Des-tyrosine-γ-endorphin effects on morphine analgesia in mice

• 1.1. The effects that were induced by a β-lipotropin fragment des-tyrosine-γ-endorphin (DTγE) devoid of opiate activity that was administered intraperitoneally or intracerebroventricularly to mice under morphine analgesia were investigated. The interaction of this peptide with the analgesic effects of morphine was examined using the hot plate and the tail flick test.
• 2.2. Intraperitoneal acute treatment with DTγE did not change the analgesic effects of morphine.
• 3.3. Intraperitoneal semi-chronic treatment performed for 4 days with DTγE enhanced morphine analgesic effects.
• 4.4. The intracerebroventricular acute treatment with DTγE reduced morphine analgesia in a dose-dependent way.
• 5.5. These results indicate that DTγE, although devoid of opioid activity per se, may interact with the opioid system, probably through an indirect mechanism.

     

Effects of intrathecal or intracerebroventricular pretreatment with pertussis toxin on antinociception induced by β-endorphin or morphine administered intracerebroventricularly in mice

We have previously demonstrated that -endorphin and morphine, when administered supraspinally, produce antinociception by activating different descending pain inhibitory systems in both rats and mice. However, the signal transduction mechanisms involved in the descending pain-inhibitory systems that are activated by -endorphin and morphine administered intracerebroventricularly (i.c.v.) have not been characterized. Therefore, in the present study, the effects of intrathecal (i.t.) and i.c.v. pretreatments with pertussis toxin (PTX) on antinociception induced by -endorphin or by morphine administered i.c.v. were studied in ICR mice. Antinociception was assessed by the tail-flick assay and by the hotplate assay. Intrathecal pretreatment with PTX (0.5 g) for 6 days effectively reduced the inhibition of the tail-flick response induced by -endorphin (1 g) or by morphine (1 g) administered i.c.v. However, i.t. pretreatment with PTX was not effective in reducing the inhibition of the hot-plate response induced by -endorphin or by morphine administered i.c.v. Intracerebroventricular pretreatment with PTX (0.5 g) for 6 days effectively reduced the inhibition of the tail-flick and hot-plate responses induced by morphine (1 g), but not that induced by -endorphin (1 g), administered i.cv. Our results suggest that there are PTX-sensitive G proteins coupled to the spinal descending pain inhibitory systems that are activated by -endorphin and morphine administered i.c.v. At a supraspinal level, i.cv. morphine- but not -endorphin-induced antinociception is mediated by PTX-sensitive G proteins. Correspondence to: Hong W. Suh at the above address     

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.     

Formalin pretreatment attenuates tail-flick inhibition induced by β-endorphin administered intracerebroventricularly or intrathecally in mice

We examined the effect of the subcutaneous (s.c.) pretreatment of formalin into both hind paws of mice on the antinociception induced by the intracerebroventricularly (i.c.v.) or intrathecally (i.t.) administration of beta-endorphin using the tail-flick test. Pretreatment with formalin (5%) for 5 h had no affect on the i.c.v. administered beta-endorphin-induced tail-flick response. However, pretreatment with formalin for 40 h attenuated the tail-flick inhibition induced by i.c.v. administered beta-endorphin. This antinociceptive tolerance to i.c.v. beta-endorphin continued up to 1 week, but to a lesser extent. Pretreatment with formalin for 5 and 40 h significantly reduced the i.t. beta-endorphin-induced inhibition of the tail-flick response, which continued up to 1 week. The s.c. formalin treatment increased the hypothalamic pro-opiomelanocortin (POMC) mRNA level at 2 h, but this returned to the basal level after 40 h. Our results suggest that the increase in the POMC mRNA level in the hypothalamus appears to be involved in the supraspinal or spinal beta-endorphin-induced antinociceptive tolerance in formalin-induced inflammatory pain.     

Differential modulation by muscimol and baclofen on antinociception induced by morphine, β-endorphin,d-Pen2,5-enkephalin and U50,488H administered intracerebroventricularly in the mouse

The present study was designed to investigate the modulatory effects of stimulation of GABA_A and GABA_B receptors at supraspinal sites on antinociception induced by supraspinally administered -, -, -, and -opioid receptor agonists. The effects of the GABA_A and GABA_B receptor agonists, muscimol and baclofen respectively, on the antinociception induced by morphine (a -receptor agonist), -endorphin (an -receptor agonist), D-Pen^2,5-enkephalin (DPDPE, a -receptor agonist) and U50,488H ({trans-3,4-di-chloroN-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl] benzeocetamide}; a -receptor agonist) injected intracerebroventricularly (i.c.v.) were studied. The anti-nociception was assayed using the tail-flick and hot-plate tests. Muscimol at doses of 25–200 ng, administered i.c.v. alone did not affect the latencies of tail-flick and hot-plate thresholds, but attenuated dose-dependently the inhibition of the tail-flick and hot-plate responses induced by i.c.v. administered morphine (2 g), -endorphin (1 g), DPDPE (10 g), and U50,488H (60 g). Baclofen (1.25–10 ng) administered i.c.v. alone did not affect the latencies of the tail-flick and hot-plate responses, but attenuated dose-dependently the inhibition of the tail-flick and hot-plate responses induced by -endorphin and U50,488H, without affecting morphine-or DPDPE-induced responses. Our results indicate that activation of GABA_A receptors at the supraspinal sites by i.c.v. injection of muscimol antagonizes antinociception induced by supraspinally administered -, -, -, and -opioid receptor agonists. On the other hand, activation of GABA_B receptors at supraspinal sites by i.c.v. baclofen antagonizes antinociception induced by i.c.v. administered - and -opioid agonists, but not - or -opioid agonists.     

Facilitation of memory retrieval by pretest morphine mediated by μ but not δ and κ opioid receptors

Mice were trained to avoid electric shock (0.6 mA) in a step-through type passive avoidance learning task, retention being measured 24 h after the training trial. Morphine 10 mg/kg administered 30 min before the test trial (pretest) facilitated memory retrieval, and the effect was completely antagonized by 1 mg/kg naloxone, a selective -opioid receptor antagonist. On the other hand, pretest administration of 0.01–10 mg/kg DTLET, a selective -opioid receptor agonist, did not produce the same effect as morphine. Nor-binaltorphimine, a -opioid receptor antagonist, did not antagonize the effect of pretest morphine, at doses of 1 and 2 mg/kg. These results suggest that the facilitation of memory retrieval by pretest morphine is mediated through - but not - or -opioid receptors.     

Increment of endogenous opioid peptides contents and μ- opioid receptor mRNA expression in immuno- suppressive rat induced by intrathecal injection of morphine

Endogenous opioid peptides (EOP) and opioid receptors are important factors in the neuroimmunology.As earlier work from our laboratory demonstrated that intrathecal injection of morphine (0.8 μg/μL) markedly decreased the lymphocyte proliferation, IL-2 production, and NK cell activity in rat spleen, our task was to recognize whether EOP and opioid receptors were involved in the immunosuppression induced by intrathecal morphine.Using in vivo push pull perfusion technique and radioimmunoaassay, it was found that the release of β-endorphin and dynorphin in rat increased in perfusate from hippocampus after inwathecal morphine.With the method of in situ hybridization     

Roles ofδ andμ opioid receptors in mediating the effects of enkephalins on avoidance conditioning

The effects on one-way active avoidance conditioning of pre-training, systemic administration of the selective -receptor agonist [d-Ala²,N-Me-Phe⁴, Glyol]enkephalin (DAGO), and the selective -receptor antagonist (d-Phe-Cys-Tyr-d-Trp-Orn-Thr-Pen-Thr-NH₂ (CTOP), were determined in Swiss-Webster mice. A low dose of DAGO (0.92 µg/kg) moderately enhanced avoidance acquisition, whereas a 100 µg/kg dose of CTOP more dramatically impaired acquisition. However, the avoidance-enhancing dose of DAGO significantly increased locomotor activity as measured in a separate group of mice in the avoidance chamber, and the avoidance-impairing dose of CTOP significantly decreased activity. Under these same training conditions, earlier studies (Schulteis et al. 1988; Schulteis and Martinez 1990) demonstrated that enkephalins impaired avoidance learning, and selective-receptor antagonists such as ICI 174,864 enhanced learning; in contrast to the present study, both of these effects were dissociated from performance effects such as alterations in locomotor activity. Taken together, the results suggested that the effects of enkephalins were mediated by the-, but not -, class of opioid receptor.     

Participation of opioid system in acupuncture actions on immunosuppression by morphine and trauma

Acupuncture therapy is an effective method in traditional Chinese medicine. Substantial studies have shown that acupuncture can ameliorate a diverse collection of ailments that     

Enhancement of blood-brain barrier permeability to sodium fluorescein by stimulation of µ opioid receptors in mice

Summary The effects of opioids on the permeability of the blood-brain barrier (BBB) were examined in mice with sodium fluorescein as an indicator of the permeability. The brain was perfused with saline 30 min after injection of sodium fluorescein (40 mg/kg, i. v.) and examined by fluorometry. Morphine hydrochloride (0.3–10 mg/kg, s. c.) markedly increased the brain level of sodium fluorescein dose-dependently without influencing the plasma level, when administered 20 min before sodium fluorescein injection. Intracerebroventricularly (i. c. v.) injected morphine hydrochloride (0.5 and 1.0 Erg) increased the brain sodium fluorescein level. Buprenorphine (0.1 and 0.5 mg/kg, s. c.) was also effective. However, pentazocine, ethylketazocine, U-50488H and SKF-10047 had no significant influence. The i.c.v. administration of [D-Ala², McPhe⁴, Gly(ol)⁵]enkephalin (0.1 g) and [D-Ala², D-Leu⁵]enkephalin (0.5 g) but not of [D-Thr², Leu⁵]enkephalin-Thr increased the brain level of sodium fluorescein significantly. A small dose of naloxone (i. p.) significantly inhibited the effects of morphine, buprenorphine, [D-Ala², McPhe⁴, Gly(ol)⁵]enkephalin and [D-Ala³, D-Leu⁵]enkephalin. ICI-174864 co-administered i. c. v. with [D-Ala², D-Leu⁵]enkephalin was ineffective in antagonizing the effect of the latter. These findings suggest that the stimulation of µ opioid receptors results in an increase in BBB permeability to sodium fluorescein. Send offprint requests to K. Saeki     

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     

Apoptosis of mature and immature T-cells induced by morphine

The immunosuppressive effects of morpbine were investigated in our previous work in vivo and in vitro. The apoptosis of mature and immature T-cell was observed presently to study the possible role of T-cell death in the mechanism of. immunosuppression produced by morphine. Administration of morphine subcutaneously to Balb/c mice of 3-wk old for 1, 5, or 10 d continually at a dose of 0, 6.25, 12.5, 25, 50, 100 mg kg~(-1) (bid) showed an exciting activities (circling around the cage) of mice at least 1 h after injection (in all doses since the     

NMDA receptors mediating Fos expression in rat spinal cord induced by subcutaneous injection of formalin

目的：研究ＮＭＤＡ和非ＮＭＤＡ受体在疼痛刺激诱发脊髓Ｆｏｓ表达中的作用．方法：大鼠单侧后足跖部皮下注射２％福尔马林，免疫组化显示Ｆｏｓ的表达．结果：注射福尔马林２ｈ后，Ｆｏｓ阳性神经元集中分布在同侧脊髓背角Ⅰ层的内侧和Ⅱ层的浅部．脊髓鞘内给予ＮＭＤＡ受体拮抗剂ＡＰＶ（１０μＬ，００１，０１，１ｇ·Ｌ－１）剂量依赖性引起福尔马林诱发的背角Ｆｏｓ阳性细胞数量减少（Ｐ＜００１）；非ＮＭＤＡ受体拮抗剂ＤＮＱＸ对Ｆｏｓ表达无明显影响．结论：ＮＭＤＡ受体介导福尔马林致痛诱导的脊髓Ｆｏｓ表达．     

Different response types of neurotrophins and their receptors to immune stress

Immune stress has been proved involved in the process of neurodegenation such as Alzherimer's disease or multiple sclerosis.The neurotrophins play an important role in neuronal survival of many nerve system diseases and the relationship between immune stress and neurotrophins have been proved in several disease models but the fine mechanism still open.In the present experiment we reported that there were different response     

The rewarding action of acute cocaine is reduced in β-endorphin deficient but not in μ opioid receptor knockout mice

Cognitive impairment is a multidimensional concept that subsumes the attention and concentration, learning and memory, problem-solving ability, visuospatial abilities, mental flexibility, psychomotor efficiency and manual dexterity. The intrinsic mechanisms of the behavioural effects may involve neuronal damage in the brain structure. A lower concentration of glutamate receptor co-agonists in the striatum indicates the general malfunction of the brain glutamatergic system. It is suggested that a selective decrease in hippocampal glutamate concentration may account for deterioration in learning and memory process, considering the important role of this neurotransmitter in the cognitive functions. Nootropic agents like piracetam and anticholinesterase inhibitors are commonly used for improving memory, mood and behaviours. The present study was undertaken to assess the nootropic potential of menthol on learning and memory employing exteroceptive and interoceptive behavioral model in young and aged mice. To delineate the mechanism by which menthol decreases cognitive impairment and protect the brain, various biochemical parameters such as brain glutamate, glycine, glutathione and thiobarbituric acid reactive substances were determined. Menthol produced significant improvement in learning and memory. Menthol exhibited excellent antioxidant effect and maintain glutamate concentration in various region of the mouse brain for management of preliminary symptoms of memory impairment.     

The antinociception induced by \-endorphin administered intrathecally is mediated by the activation of μ and κ-opioid receptors in the rat

The antinociception induced by -endorphin given supraspinally has been previously demonstrated to be mediated by the stimulation of -, but not -, - or -opioid receptors in rats and mice. The present study was designed to determine what types of opioid receptors in the spinal cord are involved in the antinociception induced by intrathecally (i.t.) administered -endorphin. Antinociception was assessed by the tailflick test in male Sprague-Dawley rats. CTOP (0.9–6.6 nmol), a selective -opioid receptor antagonist, or nor-BNI(13.6–95.3 nmol), a selective -opioid receptor antagonist, given i.t. dose-dependently reversed i.t. administered -endorphin-induced inhibition of the tail-flick response. On the other hand, naltrindole (6.6–44.4 nmol), a selective -opioid receptor antagonist, or -endorphin (1–27) (1–6.7 nmol), a selective -opioid receptor antagonist given i.t., did not antagonize the inhibition of the tail-flick response induced by i.t. administered -endorphin. The results are consistent with the previous study in mice [Tseng LF and Collins KA (1992) Eur J Pharmacol 214: 59–65] that the antinociception induced by -endorphin given i.t. is mediated by the stimulation of - and -, but not - and -opioid receptors.Abbreviations i.t. Intrathecal - CTOP D-Phe-Cys-Tyr-D-Try-Orn-Thr-Pen-Thr-NH₂ - nor-BNI Norbinaltorphimine     

Nicotine anxiogenic and rewarding effects are decreased in mice lacking β-endorphin

The endogenous opioid system plays an important role in the behavioral effects of nicotine. Thus, μ-opioid receptor and the endogenous opioids derived from proenkephalin are involved in the central effects of nicotine. However, the role played by the different endogenous opioid peptides in the acute and chronic effects of nicotine remains to be fully established. Mice lacking β-endorphin were acutely injected with nicotine at different doses to evaluate locomotor, anxiogenic and antinociceptive responses. The rewarding properties of nicotine were evaluated by using the conditioned place-preference paradigm. Mice chronically treated with nicotine were acutely injected with mecamylamine to study the behavioral expression of nicotine withdrawal. Mice lacking β-endorphin exhibited a spontaneous hypoalgesia and hyperlocomotion and a reduction on the anxiogenic and rewarding effects induced by nicotine. Nicotine induced similar antinociception and hypolocomotion in both genotypes and no differences were found in the development of physical dependence. The dissociation between nicotine rewarding properties and physical dependence suggests a differential implication of β-endorphin in these addictive related responses.     

Ergothioneine protects against neuronal injury induced by β-amyloid in mice

β-Amyloid peptides (Aβ) are neurotoxic and contribute to the development of Alzheimer’s disease (AD). Ergothioneine (EGT) has been shown to protect against loss of memory and learning abilities in mice. In this study, mice were orally fed EGT (0.5 or 2 mg/kg body weight) for 16 days before treatment (i.c.v) with a single dose of Aβ1–40 in the hippocampus. After resting for 12 days to restore the body weight, the mice were again fed EGT for additional 39 days. Active avoidance tests were conducted on days 37–39 (short-memory avoidance) and on days 37, 44 and 51 (long-memory avoidance). Water maze task was used to evaluate learning and memory abilities by acquisition test and retention test. In both long-memory avoidance and water maze tests, EGT significantly decreased the escape latency and increased the frequency of successful avoidance. Furthermore, EGT significantly prevented Aβ accumulation in the hippocampus and brain lipid peroxidation, restored acetylcholinesterase (AChE) activity, maintained glutathione/glutathione disulfide ratio and superoxide dismutase activity in brain tissues of Aβ1–40-teated mice. Thus, EGT can protect against Aβ-induced loss of memory and learning abilities in mice. Further studies are required to confirm the protective effects of EGT on the development or progression of AD.     

Comparison of tolerance development and dependence capacities of morphine, β-endorphin,and [D-MET2, PRO5]-enkephalinamide

The tolerance-development capacities of -endorphin, [D-Met², Pro⁵]-enkephalinamide, and morphine were compared in rats, and the dependence capacity of morphine was compared with that of the enkephalin analogue in mice. Tolerance to the analgesic effect, as measured by the tail-flick test, developed somewhat more rapidly in the [D-Met², Pro⁵]-enkephalinamide-treated group than in the others. A similar relationship was found for the dependence capacity. Considering that the enkephalin analogue displayed the strongest analgesic activity, the wellknown correlation between antinociceptive and tolerance development/dependence capacities of opiates seems to be valid for opioid peptides as well.