Isolation impairs place preference conditioning to morphine but not aversive learning in mice

Morphine (8–100 mg/kg IP) induces place preference conditioning in mice. The effect of two different periods of isolation (15 and 30 days) was examined. Mice isolated for 15 days but not 30 days exhibited place preference conditioning to morphine (8 mg/kg). After 30 days of isolation morphine could not induce place preference conditioning with the following doses (8, 16, 64, 100 mg/kg). Social regrouping of male mice previously isolated for 30 days with naive female mice for 15 or 30 days resulted in a reappearance of the conditioned place preference to morphine (16 mg/kg). The specificity of this associative deficit was examined by testing learning in isolated compared to non-isolated mice in two distinct settings: escape learning in the Morris water maze and passive avoidance acquisition and retention. On the Morris water maze isolated mice did not differ from non-isolated mice regarding place learning, the probe trial or extinction. Isolated mice were unimpaired in passive avoidance acquisition and retention. It was concluded that the deficits in place preference conditioning were not the result of a global learning impairment in isolated mice. Received: 10 April 1996 /Final version: 20 September 1996     

Dorsal and ventral dopaminergic innervation of the spinal cord: Functional implications

Several studies have demonstrated that a descending dopaminergic pathway innervates the dorsal and the intermediate gray matter of the spinal cord and have suggested that this pathway is involved in pain modulation and in the control of autonomie functions. Other studies have also demonstrated the presence of dopamine (DA) and DA metabolites as well as of DA receptors in the ventral cord. There is also evidence for the implication of DA in the control of motor functions at the spinal level. The occurrence of a dopaminergic innervation in the ventral horn has been, however, disputed until recently. But recent work has demonstrated that the motoneural cell groups in the ventral horn (lamina IX) are a target for descending dopaminergic fibers. In addition, the possibility that DA is a mediator of primary afferent fibers has also been postulated. Finally, the occurrence of dopaminergic cell bodies has been suggested in the spinal cord. This indicates that DA is probably implicated in a complex manner in spinal functions. In the present paper the possible involvement of DA in sensory and in motor functions at spinal level will be discussed in view of neurochemical observations made in polyarthritic rats, in which pain-related behavior and reduction of locomotor activity associated with a marked decrease in mobility, are observed.     

Conditioned locomotion and place preference elicited by tactile cues paired exclusively with morphine in an open field

A novel version of the conditioned place preference (CPP) technique was used in an attempt to determine whether tactile stimuli previously associated with morphine elicit approach and sustained contact. Empirical support for this view has been equivocal, prompting some to question the validity of the CPP technique. In the present study, rats received, during conditioning, morphine (10 mg/kg, IP) paired exclusively with an open field floor made of four quadrants of one texture (CS+) and saline with another floor made of four quadrants of a different texture (CS–). On the test for CPP, rats were given saline and placed in an open field containing either 1, 2, or 4 quadrants of the CS+ (with 3, 2, 0 quadrants of the CS–, respectively). These animals showed high absolute CPP scores on the test, spending, on average, as much as 83% and 75% of their time on the CS+ when two and one CS+ quadrants, respectively, were present. Concurrent measures of activity indicated that animals were most active when all four quadrants were CS+ and least active when zero or one CS+ quadrant was present. Thus, once an animal approached and made contact with the CS+ it tended to maintain contact with this stimulus and to reduce its approach to and contact with other stimuli. The differentiating features of this version of the CPP technique, as well as the relationship between morphine-induced conditioned locomotion and CPP, are discussed.     

臂丛神经阻滞加用地塞米松和小剂量吗啡用于术后镇痛的效果观察

目的 观察臂丛神经阻滞的局麻药液中加入地塞米松和小剂量吗啡用于术后镇痛的效果和副作用。方法 80例患者随机分为A、B、C、D四组。全部用肌间沟法臂丛神经阻滞，A组（n=20)注入0.5%布比卡因、2%利多卡因等量混合液25ml；B组（n=20)注入A组用药加地塞米松10mg(2ml)；C组（n=20)注入A组用药加吗啡2mg(0.2ml)；D组（n=20)注入A组用药加地塞米松10mg(2ml)、吗啡2mg(0.2ml)。结果 B、C、D组与A组相比起效时间显著缩短、镇痛时间显著延长，差异非常显著（P＜0.01)；而D组和B、C组相比镇痛时间又明显延长，差异非常显著（P＜0.01)；C组中有1例（5％）因发生恶心呕吐，其余多组无并发症发生。结论 臂丛神经阻滞的局麻药液中加入地塞米松和小剂量吗啡用于术后镇痛，镇痛时间长，效果可靠，副作用少，操作方便，经济实用。     

Neurochemical studies on the mesolimbic circuitry of antinociception

Previous studies using the technique of microinjection into brain nuclei indicated that the periaqueductal gray (PAG), nucleus accumbens, habenula and amygdala play an essential role in pain modulation and that these nuclei possibly act through a ‘mesolimbic neural loop‘ to exert an analgesic effect, in which Met-enkephalin (MEK) and β-endorphin (β-EP) have been implicated as the two major opioid peptides involved in antinociception. In the present study performed in rabbits, intracranial microinjection was supplemented with push-pull perfusion and radioimmunoassay to determine whether the release of enkephalins (ENK) and β-EP was increased in these nuclei when the putative neural circuit was activated by morphine administered into one of the nuclei. The results showed: (1) microinjection of morphine into the PAG increased the release of ENK and β-EP in the N. accumbens, and vice versa; (2) microinjection of morphine into the N. accumbens increased the release of ENK and β-EP in the amygdala, and vice versa; (3) morphine microinjected into the PAG caused an increase in the release of ENK and β-EP in the amygdala and vice versa, although the release of ENK in PAG was statistically not significant. These results indicate that PAG, N. accumbens and amygdala are connected in a network served by a positive feedback circuitry.     

An analysis of the paradoxical effect of morphine on runway speed and food consumption

A previously reported paradigm in which rats run down a runway for food reward followed by morphine injection was analyzed to assess the utility of the paradigm in studies of opiate reinforcement. One experiment replicated the original report that post-trial morphine caused both an increase in runway speed and a decrease in food consumption (taste aversion) over successive trials, and showed in addition that the increase in runway speed did not occur as a result of food deprivation alone, but required the animals to have consumed food in the goal box. A second study using the quaternary opiate antagonist methyl naltrexone to block the peripheral effects of morphine suggested that the increase in runway speed has a peripheral locus while the taste aversion has a central one. A third experiment in which morphine was microinjected into either the lateral ventricle or the ventral tegmental area supported these observations, in that intracranial morphine failed to result in an increased runway speed, but did produce taste aversion after microinjection into either site. These findings also suggest that the increase in runway speed caused by post-trial morphine in this experiment has a peripheral locus of effect, which is probably distinct from the central effect that supports morphine self-administration and conditioned place preference. Offprint requests to: W.A.CorrigallThe views expressed in this publication are those of the authors and do not necessarily reflect those of the Addiction Research Foundation     

鞘内注射吗啡对切口疼痛大鼠脊髓背角蛋白激酶Cγ免疫反应的影响

目的 研究鞘内注射吗啡对切口疼痛大鼠脊髓背角蛋白激酶Cγ(PKCγ)免疫反应的影响。方法 SD雄性大鼠24只,随机分为4组(每组6只):假手术组(Ⅰ组)、对照组(Ⅱ组)术前30 min鞘内注射人工脑脊液20μl,术后吗啡治疗组(Ⅲ组)、术前吗啡治疗组(Ⅳ组)分别于术后和术前30min鞘内注射吗啡5μg(10 μl)。所有大鼠均按Brennan法制成切口疼痛模型,用免疫组织化学方法观察脊髓背角PKCγ的表达。结果 Ⅱ组术侧脊髓背角PKCγ-IR表达高于非术侧及Ⅰ组(P<0.01)。与Ⅱ组比较,Ⅲ组、Ⅳ组脊髓背角PKCγ-IR表达降低(P<0.05或0.01),而Ⅲ组、Ⅳ组比较差异无显著性。结论 在大鼠切口疼痛模型中,鞘内注射吗啡的镇痛作用可能与抑制脊髓背角的PKCγ-IR免疫反应有关。     

应用小鼠在Y形迷宫中的自主选择能力测定急性及慢性东莨菪碱与吗啡对记忆的影响

应用Ｙ型迷宫研究了急性与慢性东莨菪碱和吗啡对小鼠记忆能力的影响。单剂量东莨菪碱（１ｍｇ／ｋｇｉｐ）和吗啡（１０ｍｇ／ｋｇｉｐ）均能显著损害小鼠的短时记忆（ｗｏｒｋｉｎｇｍｅｍｏｒｙ）。重复给药后东莨菪碱的这种作用很快消失。但吗啡每天一次，连续３次给药这种作用加强，连续５次给药这种作用反而减弱。东莨菪碱不能损害小鼠长时记忆（ｒｅｆｅｒｅｎｃｅｍｅｍｏｒｙ），而吗啡对长时记忆有损害作用。结果还提示小鼠短时记忆不受自发活动能力的影响。     

高浓度吗啡对体外培养的小鼠淋巴细胞增殖的抑制效应

高浓度吗啡对体外培养的小鼠淋巴细胞增殖的抑制效应北京医科大学药理学教研室陆正武，林志彬利用不同刺激原诱导的淋巴细胞增殖反应，研究吗啡的体外作用机制。结果表明：（１）高浓度吗啡（≥０．１ｍｍｏｌ·Ｌ－１）以剂量依赖方式，抑制ＣｏｎＡ／ＬＰＳ所致淋巴细胞...     

地塞米松预防术后硬膜外吗啡镇痛的部分并发症

目的：观察静脉注射地塞米松（Dex)对减少手术后与硬膜外吗啡镇痛有关的部分并发症的发生率的作用。方法：随机双盲选择48例在硬膜外麻醉下行妇科肿瘤手术病人进行观察。所有病人在手术后均接受硬膜外吗啡镇痛。Dex组病人（n=24)在手术毕静注Dex8mg，对照组病人（n=24)则给予等量生理盐水。结果：在手术后24h内，Dex组病人手术后总的恶性呕吐发生率为16．7％，明显低于对照组病人的50％（P＜0．01）。两组病人手术后皮肤瘙痒的发生率无明显差异，镇痛效果也无明显差异。结论：预防性静脉注射Dex可减少术后硬膜外吗啡镇痛引起的恶心呕吐的发生率。