmol) into the hind paw of rats induced overt nociceptive behavior over the first hour, followed by a slowly developing thermal hyperalgesia, lasting from 3 to 8 h after injection. Both effects were also induced by similar injections of capsaicin (10–1000 pmol), but these responses were shorter lasting than those caused by ET-1. Local pre-treatment with the TRPV1 antagonist capsazepine (30 nmol, i.pl.) reduced only the thermal hyperalgesia induced by ET-1, but fully suppressed both responses to capsaicin (1000 pmol). Injection of a sub-threshold dose of ET-1 (0.1 pmol, i.pl.) prior to capsaicin (1 pmol, i.pl.) markedly sensitized the hind paw to the overt nociceptive and thermal hyperalgesic effects of the later. The potentiation of capsaicin-induced nociception by ET-1 was abolished by prior i.pl. injection of BQ-123 (ET_A receptor antagonist, 10 nmol), but unaffected by BQ-788 (ET_B receptors antagonist, 10 nmol), whereas the enhancement of capsaicin-induced hyperalgesia by ET-1 was attenuated by both antagonists. Therefore, differently to what has been reported in mice, in rats TRPV1 receptors contribute selectively to thermal hyperalgesia, but not overt nociception, induced by ET-1. Importantly, although ET-1 augments capsaicin-induced overt nociception and thermal hyperalgesia, potentiation of the former relies solely on ET_A receptor-mediated signaling mechanisms, whereas both receptors contribute to the latter.     

The stimulatory effects of caffeine with oseltamivir (Tamiflu) on light–dark behavior and open-field behavior in mice

Abnormal behaviors and death associated with the use of oseltamivir (Tamiflu^®) have emerged as a major issue in influenza patients taking the drug. Here, we investigated the mechanisms underlying the effects of oseltamivir on the behavior of mice using light–dark and open-field preference tests. Oseltamivir (75 and 150 mg/kg, intraperitoneally (i.p.)) alone affected neither time spent in the open area in the light–dark preference test nor ambulation in the open-field test at 2 h post-injection. However, a non-selective adenosine A₁/A₂ receptor antagonist, caffeine (10 mg/kg, i.p.) in combination with oseltamivir (150 mg/kg, i.p.) increased time spent in the open area in the light–dark preference test. This enhancement was not inhibited by a benzodiazepine receptor antagonist, flumazenil (10–20 mg/kg, subcutaneously (s.c.)). Enhancement of ambulation in the open-field test was also observed when caffeine (10 mg/kg, i.p.) was combined with oseltamivir (150 mg/kg, i.p.). This enhancement was inhibited by a dopamine D₂ receptor antagonist, haloperidol (0.1 mg/kg, s.c.). Furthermore, an adenosine A₂ receptor antagonist, SCH58261 (3 mg/kg, i.p.) in combination with oseltamivir (150 mg/kg, i.p.) increased ambulation in the open-field test, while an adenosine A₁ receptor antagonist, DPCPX (1–3 mg/kg, i.p.) did not. These findings suggest that the actions of oseltamivir may involve the dopamine and adenosine systems. Our findings suggest that due to the interaction between central blockade of adenosine A₂ receptors by caffeine, and oseltamivir-induced behavioral changes, patients being treated with oseltamivir should be closely monitored.     

Tapentadol,but not morphine,selectively inhibits disease-related thermal hyperalgesia in a mouse model of diabetic neuropathic pain

Neuropathic pain in diabetic patients is a common distressing symptom and remains a challenge for analgesic treatment. Selective inhibition of pathological pain sensation without modification of normal sensory function is a primary aim of analgesic treatment in chronic neuropathic pain. Tapentadol is a novel analgesic with two modes of action, μ-opioid receptor (MOR) agonism and noradrenaline (NA) reuptake inhibition. Mice were rendered diabetic by means of streptozotocin, and neuropathic hyperalgesia was assessed in a 50 °C hot plate test. Normal nociception was determined in control mice. Tapentadol (0.1–1 mg/kg i.v.) and morphine (0.1–3.16 mg/kg i.v.) dose-dependently attenuated heat-induced nociception in diabetic animals with full efficacy, reaching >80% at the highest doses tested. Tapentadol was more potent than morphine against heat hyperalgesia, with ED₅₀ (minimal effective dose) values of 0.32 (0.316) and 0.65 (1) mg/kg, respectively. Non-diabetic controls did not show significant anti-nociception with tapentadol up to the highest dose tested (1 mg/kg). In contrast, 3.16 mg/kg morphine, the dose that resulted in full anti-hyperalgesic efficacy under diabetic conditions, produced significant anti-nociception in non-diabetic controls. Selective inhibition of disease-related hyperalgesia by tapentadol suggests a possible advantage in the treatment of chronic neuropathic pain when compared with classical opioids, such as morphine. It is hypothesized that this superior efficacy profile of tapentadol is due to simultaneous activation of MOR and inhibition of NA reuptake.     

Effects of the 5-HT4 receptor agonist RS67333 and paroxetine on hippocampal extracellular 5-HT levels

The 5-HT₄ receptor modulates activity of serotonergic neurons and is a new potential target for antidepressant treatment. This microdialysis study evaluated the effect of the 5-HT₄ receptor agonist, RS67333, on extracellular serotonin (5-hydroxytryptamine, 5-HT) and 5-HIAA levels in rat ventral hippocampus during chloral hydrate anaesthesia, and explored the ability of RS67333 to augment the effect of the selective serotonin reuptake inhibitor paroxetine. The effect of RS67333 was examined after acute and subchronic (3 days) administration. Acute RS67333 (1.5 mg/kg i.v.) had no effect on extracellular 5-HT or 5-HIAA levels, while acute paroxetine (0.5 mg/kg i.v.) increased 5-HT levels by 299 ± 16% and decreased 5-HIAA levels by 25 ± 4%. Administration of RS67333 80 min after paroxetine caused an additional transient increase in 5-HT levels (to 398 ± 52% of baseline). Subchronic RS67333 administration (1.5 mg/kg i.p.) increased basal 5-HT levels by 73 ± 15% and decreased 5-HIAA levels by 27 ± 13%. In conclusion, the 5-HT₄ receptor agonist RS67333 augmented the acute effect of paroxetine on extracellular 5-HT levels in the ventral hippocampus, and after 3 days increased basal hippocampal 5-HT levels.     

Involvement of monoaminergic systems in the antidepressant-like effect of nobiletin

Nobiletin isolated from citrus peels up-regulates synaptic transmission and improves memory impairment in rodents. This study investigated the antidepressant-like effect of nobiletin in the forced swimming test (FST) and tail suspension test (TST) in mice. Additionally, the monoaminergic mechanisms involved in the antidepressant-like effect of nobiletin in mice were also assessed. Nobiletin (25, 50 and 100 mg/kg, p.o.) decreased the immobility time in both the FST and TST without locomotor alterations in the open-field test (OFT). The anti-immobility effect of nobiletin (50 mg/kg, p.o.) was completely prevented by the pretreatment of mice with WAY 100635 (0.1 mg/kg, s.c., a serotonin 5-HT_1A receptor antagonist), cyproheptadine (3 mg/kg, i.p., a serotonin 5-HT₂ receptor antagonist), prazosin (62.5 μg/kg, i.p., an α₁-adrenoceptor antagonist), SCH23390 (0.05 mg/kg, s.c., a dopamine D₁ receptor antagonist) or sulpiride (50 mg/kg, i.p., a dopamine D₂ receptor antagonist). On the other hand, the pretreatment of mice with yohimbine (1 mg/kg, i.p., an α₂-adrenoceptor antagonist) or propranolol (5 mg/kg, i.p., a β-adrenoceptor antagonist) did not block the antidepressant-like effect of nobiletin in the TST. Taken together, the data demonstrated that nobiletin produced an antidepressant-like effect that seems to be dependent on its interaction with the serotonergic, noradrenergic and dopaminergic systems. Thus, the present study suggests the therapeutic potential of this dietary flavonoid for the treatment of depression.     

The endocannabinoid transport inhibitor AM404 modulates nociception in cholestasis

Cholestasis is associated with increased activity of the endogenous opioid system that results in analgesia. Endocannabinoid system can reduce pain sensitivity. Considering the interaction that has been shown between the endogenous opioid and endocannabinoid systems in nociception processing, we studied the effect of AM404, an endocannabinoid transport inhibitor, on modulation of nociception in cholestasis, a model of elevated endogenous opioid tone. Cholestasis was induced by ligation of the main bile duct using two ligatures and transection of the duct at the midpoint between them. A significant increase (P < 0.01) in TF was observed in cholestatic rats compared to unoperated and sham rats. AM404 (10 mg/kg, i.p.) significantly increased TFL at 5, 30 min but not 60 min after injection in cholestatic animals compared to the vehicle treated cholestatic group (P < 0.05, P < 0.001, respectively). AM404 injection to unoperated and sham rats did not alter baseline TFL. The effect of AM404 in cholestatic rats was blocked by co-administration of a CB₁ receptor antagonist, AM251 (1 mg/kg, i.p.) but not by the CB2 receptor antagonist, SR144528 (1 mg/kg, i.p.). Naloxone injection blocked the antinociception induced by cholestasis in bile duct ligated group. Antinociception produced by injection of AM404 in cholestatics was also attenuated by co-administration of naloxone. These data show that AM404 potentiates antinociception induced by cholestasis and indicate that there are possible interactions between opioid and cannabinoid systems in this experimental model of elevated endogenous opioid tone. The inhibitory effects of AM404 in this model are mediated by cannabinoid CB₁ and not CB₂ receptors.     

Pentoxifylline attenuates the development of hyperalgesia in a rat model of neuropathic pain

Pentoxifylline, a non-specific cytokine inhibitor, has shown to be beneficial in inflammatory pain in both experimental and clinical studies. The present study demonstrates for the first time, to our knowledge, the antihyperalgesic effect of pentoxifylline in the neuropathic pain using L5 spinal nerve transection rat model. In a preventive paradigm, pentoxifylline (12.5, 25, 50, or 100 mg/kg intraperitoneally) was administered systemically daily, beginning 1 h prior to nerve transection. Pentoxifylline (50, or 100 mg/kg i.p.) produced significant decrease in the mechanical and thermal hyperalgesia. However, pentoxifylline (100 mg/kg i.p.) did not influence the paw pressure thresholds and paw withdrawal latency in sham-operated rats. In order to understand the possible antinocicieptive effect of pentoxifylline in neuropathic pain, we examined the level of TNFα, IL-1β, IL-6 and IL-10 protein in the contralateral brain on day 7 post-transection. Pentoxifylline administration resulted in a dose-dependent reduction of the production of proinflammatory cytokines like TNFα, IL-1β and IL-6, and enhancement of IL-10. Furthermore, we investigated the activity of nuclear factor kappa B (NF-κB) in the contralateral brain on days 7 after surgery. In accordance with the change of proinflammatory cytokines, Pentoxifylline (50 or 100 mg/kg) significantly inhibited the activation of NF-κB in the brain. This research supports a growing body of literature emphasizing the importance of neuroinflammation and neuroimmune activation in the development of neuropathic pain states, and the potential preventive value of pentoxifylline in the treatment of neuropathic pain.     

l-Cysteine ethyl ester reverses the deleterious effects of morphine on,arterial blood–gas chemistry in tracheotomized rats

This study determined whether the membrane-permeable ventilatory stimulant, l-cysteine ethylester (l-CYSee), reversed the deleterious actions of morphine on arterial blood–gas chemistry in isoflurane-anesthetized rats. Morphine (2 mg/kg, i.v.) elicited sustained decreases in arterial blood pH, pO₂ and sO₂, and increases in pCO₂ (all responses indicative of hypoventilation) and alveolar–arterial gradient (indicative of ventilation–perfusion mismatch). Injections of l-CYSee (100 μmol/kg, i.v.) reversed the effects of morphine in tracheotomized rats but were minimally active in non-tracheotomized rats. l-cysteine or l-serine ethylester (100 μmol/kg, i.v.) were without effect. It is evident that l-CYSee can reverse the negative effects of morphine on arterial blood–gas chemistry and alveolar–arterial gradient but that this positive activity is negated by increases in upper-airway resistance. Since l-cysteine and l-serine ethylester were ineffective, it is evident that cell penetrability and the sulfur moiety of l-CYSee are essential for activity. Due to its ready penetrability into the lungs, chest wall muscle and brain, the effects of l-CYSee on morphine-induced changes in arterial blood–gas chemistry are likely to involve both central and peripheral sites of action.     

Therapeutic potential of α2 adrenoceptor antagonism for antipsychotic-induced extrapyramidal motor disorders

We examined the effects of JP-1302 (a selective α_2C antagonist), BRL-44408 (a selective α_2A antagonist) and yohimbine (a non-selective α₂ antagonist) on haloperidol-induced bradykinesia and catalepsy in mice to elucidate the role of α₂ adrenoceptor subtypes in modifying extrapyramidal motor disorders. JP-1302 (0.1–1 mg/kg, s.c.) dose-dependently ameliorated haloperidol-induced bradykinesia in the pole-test and reversed the catalepsy time increased by haloperidol. Antibradykinetic and anticataleptic actions of JP-1302 were statistically significant at 0.3 and 1 mg/kg, and these doses did not alter the ambulatory distance, rearing or center–perimeter residence time in the open-field test. BRL-44408 (1–10 mg/kg, s.c.) and yohimbine (0.3–3 mg/kg, i.p.) also ameliorated haloperidol-induced bradykinesia and catalepsy. However, both agents significantly decreased ambulatory distance and rearing in the open-field test, possibly reflecting their anxiogenic actions associated with α_2A antagonism. The present study shows for the first time that blockade of α_2C receptors can alleviate antipsychotic-induced extrapyramidal motor disorders without affecting gross behaviors.     

Carnosine inhibits pentylenetetrazol-induced seizures by histaminergic mechanisms in histidine decarboxylase knock-out mice

In the present study, we used both histidine decarboxylase-deficient (HDC-KO) mice and wild-type (WT) mice to elucidate the possible role of carnosine in pentylenetetrazol (PTZ)-induced seizures. In the acute PTZ challenge study, PTZ (75 mg/kg) was injected intraperitoneally (i.p.) to induce seizures. Carnosine (200, 500 or 1000 mg/kg, i.p.) significantly decreased seizure stage, and prolonged the latency for myoclonic jerks in WT mice in a dose-dependent manner. The effects of carnosine (500 mg/kg) were time-dependent and reached a peak at 1 h. However, it had no significant effect on HDC-KO mice. Carnosine (500 mg/kg) also significantly elevated the thresholds in WT mice but not HDC-KO mice following intravenous (tail vein) administration of PTZ. We also found that α-fluoromethylhistidine substantially reversed the protective effects of carnosine in WT mice. In addition, carnosine pretreatment reduced the cortical EEG activity induced by PTZ (75 mg/kg, i.p.). These results indicate that carnosine can protect against PTZ-induced seizures and its action is mainly through the carnosine–histidine–histamine metabolic pathway. This suggests that carnosine may be an endogenous anticonvulsant factor in the brain and may be used as a new antiepileptic drug in the future.     

Anti-inflammatory effect of polyamines in serotonin and carrageenan paw edemata—possible mechanism to increase vascular permeability inhibitory protein level which is regulated by glucocorticoids and superoxide radical

Serotonin paw edema of mice and carrageenan paw edema of rats were inhibited by subcutaneously or orally administered certain polyamines. They must be given at least 2 h before serotonin challenge to get inhibitions which were blocked by the concomitant injections of cycloheximide. Thirty percent inhibitory dose (ID₃₀) of polyamines (s.c.) 3 h before serotonin (s.c.) were: spermidine (8 mg/kg), spermine 28 mg/kg) and putrescine (55 mg/kg). Agmatine, cadaverine, ornithine, citrulline, lysine and arginine were not inhibitory even at 200 mg/kg. Three inhibitory polyamines were effective by oral administration but were not inhibitory by local administration into the paws. Intravenous injections of spermidine also required 2 h of lag period for inhibitions. Serotonin edema was inhibited by dexamethasone (1 mg/kg), predonisolone (1 mg/kg) or by superoxide dismutase (SOD, 5 mg/kg) in lag period requiring manner (s.c. and i.v.). High dose of cyclo-oxygenase inhibitors indomethacin and diclofenac sodium, lipo-oxygenase inhibitor BW755C (30 mg/kg s.c., respectively) and phospholipase A₂ inhibitor quinacrine (100 mg/kg s.c.) failed to inhibit serotonin edema, suggesting that arachidonate metabolites are not participating in this model. ID₃₀ of polyamines which were administered (s.c. and oral) to rats 3 h before carrageenan and determined at 3 h by paw weight were: spermidine (28 and 100 mg/kg), spermine (18 and 90 mg/kg) and putrescine (both>200 mg/kg).Adrenalectomized rats responded to polyamines just as normal rats. Local vascular permeability, irritancy and acute toxicity were also tested in mice. Polyamines were proved to be glucocorticoid-type anti-inflammatory drugs. Polyamines may be mediators of glucocorticoids for the synthesis of the postulated vascular permeability inhibitory protein (called as vasoregulin for convenience). Antiinflammatory effect of glucocorticoid is recently explained by its capacity to induce phospholipase A₂ inhibitory protein(s), (macrocortin or lipomodulin). However, this hypothesis has not yet been proved byin vivo experiment and our data suggest that there is induction by glucocorticoid of another kind of protein which does not inhibit phospholipase A₂ activity.     

Effect of nitric oxide synthase inhibitor and NMDA receptor antagonist on the development of nicotine sensitization of nucleus accumbens dopamine release: An in vivo microdialysis study

We have previously found that the neuronal nitric oxide synthase inhibitor N-nitro-l-arginine (l-NNA) and the noncompetitive N-methyl-d-aspartate (NMDA) receptor antagonist MK-801 prevent behavioral sensitization to nicotine. This study aimed to investigate the effect of l-NNA and MK-801 on a neurochemical component of nicotine sensitization by evaluating the effect of the drugs on nicotine sensitization of nucleus accumbens dopamine (DA) release. Sprague–Dawley rats were pretreated with l-NNA (15 mg/kg, i.p.), MK-801 (0.3 mg/kg, i.p.), or saline 30 min before injection of nicotine (0.4 mg/kg, s.c., once daily) for seven consecutive days. Twenty-four hours after the last drug injection, animals were challenged with local perfusion of 5 mM nicotine into the shell of nucleus accumbens for 60 min and DA release was monitored using in vivo microdialysis. In rats treated with repeated nicotine, acute nicotine challenge induced a greater increase of accumbal DA release than in saline-treated animals (maximal DA response = 969 ± 235% (mean ± S.E.M.) of basal level versus 520 ± 93%, p = 0.042). Co-administration of l-NNA or MK-801 with nicotine attenuated an increase of DA release elicited by acute nicotine challenge, compared with nicotine alone (maximal DA response = 293 ± 58% and 445 ± 90% of basal level, respectively versus 969 ± 235%, p = 0.004 and p = 0.013, respectively). These data demonstrate that l-NNA and MK-801 block the development of nicotine sensitization of nucleus accumbens DA release, further supporting the involvement of nitric oxide and NMDA receptors in the development of behavioral sensitization to nicotine.     

Central 5-HT3 receptor-induced hypothermia in mice: Interstrain differences and comparison with hypothermia mediated via 5-HT1A receptor

The selective agonist of serotonin 5-HT₃ receptor 1-(3-chlorophenyl)biguanide hydrochloride (m-CPBG) administered intracerebroventricularly (40, 80 or 160 nmol) produced long-lasting dose-dependent hypothermic response in AKR/2J mice. m-CPBG (160 nmol i.c.v.) induced profound hypothermia (delta t = −4 °C) that lasted up to 7 h. m-CPBG (40 nmol i.c.v.)-induced hypothermia was attenuated by 5-HT₃ receptor antagonist ondansetron pretreatment. At the same time, intraperitoneal administration of m-CPBG in a wide range of doses (0.5, 1.0, 5.0 or 10.0 mg/kg) did not affect the body temperature. These findings indicate: (1) the implication of central, rather than peripheral 5-HT₃ receptor in the thermoregulation; (2) the inability of m-CPBG to cross blood–brain barrier in mice. The comparison of brain 5-HT₃-induced hypothermic reaction in six inbred mouse strains (DBA/2J, CBA/Lac, C57BL/6, BALB/c, ICR, AKR/J) was performed and two highly sensitive to m-CPBG strains (CBA/Lac and C57BL/6) were found. In the same six mouse strains the functional activity of 5-HT_1A receptor was studied. The comparison of hypothermic reactions produced by 5-HT_1A receptor agonist 8-OH-DPAT (1.0 mg/kg i.p.) and m-CPBG revealed significant correlation between 5-HT₃ and 5-HT_1A-induced hypothermia in five out of six investigated mouse strains. 5-HT_1A receptor antagonist p-MPPI pretreatment (1 mg/kg i.p.) diminished hypothermia produced by centrally administered m-CPBG (40 nmol i.c.v.). The data suggest the cross-talk between 5-HT_1A and 5-HT₃ receptors in the mechanism of 5-HT-related hypothermia.     

Aspirin-triggered lipoxin induces CB1-dependent catalepsy in mice

Evidence are that inhibition of cyclooxygenase 2 (COX-2) enhances endocannabinoid signaling, indicating a crosstalk between these two eicosanoid pathways. Aspirin, a non-selective COX inhibitor, acetylates COX-2 with generation of a lipoxygenase (LOX) substrate, whose end product is the 15-epi-lipoxin A₄ (15-epi-LXA₄), an aspirin-triggered lipoxin. Our objective was to investigate whether 15-epi-LXA₄ would potentiate in vivo effects of the endocannabinoid anandamide (AEA). Catalepsy was selected as a behavioral parameter and tested 5 min after AEA injection in all experiments. AEA induced dose-dependent (200 pmol/2 μl, i.c.v.) catalepsy. A sub-dose of AEA (10 pmol/2 μl, i.c.v.) was potentiated by aspirin (300 mg/kg, p.o.) via a 5-LOX-dependent step. The cataleptic effect induced by the interaction between sub-doses of 15-epi-LXA₄ (0.01 pmol/2 μl, i.c.v.) and AEA (10 pmol/2 μl, i.c.v.) was prevented by the cannabinoid CB₁ receptors antagonist SR141716A (1 mg/kg, i.p.), but not by the antagonist of lipoxin ALX receptors Boc-2 (10 μg/kg, i.p.). While previous studies have shown that COX inhibition itself may enhance endocannabinoid effects, here we add another piece of evidence revealing that a LOX-derivative produced in consequence of COX-2 acetylation participates in this process.     

Protective effect of stilbenes containing extract-fraction from Cajanus cajan L. on Aβ25–35-induced cognitive deficits in mice

Cajanus cajan (L.) is a traditional Chinese herb medicine which contains a lot of potential active components. In the present study, we identified the effects of the stilbenes containing extract-fraction from C. cajan L. (sECC) on Aβ_25–35-induced cognitive deficits, oxidative stress and cholinergic dysfunction in mice. Mice were treated with sECC (100 and 200 mg/kg/d) for 1-week, and then received a single intracerebroventricular (i.c.v.) injection of Aβ_25–35 (5 μg/mice). Behavioral changes and neuron apoptosis in mice were evaluated using Morris water maze and TUNEL tests. Furthermore, superoxide dismutase (SOD), choline acetyl transferase (ChAT) and acetylcholine esterase (AchE) activity in hippocampus and cortex were analyzed by spectrophotometric method. The data showed that consumption of sECC (200 mg/kg) significantly ameliorated the cognitive deficits and neuron apoptosis caused by i.c.v. injection of Aβ_25–35. At the same time, the decreased SOD and ChAT activity in hippocampus and cortex were markedly increased by sECC (200 mg/kg). sECC has no effect on AchE activity in hippocampus and cortex. These findings suggest that sECC may be a potential candidate for the development of therapeutic agents to manage cognitive impairment associated with Alzheimer's disease (AD) through increasing the activity of ChAT and anti-oxidative mechanism.     

Hyperlocomotion and paw tremors are two highly quantifiable signs of SR141716-precipitated withdrawal from delta9-tetrahydrocannabinol in C57BL/6 mice

Increasing evidence suggests that marijuana abstinence leads to clinically significant withdrawal symptoms in humans. In mouse models, following chronic treatment with delta9-tetrahydrocannabinol (THC), administration of the selective cannabinoid CB1 receptor antagonist SR141716 (rimonabant) elicited varying behavioral responses, depending on mouse strain and dosing regimen. In the present study, C57BL/6 mice were injected s.c. with THC (25 mg/kg) or vehicle twice daily for 4.5 days. SR141716 (15 mg/kg) was administrated i.p. 4 h following the last THC treatment. During a 2-h observation period immediately following the SR141716 challenge, the total locomotor, ambulatory and stereotypic activities of THC-treated mice were 4.1, 3.3, and 3.8 times those of vehicle-treated mice, respectively. The number of paw tremors elicited in THC-treated mice was 111 ± 11 during the 45 min immediately following SR141716, whereas only 1.1 ± 0.4 was associated with vehicle-treated animals. In contrast, the number of scratching bouts was higher in vehicle-treated (182 ± 20) vs THC-treated (17 ± 4) mice. The present study is the first to demonstrate hyperlocomotion as an explicit sign of THC abstinence in mice. Together with paw tremors, the two unambiguous withdrawal signs may permit highly quantitative investigation of THC abstinence in C57BL/6 mice and may facilitate investigation of the mechanisms involved via both pharmacological and genetic manipulations, and ultimately potential treatments for cannabis dependence.     

Involvement of nitric oxide system in enhancement of morphine-induced conditioned place preference by agmatine in male mice

Agmatine recently has been suggested as a neurotransmitter, is able to interact with various effects of morphine like analgesia and dependence. In this study, the effects of agmatine on rewarding properties of morphine, and the possible involvement of nitric oxide (NO) system has been evaluated in an unbiased conditioned place preference (CPP) paradigm. Agmatine (1, 5 and 10 mg/kg, i.p.) alone induced neither CPP nor conditioned place aversion (CPA). Morphine (0.01, 0.05, 0.1 and 0.5 mg/kg, s.c.), while unable to show CPP or CPA, induced CPP in mice pretreated with agmatine. L-arginine (200 mg/kg, i.p.), a NO precursor, significantly enhanced the effect of agmatine (5 mg/kg) on morphine (0.5 mg/kg)-induced place preference. N^G-nitro-l-arginine methyl ester (l-NAME; 2.5 mg/kg, i.p.), a non specific nitric oxide synthase (NOS) inhibitor, and aminoguanidine (50 and 100 mg/kg, i.p.), a specific inducible NOS inhibitor, significantly reduced the effect of agmatine (5 mg/kg) on morphine (0.5 mg/kg)-induced place preference. These results suggest the possible involvement of inducible nitric oxide system in potentiating effects of agmatine on morphine-induced place preference.     

Activation of α2-adrenoceptors in the lateral hypothalamus reduces pilocarpine-induced salivation in rats

Anti-hypertensive drugs that act on central α₂-adrenoceptors and imidazoline receptors usually cause dry mouth in patients. A central area important for the control of salivary secretion and also for the effects of α₂-adrenoceptor activation is the lateral hypothalamus (LH). Therefore, in the present study we investigated the effects of the injections of moxonidine (an α₂-adrenoceptor and imidazoline agonist) alone or combined with RX 821002 (α₂-adrenoceptor antagonist) into the LH on the salivation induced by intraperitoneal (i.p.) pilocarpine (cholinergic muscarinic agonist). Male Holtzman rats with stainless steel cannula implanted into the LH were used. Saliva was collected using pre-weighted small cotton balls inserted into the animal’s mouth under ketamine anesthesia. Salivation induced by i.p. pilorcarpine (4 μmol/kg of body weight) was reduced by the injection of moxonidine (10 and 20 nmol/0.5 μl) into the LH (222 ± 46 and 183 ± 19 mg/7 min, vs. vehicle: 480 ± 30 mg/7 min). The inhibitory effect of moxonidine on pilocarpine-induced salivation was abolished by prior injections of RX 821002 (160 and 320 nmol/0.5 μl) into the LH (357 ± 25 and 446 ± 38 mg/7 min). Injections of the α₁-adrenoceptor antagonist prazosin (320 nmol/0.5 μl) into the LH did not change the effects of moxonidine. The results show that activation of α₂-adrenoceptors in the LH inhibits pilocarpine-induced salivation, suggesting that LH is one of the possible central sites involved in the anti-salivatory effects produced by the treatment with α₂-adrenoceptor agonists.     

A 5-lipoxygenase inhibitor,FR110302, inhibits ozone-induced airway hyperresponsiveness in guinea pigs and dogs

Airway hyperresponsiveness is a key feature of asthma, and attenuating airway hyperresponsiveness is an important part of asthma therapy. In the present study we examined the inhibitory effect of a potent 5-lipoxygenase inhibitor, FR 110302, on airway hyperresponsiveness induced by ozone exposure in guinea pigs and dogs. Respiratory resistance (R _rs) was measured by a forced oscillation method. Airway responsiveness was determined from the dose-response curve ofR _rs to acetylcholine. Guinea pigs were exposed to 2.5 ppm ozone for 1 h. In a control group of guinea pigs, log PC100 (the index of the ozone-induced airway hyperresponsiveness) was 0.58±0.04 (log mg/ml). Treatment with FR110302 (10 or 100 mg/kg p.o.) significantly diminished log PC100 (10 mg/kg; 0.22±0.10; 100 mg/kg; 0.11±0.06). Dogs were exposed to 3 ppm ozone for 2 h. In a control group of dogs, logD _min (another index of the ozone-induced airway hyperresponsiveness) was 1.24±0.15 (log unit). Treatment with FR110302 (1 or 3.2 mg/kg p.o.) significantly diminished logD _min (1 mg/kg: 0.60±0.18; 3.2 mg/kg: 0.27±0.12). These results suggest that FR110302 may be a useful drug for attenuating airway hyperresponsiveness in asthmatic patients.     

Pharmacological and histopathological characterization of <Emphasis Type="Italic">Bothrops lanceolatus</Emphasis> (Fer de lance) venom-induced edema

Objective: Bothrops venoms cause local edema, pain, hemorrhage and necrosis. In this study, we investigated the ability of Bothrops lanceolatus venom to cause edema in rat hind paws and examined the mediators involved. Materials and methods:Hind paw edema was induced in male Wister rats by the subplantar injection of venom (12.5–100 g/paw) in the absence and presence of antagonists. Edema was quantified by hydroplethysmometry at 0.25, 0.5, 2, 4, 6 and 24 h post-injection and was expressed as the percentage increase relative to the contralateral (control) paw. The ability of the venom to release histamine from rat peritoneal mast cells was also assessed. Results:Venom caused dose- and time-dependent edema that was maximal within 15 min but disappeared after 24 h and was accompanied by hemorrhage. Dexamethasone (1 mg/kg, s.c.), methysergide (6 mg/kg, i.p.), HOE 140 (0.6 mg/kg, i.v.) and mepyramine (6 mg/kg, i.p.) significantly (p < 0.05) reduced edema formation, whereas indomethacin (10 mg/kg, i.p.) was ineffective. Dialysis did not affect venom-induced edema. Venom (1, 10 and 30 g/ml) caused a concentration-dependent release of histamine (13 ± 1%, 61.9 ± 4.6% and 73.6 ± 2.4%, respectively; n = 5) from rat peritoneal mast cells in vitro. Histological analysis confirmed the presence of edema, hemorrhage and neutrophil infiltration. Pretreating the venom with EDTA partially inhibited the edema and hemorrhage, but did not affect the migration of neutrophils. Conclusions: B. lanceolatus venom produced dose- and time-dependent edema in rat paws. This edema was not dependent on low molecular weight substances in the venom, but was partially dependent on a hemorrhagin and also involved the release of arachidonic acid metabolites, bradykinin, histamine and serotonin.Received 22 May 2003; returned for revision 4 July 2003; accepted by M. J. Parnham 14 January 2004