Involvement of nitric oxide in clonidine-induced spinal analgesia

BACKGROUND: The chronic pain relieving effects following spinal administration of clonidine are probably connected to alpha2-adrenoreceptor-induced augmented synthesis of nitric oxide (NO) in the spinal cord. In contrast, when acute pain is considered, the possible role of NO is still speculative. The aim of the present study was to explore the role of NO in acute pain relief following intraspinal administration of clonidine. METHODS: We used the mouse tail-flick model of acute pain. Spinal injections of the following agents and their combinations were administered: clonidine, L-arginine (NO precursor), the NO production inhibitor nitro-L-arginine-methyl ester (L-NAME), the NO antagonist methylene blue (MB) and nitroglycerine (NO releasing agent). RESULTS: A 95% analgesic response was achieved with 2.0 microg clonidine. L-Arginine produced analgesia, and L-arginine administration followed by clonidine resulted in a pronounced synergistic analgesic effect. This synergistic effect was attenuated by L-NAME. Pre-treatment with MB decreased and nitroglycerine administration did not affect the clonidine-induced analgesia. CONCLUSIONS: NO may be involved in the mediation of the acute pain relieving effects of intraspinally administered clonidine. Further research is warranted to establish the potential benefits and possibility for incorporation of NO promoting agents in therapeutic regional pain regimens.     

The effect of chronic administration of caffeine on morphine-induced analgesia, tolerance and dependence in mice

Morphine-induced analgesia, and the development of morphine-induced tolerance and dependence was determined in mice which had drunk caffeinated water (1 mg/ml) for 14 days or in mice which had received (-)-N6-(phenylisopropyl)-adenosine (PIA) 1 mg/kg i.p. for 14 days. Analgesia was assessed by the tail flick assay. The development of dependence was assessed by determining the ED50 of naloxone to precipitate withdrawal jumping (3 h after 100 mg/kg morphine pretreatment or 72 h after s.c. implantation of a morphine 75 mg pellet) and by determining the extent of naloxone-precipitated hypothermia in morphine-implanted animals. In mice chronically administered caffeine, the ED50 for morphine-induced analgesia was significantly decreased while the naloxone ED50 for withdrawal jumping increased by 2-fold after both types of morphine pretreatment. In control animals (tap water for 14 days), doses of 1 and 10 mg/kg of naloxone caused significant hypothermia in morphine-implanted animals. Doses of naloxone up to 100 mg/kg did not cause significant hypothermia in morphine-implanted animals which had received chronic caffeine. The development of tolerance was determined by computing the morphine potency ratio for the tail flick assay (tolerant ED50/control ED50). In mice chronically administered caffeine, the potency ratio was decreased significantly in morphine-implanted animals when compared to control. Morphine-induced analgesia, tolerance and dependence was not changed significantly in animals chronically administered PIA. Neither the distribution of morphine to the brain nor the opioid receptor binding parameters for [3H]etorphine and [3H]naltrexone were altered in mice chronically administered caffeine or PIA.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of some adenosine analogs on morphine-induced analgesia and tolerance

1. The analogs of adenosine D- and L-phenylisopropyladenosine (D- and L-PIA) and chloroadenosine (CADO) induced analgesia in mice (hot-plate test). 2. The antinociceptive effects of the three adenosine agonists were antagonized by caffeine but were unaffected by naloxone. 3. Morphine-induced antinociception was increased by pretreatment with adenosine agonists. 4. Whereas CADO significantly attenuated the induction of morphine tolerance, D- and L-PIA did not affect the process.     

Dose-dependent effects of prolyl-leucyl-glycinamide on morphine-induced analgesia, tolerance and dependence

Prolyl-leucyl-glycinamide (PLG) at a low dose (10 ng/mouse) administered intracerebroventricularly (i.c.v.) did not affect morphine analgesia, but produced a greater increase in the ED50 of morphine-pretreated (100 mg/kg of morphine sulfate) mice as compared to control mice. PLG at doses of 10 and 100 micrograms/mouse antagonized morphine analgesia. Development of morphine tolerance was unaffected by 10 micrograms/mouse but antagonized by 100 micrograms/mouse of PLG. Development of morphine dependence was assessed by changes in body weight and temperature during naloxone-induced withdrawal. PLG (10 ng/mouse) potentiated, 10 micrograms/mouse had no effect and 100 micrograms/mouse antagonized development of morphine dependence. PLG at doses of 10 and 100 micrograms/mouse precipitated withdrawal in morphine-dependent mice. When mice were pretreated with 1.0 mg/kg naloxone i.p. 15 min before PLG, all doses of PLG had no effect on morphine analgesia, but potentiated the development of morphine tolerance and dependence. None of the doses of PLG altered whole brain levels of morphine. PLG did not alter the affinity of opioid receptors for etorphine or the maximal number of binding sites but PLG did exhibit a very weak affinity for opioid receptors. These results indicate that PLG potentiated development of morphine tolerance and dependence through a mechanism not involving opioid receptors. However, at very high doses it was a weak opioid receptor antagonist.     

Y-IP5对小鼠吗啡镇痛、耐受及躯体依赖的影响

目的:评价化合物Y-IP5对小鼠吗啡镇痛、耐受及躯体依赖的影响。方法:采用55℃热板测痛模型分析Y-IP5对小鼠吗啡镇痛和耐受的影响;采用剂量递增法皮下注射吗啡5 d,建立小鼠吗啡依赖模型,评价Y-IP5对小鼠吗啡躯体依赖的影响。结果:在热板测痛模型中,Y-IP5(2.5,5,10 mg.kg-1)不能明显增强小鼠吗啡镇痛作用(P>0.05),Y-IP5(1.25,2.5,5 mg.kg-1)能明显抑制小鼠吗啡镇痛耐受的形成(P<0.05)。伴随吗啡给予Y-IP5(1.25,2.5,5 mg.kg-1)能剂量依赖性地抑制小鼠躯体依赖的形成(P<0.05);在纳洛酮催促前单次给予Y-IP5(1.25,2.5,5 mg.kg-1),不能显著抑制小鼠吗啡躯体依赖的表达(P>0.05)。结论:Y-IP5对吗啡耐受及躯体依赖的形成可能有一定的干预作用。     

Modification of morphine-induced analgesia, tolerance and dependence by bromocriptine

The effect of two doses of bromocriptine, a dopamine agonist, on morphine-induced analgesia, tolerance and dependence was investigated in mice. Bromocriptine at doses of 0.04 and 0.08 mg/kg did not affect the baseline tail flick latency of mice but potentiated the morphine analgesia. Pretreatment of mice with 5 mg/kg of sulpiride, a D-2 antagonist, not only blocked the effect of 0.08 mg/kg of bromocriptine but also antagonized the morphine analgesia. Control animals given daily injections of 10 mg/kg of morphine rapidly developed tolerance to the analgesic effect. A combined treatment of bromocriptine with morphine given daily suppressed the development of tolerance to morphine analgesia. However, development of tolerance to morphine analgesia was not significantly modified in the animals treated daily with bromocriptine (0.08 mg/kg) plus sulpiride (5 mg/kg). Acute dependence was induced by the administration of 100 mg/kg of morphine. The administration of bromocriptine 30 min before naloxone significantly decreased the ED₅₀ value for naloxone for inducing jumping in mice. Coadministration of sulpiride and bromocriptine attenuated the ability of bromocriptine to potentiate the withdrawal syndrome of morphine dependence. The results indicate that bromocriptine potentiates morphine analgesia, suppresses the development of tolerance to morphine analgesia but exacerbates opiate withdrawal signs in morphine-dependent mice. These effects of bromocriptine appear to be mediated via D-2 receptors.     

The effect of dopaminergic modifiers on morphine-induced analgesia and respiratory depression.

The influences of the dopaminergic system on morphine-induced analgesia and respiratory depression were compared using modulators of dopaminergic activity. Blockade of dopaminergic receptors by haloperidol or pimozide produced a potentiation of morphine analgesia, while stimulation of dopaminergic activity by L-dopa methyl ester inhibited morphine analgesia. Morphine-induced depression of respiratory rate was potentiated by haloperidol and inhibited by pimozide or L-dopa methyl ester. These results suggest that the dopaminergic system plays a modulating role in morphine-induced analgesia, but not in morphine-induced respiratory depression.     

The effect of ciprofloxacin and gentamicin on spinal morphine-induced antinociception in rats

This paper investigates the possible antinociceptive effect of systemically administered ciprofloxacin and gentamicin and its influence on intrathecal morphine-induced antinociception. Using thermal nociceptive tests (hot-plate test and tail-flick test) and a motor function test (catalepsy test) in male Sprague-Dawley rats (n=5-9/dose), the following observations were made: ciprofloxacin administered intraperitoneally in the dose range 4-64 mg/kg demonstrated a modest antinociceptive effect in both nociceptive tests. Solvent of ciprofloxacin (intraperitoneally) and saline (intraperitoneally), given as a control, showed no effect. Gentamicin, administered at a dose of 0.1-4 mg/kg intraperitoneally, demonstrated a significant (P<0.05) antinociceptive effect in the tail-flick test but not in the hot-plate test. However, opioid antagonists caused no significant change in the antibiotics. Furthermore, ciprofloxacin intraperitoneally produced a significant left-shift in the hot-plate test (ED50 saline-morphine=2.86 [CI 95%: 2.2, 4.32]microg; ED50 ciprofloxacin-morphine=0.87 (CI 95% 0.68, 1.21) microg, P<0.05) and in the tail-flick test (ED50 saline-morphine=1.98 (CI 95%: 1.21, 2.84) microg; ED50 ciprofloxacin-morphine=0.37 (CI 95%: 0.23, 0.44) microg; P<0.05) for intrathecal morphine-induced antinociception. From a comparison of these data with the predicted ciprofloxacin-morphine value (hot-plate test: 1.61 (CI 95%: 1.18, 2.51]microg; tail-flick test: 0.82 (CI 95%: 0.52, 1.92) microg) we estimate that ciprofloxacin and morphine produce at least additive effects (P>0.05). This was reversed with intraperitoneal naloxone (P<0.05). Gentamicin intraperitoneally did not influence the antinociception achieved with intrathecal administration of morphine (hot-plate test: ED50 gentamicin-morphine=2.71 (CI 95%: 2.35; 3.2) microg; tail-flick test: ED50 gentamicin-morphine=2.43 (CI 95%: 1.58; 5.22]microg; P>0.05). These data show that intraperitoneal administration of ciprofloxacin and gentamicin produces a modest antinociceptive effect in the hot-plate test and tail-flick test. Ciprofloxacin, but not gentamicin, can interact at least additively to increased naloxone-reversible morphine intrathecal antinociception. Differences in the ability to penetrate the blood-brain barrier between the two antibiotics could explain the lack of effect from gentamicin in the hot plate and on morphine-induced antinociception.     

Influence of nitric oxide on morphine-induced conditioned place preference in the rat central amygdala

Effects of intra-central amygdala injections of L-arginine, a nitric oxide (NO) precursor, and N(G)-nitro-L-arginine methyl ester (L-NAME), a NO synthase (NOS) inhibitor, on morphine-induced conditioned place preference in rats were investigated by using an unbiased 3-day schedule of place conditioning design. Animals receiving once daily injections of morphine (0.5-7.5 mg/kg, subcutaneously, s.c.) or saline (1.0 ml/kg, s.c.) showed a significant place preference in a dose-dependent manner. The maximum response was observed with 5.0 mg/kg of the opioid. Co-administration of morphine (5.0 mg/kg) with L-arginine (0.3, 1.0 and 3.0 microg/rat), but not with L-NAME (0.3, 1.0 and 3.0 microg/rat), during the acquisition of morphine-induced conditioned place preference increased morphine-induced conditioned place preference. The response to L-arginine was blocked by L-NAME preadministration. L-arginine and L-NAME by themselves did not induce conditioned place preference. When L-arginine or L-NAME at 0.3-3.0 microg/rat was administered 1 min before conditioned place preference testing, L-arginine but not L-NAME caused an increase in the expression of morphine-induced conditioned place preference, the effect that was blocked by L-NAME preadministration. A dose of L-arginine (0.3 microg/rat), but not L-NAME, during expression of morphine-induced conditioned place preference produced an increase in locomotion compared with that in the control group. It may be concluded that an increase in the NO levels in the central amygdala may have an effect on the acquisition and expression of morphine-induced conditioned place preference.     

Bidirectional modulatory effect of orphanin FQ on morphine-induced analgesia: antagonism in brain and potentiation in spinal cord of the rat

1. The present study was designed to investigate further the effects of the newly discovered orphanin FQ (OFQ)–the endogenous ligand for the orphan opioid receptor (called, e.g., ORL₁ and LC132)–on pain modulation in the rat. We used the tail-flick assay as a nociceptive index.
2. When injected into a cerebral ventricle, OFQ (4 fmol–10 nmol) has no effect on basal tail-flick latency by itself at any dose, but dose-dependently antagonizes systemic morphine analgesia (400 fmol–50 nmol).
3. Injected intrathecally, OFQ (3 and 10 nmol) displayed an analgesic effect without producing motor dysfunction, and potentiated morphine analgesia (1 and 10 nmol).
4. The anti-opioid effect of OFQ in rat brain and the high level of expression of LC132/ORL₁ receptor in the locus coeruleus indicated a possible role of OFQ in the precipitation of opiate withdrawal symptoms. However, no such precipitation was observed by OFQ in morphine-dependent rats.

     

Environmental specificity of tolerance to morphine-induced analgesia in a terrestrial snail: generalization of the behavioral model of tolerance

Terrestrial snails, Cepaea nemoralis, develop tolerance to morphine-induced analgesia, such that after 7-9 days of treatment with morphine (10 mg/kg) their response latencies to an aversive thermal stimuli (38.5 degrees C) are not significantly different from those of untreated control animals. In Experiment A snails were rendered tolerant to morphine using either of two pre-injection cues (light and dark background brightness or color) and then assessed for morphine-induced alterations in thermal nociceptive responses in both environments. In Experiment B snails were made tolerant to morphine in the presence of one of two different thermal cues (a stressful temperature of 35 degrees C that is normally avoided or an ambient temperature of 22 degrees C) and then tested for morphine-induced alterations in nociceptive responses in both environments. In the two experiments tolerance to morphine-induced analgesia was displayed when snails were exposed to the pre-injection environmental cue normally associated with the administration of morphine, but not when exposed to the alternative pre-injection cue. These results demonstrate that various environmental factors (background colors or brightness as well as temperature cues and potentially thermal stress), can function as environmental specific cues for the development of tolerance to morphine-induced analgesia in molluscs, in a manner consistent with a behavioral mechanism of tolerance. Thus, these results suggest that environmental specificity of tolerance involving either classical (Pavlovian) conditioning or habituation may be a general phenomenon having an early evolutionary development and broad phylogenetic continuity.     

褪黑素抑制一氧化氮生成在小鼠免疫性肝损伤中的意义

目的探讨褪黑素（ＭＴ）抑制一氧化氮生成与保护免疫性肝损伤的关系。方法用短小棒状杆菌和脂多糖诱导小鼠免疫性肝损伤模型；分离、培养肝细胞和腹腔巨噬细胞；检测一氧化氮（ＮＯ）、丙氨酸氨基转换酶（ＡＬＴ）、丙二醛（ＭＤＡ）和谷胱甘肽过氧化酶（ＧＳＨ ｐｘ）变化。结果ＭＴ在０１～１０ｍｇ·ｋｇ－１·ｄ－１浓度范围内，明显降低小鼠免疫性肝损伤中ＭＬＴ和ＭＤＡ水平，部分恢复ＧＳＨ ｐｘ活性（Ｐ＜００５～００１），同时血浆ＮＯ水平下降（Ｐ＜００５）。左旋单甲基精氨酸则在显著降低血浆ＮＯ水平（Ｐ＜００１）同时，肝损伤征象加重。体外用ＭＴ对肝细胞和巨噬细胞无明显影响。结论褪黑素抑制体内ＮＯ过度生成，有利于保护免疫性肝损伤。     

Dietary influences on morphine-induced analgesia in rats

Morphine-induced analgesia was examined using a tail-flick apparatus in 36 adult male Sprague-Dawley rats. Rats were given ad lib access to Purina Chow alone (N = 9) or given a choice of Purina Chow and either a 0.15% saccharin solution (N = 9), a 32% sucrose solution (N = 9), or hydrogenated vegetable fat (Crisco) (N = 9). Analgesic testing was conducted immediately preceding and at 30, 60 and 90 minutes following intraperitoneal administration of morphine sulfate (0.0, 2.5, 5.0 and 10.0 mg/kg). No differences in analgesic responsiveness were observed as a function of diet preceding morphine administration. However, dietary variables did alter morphine-induced analgesia. At 30 minutes following injections of the highest dose of morphine, animals fed saccharin, sucrose or Crisco had significantly longer tail-flick latencies than rats given only Purina Chow. Sixty minutes following injections, rats fed Crisco continued to display a significantly longer tail-flick latency than rats fed only Chow. These data demonstrate that palatable substances can enhance the analgesic properties of exogenous opioids.     

瑞芬太尼对子宫切除术患者血清一氧化氮和一氧化氮合酶影响

目的观察瑞芬太尼对子宫切除术患者血清中一氧化氮(NO)、一氧化氮合酶(NOS)的影响。方法将择期行腹腔镜子宫切除术的患者(ASAⅠ～Ⅱ级)60例随机分为芬太尼组和瑞芬太尼组,每组各30例。芬太尼组麻醉维持采用芬太尼和异丙酚;瑞芬太尼组麻醉维持采用瑞芬太尼和异丙酚。于麻醉前、术毕时抽取静脉血,检测血清NO、NOS水平。结果与麻醉前比较,术毕时2组患者血清NO、NOS均降低(P<0.05);术毕时瑞芬太尼组血清NO、NOS明显高于芬太尼组(P<0.05)。结论腹腔镜CO2气腹可导致患者血清NO、NOS增高,与芬太尼相比,瑞芬太尼能减轻术后早期应激反应。     

The interference of some cytostatics on morphine-induced analgesia.

The influence of some cytostatic agents (the antibiotic daunomycin, the polypeptide peptikemio and the nitrosourea derivative BCNU) on the antinociceptive effect of morphine is here investigated. It is demonstrated that daunomycin and peptikemio significantly enhance morphine-induced analgesia, while on the other hand, BCNU is ineffective. Daunomycin neither prevents morphine binding to blood proteins nor facilitates its access to the brain. A role of calcium ions in daunomycin potentiating effect is suggested.     

Mediation of nitric oxide in inhibitory effect of morphine against electroshock-induced convulsions in mice

Nitric oxide (NO) and morphine have been coupled in many physiological as well as pathological processes. The present study examined the involvement of the L-arginine/NO pathway in the anticonvulsant properties of systemic morphine (2-30 mg/kg) against electroshock seizures (ECS) in mice. Morphine decreased the intensity of maximal electroshock seizures (MES) and increased the threshold for ECS. Neither the NOS substrate L-arginine (30, 60, and 100 mg/kg), the reversible nonspecific NOS inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME; 3, 10, and 30 mg/kg), the irreversible specific inducible NOS inhibitor aminoguanidine (20, 50, and 100 mg/kg), nor the opioid receptor antagonist naloxone (0.1, 0.3, and 1 mg/kg) did alter per se the ECS threshold or the intensity of MES at doses used. However, both naloxone and L-NAME, but not aminoguanidine, inhibited the anticonvulsant effects of morphine (30 mg/kg) against ECS, while L-arginine potentiated the anticonvulsant effects of lower doses of morphine (2 or 10 mg/kg). Low doses of naloxone (0.1 or 0.3 mg/kg) or L-NAME (3 mg/kg), which did not alter morphine effect per se, showed additive anticonvulsant effects against MES. Thus, the L-arginine/NO pathway seems to play a role in the anticonvulsant properties of morphine against ECS and this mediation involves the constitutive, but not the inducible, form of nitric oxide synthase.     

Role of S-nitrosation of cysteine residues in long-lasting inhibitory effect of nitric oxide on arterial tone

S-Nitrosation of cysteine residues plays an important role in nitric oxide (NO) signaling and transport. The aim of the present study was to investigate the role of S-nitrosothiols as a storage form of NO, which may account for the long-lasting effects in the vasculature. Rat aorta exposed to S-nitrosoglutathione (GSNO) displayed, even after washout of the drug, a persistent increase in cysteine-NO residues (detected by immunostaining using an antiserum that selectively recognized S-nitrosoproteins) and in NO content (detected by NO spin-trapping), a persistent attenuation of the effect of vasoconstrictors, and a relaxant response upon addition of low molecular weight (LMW) thiols. Rat mesenteric and porcine coronary artery exposed in vitro to GSNO, as well as aorta and mesenteric arteries removed from rats treated in vivo with GSNO, displayed similar modifications of contraction. In isolated aorta exposed to GSNO, the decrease of the contractile response and the relaxant effect of LMW thiols were both blunted by NO scavengers (oxyhemoglobin or 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) or by a cyclic GMP-dependent protein kinase inhibitor (Rp-8-bromoguanosine-3',5'-cyclic monophosphorothioate). In these arteries, mercuric chloride (which cleaves the cysteine-NO bond) exerted a transient relaxation, completely abolished the one of LMW thiols, and blunted the increase in cysteine-NO residues and NO content. Together, these data support the idea that S-nitrosation of cysteine residues is involved in long-lasting effects of NO on arterial tone. They suggest that S-nitrosation of tissue thiols is a mechanism of formation of local NO stores from which biologically active NO can subsequently be released.     

Role of nitric oxide in the rat hippocampal CA1 area on morphine-induced conditioned place preference

Effects of intrahippocampal CA1 injections of L-arginine, a nitric oxide (NO) precursor, and N(G)-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase inhibitor, on morphine-induced conditioned place preference in male Wistar rats were investigated. Animals received subcutaneous (s.c.) injections of saline (1.0 ml/kg) or morphine (0.5-7.5 mg/kg) once daily for 3 days to induce conditioned place preference. The administration of L-arginine (0.3, 1.0, and 3.0 microg/rat), but not L-NAME (0.3, 1.0, and 3.0, microg/rat), prior to administration of morphine (5.0 mg/kg) during acquisition of morphine-induced conditioned place preference increased morphine-induced conditioned place preference, but the interaction between the response to morphine and/or L-arginine was not statistically significant. The response to L-arginine was blocked by L-NAME pre-administration. L-Arginine or L-NAME by itself did not induce conditioned place preference. The administration of L-arginine but not L-NAME, 1 min before conditioned place preference testing, increased the expression of morphine-induced conditioned place preference. Pre-administration of L-NAME blocked the L-arginine response. It is concluded that NO in the rat hippocampal CA1 area may be involved in morphine-induced conditioned place preference.