Dynorphin A, kappa opioid receptors and the antinociceptive efficacy of asimadoline in streptozotocin-induced diabetic rats

Aims/hypothesis We investigated spinal and peripheral kappa opioid systems in diabetic rats.Materials and methods Dynorphin A, N-methyl-d-aspartate (NMDA) and kappa opioid receptor (KOR) were measured in spinal cord, dorsal root ganglia, peripheral nerves and foot skin of control and streptozotocin-induced diabetic rats by immunoassay and Western blotting. Behavioural assessments of paw tactile sensitivity and formalin-evoked hyperalgesia were performed in normal and diabetic rats before and after treatment with asimadoline.Results Dynorphin A protein levels were significantly increased in peripheral nerves and footpad skin of diabetic rats. Dynorphin A exhibits both anti- and pro-nociceptive properties depending on activation of either KOR or NMDA receptors. Spinal protein levels of these receptors were not changed by diabetes, while KOR levels in the sciatic and peroneal nerves were significantly increased. Exploiting the presence and elevated levels of KOR in the periphery, we investigated the effect of the peripheral KOR agonist asimadoline on formalin-evoked hyperalgesia and tactile allodynia in diabetic rats. Both formalin-evoked hyperalgesia and tactile allodynia in diabetic rats were acutely ameliorated by asimadoline. To confirm that the effect of asimadoline was related to its property as KOR agonist, diabetic rats were pretreated with the selective KOR antagonist nor-binaltorphimine. Intraplantar nor-binaltorphimine abolished the ability of asimadoline to alleviate tactile allodynia in diabetic rats. Systemic and intrathecal nor-binaltorphimine partially inhibited the effect of asimadoline against formalin-evoked hyperalgesia in diabetic rats.Conclusions/interpretation Using selective peripheral KOR agonists to take advantage of elevated peripheral KOR expression may provide a novel therapeutic approach for painful diabetic neuropathy.     

Central reinforcing effects of ethanol are blocked by catalase inhibition.

Recent studies have systematically indicated that newborn rats are highly sensitive to ethanol's positive reinforcing effects. Central administrations of ethanol (25-200mg %) associated with an olfactory conditioned stimulus (CS) promote subsequent conditioned approach to the CS as evaluated through the newborn's response to a surrogate nipple scented with the CS. It has been shown that ethanol's first metabolite, acetaldehyde, exerts significant reinforcing effects in the central nervous system. A significant amount of acetaldehyde is derived from ethanol metabolism via the catalase system. In newborn rats, catalase levels are particularly high in several brain structures. The present study tested the effect of catalase inhibition on central ethanol reinforcement. In the first experiment, pups experienced lemon odor either paired or unpaired with intracisternal (IC) administrations of 100mg% ethanol. Half of the animals corresponding to each learning condition were pretreated with IC administrations of either physiological saline or a catalase inhibitor (sodium-azide). Catalase inhibition completely suppressed ethanol reinforcement in paired groups without affecting responsiveness to the CS during conditioning or responding by unpaired control groups. A second experiment tested whether these effects were specific to ethanol reinforcement or due instead to general impairment in learning and expression capabilities. Central administration of an endogenous kappa opioid receptor agonist (dynorphin A-13) was used as an alternative source of reinforcement. Inhibition of the catalase system had no effect on the reinforcing properties of dynorphin. The present results support the hypothesis that ethanol metabolism regulated by the catalase system plays a critical role in determination of ethanol reinforcement in newborn rats.     

乙醇对大鼠中枢神经系统内源性阿片肽的影响

乙醇中毒、乙醇依赖和乙醇滥用已成为全球性的医学和社会问题,在我国乙醇滥用亦日趋严重。研究表明,大量中枢神经递质参与了乙醇中毒过程,如内源性阿片肽、多巴胺递质、γ-氨基酸能递质、谷氨酸能递质、5-羟色胺等。本文主要探讨乙醇对内源性阿片类物质的影响,以了解其在乙醇中毒以及乙醇依赖过程中发挥的作用,为临床上预防和治疗乙醇中毒以及乙醇依赖提供新的思路。     

Effects of adrenal steroid manipulations and repeated restraint stress on dynorphin mRNA levels and excitatory amino acid receptor binding in hippocampus

Adrenal steroid and stress effects were determined in hippocampus on levels of dynorphin (DYN) mRNA, expressed in dentate gyrus, and excitatory amino acid receptors, measured in Ammon's horn and dentate gyrus. Adrenalectomy (ADX) decreased DYN mRNA levels in dentate gyrus and replacement with aldosterone (ALDO), a specific type I adrenal steroid receptor agonist, prevented the decrease. Ru28362, a specific type II receptor agonist, had no effect. Likewise, kainate receptor binding to the stratum lucidum and hilus region of dorsal hippocampus was decreased after ADX and this decrease was prevented by ALDO but not by Ru28362 treatment. Similar though smaller effects were found for CNQX binding to AMPA receptors but only in the dentate gyrus molecular or infra- and supragranular layers. Although corticosterone (CORT) treatment of intact rats (40 mg/kg for 3 weeks) elevated DYN mRNA levels in dentate gyrus, up to 14 days of daily restraint stress (1 or 6 h/day) had no significant effect. Neither CORT treatment nor repeated restraint stress altered NMDA and non-NMDA glutamate receptors in hippocampus. The results of this study showing ADX-induced decreases of DYN mRNA and CNQX binding in dentate gyrus and decreased kainate binding in mossy fiber terminal regions are consistent with morphological evidence showing that adrenal steroids maintain normal integrity and structure of dentate gyrus neurons and do so via type I adrenal steroid receptors. These same parameters are apparently not sensitive to chronic restraint stress although the effects of other stressors must be examined.     

Effect of prodynorphin-derived opioid peptides on the ovulatory luteinizing hormone surge in the proestrous rat

The objective of this study was to determine whether prodynorphin-derived opioid peptides could block the spontaneous luteinizing hormone (LH) surge and ovulation, and if so, whether this inhibitory action was mediated through κ-opioid receptors. Various doses of dynorphin peptides (dynorphin A_1–17, dynorphin A_1–8, dynorphin B, α- and β-neoendorphin) were infused into the brain through third-ventricle cannulae in rats between 1330–1800 h on proestrus. Each dynorphin peptide blocked the LH surge and ovulation in a dose-dependent manner. Dynorphin A_1–17 and A_1–8 were equally effective in producing these actions, and more potent than either dynorphin B or α- or β-neoendorphin. U50,488H, a specific κ-opioid receptor agonist, also blocked the LH surge and ovulation. When a mixture of five dynorphin peptides was infused intraventricularly, each at a dose that inhibited the LH surge, both the surge and ovulation were blocked. However, when norbinaltorphimine, a specific κ-opioid receptor antagonist, was coinfused with the mixture of dynorphin peptides, the LH surge and ovulation were fully restored. These results demonstrate that prodynorphin-derived opioid peptides, acting through κ-opioid receptors, can block the LH surge and ovulation. Dynorphin A_1–17 and A_1–8 are the most potent in this regard.     

电针对分娩镇痛效应及强啡肽调控的影响

目的:探讨电针对分娩镇痛的临床疗效及机理。方法:选择2011年1～6月住院分娩并符合纳入观察标准的待产妇120例,并采用随机数字表格法在产程进入活跃期至胎儿娩出期间将其分为3组,A组应用电针镇痛,B组采用穴位按摩镇痛,C组无干预措施自然分娩。对照观察各组分娩疼痛的镇痛作用及产妇血清中强啡肽含量的变化。结果:镇痛效果A、B两组明显优于C组(P<0.000 1);血清强啡肽含量A、B两组治疗后均高于治疗前,且治疗后组间差异明显(P<0.000 1)。结论:电针、按摩可减轻分娩疼痛,并能使孕妇血清中强啡肽含量增加。电针可提高血清中强啡肽的含量,以达到镇痛的作用。     

The effect of morphine tolerance dependence and abstinence on immunoreactive dynorphin (1–13) levels in discrete brain regions, spinal cord, pituitary gland and peripheral tissues of the rat

The effect of morphine tolerance dependence and protracted abstinence on the levels of dynorphin (1–13) in discrete brain regions, spinal cord, pituitary gland and peripheral tissues was determined in male Sprague-Dawley rats. Of all the tissues examined, the highest level of dynorphin (1–13) was found to be in the pituitary gland. Among the brain regions and spinal cord examined, the levels of dynorphin (1–13) in descending order were: hypothalamus, spinal cord, midbrain, pons and medulla, hippocampus, cortex, amygdala and striatum. The descending order for the levels of dynorphin (1–13) in peripheral tissues was: adrenals, heart and kidneys. In morphine tolerant rats, the levels of dynorphin (1–13) increased in amygdala but were decreased in pons and medulla. In morphine abstinent rats, the levels of dynorphin (1–13) were increased in amygdala, hypothalamus and hippocampus. The levels of dynorphin (1–13) were increased in pituitary but decreased in spinal cord and remained so even during protracted abstinence. The levels of dynorphin (1–13) in the peripheral tissues of morphine tolerant rats were unaffected. However, in the heart and kidneys of morphine abstinent rats, the levels of dynorphin (1–13) were increased significantly. It is concluded that both morphine tolerance and abstinence modify the levels of dynorphin (1–13) in pituitary, central and peripheral tissues. Morphine abstinence differed from non-abstinence process in that there were additional changes (increases) in the levels of dynorphin (1–13) in brain regions (hypothalamus and hippocampus) and peripheral tissues (heart and kidneys) and may contribute to the symptoms of the morphine abstinence syndrome. The lower levels of dynorphin (1–13) in spinal cord may be responsible for the potentiation of morphine effects by κ-opiate agonist in morphine tolerant dependent rodents.     

Enhancement of phagocytosis by dynorphin A in mouse peritoneal macrophages

The effects of the opioid peptide dynorphin A (DynA) on phagocytosis in peritoneal macrophages was examined by flow cytometry (FCM). DynA enhanced phagocytosis in a dose-dependent manner. Leucine-enkephalin (Leu-Enk), methionine-enkephalin (Met-Enk), β-neo-endorphin (βNeo-End), DynA(9–17) and DynA(13–17) had no such activity, -Neo-endorphin ( Neo-End), dynorphin B (DynB), DynA(l–13) and DynA(6–17) enhanced phagocytosis less effectively than DynA. Naloxone did not inhibit the enhancement of phagocytosis induced by DynA. Unstimulated control phagocytosis was partially suppressed in Ca²⁺-free EGTA-containing solution and even in this solution DynA enhanced phagocytosis. However, the enhancement by DynA was suppressed in EGTA- and BAPTA-AM-containing Ca²⁺-free solution. The present study showed that enhancement of phagocytosis by DynA was independent of extracellular Ca²⁺ ([Ca²⁺]_o) and dependent on intracellular Ca²⁺ ([Ca²⁺]_i). The present results support DynA being one of the mediators from the nervous system that modulates the immune system.     

中药复方“体复康”对运动性疲劳大鼠血乳酸、β-内啡肽、亮氨酸脑啡肽及强啡肽A_(1-13)影响的实验研究

以长时期（共7周）大强度跑台运动（速度由15m／min递增至35m／min，运动时间为20～25min／d）制造大鼠疲劳模型，探索疲劳大鼠外周阿片肽的变化及中药复方的作用机理。结果表明：运动后即刻血乳酸显著高于对照组，血浆β-内啡肽、强啡肽A1-13含量显著下降，而亮氨酸脑啡肽变化不明显；经中药复方治疗后，上述变化均有不同程度的恢复。表明此运动强度下的疲劳大鼠，内源性阿片肽系统受抑制而使外用血中的β-内啡肽、强啡肽A1-13含量下降；中药复方作用后激活了此系统，主要使卜内啡肽水平升高，并对血乳酸有一定的清除作用，从而有利于消除疲劳。