Role of noradrenergic functions in the modification of naloxone-precipitated withdrawal jumping in morphine-dependent mice by diabetes

The role of noradrenergic functions in the modulation of naloxone-precipitated withdrawal jumping in morphine-dependent mice by diabetes were examined. Both diabetic and non-diabetic mice were chronically treated with morphine (8 - 45 mg/kg, s.c.) for 5 days. During this treatment, neither diabetic nor non-diabetic mice showed any signs of toxicity. After morphine treatment, withdrawal was precipitated by injection of naloxone (0.3 mg/kg, s.c.). The number of naloxone-precipitated withdrawal jumps within 5 min after injection of naloxone was significantly less in morphine-dependent diabetic mice than in morphine-dependent non-diabetic mice. However, there was no significant difference in the number of naloxone-precipitated withdrawal jumps from 5 to 15 min after injection of naloxone between diabetic and non-diabetic mice. The turnover rate of noradrenaline in the frontal cortex in morphine-dependent non-diabetic mice, but not in morphine-dependent diabetic mice, was significantly increased 5 min after administration of naloxone. These results suggest that the functional changes in central noradrenergic systems may be involved in the reduction of naloxone-precipitated jumping in morphine-dependent diabetic mice.

The neurochemistry of morphine addiction in the neocortex

Different strategies have been used in an attempt to understand the neurobiology of opioid addiction. Here, Michéle Simonato initially discusses the identification of key anatomical areas involved in the phenomenon and purposes an explanation of opioid addiction based on the theory of complexity. The variable importance of direct and indirect effects in phenotypically different neuronal populations can imply differences in the adaptive changes that occur with chronic morphine exposure. Opioid addiction is therefore proposed as a complex multicellular event, where individual neurones differentially adapt both on the basis of the signals they receive and of their second messengers and genetic programmes.

Reduction of morphine abstinence in mice with a mutation in the gene encoding CREB

Chronic morphine administration induces an up-regulation of several components of the cyclic adenosine 5'-monophosphate (cAMP) signal transduction cascade. The behavioral and biochemical consequences of opiate withdrawal were investigated in mice with a genetic disruption of the alpha and Delta isoforms of the cAMP-responsive element-binding protein (CREB). In CREBalphadelta mutant mice the main symptoms of morphine withdrawal were strongly attenuated. No change in opioid binding sites or in morphine-induced analgesia was observed in these mutant mice, and the increase of adenylyl cyclase activity and immediate early gene expression after morphine withdrawal was normal. Thus, CREB-dependent gene transcription is a factor in the onset of behavioral manifestations of opiate dependence.

Further evidence that naloxone acts as an inverse opiate agonist: implications for drug dependence and withdrawal

To test if naloxone behaved as an inverse agonist rather than as an antagonist we evaluated its responses in guinea-pig ilea with and without morphine (480 nM, 24 h). In control ilea, naloxone (100 nM) had no effect. In morphine-treated ilea, naloxone as a bolus, but not as an infusion, elicited an abstinence response. Preadministration of naloxone blocked the response to subsequent administrations. Similarly, naloxone failed to produce an abstinence response in ilea pretreated with kappa compounds (bremazocine, U50488 or xorphanol 100 nM) or with kinase inhibitors (H7 or H8 30 microM). These findings can be interpreted in the light of the two-state receptor model if naloxone behaves as an inverse agonist: Incubation with morphine increased the active state of receptors making them susceptible to the inverse agonist (naloxone); exposure to naloxone favored the inactive conformation making them insensitive to further administration of naloxone; kappa compounds behaved as antagonists preventing the response to naloxone; and kinase inhibitors interfered with the active conformation making the system insensitive to naloxone. According to this model, dependence can be viewed as an overexpression of the active receptors and withdrawal as an abrupt change from the active to the inactive state.

Possible involvement of the total amount of morphine infused in the development of acute morphine dependence in rats

The severity of naloxone-precipitated withdrawal in rats infused intravenously with morphine at the rates of 2.5, 5 and 10 mg/kg/hr over various time periods was investigated. Plasma morphine concentration reached a constant and rate-dependent level at 1 hr after the start of morphine infusion, and this level was maintained until the termination of infusion. Naloxone (2.0 mg/kg, s.c.) was challenged 18 hr after infusion was stopped, and the withdrawal was evaluated by plasma corticosterone (PCS) increase, diarrhea and body weight loss. The incidence of naloxone-precipitated withdrawal signs was related to both the infusion rate and duration of morphine infusion. The duration of morphine infusion (ET50) needed to elicit naloxone-precipitated PCS increase and diarrhea in 50% of the rats was inversely related to the morphine infusion rates, but the total amount of infused morphine (EA50) that elicited naloxone-precipitated withdrawals in 50% of rats was the same at all infusion rates. These results suggest that the total amount of morphine infused may play an important role in the development of acute physical dependence on morphine rendered by continuous intravenous morphine infusion for 1-8 hr.

Diazepam pretreatment suppresses morphine withdrawal signs in the mouse

The effect of diazepam on the development of physical dependence on morphine and on the naloxone-precipitated increase in cortical NA turnover were investigated in mice. Co-administration of diazepam (1-4 mg/kg, i.p.) during chronic morphine treatment suppressed the expression of naloxone (3 mg/kg, s.c.)-precipitated withdrawal signs (jumping, exploratory rearing and weight loss). However, a single injection of diazepam (4 mg/kg, i.p.) in morphine-dependent mice did not affect the expression of naloxone-precipitated withdrawal signs. The 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG) level and noradrenaline (NA) turnover (MHPG/NA) in the cerebral cortex were increased by naloxone (3 mg/kg) challenge. These increases in the cortical MHPG level and NA turnover were significantly prevented by co-administration of diazepam (4 mg/kg, i.p.) during chronic morphine treatment. These findings suggest that the co-administration of diazepam during chronic morphine treatment may prevent some neurochemical changes in the central noradrenergic system during chronic morphine treatment, and may suppress the development of physical dependence on morphine. Therefore, the inhibitory action of GABA via benzodiazepine binding sites may play an important role in the development of physical dependence on morphine.

Role of D1/D2 dopamine and N-methyl-D-aspartate (NMDA) receptors in morphine tolerance and dependence in mice

Chronic treatment with the dopamine (DA) agonist B-HT 920 (0.25-1 mg/kg) or bromocriptine (1 mg/kg) followed by morphine (10 mg/kg) on days 1-9 prevented the development of tolerance to the antinociceptive effect of morphine as measured by the tail-flick test in mice, but failed to suppress the development of morphine dependence as assessed by naloxone (2 mg/kg)-precipitated withdrawal jumps on day 10 of testing. Repeated administration of SKF 38393 (5 mg/kg) followed by morphine for 9 days significantly reduced naloxone-precipitated jumps on day 10 but failed to produce any significant change in tail-flick latency from the saline-pretreated group of mice on days 9 and 10 of testing. Repeated administration of B-HT 920 or bromocriptine enhanced the ability of MK-801 to attenuate the development of morphine tolerance and dependence while SKF 38393 failed to do so. The above data suggest a preferential role of D2 DA receptors in morphine tolerance and D1 receptors in the development of morphine dependence. D2 DA receptor stimulation may also play an important role in enhancing the effectiveness of MK-801 in the treatment of opiate tolerance and dependence.

Morphine dependence with or without tolerance in formalin-treated mice: further evidence for the dissociation

Pain associated-anxiety induced by formalin, which resulted in a significant delay in the development of tolerance to morphine antinociception, failed to prevent the development of physical dependence as evidenced by naloxone challenge. Dependence also developed in mice rendered tolerant to morphine. Thus, the development of morphine dependence was observed in the absence and presence of tolerance to morphine antinociception; Our results further confirm the dissociation of opioid tolerance and dependence in the animal model of experimental pain/anxiety.

Evidence for functional dissociation of dependence and tolerance in guinea-pig isolated ileal segments following 20 hour exposure to morphine in vitro

1. In the present study we have examined the relationship between tolerance and dependence in isolated ileal segments from the guinea-pig under three different conditions: fresh preparations not previously exposed to morphine (fresh/morphine naive); preparations stored overnight at 4 degrees C in modified Krebs-Henseleit saline (overnight-stored/morphine-naive); preparations stored overnight at 4 degrees C in Krebs-Henseleit saline containing 10 microM morphine and extensively washed with modified Krebs-Henseleit saline to remove residual morphine (overnight-stored/morphine-exposed). 2. Morphine produced a concentration-dependent inhibition of the response of ileal segment to 0.1 Hz, 1 ms and 10 V transmural field stimulation in fresh/morphine-naive, overnight-stored/morphine-naive and overnight-stored/morphine-exposed preparations. The maximum effect observed was similar in all three preparations-approximately 80% inhibition. Although, morphine was significantly more potent in the fresh/morphine-naive preparations (pD2 6.72 +/- 0.05, n = 8) than either the overnight-stored/morphine-native (pD2 6.42 +/- 0.11, n = 8) or the overnight-stored/morphine-exposed (pD2 6.44 +/- 0.14, n = 8), there was no significant difference between the overnight exposure to ileal segments to 10 microM morphine at 4 degrees C failed to induce tolerance to morphine. 3. The mu opiate receptor antagonist, naloxone (10 microM), produced contractions in both fresh/morphine-naive and overnight-stored/morphine-naive ileal segments following acute exposure to 10 microM morphine. Naloxone (10 microM) also produced contractions in 2/9 fresh/morphine-naive, 1/9 overnight-stored/morphine-naive and 7/9 overnight-stored/morphine-exposed preparations in the absence of morphine. The greater incidence of naloxone-induced contractions in overnight-stored/morphine-exposed preparations,suggests that dependence in this model is the product of adaptive changes that outlive the presence of morphine.4. The selective alpha2-adrenoceptor agonists, clonidine (0.3 microM) and 5-bromo-6-[2-imidazolin-2-ylamino]-quinoxaline bitartrate (UK-14304, 1 microM), inhibited naloxone-induced contractions in overnight-stored/morphine-exposed preparations of ileal segments (n = 4 preparations for each agonist), suggesting that the response is due to transmitter release from the myenteric plexus.5. The findings in the present study indicate that tolerance and dependence to morphine in ileal segments of the guinea-pig can be functionally dissociated by overnight exposure to morphine at 4 degrees C.The development of tolerance to morphine, unlike dependence, appears to be a temperature-dependent process. This also raises the possibility that naloxone possesses intrinsic negative agonism at morphine sensitive receptors, which is manifested as a functional response only after adaptive changes in the myenteric plexus following exposure to morphine.

Effect of pretreatment with pertussis toxin on the development of physical dependence on morphine

The effect of intracerebroventricular (i.c.v.) pretreatment with pertussis toxin (PTX) on the development of physical dependence on morphine was investigated in mice. Twenty four hours after PTX (0.5 microgram, i.c.v.) or vehicle pretreatment, the mice were chronically treated with morphine (8-45 mg/kg, s.c.) for 5 days. Several withdrawal signs were observed following naloxone challenge in morphine-dependent mice which had been pretreated with vehicle. In addition, 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG) and noradrenaline (NA) turnover (MHPG/NA) levels in the cerebral cortex were increased following naloxone challenge in morphine-dependent mice. These findings indicate that activation of the central noradrenergic system may mediate the expression of some withdrawal signs. In contrast, pretreatment with PTX attenuated the naloxone-precipitated withdrawal signs in morphine-dependent mice. The incidence of withdrawal signs such as jumping, "wet dog" shakes, and rearing was significantly reduced by PTX pretreatment. PTX pretreatment also prevented the naloxone-precipitated increases in MHPG concentration and NA ratio (MHPG/NA) in the cerebral cortex, suggesting that central PTX-sensitive GTP-binding proteins (G-proteins) may be involved in the elevation of NA transmission in the cortex which projects from the locus coeruleus (LC) during morphine withdrawal. The blocking effects of PTX on the behavioral and biochemical changes after withdrawal suggest that central PTX-sensitive G-proteins (Gi/Go) may play an important role in the development of physical dependence on morphine.

Involvement of delta 2 opioid receptors in the development of morphine dependence in mice

The possible involvement of delta 2 opioid receptors in the development of morphine dependence was investigated using selective delta 2 receptor antagonists, naltriben (NTB) and naltrindole 5'-isothiocyanate (5'-NTII). The degree of morphine dependence was estimated by the ED50 values of naloxone (s.c.) required to precipitate withdrawal jumping and diarrhea 72 hr after morphine pellet implantation. NTB administered s.c. as well as naloxone precipitated jumping and diarrhea in morphine-dependent mice. Chronic treatment with 5'-NTII (both i.c.v. and i.t. routes, 24 hr before, just before, 24 and 48 hr after morphine pellet implantation) increased the ED50 values of naloxone for jumping and diarrhea. These results suggest that both supraspinal and spinal delta 2 opioid receptors are involved in the development of physical dependence on systemically administered morphine. However, chronic treatment with NTB (s.c. route, 30 min before, 24 and 48 hr after morphine pellet implantation) failed to affect the ED50 values of naloxone for both withdrawal signs. These seemingly discrepant results suggest that continuous blockade of delta 2 opioid receptors (by a nonequilibrium and long-lasting antagonist, 5'-NTII) rather than intermittent blockade of delta 2 opioid receptors (by an equilibrium and relatively short-acting antagonist, NTB) is necessary to inhibit the development of morphine dependence.

Enhanced antiopiate activity in peptidomimetics of FMRFamide containing Z-2,3-methanomethionine

FMRFa is a molluscan peptide that has shown antiopiate activity in a number of mammalian test systems. The current study determined the antiopiate potency of FMRFa and two conformationally constrained peptidomimetics of FMRFa containing stereoisomers of Z-2,3-methanomethionine. Morphine abstinence signs were observed after varying doses (0.25-25.0 micrograms) of these substances were injected into the third ventricle of morphine-dependent rats. Although both peptidomimetics were far more potent than FMRFa itself, they bound with lower affinity than FMRFa to rat spinal cord receptors for the mammalian FMRFa-like peptide, NPFF.

[Antibody formation to morphine and neuromediators in morphinized rats]

The paper demonstrates induction of antibodies to morphine and neurotransmitters (dopamine, norepinephrine, serotonin) in rats treated with intraperitoneal injections of morphine hydrochloride during 2 and 4 weeks in increasing doses. A contribution of such antibodies to the mechanisms of morphine tolerance and formation of physical dependence is considered.

[Conditioned-reflex activation of electrical self-stimulation of the brain: a model of a situational craving for narcotics]

Rats with electrodes implanted into lateral hypothalamus were trained to press a lever to obtain electrical stimulation of the brain. After elaboration of self-stimulation (SS) conditioning of morphine-induced activation of SS-response was carried out. Five pairings were performed of morphine (3 mg/kg, i.p.) administration and SS in the box with distinct environmental cues (brightness, color, floor texture, background noise). After morphine withdrawal activation of SS was reproduced after simple placing of the animal in "conditioned" chamber. This effect was naloxone-sensitive. The observed effect is considered to be the adequate model of addictive substances craving.

Can cancer pain attenuate the physical dependence on chronic long-term morphine treatment?

This prospective and comparative study was designed to determine the role of cancer pain and attitudes towards morphine in attenuating the intensity and duration of physical dependence following chronic morphine treatment. Morphine was administered via a stepwise ladder approach in order of oral, spinal and intravenous routes depending on the adequacy of analgesia. On-demand titration of a dose, either upward or downward, was liberal and unlimited. Withdrawal strategy was evaluated and initiated either by patients (PI group) or their families (FI group). The manifestation of physical dependence on morphine was compared between patients who successfully withdrew (total withdrawal), and patients who failed to withdraw (episodic withdrawal), from morphine for a period of more than two weeks. Eighty-eight out of 627 patients (14.1%) were excluded from our protocol; 75% of these exclusions were due to objections toward morphine as the major form of analgesic. Drop-out due to poorly tolerated side effects was relatively rare (18.2%). Fifty-four (10.0%) achieved total withdrawal and 212 (39.3%) experienced episodic withdrawal. Non-pain-related abstinence symptoms were highly prevalent but were tolerable for both groups. Pain-related symptoms were more exaggerated during episodic withdrawal. Intolerable pain, rather than physical dependence, contributed to the failure to withdraw from morphine. Among a total of 539, addiction was found in only one patient (0.18%) who began drug use long before entering our protocol. Attitudes towards morphine affect the acceptance of treatment and hasten the withdrawal strategy. Families were more anxious about morphine than the patients themselves which led to more aggressive, but less tolerable, withdrawal.(ABSTRACT TRUNCATED AT 250 WORDS)

[An assessment of the individual sensitivity of Wistar rats to the development of morphine dependence]

A search was made for behavioral and physiological indicators which could serve predictors of the individual sensitivity of Wistar rats to the development of physical morphine dependence. Animals with high sensitivity to the development of dependence initially demonstrated intensive ambulation and low motor rearing in the "open field" and had low nociception. Stable animals exhibited high ambulation and motor rearing with insignificant grooming activity as compared to other rats. It has been revealed that rats sensitive to the development of dependence demonstrate higher anxiety in the Vogel test as compared to the stable ones. The findings obtained allowed one to derive a number of equations to predict Wistar rats' individual sensitivity to the development of physical morphine dependence.

Pharmacodynamics and kinetics of loss of tolerance and physical dependence on morphine induced by pellet implantation in the rat

The decay characteristics of tolerance and physical dependence on morphine induced by a pellet implantation procedure were determined in male Sprague-Dawley rats. Rats were implanted subcutaneously with 6 morphine pellets during a 7-day period. The pellets were removed, and at various times thereafter tolerance to the analgesic and hyperthermic effects of morphine was measured by determining the response in rats implanted with morphine and placebo pellets. Similarly, the physical dependence was assessed by monitoring withdrawal signs following an injection of naloxone. A high degree of tolerance developed to the analgesic and hyperthermic effects of morphine. Similarly, a high degree of physical dependence also developed as evidenced by a high incidence of jumping response, teeth chattering and production of fecal boli induced by injections of naloxone. In addition, loss of body weight and body temperature also occurred. The analgesic and hyperthermic response to morphine recovered very gradually. There was no significant difference in the analgesic and hyperthermic responses to morphine on day 4 after the pellet removal in rats implanted with morphine and placebo pellets. The decay of tolerance was linear with time for the analgesic effect (r = 0.98) and for the hyperthermic effect (r = 0.93). The change in symptoms of physical dependence on morphine with time depended on the specific symptom monitored. The average number of jumps and teeth chattering decreased with time in a linear fashion with r values of 0.98 and 0.99, respectively. However, the number of fecal boli and wet dog shakes increased linearly with time (r = 0.97). The recovery of loss of body weight was also linear with time. Thus, it is clear that fecal boli and wet dog shakes, which increase in number as the dependence decays, are signs of a low degree of dependence. The results suggest that different central or peripheral mechanisms may be operating in different withdrawal symptoms. These studies may prove to be useful when studying the mechanisms involved in the induction and reversibility of tolerance and dependence processes, and in long-term effects of opiates at a time when the tolerance and physical dependence is no longer evident.

Acute morphine dependence in the hamster

Two experiments investigated naloxone-precipitated withdrawal following a brief course of morphine administration in hamsters. In Experiment 1, observable withdrawal symptoms (e.g., wet-dog shakes) were elicited by two doses of naloxone (0.4 and 1.0 mg/kg) following four and eight daily injections of morphine (15 mg/kg), a regimen that replicated previous studies in our laboratory using a locomotor activity paradigm. At the lower dose of naloxone, the frequency of withdrawal signs was greater after eight than after four morphine injections. In Experiment 2, observable withdrawal symptoms were elicited by the same two doses of naloxone, 70 min after a single morphine injection. These results suggest that acute dependence in the hamster, as in other species, beings to develop with the first morphine exposure.

Effect of perinatal lead exposure on morphine tolerance in the neonatal rat

Administration of lead (at 300 and 1000 ppm) in the maternal drinking water from conception to postnatal day 10 increased the sensitivity of 10-day rat pups to noxious stimuli and disrupted the dose-response relationship to morphine antinociception. Lead-exposed rats could be made tolerant to morphine over a 5-day period (twice daily injections of 5 mg/kg morphine, postnatal days 5-10) and antinociceptive responses in tolerant rats were also disrupted by lead exposure.

[The similarity of the pathogenetic mechanisms of alcoholism and drug dependence and the means of searching for agents for treating these diseases]

The concept of the principal unity of the pivotal mechanisms underlying the formation of the syndrome of dependence on alcohol and various narcotic agents is presented. The central link of the mechanisms is the totality of the specific disturbances of neurochemical processes among which of particular importance are the specific changes in the functional state of catecholamine system. The theoretical approaches to the development of medicinal agents for treating alcoholism and drug addictions are considered. As an example there are discussed the results of using small doses of dopamine receptor stimulants (apomorphine and bromocriptine) and a neuropeptide cholecystokinin.

Evidence of single dose opioid dependence in 12- to 14-day-old chicken embryos

We have previously reported that chicken embryos injected with a single dose of methadone (Meth) on day 3, 7 or 11 of embryogenesis fail to show dependence on day 14, measured as a significant overshoot in motility above baseline after challenge with the opioid antagonist naloxone (Nx). Constant infusion of Meth from day 7 to 14 also failed to produce evidence of dependence on day 14. To address the question of whether the 14-day-old embryo is capable of expressing withdrawal, isobutylmethylxanthine (IBMX), a compound that produces quasi-opioid withdrawal, was injected directly into the embryo, resulting in a significant increase in motility. To determine whether the 14-day-old embryo could also express true opioid withdrawal, the embryos were injected with various doses of Meth or morphine (Morph), followed at different time intervals by injections of varying doses of Nx. A high dose of Morph followed 24 hours later by a low dose of Nx produced evidence of withdrawal, as did a low dose of Meth followed 1 hour later by a higher dose of Nx, U50488H, a selective kappa agonist, had no effect on motility in the 14-day-old embryo, suggesting that the decrease in motility seen after Meth was not mediated by a kappa receptor. Pretreatment with the irreversible mu antagonist, beta-funaltrexamine (B-FNA), blocked the decrease in motility seen after Meth and also prevented the overshoot in motility when Nx was given 1 hour post-Meth. We were also able to demonstrate dependence/withdrawal in the 12-day-old embryo, but higher doses of both Meth and Nx were required.(ABSTRACT TRUNCATED AT 250 WORDS)

[The functional role of the oxytocin-sensitive hippocampal system in organizing the mechanisms of morphine addiction]

The effect of oxytocin (OXT) administration into the brain ventricles on the process of narcotic dependence formation was studied before and following hippocampal lesion. OXT was found to inhibit the process of narcotic dependence formation. The hippocampal lesion weakened the inhibitory effect. A specific hippocampal involvement in the processes of narcotic reinforcement was suggested.

Procedures that produce context-specific tolerance to morphine in rats also produce context-specific withdrawal

Rats previously injected with morphine in the presence of a distinct environment (paired animals) were more tolerant to the analgesic effects of morphine in that environment than were rats previously injected with morphine in another environment (unpaired animals). When injected with saline instead of morphine in the distinct environment, paired animals were more reactive to pain (hyperalgesic) than unpaired animals, but no more reactive to pain than animals never given morphine. More important, the paired animals also exhibited more withdrawal symptoms (wet dog shakes, genital licking, circling, rearing, and defecation) during abstinence and naltrexone-precipitated withdrawal in the distinct environment than did the unpaired and saline animals. Thus, procedures that are capable of producing context-specific opiate tolerance are also capable of producing context-specific opiate withdrawal.

Production of physical dependence in rats by drinking a morphine solution

The plasma concentrations of morphine and glucose, the body weight, and the severity of the naloxone-precipitated withdrawal syndrome were studied in female rats in which morphine dependence was induced by administration of the opiate, with or without sucrose, in their drinking water. It was found that sucrose encouraged the animals to consume more morphine and that the initial plasma concentrations of the opiate, as well as the rate of development of physical dependence, were higher than the group not given sucrose. Plasma glucose concentrations, maximum plasma morphine levels and the maximum severity of the naloxone-precipitated withdrawal syndrome were, however, not significantly different between the two groups. The findings suggest that both regimens of administering the opiate in drinking fluid are effective in inducing morphine dependence in rats; the addition of sucrose tends to speed up the development of physical dependence, probably by increasing intake of the opiate through consuming more sucrose solution.