Modification of morphine-induced analgesia, tolerance and dependence by bromocriptine

The effect of two doses of bromocriptine, a dopamine agonist, on morphine-induced analgesia, tolerance and dependence was investigated in mice. Bromocriptine at doses of 0.04 and 0.08 mg/kg did not affect the baseline tail flick latency of mice but potentiated the morphine analgesia. Pretreatment of mice with 5 mg/kg of sulpiride, a D-2 antagonist, not only blocked the effect of 0.08 mg/kg of bromocriptine but also antagonized the morphine analgesia. Control animals given daily injections of 10 mg/kg of morphine rapidly developed tolerance to the analgesic effect. A combined treatment of bromocriptine with morphine given daily suppressed the development of tolerance to morphine analgesia. However, development of tolerance to morphine analgesia was not significantly modified in the animals treated daily with bromocriptine (0.08 mg/kg) plus sulpiride (5 mg/kg). Acute dependence was induced by the administration of 100 mg/kg of morphine. The administration of bromocriptine 30 min before naloxone significantly decreased the ED₅₀ value for naloxone for inducing jumping in mice. Coadministration of sulpiride and bromocriptine attenuated the ability of bromocriptine to potentiate the withdrawal syndrome of morphine dependence. The results indicate that bromocriptine potentiates morphine analgesia, suppresses the development of tolerance to morphine analgesia but exacerbates opiate withdrawal signs in morphine-dependent mice. These effects of bromocriptine appear to be mediated via D-2 receptors.     

Facilitation of morphine-induced tolerance and physical dependence by prolyl-leucyl-glycinamide

The pretreatment of mice with 30 mg/kg morphine s.c. did not alter the analgesic effect of morphine in mice pretreated with saline but decreased the analgesic effect of morphine in mice pretreated with prolyl-leucyl-glycinamide (PLG). Tolerance was evaluated by the effect of PLG on morphine-induced enhancement of naloxone potency which is a measure of the capacity of naloxone to antagonize morphine-induced analgesia and is postulated to be an indicator of tolerance development. The naloxone potency of PLG-treated mice was 2-fold greater than that of control mice. PLG did not alter the whole brain levels of morphine, nor did it alter the naloxone potency in mice which were not pretreated with 30 mg/kg morphine. In mice treated with 100 mg/kg morphine or implanted with 50 mg morphine pellets for 24 or 72 h, the amount of naloxone required to induce jumping was not altered by PLG. However, PLG treatment did increase the hypothermia and body weight loss seen after naloxone-induced withdrawal. Administration of PLG to morphine-dependent mice 1 h prior to naloxone did not modify the resultant hypothermia or body weight loss. These results indicate that PLG facilitated the development of morphine tolerance and dependence.     

Analgesic activity of ZC88, a novel N-type voltage-dependent calcium channel blocker, and its modulation of morphine analgesia, tolerance and dependence

ZC88 is a novel non-peptide N-type voltage-sensitive calcium channel blocker synthesized by our institute. In the present study, the oral analgesic activity of ZC88 in animal models of acute and neuropathic pain, and functional interactions between ZC88 and morphine in terms of analgesia, tolerance and dependence were investigated. In mice acetic acid writhing tests, ZC88 (10-80 mg/kg) administered by oral route showed significant antinociceptive effects in a dose-dependent manner. The ED50 values of ZC88 were 14.5 and 14.3 mg/kg in male and female mice, respectively. In sciatic nerve chronic constriction injury rats, mechanical allodynia was ameliorated by oral administration of ZC88 at doses of 14, 28 and 56 mg/kg, suggesting ZC88 relieved allodynic response of neuropathic pain. When concurrently administered with morphine, ZC88 (20-80 mg/kg) dose-dependently potentiated morphine analgesia and attenuated morphine analgesic tolerance in hot-plate tests. ZC88 also prevented chronic exposure to morphine-induced physical dependence and withdrawal, but not morphine-induced psychological dependence in conditioned place preference model. These results suggested that ZC88, a new non-peptide N-type calcium channel blocker, had notable oral analgesia and anti-allodynia for acute and neuropathic pain. ZC88 might be used in pain relief by either application alone or in combination with opioids because it enhanced morphine analgesia while prevented morphine-induced tolerance and physical dependence.     

Effects of (-)-N6-(R-phenylisopropyl)-adenosine (PIA) and caffeine on nociception and morphine-induced analgesia, tolerance and dependence in mice

(-)-N6-(R-phenylisopropyl)-adenosine (PIA) was shown to possess analgesic activity in both the tail flick and acetic acid writhing assays. The analgesic actions of PIA were antagonized by caffeine in a dose-dependent manner. An apparent pA2 analysis in vivo suggested that the antagonism by caffeine was not competitive. Subanalgesic doses of PIA potentiated morphine-induced analgesia, tolerance and dependence. Caffeine antagonized these effects of morphine. PIA attenuated while caffeine exacerbated opiate withdrawal. While a low dose of caffeine antagonized PIA effects on withdrawal, a low dose of PIA did not antagonize the effects of caffeine. These results indicate that PIA can facilitate, and caffeine can antagonize the actions of morphine and that caffeine may be exerting some of its actions independent of adenosine receptor antagonism.     

Increased analgesic tolerance to acute morphine in fosB knock-out mice: a gender study

The proteins of Fos family are a potential candidate to link molecular mechanisms of morphine action with behavioural effects such as morphine-induced reward, dependence and tolerance. We used both male and female mice lacking fosB gene to study its contribution to morphine effects. Morphine analgesia (tail-flick test) and hypothermia were studied using morphine at cumulative doses in morphine-naïve and morphine-tolerant (tolerance induced by 24 h prior 100 mg/kg morphine administration) mice. FosB −/− mice, as compared to fosB +/+ mice, developed enhanced tolerance to morphine-induced analgesia. No effects of genotype or gender on tolerance to morphine-induced hypothermia were observed. These results suggest that fosB may be involved in the development of tolerance to morphine analgesia but not hypothermia. The gender study implicates that lack of FosB proteins in female fosB −/− mice enhanced morphine analgesic potency. In conclusion, we show that fosB gene is important to analgesia but not hypothermia phenotype indicating its role in morphine effects.     

Analgesic activity of anticancer agent suramin.

Suramin exhibited morphine-like analgesic activity in mice. It antagonized both thermal (hot-plate) and acetic acid-evoked writhing responses with ED50 values 1/100 and 1/68, respectively, that of morphine. The suramin- and morphine-induced hot-plate analgesia was suppressed by administration of 0.5 mg/kg naloxone. However, lower doses (5-30 micrograms/kg) of naloxone produced dose-related potentiation or suppression of suramin and morphine analgesia. This potentiation effect may be due to the inhibition of writhing by naloxone itself rather than be a direct antagonism of the morphine effect.     

Extracellular signal-regulated kinase (ERK) inhibition does not prevent the development or expression of tolerance to and dependence on morphine in the mouse

The clinical use of opioids is limited by the development of tolerance and physical dependence. Opioid tolerance and dependence are believed to result from complex adaptations in the CNS, representing a form of neural plasticity. Extracellular signal-regulated kinases (ERKs) are involved in many forms of neural plasticity, and therefore could also be involved in the development of opioid tolerance and dependence. In this study, we investigated the effect of a systemically bioavailable MEK (ERK kinase) inhibitor, SL327, upon the development and the expression of tolerance to and dependence on morphine in mice. In tolerance and dependence development studies, two strains of mice were treated daily for 8 or 9 days with 5mg/kg morphine s.c. Tolerance development was assessed by tail flick latency. Withdrawal was then precipitated by subcutaneous injection of 2mg/kg naloxone s.c. and signs recorded. Co-administration of 50mg/kg SL327 i.p. prior to morphine administration had no effect on the development of tolerance or withdrawal signs. To study possible effects of ERK inhibition on the expression of tolerance and dependence, mice were implanted with 75mg morphine pellets s.c. Tolerance and dependence were assessed as previously described. An acute i.p. injection of 50mg/kg SL327 after 4 days of morphine exposure had no effect on the expression of either morphine tolerance or physical dependence. To verify that this dose of SL327 inhibited morphine-induced ERK modulation, mice received an acute i.p. injection of 50mg/kg SL327 prior to morphine administration, and sacrificed 30min later. Western blots demonstrated that SL327 did inhibit morphine-induced ERK modulation. Taken together, these data suggest that unlike many other observed forms of neural plasticity, the ERK signaling cascade is not involved in the development or expression of opioid tolerance and dependence.     

Stress-induced analgesia and morphine responses are changed in catechol-O-methyltransferase-deficient male mice

Catechol-O-methyltransferase (COMT) polymorphisms modulate pain and opioid analgesia in human beings. It is not clear how the effects of COMT are mediated and only few relevant animal studies have been performed. Here, we used old male Comt gene knock-out mice as an animal model to study the effects of COMT deficiency on nociception that was assessed by the hot plate and tail flick tests. Stress-induced analgesia was achieved by forced swim. Morphine antinociception was measured after 10 mg/kg of morphine subcutaneously. Morphine tolerance was produced with subcutaneous morphine pellets and withdrawal provoked with subcutaneous naloxone. In the hot plate test, morphine-induced antinociception was significantly greater in the COMT knock-out mice, compared to the wild-type mice. This may be due to increased availability of opioid receptors as suggested by previous human studies. In the tail flick test, opioid-mediated stress-induced analgesia was absent and morphine-induced analgesia was decreased in COMT knock-out mice. In the hot plate test, stress-induced analgesia developed to all mice regardless of the COMT genotype. There were no differences between the genotypes in the baseline nociceptive thresholds, morphine tolerance and withdrawal. Our findings show, for the first time, the importance of COMT activity in stress- and morphine-induced analgesia in mice. COMT activity seems to take part in the modulation of nociception not only in the brain, as suggested earlier, but also at the spinal/peripheral level.     

Effects of intragastric agmatine on morphine-induced physiological dependence in beagle dogs and rhesus monkeys

Our previous studies demonstrated that subcutaneous injection of agmatine inhibits tolerance to and physiological dependence on morphine in mice and rats. In the present study we further evaluated the effects of intragastric (i.g.) administration of agmatine on morphine-induced physiological dependence in mice, rats, beagle dogs and rhesus monkeys. When agmatine (5-40 mg/kg, i.g.) was co-administered with morphine during the development of morphine-induced physiological dependence, it inhibited the abstinent syndrome precipitated by naloxone in mice, rats and beagle dogs. In addition, agmatine (40 mg/kg, i.g.) inhibited the abstinent syndrome precipitated by naloxone in mice when it was administered on the test day. In naloxone precipitated and naturally abstinent morphine dependent model in rhesus monkeys, agmatine (40 or 80 mg/kg, i.g.) inhibited the development of physiological dependence when it was co-administered with morphine. After the development of morphine dependence, agmatine (80 mg/kg, i.g.) inhibited the naturally abstinent syndrome during the 7-d abstinent period. All these results suggested that intragastric administration of agmatine inhibits morphine-induced physiological dependence in animal models.     

The effects of naltrexone on the development of physical dependence on morphine

A single i.p. injection of naltrexone (20 mg/kg) partially inhibited the development of physical dependence upon morphine in mice rendered dependent on morphine by implantation of a pellet containing 75 mg of morphine free base for three days. This was evidenced by an increase in the dose of naloxone (ED50) required to precipitate withdrawal jumping response. The increase in naloxone ED50 was much more pronounced when naltrexone was given prior to and during the course of pellet implantation. Inhibition was also observed when naltrexone was administered one day after the morphine pellet implantation, i.e., after some dependence had already developed. Naltrexone administration prior to and during the development of dependence also inhibited, but only partially, the loss of body weight and hypothermic response observed during abrupt withdrawal of morphine in morphine-dependent mice. The inhibitory effect of naltrexone on morphine dependence development was not associated with changes in brain morphine concentration.     

Central effects of the potent and highly selective mu opioid antagonist D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2 (CTOP) in mice

The ability of the selective cyclic mu-opioid receptor antagonist, D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2 (CTOP), to inhibit the acute and chronic effects of morphine in vivo was studied in mice. Intracerebroventricular (i.c.v.) administration of CTOP antagonized the analgesic effect of morphine in a dose-dependent manner, as measured by the heat-irradiant (tail-flick) method. CTOP was more effective than naloxone in inhibiting analgesia on a molar basis. CTOP also antagonized the acute morphine-induced hypermotility. CTOP caused withdrawal hypothermia and a loss of body weight in morphine-dependent animals. After the development of morphine-induced chronic dependence, CTOP administered i.c.v. caused a dose-dependent loss of body weight and hypothermia, and was about 10-400 times more potent than naloxone. CTOP administered alone to drugnaive mice did not cause antinociception, changes in body weight or body temperature.     

Dose-dependent effects of prolyl-leucyl-glycinamide on morphine-induced analgesia, tolerance and dependence

Prolyl-leucyl-glycinamide (PLG) at a low dose (10 ng/mouse) administered intracerebroventricularly (i.c.v.) did not affect morphine analgesia, but produced a greater increase in the ED50 of morphine-pretreated (100 mg/kg of morphine sulfate) mice as compared to control mice. PLG at doses of 10 and 100 micrograms/mouse antagonized morphine analgesia. Development of morphine tolerance was unaffected by 10 micrograms/mouse but antagonized by 100 micrograms/mouse of PLG. Development of morphine dependence was assessed by changes in body weight and temperature during naloxone-induced withdrawal. PLG (10 ng/mouse) potentiated, 10 micrograms/mouse had no effect and 100 micrograms/mouse antagonized development of morphine dependence. PLG at doses of 10 and 100 micrograms/mouse precipitated withdrawal in morphine-dependent mice. When mice were pretreated with 1.0 mg/kg naloxone i.p. 15 min before PLG, all doses of PLG had no effect on morphine analgesia, but potentiated the development of morphine tolerance and dependence. None of the doses of PLG altered whole brain levels of morphine. PLG did not alter the affinity of opioid receptors for etorphine or the maximal number of binding sites but PLG did exhibit a very weak affinity for opioid receptors. These results indicate that PLG potentiated development of morphine tolerance and dependence through a mechanism not involving opioid receptors. However, at very high doses it was a weak opioid receptor antagonist.     

Influence of prazosin and clonidine on morphine analgesia,tolerance and withdrawal in mice

Rapid development of tolerance and dependence limits the usefulness of morphine in long-term treatment. We examined the effects of clonidine (₂-adrenoceptor agonist) and prazosin (₁-adrenoceptor antagonist) on morphine analgesia, tolerance and withdrawal. Morphine tolerance was induced using a 3-day cumulative twice-daily dosing regimen with s.c. doses up to 120 mg/kg. Tolerance was assessed on day 4, as loss of the antinociceptive effect of a test dose of morphine (5 mg/kg). After 10 h, morphine withdrawal was precipitated with naloxone (1 mg/kg). Prazosin had no analgesic effect alone but dose-dependently potentiated morphine analgesia in morphine-naive mice. Another ₁-adrenoceptor antagonist, corynanthine, had similar effects. Prazosin also increased the analgesic potency of the morphine test dose in morphine-tolerant mice. Naloxone-precipitated vertical jumping was not affected, but weight loss was reduced by prazosin. Acutely administered clonidine potentiated morphine analgesia and alleviated opioid withdrawal signs, as expected. We conclude that in addition to the already established involvement of ₂-adrenoceptors in opioid actions, also ₁-adrenoceptors have significant modulatory role in opioid analgesia and withdrawal.     

The effect of adenosine receptor agonists on analgesic effects of morphine

The effect of adenosine, S-phenylisopropyladenosine (S-PIA) and dipyridamole (an adenosine reuptake inhibitor) on the analgesic action of morphine in mice and rats was investigated in the hot-plate (56 degrees C) and tail immersion (52 degrees C) tests. Adenosine, 50 and 100 mg/kg, induced analgesia in mice and rats in the hot-plate test and potentiated the action of morphine (particularly in mice). The analgesic effects of adenosine were completely abolished by caffeine (10 mg/kg in mice and rats), and partially inhibited by naloxone (1 mg/kg, only in mice). S-PIA given alone (0.6 mg/kg) produced in mice some analgesic effect in the hot-plate test: the effect was abolished by caffeine and partially by naloxone. The effect of S-PIA on the action of morphine depends on the dose and the animal species. Dipyridamole alone did not affect the reactivity of animals in tests for analgesia, but potentiated the action of morphine.     

Effect of propranolol on antinociceptive and withdrawal characteristics of morphine

Propranolol at a dose (10 mg/kg) which did not alter tail-flick latency by itself, did not alter the ED50 of morphine when given 10 min prior to the narcotic. Propranolol at doses of 10 and 25 mg/kg given 10 min prior to naloxone challenge did not significantly alter the frequency of naloxone induced jumping 72 hr after morphine pellet implantation. The ED50 of naloxone in morphine pelleted mice was not altered by treatment with propranolol at 0, 24, and 48 hr after pellet implantation. Naloxone caused hyperactivity in mice when administered 72 hr after morphine pellet implantation. An injection of 25 mg/kg propranolol 10 min prior to naloxone did not block this hyperactivity. In addition, administration of 10 mg/kg of propranolol every 8 hr to rats during withdrawal from morphine failed to alleviate the withdrawal syndrome as evidenced by changes in either body weight or water intake. These data suggest that the beta-adrenergic blocking agent, propranolol, does not alter the antinociceptive activity or lessen the withdrawal syndrome of morphine in rodents.     

On the mechanism(s) of morphine-induced hypothermia

The effects of morphine on core body temperature of mice in the presence or absence of catecholamine receptor antagonists were examined. Administration of different doses of morphine (20, 30 and 40 mg/kg) to mice caused a hypothermic effect. Pre-treatment of animals with the opioid receptor antagonist naloxone (1, 1.5 and 3 mg/kg), the D-2 receptor antagonists sulpiride (25 and 50 mg/kg), pimozide (0.0625, 0.125 and 0.25 mg/kg) and the adenosine receptor antagonist theophylline (25 and 50 mg/kg) decreased the morphine-induced hypothermia. The D-1 receptor antagonist SCH 23390 (0.1 and 0.2 mg/kg), the peripheral D-2 antagonist domperidone (10 and 30 mg/kg), the serotonin (5-HT) antagonist methysergide (5 and 10 mg/kg), the adrenoceptor antagonist phenoxybenzamine (2.5 and 5 mg/kg) and the β-adrenoceptor antagonist propranolol (5 and 10 mg/kg) did not inhibit the morphine response. The antimuscarinic drug atropine (5 and 10 mg/kg) caused a slight decrease in the morphine response. In animals pre-treated with reserpine (5 mg/kg), a hyperthermic response was observed after morphine injection. It is concluded that indirect dopaminergic or adenosine receptor mechanism(s) may be involved in the morphine-induced hypothermia in mice.     

Quercetin,a bioflavonoid,reverses development of tolerance and dependence to morphine

Quercetin, a bioflavonoid (25 and 50 mg/kg), when chronically administered for 9 days, failed to produce any significant change in tail flick latency as compared to control mice. However, repeated administration of quercetin (25 and 50 mg/kg) for 9 days attenuated the development of tolerance to the analgesic effect of morphine (10 mg/kg). Quercetin (25 and 50 mg/kg) also suppressed naloxone (2 mg/kg)‐precipitated withdrawal jumps on day 10 in morphine‐tolerant mice. Pretreatment of mice with quercetin (10–50, ip) significantly reversed the morphine (5 mg/kg)‐induced delay in gastric transit, whereas a higher dose of quercetin (100 mg/kg) did not have any significant effect on morphine‐induced delay in gastric transit. Quercetin per se had no effect on gastric transit. In conclusion, the results of the present study suggest potential use of quercetin in alleviating the adverse effects of opioid treatment. Drug Dev. Res. 57:167–172, 2002. © 2003 Wiley‐Liss, Inc.     

On the Mechanism(s) of Cholecystokinin (CCK): Receptor Stimulation Attenuates Morphine Dependence in Mice

Abstract: In the present study, effect of cholecystokinin (CCK) agonists and on dependence to morphine in mice has been investigated. The influence of dopaminergic, adrenergic, cholinergic and serotonergic on attenuation of naloxone-induced jumping in morphine-dependent mice by CCK agonists were also considered. Mice were treated subcutaneously with morphine (50, 50 and 75 mg/kg) three times daily (10 a.m. 1 p.m. and 4 p.m.) for 3 days, and a last dose of morphine (50 mg/kg) was administered on the 4th day. Withdrawal syndrome (jumping) was precipitated by naloxone (5 mg/kg) which was administered intraperitoneally 2 hr after the last dose of morphine. To study effects of CCK receptor agonists, 10 injection of morphine (3 administrations each day) for dependence and a dose of 5 mg/kg of naloxone for withdrawal induction were employed. The CCK agonists CCK-8 (0.001- 0.1 mg/kg), unsulfated CCK-8 (CCK-8U; 0.001-0.1 mg/kg) and caerulein (0.00001-0.01 mg/kg) were able to prevent withdrawal signs precipitated by naloxone (5 mg/kg). Sulpiride and pimozide increased response induced by CCK-8 agonists. The dopamine antagonists also attenuates jumping by themselves. SCH 23390 did not alter the CCK-8 effect, but decreased the jumping by itself. Phenoxybenzamine, propranolol, methysergide and atropine did not change the caerulein effect significantly. However, single administration of atropine increased and methysergide decreased jumping. It is concluded that CCK mechanism(s) may be involved in morphine dependence, and dopaminergic mechanism(s) may interact with CCK in attenuation of naloxone-induced jumping.     

胍丁胺对吗啡所致小鼠耐受和物质依赖的作用

目的 观察胍丁胺对吗啡所致耐受和依赖的作用。方法 分别在小鼠耐受和跳跃实验中观察胍丁胺抑制吗啡所致耐受和物质依赖的作用,结果：胍下胺０．１２５～２．５ｍｇ．ｋｇ＾－１剂量依赖性地阻止小鼠对吗啡耐受,用吗啡预处理小鼠使吗啡镇痛ＥＤ５０（２０．１,１４．４－２８．０ｍｇ．ｋｇ＾－１）与盐水组相比（６．３,５．１－７．８ｍｇ．ｋｇ＾－１）增加３倍以上,用胍丁胺和吗啡共同预处理小鼠则使吗啡丧失引直耐受的能     

Overexpression of type 7 adenylyl cyclase in the mouse brain enhances acute and chronic actions of morphine

The mechanisms by which morphine-induced analgesia and tolerance and physical dependence on morphine arise have been the subject of intense study, and much work has pointed to the involvement of cAMP-mediated events in the neuroadaptive phenomena leading to morphine tolerance and/or dependence. We overexpressed an opioid receptor-stimulatable form of adenylyl cyclase (type 7) in the central nervous system of mice and demonstrated significant effects of this manipulation on the animals' acute response to morphine, the development of morphine tolerance, and development of sensitization to morphine. Measurements of the acute analgesic response to morphine demonstrated that the ED(50) values for the transgenic mice were significantly lower than the ED(50) values determined for the "wild-type" animals. During chronic treatment with morphine, the transgenic mice developed tolerance more rapidly than the wild-type mice, and transgenic animals of the C57BL/6xSJL background showed a larger sensitization to morphine's effects on locomotor activity than did wild-type mice of the same background. These results indicated that cAMP-generating systems may simultaneously modulate the development of tolerance and sensitization. Interestingly, the signs of physical dependence on morphine in the transgenic mice did not differ from those in their wild-type litter mates, indicating that separate mechanisms may modulate opiate tolerance and opiate dependence.