Inhibition of acetylcholine turnover in rat hippocampus by intraseptal injections of β-endorphin and morphine

Summary Intraseptal administration of morphine (70 nmol) or -endorphin (0.7 nmol) reduced the rate of acetylcholine (ACh) turnover (TR_ACh) in rat hippocampus but not in striatum or cortex. These intraseptal injections failed to modify the ACh content and did not elicit analgesia. Naltrexone (15 mol/kg, i.p.) completely antagonized the decrease of hippocampal TR_ACh elicited by the two opiate receptor agonists. Furthermore, intraseptal injections of naltrexone partially blocked the decrease in hippocampal TR_ACh induced by intraperitoneal administration of morphine (70 mol/kg, i.p.). These data suggest that opiate agonists decrease hippocampal TR_ACh by regulating septal cholinergic neurons, and that this effect is not associated with analgesia.     

Effects of some GABA-mimetic drugs on the antinociceptive activity of morphine and β-endorphin in rats

Summary Intracerebroventricular administration of muscimol, a potent GABA-receptor agonist, counteracted the antinociceptive effect of morphine or -endorphin in rats as measured by the tail flick method. Muscimol's activity was reversed by bicuculline. Isoguvacine, another GABA agonist, as well as nipecotic acid and guvacine, two inhibitors of neuronal and glial uptake of GABA, also antagonized morphine's antinociceptive effect. A role of the central GABA-ergic system in mediating opiate antinociception is proposed.This study was supported by C.N.R. grant no. CT 77.01401.04     

Different types of opioid receptors mediating analgesia induced by morphine,DAMGO, DPDPE,DADLE and β-endorphin in mice

Summary The effects of intracerebroventricular (i.c.v.) administration of d-Phe-Cys-Tyr-d-Try-Orn-Thr-Pen-Thr-NH₂ (CTOP), a selective mu-opioid receptor antagonist, (Allyl)2-Tyr-Aib-Aib-Phe-Leu-OH (ICI 174864) and (N,N-Bisallyl-Tyr-Gly-Gly--(CH₂S)-Phe-Leu-OH (ICI 154129), selective delta-opioid receptor antagonists on blocking analgesia induced by -endorphin, morphine, d-Ala²-NMePhe⁴-Gly-ol-enkephalin (DAMGO), d-Ala²-d-Leu⁵-enkephalin (DADLE) and d-Pen²-enkephalin (DPDPE) administered i.c.v. were studied in male ICR mice. The analgesia was assessed by the tail-flick and paw-licking (hot-plate) tests. The potencies of opioid agonists injected i.c.v. for producing analgesia were DAMGO > DADLE > -endorphin > morphine > DPDPE. Intracerebroventricular administration of CTOP (0.05 g) selectively antagonized inhibition of the tail-flick and paw-licking response induced by morphine, DAMGO or DADLE but not -endorphin or DPDPE. ICI 174864 (5 g) and ICI 154129 (5 g) injected i.c.v. selectively antagonized analgesia induced by DPDPE or DADLE but not -endorphin, morphine or DAMGO injected i.c.v. These results indicate that analgesia induced by morphine and DAMGO is mediated by the stimulation of mu-opioid receptors while analgesia induced by DPDPE is mediated by the stimulation of delta-opioid receptors. DADLE-induced analgesia is mediated by the stimulation of both mu- and delta-opioid receptors. Analgesia induced by -endorphin is mediated by neither munor delta-opioid receptors.Abbreviations i.c.v. intracerebroventricular - i.t. intrathecal - CTOP d-Phe-Cys-Tyr-d-Try-Orn-Thr-Pen-Thr-NHZ - DAMGO d-Ala²-NMePhe²-Gly-ol-enkephalin - DADLE d-Ala²-d-Leus-enke-phalin - DPDPE dd-Pen²-dd-Pen⁵-enkephalin - ICI 174864 (Allyl)2Tyr-Aib-Aib-Phe-Leu-OH - ICI 154129 (N,N-Bisallyl-Tyr-Gly-Gly-(CH₂S)-Phe-Leu-OH     

Differential cross-tolerance development between single and repeated immobilization stress on the antinociceptive effect induced by β-endorphin, 5-hydroxytryptamine,morphine, and WIN55,212-2 in the inflammatory mouse pain mode

We have evaluated the possible underlying mechanisms of immobilization stress-induced analgesia (SIA) by behavioral cross-tolerance studies and molecular studies. In the behavioral studies, the cross-tolerance between single or repeated immobilization SIA and the antinociceptive effects of β-endorphin, morphine, 5-hydroxytryptamine (5-HT), or WIN55,212-2 were assessed. Both single and repeated (×7) immobilization stress significanly attenuated the β-endorphin and 5-hydroxytryptamine-induced antinociception in the 2nd phase of formalin response, respectively. However, these cross-tolerances disappeared in prolonged repetition of the stress (×14). Neither single nor repeated (×7 and ×14) immobilization stress affected the antinociceptive effect of morphine or WIN55,212-2 at all. We also found that immobilization stress activated hypothalamic proopiomelanocortin (POMC) gene and β-endorphin expression. Since, it has potent inhibitory activity on the noxious stimuli-induced POMC expression, immobilization stress seemed to dissipate the POMC gene expression process. Meanwhile, we did not find any changes in the opioid receptors’ (mu-, delta- and kappa-receptor) and the cannabinoid receptors’ (CB1 and CB2) expressions in the midbrain regions elicited by single or repeated stress. These results suggested that a single immobilization stress activates the descending pain modulatory system, which is mainly mediated through endorphinergic and serotonergic activation. Moreover, the tolerance of SIA induced by repeated stresses may be due to the prolonged activation of these systems induced by repeated immobilization.     

Agmatine inhibited tolerance to and dependence on morphine in guinea pig ileum in vitro

目的：观察胍丁胺对吗啡耐受和物质依赖豚鼠回肠纵肌（ＧＰＩＬＭ）的作用．方法：本实验在离体电场刺激实验中进行．结果：吗啡抑制ＥＦＳ引起的ＧＰＩＬＭ收缩［ＩＣ５０＝１４０（１０７－１８２）ｎｍｏｌ·Ｌ－１］．用吗啡２７０ｎｍｏｌ·Ｌ－１与ＧＰＩＬＭ温浴使吗啡ＩＣ５０增大３７倍（耐受），对纳络酮发生收缩反应（物质依赖）．分别用吗啡加纳络酮和吗啡加胍丁胺与ＧＰＩＬＭ温浴使吗啡失去此致耐受作用，使标本对纳络酮收缩反应幅度分别减少了９０％和７５％．胍丁胺的这些作用几乎可被咪唑克生完全阻断．结论：胍丁胺通过激活咪唑啉受体抑制离体ＧＰＩＬＭ对吗啡耐受和物质依赖的形成过程     

Effects of naloxone, β-endorphin and ACTH on acquisition of schedule-induced polydipsia

A series of three experiments examined the possible involvement of endogenous opioid peptides in the development of schedule-induced polydipsia in rats. Repeated pretraining treatment with 2 mg/kg naloxone impaired acquisition of schedule-induced polydipsia, whereas the same treatment injected after training increased drinking. This later effect was time dependent, since a 30-min delay in the injection of naloxone resulted in a disappearance of its effect. Post-training injections of 10 g/kg -endorphin or ACTH delayed the development of drinking. These findings are consistent with the hypothesis that endogenous opioid peptides modulate the development of schedule-induced polydipsia.     

Comparison of the densities of 5-HT4 receptors, β1- and β2-adrenoceptors in human atrium: functional implications

We measured in human atrium the density of 5-HT₄ receptors, labelled with [¹²⁵I]-SB 207710 (1-butyl-4-piperidinyl) methyl 8-amino-7-iodo-1, (4-benzodioxan-5-carboxylate), and compared it with the density of ₁- and ₂-adrenoceptors, labelled with (–)-[¹²⁵I]-cyanopindolol. [¹²⁵I]-SB 207710 (5–1200 pmol/l) labelled a small population of saturable binding sites (B _max 4 fmol/mg protein) with a pK_D of 9.7 and with 5-HT₄ receptor characteristics, as assessed with competing ligands. The density of atrial binding sites with 5-HT₄ receptor characteristics was 10 and 5 times lower, respectively, than the density of ₁- and ₂-adrenoceptors. We suggest that the small 5-HT₄ receptor population may in part explain why the positive inotropic effects of 5-HT are smaller than those of catecholamines mediated through ₁- and ₂-adrenoceptors.     

Naltrexone and β-funaltrexamine antagonism of the antinociceptive and response rate-decreasing effects of morphine, dezocine, and d-propoxyphene

  Rationale: Patterns of competitive and insurmountable antagonism provide important data to guide the classification and characterization of different types of opioid agonists as well as infer the mechanism of action for agonists. Objective: Experiments with the competitive antagonist, naltrexone, and the insurmountable antagonist, β-funaltrexamine (β-FNA), were conducted to determine whether the antinociceptive and rate-decreasing effects of the opioid agonists dezocine and d-propoxyphene are 1) mediated through μ opioid receptors in rats, and 2) differ from morphine with respect to relative efficacy. Methods: The rat tail-withdrawal assay was used to measure antinociception and a fixed ratio 20 (FR20) schedule of food delivery was used to measure rate suppression. Results: Naltrexone (0.01–1.0 mg/kg) was approximately equipotent as an antagonist of the antinociceptive and rate-decreasing effects of both morphine and dezocine and as an antagonist of the antinociceptive effects of d-propoxyphene. Naltrexone failed to block the rate-decreasing effects of d-propoxyphene. β-FNA (5 and 10 mg/kg) also antagonized the antinociceptive and rate-decreasing effects of morphine and dezocine as well as the antinociceptive effects of d-propoxyphene. β-FNA failed to produce a dose-dependent antagonism of the rate-decreasing effects of d-propoxyphene. Conclusions: These data suggest that the antinociceptive effects of morphine, dezocine, and d-propoxyphene and the rate-decreasing effects of morphine and dezocine are mediated through μ opioid receptors. Overall, high doses of β-FNA produced a greater degree of antagonism of the behavioral effects of dezocine than morphine or d-propoxyphene, confirming other reports that dezocine is a lower efficacy agonist than morphine. Additionally, the degree of antagonism produced by β-FNA was greater for the antinociceptive effects of all three compounds than for the rate-decreasing effects. Received: 14 August 1998 / Final version: 4 December 1998     

Fruitful adrenergic α(2C)-agonism/α(2A)-antagonism combination to prevent and contrast morphine tolerance and dependence

The functional in vitro study of the enantiomers of imidazolines 4-7 highlighted the role played by the nature of the ortho phenyl substituent in determining the preferred α(2C)-AR configuration. Indeed, the (S) enantiomers of 4-6 or (R) enantiomer of 7 behave as eutomers and activate this subtype as full agonists; the corresponding distomers are partial agonists. Because in clinical pain management with opioids α(2C)-AR agonists, devoid of the α(2A)-AR-mediated side effects, may represent an improvement over current therapies with clonidine like drugs, 4 and its enantiomers, showing α(2C)-agonism/α(2A)-antagonism, have been studied in vivo. The data suggest that partial α(2C)-activation is compatible with effective enhancement of morphine analgesia and reduction both of morphine tolerance acquisition and morphine dependence acquisition and expression. On the contrary, full α(2C)-activation appears advantageous in reducing morphine tolerance expression. Interestingly, the biological profile displayed by 4 (allyphenyline) and its eutomer (S)-(+)-4 has been found to be very unusual.     

Levels of immunoreactive dynorphin A_(1-13) during development of morphine dependence in rats

目的：研究吗啡依赖大鼠组织内免疫活性强啡肽Ａ１－１３含量的动态变化及其与依赖程度的关系．方法：用纳洛酮催促的戒断症状评分测定吗啡依赖程度，用放射免疫测定组织内强啡肽Ａ１－１３水平．结果：在３－６天给药期内，吗啡可进行性降低脊髓、垂体、血浆内免疫活性强啡肽Ａ１－１３水平，升高海马及下丘脑的强啡肽Ａ１－１３水平，继续给药至１２天，各组织内免疫活性强啡肽Ａ１－１３水平不再有显著性变化．结论：吗啡依赖形成过程中脊髓、垂体及血浆内强啡肽Ａ１－１３呈进行性降低，其趋势与吗啡依赖程度一致     

Association of genes coding for the α-4, α-5, β-2 and β-3 subunits of nicotinic receptors with cigarette smoking and nicotine dependence

We assessed whether smoking behavior was associated with nine polymorphisms in genes coding for the nicotinic receptor subunits α-4 (rs1044394, rs1044396, rs2236196 and rs2273504), α-5 (rs16969968), β-2 (rs2072661 and rs4845378) and β-3 (rs4953 and rs6474413). We conducted an Internet survey and collected saliva by mail for DNA and cotinine analyses, in Switzerland in 2003. We conducted DNA analyses for 277 participants and cotinine analyses for 141 current daily smokers. Cotinine levels were higher in carriers of the CC genotype of CHRNA4 rs1044396 (371 ng/ml) than in those with the CT or TT genotypes (275 ng/ml, p = 0.049), a difference of 0.53 standard deviation units. However, this difference was not robust to correction for multiple testing using Bonferroni adjustment. These 9 polymorphisms were not otherwise associated with smoking behavior and nicotine dependence. There were possible associations between the temperament trait novelty seeking and CHRNA4 rs1044396, CHRNA5 rs16969968 and CHRNB2 rs4845378, but these associations were not robust to correction for multiple testing. We conclude that the analysis of polymorphisms in genes coding for four nicotinic acetylcholine receptor subunits (CHRNA4, CHRNA5, CHRNB2 and CHRNB3) and several smoking-related phenotypes revealed no statistically significant association.     

Levels and circadian rhythmicity of plasma ACTH,cortisol, and β-endorphin as a function of family history of alcoholism

Rationale Individuals with a family history of alcoholism may present a dysfunction in the activity of the hypothalamic–pituitary–adrenal (HPA) axis that predates the development of alcoholism. Objective The present study investigated the hypothesis that this HPA-axis dysfunction is associated with alterations in the pattern of the circadian (24 h) secretions of adrenal corticotropic hormone (ACTH), cortisol, and β-endorphin. Methods Men with [high risk (HR)] or without [low risk (LR)] family history of alcoholism participated in the study. Blood samples were drawn every 30 min for 24 h for estimation of the plasma hormone levels. Participants ingested meals at predetermined intervals and filled out mood questionnaires prior to the placement of the catheter and 1 h after each meal. Results The circadian peaks for β-endorphin, ACTH, and cortisol occurred between 0800 and 0830 hours in both LR and HR participants. The plasma ACTH and β-endorphin concentrations were lower in HR than LR participants, while the plasma cortisol concentrations were similar between HR and LR participants. For each hormone, the total 24-h secretion was estimated from the area under the 24-h time–concentration curve (AUC). For ACTH and β-endorphin, but not the cortisol, AUC were lower in HR than LR participants. LR participants reported being more nervous than HR participants. For the LR participants, but not HR participants, the initial mood ratings of “nervous” were positively correlated with the initial plasma cortisol and β-endorphin concentrations as well as with the cortisol and β-endorphin AUC. Conclusions HR participants presented lower plasma concentrations as well as lower AUC for β-endorphin and ACTH but not for cortisol. This suggests a dysfunction of the HPA-axis in HR participants that predates the development of alcoholism and a dissociation between plasma ACTH and cortisol levels as a function of family history of alcoholism.     

Inhibition of agmatine on psychological dependence induced by morphine and the possible mechanism

Agmatine is the endogenous ligand of imidazoline receptor, it enhanced morphine analgesia, inhibited tolerance to and physical dependence on morphine. In the present study, the effect of agmatine on the psychological dependence on morphine and the possible mechanism was evaluated.     

Modulation of brain α2-adrenoceptor and μ-opioid receptor densities during morphine dependence and spontaneous withdrawal in rats

Summary The densities of brain ₂-adrenoceptors and -opioid receptors, quantitated by means of the binding of the agonists [³H]clonidine and [³H]dihydromorphine, respectively, were studied during the development of morphine dependence and spontaneous withdrawal in the rat. The oral administration of morphine (12–130 mg/kg for 3–21 days) led to inconsistent changes in ₂-adrenoceptor density while the density of -opioid receptors was down-regulated. In contrast, spontaneous opiate withdrawal (3–72 h) significantly increased the density of ₂-adrenoceptors while the density of -opioid receptors was rapidly up-regulated to control values. In the hypothalamus, but not in other brain regions, the increase in ₂-adrenoceptor density after withdrawal followed a time course (3–72 h) related to the severity of the abstinence syndrome. Thus, there was a positive and significant correlation between the severity of withdrawal and the density of ₂-adrenoceptors in the hypothalamus. Short-term treatment with clonidine (2 × 0.5 mg/kg, i. p.) prevented the morphine withdrawal-induced increases in ₂-adrenoceptor density in various brain regions, but not in the hypothalamus. The main results suggest that modulation of hypothalamic ₂-adrenoceptor density during morphine withdrawal is a relevant physiological mechanism by which the opiate abstinence syndrome is counteracted. Send offprint requests to J. A. García-Sevilla     

Synthesis and in vitro antitumor activity of new quinoline, pyrimido[4,5-b]quinoline, [1,2,3]triazino[4,5-b]quinoline, and [1,2,4]triazolo[2′,3′:3,4]pyrimido[6,5-b]quinoline analogs

New series of quinoline, pyrimido[4,5-b]quinoline, [1,2,3]triazino[4,5-b]quinoline, and [1,2,4]triazolo[2′,3′:3,4]pyrimido[6,5-b]quinoline analogs have been synthesized and characterized by analytical and spectrometrical methods (IR, ¹H NMR, ¹³C NMR, MS). Fifteen of the newly synthesized compounds; namely, 3a, b, 4b, 6a, b, 10a–f, and 14a–d were evaluated for their in vitro antitumor activity at the National Cancer Institute (NCI) 60 cell lines panel assay. Compounds 4b and 10f are the most active members in this study, demonstrating significant broad spectrum antitumor activity against most of the tested sub-panel tumor cell lines. The detailed synthesis, spectroscopic, and biological data are described.     

Biologically active conformation of [Met5]- and [Leu5]enkephalin on δ opioid receptor

Investigations of the conformation of endogenous enkephalins are generally based on structural comparisons of enkephalins with other opiates and on experimental pharmacological studies. Based on such investigations, we now propose a model of the biologically active (receptor-bound) conformation of [Met⁵]- and [Leu⁵]enkephalin on the δ opioid receptor. The model helps with the design of new opioid analgesics.     

Plasma nicotine,plasma β-endorphin and mood states during periods of chronic smoking,abstinence and nicotine replacement

Nicotine is known to release neuroendocrine substances which may subsequently reinforce smoking behavior by improving mood states. The purpose of this study was to examine changes in plasma-endorphin and mood states during periods of chronic smoking, abstinence from smoking, and abstinence while chewing nicotine gum. A modified A-B-A-C design was used. Normal male volunteers were randomly assigned to an experimental or control group. Over a 12-day protocol, experimental subjects smoked ad libitum for 2 days, were abstinent for 4 days, resumed smoking for 2 days, and then chewed nicotine gum for the final 4 days. Control subjects smoked ad libitum throughout the entire protocol. Results indicated that changes in plasma-endorphin levels were not related to changes in the four smoking conditions. Plasma nicotine and mood states were related, such that dysphoric moods increased during abstinence from smoking in comparison to the control group. To investigate further the relationships between nicotine,-endorphin and reinforcement for smoking, it may be necessary to characterize endogenous opioid peptide release in the central nervous system during smoking.     

Naloxone and β-endorphin alter the effects of post-training epinephrine on memory

These experiments examined the involvement of opioid peptides in the memory-modulating effects of post-training epinephrine (Epi). Mice were trained on inhibitory avoidance (IA) and Y-maze discrimination (YMD) tasks and given post-training injections followed by retention tests 24 h later. In the IA task retention was enhanced by low doses of Epi and impaired by high doses. In both tasks, naloxone facilitated retention and blocked the memory-impairing effects of Epi. These findings are consistent with other evidence suggesting that the memory-impairing effects of -endorphin are mediated by the release of opioid peptides. Previous studies have shown that a novel exploratory experience given 1 h prior to training blocks the release of brain -endorphin and blocks the memory-enhancing effects of post-training naloxone. In the present study we found that a novel experience given 1 h prior to training blocked the memory-impairing effect of post-training Epi otherwise obtained in both tasks. The effects of a low, memory-enhancing dose of Epi appear not to involve the release of opioid peptides: a low dose of Epi blocked the memory-impairing effect of -endorphin. Further, low doses of Epi and naloxone, which were ineffective when administered alone, significantly enhanced retention when administered together. We interpret these findings as indicating that the memory-enhancing and memory-impairing effects of Epi are mediated by different mechanisms.     

Radioimmunoassay of β-endorphin basal and stimulated levels in extracted rat plasma

Summary A sensitive radioimmunoassay for -endorphin is described. Antibodies against human -endorphin which exhibit a high avidity for the C-terminal of the peptide were raised in rabbits following the injection of thyroglobulin-coupled human -endorphin (h-E) as immunogen. Methionineenkephalin, - -endorphin, as well as ACTH peptides did not cause interference in the radioimmunoassay. -Lipotropin, however, showed a 50% cross-reactivity. The sensitivity of the assay is 25 pg/0.5 ml tube volume for -endorphin. -Endorphin was extracted with a high recovery from the rat plasma using silicic acid and -endorphin levels as low as 100 pg/ml could be measured.Basal levels of -endorphin-like immunoreactivity in plasma of rats were about 400 pg/ml. -Endorphin levels in adrenalectomized rats and in animals chronically treated with the cortisol synthesis blocker metyrapone were found to be markedly increased (about 7-fold). Exposure of the rats to electrically induced foot-shocks caused a similar increase of immunoreactive -endorphin in plasma. A significant increase was also seen after insulin injection.