The mGlu5 receptor antagonists MPEP and MTEP attenuate behavioral signs of morphine withdrawal and morphine-withdrawal-induced activation of locus coeruleus neurons in rats

N-Methyl-D-aspartate (NMDA) antagonists have been demonstrated to suppress the signs of opiate withdrawal; however, side effects limit their clinical use. Since the metabotropic glutamate (mGlu) 5 receptor has been shown to affect glutamate release and modulate NMDA receptor function, we examined the effects of two selective mGlu5 receptor antagonists, 2-methyl-6-(phenyl-ethynyl)-pyridine (MPEP) and 3-[(2-methyl-1,3-thiazol-4-yl)ethynyl]pyridine (MTEP), on morphine withdrawal. Pretreatment with MPEP or MTEP (1, 3, and 10 mg/kg, i.p.) significantly attenuated behavioral signs of morphine withdrawal. Specifically, both MPEP and MTEP attenuated the occurrence/severity of chews, digging, salivation, and weight loss, and increased the occurrence of erections. Neither compound changed the occurrence of wet-dog shakes, ptosis, irritability, or lacrimation. Both MPEP and MTEP produced a modest, but significant, attenuation of morphine-withdrawal-induced activation of locus coeruleus neurons in anesthetized rats. These results indicate a role for mGlu5 receptors in morphine withdrawal and suggest the potential for mGlu5 antagonists in the treatment of withdrawal from opiates and other drugs of abuse.     

Correlation between brain nitric oxide synthase activity and opiate withdrawal

The opiate withdrawal induced by administration of naloxone to morphine-dependent mice correlates with an increment of calcium- dependent nitric oxide synthase (NOS) activity in the cerebellum. L-NAME, an irreversible competitive inhibitor of NOS (0.5, 5, 25, 50 mg/kg) injected sc. 45 min. prior to naloxone significantly reduced the number of escape jumps and other motor symptoms of abstinence. In addition, L-NAME also decreased NOS activity in cerebellum. L-arginine, but not D-arginine, when coadministered with L-NAME, prevented both the inhibition of NOS activity and the reduction of withdrawal symptoms induced by L-NAME in morphine-withdrawn animals. These results demonstrate a hyperactivity of the L-arginine: NO pathway in opiate withdrawal and suggests the possibility of a therapeutic use of NOS inhibitors in this state.Abbreviations EAA Excitatory amino acid - LC Locus coeruleus - L-NAME N-nitro L-arginine methyl ester - NMDA N-methyl-D-aspartate - NO Nitric oxide - NOS Nitric oxide synthase     

Modification of quasi-morphine withdrawal with serotonin agonists and antagonists: evidence for a role of serotonin in the expression of opiate withdrawal

Methylxanthines produce a quasi-morphine withdrawal syndrome (QMWS) in opiate naive rats. Additionally, methylxanthine-induced suppression of conditioned behavior in rats is reversed by the alpha₂ adrenergic agonist clonidine which also attenuates true opiate withdrawal and the QMWS. Therefore, the operant behavioral effect of 3-isobutyl-1-methylxanthine (IBMX) provide a model with which to study mechanisms involved in the expression of opiate withdrawal. In order to examine the role of serotonin (5-HT) in the rate-decreasing effects of IMBX on operant behavior, the 5-HT precursor 5-hydroxytryptophan, and 5-HT reuptake blocker fluoxetine were administered in combination with IBMX to rats performing a, fixed-ratio 30 operant for food reinforcement. Both drugs failed to reverse the behavioral suppression caused by relatively low doses of IBMX, suggesting that elevated 5-HT neurotransmission contributes to, rather than attenuates, the QMWS. The relatively selective 5-HT₂ antagonists mianserin and pirenperone blocked the IBMX-induced suppression, whereas the classic 5-HT antagonist methysergide had no effect. The results indicate that the operant behavioral effects of IBMX and possibly the QMWS may be mediated by serotonergic mechanisms.     

A preliminary description of acute physical dependence on morphine in the vervet monkey

Previous animal studies have suggested the rapid development of opiate dependency in 24 hours or less. However, the development of dependence on opioids within twenty-four hours has yet to be demonstrated in previously opiate-free human or nonhuman primate subjects. Following naloxone administration, cable-restrained monkeys which received intravenous morphine hourly for only six hours exhibited a behavioral syndrome characteristic of opioid withdrawal in this particular species. These data indicate that acute physical dependence on morphine may be induced after six hours in a primate species.     

The opiate quasiwithdrawal syndrome in rhesus monkeys: Comparison of naloxone-precipitated withdrawal to effects of cholinergic agents

The effects of the cholinergic agents UM-1046 (3-cyclopropyl-methyl-1,2,3,4,5,6-hexahydro-8-hydroxy-6-methyl-3-benzazocine hydrochloride) and physostigmine in normal rhesus monkeys were compared to naloxone-precipitated withdrawal in morphine-dependent subjects. The two cholinergic drugs produced effects that resembled one another, as well as some of the effects of naloxone in morphine-dependent subjects. The constellation of signs produced by the cholinergic drugs, while overlapping, was not identical to that produced by naloxone in opiate-dependent subjects. Although cholinergic agents produce many of the signs of opiate withdrawal, the withdrawal syndrome in its complete manifestation involves many different neurotransmitter systems.     

Effect of dopamine agonists and antagonists on the lorazepam withdrawal syndrome in rats

1. The effects of dopaminergic agonists and antagonists were investigated on withdrawal signs in lorazepam-dependent rats. Physical dependence was developed by giving lorazepam admixed with food in the following dose schedules: 10 x 4, 20 x 4, 40 x 4, 80 x 4 and 120 x 7 mg/kg, daily for x days. 2. The parameters observed during the periods of administration of lorazepam and after its withdrawal were spontaneous locomotor activity (SLA), reaction time to pain, foot shock aggression (FSA) and audiogenic seizures. 3. During the withdrawal period, rats were divided into groups of 10 rats each. One group did not receive any drug and served as the control withdrawal groups. Three other groups received, separately, one of the following dopamimetic drugs: (i) 200 mg/kg per day, i.m., L-dihydroxyphenylalanine (DOPA; +50 mg/kg per day, i.m., carbidopa); (ii) 2 mg/kg per day, i.m., amphetamine; or (iii) 1 mg/kg per day, i.m., apomorphine. The remaining groups received one of the following dopamine antagonists: (i) 0.1 mg/kg per day, i.m., SCH 23390; (ii) 0.5 mg/kg per day, i.m., haloperidol; (iii) 0.5 mg/kg per day, i.m., centbutindol; and (iv) either 1 or 20 mg/kg per day, i.m., clozapine. 4. The withdrawal signs observed in the control group were hyperkinesia, hyperaggression and audiogenic seizures. 5. L-Dihydroxyphenylalanine (+ carbidopa), amphetamine and apomorphine potentiated hyperaggression and audiogenic seizures. The dopamine D2 receptor antagonists haloperidol, centbutindol and clozapine (at 20 mg/kg, i.m.) blocked all withdrawal signs. The D1 receptor antagonist SCH 23390 inhibited hyperkinesia and hyperaggression. The D4 receptor antagonist clozapine (at 1 mg/kg, i.m.) had no effect on any of the withdrawal signs. 6. It may be concluded that dopamine D2 receptors exert a dominant facilitatory influence, with partial contribution of D1 receptors, on the benzodiazepine withdrawal syndrome.     

Attenuating effect of adenosine receptor agonists on the development of behavioral sensitization induced by sporadic treatment with morphine

The aim of the study is to investigate the effect of adenosine receptor agonists on the development of morphine-induced sensitization to the locomotor activity of mice. Selective A1 (N⁶-cyclopentyladenosine - CPA) and A2A (2-p-(2-carboxyethyl) phenethylamino-5'-N-ethylcarboxamidoadenosine hydrochloride - CGS 21680) adenosine receptor agonists or non-selective A1/A2A (5'-N-ethylcarboxamidoadenosine - NECA) adenosine agonists as representatives of adenosinergic drugs have been used in the experiment. Behavioral sensitization has been obtained by sporadic treatment with morphine (10.0 mg/kg, i.p.). We have shown that adenosine receptor agonists co-administered with morphine significantly attenuates increase in the locomotor activity of mice evoked by challenge dose of morphine. These effects have been observed after stimulation of the selective A1 or A2A and non-selective A1/A2A adenosine receptors, namely both receptors were involved in morphine-induced sensitization. Thus, we have demonstrated that adenosine agonists are able to inhibit behavioral sensitization induced by sporadic applications of morphine.     

Antagonism of morphine-induced behavioral suppression by opiate receptor alkylators

Experiments were conducted to test the in vivo opiate specificity and long-lasting effects of two non-equilibrium opiate antagonists: β-chlornaltrexamine (β-CNA) and the β-fumarate methyl ester derivative of naltrexone (β-FNA). β-CNA (2.5 or 5.0 μg, ICV) partially antagonized suppression of conditioned autoshaped behavior by morphine, when morphine was administered 48–72 hr after β-CNA. β-CNA had no effect on amphetamine-induced suppression of autoshaped responding, nor did it antagonized the suppression in rearing activity induced by either morphine or amphetamine. Similarly, β-FNA (5 mg/kg, IP) antagonized the suppression of conditioned behavior by morphine, for up to 48 hr, while having no effect on amphetamine-induced suppression of autoshaped responding, or on the suppression of rearing activity induced by morphine or amphetamine. Further peripherally administered β-FNA acts in the brain, since it antagonized analgesia following ICV morphine administration.     

Purinergic drugs and calcium channel antagonists attenuate the withdrawal syndrome from barbital

The effects of some adenosine agonists and calcium channel antagonists on the induction of tolerance to and dependence on barbital in mice have been studied. The concurrent administration of barbital and one of the following adenosine agonists, D- or L-phenylisopropyl adenosine, cyclopentyl adenosine and chloroadenosine, or the adenosine antagonists theophylline or 8-phenyltheophylline did not change the intensities of tolerance to and dependence on the barbiturate. N-ethylcarboxamide adenosine administered during the period of chronic administration of barbital significantly reduced the withdrawal syndrome. The administration of the calcium channel antagonists diltiazem, verapamil or nifedipine was also ineffective in altering the processes of tolerance and physical dependence when given concomitantly with barbital. Abstinence behavior was significantly reduced when mice were treated during the first 48 h of withdrawal from the barbiturate with either L-phenylisopropyl adenosine, N-ethylcarboxamide adenosine, nifedipine or verapamil. These results are discussed in relation to the attenuation of tolerance to and dependence on benzodiazepines induced by similar treatments.     

Increased food and water intake produced in rats by opiate receptor agonists

It has been suggested that endogenous opiate mechanisms may be involved in the physiological control of food and water intake. Support for this hypothesis has been obtained from studies of the effects of narcotic antagonists which reduce feeding and drinking, but it is also necessary to show that food and water intake can be facilitated by opiate agonists. In the present study the food intake of freely-feeding rats was increased by subcutaneous injections of morphine, a stabilised enkephalin analogue (RX 783030), and ethylketocyclazocine. Water intake was also increased but this effect was more variable than the increased eating. The increased food intake produced by the putative mu receptor agonists morphine and RX 783030 was blocked by a dose of naloxone which did not affect the facilitation of eating produced by ethylketocyclazocine, which may act at a separate population of receptors known as kappa receptors. These data are consistent with the possibility that opiate receptors are involved in the control of feeding and drinking.     

Interactive role of adenosine and dopamine in the opiate withdrawal syndrome

Adenosine reduces opioid withdrawal symptoms by activating A₁ adenosine receptors, probably by inhibiting excitatory amino acid release. Since blockade of A_2A adenosine receptors seems to enhance dopaminergic striatopallidal transmission, we evaluated the role of the purinergic system in the opiate withdrawal syndrome by using two A₁ receptor agonists [N⁶-cyclohexyladenosine, CHA and 2-chloro-N⁶-cyclopentyladenosine, CCPA], and two A_2A receptor antagonists (SCH 58261 and 8-(3-chlorostyryl)caffeine, CSC).Male adult rats received increasing doses of morphine sulphate suspended in 5 ml/kg of a sustained release preparation (40–100 mg/kg s.c.) daily for 4 days and 20 h after the last administration, the withdrawal syndrome was evoked by naloxone (5 mg/kg i.p.). Animals were observed for 30 min for signs of opiate withdrawal. Other groups of rats were implanted with concentric probes for microdialysis and dopamine levels were measured in the nucleus accumbens. CHA and CCPA (0.05, 0.1 or 0.5 mg/kg i.p.) significantly reduced "wet-dog" shakes, diarrhoea, teeth chattering, jumping and writhing. SCH 58261 and CSC (0.1, 0.5 or 1 mg/kg i.p.), given 10 min before naloxone, also reduced signs of opiate withdrawal. CHA plus SCH 58261 and CCPA plus CSC greatly enhanced the reduction of withdrawal signs observed with CHA and CCPA or CSC and SCH 58261 alone. In vivo microdialysis showed that naloxone significantly decreased DA release; this effect was prevented by pretreatment with systemic SCH 58261 and CSC, but not with CHA and CCPA. Our results demonstrate that A₁ and A_2A adenosine receptors mediate the effect induced by adenosine in opiate withdrawal syndrome and suggest that adenosine A₁ agonists and adenosine A_2A antagonists may be beneficial in the treatment of this syndrome.L. Stella and V. de Novellis share first authorship     

Modulation of Fas receptor proteins and dynamin during opiate addiction and induction of opiate withdrawal in rat brain

The Fas receptor is involved in the regulation of apoptosis but also can function as a non-apoptotic signal transducer. This study was mainly designed to quantitate Fas proteins in rat brain during heroin addiction and opiate withdrawal. In rat, mouse and human brains, and in SH-SY5Y cells, similar forms of Fas were immunodetected with different antibodies (i.e., 35 kDa native Fas and 48- and 51-kDa glycosylated Fas). Acute (2 h) treatments with the -opioid receptor agonists heroin (10 mg/kg) and morphine (30 mg/kg) increased the immunodensity of native Fas (124% and 36%) but not that of glycosylated Fas in the cerebral cortex. Chronic (5 days) heroin (5–30 mg/kg) and morphine (10–100 mg/kg) were also associated with increased native Fas (76% and 45%) and with different expressions of glycosylated Fas. In heroin-dependent rats, opiate withdrawal (48 h) resulted in a sustained increase in native Fas (107%) and in up-regulation of 51 kDa glycosylated Fas (51%). Acute treatments with selective -receptor (SNC-80, 10 mg/kg) or -receptor (U 50488-H, 10 mg/kg) agonists did not alter the content of native or glycosylated Fas. Chronic pentazocine (10–80 mg/kg, 5 days), a mixed opiate drug and ₁ receptor agonist, decreased native (48%) and glycosylated (38–82%) Fas proteins. Similarly, the selective ₁ agonist (+)-SKF 10047 also decreased native Fas (37%) and the effect was blocked by the ₁ antagonist BD 1063. Brain dynamin was up-regulated by acute and/or chronic heroin (30–39%), morphine (47–85%), pentazocine (51%) and heroin withdrawal (74%). The main results indicate that chronic heroin/morphine treatment and heroin withdrawal are associated with up-regulation of 35 kDa native Fas (and with different expressions of glycosylated Fas), and also with concomitant increases of dynamin in rat brain.     

Opiate dependence following acute injections of morphine and naloxone: The assessment of various withdrawal signs

The injection of high dose of naloxone 15 minutes after a single injection of morphine in mice was found to produce a jumping response which was behaviorly similar to the jumping response observed during the withdrawal from chronic morphine administration. In addition the jumping response following the acute administration of morphine-naloxone was increased by the injection of atropine and attenuated by oxotremorine. These data are consistent with the reports of effect of these cholinergic drugs on the jumping response which occurred during withdrawal after chronic morphine administration. However, other symptoms associated with opiate withdrawal (hypothermia, weight loss and diarrhea) were not produced by the acute injection of morphine-naloxone. It is therefore suggested that this single injection paradigm is particular to the jumping response than a demonstration of the rapid development of opiate dependence.     

The opiate receptor binding interactions of 3H-methionine enkephalin, an opioid peptide.

3H-Methionine enkephalin binds stereospecifically with high affinity to opiate receptors in rat brain membranes. Equilibrium experiments indicate two distinct dissociation constants with KD values of 1.8 and 5.8 nM respectively. 3H-Methionine enkephalin associates and dissociates from the opiate receptor with 8--10 fold slower kinetics than 3H-opiates. Though several opiates have similar affinities for sites labeled by 3H-methionine enkephalin, 3H-dihydromorphine and 3H-naloxone, some opiates such as morphine, dihydromorphine and oxymorphone are only one tenth as potent in competing for 3H-methionine enkephalin as for 3H-dihydromorphine and 3H-naloxone binding. As with other opiate agonists, 5--10 mM sodium selectively decreases the binding of 3H-methionine enkephalin. At 26 degrees C, 0.1--1.0 mM manganese but not magnesium or calcium increases the binding of 3H-methionine enkephalin, while at 0 degrees C manganese decreases the binding of methionine enkephalin.     

Cardiovascular changes during morphine withdrawal in the rat: Effects of clonidine

Arterial blood pressure and heart rate were measured in unrestrained rats as an index of the autonomic component of the morphine withdrawal syndrome. Physical dependence was produced by a constant infusion of morphine at increasing doses over 7 days. Signs of physical dependence observed during abrupt withdrawal included classical behavioral symptoms such as withdrawal body shakes (WBS) and increased autonomic responsiveness which was indicated by a sustained increase in mean arterial pressure (MAP) up to 23 mmHg. Injection of naloxone in morphine dependent rats also evoked a dose-related increase in MAP to about 40 mmHg. The antiwithdrawal effects of clonidine were tested in this model pretreating dependent rats with this agent (6–60 μg/kg). Clonidine inhibited the pressor response produced by naloxone by 23–60%. These findings indicate that the increase in MAP during opiate withdrawal provides an objective and quantitative index of the intensity of the narcotic withdrawal syndrome in dependent rats.     

Agonist--antagonist properties of phenoxybenzamine in antinociception and opiate dependence tests

The doe—response curve for phenoxybenzamine inhibition of stereospecific ³H-naloxone binding in brain homogenates was found to shift to the right in the presence of 100 mM NaCl. From the ratios of the IC₅₀ in the presence of Na⁺ to the IC₅₀ in the presence of Na⁺ calculated in this study for phenoxybenzine and some opiates it was predicted that phenoxybenzamine would have mixed agonist—antagonist properties in antinociceoption and that its antagonist activity would be in the rank order: butorphanol (1.8) ? phenoxybenzamine (4.3) > M2230 (5.7) > pentazocine (6.9) ? levorphanol (13.6). Phenoxybenzamine antagonized the oxymorphone-induced Straub tail reaction in mice and induced the abstinence syndrome in non-withdrawn morpine-dependent mice as predicted by the Na⁺ response ratio. In the mouse tail flick assay phenoxybenzamine acted like the mized agonist—antagonist benzomorphinas as predicted. In “physical dependence capabilty” phenoxybenzamine was intermediate between butorphanol and pentazocine as predicted by the Na⁺ response ratios. The success of the Na⁺ response ratio derived from phenoxybenzamine's properties in the vitro opiate binding assay in predicting the behavior and rank order of phenoxybenzamine in in vivo tests, plus the ability of naloxone to antagonize phenoxybenzamine's antinociceptive action suggest that phenoxybenzamine's antinociceptive action may be mediated by the brain opiate receptor rather than by central α-adrenergic receptor blockade.     

NMDA receptor antagonists inhibit opiate antinociceptive tolerance and locomotor sensitization in rats

Rationale N-Methyl-d-aspartate (NMDA) receptors have an important role in different forms of behavioral and neural plasticity. Evidence suggests that these receptors may also be involved in plasticity arising from long-term treatment with different drugs of abuse, including tolerance, sensitization, and physical dependence. There is abundant evidence demonstrating that NMDA receptors are involved in tolerance to opiate-induced antinociception; however, the role of these receptors in sensitization to the locomotor effects of opiates is more controversial. Objective The ability of NMDA receptor antagonists to modify the development of sensitization to the locomotor stimulant effect of three different opiates was examined. In selected studies, the ability of the antagonists to modify tolerance to the antinociceptive effects of the opiates was also examined. Materials and methods Adult male Sprague–Dawley rats were used to assess the effects of NMDA receptor antagonists (MK-801, memantine or LY235959) on tolerance and sensitization to three opiates: morphine, methadone, or buprenorphine. It was predicted that low, selective doses of the antagonists would inhibit the development of opiate tolerance and sensitization. Results Consistent with our predictions, the noncompetitive NMDA receptor antagonists MK-801 and memantine and the competitive NMDA receptor antagonist LY235959 inhibited the development of sensitization to the locomotor stimulant effect of morphine. Additionally, MK-801 inhibited the development of tolerance and sensitization to methadone and buprenorphine in a similar manner. Conclusions The results, together with previous research, suggest that NMDA receptors are broadly involved in opiate-induced plasticity, including the development of opiate tolerance and sensitization.     

Randomised double-blind comparison of lofexidine and clonidine in the out-patient treatment of opiate withdrawal

This study compares the clinical response to lofexidine and clonidine in the out-patient treatment of opiate withdrawal in 50 opiate addicts, using a randomised double-blind study design. Patients were taking 40 mg or less methadone daily, or equivalent amounts of other opiates. Fifty-eight percent of those starting treatment completed detoxification, and were opiate free at 4 weeks: more patients completed withdrawal in the lofexidine group, but the difference was not significant. Clonidine produced more hypotensive effects: more home visits were also required by medical staff. There was no other significant difference in side effects. Both drugs can be used successfully in out-patient detoxification, but lofexidine is more economical in regard to staff time.