Morphine Abstinence Research Articles

Changes in sympathetic nerve activity during morphine abstinence in the rat.

The aim of the study was to examine sympathetic nerve activity, heart rate and blood pressure during naloxone-precipitated withdrawal reactions in morphine-dependent rats. In two groups of rats, one group conscious and the other anaesthetized with chloralose, renal sympathetic nerve activity (rSNA), heart rate (HR) and mean arterial blood pressure (MAP) were recorded before and during naloxone-precipitated abstinence. The conscious rats showed a biphasic pattern in the withdrawal responses. Initially, after small doses of naloxone, rSNA and HR increased and increased somatomotor activity including 'wet-dog' shakes were observed. However, upon further administration of naloxone, rSNA and HR promptly decreased while MAP increased. As rSNA was lowered, the withdrawal behaviour of the rats was markedly diminished and the animals rested calmly in the cages. In contrast, the anaesthetized group reacted with an immediate decrease in rSNA after the lowest dose of naloxone, followed by an increase in MAP and HR after higher doses of naloxone, although rSNA was still decreased. In both groups, rSNA remained below pre-naloxone control levels when the increased MAP was lowered to the pre-naloxone level with sodium nitroprusside, indicating a central origin of the sympathetic inhibition. It is concluded that naloxone elicits a biphasic rSNA response in the conscious, morphine-dependent rat. This includes an initial increase upon low naloxone doses followed by a pronounced inhibition of rSNA after higher doses. In chloralose-anaesthetized rats, rSNA declined already after low doses of naloxone. It is suggested that there might be a tonic, excitatory input on rSNA, mediated by the activation of opiate receptors by high levels of circulating morphine in the addicted animal. Naloxone will therefore decrease the tonic sympathetic nerve activity in these rats.

Effects of peripheral and central administration of calcium channel blocker in the naloxone-precipitated abstinence syndrome in morphine-dependent rats

The effects of two calcium channel blockers (verapamil and flunarizine) were evaluated on the naloxone-precipitated syndrome in morphine-dependent rats. The withdrawal signs in saline-treated rats were mainly diarrhea, body weight loss, jumping and ptosis. On i.p. administration, verapamil and flunarizine prevented diarrhea and body weight loss but not jumping. Verapamil also reduced the incidence of ptosis at the highest dose tested (40 mg/kg). Administered i.c.v., 160 μg verapamil reduced the body weight loss and the number of jumps without modifying diarrhea or ptosis. The results show that calcium channel blockers inhibit morphine abstinence syndrome manifestations through both peripheral and central mechanisms.

Cyclophosphamide and cortisol reduce the severity of morphine withdrawal

Cyclophosphamide and cortisol, two nonspecific immunomodulators, significantly reduced the behavioral indices of naloxone-precipitated withdrawal in morphine dependent rats. Each immunomodulator reduced the morphine abstinence syndrome when administered either prior to or after chronic morphine treatment. Morphine exerts numerous effects on all levels of the central nervous system with tolerance, physical dependence, and a withdrawal syndrome being characteristics of this drug class. It is suggested that the degree of opiate dependence is directly correlated with the intensity of the behavioral withdrawal signs. Therefore, success in modifying the abstinence syndrome may lead to a better understanding of the dynamics of opiate dependence. The results reported herein coupled with similar findings for alpha-interferon and cyclosporine, suggest that opiate dependence may involve the immune system.

Taurine inhibits wet-dog shakes and hippocampal seizures induced by opioid peptides in rats.

Wet dog shakes (WDS) are paroxysmal shudders of head, neck and trunk. This behavior has been observed when dipping animals into cold water (41), application of xylene to the für (39) and tactile stimulation around ears (1). Pharmacological studies revealed that WDS can be produced by administration of thyrotropin-releasing hormone (9,24,29,41,42), 5-Hydroxytryptamine (3,12), or kainic acid (5,25). WDS are also known as a classical sign of morphine abstinence in rats (40,43). In 1976, Bloom et al. first reported that this shaking behavior was elicited by acute administration of β-endorphln into the lateral ventricle in rats. Similar observations were made in rats with enkephalin (15). In addition, it was found that epileptic discharges were provoked by the intraventricular (icv) injection of opioid peptides and WDS always accompanied the onset of seizure discharges (15,16,37). These findings suggest that there may be an association between electrical seizure activities and WDS.KeywordsSeizure ActivityOpioid PeptideAminobutyric AcidIntraventricular InjectionSeizure DischargeThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Calcium channel inhibitors suppress the morphine-withdrawal syndrome in rats.

The effects of the Ca2+-channel blockers verapamil and nimodipine, on the behavioural signs of naloxone (1 mg kg-1)-induced abstinence syndrome in morphine-dependent rats, were evaluated. The content of noradrenaline (NA) and of its metabolite 3-methoxy-4-hydroxyphenylglycol (MHPG) was measured, using high performance liquid chromatography and electrochemical detection or gas chromatography-mass spectrometry, in various brain regions of these animals. Possible interactions of nimodipine and verapamil with opioid receptors were evaluated by examining their ability to displace [3H]-naloxone binding to brain membranes. Verapamil (5, 10 and 50 mg kg-1) and nimodipine (1, 5 and 10 mg kg-1) dose-dependently reduced most of the signs of morphine abstinence. Naloxone-precipitated abstinence decreased the NA content in the cortex, hippocampus, brainstem and cerebellum. In the same brain regions the content of MHPG increased, suggesting an increased release of the amine during morphine abstinence. Nimodipine (10 mg kg-1 i.v.) did not change the content of NA or MHPG in the cortex, hippocampus and brainstem. However, nimodipine pre-treatment markedly reduced the changes in NA and MHPG content induced by the abstinence syndrome. Neither verapamil nor nimodipine displaced [3H]-naloxone from its binding sites. These results suggest that Ca2+-channel blockers suppress the behavioural and neurochemical expressions of morphine abstinence by a mechanism that differs from those of opioids or alpha 2-adrenoceptor agonists.

Clonidine in Morphine Withdrawal

Reports of an antiwithdrawal effect for clonidine hydrochloride in acute opioid withdrawal are inconsonant with experimental findings that other nonopioids are ineffective. In the present investigation the antiwithdrawal effects of clonidine, morphine sulfate, and placebo were compared in volunteer addicts whose dependence was maintained by 15 mg of morphine sulfate given subcutaneously four times daily. Clonidine was effective but had a differential effect on the signs and symptoms of morphine abstinence. Compared with morphine, clonidine was more effective in suppressing autonomic signs of abstinence but less effective in reducing subject-reported symptoms and discomfort. It is concluded that the perception of the clinical usefulness of clonidine depends on whether objective measures or subjects' reports are treated.

Comparison of abstinence syndromes following chronic administration of mu and kappa opioid agonists in the rat

Abstinent states were compared following chronic administration of mu and kappa opioid agonists, morphine and ethylketocyclazocine, respectively. Rats were prepared with chronic EEG and EMG electrodes and indwelling IV cannulae. One group of rats was chronically administered IV morphine, while a second group received chronic injections of IV ethylketocyclazocine. Morphine abstinence was associated with suppression of REM sleep occurrences, increases in number of wet-dog shakes, and a decline in EEG spectral power during slow-wave sleep episodes. In contrast, the ethylketocyclazocine abstinence syndrome included minor abstinence signs. Differences in abstinent states between morphine and ethylketocyclazocine indicate the involvement of separate receptor populations in the process of dependence on morphine and ethylketocyclazocine.

Desensitization and coupled receptors: A model of drug dependence

It is assumed that certain drug receptors are so coupled with certain physiological receptors that stimulation of either receptor increases the sensitivity of the other. If the drug receptor suffers tolerance (i.e. slow desensitization) and if insensitivity of the drug receptor also makes the physiological receptor insensitive, then tolerance must be responsible for a physiological deficiency. This may be remedied by increased drug administration which will raise the sensitivity of the remaining physiological receptors so that a normal or near-normal physiological situation is achieved. Thus the organism is not only tolerant to the drug but also dependent on it. If such theoretical considerations apply to opiate receptors (as drug receptors) and to catecholamine receptors (as physiological receptors), then the theory predicts that acute morphine administration increases the sensitivity of dopamine receptors, that sympathetic stimulation decreases pain sensitivity, that opioid tolerance provokes increased catecholamine activity, that alpha-receptor stimulants attenuate and alpha-receptor antagonists exacerbate morphine abstinence, and that catecholaminergic inhibition results in increased morphine toxicity. All of these predictions have been verified experimentally.

β-Endorphin suppression of acute morphine abstinence in morphine dependent monkeys: Effective given intraventricularly but ineffective given intravenously

Six female adult Macaca mulatta monkeys were made dependent upon morphine sulfate and were implanted with a chronic indwelling needle in the lateral ventricle of the brain for sterile intraventricular injections. Both β-endorphin and morphine, in a dose dependent manner given intraventricularly suppressed the signs of 14 hour acute morphine abstinence. On a molar basis, β-endorphin was more active than morphine in suppressing the signs of morphine abstinence. When given intravenously in much larger doses, β-endorphin was ineffective in contrast to morphine which was effective in suppressing abstinence.

Morphine and clonidine oral self-administration: A study in morphine dependent or abstinent rats

1. The ability of morphine and of clonidine to support self-administration has been evaluated in morphine dependent or abstinent rats, using an orally reinforced operant technique (F.R. 20). 2. It was found that: — Morphine drinking can function as a reinforcer of an operant response both in dependent and abstinent rats. — The bitter taste of morphine becomes a secondary reinforcer for rats usually working for the alkaloid. — Clonidine supports oral self-administration in morphine abstinent, but not in morphine dependent rats. 3. The data are in line with clinical findings and give a further evidence that oral self administration in rats can be an useful model for the analysis of drug dependence.

Receptor-mediated stimulation of brain GTPase by opiates in normal and dependent rats

In membranes from rat brain striatum, opiate agonists stimulated low-K m GTPase. Half-maximal enhancement of enzyme activity was obtained with 0.09 μM morphine and 3.8 μM levorphanol. This order of potency corresponded to that of the affinities of these compounds in binding to opiate receptor. The effect was inhibited by the antagonist naloxone. As shown by the use of the enantiomers levorphanol and dextrorphan, only the pharmacologically active stereoisomer stimulated GTPase. In membranes isolated from morphine-dependent rats, the activity of GTPase was reduced 20–40% relative to that in control rats. After the precipitation of morphine abstinence by naloxone, brain GTPase activity was intermediate between the respective values for naive and dependent animals.

THE INFLUENCE OF SELECTIVE DOPAMINERGIC AND CHOLINERGIC AGONISTS AND ANTAGONISFS ON PRECIPITATED OPIATE ABSTINENCE

The effects of selective dopaminergic and cholinergic agonists and antagonists on morphine abstinence were assessed. Morphine dependence in rats was induced by the subcutaneous implantation of morphine pellets, and abstinence was precipitated using the benzomorphan antagonist Mr-1452. Withdrawal was assessed by scoring and counting behavioural signs; body weight and temperature changes were also measured. Atropine, sulpiride and clozapine attenuated certain withdrawal signs, whereas oxotremonne and the D-1 receptor agonist compound SKF-38393 intensified the overall abstinence syndrome. In addition, treatment with the D-2 receptor agonist compound LY-141865, although blocking the majority of signs, uncovered other dose-dependent behaviours, e.g. copulatory mounting, stereotyped circling and aggression. Compound LY-141865 also attenuated the cholinergic withdrawal signs in a similar way to atropine. These results support the concept of an acetylcholine-dopamine link during opiate abstinence.

Macromolecular changes in brain stem of morphinized rats

Incorporation of [3H]valine into trichloroacetic acid-(TCA)-precipitable, water-soluble or membrane-bound material of whole brain and brain-stem did not differ significantly in morphine-intoxicated, morphine abstinent and control rats. The animals were intoxicated with morphine (final dose 340 mg/kg b.w.) for 15 days, using an ingestion method with no impairment of the caloric intake compared to controls. Abstinent rats were withdrawn from morphine for 2 days after 13 days of intoxication. Measurements of [3H]valine or [14C]valine incorporated into soluble or membrane-bound brain stem proteins failed to demonstrate any significant changes in specific protein bands from morphinized rats. Separation was achieved by polyacrylamide gel electrophoresis with or without sodium-dodecyl sulphate (SDS) or by isoelectric focusing. After immunoabsorption chromatography to remove those proteins antigenically similar to serum proteins, an increase in the staining intensity and in incorporation of [3H]valine into two protein bands (with isoelectric points (Ip:s) 5.75 and 7.7) was seen in brain stem from long-term morphine-intoxicated rats. The results show that macromolecular interactions are involved in long-term morphine actions.

The role of central serotoninergic neurotransmission in the morphine abstinence syndrome in rats

It was found that 200 mg/kg of DL- p-chlorophenylalanine (PCPA) and 2 mg/kg of methergoline drugs inhibiting central serotoninergic transmission-decreased naloxone precipitated abstinence wet dog shakes in morphine-dependent rats. The inhibitory effect of PCPA was reversed by 200 mg/kg of 5-hydroxy-L-tryptophan (5-HTP) but not by the same amount of L-tryptophan (TP). 5-HTP alone (200 mg/kg) increased wet dog shakes epissodes, whereas TP alone in the same dosage practically did not have any influence on the wet dog shakes in morphine-dependent rats. These findings suggest that brain serotonin may play some role in the expression of wet dog shakes in morphine-dependent rats.

Alteration in the effect of GTP on cerebral β-adrenergic receptor binding during morphine withdrawal

The alteration in the effect of GTP on the binding of β-adrenergic agonists and antagonists in the rat cerebral cortex during morphine withdrawal was examined. Guanosine 5′-triphosphate (GTP), which is known to increase the coupling of β-receptors and adenylate cyclase, had no effect on the inhibition of cerebral [ 3H]dihydroalprenolol ([ 3H]DHA) binding by 1-isoproterenol (1-ISP) in animals rendered morphine-dependent. In morphine-abstinent rats, however, GTP increased the dissociation constant (K D) of the high affinity sites of 1-ISP for the inhibition of [ 3H]DHA binding as well as the number of high affinity binding sites for 1-ISP. These GTP-induced changes in the binding sites in morphine-abstinent animals were not observed for pindolol, a β-adrenergic antagonist, but could be reproduced with 5′-guanylimidodiphosphate, a GTP analogue. On the other hand, increasing the temperature for the assay induced a similar effect on 1-ISP binding sites in normal synaptic membranes. However, at the maximal point of the temperature-induced effect, the addition of GTP further increased the K D value of the high affinity binding site for 1-ISP in the cerebral cortex from morphine-abstinent animals. This suggests that the mechanisms underlying the alteration in the density and affinity of β-receptors following morphine abstinence may be different from the effects of temperature on cerebral β-adrenergic receptor sites. The present results suggest that in addition to the previously reported increase in β 1-receptors and activation of adenylate cyclase, the coupling between β-adrenergic receptor and adenylate cyclase in the brain may be facilitated during morphine withdrawal and that this change may also contribute to the occurrence of the morphine withdrawal syndrome.

Picrotoxin microinjections into the brain: A model of abrupt withdrawal ‘jumping’ behaviour in rats not exposed to any opiate?

Picrotoxin microinjections (0.5 μ1 per side) given into the locus coeruleus, superior colliculus and central grey of freely moving Wistar rats produced an accelerating galloping locomotion, most often forwards but also upwards. Systematic administration of apomorphine (0.7–2.0 mg/kg s.c.) given 20 min earlier increased the number of rats that displayed the so-called ‘running and jumping’ behaviour after picrotoxin (0.1–0.2 μg). The dose-effect curve, however, varied according to the brain structure selected. Systematic administration of morphine (1.0–10.0 mg/kg i.p.) was found to reduce the occurrence of running and jumping behaviour when it was elicited via the locus coeruleus might be a suitable model of partial morphine abstinence syndrome, i.e. withdrawal jumping, in experimental animals not exposed to any opiate. The superior colliculus and central grey appear to be involved in mediating an opiate-unrelated phenomenon on ‘withdrawalrs jumping in rats not exposed to any opiate.

Self-administration of dynorphin-[1–13] and D-ala 2-dynorphin-[1–11] (kappa opioid agonists) in morphine (mu opioid agonist)-dependent rats

Adult female Sprague-Dawley rats were prepared with permanent cortical EEG and temporalis EMG electrodes and i.v. cannulae. They were made tolerant to and physically dependent on morphine by automatic, hourly injections. These physically dependent rats were then trained to lever press for 10 mg/kg injections of morphine on a fixed ratio (FR) schedule of reinforcement. Upon stabilization of morphine self-administration at a FR-10, dynorphin-[1–13] (DYN) or D-ala 2-dynorphin-[1–11] (D-ala 2-DYN) at doses of 125 or 250 ug/kg/inj was substituted for morphine. Rats self-administered these opioid-like peptides at both dose levels. As expected, self-injections were more numerous at the lower dose. No signs of morphine withdrawal were seen during the peptide substitutions. Following DYN or D-ala 2-DYN abstinence, no withdrawal symptoms were noted. The question is raised as to whether DYN or D-ala 2-DYN and morphine are producing their reinforcing effects in sustaining self-administration via the same receptor populations. Since morphine abstinence is associated with severe withdrawal symptoms and the peptides studied are not, the involvement of separate receptor populations in the process of dependence on morphine and these opioid-like peptides is indicated. In conclusion, both a mu and two kappa agonists exhibited an analogous reinforcing property in the rat. However, the degree of physical dependence and the intensity of withdrawal differed; being higher with the mu agonist and lower with the kappa agonists.

Clonidine withdrawal: Activation of brain noradrenergic neurons with specifically reduced α2-receptor sensitivity

The firing rate of brain norepinephrine (NE) neurons in locus coeruleus (LC) was studied by means of single cell recording techniques in rats during, and after cessation of, chronic clonidine treatment (100–500 μg/kg/day, 14 days). In addition, the sensitivity of α 2- and oplate receptros, respectively, on the LC neurons was assessed utilizing microiontophoretic methodology. Whereas the average basal firing rate of LC neurons, randomly encountered throughout the nucleus was reduced during ongoing treatment, it was largely increased in a dose-related manner after discontinuation of treatment (maximum activation, 60 per cent above control base-line, obtained about 30 h after withdrawal). After chronic clonidine treatment the LC neurons displayed a reduced responsiveness to the inhibitory effect of systemic or microiontophoretic administration of clonidine but not to the inhibitory effect of morphine. Since the activity of LC neurons seems to be controlled by inhibitory noradrenergic axon collaterals via α 2-receptors on the soma of the cells, a reduced sensitivity at these α 2-receptor sites may be causally related to the LC activation in clonidine withdrawal. Clinically, sudden discontinuation of chronic clonidine treatment can be associated with a withdrawal reaction, which resembles the morphine abstinence syndrome and includes both signs of sympathetic overactivity such as tachycardia and hypertension and mental symptoms like anxiety. Previous experimental and clinical data indicate that activation of brain NE neurons such as those in the LC may be causally related to the morphine abstinence reaction. The present results suggest a similar mechanism underlying the clonidine withdrawal reaction.

A dual role for GABA in quasi-morphine abstinence behavior induced by di-n-propylacetate involving both initiation and termination.

Di-n-propylacetate (DPA) induces a behavioral syndrome in rats resembling morphine abstinence behavior. The inhibitory action of DPA on GABA degradation, resulting in an enhanced release of GABA, is probably responsible for this behavioral effect, since GABA antagonists, like bicuculline and picrotoxin, have been shown to suppress this behavior. However, the time-course of the DPA-induced behavior is much shorter than that of the DPA-induced increase of GABA concentrations. Therefore, we have studied the influence of enhanced GABA levels caused by a first injection of DPA and the behavior evoked by a second injection of DPA at different time intervals after the first injection. The results indicate that GABA fulfills a role in both the initiation and termination of DPA-induced behavior. The mechanism responsible for this dual action of GABA is ascribed to a differential sensitivity to DPA of the nerve terminal and glial metabolic compartments of GABA in the brain. The increase of GABA in the nerve terminal caused by DPA is probably responsible for the initiation of the quasi-abstinence behavior, whereas the overflow of GABA into the synaptic cleft may be responsible for the suppression of this behavior via stimulation of presynaptic autoreceptors. Another mechanism responsible for the rapid termination of the DPA-evoked behavior could be the formation of DPA metabolites which antagonize this behavior. From the results of experiments using some primary metabolites of DPA, a role for these metabolites in the termination of the DPA-induced behavior seems unlikely.

Comparison of two α-noradrenergic agonists (clonidine and guanfacine) on norepinephrine turnover in the cortex of rats during morphine abstinence

The effects of the α-agonists clonidine and guanfacine on rat cortical norepinephrine turnover during morphine withdrawal were assessed. Cortical norepinephrine levels were measured, after administration of α-methyl-p-tyrosine, by fluorometric assay. Chronic treatment with morphine did not affect norepinephrine levels or norepinephrine turnover. In control animals, doses up to 200 μg/kg clonidine and 1060 μg/kg guanfacine did not affect norepinephrine steady state levels, but did reduce α-methyl-p-tyrosine-induced norepinephrine depletion. As little as 5 μg/kg clonidine reversed the accelerated turnover observed during naloxone precipitated morphine withdrawal; while for guanfacine, the minimum effective dose was 212 μg/kg. The ED 50 for guanfacine's reversal of the withdrawal-induced acceleration of turnover was approximately 60 times that for clonidine.