Cross-tolerance between spinal neostigmine and morphine in the rat

Background. Direct or indirect acting cholinergic muscarinicagonists such as neostigmine, are potent antinociceptives whenadministered intrathecally (i.t.). This study examines whetherspinal neostigmine tolerance and cross-tolerance to spinal morphineoccurs. Methods. Rats (32/group) were implanted with miniosmotic pumpsdelivering either i.t. saline 1 µl h^–1 (S), morphine10 nmol µl^–1 h^–1 (M), or neostigmine 3 nmolµl^–1 h^–1 (N). Latencies (infrared thermalwithdrawal rear paw) were measured daily for 6 days after whichfour animals from each group were given one i.t. challenge doseof morphine (m) 0.1, 1, 10, or 100 nmol, or neostigmine (n)0.3, 3, 10, or 30 nmol. Results. Neostigmine and morphine-infused animals both developedtolerance to spinal neostigmine, but neostigmine-infused animalsshowed no significant cross-tolerance to spinal morphine; meanED₅₀ nmol (CI 95%) dose–response values were Sn 2.6 (1.9–3.5),Mn 15.6 (9.9–24.6)*, Nn 18.7 (11.7–29.8)*, Sm 0.7(0.4–1.1), Nm 1.2 (0.8–2.0), Mm 152 (50–461)*(*significance vs saline infused control group). Conclusion. Thus, unidirectional cross-tolerance from morphineto neostigmine was evident. Previous studies suggest morphinehas a cholinergic mechanism of action partially accounting forits antinociceptive effect, which may explain this observedunidirectional cross-tolerance. Br J Anaesth 2003; 91: 427–9     

The interaction between intrathecal neostigmine and GABA receptor agonists in rats with nerve ligation Injury

Nerve ligation injury may produce a pain syndrome that includes tactile allodynia. Reversal effects on tactile allodynia have been demonstrated after the intrathecal administration of gamma-aminobutyric acid (GABA) receptor agonists or cholinesterase inhibitors in rats. We examined the drug interactions between neostigmine and muscimol or baclofen in a rat model of nerve ligation injury. Rats were prepared with tight ligation of the left L5-6 spinal nerves and chronic intrathecal catheter implantation. Tactile allodynia was measured by applying von Frey filaments ipsilateral to the lesioned hindpaw. Thresholds for paw withdrawal were assessed. Neostigmine (0.3-10 microg), muscimol (0.1-10 microg), and baclofen (0.1-3.0 microg) were administered to obtain the dose-response curve and the 50% effective dose (ED(50)). Fractions of ED(50) values were administered intrathecally to establish the ED(50)s of drug combinations (neostigmine-muscimol and neostigmine-baclofen). The drug interactions were performed. Intrathecal neostigmine, muscimol, baclofen, and their combinations produced a dose-dependent increase in withdrawal threshold of the lesioned hindpaw. Both analyses revealed a synergistic interaction for the neostigmine-muscimol combination, whereas the effect of the neostigmine-baclofen combination was additive. These results suggest that the activation of both muscarinic and GABA(A) receptors is required for synergistic interaction. IMPLICATIONS: This study indicates that drug interaction is synergistic for the neostigmine-muscimol combination, whereas the effect of the neostigmine-baclofen combination is additive. In a rat model of nerve ligation injury, neostigmine, muscimol, baclofen, and their combinations provide an antagonism on touch-evoked allodynia at the spinal level.     

Anesthetic potency of nalbuphine and interaction with morphine in rats

The contribution to anesthesia by nalbuphine was determined in rats by measurement of the reduction in the anesthetic requirement for cyclopropane produced by increasing doses of nalbuphine while maintaining a constant level of anesthesia (MAC). The respiratory effect of nalbuphine was evaluated by measurement of arterial PCO2 at this constant MAG level. The response produced by the addition of morphine to a constant dose of nalbuphine in further reducing the cyclopropane anesthetic requirement was also evaluated, as was the effect on arterial PCO2. The anesthetic contribution of nalbuphine was dose dependent until a plateau contribution of 0.22 MAC was achieved. Arterial PCO2 increased to a plateau level of 48 torr with nalbuphine administration from a PCO2 of 41 torr with cyclopropane alone. Further increase in PCO2 did not occur until exceedingly high nalbuphine doses were used. Morphine did not supplement the anesthetic contribution of nalbuphine, and there was no increase in PCO2 when morphine was added in nalbuphine during cyclopropane anesthesia. These results suggest that nalbuphine produces analgesia by acting at kappa opioid receptors and that nalbuphine binds but produces minimal effects on mu opioid receptors within the central nervous system.     

Anesthetic potency of dezocine and its interaction with morphine in rats

A new partial agonist-antagonist analgesic drug, dezocine, was evaluated in rats for its anesthetic potency using a MAC-reduction model. Respiratory effects as shown by changes in PaCO2 were also analyzed. A reduction of approximately 50% in cyclopropane MAC was found with doses of 6 mg/kg or more. This is the largest reduction for any drug of this class. PaCO2 levels increased up to 52 mm Hg with doses of dezocine up to 2 mg/kg. No evidence of reversal of respiratory depression or of further respiratory depression was found with increasing dosages. Combining dezocine with morphine resulted in a further reduction in cyclopropane MAC without a significant change in PaCO2. This suggests that dezocine acts primarily on the same receptor (mu) as morphine and that this receptor activity is further modulated by effects of dezocine on a second opioid receptor.     

Pharmacologic interaction between cannabinoid and either clonidine or neostigmine in the rat formalin test

BACKGROUND: Although spinal cannabinoid receptor agonist (WIN 55,212-2) has been shown to encounter various models of pain, the role of two subtypes of cannabinoid receptor for the antinociceptive effect of cannabinoids has not been investigated at the spinal level. Spinal alpha 2 receptor agonist (clonidine) and cholinesterase inhibitor (neostigmine) are also active in the modulation of nociception. The authors examined the properties of drug interaction after coadministration of WIN 55,212-2-clonidine, and intrathecal WIN 55,212-2-neostigmine, and further clarified the role of cannabinoid 1 and 2 receptors in cannabinoid-induced antinociception at the spinal level. METHODS: Catheters were inserted into the intrathecal space of male Sprague-Dawley rats, and 50 microl of 5% formalin solution was injected into the hind paw to evoke the pain. Isobolographic analysis was used for evaluation of pharmacologic interaction. RESULTS: Intrathecal 55,212-2, clonidine, and neostigmine dose-dependently suppressed the flinching observed during phase 1 and 2 in the formalin test. Isobolographic analysis revealed a synergistic interaction after intrathecal delivery of WIN 55,212-2-clonidine or WIN 55,212-2-neostigmine mixture in both phases. The antinociceptive effect of WIN 55,212-2 was antagonized by cannabinoid 1 receptor antagonist (AM 251) but not by cannabinoid 2 receptor antagonist (AM 630). No antinociceptive effect was seen after intrathecal administration of cannabinoid 2 receptor agonist (JWH 133). CONCLUSIONS: Intrathecal 55,212-2, clonidine, and neostigmine attenuate the facilitated state and acute pain. WIN 55,212-2 interacts synergistically with either clonidine or neostigmine. The antinociception of WIN 55,212-2 is mediated through the cannabinoid 1 receptor, but not the cannabinoid 2 receptor, at the spinal level.     

Antinociceptive effect of low-dose intrathecal neostigmine combined with intrathecal morphine following gynecologic surgery

BACKGROUND: The purpose of this study was to determine whether combination of 1-5 microg intrathecal neostigmine would enhance analgesia from a fixed intrathecal dose of morphine. METHODS: A total of 60 patients undergoing gynecologic surgery were randomized to one of five groups. Patients received 15 mg bupivacaine plus 2 ml of the test drug intrathecally (saline, 100 microg morphine, or 1-5 microg neostigmine). The control group received spinal saline as the test drug. The morphine group received spinal morphine as test drug. The morphine + 1 microg neostigmine group received spinal morphine and 1 microg neostigmine. The morphine + 2.5 microg neostigmine group received spinal morphine and 2.5 microg neostigmine. Finally, the morphine + 5 microg neostigmine group received spinal morphine and 5 microg neostigmine. RESULTS: The groups were demographically similar. The time to first rescue analgesic (minutes) was longer for all patients who received intrathecal morphine combined with 1-5 microg neostigmine (median, 6 h) compared with the control group (median, 3 h) (P < 0.02). The morphine group (P < 0.05) and the groups that received the combination of 100 microg intrathecal morphine combined with neostigmine (P < 0.005) required less rescue analgesics in 24 h compared with the control group. The incidence of perioperative adverse effects was similar among groups (P > 0.05). CONCLUSIONS: The addition of 1-5 microg spinal neostigmine to 100 microg morphine doubled the duration to first rescue analgesic in the population studied and decreased the analgesic consumption in 24 h, without increasing the incidence of adverse effects. The data suggest that low-dose spinal neostigmine may improve morphine analgesia.     

Intestinal inflammation and morphine tolerance alter the interaction between morphine and clonidine on gastrointestinal transit in mice

BACKGROUND: Morphine and clonidine show synergy or antagonism inhibiting gastrointestinal transit depending on their proportion and level of effect. Their interaction during morphine tolerance and intestinal inflammation were assessed. METHODS: Gastrointestinal transit in mice was evaluated with charcoal and antitransit effects expressed as percent mean values +/- SEM. Tolerance was induced with a morphine pellet (75 mg) implanted for 72 h, and inflammation with intragastric croton oil. Dose-response curves for morphine and clonidine alone and combined at a 1:1 potency ratio were obtained, and doses producing a 50% and 60% inhibition were calculated (ED50, ED60). Interaction was established by isobolograms, interaction indexes, and analysis of variance. RESULTS: In naive and tolerant mice, the combination induced linear dose-response curves up to the ED60 and then reached a plateau. In naive mice, ED50 values were as follows: morphine 1.52 +/- 0.15 mg/kg, clonidine 0.09 +/- 0.008 mg/kg, and combined 0.506 +/- 0.084 mg/kg (0.478 +/- 0.08 mg/kg morphine plus 0.028 +/- 0.004 mg/kg clonidine). During tolerance, ED50 values were as follows: morphine 9.73 +/- 0.8 mg/kg, clonidine 0.09 +/- 0.007 mg/kg, combination 0.131 +/- 0.09 mg/kg (morphine 0. 13 +/- 0.09 mg/kg plus clonidine 0.0013 +/- 0.0005 mg/kg). In both groups, the interaction was synergistic up to the ED60 and antagonistic thereafter; synergy was enhanced during tolerance. During inflammation, ED50 values were as follows: morphine 0.17 +/- 0.04 mg/kg, clonidine 0.015 +/- 0.006 mg/kg, combined 0.62 +/- 0.04 mg/kg (morphine 0.568 +/- 0.04 mg/kg plus clonidine 0.052 +/- 0.004 mg/kg); thus, potencies of morphine and clonidine increased 9.3 and 7.1 times, while the combination remained unaltered. Moreover, inflammation transformed synergy into antagonism. CONCLUSIONS: The interaction between morphine and clonidine was significantly altered during tolerance and inflammation. During tolerance, synergy was present up to 60% effect and then became antagonistic. Inflammation converted synergy to antagonism. A common pathway in signal transduction could partially explain the results.     

Effects of neostigmine on bronchoconstriction with continuous electrical stimulation in rats

Purpose  

When neostigmine is used to reverse muscle relaxants in patients with asthma without signs of airway inflammation, asthma attack is occasionally encountered. It is likely that abnormally increased electrical impulses traveling from the brain through cholinergic nerves to airway smooth muscles may be one of the pathogeneses of asthma attack. We applied continuous electrical field stimulation (c-EFS) or continuous electrical stimulation (c-ES) of low frequency to the vagal nerve of the rat in vitro and in vivo to determine the role of cholinergic nerve activation in inducing airway constriction.     

不同剂量咪达唑仑与乳化异氟醚对大鼠催眠效应的相互作用

目的 评价不同剂量咪达唑仑与乳化异氟醚对大鼠催眠效应的相互作用.方法 成年雄性SD大鼠125只,体重240～300 g,随机分为5组(n=25),采用改良序贯法进行实验,M组和I组分别经尾静脉注射咪达唑仑、乳化异氟醚,首剂量分别为17.3 mg/kg、0.55 ml/kg;MI1组、MI2组和MI3组分别经尾静脉注射1/4、1/2、3/4咪达唑仑催眠效应半数有效剂量(ED50)+乳化异氟醚(首剂量分别为0.22、0.19、0.12 ml/kg),各组相邻剂量比值均为0.85,采用改良序贯法计算各组咪达唑仑、乳化异氟醚催眠效应的ED50,及其95%可信区间(95%CI).催眠有效的标准:前爪翻正反射消失.采用等辐射分析法判断不同剂量咪达唑仑与乳化异氟醚催眠效应的相互作用.结果 M组咪达唑仑催眠效应的ED50及其95%CI为26(22～30)mg/kg;I组、MI1组、MI2组及MI3组乳化异氟醚催眠效应的ED50及其95%CI分别为0.67(0.61～0.73)、0.30(0.28～0.33)、0.22(0.18～0.26)、0.18(0.16～0.20)ml/kg.MI1,组、MI1组、MI3组两药相互作用系数分别为1.51(P<0.01)、1.21(P<0.05)、0.98(P0.05).结论 咪达唑仑6.5、13 mg/kg复合乳化异氟醚时两药的催眠效应为协同作用,咪达唑仑19.5 mg/kg复合乳化异氟醚时两药的催眠效应为相加作用.     

吗啡预处理对缺血性心肌保护作用的研究进展

实验研究证实吗啡可以模拟缺血预处理.近年来吗啡预处理的心肌保护作用在在体、离体和心肌细胞3种动物模型都得到实验证实,其保护作用分为两个时相:即时相和延迟相.吗啡预处理的心肌保护作用主要由阿片受体介导,与线粒体KATP通道、诱导型NO合酶和环氧化酶等有关.将来在研究其分子机制的同时也会加强对其临床应用的研究.     

A study of the analgesic interaction between intrathecal morphine and subcutaneous nalbuphine in the rat

Nalbuphine reverses opioid-induced respiratory depression, but the effect on analgesia is unclear. The analgesic interaction between subcutaneous (sc) nalbuphine and intrathecal morphine in conscious, male, Sprague-Dawley rats implanted with chronic intrathecal catheters was investigated. Nalbuphine (10 mg/kg) injected 30 min after intrathecal morphine (4 micrograms) significantly antagonized the effect of morphine in the tail flick test. The antagonism was rapid in onset and persisted beyond the experimental period of 240 min. The magnitude and the duration of the effect were comparable to that observed with sc naloxone (1 mg/kg). In contrast to the results in the tail flick test, nalbuphine enhanced the effect of intrathecal morphine in the noninflamed paw pressure test. Nalbuphine (10 mg/kg) alone had no effect on the time course of tail flick latency but significantly increased paw pressure threshold during the 15-90 min interval after sc injection. Nalbuphine (0.5 mg/kg, sc) alone had no antinociceptive effect in either pain test and did not antagonize the antinociceptive effect of intrathecal morphine (4 micrograms) in the tail flick test. However, sc nalbuphine (0.5 mg/kg), injected 30 min after intrathecal morphine (1.5 micrograms), significantly enhanced the effect of morphine in the paw pressure test compared with intrathecal morphine + sc saline-treated rats. The results indicate a complex analgesic interaction between intrathecal morphine and sc nalbuphine. The net analgesic effect during the interaction was determined by the following: 1) the doses of morphine and nalbuphine; 2) the time after nalbuphine administration; and 3) the nature of the nociceptive stimulus. At lower doses, sc nalbuphine appeared to potentiate the effect of intrathecal morphine in the noninflamed paw pressure test.     

脊髓背角自噬与大鼠吗啡耐受形成的关系

目的 探讨脊髓背角自噬与大鼠吗啡耐受形成的关系.方法 雄性成年SD大鼠,体重250～ 300 g,取鞘内置管成功的大鼠24只,采用随机数字表法,将其分为3组(n=8):对照组(C组)、吗啡耐受组(M组)和吗啡+自噬增强剂雷帕霉素组(MR组).采用鞘内注射吗啡20 μg,2次/d,连续7d的方法制备吗啡耐受模型.C组给予等容量生理盐水.MR组鞘内注射吗啡20 μg,2次/d,连续7d,并于第3天第2次注射吗啡同时鞘内注射雷帕霉素2.3μg,连续3d.于鞘内注射前及第1、3、5、7天第2次鞘内注射后30 min测定机械缩足反应阈(MWT).最后1次MWT测定结束后1h取L4-6段脊髓背角,采用Western blot法测定总哺乳动物雷帕霉素靶蛋白(mTOR)和磷酸化mTOR(p-mTOR)及自噬标记蛋白LC3Ⅱ的表达.以p-mTOR占总mTOR表达水平的百分比反映mTOR的活性.结果 随鞘内注射时间延长,M组和MR组MWT逐渐降低(P＜0.05);与C组比较,M组和MR组鞘内注射期间MWT升高,脊髓背角mTOR活性降低,LC3Ⅱ表达上调(P＜0.05);与M组比较,MR组鞘内注射第3、5、7天MWT升高,脊髓背角mTOR活性降低,LC3Ⅱ表达上调(P＜0.05).结论 脊髓背角自噬增强是吗啡耐受形成时机体的适应性调节机制,可延缓吗啡耐受形成.     

Peripheral antinociceptive action of morphine and the synergistic interaction with lamotrigine

BACKGROUND: Lamotrigine inhibits glutamate release through the preferential blockade of voltage-dependent Na+ channels. In contrast, morphine reduces release of excitatory amino acids through the activation of opioid receptors and also inhibits tetrodotoxin-resistant Na+ channels on peripheral afferent neurons. The current study was designed to investigate the antinociceptive effects of locally administered morphine and lamotrigine. The interaction between morphine and lamotrigine at the periphery was also examined. METHODS: Morphine, lamotrigine, or a combination of morphine and lamotrigine was administered locally to female Wistar rats, and the antinociceptive effect was determined in the formalin test. Isobolographic analyses were used to define the nature of the functional interactions between morphine and lamotrigine. RESULTS: Peripheral administration of either morphine or lamotrigine produced a dose-related antinociceptive effect. Isobolographic analyses revealed that peripheral morphine and lamotrigine interacted synergistically in the formalin test. CONCLUSIONS: The study shows a functional interaction between lamotrigine and morphine at the peripheral level.     

Antiallodynic effects of systemic and intrathecal morphine in the spared nerve injury model of neuropathic pain in rats

BACKGROUND: The efficacy of opioids for neuropathic pain remains controversial. The effects of morphine on pain behavior were investigated in two animal models of neuropathic pain: the spared nerve injury (SNI) model and the spinal nerve ligation (SNL) model. METHODS: Nerve injuries were created in rats either by tight ligation and section of the left tibial and common peroneal nerves (SNI) or by unilateral ligation of L5 and L6 spinal nerves (SNL). Paw withdrawal threshold to mechanical stimuli was measured using the up-down method in the hairy and glabrous skin territories of the sural nerve for SNI rats or in the mid-plantar paw of SNL rats. RESULTS: Before SNI, the median paw withdrawal thresholds in hairy and glabrous skin were similar (26 g [25%, 75% quartiles: 26, 26 g]). The paw withdrawal threshold decreased after SNI in both hairy and glabrous skin (P < 0.001). Thirty days after the SNI, the threshold in hairy skin (0.3 g) was significantly lower than in glabrous skin (1.9 g; P < 0.001). In blinded experiments, both subcutaneous and intrathecal morphine (0.1-10 microg) dose-dependently attenuated mechanical allodynia induced by SNI measured in the hairy skin, an effect that was naloxone reversible. The ED50 for the intrathecal morphine was 0.52 microg (95% confidence interval, 0.31-0.90 microg). Morphine (1 microg intrathecal) attenuated SNI-induced mechanical allodynia in glabrous skin with potency similar to that in hairy skin. In SNL rats, morphine (30 microg intrathecal) almost completely reversed the SNL-induced mechanical allodynia. CONCLUSIONS: (1) SNI-induced mechanical allodynia is characterized by a lower paw withdrawal threshold in hairy versus glabrous skin; (2) systemic and intrathecal morphine reverse SNI-induced mechanical allodynia in a dose-dependent fashion; and (3) intrathecal morphine also reverses SNL-induced mechanical allodynia. These results suggest that intrathecal opioids are likely to be effective in the treatment of neuropathic pain.     

Antagonism of atracurium with neostigmine

In 36 patients in whom anaesthesia was maintained with nitrous oxide and 0.5% isoflurane an atracurium-induced neuromuscular block was either allowed to recover spontaneously or antagonised with one of four doses of neostigmine (15 micrograms/kg, 35 micrograms/kg, 55 micrograms/kg or 75 micrograms/kg). The recovery times to a train-of-four ratio of 0.5, 0.75 and 0.9 were recorded. In patients given neostigmine, antagonism was at an average T1 of between 8.8% and 14.9%. There was no difference in the recovery times between the patients given neostigmine 35 micrograms/kg, 55 micrograms/kg or 75 micrograms/kg. Recovery after neostigmine 15 micrograms/kg was significantly slower than after the higher doses. One patient given neostigmine 75 micrograms/kg showed an unusual bimodal pattern of recovery. There appears to be no benefit in giving a larger dose than 35 micrograms/kg of neostogmine as a single bolus.     

Inhalation injury associated with smoking, alcohol and drug abuse: An increasing problem

This study investigated the association of inhalation injury (IHI) with smoking, alcohol and drug abuse in patients admitted to the Welsh Centre for Burns between 1995 and 2006. Common characteristics of these individuals were identified and contrasted with inhalation injury not associated with these social factors.Two hundred and fourteen patients were identified with inhalation injury. Ninety-two of these were associated with smoking, alcohol abuse and/or drug abuse. The proportion of IHI cases associated with smoking remained stable but IHI associated with alcohol and drug abuse increased dramatically over the course of the study and if current trends continue will increase further in future years.This study also showed that IHI associated with smoking alcohol and drug abuse were found to be largely caused by housefires and deliberate self-harm, and occurred between 22:00 and 05:59 h. These results were in sharp contrast with IHI not associated with these factors.