Increase In Tail-flick Latency Research Articles

Activation of a Gq-coupled membrane estrogen receptor rapidly attenuates α2-adrenoceptor-induced antinociception via an ERK I/II-dependent, non-genomic mechanism in the female rat

Though sex differences in pain and analgesia are known, underlying mechanisms remain elusive. This study addresses the selective contribution of membrane estrogen receptors (mERs) and mER-initiated non-genomic signaling mechanisms in our previously reported estrogen-induced attenuation of α2-adrenoceptor-mediated antinociception. By selectively targeting spinal mERs in ovariectomized female rats using β-estradiol 6-(O-carboxy-methyl)oxime bovine serum albumin (E2BSA) (membrane impermeant estradiol analog), and ERα selective agonist 4,4′,4″-(4-propyl-[1H]-pyrazole-1,3,5-triyl)trisphenol (PPT), ERβ selective agonist 2,3-bis(4-hydroxyphenyl)-propionitrile (DPN), G-protein-coupled estrogen receptor 30 (GPR30) agonist G1 and Gq-coupled mER (Gq-mER) agonist STX, we provide strong evidence that Gq-mER activation may solely contribute to suppressing clonidine (an α2-adrenoceptor agonist)-induced antinociception, using the nociceptive tail-flick test. Increased tail-flick latencies (TFLs) by intrathecal (i.t.) clonidine were not significantly altered by i.t. PPT, DPN, or G1. In contrast, E2BSA or STX rapidly and dose-dependently attenuated clonidine-induced increase in TFL. ICI 182,780, the ER antagonist, blocked this effect. Consistent with findings with the lack of effect of ERα and ERβ agonists that modulate receptor-regulated transcription, inhibition of de novo protein synthesis using anisomycin also failed to alter the effect of E2BSA or STX, arguing against a contribution of genomic mechanisms. Immunoblotting of spinal tissue revealed that mER activation increased levels of phosphorylated extracellular signal-regulated kinase (ERK) but not of protein kinase A (PKA) or C (PKC). In vivo inhibition of ERK with U0126 blocked the effect of STX and restored clonidine antinociception. Although estrogen-induced delayed genomic mechanisms may still exist, data presented here indicate that Gq-mER may solely mediate estradiol-induced attenuation of clonidine antinociception via a rapid, reversible, and ERK-dependent, non-genomic mechanism, suggesting that Gq-mER blockade might provide improved analgesia in females.

Study the antinociceptive effect of intracerebroventricular injection of aqueous extract of origanum vulgare leaves in rat: possible involvement of opioid system.

The aim of study was to investigate the antinociceptive effect of intracerebroventricular (ICV) microinjection of Origanum vulgare (ORG) extract and possible involvement of opioid receptors. Cannula was inserted into left ventricle of male rats. Five days after surgery Tail Flick Latency (TFL) was measured after ICV microinjection of, ORG (1, 3 and 6 µg / rat). Effective dose of ORG was injected ICV in concomitant with morphine (2 mg/kg, IP), naloxone (2 mg / kg, IP) and saline (0.5 µl/rat) and TFL was recorded. The co- administrationof ORG extract with morphine showed a significant increase in TFL and naloxone, pretreatment significantly inhibited the antinociceptive activity of ORG and morphine. The aqueous extract of ORG possesses antinociceptive activities in the tail-flick test in a dose dependent manner. ORG - induced antinociception may have been mediated by opioid systems.

Morphine deteriorates spatial memory in sodium salicylate treated rats

Tolerance and cross-tolerance for the effects of morphine (M) and sodium salicylate on nociception and learning were examined. The anti-nociceptive effects were measured by using the classic tail flick (TF) and hot plate (HP) tests and learning was measured with the Morris water maze (MWM). Tolerance or cross-tolerance was induced by daily injection (i.p.) of morphine sulfate (10mg/kg for 7 days) or sodium salicylate (300mg/kg for 6 days). The injection of sodium salicylate increased both TF and HP latencies. This anti-nociceptive effect was progressively decreased across six injections and tolerance to sodium salicylate was developed. When M was injected to sodium salicylate-tolerant rats, a weakened anti-nociceptive effect was seen, indicating cross-tolerance to M. Acute treatment with M also increased TF latency. This anti-nociceptive effect was successively decreased across seven injections and tolerance to M was developed. When sodium salicylate was injected to M-tolerant rats, a diminished anti-nociceptive effect was seen, indicating cross-tolerance to sodium salicylate. Acute M impaired water maze performance, while chronic M and sodium salicylate had no effects on MWM performance. However, when M was injected to rats that had received sodium salicylate after each training trial for 7 days, these rats spent less time in target quadrant as compared to M and saline groups. It is concluded that chronic sodium salicylate induces tolerance to anti-nociceptive effects of M and vice versa. Also chronic salicylate may produce lasting metaplastic changes in brain mechanisms behind spatial learning and memory, which can be visualized in cross-sensitization to morphine.

Anti-inflammatory and analgesic activities of Dashanga Ghana: An Ayurvedic compound formulation

Background and Objectives : Inflammation is the self-protective reaction of tissues towards infection, irritants, or foreign substances. Though it is a part of host defence mechanism, when it becomes severe, it turns out to be a hopeless condition which causes damage of tissues; hence control of inflammation becomes essential. In Ayurvedic texts, a number of medicinal preparations to combat inflammation have been found; among them, Dashanga Yoga is one, which is said to be significant in combating inflammation. To revalidate this claim, the present experimental study was undertaken. Materials and Methods : Wistar strain albino rats weighing 200 ± 20 g and Swiss albino mice (26 ± 2 g) of either sex were used in the study. Pharmacologically validated models were used to evaluate anti-inflammatory and analgesic effects. Dashanga Yoga was administered at dose of 45 mg/kg and 65 mg/kg for rat and mouse, respectively. Results : Dashanga Yoga significantly inhibited carrageenan-induced paw edema (P < 0.01) at both three and six hours; however, it failed to suppress formalin-induced paw edema. It decreased the formation of granulation tissue non-significantly in the chronic inflamatory model. In analgesic activity, pretreatment with Dashanga Yoga failed to inhibit the early phase of pain, whereas moderate inhibition occurred in the late phase of pain in the formalin-induced paw-licking model. In the tail fl ick model, Dashanga Yoga significantly increased tail flick latency at 120, 180, and 240 minutes in comparison to the control group. Conclusion : The results revealed that Dashanga Yoga has anti-inflammatory and analgesic activity. Hence, it can be used in the management of pain and inflammatory conditions.

Anxiolytic and anti-nociceptive activity of hydroalcholic leaf extract of Cnidoscolous acontifolius

The Cnidoscolous acontifolius hydroalcholic leaf extract (CAHLE) has been described as exhibiting biological activity in the central nervous system assays. The objectives of this study were to investigate the anxiolytic and antinociceptive effects of CAHLE in mice. Swiss albino mice (18 to 22 g) were randomly allotted to thirteen groups (n = 5 each). Groups 1 to 5 and 9 to 13 were treated with graded doses of CAHLE (100, 200, 400, 800 and 1600 mg/kg), Groups 6 and 7 received normal saline (10 ml/kg) and diazepam (1 mg/kg), respectively, while group 8 received 5 mg/kg of pentazocine hydrochloride (HCl). All drugs and test compounds were administered via intraperitoneal route except for pentazocine which was given subcutaneously. Data analysis was by one factor analysis of variance (ANOVA) followed by post hoc analysis using Student Newman Kuels multiple comparison tests. CAHLE treated mice showed increase open arm entries and open arm exploration time compared to control group in the elevated plus maze test. CAHLE treated mice also exhibited a time-dependent and a dose-dependent increase in tail flick latency. CAHLE treated mice also exhibited longer lasting protection from pain compared to standard. The study concluded that CAHLE possesses mild anxiolytic and analgesic properties to warrant its use in treatment of anxiety and relief of pain. Key words: Anxiolytic, antinociceptive, central nervous system.

Changes in Cannabinoid Receptor Subtype 1 Activity and Interaction with Metabotropic Glutamate Subtype 5 Receptors in the Periaqueductal Gray- Rostral Ventromedial Medulla Pathway in a Rodent Neuropathic Pain Model

This study analyzed the effect of intra-ventrolateral periaqueductal grey (VL PAG) cannabinoid receptor (CB) stimulation on pain responses and rostral ventromedial medulla (RVM) neural activity in the chronic constriction injury (CCI) model of neuropathic pain in rats. Interaction between CB1 and metabotropic glutamate 1 and 5 (mGlu(1)/mGlu(5)) receptors was also investigated together with the expression of the CB1 receptor associated Gαi3 and cannabinoid receptor interacting 1a (CRIP 1a) proteins and the endocannabinoid synthesising and hydrolysing enzymes. In rats not subjected to CCI-induced pain, intra-VL PAG (R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl) pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone mesylate (WIN 55,212-2) (2-4-8 nmol), a CB receptor agonist, increased the tail flick latency and changed the ongoing activity of RVM OFF and the tail flick-related activity of the ON and OFF cells, accordingly. These effects were prevented by SR141716A and MPEP, selective CB(1) and mGlu(5) receptor antagonists, respectively, though not by CPCCOEt, a selective mGlu(1) receptor antagonist. A higher dose up to 16 nmol of WIN 55,212-2 was necessary to increase tail flick latency and change ON and OFF cell activity in CCI rats. Consistently, CCI rats showed a decrease in the expression of CB(1) receptors, NAPE-PLD, Gαi3 and CRIP 1a proteins;the expression of diacylglycerol lipase A (DAGLA) was increased while fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MGL) did not change. As in control rats, MPEP and SR141716A also blocked WIN 55,212-2- induced effects in CCI rats. These data demonstrate a down regulation of the endocannabinoid system and a functional interaction between mGlu(5) and CB(1) receptors for cannabinoid-mediated effect in the PAG-RVM pain circuitry in neuropathic pain inflicted rats.

Attenuating effect of seeds of Adenanthera pavonina aqueous extract in neuropathic pain in streptozotocin-induced diabetic rats: an evidence of neuroprotective effects

The aim of present study was to investigate the attenuating effects of Adenanthera pavonina L., Leguminosae-Mimosaceae seeds aqueous extract (APSAE), in streptozotocin (STZ)-induced diabetic neuropathy in rats. APSAE (50, 100 and 200 mg/kg per day) was given to diabetic rats for twelve weeks. Cold and hot water tail immersion tests, photoactometer and Rota-rod tests were performed to assess degree of colder, thermal, spontaneous motor activity and motor co-ordination changes respectively at different time intervals i.e., week 0, 4, 8 and 12. Tissue superoxide anion and total calcium levels were determined after twelve weeks to assess biochemical alterations. Histopathological evaluations of sciatic nerve were also performed to assess nerve damage. APSAE treatment increased tail flick latency significantly in diabetic rats. APSAE also reduced superoxide anion and total calcium levels. These results suggested that APSAE has attenuated development of diabetic neuropathy in streptozotocin-induced diabetic rats when compared with pregabalin (10 mg/kg, p.o.) and could be beneficial in preventing the progression of diabetic nephropathy.

Endogenous Endomorphin-2 Contributes to Spinal ĸ-Opioid Antinociception

Background/Aims: Multiple opioid receptor (OR) types and endogenous opioid peptides exist in the spinal dorsal horn and there may be interactions among these receptor types that involve opioid peptides. In a previous study we observed that antinociceptive effects of the selective ĸ-opioid receptor (ĸOR) agonist, U50,488H, was attenuated in µ-opioid receptor (µOR) knockout mice as compared to wild-type mice when administered spinally. This suggests that an interaction between ĸORs and µORs exits in the spinal cord. The present study was aimed at investigating whether endogenous opioid peptides were involved in such interaction. Methods: We examined whether the presence of antibodies to endogenous opioid peptides, endomorphin-2, met-enkephalin and dynorphin A affected the antinociceptive effects of spinal U50,488H in rats. The tail-flick test was used to assess pain thresholds. Results: The increase in tail-flick latency after spinal U50,488H was attenuated when the rats were pretreated intrathecally with antiserum against endomorphin-2. Pretreatments with antisera against met-enkephalin and dynorphin A had no effect on U50,488H antinociception. The antisera alone did not affect pain threshold. Conclusion: The results suggest that endomorphin-2, an endogenous opioid peptide highly selective to the µOR, plays a role in antinociception induced by ĸOR activation in the spinal cord.

Dopamine Release is Involved in Antinociceptive Effect of Theophylline

ABSTRACTThe methylxanthines, e.g., theophylline, are widely used for the treatment of bronchial asthma. Additionally, a pain relieving effect of theophylline has been reported in patients as well as in experimental animals. The mechanism of this antinociceptive action is not clear. In this study, involvement of dopaminergic system in theophylline-induced antinociception was evaluated using tail flick test model. Swiss albino mice, (either sex, weighing 25–30 g) with base line tail flick latencies (TFL) between 2.0 and 3.5 s, were used. TFL was recorded before and at intervals of 15, 30, 45, and 60 min. after drug treatment. The experimental protocol was duly approved by the Institutional Animal Ethics Committee, All India Institute of Medical Sciences, New Delhi, India. To determine the role of dopaminergic system, the mice were pretreated with either D1 or D2 dopaminergic receptor antagonists SCH 23390 and haloperidol, respectively, prior to treatment with theophylline. Another group of animals received apomorphine along with theophylline. The dose of theophylline used, i.e., 10 mg/kg, intraperitoneally (i.p.), had shown a significant increase in TFLs. The theophylline-induced antinociception, 10 mg/kg, i.p., was reversed by pretreatment with both D1 and D2 dopaminergic receptor antagonists SCH 23390 and haloperidol as well as with apomorphine (1 mg/kg) pretreatment. The results suggest that theophylline-induced antinociception is due to release of dopamine.

Amitriptyline prolongs the antihyperalgesic effect of 2‐ or 100‐Hz electro‐acupuncture in a rat model of post‐incision pain

The mechanisms through which electro-acupuncture (EA) and tricyclic antidepressants produce analgesia seem to be complementary: EA inhibits the transmission of noxious messages by activating supraspinal serotonergic and noradrenergic neurons that project to the spinal cord, whereas tricyclic antidepressants affect pain transmission by inhibiting the reuptake of norepinephrine and serotonin at the spinal level. This study utilized the tail-flick test and a model of post-incision pain to compare the antihyperalgesic effects of EA at frequencies of 2 or 100 Hz in rats treated with intraperitoneal or intrathecal amitriptyline (a tricyclic antidepressant). A gradual increase in the tail-flick latency (TFL) occurred during a 20-min period of EA. A strong and long-lasting reduction in post-incision hyperalgesia was observed after stimulation; the effect after 2 Hz lasting longer than after 100-Hz EA. Intraperitoneal or intrathecal amitriptyline potentiated the increase in TFL in the early moments of 2- or 100-Hz EA, and the intensity of the antihyperalgesic effect of 100-Hz EA in both the incised and non-incised paw. In contrast, it did not significantly change the intensity of the antihyperalgesic effect of 2-Hz EA. The EA-induced antihyperalgesic effects lasted longer after intraperitoneal or intrathecal amitriptyline than after saline, with this effect of amitriptyline being more evident after 100- than after 2-Hz EA. The synergetic effect of amitriptyline and EA against post-incision pain shown here may therefore represent an alternative for prolonging the efficacy of EA in the management of post-surgical clinical pain.

A reassessment of stress-induced “analgesia” in the rat using an unbiased method

An increased tail-flick latency to noxious heat during or after stress in the rodent is usually interpreted as a stress-induced reduction in pain sensitivity and often described as a form of stress-induced “analgesia.” However, this measure is an indirect and flawed measure of the change in nociceptive threshold to noxious heat. A major confound of the latency measure is the initial temperature of the tail, which can drop down to room temperature during stress, the consequence of a marked sympathetically mediated vasoconstriction in the skin of the extremities. We addressed this issue with tail-flick tests during contextual fear using infrared thermography to monitor temperature changes and a CO2 laser to deliver the heat stimulus. The experiment revealed a 4.2°C increase of the nociceptive threshold, confirming a true antinociceptive effect. However, its contribution to the increased withdrawal latency was less than two-thirds (63.2%). Nearly one-third (32.2%) was due to the drop in tail temperature (4.4°C), which also slowed conduction along sensory fibers (2.2%, included in the 32.2%). The remaining 4.6% was due to an increase in decisional/motor latency. This new unbiased method establishes beyond doubt that a conditioned stress response is associated with true antinociception to noxious heat. It also confirms that stress-induced changes in skin temperature can be a major confound in tail-flick tests. The present study shows, for the first time, the exact contribution of these two components of the tail-flick latency for a stress response.Less than two-thirds of the increase in tail-flick latency to noxious heat, evoked by conditioned fear, reflects true antinociception. The remaining is due to skin vasoconstriction.

Exploring the possible mechanisms of action behind the antinociceptive activity of Bacopa monniera

Aim:Earlier studies have demonstrated that Bacopa monniera (BM), a plant described in Ayurveda for many CNS actions was found to exhibit antidepressant (methanolic extract at 20mg/kg and 40mg/kg p.o.) as well as antinociceptive activity (aqueous extract (AE) at 80 mg/kg, 120 mg/kg and 160 mg/kg p.o.). The present study sought to explore the possible mechanisms of antinociceptive effects of aqueous extract of Bacopa monniera (AEBM) at 80 mg/kg, 120 mg/kg and 160 mg/kg given orally.Materials and Methods:AEBM was given singly as well as with selective α2 receptor blocker Yohimbine, selective β1 receptor blocker Atenolol, serotonin receptor antagonist Cyproheptadine and a non-selective opioid receptor antagonist naloxone in experimental groups of mice and rats under strict protocols and conditions.Results:We observed that the antinociceptive effects of AEBM in the acetic acid writhing test was prevented by prior treatment with the selective Yohimbine (1 mg/kg, i.p; 14.50 ± 2.26 and 37.17 ± 2.14 writhes in the AEBM-treated and yohimbine pre-treated AEBM groups, respectively) and selective β1 Atenolol receptor blocker (1 mg/kg, i.p; 14.50 ± 2.26 and 31.00 ± 5.44 writhes in the AEBM-treated and yohimbine pre-treated AEBM groups, respectively). In the formalin test, the reduction in licking time with AEBM was found to be reversed by prior treatment with serotonin receptor antagonist Cyproheptadine (1 mg/kg, i.p; 47.33 ± 2.25s and 113.50 ± 3.83s (during phase I i.e. 0-5 min) and 26.67 ± 3.83s and 88.17 ± 7.27s (during phase II i.e. 20-30 min) in the AEBM-treated and Cyproheptadine pre-treated AEBM groups, respectively). The % increase in tail flick latency with AEBM was prevented by prior treatment with the non-selective opioid receptor antagonist naloxone (2mg/kg, i.p; 282.35 and 107.35 in the AEBM-treated and naloxone-treated groups, respectively).Conclusions:Our results indicate, that the endogenous adrenergic, serotonergic and opioidergic systems are involved in the analgesic mechanism of action of the aqueous extract of Bacopa monniera.

Evidence for Improved Neuropharmacological Efficacy and Decreased Neurotoxicity in Mice with Traditional Processing ofRhizoma Arisaematis

Rhizoma Arisaematis (RA, the rhizome of Pinellia pedatisecta Schott) is a traditional Chinese medicine commonly used in the treatment of convulsions, inflammation, and cancer. Despite the fact that it has been used for more than 2000 years, the pharmacological and toxic effects of traditionally processed products of RA are still unclear. In this study, we attempted to investigate the effects exerted by untreated crude RA and different preparations of RA treated with alumen in combination with ginger juice (Zhinanxing) or bile juice (Dannanxing) in ICR mice. The results showed that both the Zhinanxing and Dannanxing water extracts exerted significantly increased sedative effects, as indicated by the inhibitory effects on ambulatory distances, jumps, vertical-plane entries, and prolonged pentobarbital-induced sleeping time. The extracts also exerted significantly increased analgesic effects (increase of tail flick latency in nociceptive testing) in mice than did the unprocessed crude RA after oral administration for one to three days, and effects persisted 18 days after the cessation of treatment. By contrast, the toxic effects, such as an increase in stereotype-1 episodes of locomotor activities and reduction of the retention time on a rotating rod (motor equilibrium dysfunction), were observed only in mice treated with the unprocessed crude RA for three consecutive days, and effects persisted for 18 days after the cessation of treatment. These neurotoxic effects were accompanied by an increase in plasma lipid peroxidation (LPO), decrease in whole blood nitric oxide (NO(x)) levels, and inhibition of Na(+)/K(+)-ATPase activities in membrane fractions of erythrocytes and in the cerebral cortex. In conclusion, these findings provide scientific evidence that the processed RA indeed possesses not only enhanced neuropharmacological efficacy but also reduced neurotoxic effects as compared to the unprocessed crude RA. The signaling of NO(x)/oxidative stress/Na(+)-K(+)- ATPase activities played a role, at least in part, in the underlying mechanisms of neurotoxic effects induced by the crude RA.

Determination of α2-adrenoceptor and imidazoline receptor involvement in augmentation of morphine and oxycodone analgesia by agmatine and BMS182874

Studies have demonstrated that clonidine (α2-adrenoceptor and imidazoline receptor agonist) and BMS182874 (endothelin ETA receptor antagonist) potentiate morphine and oxycodone analgesia. Agmatine, an endogenous clonidine-like substance, enhances morphine analgesia. However, its effect on oxycodone analgesia and its interaction with endothelin ETA receptor antagonists are not known. The present study was performed to determine the effect of agmatine on morphine and oxycodone analgesia and the involvement of α2-adrenoceptors, imidazoline receptors, opioid receptors, and endothelin receptors. Antinociception at various time intervals was determined by the tail-flick latency method in mice. Agmatine produced dose-dependent increase in tail-flick latency, while BMS182874 did not produce any change over the 360-min observation period. Agmatine significantly potentiated morphine as well as oxycodone analgesia which was not altered by BMS182874. BMS182874 pretreatment did not increase the analgesic effect produced by agmatine alone. Agmatine-induced potentiation of morphine and oxycodone analgesia was blocked by idazoxan (imidazoline receptor/α2-adrenoceptor antagonist) and yohimbine (α2-adrenoceptor antagonist). BMS182874-induced potentiation of morphine or oxycodone analgesia was not affected by yohimbine. However, idazoxan blocked BMS182874-induced potentiation of oxycodone but not morphine analgesia. This is the first report demonstrating that agmatine potentiates not only morphine but also oxycodone analgesia in mice. Potentiation of morphine and oxycodone analgesia by agmatine appears to involve α2-adrenoceptors, imidazoline receptors, and opioid receptors. In addition, imidazoline receptors may be involved in BMS182874-induced potentiation of oxycodone but not morphine analgesia. It is concluded that agmatine may be used as an adjuvant in opiate analgesia.

Midazolam enhances the analgesic properties of dexmedetomidine in the rat

ObjectiveTo investigate the analgesic properties of different dose combinations of midazolam and dexmedetomidine administered intraperitoneally (IP) in the rat. Study designProspective experimental trial. AnimalsSeventy adult male Sprague Dawley rats weighing 250-300 g. MethodsDexmedetomidine (D) 0.03, 0.06, 0.09, 0.12, 0.15, 0.18, 0.21 mg kg−1 and midazolam (M) 5, 10, 25, 50 mg kg−1 were administered IP, alone then in combinations ranging from 0.03 D:5 M to 0.18 D:30 M mg kg−1. Analgesia was evaluated using the tail-flick test at time 0 (before injection), 15, 30, 45, 60 and 75 minutes. ResultsMidazolam at all doses administered (5-50 mg kg−1) did not significantly change tail-flick latencies from baseline values whereas D showed clear dose-dependent increases in tail-flick latency for doses administered in the range of 0.03-0.18 mg kg−1. Tail-flick latencies in rats administered D + M combinations were significantly greater than D alone (p<0.05). ConclusionsA dose-related analgesic effect was demonstrated for D in the rat, which was enhanced by co-administration of M. Clinical relevanceThe combination of D + M administered IP to rats at doses of 0.12:20 and 0.09:15 mg kg−1 was shown to be a good combination to provide sedation/analgesia with a duration of action greater than 60 minutes. The onset of sedation was rapid (1-3 minutes), and onset of profound analgesia was reached within 5-10 minutes.

Two histamine H2 receptor antagonists, zolantidine and cimetidine, modulate nociception in cholestatic rats

Cholestasis is associated with analgesia. The histamine H(2) receptors control pain perception. The involvement of histamine H(2) receptors on modulation of nociception in a model of elevated endogenous opioid tone, cholestasis, was investigated in this study using zolantidine and cimetidine as two H(2) receptor antagonists and dimaprit as a selective H(2) receptor agonist. Cholestasis was induced by ligation of the main bile duct using two ligatures and transsection of the duct at the midpoint between them. A significant increase in tail-flick latencies was observed in cholestatic rats compared to non-cholestatic rats. Administration of zolantidine (10, 20 and 40 mg/kg) and cimetidine (25, 50 and 100 mg/kg) in the cholestatic group significantly increased tail-flick latencies while dimaprit (10 and 20 mg/kg) injection in the cholestatic group decreased tail-flick latencies compared to the saline treated cholestatic group. Antinociception produced by injection of zolantidine and cimetidine in cholestatic rats was attenuated by co-administration of naloxone. Drug injection in non-cholestatic rats did not alter tail-flick latencies compared to the saline treated rats at any of the doses. At the doses used here, none of the drugs impaired motor coordination as revealed by the rota rod test. These data show that the histamine H(2) receptor system may be involved in the regulation of nociception during cholestasis. According to the hypothesis that increasing the nociception threshold in cholestasis may lead to a decrease in the perception of pruritus, the provision of the drugs that increase the threshold to nociception may be a novel approach to the treatment of cholestatic pruritus.

Evaluation of analgesic efficacy, gastrotoxicity and nephrotoxicity of fixed-dose combinations of nonselective, preferential and selective cyclooxgenase inhibitors with paracetamol in rats

Nonsteroidal anti-inflammatory drugs (NSAIDs) are combined with paracetamol (PCM) with a view to enhance analgesic efficacy and reduce gastric toxicity. However, there are reports of enhanced nephrotoxicity with nonselective NSAID with PCM combinations. The present study investigated the analgesic efficacy, gastrotoxicity and nephrotoxicity of nonselective, preferential and selective cyclooxgenase inhibitors and their combination with PCM in rats. Graded doses of ibuprofen, meloxicam and celecoxib alone and their combination with fixed dose of PCM were administered to the rats by gavage for 14 days. The results showed that PCM potentiated the analgesic effect of all three classes of NSAIDs significantly as evidenced by increase in tail-flick latency in radiant heat method. Dose-dependent gastromucosal damage was produced by all the drugs, which was augmented significantly with PCM in the form of decreased total carbohydrate/protein ratio of mucin and increased gastric ulcer index. It was further confirmed by histopathology of rat’s stomach. The renal histopathology was conducted to evaluate inflammation, tubular damage, papillary necrosis, and interstitial changes. Increased nephrotoxicity was observed with all NSAIDs in dose-dependent manner and in combination with PCM. Our study revealed the augmented analgesia as well as enhanced gastrotoxicity and nephrotoxicity with all three major NSAIDs classes when combined with PCM. These findings highlighted the need for large pharmacoepidemiological studies to evaluate the magnitude of gastrotoxicity and nephrotoxicity in population who are on long-term treatment with NSAID combinations.

Towards a better understanding of the psychopharmacology of nutmeg: Activities in the mouse tetrad assay

Ethnopharmacological relevance Nutmeg, the seeds of Myritica fragrans (family Myristicaceae), is a well known kitchen spice with a long-standing reputation as a psychoactive herb. Nutmeg at high doses is considered a cheap substitute to several drugs of abuse. Earlier reports have attributed amphetamine-like activities to nutmeg. Aim of the study To characterize the neuropharmacological effects of different nutmeg extracts, administered orally and intraperitoneally, in comparison to Δ 9-terahydrocannabinol, amphetamine, and morphine. Materials and methods Methanolic (ME), dichloromethane (DE), and hexane (HE) extracts were obtained from a chromatographically fingerprinted batch of nutmeg. Biological evaluation was conducted in sets of 6–8 mice in the tetrad assay at doses ranging from 100 to 500 and 500 to 1000 mg/kg for i.p. and oral administration, respectively. Results While oral administration of all the nutmeg extracts at 500 mg/kg caused a significant increase in locomotor activity, the i.p. administration of DE showed significant reduction in rectal temperature along with a significant increase in tail flick latency at 300 mg/kg. A significant decrease in core body temperature was observed with HE at 100 mg/kg, while higher doses caused significant increases in hot plate latency. Conclusion Different behavioral effects were observed that varied by the type of extract as well as by the route of administration.

Estrogen-dependent, sex-specific modulation of mustard oil-induced secondary thermal hyperalgesia by orphanin FQ in the rat

Activation of opioid receptor-like 1 receptor (ORL 1) by intrathecal administration of orphanin FQ (OFQ), an endogenous ligand for the ORL 1 receptor, has been shown to produce antinociception. In addition, we have recently shown gonadal hormone-dependent, sex-specific modulation of acute spinal nociception such that estrogen attenuated OFQ-induced antinociception in the female whereas testosterone was required for the expression of antinociception in the male. However, sex-related differences in the role of OFQ under hyperalgesic conditions are unknown. Hence, we investigated whether OFQ produces sex-specific modulation of mustard oil-induced secondary thermal hyperalgesia in the rat. Mustard oil application to the hind limb significantly reduced the tail-flick latencies (TFL) in male, and ovariectomized (OVX), estradiol treated ovariectomized (OVX + E), proestrous (ProE) and diestrous (DiE) females. Intrathecal administration of OFQ not only attenuated mustard oil-induced decrease in TFLs, i.e. reversed hyperalgesia, but also led to a significant increase in TFLs above the baseline, i.e. produced antinociception in male, OVX, and diestrous rats. However, OFQ failed to alter TFLs in proestrous or OVX + E females, thus these two groups with elevated estrogen levels remained hyperalgesic following mustard oil treatment. These findings demonstrate that OFQ modulates mustard oil-induced secondary hyperalgesia in an estrogen-dependent, sex-specific manner.

Muscarinic and α 1-adrenergic mechanisms contribute to the spinal mediation of stimulation-induced antinociception from the pedunculopontine tegmental nucleus in the rat

The effects of intraperitoneal (i.p.) or intrathecal (i.t.) injection of antagonists of acetylcholine, noradrenaline, serotonin, dopamine, opioids and GABA on stimulation-produced antinociception (SPA) from the pedunculopontine tegmental nucleus (PPTg) of rats were studied using the tail-flick test. The electrical stimulation of the PPTg produced a strong and long-lasting increase in tail-flick latency. The intensity and duration of the effect were significantly reduced in rats pretreated with i.p. or i.t. atropine (a non-selective muscarinic cholinergic antagonist), or i.t. phenoxybenzamine or WB 4101 (non-selective and selective α 1-adrenergic antagonists, respectively). Intraperitoneal phenoxybenzamine, i.p. or i.t. methysergide or naloxone (non-selective serotonin and opioid antagonists, respectively), or i.t. idazoxan (a selective α 2-adrenergic antagonist) only reduced the duration of the effect. The duration of SPA from the PPTg was increased by i.t. phaclofen (a GABA B antagonist). The effect from the nucleus was not altered following i.t. bicuculline (a GABA A antagonist), or i.p. or i.t. mecamylamine, propranolol or haloperidol (non-selective nicotinic cholinergic, β-adrenergic and dopaminergic antagonists, respectively). Thus, SPA from the PPTg involves the spinal activation of muscarinic and α 1-adrenergic but not nicotinic cholinergic, β-adrenergic and dopaminergic mechanisms. Serotonergic, endogenous opioid and α 2-adrenergic mechanisms are involved in the duration but not in the intensity of the effect.