Increase in the Extracellular Histamine Concentration in the Rat Striatum by μ-Opioid Receptor Activation

Abstract: The effects of morphine and selective ligands for μ-, κ-, and δ-opioid receptors on the extracellular histamine (HA) concentration in the striatum of freely moving rats were examined by in vivo microdialysis. On the day after implantation of the dialysis probe, the HA output per 30-min period was measured using HPLC-fluorometry. Morphine (3.8 mg/kg, s.c.) significantly increased the HA output by ∼200% 1–3 h after treatment. This effect was completely antagonized by naltrexone (1.6 mg/kg, s.c.). The HA output decreased to a level below 10% of the basal value by 4 h after treatment with ( S )-α-fluoromethylhistidine (77 mg/kg, s.c.). In such animals, morphine (3.8 mg/kg, s.c.) had no influence on the HA output. [ d -Ala²,MePhe⁴,Gly(ol)⁵]Enkephalin (DAGO; 0.2 µg, i.c.v.), a selective μ-agonist, significantly increased the HA output by ∼150% 0.5–1.5 h after treatment, and this effect was also completely blocked by naltrexone. A selective κ-agonist, U-50,488 (3.8 and 7.6 mg/kg, s.c.), and a selective δ-agonist, [ d -Pen², d -Pen⁵]enkephalin (0.5 and 2 µg, i.c.v.), had no effect on the HA output. These findings suggest that the stimulation of μ-opioid receptors by morphine and DAGO increases the extracellular HA concentration by accelerating HA release from nerve endings.     

Withania somnifera root extract prolongs analgesia and suppresses hyperalgesia in mice treated with morphine

Previous studies demonstrated that Withania somnifera Dunal (WS), a safe medicinal plant, prevents the development of tolerance to the analgesic effect of morphine.In the present study, we investigated whether WS extract (WSE) (100 mg/kg, i.p.) may also modulate the analgesic effect induced by acute morphine administration (2.5, 5, 10 mg/kg, s.c.) in the tail-flick and in the hot plate tests, and if it may prevent the development of 2.5 mg/kg morphine-induced rebound hyperalgesia in the low intensity tail-flick test. Further, to characterize the receptor(s) involved in these effects, we studied, by receptor-binding assay, the affinity of WSE for opioid (μ, δ, k), cannabinoid (CB₁, CB₂), glutamatergic (NMDA), GABAergic (GABA_A, GABA_B), serotoninergic (5HT_2A) and adrenergic (α₂) receptors.The results demonstrated that (i) WSE alone failed to alter basal nociceptive threshold in both tests, (ii) WSE pre-treatment significantly protracted the antinociceptive effect induced by 5 and 10 mg/kg of morphine only in tail-flick test, (iii) WSE pre-treatment prevented morphine-induced hyperalgesia in the low intensity tail-flick test, and (iv) WSE exhibited a high affinity for the GABA_A and moderate affinity for GABA_B, NMDA and δ opioid receptors.WSE prolongs morphine-induced analgesia and suppresses the development of morphine-induced rebound hyperalgesia probably through involvement of GABA_A, GABA_B, NMDA and δ opioid receptors. This study suggests the therapeutic potential of WSE as a valuable adjuvant agent in opioid-sparing therapies.     

Morphine promotes apoptosis via TLR2, and this is negatively regulated by β-arrestin 2

We have previously reported that morphine induces apoptosis. However, the underlying molecular mechanisms remain to be elucidated. Toll-like receptor 2 (TLR2), a key immune receptor in the TLR family, modulates cell survival and cell death in various systems. Evidence indicates that β-arrestin 2 acts as a negative regulator of innate immune activation by TLRs. Here, we investigated the roles of TLR2, the downstreaming mediator MyD88, and β-arrestin 2 in morphine-induced apoptosis. We showed that overexpression of TLR2 in HEK293 cells caused a significant increase in apoptosis after morphine treatment. Inhibition of MyD88 by transfecting dominant negative MyD88 or overexpression of β-arrestin 2 by transfecting β-arrestin 2 full length plasmid in TLR2 overexpressing HEK293 cells attenuated morphine-induced apoptosis. Our study thus demonstrates that TLR2 signaling mediates the morphine-induced apoptosis, and β-arrestin 2 is a negative regulator in morphine-induced, TLR2-mediated apoptosis.     

吗啡对猕猴瞳孔光反应能力的影响

光照能明显改变正常人和动物瞳孔的大小,而精神疾病及药物滥用则影响人和动物瞳孔对光的反应性.因此,瞳孔对光反应异常可以用作检测精神疾病和药物滥用的指标.有关药物滥用是如何影响瞳孔对光的反应性的研究还很少.为定量地测量成瘾性药物对瞳孔光反应变化的影响,该文采用猕猴为实验对象,通过在黑暗环境中测量猕猴在吗啡给予前和吗啡给予后的不同时间段,其瞳孔直径大小以及其对光反应能力的变化情况,来系统研究吗啡是如何影响这种非自主性反射系统的.研究发现,吗啡给予降低了猕猴在黑暗环境中的扩瞳反应,并且降低了瞳孔对光反应的收缩率.该文为将瞳孔对光反应特征用作鉴定吸毒者的检测手段提供了实验依据.     

Morphine modulates monocyte-macrophage conversion phase

Monocyte migration and their activation into the macrophage phenotype play a role in the modulation of tissue injury. We studied the effect of morphine on the monocyte-macrophage conversion phase (MMCP). Phorbol 12-myristate 13-acetate (PMA) activated THP-1 cells and promoted their adhesion to the substrate. Morphine inhibited PMA-induced MMCP. However, opiate receptor antagonists attenuated this effect of morphine. Interestingly, PMA as well as morphine-stimulated superoxide production by monocytes. Superoxide dismutase (SOD) not only inhibited PMA-mediated MMCP but also attenuated the inhibitory effect of morphine. PMA not only enhanced adhesion of monocytes to a filter but also promoted their migration. These findings suggest that the PMA-induced macrophage phenotype conversion may be accelerating their migration; whereas, morphine may be preventing the migration of monocytes by inhibiting MMCP.     

Temporal Variation in Drug Interaction Between Lithium and Morphine‐Induced Analgesia

The administration‐time‐dependent aspects of the drug interaction between lithium and morphine‐induced analgesia were studied using the mouse hot‐plate test at six different times of day, each scheduled at 4 h intervals. Lithium treatment alone, in doses of 1 to 10 mmol/kg administered intraperitoneally (i.p.) did not significantly alter test latencies compared to the corresponding clock‐time in saline‐injected controls. Basal pain sensitivity and morphine‐induced antinociceptive activity displayed significant circadian rhythms as assessed by the hot‐plate response latencies, with higher values occurring during the nocturnal activity than during the daytime rest span. Acute administration of lithium, in a dose of 3 mmol/kg, 30 min prior to morphine dosing did not influence morphine‐induced analgesia compared to all the clock‐time test‐matched morphine groups, except the 9 HALO (Hours After Lights On) one. There was a prominent potentiation of the morphine‐induced antinociception at this biological time during combined drug treatment. The latter finding demonstrates that administration‐time‐dependent differences in drug‐drug interactions need to be considered in both experimental designs and clinical settings.     

Accumulation and excretion of morphine by Calliphora stygia, an Australian blow fly species of forensic importance

This study examined the ability of the forensically important blow fly, Calliphora stygia to actively excrete morphine, thereby maintaining a low morphine level within its body when fed on a diet containing morphine at low (7 pmol g⁻¹) and high (17.5 pmol g⁻¹) concentrations. Morphine was accumulated within the bodies of maggots (≈70% within the tissues) at concentrations which were lower than that of the meat (3-24%). The morphine content of the initial developing stages (second and third instar maggots) maintained on the high morphine diet was higher than those on the low morphine diet. Morphine was cleared from the body with negatively exponential kinetics (High morphine group: Morphine (pmol g⁻¹ wet weight) = 8425e^−0.014t. Low morphine group: Morphine (pmol g⁻¹ wet weight) = 2180e^−0.010t). Clearance constants for morphine by animals in both groups were similar and thus both groups had a similar ability to excrete morphine. The Malpighian tubules of maggots were able to actively secrete morphine using a transport mechanism that transports small type II organic cations, such as morphine and quinine. The rate of morphine secretion by the Malpighian tubules could explain the clearance of the drug by the maggots. As the morphine was transported across the Malpighian tubules cells, a significant proportion was metabolised into a compound that is yet to be fully characterised.     

Substance P N-terminal fragment SP(1-7) attenuates chronic morphine tolerance and affects dynorphin B and nociceptin in rats

The N-terminal substance P fragment SP_1-7 is known to modulate hyperalgesia and opioid withdrawal in animal models. This study examined the effects of intraperitoneal (i.p.) injections of SP_1-7 on chronic morphine tolerance and on the levels of dynorphin B (DYN B) and nociceptin/orphanin FQ (N/OFQ) in various brain areas of male Sprague-Dawley rats. Morphine tolerance was induced by subcutaneous injections of the opioid (10 mg/kg) twice daily for 7 days. SP_1-7 injected i.p. (185 nmol/kg) 30 min prior to morphine reduced the development of morphine tolerance. Immunoreactive (ir) DYN B and N/OFQ peptide levels were measured in several areas of the central nervous system. Levels of ir DYN B in rats treated with SP_1-7 and morphine were decreased in the nucleus accumbens, substantia nigra and ventral tegmental area and increased in the frontal cortex. The ir N/OFQ levels were increased in the periaqueductal gray and decreased in the nucleus accumbens. Since the concentration profiles of the two peptides were altered by SP_1-7 in the areas that are implicated in the modulation of opioid tolerance and analgesia, it is suggested that DYN B and N/OFQ systems may be involved in the effects of SP_1-7 on opioid tolerance.     

婴幼儿机械通气时使用右旋美托咪定和咪达唑仑的效果评价

目的:比较婴幼儿在机械通气镇静时使用右旋美托咪定和咪达唑仑效果。方法:收集我院2009年2月至2011年10月入住ICU需要机械通气且镇静时间大于24h的患儿60例,随机分为3组,每组20例,右旋美托咪啶1组(输注剂量为0.25μg.kg-1.h-1,D1组)、2组(输注剂量为0.5μg.kg-1.h-1,D2组)维持镇静,咪达唑仑组(输注剂量为0.05 mg.kg-1.h-1,M组)维持镇静。同时根据病情需要间断给予吗啡镇痛。镇静的疗效评估采用Ramsay镇静评分以及脑电双屏指数(BIS)评价。结果:60例患儿分为3组,每组20例,咪达唑仑组(M组)的输注持续时间(h)为22±8 h,0.25μg(D1组)和0.5μg(D2组)右旋美托咪啶组输注持续时间分别为21±10 h和22±9 h;M组的平均输注速率为0.22±0.05 mg.kg-1.h-1,D1组和D2组平均输注速率分别为0.28±0.07μg.kg-1.h-1和0.21±0.05μg.kg-1.h-1;三组差异无统计学意义。其中M组、D1组、D2组使用吗啡的剂量是分别为36 mg.kg-1.24h-1、29 mg.kg-1.24h-1和20mg.kg-.124h-1。D1组与M组使用吗啡的剂量差异无统计学意义。D2组与M组使用吗啡的剂量差异有统计学意义(P<0.05)。三组患儿BIS值和Ramsay评分监测差异无统计学意义。结论:右旋美托咪啶应用于婴幼儿是安全有效的,0.5μg.kg-1.h-1右旋美托咪啶组镇静更加有效,24小时吗啡的使用剂量显著减少。     

恒河猕猴吗啡成瘾模型的初步建立

吗啡成瘾的非人灵长类动物恒河猕猴(Macaca mulatta)模型的实验结果表明,猕猴可建立吗啡条件化位置偏好(conditioned place preference,CPP),且其与吗啡线索相关的记忆可持续(36.3±1.3)月。该研究可以为药物成瘾研究提供有效的非人灵长类动物行为模型。