Development and characteristics of reverse tolerance to repeatedly administered morphine in mice manifested by enhanced motor activities

Characteristics of changes in ambulatory activity after repeated administration of morphine, 5, 10 or 20 mg/kg s.c., were investigated in male mice of dd strain. The drug was administered 10 times at intervals of 1, 3-4 or 7 days, and the ambulatory activity of each mouse was measured by a tilting-type round activity cage with a 25 cm diameter for 180 min after each administration. Morphine, 5-20 mg/kg induced a dose-dependent increase in the ambulatory activity, and this effect attained to a peak at 60-90 min and persisted for 120-180 min after the administration. An augmentation of sensitivity (a reverse tolerance) to the ambulation-increasing effect of morphine was induced by the repeated administration of 10 and 20 mg/kg morphine, regardless of the intervals. The reverse tolerance achieved the maximum on the 5-6th administration day, and almost the same level of sensitivity was maintained until the 10th administration day. There was no significant difference in the activity counts at the peak time among the groups of mice varying the administration intervals. However, the persistence of increased ambulatory activity tended to be longer in the group of mice given morphine at intervals of 7 days than in the group given it at intervals of 1 day. The reverse tolerance, once produced, attenuated 2 months after the cessation of the repeated administration. However, the ambulatory activity counts did not return to those on the 1st administration day.(ABSTRACT TRUNCATED AT 250 WORDS)     

Chronic electroconvulsive treatment counteracts cortical beta-adrenoceptor upregulation induced by morphine abstinence.

Morphine treatment (20 mg/kg for 7 consecutive days) did not affect the density of [3H]dihydroalprenolol ([3H]DHA) binding sites in the cortical membranes of the rat, but during naloxone-precipitated abstinence syndrome the density of these sites increased. Electroconvulsive treatment for 6 days, which by itself decreased the density of [3H]DHA binding sites, prevented the increase.     

Activation of the cAMP/PKA/DARPP-32 signaling pathway is required for morphine psychomotor stimulation but not for morphine reward.

Activation of the cAMP/PKA pathway in the dopaminoceptive neurons of the striatum has been proposed to mediate the actions of various classes of drugs of abuse. Here, we show that, in the mouse nucleus accumbens and dorsal striatum, acute administration of morphine resulted in an increase in the state of phosphorylation of the dopamine- and cAMP-regulated phosphoprotein of 32 kDa (DARPP-32) at Thr34, without affecting phosphorylation at Thr75. The ability of morphine to stimulate Thr34 phosphorylation was prevented by blockade of dopamine D1 receptors. DARPP-32 knockout mice and T34A DARPP-32 mutant mice displayed a lower hyperlocomotor response to a single injection of morphine than wild-type controls. In contrast, in T75A DARPP-32 mutant mice, morphine-induced psychomotor activation was indistinguishable from that of wild-type littermates. In spite of their reduced response to the acute hyperlocomotor effect of morphine, DARPP-32 knockout mice and T34A DARPP-32 mutant mice were able to develop behavioral sensitization to morphine comparable to that of wild-type controls and to display morphine conditioned place preference. These results demonstrate that dopamine D1 receptor-mediated activation of the cAMP/DARPP-32 cascade in striatal medium spiny neurons is involved in the psychomotor action, but not in the rewarding properties, of morphine.     

Testosterone production by the prepubertal mouse testis is not depressed by ethanol

The purpose of the present study was to evaluate the sensitivity of testicular steroidogenesis during pubertal development to inhibition by ethanol. In vivo and in vitro human chorionic gonadotropin (hCG)-stimulated steroidogenesis were examined in CFW mice as a function of age. Plasma androstenedione, testosterone, and dihydrotestosterone (DHT) increased from ages 23 to 60 days in control mice. Acute ethanol treatment (3 g/kg) yielded static levels of androstenedione (0.45 +/- 0.03 ng/mL), testosterone (6.4 +/- 0.56 ng/mL), and DHT (2.3 +/- 0.18 ng/mL) from ages 23 to 60 days, 30 to 60 days, and 35 to 60 days, respectively, resulting in reduction of plasma androstenedione, testosterone, and DHT (P less than 0.05) relative to control values, but not until ages 35, 50, and 45 days, respectively. A similar insensitivity of the prepubertal testis to ethanol was seen in vitro. Inhibition of in vitro androstenedione and testosterone accumulation was seen only after ages 26 and 45 days, respectively. The data indicate that testosterone production by the pubertal testis is relatively insensitive to direct inhibition by ethanol. Previous studies have shown that chronic ethanol treatment of adolescent mice delays testicular maturation. The present study suggests that if chronic ethanol-induced delayed testicular development were due to impaired steroidogenesis, such impairment would be secondary to reduced gonadotropin stimulation and/or due to a chronic, rather than an acute, effect of ethanol.     

吗啡/芬太尼一次性硬膜镇痛效果观察

目的观察芬太尼在硬膜外腔一次注药后的镇痛作用和用药后尿潴留并发症。方法（1）371例硬膜外腔穿刺节段为T8～T10的患者随机分为A（芬太尼）组、B（吗啡）组和C（无镇痛）组;（2）521例硬膜外腔穿刺节段为T12～L3的患者分为a（芬太尼）组、b（吗啡）组和c（无镇痛）组。于术后4.5h、6.5h分别比较疼痛程度,术后6.5h比较尿潴留情况。结果3组（A、B、C组或a、b、c组）疼痛、尿潴留差异有统计学意义（P〈0.05）。疼痛在4h时A、B组（或a、b组）差异无统计学意义（P〉0.05）;疼痛、尿潴留在6.5h时A组与B组（或a组与b组）差异均有统计学意义（P〈0.05）。结论应用苏太尼、吗啡在4.5h内时镇痛无差异,随着时间延长,芬太尼镇痛作与吗啡相比镇痛作用减弱,在6.5h时芬太尼的尿潴留发生率少于吗啡,在临床镇痛时要辩证镇痛时间和尿潴留统一。     

nNOS参与OGD介导的促神经干细胞增殖效应

目的：体外研究脑缺血促神经发生的机制。 方法： 体外培养神经干细胞（neural stem cells,NSCs）与海马神经元,并采用氧糖剥夺模型（oxygen and glucose deprivation, OGD）模拟在体缺血,通过RT-PCR、Western blot、免疫细胞化学、酶活性测定、亚硝酸盐/硝酸盐（nitrite/nitrate,NOx） 含量测定等多种方法研究神经干细胞的生物学行为以及介导这种效应的分子机制。结果： （1）OGD通过直接和间接（神经元）作用增加神经干细胞中BrdU＋ 细胞比例。（2）OGD上调神经干细胞中神经元型一氧化氮合酶（neuronal nitric oxide synthase,nNOS）并下调神经元中nNOS,且都有利于神经干细胞增殖。（3）采用nNOS基因敲除小鼠来源的神经干细胞以及神经元（用于共培养）进行实验,发现OGD并不能升高神经干细胞中BrdU＋ 细胞比例。 结论：神经干细胞和神经元中nNOS水平变化共同参与了OGD诱导的促神经干细胞增殖效应。     

Anxiolytic effects of acute morphine can be modulated by nitric oxide systems

This study was performed to investigate whether nitric oxide (NO) precursor (L-arginine), NO donor (S-nitroso-N-acetylpenicillamine, SNAP) and NO synthase inhibitors [N(G)-nitro-L-arginine-methylester (L-NAME) and N(G)-nitro-L-arginine (L-NOARG)] modulate morphine-induced anxiolytic effects in the plus-maze. L-Arginine (100, 200 and 300 mg kg(-1), i.p.) and SNAP (4, 8 and 10 mg kg(-1), i.p.) reduced the anxiolytic effect of morphine (20 mg kg(-1), s.c.). L-NAME (10, 20 and 40 mg/kg, i.p.) and L-NOARG (10, 15 and 20 mg kg(-1), i.p.) enhanced the anxiolytic effects of morphine (20 mg kg(-1), s.c.). On the other hand, L-arginine and SNAP increased the morphine-induced locomotor activity. L-NAME decreased the morphine-induced locomotor activity, but L-NOARG did not modify the morphine-induced locomotor activity. Therefore, these results suggest that the anxiolytic effects of morphine can be modulated by NO systems.     

Analgesic tolerance produced by morphine pellets is facilitated by analgesic testing

Analgesic tolerance induced by morphine pellets was examined in rats using the nociceptive tail flick reflex. Analgesic responses of animals who received preliminary tail flick tests after morphine implantation were significantly lower than responses of naive, nontested animals. Previously tested animals were also significantly more tolerant to a morphine challenge than nontested animals. A dose curve to morphine was not obtained, at the doses used here, from previously tested animals, whereas naive animals responded to morphine in a dose dependent manner. Environmental modulation of the tail flick reflex represents an elementary form of behavioral plasticity which may prove useful for neural analyses of simple reflex systems.     

Morphine-induced immunomodulation is not related to serum morphine concentrations

Morphine pellets produced atrophy of the spleen and thymus and affected mitogen-induced lymphocyte proliferation in mice as characterized by marked suppression of concanavalin A-induced blastogenesis at 48 h, and mild stimulation at 120 h. Morphine blood levels in these animals indicated that changes in the immunomodulatory effects of morphine over time were not related to dramatic shifts in circulating morphine. Enclosure of the pellet in nylon mesh did not alter blood levels or morphine-induced immunomodulation.     

Non-stereospecific excitatory actions of morphine may be due to GABA-A receptor blockade

An explosive motor behavior (EMB) similar to that seen following morphine injection into the rat periaqueductal gray (PAG) was observed following an injection of GABA-A receptor antagonists into the rat PAG. In general, the potencies of certain opiates and known GABA-A antagonists in producing EMB following their injections into the PAG paralleled their potencies as GABA antagonists in a radioreceptor assay. We suggest that one of the dual actions of morphine in the CNS may be GABA blockade.     

Adenosine is required for ethanol-induced heterologous desensitization

Recent evidence suggests that ethanol initially causes an increase in receptor-dependent cAMP levels, followed by heterologous desensitization of receptors coupled to GS after chronic exposure. Here we investigated the role of adenosine in mediating these responses. We found that ethanol caused accumulation of extracellular adenosine in NG108-15 and S49 lymphoma cells. This adenosine activated adenosine receptors to increase intracellular cAMP levels. The addition of adenosine deaminase, to degrade accumulated extracellular adenosine, or isobutyl-methylxanthine, an adenosine receptor antagonist, completely blocked ethanol-induced increases in cAMP levels in NG108-15 cells. Chronic exposure of NG108-15 and S49 wild type cells to ethanol resulted in heterologous desensitization of adenosine receptor- and prostaglandin E1 receptor-dependent cAMP signal transduction. Coincubation of NG108-15 and S49 wild type cells with adenosine deaminase and ethanol for 48 hr prevented heterologous desensitization. Moreover, mutant S49 cells, which are unable to transport adenosine, did not accumulate extracellular adenosine after incubation with ethanol and did not develop ethanol-induced heterologous desensitization. Our results suggest that adenosine is an important mediator of both the acute and chronic effects of ethanol on cAMP signal transduction.     

Evidence that morphine is metabolized to hydromorphone but not to oxymorphone

A minor pathway for the biotransformation of morphine to hydromorphone has been identified in humans. Recently, an unsubstantiated claim that morphine is metabolized to hydromorphone and then to oxymorphone was published. The goal of this study was to determine if credible evidence that oxymorphone is a metabolite of either morphine or hydromorphone exists. Urine specimens from pain patients who were treated exclusively with high daily doses of morphine (N = 34) or hydromorphone (N = 26) were analyzed by liquid chromatography-tandem mass spectrometry for oxymorphone, hydromorphone, and morphine (LOD = 25 ng/mL). Specimens were also tested for a variety of other medications. Criteria for inclusion of patients' specimens were as follows: 1. patients were undergoing exclusive dosing with either morphine or hydromorphone; 2. non-prescribed medications were not detected; and 3. urine concentrations of morphine were > 100,000 ng/mL for the high-dose morphine group and > 1,000 ng/mL of hydromorphone for the high-dose hydromorphone group. Consistent with earlier reports, hydromorphone was detected in patients treated with high-dose morphine. The ratio of hydromorphone to morphine ranged from 0.2 to 2.2%. Oxymorphone was not detected in any specimen from high-dose morphine or high-dose hydromorphone patients. The authors conclude, based on these data, that oxymorphone is not a metabolite of morphine or hydromorphone.