Several delta-opioid receptor ligands display no subtype selectivity to the human delta-opioid receptor

Pharmacological studies performed in vivo suggested that the delta-opioid receptor could exist as two distinct subtypes, delta(1) and delta(2), while in vitro studies are inconclusive. Therefore, we measured the binding and functional selectivity of several putative delta(1)- and delta(2)-opioid receptor-selective compounds in membranes from Chinese hamster ovary cells stably expressing the human delta-opioid receptor. The compounds characterized were the agonists [D-Pen(2),D-Pen(5)]enkephalin (DPDPE, delta(1)) and deltorphin II (delta(2)), and the antagonists 7-benzylidenenaltrexone (BNTX, delta(1)), naltriben (delta(2)), naltrindole 5'-isothiocyanate (delta(2)), and naltrindole (delta(1) and delta(2)). In competition binding assays, all compounds tested showed no preference for the [3H]DPDPE, [3H]deltorphin II, or [3H]naltrindole binding sites. BNTX also showed no selectivity for the delta-opioid receptor over the mu-opioid receptor. In functional assays, the stimulation of [35S]GTPgammaS binding induced by either DPDPE or deltorphin II was potently inhibited by both delta(1)- and delta(2)-opioid receptor-selective antagonists. Together, these results indicate that these compounds are not selective for either the delta(1)- or delta(2)-opioid receptor binding sites in binding or functional assays.     

吗啡联合小剂量阿片受体拮抗剂应用研究进展

吗啡是临床常用的强效阿片类镇痛药，临床应用中出现恶心、呕吐、镇静、瘙痒、便秘、尿潴留、呼吸抑制等副作用，长期应用又出现耐受和依赖。大剂量阿片受体拮抗剂能拮抗吗啡所产生的全部效应，而小剂量的阿片受体拮抗剂不仅能减少或减轻吗啡所致的副作用，还能增强吗啡的镇痛效能。本文就小剂量阿片受体拮抗剂与吗啡的联合应用、小剂量阿片受体拮抗剂增强吗啡镇痛效能、减弱吗啡耐受和依赖的作用机制，以及拮抗副作用等方面的研究进展进行综述。     

Agonist-specific down-regulation of the human delta-opioid receptor

Down-regulation of the delta-opioid receptor contributes to the development of tolerance to delta-opioid receptor agonists. The involvement of the carboxy terminus of the mouse delta-opioid receptor in peptide agonist-mediated down-regulation has been established. In the present study, we examined the down-regulation of the truncated human delta-opioid receptor by structurally distinct delta-opioid receptor agonists. Chinese hamster ovary (CHO) cells, expressing the full-length or truncated epitope-tagged human delta-opioid receptors were incubated with various delta-opioid receptor agonists (100 nM, 24 h), and membrane receptor levels were determined by [(3)H]naltrindole saturation binding. Each delta-opioid receptor agonist tested down-regulated the full-length receptor. Truncation of the carboxy terminus abolished down-regulation by all delta-opioid receptor agonists, except SNC80 ((+)-4-[(alphaR)-alpha-((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]N,N-diethylbenzamide). In addition, truncation of the C-terminus completely attenuated [D-Pen(2)-D-Pen(5)]enkephalin (DPDPE), but not SNC80-mediated [32P] incorporation into the protein immunoreactive with an anti-epitope-tagged antibody. These findings suggest that SNC80-mediated phosphorylation and down-regulation of the human delta-opioid receptor involves other receptor domains in addition to the carboxy terminus. Pertussis toxin treatment did not block SNC80-mediated down-regulation of the truncated Et-hDOR, indicating that the down-regulation is independent of G(i/o) protein activation and subsequent downstream signaling.     

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。     

Effects of the histamine (H)3 receptor antagonist ABT-239 on acute and repeated nicotine locomotor responses in rats

The addictive potential of nicotine is linked to psychomotor and cognition-enhancing effects. Histamine (H)(3) receptor antagonism has similarly received attention for a role in cognition, however, the role of H(3) receptors are far less studied for affects on nicotine-induced locomotor responses. In the present study we tested whether the H(3) receptor antagonist 4-(2-{2-[(2R)-2 methylpyrrolidinyl] ethyl}-benzofuran-5-yl) benzonitrile (ABT-239) influenced the psychomotor responses to acute and repeated nicotine, including sensitization and conditioned locomotion. ABT-239 (0.3-3 mg/kg) did not alter basal, nicotine-evoked (0.4 mg/kg) locomotor responses, the expression of sensitization, or cue-conditioned locomotion. However, in combination studies rats pretreated with a separate dose of ABT-239 (1 mg/kg) prior to nicotine (0.4 mg/kg) for 5 days and then challenged with nicotine (0.4 mg/kg) after a 5-day withdrawal period, showed significantly higher locomotor hyperactivity in comparison with the effect observed in nicotine-pretreated and challenged rats. Our findings implicate a limited role for H(3) receptors in locomotor responses to nicotine.     

PLASMA CATECHOLAMINE CONCENTRATIONS DURING MORPHINE WITHDRAWAL IN CONSCIOUS GUINEA-PIGS

1. Plasma noradrenaline (NA) and adrenaline (AD) concentrations and locomotor activity were measured in conscious normal and adrenalectomized guinea-pigs before and after injection of a single dose of morphine (15 mg/kg) and following precipitation of withdrawal with naloxone 2 h later. Arterial blood samples were obtained via carotid catheters inserted 3 days before experiment. Normal guinea-pigs given saline instead of morphine were used as controls. 2. Increased locomotor activity occurred following naloxone injection in both intact and adrenalectomized morphine-treated guinea-pigs. 3. Plasma AD concentration was significantly elevated only during the naloxone-precipitated withdrawal period, whereas plasma NA concentration was also elevated during the morphine treatment period. No significant changes occurred in saline-treated guinea-pigs given naloxone. 4. In adrenalectomized guinea-pigs AD did not reach detectable levels in the plasma at any time during the experiments, thus showing that the increased plasma AD level during morphine withdrawal in normal animals reflected adrenal medullary release. 5. It was concluded that measurements of plasma AD concentration and locomotor activity in guinea-pigs should be useful for the study of the interactions between behavioural and autonomic mechanisms involved in opiate dependence and withdrawal, since the effects of morphine and morphine withdrawal on the autonomic nervous system are clearly different in this species.     

In vivo binding of naloxone to opioid receptors in morphine-dependent mice

In vivo binding assay of opioid receptors for naloxone was tested in morphine-dependent mice. The content of naloxone in the brain (whole brain minus cerebellum) and cerebellum was determined as the total binding and non-specific binding, respectively, 20 min after the intravenous injection of [3H]-naloxone. Acute treatment with 8 mg/kg of morphine sulfate markedly enhanced the non-specific binding of naloxone. In contrast, withdrawal for 6 hr after 72 hr of implantation of morphine decreased the non-specific binding of naloxone. The Scatchard analysis of the specific binding revealed two binding sites. The apparent low affinity Kd values of both morphine-tolerant and morphine-withdrawn mice were significantly decreased when compared to their respective controls. The apparent high affinity Kd and the high and low Bmax values were not altered by the morphine dependent-tolerant state.     

Morphine promotes phosphorylation of the human delta-opioid receptor at serine 363

After prolonged stimulation, the delta-opioid receptor becomes desensitized by regulatory mechanisms such as receptor phosphorylation, internalization and down-regulation. In this study, we demonstrate that morphine treatment causes phosphorylation of S363 in the C-terminus of the human delta-opioid receptor. Morphine-mediated phosphorylation reached 53+/-8% of maximum deltorphin II-mediated phosphorylation. Phosphorylation of S363 may contribute to delta-opioid receptor desensitization by morphine.     

咪唑克生对吗啡镇痛、耐受和身体依赖的影响

目的:观察咪唑克生对吗啡镇痛及吗啡所致耐受和躯体依赖的影响.方法:采用小鼠醋酸扭体实验和55℃热板实验观察咪唑克生对基础痛阈及吗啡镇痛作用的影响;采用小鼠热辐射甩尾实验和小鼠55℃热板实验观察咪唑克生对吗啡耐受形成过程的影响;采用大鼠、小鼠身体依赖模型观察咪唑克生对吗啡所致身体依赖的影响.结果:咪唑克生(3-9mg/kg)能显著降低小鼠基础痛阈,抑制吗啡镇痛;加重吗啡所致耐受;诱发大、小鼠发生戒断综合征.结论:咪唑啉受体参与痛阈形成;咪唑克生能抑制吗啡镇痛,加重吗啡所致耐受;并诱发吗啡依赖性动物发生戒断综合征.     

Conditioned place preference for cocaine is attenuated in mice over-expressing the 5-HT3 receptor

The serotonin 5-HT(3) receptor is thought to play a role in the reward pathway and drug abuse by modulating dopamine release within the mesolimbic pathway. Dopamine release stimulated by cocaine and methamphetamine is blocked by administration of 5-HT(3) receptor antagonists. Animal studies demonstrate that 5-HT(3) receptor antagonists decrease cocaine and methamphetamine preference. We have developed a 5-HT(3) receptor over-expressing mouse to study the role of this receptor in substance abuse. No changes in either the dopamine receptors (D1, D2, D3, and D4) or in the dopamine transporter (DAT) were found over a wide range of brain regions. 5-HT(3) receptor over-expressing mice failed to develop conditioned place preference to 10 mg/kg or 6 mg/kg cocaine but showed a modest preference for 4 mg/kg cocaine. 5HT(3) receptor over-expressing mice were more sensitive to the locomotor activating effects of low dose cocaine and methamphetamine. Further, brain slices from the transgenic mice release more dopamine in response to low concentrations of cocaine. These data suggest that 5HT(3) receptor over-expression in the forebrain decreases cocaine preference and increases acute sensitivity with a corresponding increase in the amount of dopamine released in response to cocaine.     

侧脑室注射八肽胆囊收缩素及其受体拮抗剂对吗啡依赖大鼠戒断症状的影响

目的观察侧脑室给予八肽胆囊收缩素(CCK-8)及其受体拮抗剂慢性干预对吗啡依赖大鼠戒断症状的影响,并在体外观察CCK-8对μ阿片受体结合反应的影响,初步探讨CCK-8对吗啡依赖过程的影响及其相关受体机制。方法建立大鼠吗啡依赖及纳络酮催促戒断模型,侧脑室注射CCK-8及CCK1受体拮抗剂devazepide、CCK2受体拮抗剂LY-288,513慢性干预,观察其对戒断症状的影响;应用放射配基结合实验体外检测CCK-8对μ阿片受体结合特征的影响。结果①吗啡注射前10 min侧脑室注射CCK-8和CCK受体拮抗剂devazepide、LY-288,513慢性干预均能降低吗啡依赖大鼠的戒断症状评分,并可明显改善体重下降、跳跃、齿颤、流涎等戒断症状,与戒断组相比差异均有显著性(P<0.01);②10-8～10-6 mol.L-1 CCK-8可以剂量依赖性地抑制大鼠脑组织中μ阿片受体与其配基的结合(P<0.01),降低μ阿片受体结合反应的Bmax值,而对Kd值无影响;且此抑制作用可被CCK1及CCK2受体拮抗剂翻转(P<0.01)。结论 CCK-8及其受体拮抗剂慢性干预均能减轻吗啡依赖大鼠戒断症状;CCK-8通过抑制μ阿片受体与其配基的结合,降低μ阿片受体的Bmax值,发挥其"抗阿片作用"。     

Alteration in the brain content of substance P (1–7) during withdrawal in morphine-dependent rats

Previous studies have shown that substance P (SP) may modulate the abstinence reaction to opioid withdrawal. Its N-terminal fragment SP_1–7 may inhibit the intensity of the withdrawal reactions in morphine dependent mice. This study was designed to determine whether the endogenous concentrations of the SP_1–7 fragment in the brain are affected during naloxone-precipitated withdrawal in the male rat. The amounts of the peptide was assessed by a specific radioimmunoassay in extracts of discrete brain regions (including the cerebral cortex, hippocampus, hypothalamus, nucleus accumbens, striatum, substantia nigra, ventral tegmental area and the spinal cord) during morphine tolerance and withdrawal. The results indicated that the concentrations of SP_1–7 were significantly elevated in the ventral tegmental area both in morphine tolerant rats and during naloxone-precipitated withdrawal. During morphine withdrawal significant increases in the peptide concentration were also observed in the hypothalamus and the spinal cord. It was concluded that the enhanced content of SP_1–7 may also indicate the involvement of the SP system during opioid withdrawal in the rat. The enhanced production of SP_1–7 may reflect an increased release and/or metabolism of SP, which, in turn, counteracts the withdrawal.     

不同阿片受体在羟考酮引起小鼠高活动性和镇痛过程中的作用

目的研究μ、δ、κ三种阿片受体在羟考酮引起小鼠高活动性和镇痛过程中的作用。方法采用小动物自主活动测定和热板镇痛实验方法。结果羟考酮(1.25,2.5,5.0mg.kg-1,s.c)使小鼠的自发活动明显增加,并成明显的量效关系。非选择性阿片受体拮抗剂naloxone能剂量依赖性的降低羟考酮引起的小鼠自发活动增加。选择性μ受体拮抗剂naloxonazine对羟考酮(5.0mg.kg-1,s.c)引起的小鼠自发活动增加没有影响,而选择性δ受体拮抗剂naltrindole能剂量依赖性的降低羟考酮引起的小鼠自发活动的增加,选择性κ受体拮抗剂nor-Binltorphimine增强羟考酮引起小鼠高活动性的作用;naloxonazine和naltrindol不影响羟考酮的镇痛作用,而nor-Binltorphimine能拮抗羟考酮的镇痛作用。结论羟考酮引起小鼠自发活动增加可能是通过δ介导的,而羟考酮的镇痛作用可能是通过κ受体介导的。     

噻吩诺啡强镇痛和低依赖药理学特性与其激动中枢阿片受体的关系

目的从整体动物水平探讨噻吩诺啡强镇痛和低依赖的药理学特性与激动中枢阿片受体的关系。方法在小鼠乙酸扭体和热辐射甩尾模型上,利用阿片μ和κ受体特异性拮抗剂评价噻吩诺啡对阿片μ和κ受体选择性作用的强度;在小鼠躯体依赖模型上,利用κ受体特异性拮抗剂评价噻吩诺啡低依赖性是否与其激动中枢κ受体的作用有关。结果在小鼠乙酸扭体模型和热辐射甩尾模型上,脑室注射κ受体特异性拮抗剂nor-binaltorphimine(Nor-BNI)可以显著抑制噻吩诺啡的镇痛效果,使其镇痛作用分别下降28%(乙酸扭体模型)和29%(热辐射甩尾模型);μ受体特异性拮抗剂纳络肼也能显著抑制噻吩诺啡的镇痛效果,使其镇痛作用分别下降40%(乙酸扭体模型)和44%(热辐射甩尾模型),略强于κ受体拮抗剂Nor-BNI。在小鼠躯体依赖模型上,Nor-BNI伴随噻吩诺啡连续给药后纳洛酮催促,小鼠未出现跳跃等躯体依赖的戒断症状。结论噻吩诺啡在小鼠疼痛模型上的镇痛作用与其激动中枢μ和κ受体均有关。噻吩诺啡躯体依赖潜能低与其激动中枢κ受体无必然联系。     

Motility,rigidity and turnover of dopamine in the striatum after administration of morphine to rats: A re-evaluation of their mechanisms

Whether the delayed behavioural activation and the increase in dopamine (DA) turnover in the striatum reflect signs of rebound effects or of counter-regulatory processes directed against locomotor depression and/or muscular rigidity was studied in rats. Administration of a large dose of morphine (30 mg/kg i.p.) induced strong muscular rigidity, which was measured as tonic activity in the electromyogram (EMG). This effect was maximal after one hour and disappeared during the fourth hour. The locomotor activity, on the other hand, disappeared after 30 min and re-appeared during the fourth hour, followed by a locomotor stimulation with a maximum after 4.5 hr. Striatal lesions produced with kainic acid did not affect the complete locomotor depression (akinesia), except by slightly prolonging this effect, and did not influence the delayed locomotor stimulation. These lesions did not inhibit, but, on the contrary, enhanced the increase in striatal concentration of 3,4-dihydroxyphenylacetic acid (DOPAC). Injections of morphine (10 μg) into the substantia nigra led to an increase in the level of DOPAC in the ipsilateral, but not the contralateral striatum. These results, in conjunction with those of other authors, suggest that the increase in DA turnover in the striatum and the delayed locomotor stimulation ought to be regarded as actions of morphine on sites different from those mediating muscular rigidity.     

The selectivity of the opioid antagonist, naltrindole, for delta-opioid receptors

In the mouse vas deferens, naltrindole gave pKB values of 9.7, 8.3, and 7.5 at the delta-, mu-, and kappa-sites and in binding assays, pIC50 values of 9.6, 7.8 and 7.2 at the same sites. The affinity of naltrindole for the delta binding site was increased in the presence of sodium ions and 5'-guanylylimidophosphate. Naltrindole is, thus, a potent opioid antagonist with marked selectivity for the delta-opioid receptor.     

Direct influence of C-terminally substituted amino acids in the Dmt-Tic pharmacophore on delta-opioid receptor selectivity and antagonism

A series of 17 analogues were developed on the basis of the general formula H-Dmt-Tic-NH-CH(R)-R' (denotes chirality; R = charged, neutral, or aromatic functional group; R' = -OH or -NH(2)). These compounds were designed to test the following hypothesis: the physicochemical properties of third-residue substitutions C-terminal to Tic in the Dmt-Tic pharmacophore modify delta-opioid receptor selectivity and delta-opioid receptor antagonism through enhanced interactions with the mu-opioid receptor. The data substantiate the following conclusions: (i) all compounds had high receptor affinity [K(i)(delta) = 0.034-1.1 nM], while that for the mu-opioid receptor fluctuated by orders of magnitude [K(i)(mu) = 15.1-3966 nM]; (ii) delta-opioid receptor selectivity [K(i)(mu)/K(i)(delta)] declined 1000-fold from 22,600 to 21; (iii) a C-terminal carboxyl group enhanced selectivity but only as a consequence of the specific residue; (iv) amidated, positive charged residues [Lys-NH(2) (6), Arg-NH(2) (7)], and a negatively charged aromatic residue [Trp-OH (11)] enhanced mu-opioid affinity [K(i)(mu) = 17.0, 15.1, and 15.7 nM, respectively], while Gly-NH(2) (8), Ser-NH(2) (10), and His-OH (12) were nearly one-tenth as active; and (v) D-isomers exhibited mixed effects on mu-opioid receptor affinity (2' < 3' < 4' < 1' < 5') and decreased delta-selectivity in D-Asp-NH(2) (1') and D-Lys(Ac)-OH (5'). The analogues exhibited delta-opioid receptor antagonism (pA(2) = 6.9-10.07) and weak mu-opioid receptor agonism (IC(50) > 1 microM) except H-Dmt-Tic-Glu-NH(2) (3), which was a partial delta-opioid receptor agonist (IC(50) = 2.5 nM). Thus, these C-terminally extended analogues indicated that an amino acid residue containing a single charge, amino or guanidino functionality, or aromatic group substantially altered the delta-opioid receptor activity profile (selectivity and antagonism) of the Dmt-Tic pharmacophore, which suggests that the C-terminal constituent plays a major role in determining opioid receptor activity as an "address domain".     

Comparison in the mouse of the effect of the opiate delta receptor antagonist ICI 154129 and naloxone in tests of extinction, passive avoidance and food intake

The effects of 30 and 80 mg/kg ICI 154,129, an opiate delta receptor antagonist, were compared with those of 0.1 and 10 mg/kg naloxone using tests of food-intake, passive avoidance and extinction in mice. Whereas naloxone depressed food intake and facilitated extinction, ICI 154,129 failed to affect food intake, passive avoidance or extinction although the mice reared significantly more during the test of food intake.     

Involvement of Raf-1 in chronic delta-opioid receptor agonist-mediated adenylyl cyclase superactivation

Chronic delta-opioid receptor agonist treatment of Chinese hamster ovary (CHO) cells stably expressing the human delta-opioid receptor (hDOR/CHO) leads to increased cAMP formation after the removal of the agonist (adenylyl cyclase superactivation). We have previously found that at the same time, chronic delta-opioid receptor agonist treatment augments phosphorylation of the adenylyl cyclase VI isoenzyme. Since phosphorylation of adenylyl cyclase VI by Raf-1 protein kinase was recently shown, we tested the role of Raf-1 in adenylyl cyclase superactivation in hDOR/CHO cells. We found that pretreatment of the cells with the selective Raf-1 inhibitor GW5074 (3-(3,5-dibromo-4-hydroxybenzylidene-5-iodo-1,3-dihydro-indol-2-one) (10 microM, 30 min) attenuates chronic deltorphin II-mediated increase in forskolin-stimulated cAMP formation by 40% (n = 6, P < 0.05). Better understanding of the molecular mechanism of adenylyl cyclase superactivation should aid in the development of analgesics that act longer and have fewer side effects.     

In vivo type 1 cannabinoid receptor availability in Alzheimer's disease

The endocannabinoid system (ECS) is an important modulatory and potentially neuroprotective homeostatic system in the brain. In Alzheimer's disease (AD), the role of type 1 cannabinoid receptor (CB₁R) is unclear, with contradictory findings in post-mortem studies showing upregulation, downregulation or unchanged CB₁R status. We have investigated CB₁R availability in vivo in patients with AD, in relation to amyloid deposition, cognitive functioning and apolipoprotein E (ApoE) genotype. Eleven AD patients and 7 healthy volunteers (HV) underwent combined [¹⁸F]MK-9470 PET and [¹¹C]PIB PET scans to assess CB₁R availability and amyloid deposition, respectively, and T1 volumetric MRI for partial volume correction. We found no difference in CB₁R availability between AD and HV, VOI-based fractional uptake values (FUR) were 0.043±0.01 for AD and 0.045±0.01 for controls (p=0.9). CB₁R availability did not correlate with neuropsychological test scores and was not modulated by ApoE genotype. As expected, global [¹¹C]PIB SUVR (standardized uptake value ratio) was increased in AD (SUVR 1.9±0.3) compared to HV (1.2±0.1) with p<0.001, but no correlation was found between amyloid β (Aβ) deposition and CB₁R availability. In conclusion, we found no in vivo evidence for a difference in CB₁R availability in AD compared to age-matched controls. Taken together with recently reported in vivo CB₁R changes in Parkinson's and Huntington's disease, these data suggest that the CB₁R is differentially involved in neurodegenerative disorders.