Expression Of Opiate Withdrawal Research Articles

Treatments to Combat Opiate Dependence

The current opioid epidemic is a pressing public health concern that has been difficult to address because there is no generally accepted hypothesis to explain the underlying neurophysiological mechanism(s) that lead to tolerance and withdrawal, which in turn could serve as the basis for developing therapeutic interventions. As a step to developing such a unifying mechanistic hypothesis we studied both the electrophysiological firing patterns of individual neurons and behaviors indicative of tolerance and withdrawal in rats following chronic administration of morphine. Neuronal activity recordings from the ventral tegmental area (VTA), nucleus accumbens (NAc), prefrontal cortex (PFC), thalamus, hypothalamus, hippocampus (HIPP), Amygdala (AMYG) and caudate nucleus (CN) following exposure of repetitive (chronic) morphine produced a new baseline pattern of neuronal firing rates, which we refer to as an “opioid-induced pattern” in the mesocorticolimbic neuronal activity circuit, which is thought to be involved in mediating the “reward” effects of opioid and other drugs of abuse. These changes in neuronal firing rate was paralleled by behavioral changes indicative of the development of dependence such as tolerance and withdrawal suggesting a possible cause-effect relationship between the opioid induced pattern change of baseline neuronal firing and the development of opioid tolerance and withdrawal. Briefly, (i) morphine produces a new baseline pattern of neuronal firing (i.e., an “opioid-induced pattern”), (ii) there is an intrinsic neurophysiological mechanism that seeks to maintain newly established patterns of baseline neuronal firing once established, (iii) continued morphine administration maintains the new pattern of baseline neuronal activity so that withdrawal behaviors do not occur, but (iv) eventual discontinuation of the drug leads to opioid withdrawal symptoms. Consistent with this proposed hypothesis, co-administration of the immunomodulator such as interferon, cyclosporin and cortisol attenuated both the development of an altered baseline pattern of neuronal firing and the parallel behavioral changes. This observation suggests that immunomodifiers treatment to morphine dependence subject restore the neuronal firing rate to its pre-morphine baseline and thus alleviate the withdrawal symptoms that make is so difficult for addicts to discontinue opioid use. The studies in this review describe in more detail the findings that led to our proposed hypothesis for the underlying neurophysiological basis of the development of opioid tolerance and withdrawal and the possible use of immunomodulators to decrease the development of dependence and thereby attenuate withdrawal symptoms that make it so difficult for addicts to discontinue drug use. Repetitive use of opioids results in dependence on the drug, a complex condition that is considered to be an opiate use disorder (OUD). The reduction or cessation of opioid consumption leads to severe withdrawal behaviors. The degree of opiate dependence can be assessed by the intensity of the withdrawal behavior. To prevent this devastating opiate withdrawal syndrome, the subject will continue to take the drug. Success in modifying the withdrawal behavior may shed light on the dynamics of OUD and help to curb the opiate epidemic. Classical therapeutic addiction research has focused on cellular and molecular alterations within neurons and their neuronal circuits. As such, most of the pharmacotherapies for opioid addiction are designed to target the neuronal processes known to be affected by drug intake. In addition to the pivotal role of neurons in the initiation, transition, and maintenance of opioid dependence, the glial cells within the central nervous system are also of particular importance. According to some studies, 60 to 80% of the cellular brain is composed of glial cells. Recent studies have shown that glial cells participate in synaptogenesis, neuronal excitability, and neurotransmission. Following opioid exposure, glial cells demonstrate robust changes in their morphology and physiology in key central nervous system regions known to contribute to drug dependence. They play a pivotal role in opioid-addiction like behaviors. Glial cells are also part of the immune system. This review summarizes studies demonstrating that the immune system participates in the expression of opiate withdrawal and that a single dose of immunological substances such as α-interferon, cyclosporine, or cortisol significantly attenuates the severity of the naloxone-induced withdrawal symptoms in opioid-dependent animals. These preclinical studies provide a new approach to treat opiate dependence using immunomodulators that do not belong to the opiate family. We hope that this review will encourage translational studies to use immunomodulators in combating the opioid epidemic and save lives.

Effects of morphine withdrawal on μ-opioid receptor-stimulated guanylyl 5′-[γ-[ 35S]thio]-triphosphate autoradiography in rat brain

Abstinence from chronic morphine results in characteristic withdrawal symptoms in humans and experimental animals. Despite a large number of studies, the cellular mechanisms underlying opiate withdrawal symptoms are not clearly understood, in particular, the regulation of μ-opioid receptor function during this process. The present study investigated the μ-opioid receptor-stimulated G-protein activity using guanylyl 5′-[γ-[ 35S]thio]-triphosphate ([ 35S]-GTPγS) autoradiography. [ 35S]-GTPγS binding was performed using coronal rat brain sections (20 μm) in the presence or absence of the μ-opioid selective agonist [ d-Ala 2, N-MePhe 4Gly 5-ol] enkephalin (DAMGO). In experiment 1, rats (male, Sprague–Dawley) were injected every 12 h with increasing doses of morphine (5–100 mg/kg, s.c.) for 12 days; a separate group of rats which received saline injections served as control. Opiate withdrawal was induced by abstinence from morphine. Thirty-six hours after the last morphine injection, spontaneous withdrawal symptoms were assessed. Rats were then decapitated and brains rapidly removed. In experiment 2, withdrawal symptoms were precipitated with the opioid receptor antagonist naloxone (1 mg/kg). Brains were taken at 5, 10, 20 and 60 min after naloxone injection. In experiment 3, morphine dependence was induced by implantation of three morphine pellets (75 mg per pellet). After 7 days, withdrawal symptoms were precipitated by naloxone (1 mg/kg) and brains were removed 30 min after naloxone injection. [ 35S]-GTPγS binding was measured in the locus coeruleus, nucleus parabrachialis, nucleus accumbens and central nucleus of amygdala. Although clear withdrawal symptoms were observed in all morphine-withdrawn rats, no significant changes in [ 35S]-GTPγS binding were detected in animals undergoing withdrawal. The present lack of differences between morphine-withdrawn and control rats indicates that μ-opioid receptor-stimulated G-protein activity is not modulated by chronic morphine administration and is not involved in the expression of opiate withdrawal.

Involvement of nuclear factor-kB in the expression of opiate withdrawal

1. To investigate the role of NF-kB in the expression of opiate withdrawal, the effects of PDTC, an inhibitor of NF-kBactivation, was studied on acute opiate withdrawal induced by morphine in vivo. 2. After a 4 min in vivo exposure to morphine, a strong contracture of guinea pig isolated ileum was observed after the addition of naloxone. 3. PDTC (1x10 −8-5x10 −8-1x10 −7 M) was able to reduce the naloxone-induced contracture after exposure to the opioid agonist in a concentration-dependent fashion. 4. The results of the present study indicate that NF-kB is involved in the expression of opiate withdrawal thus extending and explaining previous papers performed with dexamethasone and selective arachidonic acid metabolites inhibitors.

Role of endogenous adenosine in the expression of opiate withdrawal in rats

Samples of extracellular fluid from striatum and nucleus accumbens of anaesthetised rats undergoing opiate withdrawal were collected using microdialysis and then analysed for adenosine and its metabolites using high performance liquid chromatography (HPLC) and ultraviolet (UV) detection. Although the amount of adenosine present in the dialysate from either brain region was below the limit of detection by 90 min after probe placement, the metabolites could still be detected. Samples of dialysates collected from the nucleus accumbens contained significantly higher concentrations of hypoxanthine and inosine following naloxone challenge. The data are compatible with the hypothesis that endogenous adenosine might be involved in the expression of the opiate abstinence syndrome.

Adenosine kinase inhibitors attenuate opiate withdrawal via adenosine receptor activation

Previous studies have demonstrated a role for adenosine in mediating opiate effects. This study examines the effects of indirect activation of adenosine receptors, via treatment with adenosine kinase inhibitors, on the expression of opiate withdrawal in mice. Mice receive chronic morphine treatment via implantation of subcutaneous morphine pellets (75 mg) for 72 h. Mice then receive parenteral treatment with adenosine kinase inhibitors, either 5′-amino-5′-deoxyadenosine (2, 5, 20, 40 mg/kg, intraperitoneal or i.p.) or iodotubericidin (1, 2, 5 mg/kg, i.p.), followed by naloxone injection and opiate withdrawal signs are measured over 20 min. Both adenosine kinase inhibitors significantly reduce the following opiate withdrawal signs in a dose-dependent manner compared to vehicle: withdrawal jumps, teeth chattering, forepaw tremors, and forepaw treads. Additionally, 5′-amino-5′-deoxyadenosine significantly reduces withdrawal-induced diarrhea and weight loss. Effects of 5′-amino-5′-deoxyadenosine (40 mg/kg) on opiate withdrawal signs appear to be mediated via adenosine receptor activation as they are reversed by pretreatment by adenosine receptor antagonist caffeine (20 mg, i.p.) but not by selective phosphodiesterase inhibitor Ro 20-1724 (10 mg/kg, i.p.). Adenosine receptor activation via adenosine kinase inhibitor treatment attenuates opiate withdrawal and these agents may be generally useful in the treatment of drug withdrawal syndromes.

Effect of Adenosine Receptor Agonists and Antagonists on the Expression of Opiate Withdrawal in Rats

The effects of the selective A 1 adenosine receptor agonist N 6-cyclopentyladenosine (CPA) and the selective A 2a agonist 2-[p-(2-carboxethyl)phenylethyl-ethylamino]-5′-ethylcarboxamidoadenosine (CGS 21680) (each at 0.03, 0.1 and 0.3 mg/kg, SC) as well as the selective A 1 adenosine receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), non-selective antagonists 3-isobutyl-1-methylxanthine (IBMX), aminophylline, 3,7-dimethyl-1-propargyl-xanthine (DMPX) and 8(p-sulfophenyl)-theophylline (8-SPT) were investigated (each at 5, 10 and 30 mg/kg, SC) for their ability to alter the naloxone-precipitated opiate withdrawal syndrome in morphine-dependent rats. Effects of CPA and CGS 21680 on opiate withdrawal in the presence of aminophylline were also investigated. Both CPA and CGS 21680, caused a significant reduction in the incidence of body shakes, teeth chatter and paw shakes and decreased the amount of faecal matter produced. DPCPX, IBMX, DMPX, 8-SPT and aminophylline significantly increased the incidence of jumps and decreased the amount of faecal matter produced. The incidence of body shakes was significantly increased by DMPX, 8-SPT and IBMX. Neither CPA nor CGS 21680 were able to reverse the significant increase in the incidence of jumps caused by aminophylline. These data suggest that there is a role for endogenous adenosine in the modulation of the opiate abstinence syndrome and both A 1 and A 2a adenosine receptors are involved in this phenomenon.

Participation of Noradrenergic Pathways in the Expression of Opiate Withdrawal: Biochemical and Pharmacological Evidence

MALDONADO, R. Participation of noradrenergic pathways in the expression of opiate withdrawal: Biochemical and pharmacological evidence. NEUROSCI BIOBEHAV REV 21(1) 91–104, 1997.—Several lines of biochemical and pharmacological evidence provide support for the involvement of the noradrenergic system in the expression of the somatic symptoms of opiate withdrawal. Early studies reported changes in brain noradrenaline and metabolite levels during opiate dependence. The significance of these changes has been clarified in recent microdialysis studies indicating that acute morphine decreases the extraneuronal levels of noradrenaline, whereas an increase in release of the neurotransmitter occurs during opiate withdrawal in several brain areas. Changes in the sensitivity and density of α 2- and β-adrenoceptors have also been reported, probably as a consequence of the decreased presynaptic noradrenergic activity induced during morphine dependence. In addition, the administration of α 2-agonists, such as clonidine, or β-antagonists, such as propranolol, has been reported to attenuate some manifestations of opiate withdrawal. The noradrenergic structure mediating the expression of opioid abstinence seems to be the locus coeruleus. However, the activation of the locus coeruleus during morphine withdrawal seems to be primarily due to the afferent projections containing excitatory amino acids and derived from the nucleus paragigantocellularis, although intrinsic modifications, consisting of an up-regulation of the cAMP pathway, seem also to be involved in this activation. The participation of the mesolimbic dopaminergic system in opiate dependence and its relation with the changes produced in the noradrenergic system are also discussed. Copyright © 1996 Elsevier Science Ltd.

Protein kinases in the locus coeruleus and periaqueductal gray matter are involved in the expression of opiate withdrawal.

The aim of this study was to evaluate the role played in the behavioral expression of morphine withdrawal syndrome by protein kinases in the locus coeruleus and the periaqueductal gray matter. Two different families of specific protein kinases have been investigated: serine/threonine and tyrosine kinases. Rats were implanted with cannulas into both the lateral ventricle and the locus coeruleus or the periaqueductal gray matter. Physical dependence was induced by chronic peripheral administration of morphine (from 7 to 30 mg/kg) and withdrawal syndrome was precipitated by injection of naloxone (2 micrograms) into the lateral ventricle. The administration of the serine/threonine kinase inhibitor 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine, H7 (1, 3, 10, and 30 nmol per side) into the locus coeruleus induced a strong attenuation of morphine withdrawal behavior. Signs related to the motor component of abstinence, such as jumping, rearing, and hyperactivity, were the most severely reduced. However, this effect was not dose-dependent, and the response was almost the same with all the doses used. A similar attenuation was observed after the injection of H7 (1, 3, and 10 nmol per side) into the periaqueductal gray matter, but in this case motor signs were less strongly reduced and a larger number of signs were modified, mainly when using the highest dose. The administration of the tyrosine kinase inhibitor 2-hydroxy-5-[N(2,5-dihydroxyphenyl)methyl]amino]-benzoic acid 3-phenylpropyl ester, KB23 (0.3, 1, and 3 nmol per side) into the locus coeruleus or the periaqueductal gray matter had no effect on the withdrawal syndrome behavior, except on teeth chattering. These results suggest that in the locus coeruleus and in the periaqueductal gray matter, serine/threonine kinases are implicated in the behavioral expression of morphine abstinence. In these brain structures, tyrosine kinases appear not to be involved.

RP 67580, a selective antagonist of neurokinin-1 receptors, modifies some of the naloxone-precipitated morphine withdrawal signs in rats

In order to clarify the participation of substance P in the expression of opiate withdrawal, we have investigated the effects induced by the new selective neurokinin-1 antagonist RP 67580 on naloxone-induced morphine withdrawal syndrome in rats. Intracerebroventricular administration of RP 67580 elicited a decrease in 7 of the 13 withdrawal signs evaluated. Mastication, salivation and signs related to the motor component of withdrawal (jumping, rearing and locomotor activity) were particularly reduced. One sign, wet dog shakes, was increased, but it was also enhanced by the inactive enantiomer RP 68651. Our results indicate that blockade of NK1 receptors induces a decrease in the expression of naloxone-precipitated morphine abstinence in rats, and support the participation of substance P in the opiate withdrawal response.

Effect of adenosine analogues on the expression of opiate withdrawal in rats

The aim of this study was to test whether convergent dependence occurs in vivo. The adenosine A 1 receptor agonist N 6-[( R)]-1-methyl-2-phenylethyl]adenosine, (R-PIA), the A 2 agonist 2-(phenylamino)adenosine (CV-1808), the nonselective A 1, A 2 agonist (adenosine-5′-ethylcarboxamide (NECA), and the α 2-adrenoceptor agonist clonidine were screened (each at 30, 100, and 300 μg/kg, SC) for their ability to alter naloxine-precipitated withdrawal signs in morphine-dependent rats. The results indicate that there is convergent dependence involving opioid and adenosine A 1 receptors on those effects expressed by withdrawal diarrhoea, paw-shakes, teeth-chattering, body-shakes, and jumping. Further, dependence expressed by body-shakes involves convergence involving A 1 receptors, as well as α 2-adrenoceptors; while A 1 receptors are involved in dependence expressed by jumping, stimulation of α 2-adrenoceptors augments this signs. Adenosine analogues may be of clinical value for detoxification of opiate addicts.

The serotonin2 antagonist ritanserin blocks quasi-morphine withdrawal at a time when mianserin is no longer effective

A quasi-morphine withdrawal syndrome (QMWS), produced in opiate-naive rats with an injection of isobutylmethylxanthine (IBMX) and the opioid antagonist naloxone, allows one to study the expression of opiate withdrawal in the absence of the acute or chronic effects of opiates and the adaptive processes termed dependence. The allegedly selective and long-acting serotonin2 (5-HT2) antagonist ritanserin attenuated the QMWS-induced suppression of fixed ratio (FR) operant responding, which is a sensitive measure of the expression of a QMWS. When administered 30 min prior to precipitation of the QMWS, the lowest dose of ritanserin tested (0.158 mg/kg) was the most effective in blocking the expression of withdrawal; however, there was not complete reversal of the behavioral suppression. Acutely, the two higher doses of ritanserin tested (2.5 and 10 mg/kg) suppressed responding when given alone. This may have masked their ability to attenuate a QMWS. At a dose of 2.5 mg/kg, ritanserin completely blocked the QMWS-induced suppression of responding 24 h post-administration, at a time when its actions at other receptors (e.g., alpha 2) have dissipated. At an equivalent dose, the shorter-acting 5-HT2 antagonist mianserin was unable to attenuate the QMWS-induced suppression of FR operant responding 24 h post-administration. The 5-HT2 antagonists reportedly produce a paradoxical down-regulation of 5-HT2 binding sites upon chronic treatment, rather than the expected supersensitivity. Chronic treatment with ritanserin (2.5 mg/kg/day for 7 days), but not mianserin (same regimen), attenuated a QMWS 24 h after the final injection, thus supporting with a functional measure, the down-regulation of such binding sites by ritanserin.(ABSTRACT TRUNCATED AT 250 WORDS)

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 alpha 2 adrenergic agonist clonidine which also attenuates true opiate withdrawal and the QMWS. Therefore, the operant behavioral effects 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 IBMX 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.

Adenosine triphosphate blocks opiate withdrawal symptoms in rats and mice.

The effect of adenosine triphosphate (ATP) on the expression of opiate withdrawal was examined using a chronic model of morphine-dependence. ATP was studied for its ability to modify or block jumping in morphine-abstinent mice. In mice administered 2 mg/kg ATP intravenously, the naloxone ED50 for withdrawal jumping increased by 11-fold in comparison to saline-treated mice. Nalaxone-precipitated morphine-withdrawal in the rats, has been shown to induce a specific pattern of intestinal hypermyoelectric activity and to increase the arterial blood pressure. Administration of ATP at dose of 1 and 2 mg/kg intravenously inhibited the induction of hypermyoelectric activity pattern in 80 and 100% of animals tested respectively. ATP also blocked the increase in mean arterial blood pressure seen during withdrawal in a dose-dependent fashion. Investigations were carried out to determine if blocking of the alpha 2-adrenoreceptors with yohimbine would result in an alteration in antiwithdrawal action of ATP. Yohimbine reversed the effect of ATP in blocking naloxone-precipitated withdrawal on the myoelectric activity of jejunum and colon, however, it failed to antagonize the effect of ATP on withdrawal jumping and to block the effect of ATP on the pressor response produced by naloxone in morphine-dependent animals.

Attenuation of isobutylmethylxanthine-induced suppression of operant behavior by pretreatment of rats with clonidine

Administration of 3-isobutyl-1-methylxanthine (IBMX) to rats performing a FR30 operant for food reinforcement produces a does-dependent suppression of behavior. Operant behavior suppressed by 5 mg IBMX/kg is attenuated by pretreatment, 30 min before the operant session, with the α 2 adrenergic agonist clonidine (5–30 μg/kg). Clonidine itself causes a dose-dependent reduction in FR30 responding prior to the administration of IBMX. However, doses of clonidine which also suppressed responding were not more effective than lower doses in attenuating the suppresion of operant behavior caused by IBMX, perhaps due to postsynaptic or nonspecific actions of clonide. Methylxanthines, alone or in combination with the opiate antagonist naloxone, produce signs of opiate withdrawal. This quasi-morphin withdrawalsyndrome may be useful in studies of either the development or expression of opiate withdrawal. Since clonidine attenuates the rate-suppressant effect of IBMX, it is likely that a significant component of IBMX's behavioral effects are due to increases in NE neurotransmission. These results are similar to those obtained with true opiate withdrawal in rats, strengthening the idea that suppression of operant behavior by IBMX involves mechanisms in common with opiate withdrawal. It may be a useful way of objectively studying the expression of the withdrawal syndrome in the absence of opiates and/or a way of determining if a drug can selectively block withdrawal.

Yohimbine exacerbates and clonidine attenuates acute morphine withdrawal in rats

The involvement of α2-noradrenergic receptors in the expression of opiate withdrawal was studied using an operant behavioral model of acute morphine dependence. Clonidine, an α2-agonist, attenuated and yohimbine, an α2-antagonist, exacerbated the naloxone-induced suppression of fixed ratio 15 responding in rats pretreated several hours earlier with a single, moderate dose of morphine. These data indicate that the α2-agonist action of clonidine is responsible for its amelioration of withdrawal symptoms. It also validates the acute dependence model for studying the pharmacology of opiates and associated adaptive processes.

Prenatal withdrawal from opiates interferes with hatching of otherwise viable chick fetuses.

Fetal chicks were made opiate-dependent by injections of N-desmethyl-1-alpha-acetylmethadol into the chorioallantois on day 3 of embryogenesis. The injections had no effect on subsequent hatchability; however, spontaneous fetal motility was significantly depressed. Injection of naloxone caused a significant increase in the motility of the opiate-exposed fetuses but had no effect on control fetuses. That naloxone's effect was an expression of opiate withdrawal and not due to antagonism of depressed motility is also supported by the observation that naloxone significantly reduced the hatchability of opiate-exposed chicks and not of control chicks. Thus the withdrawal of a developing organism from a narcotic may be more deleterious to its survival than continued exposure.