Precipitated Opiate Withdrawal Research Articles

Male and female rats show opiate withdrawal-induced place aversion and extinction in a Y-maze paradigm

Gender differences have been observed in the vulnerability to drug abuse and in the different stages of the addictive process. In opiate dependence, differences between sexes have been shown in humans and laboratory animals in various phases of opiate addiction, especially in withdrawal-associated negative affective states. Using a Y-maze conditioned place aversion paradigm, we investigated potential sex differences in the expression and extinction of the aversive memory of precipitated opiate withdrawal state in morphine-dependent rats. No significant difference between sexes was observed in the occurrence of withdrawal signs following naloxone injection during conditioning. Moreover, opiate withdrawal memory expression and extinction following repeated testing was demonstrated in both male and female rats, with no significant differences between sexes. Finally, we report spontaneous recovery following extinction of opiate withdrawal memory. Altogether these data provide further evidence that persistent withdrawal-related memories may be strong drivers of opiate dependence, and demonstrate that both males and females can be used in experimental rodent cohorts to better understand opiate-related effects, reward, aversive state of withdrawal, abstinence and relapse.

Disruption of the CRF2 Receptor Pathway Decreases the Somatic Expression of Opiate Withdrawal

Escape from the extremely aversive opiate withdrawal symptoms powerfully motivates compulsive drug-seeking and drug-taking behaviors. The corticotropin-releasing factor (CRF) system is hypothesized to mediate the motivational properties of drug dependence. CRF signaling is transmitted by two receptor pathways, termed CRF(1) and CRF(2). To investigate the role for the CRF(2) receptor pathway in somatic opiate withdrawal, in the present study we used genetically engineered mice deficient in the CRF(2) receptor (CRF(2)-/-). We employed a novel, clinically relevant mouse model of 'spontaneous' opiate withdrawal as well as a classical opioid receptor antagonist (naloxone)-precipitated opiate withdrawal paradigm. To induce opiate dependence, mice were treated with intermittent escalating morphine doses (20-100 mg/kg, i.p.). We found that 8-128 h after the last opiate injection, CRF(2)-/- mice showed decreased levels of major somatic signs of spontaneous opiate withdrawal, such as paw tremor and wet dog shake, as compared to wild-type mice. Similarly, challenge with naloxone 2 h after the last morphine injection induced lower levels of paw tremor and wet dog shake in CRF(2)-/- mice as compared to wild-type mice. Despite the differences in somatic signs, wild-type and CRF(2)-/- mice displayed similar plasma corticosterone responses to opiate dosing and withdrawal, indicating a marginal role for the hypothalamus-pituitary-adrenal axis in the CRF(2) receptor mediation of opiate withdrawal. Our results unravel a novel role for the CRF(2) receptor pathway in opiate withdrawal. The CRF(2) receptor pathway might be a critical target of therapies aimed at alleviating opiate withdrawal symptoms and reducing relapse to drug intake.

Conditioned drug reward enhances subsequent spatial learning and memory in rats

Chronic exposure to drugs of abuse alters neural processes that normally promote learning and memory. A context that is repeatedly paired with reinforcing drugs will acquire secondary reinforcing properties (conditioned reward). However, the effects of conditioned reward on spatial learning are unknown. Using the conditioned place preference procedure and Morris water maze task, we examined the role of conditioned reward or aversion in spatial learning. Groups of rats acquired morphine (10 mg/kg), cocaine (10 mg/kg), or oral sucrose (15%) conditioned place preference (CPP). Another group of morphine-dependent rats acquired conditioned place aversion (CPA) to a context paired with precipitated opiate withdrawal induced by naloxone injections (1 mg/kg). To examine the role of conditioned reward or aversion in spatial learning, rats were then exposed to the previously morphine-, cocaine-, sucrose- or naloxone-paired context for 10 min before training of spatial learning in the Morris water maze. Exposure to the morphine- or cocaine-paired but not the sucrose- or the naloxone-paired context decreased the latency to find the platform in the Morris water maze test. Our results provide the first evidence that conditioned drug reward promotes spatial learning. We speculate that this enhancement of spatial learning by the drug-paired context may promote contextual-cue-induced relapse to drug taking by facilitating exploratory drug-seeking behaviors.

Associative Mechanisms and Drug-Related Behavior

Associative Mechanisms and Drug-Related Behavior

Buprenorphine and a CRF1 antagonist block the acquisition of opiate withdrawal-induced conditioned place aversion in rats.

Conditioned place aversion in rats has face validity as a measure of the aversive stimulus effects of opiate withdrawal that reflects an important motivational component of opiate dependence. The purpose of the present study was to validate conditioned place aversion as sensitive to medications that will alleviate the aversive stimulus effects of opiate withdrawal in humans, and to extend this model to the exploration of the neuropharmacological basis of the motivational effects of opiate withdrawal. Male Sprague-Dawley rats were implanted with two subcutaneous morphine pellets and 5 days later began place conditioning training following subcutaneous administration of a low dose of naloxone. Animals were subjected to three pairings of a low dose of naloxone (15 microg/kg, s.c.) to one arm of a three-chambered place conditioning apparatus. Buprenorphine administered prior to each pairing dose-dependently blocked the place aversion produced by precipitated opiate withdrawal. A corticotropin-releasing factor-1 (CRF1) receptor antagonist (antalarmin) also reversed the place aversion produced by precipitated opiate withdrawal. Antalarmin did not produce a place preference or place aversion by itself in morphine-dependent rats. No effect was observed with pretreatment of the dopamine partial agonist terguride or the selective serotonin reuptake inhibitor fluoxetine. Also, chronic pretreatment with acamprosate (a glutamate receptor modulator used to prevent relapse in alcohol dependence) did not alter naloxone-induced place aversion. Buprenorphine by itself in dependent rats produced a mild place preference at low doses and a mild place aversion at higher doses. These results suggest that buprenorphine blocks the aversive stimulus effects of precipitated opiate withdrawal in rats and provides some validity for the use of place conditioning as a measure that is sensitive to potential opiate-dependence medications. In addition, these results suggest that CRF1 antagonists can block the aversive stimulus effects of opiate withdrawal and may be potential therapeutic targets for opiate dependence.

Buprenorphine and naloxone co-administration in opiate-dependent patients stabilized on sublingual buprenorphine

Buprenorphine and naloxone sublingual (s.l.) dose formulations may decrease parenteral buprenorphine abuse. We evaluated pharmacologic interactions between 8 mg s.l. buprenorphine combined with 0, 4, or 8 mg of naloxone in nine opiate-dependent volunteers stabilized on 8 mg s.l. buprenorphine for 7 days. Combined naloxone and buprenorphine did not diminish buprenorphine's effects on opiate withdrawal nor alter buprenorphine bioavailability. Opiate addicts stabilized on buprenorphine showed no evidence of precipitated opiate withdrawal after s.l. buprenorphine-naloxone combinations. Buprenorphine and naloxone bioavailability was ∼40 and 10%, respectively. Intravenous buprenorphine and naloxone produced subjective effects similar to those of s.l. buprenorphine and did not precipitate opiate withdrawal.

Localization of mu-opioid receptors to locus coeruleus-projecting neurons in the rostral medulla: morphological substrates and synaptic organization.

The increase in discharge activity of locus coeruleus (LC) neurons following precipitated opiate withdrawal has been reported to be caused, in part, by excitatory amino acid release most likely originating from the nucleus paragigantocellularis lateralis (PGCl) in the rostral ventral medulla. Activation of glutamate-containing neurons in the PGCl may depend on changes in the occupancy of opioid receptive sites located on LC-projecting neurons which subsequently effect excitatory amino acid release in the LC during opiate withdrawal. To determine whether the mu-opioid receptor (MOR) is localized to plasmalemmal sites of LC-projecting neurons in the PGCl, we combined retrograde transport of the protein-gold tracer, wheat germ agglutinin-conjugated to inactive horseradish peroxidase (WGA-AU-apoHRP), from the LC with immunocytochemical detection of MOR in the same section of tissue throughout the rostral medulla. Light microscopic analysis indicated that neurons containing either the retrograde tracer or immunoperoxidase labeling for the MOR were numerous throughout the ventral medulla and that individual PGCl neurons contained both WGA-Au-apoHRP as well as MOR. By electron microscopy, WGA-Au-apoHRP was commonly identified in lysosomes within somata and large proximal dendrites. The somata contained either spherical or invaginated nuclei and were often surrounded by numerous myelinated axons. Gold deposits could also be identified in the cytoplasm of smaller dendritic processes in the PGCl, although these were not necessarily associated with lysosomes. The smaller dendritic processes were often the target of afferent input by axon terminals containing heterogeneous types of synaptic vesicles. Of 150 cellular profiles exhibiting WGA-Au-apoHRP retrograde labeling, 31% contained immunoperoxidase labeling for MOR. These results indicate that the MOR is distributed along plasmalemmal sites of morphologically diverse neurons in the PGCl which project to the LC.

Modulation of immunoreactive protein kinase C-α and β isoforms and G proteins by acute and chronic treatments with morphine and other opiate drugs in rat brain

The abundance of protein kinase C-alpha and beta isoforms (PKC-alphabeta), PKC-alpha messenger (m) RNA and guanine nucleotide-binding G protein subunits (G alpha(i1/2), G alpha(o), and G beta) were quantitated in the rat cerebral cortex after acute and chronic treatments with various opiate drugs. Acute (100 mg/kg for 2 h) and chronic (10 to 100 mg/kg for 5 days) treatment with morphine decreased similarly the immunoreactivity of PKC-alphabeta (28% and 32%, respectively). Acute (2 h) and chronic treatment (5 days) with other mu-agonists heroin (30 mg/kg and 10 to 30 mg/kg) and methadone (30 mg/kg and 5 to 30 mg/kg) also induced similar decreases of PKC-alphabeta (acute: 25% and 23%; chronic: 28% and 18%). After the chronic treatments, spontaneous (48 h) or naloxone (2 mg/kg)-precipitated opiate withdrawal (2 h) resulted in up-regulation of PKC-alphabeta above control levels (30-38%), and in the case of morphine withdrawal in a concomitant marked increase in the expression of PKC-alpha mRNA levels (2.3-fold). Acute (2 h) treatments with pentazocine (80 mg/kg, mixed kappa/delta-agonist and mu-antagonist), spiradoline (30 mg/kg, selective kappa-agonist) and [D-Pen2, D-Pen5] enkephalin (14 nmol i.c.v., selective delta-agonist) induced significant decreases of PKC-alphabeta (19-33%). Chronic (5 days) treatment with pentazocine (10 to 80 mg/kg), but not spiradoline (2 to 30 mg/kg), also induced a similar decrease of PKC-alphabeta (35%). In pentazocine- or spiradoline-dependent rats, naloxone (2 mg/kg) did not induce up-regulation of brain PKC-alphabeta. Acute (10 mg/kg for 2 h) and chronic (2x10 mg/kg for 5 and 14 days) treatment with naloxone did not alter PKC-alphabeta immunoreactivity. Chronic, but not acute, treatment with mu-agonists (morphine, heroin and methadone) increased the immunoreactivities of G alpha(i1/2) (33-37%), G alpha(o), (25-41%) and G beta (10-33%) protein subunits. In heroin- and methadone-dependent rats naloxone (2 mg/kg)-precipitated withdrawal (2 h) did not modify the up-regulation of these G proteins induced by chronic mu-opiate treatment. In marked contrast to mu-agonists, chronic treatment with high doses of pentazocine and spiradoline or acute treatment with [D-Pen2, D-Pen5] enkephalin did not result in up-regulation of these G protein subunits. After chronic treatment with mu-agonists, significant negative correlations were found when the percentage changes in immunoreactivity of PKC-alphabeta were related to the percentage changes in immunoreactivity of G alpha(i1/2), (r = -0.53, n = 29) and G beta (r = -0.41, n = 24) in the same brains. PKC-alphabeta abundance did not correlate significantly with the density of G alpha(o) (r = -0.21, n = 28). Together the results indicate that the brain PKC-alphabeta system may play a major regulatory role in opiate tolerance and dependence. Moreover, the possible in vivo cross-communication between this regulatory enzyme and specific inhibitory G proteins may also be of relevance in the cellular and molecular processes of opiate addiction.

Dose Dependent Effects of Yohimbine on Methadone Maintained Patients

Twelve methadone-maintained patients were randomized into a controlled crossover study with active and placebo yohimbine 20 mg once a day (n = 4), 5mg three times a day (n = 4) or 10 mg three times a day (n = 4) for seven days to evaluate the effect of yohimbine on naloxone precipitated opiate withdrawal. The yohimbine dose of 10 mg TID was well tolerated and was associated with an average decrease of 30% in precipitated withdrawal symptoms.

Chronic ethanol produces a decreased sensitivity to the response-disruptive effects of GABA receptor complex antagonists

Disruption of responding for food reinforcement may reflect the motivational state subsequent to the onset of an aversive event and has previously been shown to be sensitive to spontaneous withdrawal from ethanol and precipitated opiate withdrawal. The purpose of this study was to attempt to precipitate ethanol withdrawal with bicuculline methiodide, a competitive GABA A receptor antagonist, and Ro 15-4513, a benzodiazepine inverse agonist. A quantitative operant measure of food-motivated behavior was used to evaluate the reactivity of the GABA A-benzodiazepine receptor complex during chronic ethanol treatment in rats. In the present study, rats were trained to lever-press for food reinforcement on a fixed ratio 15 schedule and then maintained for 2 weeks on a liquid diet containing 35% ethanol-derived calories or a control liquid diet that was prepared isocalorically with sucrose. Chronic ethanol treatment attenuated the disruptive effects on operant responding that were produced by bicuculline methiodide (100 ng ICV) and Ro 15-4513 (3 and 6 mg/kg). The inability of these drugs to “precipitate” EtOH withdrawal may reflect the noncompetitive interaction of ethanol with the GABA-benzodiazepine-ionophore receptor complex. These data are consistent with recent biochemical studies indicating that chronic ethanol treatment modulates the GABA A-benzodiazepine-ionophore receptor complex by altering the expression of specific molecular components and inhibitating the activity of the receptor complex.

What is learned during opiate withdrawal conditioning? Evidence for a cue avoidance model

How conditioned opiate withdrawal gives rise to avoidance behaviour was examined using a defensive burying procedure in rats made dependent with a morphine pellet. The subjects underwent withdrawal precipitated by naloxone (0.1 mg/kg, SC) on two or three occasions in a box containing only a small object. When exposed to the object in the presence of sawdust one or more days later, the subjects avoided contact and buried this object, i.e., pushed and piled the sawdust against it. The behaviour was seen only when withdrawal had been paired with the object, which was the case even with a choice of objects on the test. Approach but no burying was seen in nondependent animals when the object was paired with 1 mg/kg morphine. Burying, therefore, was concluded to be a defensive response elicited in rats by an object specifically paired with precipitated opiate withdrawal. Consideration of burying and other defensive responses reported to be elicited by cues of withdrawal (conditioned place and taste aversion, and suppression), with respect to the behavioural demands of these responses and the test conditions needed to see them, suggested that a goal of avoidance may be a primary event encoded in a withdrawal cue, as is known for predictors of nonpharmacological noxious events (e.g., shock).

Locus ceruleus discharge characteristics of morphine-dependent rats: Effects of naltrexone

Spontaneous and sensory-evoked discharge was recorded from locus ceruleus (LC) neurons of halothane-anesthetized rats that were chronically administered morphine. LC spontaneous discharge rates of morphine-treated rats were comparable to those of rats chronically administered saline. Administration of 1.0 μg morphine (i.c.v.), a dose which completely inhibits LC discharge of morphine-naive rats, had no effect on LC spontaneous discharge of morphine-treated rats, demonstrating that opiate tolerance had developed. Naltrexone, 0.3 and 1.0 μg i.c.v., produced increases in LC spontaneous discharge rates that were 172 and 166% greater that baseline, respectively. Additionally, naltrexone disrupted LC discharge evoked by repeated sciatic nerve stimulation such that evoked discharge was decreased with respect to tonic discharge, and postactivation inhibition was attenuated. Naltrexone did not alter spontaneous or sensory-evoked LC discharge of rats chronically administered saline indicating that these neuronal effects are specific to opiate withdrawal. Pretreatment of rats with dexamethasone, or with an antagonists of corticotropin-releasing factor (CRF), a-helical CRF 9−41, did not attenuate the effects of naltrexone on LC discharge of morphine tolerant rats. The present study confirms other reports of LC activation associated with antagonist precipitated opiate withdrawal in vivo, and extends these observations by characterizing the disruptive effect of opiate withdrawal on the response of LC cells to phasically presented sensory stimuli, and demonstrating that the withdrawal response is not mediated by release of endogenous CRF.

Severity of precipitated opiate withdrawal predicts drug dependence by DSM-III-R criteria.

Drug diagnoses in DSM-III-R are based on the dependence syndrome concept which hypothesizes that dependence on drugs is defined by behavioral and physiological changes but is separate from the social problems related to drug use. Previous studies provide support for the dependence syndrome in drug use; however, no study has examined whether biological indications of addiction are related to the dependence syndrome. The present study tests this relationship in 52 opiate addicts who were administered the Naloxone Challenge Test. The severity of withdrawal was correlated positively with the opiate dependence score, derived from the number of DSM-III-R criteria met. We also found that opiate withdrawal was inversely related to cocaine dependence and unrelated to any other drug use. Opiate withdrawal was not correlated with a global measure of social problems or to frequency or length of drug use. Our results support the validity of the dependence syndrome in opiate addiction because dependence is correlated with severity of withdrawal, is fairly specific to the drug, and is not related to social problems.

Naltrexone precipitated opiate withdrawal in methadone addicted human subjects: Evidence for noradrenergic hyperactivity

The noradrenergic alpha-2 receptor agonist, clonidine, suppresses many of the effects of opiate withdrawal in both humans and other animals and this is consistent with the data indicating important interactions of opiate and noradrenergic systems in brain. This evidence supports the hypothesis that central noradrenergic hyperactivity is involved in the expression of major signs and symptoms of the opiate withdrawal syndrome, but to date clinical studies have not provided biochemical data consistent with this idea. In order to assess whether naltrexone precipitated opiate withdrawal in methadone addicted human subjects is associated with changes in noradrenergic function, a double-blind study was completed in which 15 methadone-dependent subjects received naltrexone and 8 subjects received placebo. Signs and symptoms of the opiate abstinence syndrome increased significantly in the 15 subjects who received naltrexone compared with the 8 who received placebo. Plasma concentrations of free MHPG also increased significantly in those subjects who took naltrexone compared to the placebo treated subjects. In addition, withdrawal signs and symptoms were significantly correlated with plasma MHPG concentration. Since several compounds which suppress central noradrenergic activity also reduce the severity of the withdrawal syndrome, the noradrenergic hyperactivity suggested by the present clinical study may be a functional mechanism for at least part of the opiate withdrawal syndrome.