Differential effects of opiate agonists-antagonists on morphine-induced hyperexcitability and analgesia in mice

The effects of two opiate agonists-antagonists, butorphanol (4.0 and 8.0 mg/kg) and buprenorphine (0.1 and 1.0 mg/kg), were assessed on locomotor activity and analgesia in DBA/2 and C57BL/6 mice. Diferrent behavioral effects were evident in these strains, which might becharacterized by different reactions to the effects of opiates and by differences in endorphin distributions and opiate receptor populations. In particular, buprenorphine acted as an agonist-antagonist to morphine in both strains while a dissociation of buturphanol effects was evident, depending on the strain considered. The clinical implications of these findings are discussed.     

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prevented both the inhibition of NOS activity and the reduction of withdrawal symptoms induced by L-NAME in morphine-withdrawn animals.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     

Changes induced by sodium cromoglycate on brain serotonin turnover in morphine dependent and abstinent mice

This study was designed to explain the action of sodium cromoglycate (CRO) on the brain serotonergic system in control, morphine tolerant (by SC implantation of a 75 mg morphine pellet), and also in morphine dependent mice just before naloxone-precipitated withdrawal. After SC injections of CRO in control mice, morphine tolerant mice (day 4 of addiction), and 1 h before abstinence (withdrawal was induced by SC injection of 1 mg/kg naloxone on day 4 of addiction), animals were decapitated and various brain areas were rapidly removed. 5HT (Serotonin) and 5HIAA (5-hydroxyindole-3-acetic acid) were measured by high performance liquid chromatography coupled with electrochemical detection (HPLC-ECD). The ratio 5HIAA/5HT provided one index by which the turnover of the indoleamine was measured. CRO increased the turnover of 5HT in most of the brain areas studied in both control and morphine dependent mice. Furthermore, previous administration of CRO prior to naloxone challenge induced a significant increase in the 5HIAA/5HT ratio in the hypothalamus and striatum. These results are discussed as the reason for the preventive effect of CRO on jumping behaviour in morphine abstinent mice.     

Comparison of a lactose-free formulation of sodium cromoglycate and sodium cromoglycate plus lactose in the treatment of asthma

Summary

A double-blind, parallel group, 7-centre trial was carried out to compare the clinical efficacy and patient acceptability of two formulations of sodium cromoglycate for inhalation in patients suffering from asthma. Each single-dose capsule for use in a breath-actuated inhaler contained either a blend of sodium cromoglycate (20?mg) plus lactose (20?mg) or a lactose-free pelletized formulation of sodium cromoglycate (20?mg). Data were summarized from 529 asthmatic patients who had been using the blend formulation for at least 3 months previously. Two hundred and sixty-five patients then received pelletized sodium cromoglycate and 264 patients remained on sodium cromoglycate plus lactose for at least 3 months. Regular assessments were made by patients and clinicians during the trial period of treatment effectiveness. No clinically significant differences were observed between the two formulations after 3 months on test treatment. After a treatment period of 6 months, the pelletized formulation was shown to have some advantages over the blend formulation which were not observed at 3 months, with a significantly higher proportion of ‘very effective’ assessments being recorded by both patients and clinicians. The capsules of pelletized sodium cromoglycate required significantly less inhalations to empty compared to the capsules of the blend. No differences were observed between the two formulations with regard to the incidence of transient cough and throat irritation after inhalation.     

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.     

Changes induced by sodium cromoglycate in brain catecholamine turnover in morphine dependent and abstinent mice

The effects of sodium cromoglycate (CRO) were studied in relation to the metabolism of brain catecholamines: dopamine (DA) and noradrenaline (NA), and their metabolites 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 4-hydroxy-3-methoxyphenylethyleneglycol (MHPG). CRO was injected SC in control mice, morphine-tolerant mice (tolerance was induced by SC implantation of a 75 mg morphine pellet; CRO was administered on day 4 of addiction) and 30 min before abstinence (withdrawal was induced by SC injection of naloxone (1 mg/kg) on day 4 of addiction). Brain catecholamines and their metabolites were measured using high performance liquid chromatography coupled with electrochemical detection (HPLC-ECD), for DA, NA, DOPAC and HVA, and coupled with fluorescence detection for MHPG. The ratios of DOPAC + HVA/DA and MHPG/NA were kept as an index of DA and NA turnovers, respectively. CRO administered 30 min before naloxone-precipitated withdrawal diminished significantly NA levels in frontal cortex. CRO increased DA turnover in striatum and frontal cortex in naive animals and significantly diminished DA levels in frontal cortex and DOPAC levels in frontal cortex and midbrain in morphine-dependent mice. These findings are discussed in relation to the protective effects of CRO on opiate withdrawal and the effects of CRO on locomotor activity.This work was supported by a grant from the Fondo de Investigaciones Sanitarias de la Seguridad Social (FIS, programme no. 0166/93).     

Peristalsis in the isolated guinea-pig ileum during opiate withdrawal

Summary Naloxone enhances peristalsis in isolated intestinal segments from morphine-dependent guinea-pigs to a greater degree than in naive preparations. These data suggest that a peripheral mechanism may be involved in the expression of opiate withdrawal in the small intestine, and indicate that the action of this mechanism leads, at least in vitro, to an increase in the number of peristaltic waves.     

Effects of dynorphin A(1–13) on opiate withdrawal in humans

The objectives of the current study were to determine 1) the effects of various doses of dynorphin A (1–13) on opiate withdrawal in humans and 2) the safety of dynorphin at these doses. Opiate dependent subjects who had been stabilized on morphine received a single IV dose of placebo, 150, 500 or 1000μg/kg dynorphin after exhibiting spontaneous withdrawal using a randomized, double-blinded, between-subjects study design. Observer Withdrawal Scores were lower in the 150 and 1000μg/kg groups as compared to placebo (P<0.05) but no significant differences were observed on the observer-rated Wang or Sickness Scales. Significant decreases were also found for self-reported symptoms of nervousness, runny nose, sneezing, and painful joints in the 500μg/kg group. Significant increases in serum prolactin levels were seen after all dynorphin doses; however, these were not dose-related. Dynorphin A (1–13) was well tolerated and safe, with no changes in physiologic parameters. We conclude that dynorphin A (1–13) has a modest effect in reducing mild opiate withdrawal in humans and is well tolerated at doses up to 1000μg/kg. Received: 24 March 1997/Final version: 22 November 1997     

Gossypin-induced analgesia in mice

A flavonoid, gossypin, was evaluated for its analgesic action by using acetic acid-induced writhing in mice and was compared with morphine. Gossypin inhibited writhing in a dose-dependent manner. This action was antagonised by naloxone. The pA2 values for morphine-naloxone and gossypin-naloxone were almost identical suggesting a definite involvement of opiate receptors in the analgesic action of gossypin.     

Interaction between ACTH fragments, brain opiate receptors and morphine-induced analgesia.

The present study confirms that N-terminal fragments of ACTH have an affinity for rat brain opiate receptors in vitro. Such peptides, devoid of corticotrophic activity, were found to inhibit morphine-induced analgesia if they also possessed affinity for opiate receptors in vitro. The structure-activity relationship for these two parameters is comparable to that observed for the same peptides on the induction of excessive grooming.     

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.     

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.     

Comparison of 1 mg and 5 mg sodium cromoglycate metered dose inhalers in the treatment of asthma: A 12-week double-blind,parallel group trial

Summary

A double-blind, parallel group trial of a 1?mg sodium cromoglycate metered dose inhaler, a 5?mg formulation and a placebo aerosol was undertaken in 139 asthmatic patients with extrinsic allergic asthma. None of the patients had previously been treated with sodium cromoglycate and few (15%)were familiar with the use of a pressurized aerosol device. Each test treatment was taken at a dose of 2 ‘puffs’ 4-times per day for a period of 12 weeks. Response to treatment was assessed by analysis of symptom scores, medication usage and 3-times daily home measurements of PEFR recorded on diary cards, and by assessment of asthma severity and lung function in the clinic at the beginning and end of a 2-week baseline period and at intervals of 3 weeks throughout the trial. Analysis of patient-generated data (symptom scores and PEFR)demonstrated statistically significant differences in favour of each active treatment compared with placebo treatment. Clinic assessments of asthma severity and the investigator's opinion of treatment also showed the superiority of each sodium cromoglycate treatment regimen over placebo. These differences were statistically significant after 9 weeks (high dose)and 12 weeks (both doses). No statistically significant differences were demonstrated between the two active treatment groups in the clinic assessments of asthma severity, or in the home or clinic measurements of PEFR. There was, however; a consistent trend in favour of the higher dose formulation with respect to diary card symptom scores. In general, improvement in the low-dose sodium cromoglycate treatment group was slower than in the high-dose group suggesting an advantage for the 5?mg sodium cromoglycate inhaler in terms of onset of therapeutic response. The results indicate that sodium cromoglycate administered by pressurized aerosol at a dose of 2×1?mg or 2×5?mg 4-times daily is effective in the treatment of asthma and suggest that the higher dose formulation may provide more rapid control of symptoms.     

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.     

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.     

Morphine withdrawal in mice selectively bred for differential sensitivity to ethanol

Mice which have been selectively bred for differences in sensitivity to acute doses of alcohol have also been shown to differ in severity of seizures upon withdrawal from chronic alcohol administration. We investigated the responsiveness of these mice to withdrawal from chronic morphine treatment. Mice were made dependent on morphine via pellet implantation, and withdrawal was precipitated with naloxone challenge. Mice which are less sensitive to the hypnotic effects of ethanol (short sleep: SS) displayed more jumping and wet dog shakes during withdrawal than did the more senstive long sleep (LS) mice. In addition, the amount of jumping was dependent on the dose of naloxone in both lines. Differences between lines in naloxone precipitated withdrawal may reflect differences in alterations in extrapyramidal dopaminergic activity, but other substrates for the observed differences cannot be discounted. Finally, the observed difference between SS and LS mice in severity of morphine withdrawal parallels the previously reported difference between these lines in seizure severity during withdrawal from alcohol.     

Inhibition of morphine-induced analgesia and locomotor activity in strains of mice: a comparison of long-acting opiate antagonists

The long-acting opiate antagonistic potency of naloxazone (NXZ), beta-chlornaltrexamine (beta-CNA) and beta-funaltrexamine (beta-FNA) was compared using three inbred strains of mice, in which morphine induces either analgesia (DBA/2), locomotion (C57BL/6), or both responses (C3H/He). The antagonists were applied SC 24-120 hr before morphine (10 or 20 mg/kg, IP), followed by the tests after 30 min. The minimal dose which completely antagonized morphine-induced analgesia in DBA and locomotion in C57 mice during 24 hr were: for NXZ 50 and 100 mg/kg, for beta-CNA 0.8 and 6.2 mg/kg, for beta-FNA 1.6 and 12.5 mg/kg, respectively. beta-FNA and beta-CNA more potently blocked morphine-induced analgesia in DBA mice than the activity response in the C57 strain. In contrast, beta-FNA prevented morphine-induced locomotion at a lower dose (6.2 mg/kg) than analgesia (greater than 50 mg/kg) in C3H mice, while beta-CNA was equipotent (1.6 mg/kg). In general, beta-CNA turned out to be the most reactive compound, antagonizing morphine effects in low doses up to 120 hr. beta-FNA selectively antagonized either morphine-induced analgesia or locomotion, depending on the strain used. This suggests that a given morphine response might be caused by a genetically determined multiplicity of opiate receptor types and their mutual interactions.     

REM sleep deprivation decreases the grooming and shaking behaviour induced by enkephalinase inhibitor or opiate withdrawal

Intraventricular administration of enkephalinase inhibitor, phosphoramidon (1 X 10(-8)-5.6 X 10(-7) moles ICV) induced a behavioural syndrome consisting of excessive grooming with the body scratching as the most prominent symptom and wet-dog-shakes (WDS). The frequency of the phosphoramidon-induced WDS and body scratching were decreased by the pretreatment with the opiate receptor blocking agent, naltrexone (2.9 X 10(-6) moles/kg IP). Both the phosphoramidon-induced WDS in naive rats and naloxone-precipitated withdrawal WDS were decreased in REM sleep deprived rats compared with animals allowed normal sleep (control and stress groups). The results are discussed in light of a possible functional insufficiency of endorphinergic system during REMSD. It has been suggested that this insufficiency might be a background to the increased neuronal excitability during REMSD.     

Adenosine receptor agonists attenuate and adenosine receptor antagonists exacerbate opiate withdrawal signs

Previous studies have demonstrated a role for adenosine in mediating opiate effects. Adenosine receptors and their functions have been shown to be regulated by chronic opiate treatment. This study examines the role of adenosine receptors in the expression of opiate withdrawal behaviors. The effects of single doses of parenterally administered adenosine receptor subtype-selective agonists and antagonists on opiate withdrawal signs in morphine-dependent mice were measured. Mice received subcutaneous morphine pellet treatment for 72 h and then underwent naloxone-precipitated withdrawal after pretreatment with adenosinergic agents. Adenosine agonists attenuated different opiate withdrawal signs. The A₁ agonistR-N ⁶(phenylisopropyl)adenosine (0, 0.01, 0.02 mg/kg, IP) significantly reduced wet dog shakes and withdrawal diarrhea, while the A_2a-selective agonist 2-p-(2-carboxethyl) phenylethylamino-5'-N-ethylcarboxamidoadenosine or CGS 21680 (0, 0.01, 0.05 mg/kg, IP) significantly inhibited teeth chattering and forepaw treads. Adenosine receptor antagonists enhanced different opiate withdrawal signs. The adenosine A₁ antagonist 1,3-dipropyl-8-cyclopentylxanthine (0, 1, 10 mg/kg, IP) significantly increased weight loss and the A₂ antagonist, 3,7-dimethyl-1-propargylxanthine (0, 1 and 10 mg/kg, IP) enhanced wet dog shakes and withdrawal diarrhea. Treatment effects of adenosinergic agents were not due to nonspecific motor effects, as demonstrated by activity monitoring studies. These results support a role for adenosine receptors in the expression of opiate withdrawal and suggest the potential utility of adenosine agonists in its treatment.Abstracts were presented at meetings of the Fifth International Symposium on Adenosine and Adenine Nucleotides in Philadelphia, Pa, May 9–13, 1994 and Society for Neuroscience in Miami Beach, FLa., November 13–18, 1994