Influence of dipeptides on precipitated morphine withdrawal in the mouse

Effects of various dipeptides on naloxone-precipitated morphine withdrawal were studied in the mouse. Mice were rendered dependent on morphine by implantation of morphine pellets and the withdrawal syndrome was measured by the latency of the onset of stereotyped jumpings. In accordance with previous data, subcutaneous injection of Z-prolyl-D-leucine significantly delayed the onset of morphine withdrawal. The all-L enantiomer of the dipeptide (Z-L-prolyl-L-leucine) did not affect morphine withdrawal in the dose studied. Replacement of L-proline by L-glutamate or L-pyroglutamate (Z-L-glutamyl-L-leucine and L-pyroglutamyl-L-leucine) resulted in dipeptides which were more potent towards morphine withdrawal than Z-prolyl-D-leucine. Z-L-glycyl-L-proline attenuated the morphine withdrawal syndrome more effectively than Z-L-prolyl-D-leucine, but Z-L-leucyl-L-glycine was ineffective in this respect. The data reveal that certain dipeptides—which in their nonprotected forms are normal sequences of endogenous peptides—affect morphine withdrawal more potently than Z-prolyl-D-leucine, a synthetic dipeptide known to attenuate morphine dependence.     

Modification of morphine withdrawal by interferon

Naloxone was administered to morphine dependent rats to elicit the opioid abstinence syndrome. Recombinant leukocyte A interferon treatment one hour prior to naloxone injection eliminated almost all of the abstinence behavioral signs observed.     

Petrosaspongiolide M reduces morphine withdrawal in vitro

The bee venom phospholipase A(2) (PLA(2)) inhibitory activity of petrosaspongiolide M (PM), a marine metabolite displaying a potent anti-inflammatory activity and able to covalently bind and block group II and III secretory PLA(2) enzymes, has been investigated by mass spectrometry and molecular modeling. The model reveals interesting insight on the PM-PLA(2) inhibition process and may prove useful in the design of new anti-inflammatory agents targeting PLA(2) secretory enzymes. In this paper, the effect of PM has been investigated on opiate withdrawal in an in vitro model. After a 4 min in vitro exposure to morphine a strong contracture of guinea pig isolated ileum was observed after the addition of naloxone. PM treatment 1 x 10(-8), 5 x 10(-8), 1 x 10(-7) M was able to reduce morphine withdrawal. These results suggest that PM effect in this in vitro model of opiate withdrawal may be due to extracellular type II PLA(2) inhibition.     

Naloxone-precipitated morphine withdrawal increases pontine glutamate levels in the rat

Extracellular fluid (ECF) levels of glutamate (Glu) and aspartate (Asp) were measured in the locus coeruleus (LC) during morphine withdrawal by using microdialysis in conscious morphine-dependent Sprague-Dawley rats. Guide cannulae were implanted chronically and rats were given intracerebroventricular (i.c.v.) infussions of morphine (26 nmol/1 μl/ht) of saline (1 μl/hr) for 3 days. Microdialysis probes (2 mm tip) were inserted into the LC 24 hr before precipitation of withdrawal by i.c.v. injection of naloxone (12 or 48 nmol/5 μl). Behavioral evidence of withdrawal (teeth-chattering, wet-dog shakes, etc.) was detected following naloxone challenge in morphine, but not in saline-infused rats. Increases (P<0.01) in ECF levels of Glu (and Asp, to a lesser degree) were noted after naloxone-precipitated withdrawal only in the morphine group. The ECF Glu levels in the LC increased from 9.6 ± 2.7 to 15.5 ± 5.0 μM following 12 nmol/5 μl naloxone, and from 9.5 ± 1.9 to 20.5 ± 3.3 μM following 48 nmol/5 μl naloxone, before and in the first 15 min sample after the precipitation of withdrawal in the morphine-dependent rats, respectively. These results provide direct evidence to support the role of excitatory amino acids within the LC in morphine withdrawal.     

Mechanisms mediating the thermal response to morphine withdrawal in rats

Studies were undertaken to evaluate the role of peripheral adrenergic mechanisms and the adrenal gland in the thermal responses which accompany morphine withdrawal in the rat. Ovariectomized rats were addicted to morphine and subsequently withdrawn by administration of naloxone. This treatment resulted in a significant rise (5-6 degrees C) in tail skin temperature (TST) and fall in colonic temperature (2-4 degrees C). Systemic administration of clonidine (0.5 mg/kg) completely suppressed this surge in TST and significantly attenuated the fall in core temperature. Similar results were observed following the systemic administration of ST-91, another alpha 2-adrenergic agonist which does not cross the blood-brain barrier. Central administration of ST-91 (50 micrograms/5 microliters, icv) was also successful in attenuating these temperature changes in the morphine-dependent rat. Adrenalectomy and peripheral administration of propranolol (10 mg/kg sc) both resulted in a significant attenuation of the surge in TST and the fall in core temperature in the morphine-dependent rat which suggest some peripherally mediated event is necessary to produce the full skin temperature surge. Collectively, the data suggest a role for the adrenal gland and adrenergic receptors in producing the surge in TST in morphine-dependent rats. It also suggests that the blocking effects of the alpha 2-adrenergic agonist can be mediated both centrally and peripherally.     

Involvement of central endothelin receptors in neonatal morphine withdrawal

The involvement of central endothelin (ET) receptors in neonatal morphine tolerance has been demonstrated. The present study investigates the role of central ET receptors in morphine withdrawal in neonatal rats. The aim was to determine whether activation of G-proteins coupled to opioid and ET receptors by morphine and various ET receptor modulators is affected during morphine withdrawal in neonatal rats. Pregnant female rats were rendered tolerant to morphine by chronic exposure to morphine pellets during 7 days. On Day 8, pellets were removed and rats were allowed to undergo withdrawal for 24 hrs. Rat pups were delivered by cesarean section. G-protein stimulation induced by morphine; ET-1; the ET(A) receptor antagonist, BMS182874; and the ET(B) receptor agonist, IRL1620, were determined in the brain of neonatal rats undergoing morphine withdrawal by [35S]GTPgammaS binding assay. Morphine produced higher (P < 0.05) maximal stimulation of G-protein in the morphine-withdrawal group (83.60%) compared with the placebo group (66.81%). ET-1-induced G-protein stimulation was also altered, and the median effective concentration (EC50) during morphine withdrawal (170.60 nM) was significantly higher than placebo (62.5 nM; P< 0.05). The maximal stimulation induced by the ET(A) receptor antagonist, BMS182874, in the morphine-withdrawal group (86.07%; EC50 = 31.25 nM) was significantly higher than in the placebo group (EC50 > 1000 nM). The ET(B) agonist, IRL1620, induced G-protein stimulation was similar in placebo (73.43%, EC50 = 13.26 nM) and morphine-withdrawal groups (75.08%, EC(50) = 11.70 nM), respectively. To our knowledge, this is the first report indicating involvement of central ET(A) receptors in neonatal morphine withdrawal.     

Purinoreceptors are involved in the control of acute morphine withdrawal.

The effects exerted by P1 and P2 purinoceptor agonists and antagonists on the acute opiate withdrawal induced by morphine were investigated in vitro. Following a 4 min in vitro exposure to morphine, the guinea-pig isolated ileum exhibited a strong contracture after the addition of naloxone. The P1 purinoceptor agonist, adenosine, was able dose-dependently to reduce morphine withdrawal whereas alpha,beta-methylene ATP (APCPP), a P2 purinoceptor agonist, increased morphine withdrawal. Caffeine, a P1 purinoceptor antagonist, was able significantly and in a concentration dependent manner to increase morphine withdrawal whereas quinidine, a P2 receptor antagonist, reduced it. The results of our experiments indicate that both P1 and P2 purinoceptor agonists and antagonists are able to influence opiate withdrawal in vitro, suggesting an important functional interaction between the purinergic system and opioid withdrawal.     

Orphanin FQ/nociceptin inhibits morphine withdrawal

The influence of orphanin FQ/nociceptin (OFQ/N) on the morphine-withdrawal symptom was investigated. Withdrawal syndrome was induced in the morphine-dependent rats by an intraperitoneal (i.p.) injection of 2 mg/kg naloxone hydrochloride--an opioid receptors antagonist. Wet-dog shakes were used as a measure of the abstinence syndrome. Intraventricular injections of OFQ/N (5-20 microg/animal) caused significant inhibition of the withdrawal signs at doses between 15-20 microg, in the morphine-dependent rats. OFQ/N alone did not change behavior of the morphine-dependent animals. The obtained results indicate that OFQ/N can inhibit the morphine withdrawal symptoms induced by naloxone.     

Similarities between morphine withdrawal in the rat and the menopausal hot flush

Skin temperature, cardiovascular and neuroendocrine responses to morphine withdrawal in the rat were evaluated in an effort to develop a potential animal model for the menopausal hot flush in women. Morphine dependency was produced by s.c. implantation of pellets containing morphine alkaloid. In response to precipitous, naloxone-induced withdrawal, rats showed surges in tail skin temperature (TST) which were similar in magnitude (4.8 to 7.2 degrees C) and duration (60 to 90 min.) to peripheral skin temperature increases reported during menopausal hot flushes. Additionally, a brief period of accelerated heart rate (59%) and a 9-fold hypersecretion of luteinizing hormone (LH) preceded the TST response to morphine withdrawal. These cardiovascular and neuroendocrine responses are observed to precede or coincide with the menopausal hot flush. Additionally, protracted morphine withdrawal subsequent to abstention, resulted in TST instability characterized by spontaneous, high amplitude TST fluctuations. Thus, the alteration in skin temperature, heart rate and LH secretion during precipitated morphine withdrawal in the rat are similar in magnitude, duration and in their temporal relationship to those observed during the hot flush. These data suggest a possible opioid etiology in this vasomotor disturbance. Acute withdrawal in the morphine addicted rats may serve as an animal model by which to study the neural mechanism underlying the menopausal hot flush.     

Trans-cranial electrical stimulation attenuates the severity of naloxone-precipitated morphine withdrawal in rats

The expression of morphine withdrawal in rats has been demonstrated as dependent upon the integrity of specific brain regions. Focal intracranial electrical stimulation of some of these sites results in the attenuation of withdrawal severity. The present study demonstrates that electrical auricular stimulation, in a paradigm known to attenuate nociceptive responses of several brain nuclei, attenuates the severity of naloxone-precipitated morphine withdrawal in rats. This simple non-invasive treatment, based on long-standing principles of electroacupuncture, may provide a useful adjunct for therapy of the narcotic withdrawal syndrome.     

Morphine withdrawal modifies antinociceptive effects of acute morphine in rats

Repeated opioid use is known to cause tolerance of antinociceptive effects. Whether opioid abstinence modifies antinociceptive effects is unknown. Here we reported that morphine withdrawal for 18 h and 4 days after repeated morphine treatment largely reduced tail-flick latencies compared with control, while the rats showed severe withdrawal syndromes. However, the latencies and withdrawal syndromes were restored to control level at 20 days withdrawal. Similarly, antinociceptive effects of acute morphine were decreased at 18 h and further decreased at 4 days but restored to control level at 20 days withdrawal. Behavioral stress that was given to the rats at 18 h withdrawal further reduced tail-flick latencies and antinociceptive effects. Conversely, the glucocorticoid receptor antagonist RU38486 increased tail-flick latencies and antinociceptive effects at 4 days withdrawal. These results suggest that morphine withdrawal could evoke behavioral stress to modify antinociceptive effects, implicating a significant influence of opioid abstinence on chronic pain treatment.     

Dopaminergic mechanisms in withdrawal hypothermia in morphine dependent rats.

The role of several putative neurotransmitters in the development of tolerance and dependence to the narcotic analgesics has been the subject of a recent review (1), which demonstrated the lack of a consensus on the precise role of the catecholamines in this syndrome. A definitive role for brain dopamine in withdrawal aggression and withdrawal hypothermia has been suggested (2,3,4), although in the case of the hypothermia few details are available. We therefore decided to assess the importance of dopamine in withdrawal using apomorphine and pimozide, drugs claimed to be specific for dopamine receptors.     

慢性吗啡给予、戒断及再给药过程中大鼠海马感觉门控的动态变化

药物成瘾被认为是药物长期作用于脑而产生的一种慢性复吸性脑疾病,长期反复的药物（如吗啡）滥用会导致一系列严重后果,如药物依赖、药物耐受、强迫性药物寻求等。本实验利用条件化位置偏好（conditioned place preference,CPP）模型来检测大鼠对吗啡依赖和心理渴求等过程;采用双声刺激听觉诱发电位来研究大鼠在慢性吗啡给予、戒断以及再给药过程中海马感觉门控（N40）的动态变化。吗啡组大鼠注射吗啡（10mg／kg,i．p．）12d,经历第一次戒断12d,再次注射吗啡（2．5mg／kg,i．P．）1d,之后经历第二次戒断2d;对照组大鼠注射同体积生理盐水,其余实验条件与吗啡组相同。CPP实验表明,这种药物给予方法促使大鼠对吗啡产生药物依赖和心理渴求。双声刺激诱发电位实验表明,吗啡组大鼠在吗啡给予期间海马感觉门控受到损伤;第一次戒断期的第1～2天海马感觉门控能力减弱,第3天增强,第4～12天逐渐恢复到正常水平;再次给予吗啡后海马感觉门控能力与对照组相比显著降低,并且随后2d的戒断期内海马感觉门控能力也一直保持较低水平,表明再次给药使大鼠海马感觉门控对吗啡更加敏感化。结果提示,长期反复的吗啡给予及再给药干扰了海马的感觉门控能力,吗啡成瘾对大脑可能产生长期影响。     

Metabolic enzymes link morphine withdrawal with metabolic disorder

Energy metabolism is a fundamental biological process that is vital for the survival of all species. Disorders in the metabolic system result in deficiency or redundancy of certain nutrients, including carbohydrates, lipids, amino acids, etc. Abnormality of the energy metabolism system leads to a number of metabolic diseases, such as the metabolic syndrome. Broadly speaking, the term ＂metabolic diseases＂ now tends to be widened to the category that refers to all diseases with metabolism disorder. It is shown that many diseases associate with metabolic disorders. For example, most malignant tumors progress with mal-nutrition and high consumption, that is, cachexia. Many components of the energy metabolism system, such as lactate dehydrogenase （LDH）, are now widely applied in clinical examinalions as special markers for tumors and some other diseases. Opioid dependence and addiction are neurobiological diseases associated with malregulation of the metabolic system. However, how chronic drug administration induces metabolic abnormality is not understood. In a recent issue of Cell Research, research group of Jing-Gen Liu reports an interesting discovery that three metabolic enzymes are changed in mice after chronic morphine treatment, suggesting new roles of metabolic enzymes as a potential link that associates metabolic disorder with opioid dependence.[第一段]     

Fluctuations of acetylcholinesterase in the mouse spinal cord and in vivo sodium effect during the development of morphine tolerance,dependence, and withdrawal

Tolerance to and physical dependence on morphine were produced and assessed in Swiss inbred albino mice by giving morphine sulphate (s.c.) three times a day for a period of 15 days in an increasing dose of 10 mg/kg every 24 hours. Physical dependence was assessed taking naloxone induced jumping as well as weight loss during normal withdrawal into consideration. The effect of sodium ions in the potency of naloxone in antagonizing morphine's effect was also analyzed. The spinal cord was assayed for acetylcholinesterase employing both biochemical and histochemical parameters. It was found that the amount of the enzyme increased with the development of tolerance but the amount decreased as the animals became physically dependent. However, the values were significantly above the control. Administration of naloxone brought about a sudden and significant fall in the level of the enzyme. Normal withdrawal too was characterized by a weak activity of the enzyme. It has been found that sodium ions can influence naloxone antagonism in an in vivo system.