眼镜蛇毒粗毒毒素Ⅳ对小鼠吗啡行为敏化的影响

目的 探讨眼镜蛇毒毒素Ⅳ对吗啡行为敏化的影响.方法 测定小鼠自主活动,观察毒素Ⅳ对小鼠自主活动影响.昆明种小鼠慢性吗啡处理,建立吗啡诱导行为敏化模型,观察毒素Ⅳ对吗啡行为敏化影响.结果 毒素Ⅳ(0.027、0.04、0.08 mg/kg)腹腔注射后,均能减少小鼠自主活动,降低吗啡诱导的高活动性,抑制小鼠吗啡行为敏化的获得,阻断小鼠吗啡行为敏化表达,其中中、高剂量毒素Ⅳ作用较显著.结论 毒素Ⅳ对中枢神经系统具有抑制作用,可以阻止吗啡成瘾行为形成,对吗啡诱导的敏化行为具有抑制作用,提示毒素Ⅳ对吗啡精神依赖性可能具有干预作用.     

归元片对小鼠吗啡行为敏化的影响

目的 :探讨中药复方制剂归元片对吗啡行为敏化的影响。方法 :测定小鼠的自主活动 ,观察归元片对小鼠自主活动的影响。给小鼠慢性吗啡处理 ,建立吗啡诱导的行为敏化小鼠模型 ,观察归元片对吗啡行为敏化的影响。结果 :(1)归元片 (2 5 - 10g·kg- 1 )明显抑制小鼠的自主活动 ,并呈剂量依赖性 ;(2 )归元片剂量依赖性地阻断小鼠吗啡行为敏化的获得和表达 ,但对行为敏化的转换无影响。结论 :归元片对中枢神经系统具有抑制作用 ,可以阻止吗啡成瘾行为的形成 ,对吗啡诱导的敏化行为具有抑制作用。提示归元片对吗啡的精神依赖性可能具有干预作用     

Y-IP5对小鼠吗啡行为敏化和条件性位置偏爱的影响

目的探讨新型化合物Y-IP5对吗啡诱导小鼠行为敏化和条件性位置偏爱(conditioned place preference,CPP)的影响。方法测定小鼠的自发活动,观察Y-IP5对小鼠自发活动及急性给予吗啡所诱导小鼠高活动性的影响;慢性吗啡处理小鼠,建立小鼠吗啡行为敏化和CPP模型,观察Y-IP5对行为敏化形成、转化、表达及CPP形成的影响。结果单次或多次给予Y-IP5都不影响小鼠的自发活动,但能抑制急性给予吗啡所致的小鼠高活动性(P<0.05);Y-IP5本身不诱导小鼠形成行为敏化和CPP,但能抑制吗啡诱导小鼠形成行为敏化和CPP(P<0.05),但Y-IP5对吗啡诱导小鼠行为敏化的转化和表达无抑制作用。结论Y-IP5对阿片类药物的精神依赖可能具有干预作用。     

槟榔碱对小鼠吗啡行为敏化的影响

目的:探讨槟榔嚼块的主要成分—槟榔碱,对小鼠吗啡行为敏化过程的影响。方法:测定小鼠的自主活动,观察ip槟榔碱对小鼠的自主活动及单次给予吗啡所诱导的小鼠高活动性的影响;建立吗啡诱导的小鼠行为敏化模型,观察槟榔碱对行为敏化形成、表达的影响。结果:(1)单次ip槟榔碱(0·25-2·0mg·kg-1)可剂量依赖性地抑制小鼠的自主活动(P<0·05),多次给药后这种抑制作用既不产生耐受,也不形成敏化;(2)槟榔碱(2·0mg·kg-1)可增强单次给予吗啡所诱导的小鼠的高活动性(P<0·05);(3)槟榔碱(2·0mg·kg-1)可增强吗啡诱导小鼠行为敏化的形成(P<0·05);(4)虽然槟榔碱(2·0mg·kg-1)多次给药降低吗啡诱导小鼠行为敏化表达的程度(P<0·05),但是槟榔碱(0·5-2·0mg·kg-1)单次给药不影响吗啡诱导小鼠行为敏化的表达。结论:槟榔嚼块中的主要成分槟榔碱能增强小鼠吗啡诱导的急性高活动性和吗啡行为敏化的形成,提示槟榔嚼块有可能增强吗啡的成瘾性。     

噻诺啡灌胃对小鼠吗啡行为敏化的影响

目的研究ig噻诺啡对小鼠吗啡行为敏化的影响。方法测定小鼠的自主活动，观察ig噻诺啡对小鼠自主活动及急性给予吗啡所诱导小鼠活动增强效应的影响；建立小鼠吗啡行为敏化模型，观察ig噻诺啡对行为敏化形成、转化及表达的影响。结果单次ig噻诺啡(1.25-5.0 mg·kg^-1)可剂量依赖性地降低小鼠的自主活动(P<0.01)，但多次给药可产生耐受。噻诺啡可有效地抑制急性给予吗啡所诱导的小鼠高活动性(P<0.05)及小鼠吗啡行为敏化的形成、转化和表达(P<0.05或P<0.01)。结论噻诺啡可抑制小鼠中枢神经系统，对阿片类药物的滥用和成瘾可能具有干预作用。     

噻诺啡对小鼠甲基苯丙胺行为敏化的影响

目的:探讨新型阿片受体部分激动剂-噻诺啡对小鼠甲基苯丙胺行为敏化过程的影响。方法:测定小鼠的自主活动,观察噻诺啡对小鼠的自主活动及急性甲基苯丙胺处理所致小鼠活动增强效应的影响。小鼠腹泻注射甲基苯丙胺2mg·kg~(-1)·d~(-1),连续7d,建立甲基苯丙胺诱导的小鼠行为敏化模型,观察噻诺啡对小鼠行为敏化的影响。结果:单次皮下注射噻诺啡(0.0625～1.0mg·kg~(-1))可剂量依赖性地抑制小鼠的自主活动(P<0.05),连续给药7d,噻诺啡对小鼠自主活动的抑制作用不产生敏化,而耐受。噻诺啡对急性甲基苯丙胺处理所致小鼠的高活动性无明显影响。噻诺啡对甲基苯丙胺诱导的小鼠行为敏化的形成和表达无显著作用,但可剂量依赖性地抑制敏化的转化(P<0.05或P<0.01)。结论:噻诺啡对中枢神经系统具有抑制作用,并且可以阻止甲基苯丙胺诱导小鼠产生行为敏化的转化过程,提示噻诺啡可能对甲基苯丙胺的成瘾行为具有一定的干预作用。     

甲基苯丙胺诱导小鼠行为敏化模型的构建与评估

目的:探讨不同剂量水平甲基苯丙胺(MA)所诱导的小鼠行为敏化模型的构建与评估方法。方法:40只C57BL/6J小鼠,随机分为5组:生理盐水对照组(NS)和0.5、2、5、10mg·kg-1MA剂量组,各组在形成期连续5d每天腹腔注射(ip)不同剂量药物并记录自主活动情况,转化期停药观察2d后,在d8表达期给予最后一次等量剂量MA,并记录自主活动情况。结果:(1)不同剂量MA作用于实验小鼠,在小剂量水平即能够诱导出明显的行为敏化现象,且随着药物浓度增大,呈现剂量依赖性变化;(2)在10mg·kg-1大剂量水平,小鼠表现为明显的刻板行为,在表达期同样出现了刻板行为的增强现象。结论:本实验为不同剂量的小鼠MA敏化模型提供了比较标准的构建和评估方法;2mg·kg-1MA作用于实验小鼠,诱导出了明显的行为敏化现象,同时其他精神运动改变如刻板行为出现较少,是构建药物依赖行为敏化模型较理想的剂量;利用该行为敏化模型可进一步分析和评估药物依赖治疗性药物的疗效。     

归元片对小鼠甲基苯丙胺行为敏化的影响

目的:探讨中药复方制剂归元片对甲基苯丙胺行为敏化的影响.方法:测定小鼠的自主活动,观察归元片对小鼠自主活动及甲基苯丙胺急性活动增强效应的影响.小鼠慢性甲基苯丙胺处理,建立甲基苯丙胺诱导的行为敏化小鼠模型,观察归元片对甲基苯丙胺行为敏化获得和表达的影响.结果:归元片呈剂量依赖性降低小鼠的活动性,对甲基苯丙胺的急性高活动效应有抑制作用.归元片阻断小鼠甲基苯丙胺行为敏化的获得和表达.结论:归元片对中枢神经系统功能具有抑制作用,能抑制甲基苯丙胺行为敏化的获得和表达,提示归元片能抑制甲基苯丙胺的奖赏效应,可能对防治甲基苯丙胺的滥用和成瘾有效.     

ι-四氢巴马汀抑制羟考酮引起小鼠行为敏化的实验研究

目的探讨ι-四氢巴马汀(-tetrahydropalmatine,ι-THP)对羟考酮(oxycodone,oxy)行为敏化的影响和作用机制。方法采用连续7d给小鼠注射羟考酮(5mg.kg-1,ip),停药5d,d13用相同剂量的羟考酮(5mg.kg-1,ip)激发致小鼠行为敏化模型,利用红外光束自主活动测定仪测定小鼠自发活动的实验方法。结果ι-THP(6.25,12.5,18.75mg.kg-1,ig)一次或多次给药,对小鼠的自发活动没有影响,但ι-THP(18.75mg.kg-1,ig)能抑制羟考酮(5mg.kg-1,ip)引起的小鼠行为敏化的形成和表达。阿朴吗啡(0.5、1.0mg.kg-1,ip)给药后50min自身不影响小鼠的自发活动,但阿朴吗啡(1.0mg.kg-1,ip)能翻转ι-THP(18.75mg.kg-1,ig)抑制羟考酮小鼠行为敏化形成的作用,但不影响ι-THP抑制羟考酮行为敏化表达的作用。结论ι-THP抑制羟考酮引起的小鼠行为敏化的形成和表达,ι-THP抑制羟考酮行为敏化的形成可能与抑制DA受体相关,而抑制表达可能与抑制DA受体无关。     

地高辛对小鼠吗啡行为敏化的影响

目的:探讨地高辛对小鼠吗啡行为敏化的影响.方法:测定小鼠的自主活动,观察地高辛对小鼠自主活动的影响.急性吗啡(10 mg·kg-1,ip)处理小鼠前给予地高辛,观察地高辛对急性吗啡引起小鼠高活动性的影响.慢性吗啡处理小鼠,建立吗啡行为敏化模型,观察地高辛对吗啡行为敏化的影响.结果:(1)地高辛(0.5 mg·kg-1-...     

A new buprenorphine analogy, thenorphine, inhibits morphine-induced behavioral sensitization in mice

AIM: To investigate effects of thenorphine, a new compound of partial agonist of μ-opioid receptor, on the loco-motor activity and the behavioral sensitization to morphine in mice. METHODS: Locomotor activity was observed after administration of thenorphine or co-administration of thenorphine and morphine in mice. Mice were induced behavioral sensitization to morphine by intraperitoneal injection of 20 mg/kg morphine once daily for 7 d. Thenorphine was co-administrated with morphine to observe the effects of thenorphine on the development, transfer and expression of morphine-induced behavioral sensitization. RESULTS: A single dose of thenorphine (0.0625, 0.25, and 1.0 mg/kg) could dose-dependently inhibit the locomotor activity in mice (P<0.05), repeated administrations of thenorphine, however, were not able to induce locomotor sensitization, but induced tolerance. Pretreatment with thenorphine 30 min prior to morphine effectively inhibited the psychomotor effect of morphine in mice (P<0.01). Co-adminis     

Sensitization to MDMA locomotor effects and changes in the functionality of 5-HT(2A) and D₂ receptors in mice

The behavioral and neurochemical adaptations related to chronic 3,4-methylenedioxymethamphetamine (MDMA) treatment are largely unknown. In this study, we assessed whether repeated administration of MDMA would induce (a) context-dependent locomotor sensitization in mice and (b) changes in serotonin 5-HT(2A) and dopamine D? receptor functionality as measured by [3?S]GTPγS binding. Mice were treated with MDMA (10 mg/kg, intraperitoneally) or saline every other day for 11 days either in their home cages or in the environment where locomotor activity was measured. After a 10-day withdrawal period, mice were challenged with MDMA (5 and 10 mg/kg) and saline before locomotor activity measurements. During repeated MDMA treatment, locomotion was progressively enhanced, indicating the development of behavioral sensitization. The MDMA challenge at a dose of 5 mg/kg increased locomotor activity to a greater extent in mice pretreated with MDMA in the testing apparatus than in mice pretreated in the home cages, revealing that contextual cues paired with repeated drug exposure can enhance the expression of behavioral sensitization to MDMA. In contrast, a challenge administration of MDMA at 10 mg/kg induced similar locomotor sensitization in mice pretreated in both environments. An increase in the functionality of cortical 5-HT(2A) receptors was observed in mice pretreated with MDMA compared with mice pretreated with saline, but this activation was significantly greater in mice pretreated in the locomotor environment. In contrast, the functional activity of striatal D? receptors was significantly decreased only in mice pretreated with MDMA in the testing apparatus. These results reveal neuroadaptations in cortical 5-HT(2A) and striatal D? receptors after MDMA-induced behavioral sensitization in mice.     

Effects of serotonergic manipulations on the behavioral sensitization and disinhibition associated with repeated amphetamine treatment

This study investigated the effects of repeated amphetamine treatment on locomotor activity and behavioral inhibition in the elevated plus-maze, and the influence of serotonin (5-HT) neurotransmission on these behaviors. Acute administration of amphetamine (1.0 mg/kg subcutaneously [SC]) stimulated locomotor activity, which was attenuated by acute citalopram (5.0 mg/kg SC) pretreatment. Repeated daily treatment with amphetamine (15 days) sensitized the rats to the amphetamine-induced locomotor stimulation. Acute pretreatment with the 5-HT precursor l-5-hydroxytryptophan (5-HTP; 25 mg/kg IP) or chronic treatment with the selective 5-HT reuptake inhibitor citalopram (5.0 mg/kg SC, twice daily), did not alter the expression of amphetamine-induced locomotor sensitization. In the elevated plus-maze, animals subjected to repeated amphetamine treatment expressed behavioral disinhibition after amphetamine exposure (1.0 mg/kg SC; -35 min), which was antagonized both by acute 5-HTP and chronic citalopram treatment. In summary, these findings suggest that behavioral sensitization to amphetamine is associated with amphetamine-induced behavioral disinhibition, and that acute 5-HTP as well as chronic citalopram treatment counteract the expression of amphetamine-induced behavioral disinhibition, but not locomotor sensitization. It appears likely that the antagonistic effects of 5-HTP and citalopram on behavioral disinhibition derive from a drug-induced facilitation of brain 5-HT neurotransmission.     

Tolerance to the increased locomotor activity produced by l-5-hydroxytryptophan following peripheral decarboxylase inhibition in mice

The development of tolerance to hyperactivity produced by l-5-hydroxytryptophan (5-HTP) was studied in mice pretreated with the peripheral decarboxylase inhibitor MK-486. The results of Experiment I indicated that partial tolerance developed to 5-HTP given twice daily (i.p.) at a dose of 400 mg/kg, but not at a dose of 800 mg/kg. Sustained hyperactivity at the greater dose (800 mg/kg) apparently resulted from the induction of seizures and stereotypy rather than increased locomotor activity. When 5-HTP (400 mg/kg) or saline was administered three times daily (Experiments II and III), the locomotor activity of saline control groups did not differ significantly from chronic 5-HTP-treated groups, but both differed significantly from that of acute 5-HTP-treated animals. Cessation of treatments resulted in a recovery of 5-HTP-induced hyperactivity for experimental animals when later retested. These findings suggest that mice develop tolerance to the effects of 5-HTP on locomotor activity and agree with the hypothesis that behavior change is more closely correlated with the rate of change in concentration of neurotransmitters than the absolute concentrations.     

Repeated alcohol: behavioral sensitization and alcohol-heightened aggression in mice

RATIONALE: Repeated administration of psychomotor stimulants or opiates can induce behavioral sensitization, typically detected as progressive and long-lasting increases in the motor-activating effects of these drugs. This phenomenon may be relevant to seizure susceptibility, drug self-administration, and sexual behavior. Repeated administration of alcohol can also induce behavioral sensitization and may have consequences on how alcohol affects aggressive behavior. OBJECTIVES: To (1) determine the enduring nature of locomotor sensitization to alcohol; (2) examine subsequent changes to morphine and amphetamine effects on locomotor behavior; and (3) test whether behavioral sensitization to alcohol or morphine is relevant to alcohol-heightened aggression. METHODS AND RESULTS: In the first experiment, male CFW mice were given ten injections of alcohol (2.4 g/kg/day), morphine (30.0 mg/kg/day), or saline. Video tracking confirmed locomotor sensitization--an approximate 200% increase in the motor-stimulating effects of these drugs. Challenges with 2.0 g/kg alcohol revealed that locomotor sensitization to alcohol persisted for at least 2 months. Alcohol-sensitized mice showed evidence of cross-tolerance to the sedative effects of morphine (5 mg/kg) but showed no evidence of cross-sensitization to the stimulant effects of 30.0 mg/kg morphine or 1.0 mg/kg amphetamine. In the second experiment, under conditions resulting in species-typical aggressive behavior against a male intruder, there were no differences in the aggressive behavior relative to saline control mice following alcohol or morphine sensitization. However, in the mice sensitized to alcohol, but not to morphine, there was a vertical shift in the dose-effect curve for moderate doses of alcohol (0.6-1.7 g/kg, p.o.). In addition, twice as many alcohol-sensitized mice consistently showed alcohol-heightened aggression when compared with the saline control mice (74% vs 37%, respectively). CONCLUSIONS: Repeated administration of alcohol can sensitize locomotor stimulation and may also render mice more vulnerable to increased aggression after alcohol. Moreover, the results suggest that at least some of the neuroadaptations caused by repeated administration of alcohol are relevant to alcohol-heightened aggression.     

Morphine-induced sensitization in mice: changes in locomotor activity by prior scheduled exposure to GABAA receptor agents

This study investigated the effects of a gamma-amino-butyric acid type A (GABAA) receptor agonist and antagonist on morphine-induced locomotor sensitization in male albino mice. Subcutaneous administration to mice of a high dose of morphine (30 mg/kg), but not lower doses (5, 10 and 20 mg/kg) increased locomotion. The maximum locomotor activity was achieved during a 20-min measurement period. The locomotor response to a low dose of morphine (5 mg/kg, subcutaneously) given on day 9 was enhanced in mice pretreated with morphine (7.5, 15 and 30 mg/kg/day x 3 days), indicating that sensitization had developed. Three-day intracerebroventricular (i.c.v.) administration of the GABAA receptor agonist, muscimol (0.025, 0.05, 0.1 and 0.2 microg/mouse/day) significantly decreased both morphine-induced motor stimulation and locomotor sensitization. On the other hand, a 3-day pretreatment with the GABAA-receptor antagonist, bicuculline (0.25, 0.5 and 1 microg/mouse/day) reduced morphine (15 mg/kg)-induced locomotor sensitization. Repeated i.c.v. injections of a lower dose of bicuculline (0.25 microg/mouse/day x 3 days) by itself also decreased morphine-induced locomotion. Furthermore, repeated i.c.v. administration of bicuculline (0.25, 0.5 and 1 microg/mouse/day x 3 days) decreased the effect of i.c.v. injection of muscimol (0.1 microg/mouse/day x 3 days) on locomotor activity induced by morphine (5 mg/kg) in both control and sensitized mice. The magnitude of this response was, however, variable. The results indicate that GABAA receptors might be involved in the acquisition of morphine-induced sensitization.     

Behavioral sensitization and voluntary ethanol drinking in alcohol-preferring AA rats exposed to different regimens of morphine treatment

The purpose of the study was to investigate the effects of three different regimens of morphine treatment on subsequent voluntary ethanol drinking in alcohol-preferring AA (Alko Alcohol) rats. The rats were given morphine subcutaneously either intermittently on alternating days (15 x 10 mg/kg or 5 x 5-20 mg/kg in escalating doses) or subchronically on four consecutive days (3-20 mg/kg/d). Horizontal locomotor activity was monitored after challenges with additional morphine injections (3 mg/kg) ten days and six weeks after termination of the pretreatment to test if behavioral sensitization was induced by repeated morphine administration. Both intermittent pretreatments induced sensitized locomotor response after the first challenge, whereas subchronic injections did not. After the challenge the rats were given a free choice between tap water and 10% (v/v) ethanol solution for four weeks. The rats pretreated and challenged with morphine did not differ significantly in the acquisition of ethanol drinking from the saline-treated controls. In contrast, ethanol drinking was impaired during the first week of ethanol access in the saline-treated rats given a single morphine injection. The second morphine challenge given after the ethanol-drinking phase did not reveal sensitization in any of the groups. The results suggest that pattern of morphine administration rather than the dose or number of exposures to the drug is the most important factor in induction of behavioral sensitization, and that exposure to ethanol may interfere with this process. They also support earlier findings showing that acute morphine may suppress voluntary ethanol drinking, but failed to provide clear evidence for behavioral sensitization to morphine contributing to predilection towards ethanol in AA rats.     

Serotonin 5-HT2 receptor antagonist does not reverse established ethanol-induced sensitization but blocks its development and expression

Several substances that inhibit the induction or expression of behavioral sensitization have been proposed, but patients who present for treatment often have already an established sensitized drug response. Serotonergic agents, including serotonin-2 (5-HT(2)) antagonists, reverse cocaine sensitization, but there is no evidence for the same effect with ethanol, although serotonin involvement in ethanol sensitization has been well reported. To evaluate a 5-HT(2C) antagonist effect on reversing established ethanol sensitization, three experiments were performed assessing locomotor activity of mice under different treatments. First, mice received daily intraperitoneal saline (S), mianserin 10 (M1) or 20 mg/kg (M2), ethanol 2 g/kg (E), or ethanol+mianserin for 21 days. Then, each treatment was withdrawn for 3 days, and mice were randomly challenged with S, E, M1, or M2. During the next 7 days, S and E groups were subjected to daily treatment with S, E, M1, or M2. On the eighth day, all rats were tested under ethanol challenge. The saline group expressed sensitization under ethanol challenge similarly to the ethanol group. Mianserin+ethanol blocked the development of sensitization, suggesting an involvement of the 5-HT(2C) receptor subtype on ethanol-induced sensitization. Ethanol challenge to the chronic mianserin group did not express sensitization, implicating a role for mianserin in protection against stress. Mianserin did not reverse established ethanol sensitization, suggesting that cocaine- and ethanol-induced sensitization involved different mechanisms.     

Relevance of MDMA ("ecstasy")-induced neurotoxicity to long-lasting psychomotor stimulation in mice

Rationale. Although many studies have focused on the mechanisms underlying MDMA-induced neurotoxicity, little is known about the subsequent long-term response to psychostimulants following exposure to a neurotoxic dose of MDMA. Objectives. We investigated the effect of pre-exposure to neurotoxic and non-neurotoxic doses of MDMA on the response of mice to the psychomotor stimulating effects of MDMA and cocaine. Methods. To investigate MDMA-induced neurotoxicity, male Swiss Webster mice were subjected to three regimens of MDMA: i) 40 mg/kg×2, ii) 30 mg/kg×2, and iii) 15 mg/kg×2 for 2 days. On day 5 following the last exposure to MDMA, the levels of dopaminergic and serotonergic markers were determined. For the behavioral experiments, mice received either a single injection of 10 mg/kg MDMA [MDMA(L)] or one of the following doses of MDMA: 30 mg/kg×2 or 15 mg/kg×2 for 2 days [MDMA (H)]. A third group received saline as a control. On day 5 after the last pretreatment injection, the first MDMA (10 mg/kg) challenge was given, and on day 12, cocaine (20 mg/kg) was administered. Subsequently, mice were re-challenged with MDMA on days 35, 50 and 80, after which locomotor activity was monitored by infrared beam-interrupts. On day 83, mice were killed to detect the levels of dopaminergic and serotonergic markers. Results. MDMA-induced mortality and depletion of dopaminergic and serotonergic markers were dose-dependent. MDMA (H) mice endured a sensitized response to MDMA challenge from days 5 through 80, e.g. a persistent 3-fold increase in locomotor activity compared to the response of mice that were not pretreated with a neurotoxic dose of MDMA. The depletion of DAT and 5-HTT binding sites was sustained throughout this time period (64–68% of control). The MDMA (L) mice showed a sensitized response to MDMA only on day 5. Both MDMA (L) and MDMA (H) mice were sensitized to the cocaine challenge. Conclusions. The induction of sensitization to the locomotor stimulating effects of MDMA and cocaine was independent of MDMA-induced neurotoxicity. However, the long-lasting maintenance of the sensitized response to MDMA may be related to the enduring neurotoxicity caused by MDMA. Electronic Publication     

Comparison of the effects of mGluR1 and mGluR5 antagonists on the expression of behavioral sensitization to the locomotor effect of morphine and the morphine withdrawal jumping in mice

The aim of the present study was to compare the influence of group I metabotropic glutamate receptor (mGluR) antagonists (mGluR1 and mGluR5) on the expression of sensitization to the locomotor effect of morphine. We also tested how these compounds affect the morphine withdrawal jumps in mice. In our study, the mGluR1 antagonist EMQMCM [3-ethyl-2-methyl-quinolin-6-yl-(4-methoxy-cyclohexyl)-methanone methanesulfonate] and the mGluR5 antagonist MTEP ([(2-methyl-1,3-thiazol-4-yl) ethynyl] pyridine) were used. Sensitization was induced by five intraperitoneal (i.p.) injections of morphine at the dose of 10 mg/kg, every 3 days. Morphine dependence was induced by subcutaneous (s.c.) implantation of pellets containing 37.5 mg of morphine base for three days. Our data indicate that pretreatment with EMQMCM (5, 10, 20 mg/kg) and MTEP (5, 10 mg/kg) on the challenge day, inhibited the expression of sensitization to the locomotor effect of morphine in mice. Antagonists of both subtypes of the group I mGlurs given alone, did not modify the acute locomotor effect of morphine. On the other hand, EMQMCM did not attenuate the morphine withdrawal jumps precipitated by naloxone (4 mg/kg). The results suggest that both subtypes of the group I mGluRs (mGluR1 and mGluR5) take part in the expression of morphine sensitization processes but mGluR1 is not involved in the expression of morphine withdrawal jumps in mice. These findings may have implications for the treatment of opiate addiction in future.