Effects of chronic buprenorphine treatment on levels of nucleus accumbens glutamate and on the expression of cocaine-induced behavioral sensitization in rats

Investigation into the biomolecular bases of blunted cocaine-induced glutamate release within the nucleus accumbens elicited by adolescent exposure to phenylpropanolamine

Globally, phenylpropanolamine (PPA) is a prevalent primary active ingredient in over-the-counter cough and cold, as well as weight-loss medications. Previously, we showed that a sensitization of cocaine-induced glutamate release within the nucleus accumbens (NAC) and the expression of cocaine-conditioned reward is not apparent in adult mice with a prior history of repeated PPA exposure during adolescence. As NAC glutamate is a purported driver of cocaine reward and reinforcement, the present study employed in vivo microdialysis and immunoblotting approaches to inform as to the receptor and transporter anomalies that might underpin the disrupted glutamate response to cocaine in adolescent PPA-exposed mice. For this, male and female C57BL/6J mice were pretreated, once daily, with either 0 or 40mg/kg PPA during post-natal days 35-44. Adolescent PPA pretreatment significantly altered the expression of mGlu2/3 and α2 receptors in the NAC, with less robust changes detected for EAAT2, D2 receptors, DAT and NET. However, we detected no overt change in the capacity of these receptors or transporters to affect extracellular glutamate levels in adolescent PPA-pretreated mice. The present findings contrast with the pronounced changes in the capacity of mGlu2/3 receptors, EAAT, DAT and NET to regulate NAC extracellular glutamate reported previously for juvenile PPA-pretreated mice, indicating further that the long-term biochemical consequences of PPA depend on the critical period of neurodevelopment during which an individual is PPA-exposed, although the specific biomolecular changes underpinning the cocaine phenotype produced by adolescent PPA remain to be elucidated.

Behavioral sensitization to psychostimulants and opioids: What is known in rodents and what still needs to be explored in humans?

Repeated exposure to substances of abuse results in an increase in some behavioral responses. This phenomenon, called behavioral sensitization (BS), is well described in preclinical models. However, its existence in humans is still a matter of debate. After a review of preclinical evidence of BS and its mechanisms in animal models, we reviewed the evidence supporting the existence of BS in humans, despite the limited research available in this regard. We focused our review on opioids and psychostimulants, since they share the ability to promote addictive behaviors. Further, they induce BS despite their distinct sedative and stimulant properties. Moreover, we proposed future research perspectives in this review to address the remaining unsolved questions, especially regarding BS in humans using a harm reduction approach.

An Examination of the Complex Pharmacological Properties of the Non-Selective Opioid Modulator Buprenorphine

The goal of this review is to provide a recent examination of the pharmacodynamics as well as pharmacokinetics, misuse potential, toxicology, and prenatal consequences of buprenorphine. Buprenorphine is currently a Schedule III opioid in the US used for opioid-use disorder (OUD) and as an analgesic. Buprenorphine has high affinity for the mu-opioid receptor (MOR), delta (DOR), and kappa (KOR) and intermediate affinity for the nociceptin (NOR). Buprenorphine's active metabolite, norbuprenorphine, crosses the blood-brain barrier, is a potent metabolite that attenuates the analgesic effects of buprenorphine due to binding to NOR, and is responsible for the respiratory depressant effects. The area under the concentration curves are very similar for buprenorphine and norbuprenorphine, which indicates that it is important to consider this metabolite. Crowding sourcing has identified a buprenorphine street value (USD 3.95/mg), indicating some non-medical use. There have also been eleven-thousand reports involving buprenorphine and minors (age < 19) at US poison control centers. Prenatal exposure to clinically relevant dosages in rats produces reductions in myelin and increases in depression-like behavior. In conclusion, the pharmacology of this OUD pharmacotherapy including the consequences of prenatal buprenorphine exposure in humans and experimental animals should continue to be carefully evaluated.

Buprenorphine reduces methamphetamine intake and drug seeking behavior via activating nociceptin/orphanin FQ peptide receptor in rats

Buprenorphine, which has been approved for the treatment of opioid dependence, reduces cocaine consumption by co-activating μ-opioid receptors and nociceptin/orphanin FQ peptide (NOP) receptors. However, the role of buprenorphine in methamphetamine (METH) reinforcement and drug-seeking behavior remains unclear. This study investigated the effects of buprenorphine on METH self-administration and reinstatement of METH-seeking behavior in rats. We found that buprenorphine pretreatment had an inhibitory effect on METH self-administration behavior, and that buprenorphine at a dose of 0.3 mg/kg could inhibit motivation to respond for METH. Pretreatment with the NOP receptor antagonist thienorphine (0.5 mg/kg) or SB-612111 (1 mg/kg) could reverse the inhibitory effect of buprenorphine (0.1 mg/kg) on the METH self-administration. Moreover, treatment with buprenorphine (0.1 mg/kg and 0.3 mg/kg) significantly reduced the drug-seeking behavior induced by context or by METH priming but failed to reduce the drug-seeking behavior induced by conditional cues. Additionally, the NOP receptor antagonist SB-612111 reversed the inhibitory action of buprenorphine on the drug-seeking behavior induced by METH priming. The results demonstrated that buprenorphine reduced either METH intake or the drug-seeking behavior by activating NOP receptors, providing empirical evidence for the clinical use of buprenorphine in the treatment of METH relapse and addiction.

Effects of Buprenorphine on the Memory and Learning Deficit Induced by Methamphetamine Administration in Male Rats

Little is known about the effects of methamphetamine (Meth) and buprenorphine (Bup) on memory and learning in rats. The aim of this investigation was to examine the impact of Meth and Bup on memory and learning. Fourteen male Wistar rats weighing 250–300 g were assigned to four groups: Sham, Meth, Bup, and Meth + Bup and were treated for 1 week. Spatial learning and memory, avoidance learning, and locomotion were assessed using the Morris water maze, passive avoidance learning, and open field tests, respectively. Meth and Bup impaired spatial learning and memory in rats. Co-administration of Meth + Bup did not increase the time spent in the target quadrant compared to Meth alone in the MWM. The Bup and Meh + Bup groups were found with an increase in step-through latency (STLr) and a decrease in the time spent in the dark compartment (TDC). Meth and Bup had no effects on locomotor activity in the open field test. Bup showed a beneficial effect on aversive memory. Since Bup demonstrates fewer side effects than other opioid drugs, it may be preferable for the treatment of avoidance memory deficits in patients with Meth addiction.

Novel Targets to Treat Depression: Opioid-Based Therapeutics

After participating in this activity, learners should be better able to:• Identify the effects of dysregulated opioid signalling in depression• Evaluate the use of opioid compounds and ketamine in patients with depression ABSTRACT: Major depressive disorder (MDD) remains one of the leading causes of disability and functional impairment worldwide. Current antidepressant therapeutics require weeks to months of treatment prior to the onset of clinical efficacy on depressed mood but remain ineffective in treating suicidal ideation and cognitive impairment. Moreover, 30%-40% of individuals fail to respond to currently available antidepressant medications. MDD is a heterogeneous disorder with an unknown etiology; novel strategies must be developed to treat MDD more effectively. Emerging evidence suggests that targeting one or more of the four opioid receptors-mu (MOR), kappa (KOR), delta (DOR), and the nociceptin/orphanin FQ receptor (NOP)-may yield effective therapeutics for stress-related psychiatric disorders. Furthermore, the effects of the rapidly acting antidepressant ketamine may involve opioid receptors. This review highlights dysregulated opioid signaling in depression, evaluates clinical trials with opioid compounds, and considers the role of opioid mechanisms in rapidly acting antidepressants.

Effects of Cebranopadol on Cocaine-induced Hyperactivity and Cocaine Pharmacokinetics in Rats

Cebranopadol is known as a highly potent analgesic. Recent studies also demonstrated that administration of cebranopadol significantly decreased cocaine self-administration and significantly reduced cue-induced cocaine-seeking behaviors in rats. However, it was unclear whether these interesting behavioral observations are related to any potential effects of cebranopadol on cocaine pharmacokinetics or cocaine-induced hyperactivity. In principle, a promising therapeutic candidate for cocaine dependence treatment may alter the cocaine pharmacokinetics and/or attenuate cocaine-induced reward and hyperactivity and, thus, decrease cocaine self-administration and reduce cue-induced cocaine-seeking behaviors. In this study, we examined possible effects of cebranopadol on cocaine pharmacokinetics and cocaine-induced hyperactivity for the first time. According to our animal data in rats, cebranopadol did not significantly alter the pharmacokinetics of cocaine. According to our more extensive locomotor activity testing data, cebranopadol itself also dose-dependently induced hyperactivity in rats at doses higher than 50 µg/kg. Cebranopadol at a low dose of 25 µg/kg (p.o.) did not induce significant hyperactivity itself, but significantly potentiated cocaine-induced hyperactivity on Days 4 to 7 after the repeated daily dosing of the drug.

Effects of cocaine base paste on anxiety-like behavior and immediate-early gene expression in nucleus accumbens and medial prefrontal cortex of female mice

RATIONALE

Cocaine base paste (CBP) is an illegal drug of abuse usually consumed by adolescents in a socio-economically vulnerable situation. Repeated drug use targets key brain circuits disrupting the processes that underlie emotions and cognition. At the basis of such neuroadaptations lie changes in the expression of immediate-early genes (IEGs). Nevertheless, changes in transcriptional regulation associated with CBP consumption remain unknown.

OBJECTIVES

We aimed to describe behavioral phenotype related to locomotion, anxiety-like behavior, and memory of CBP-injected mice and to study IEGs expression after an abstinence period.

METHODS

Five-week-old female CF-1 mice were i.p. injected daily with vehicle or CBP (40 mg/kg) for 10 days and subjected to a 10-day period of abstinence. Open field and novel object recognition tests were used to evaluate locomotion and anxiety-like behaviors and recognition memory, respectively, during chronic administration and after abstinence. After abstinence, prefrontal cortex (mPFC) and nucleus accumbens (NAc) were isolated and gene expression analysis performed through real-time PCR.

RESULTS

We found an increase in locomotion and anxiety-like behavior during CBP administration and after the abstinence period. Furthermore, the CBP group showed impaired recognition memory after abstinence. Egr1, FosB, ΔFosB, Arc, Bdnf, and TrkB expression was upregulated in CBP-injected mice in NAc and FosB, ΔFosB, Arc, and Npas4 expression was downregulated in mPFC. We generated an anxiety score and found positive and negative correlations with IEGs expression in NAc and mPFC, respectively.

CONCLUSION

Our results suggest that chronic CBP exposure induced alterations in anxiety-like behavior and recognition memory. These changes were accompanied by altered IEGs expression.

Topiramate in the treatment of cocaine use disorder

PURPOSE

The literature on topiramate use in cocaine-dependent patients was reviewed.

SUMMARY

Six randomized, double-blind, controlled clinical trials evaluating the use of topiramate in patients who were cocaine dependent were analyzed. The results from the studies indicated that topiramate, when used in combination with cognitive behavioral therapy, may be effective in reducing short-term cocaine use and should be considered as a possible treatment option. Other trials suggested that topiramate was not effective in patients with a dual diagnosis of opioid and cocaine dependence. Two trials suggested that short-term abstinence assisted by pharmacotherapy is a predictor of longer-term (6 months and 1 year, respectively) abstinence. Cocaine use is dependent on multiple factors; therefore, a reduction in use or craving is not definitively associated with abstinence. However, decreased use reduces potential patient harm and the amount of money spent on illicit cocaine. The findings of this literature review should be used to encourage the completion of more trials that are appropriately designed. Topiramate was shown to be effective for increasing cocaine abstinence, the proportion of cocaine nonuse days, and the proportion of patients to attain 3 consecutive weeks of cocaine abstinence and decreasing the abuse liability of cocaine. Conflicting results in clinical trials do not provide a definitive answer regarding topiramate's efficacy in managing cocaine dependence.

CONCLUSION

Available research neither validates nor invalidates the hypothesis that topiramate is efficacious in attaining abstinence in cocaine-dependent patients.

Buprenorphine requires concomitant activation of NOP and MOP receptors to reduce cocaine consumption

Buprenorphine's clinical use is approved for the treatment of heroin addiction; however, evidence supporting its efficacy in cocaine abuse also exists. While for heroin it has been demonstrated that the effect of buprenorphine is mediated by its ability to activate μ-opioid peptide receptor (MOP) receptors, the mechanism through which it attenuates cocaine intake remains elusive. We explored this mechanism using operant models where rodents were trained to chronically self-administer cocaine for 2 hours daily. Buprenorphine (0.3, 1.0 and 3.0 mg/kg) given intraperitoneally 90 minutes before access to cocaine significantly and dose dependently reduced its intake. Pre-treatment with naltrexone or with the selective nociceptin/orphanin FQ peptide (NOP) antagonist SB-612111 did not prevent buprenorphine-induced reduction of cocaine intake. However, when naltrexone and SB-612111 were combined, the effect of buprenorphine on cocaine was completely prevented. To confirm that co-activation of MOP and NOP receptors is the underlying mechanism through which buprenorphine reduces cocaine intake, three compounds, namely, AT-034, AT-201 and AT-202, with a range of affinity and intrinsic activity profiles for MOP and NOP receptors, but weak ability for kappa-opioid peptide receptor (KOP) transmission, were tested. Consistent with our hypothesis based on buprenorphine's effects, results demonstrated that AT-034 and AT-201, which co-activate MOP and NOP receptors, reduced cocaine self-administration like buprenorphine. AT-202, which selectively stimulates NOP receptors, was not effective. Together, these data demonstrate that for buprenorphine, co-activation of MOP and NOP receptors is essential to reduce cocaine consumption. These results open new vistas on the treatment of cocaine addiction by developing compounds with mixed MOP/NOP agonist properties.

Cebranopadol Blocks the Escalation of Cocaine Intake and Conditioned Reinstatement of Cocaine Seeking in Rats

Cebranopadol is a novel agonist of nociceptin/orphanin FQ peptide (NOP) and opioid receptors with analgesic properties that is being evaluated in clinical Phase 2 and Phase 3 trials for the treatment of chronic and acute pain. Recent evidence indicates that the combination of opioid and NOP receptor agonism may be a new treatment strategy for cocaine addiction. We sought to extend these findings by examining the effects of cebranopadol on cocaine self-administration (0.5 mg/kg/infusion) and cocaine conditioned reinstatement in rats with extended access to cocaine. Oral administration of cebranopadol (0, 25, and 50 μg/kg) reversed the escalation of cocaine self-administration in rats that were given extended (6 hour) access to cocaine, whereas it did not affect the self-administration of sweetened condensed milk (SCM). Cebranopadol induced conditioned place preference but did not affect locomotor activity during the conditioning sessions. Finally, cebranopadol blocked the conditioned reinstatement of cocaine seeking. These results show that oral cebranopadol treatment prevented addiction-like behaviors (i.e., the escalation of intake and reinstatement), suggesting that it may be a novel strategy for the treatment of cocaine use disorder. However, the conditioned place preference that was observed after cebranopadol administration suggests that this compound may have some intrinsic rewarding effects.

The effects of methamphetamine and buprenorphine, and their interaction on anxiety-like behavior and locomotion in male rats

Methamphetamine (Meth) abuse and dependence are major global problems. Most of previous studies showed that Meth is anxiogenic. While buprenorphine (Bup) is used to treat anxiety-related behaviors, the effects of Meth in combination with Bup on anxiety-like behavior are unclear. In this study, we examined the effects of these drugs on anxiety-like behavior with the elevated plus maze (EPM) and open field (OF) tests, which are widely used to assess anxiety-like behavior in small rodents. Forty male Wistar rats were divided into four groups: sham, Meth, Bup, and Bup+Meth. The groups were administered their assigned treatments for 7days. The time spent in the open arms, and number of total entries into the arms (total activity) in the EPM were recorded. In addition, locomotor activity and number of entrances into the center area in the OF were recorded. The 7-day administration of Meth or Bup increased open arm exploration in the EPM. In contrast, the combined administration of Bup and Meth had the opposite effects. In addition, Meth and Bup had no effects on total and locomotor activity. Furthermore, the rats in the Meth and Bup groups spent more time in the center of the OF, while the group given both Bup and Meth spent less time in the center of the OF. The administration of Meth and Bup alone was anxiolytic in rats, whereas the coadministration of Bup and Meth was anxiogenic.

Nociceptin receptor activation does not alter acquisition, expression, extinction and reinstatement of conditioned cocaine preference in mice

Growing evidence indicates that targeting nociceptin receptor (NOP) signaling may have therapeutic efficacy in treating alcohol and opioid addiction. However, little is known about the therapeutic value of selective NOP agonists for the treatment of cocaine dependence. Recently, we identified a highly selective, brain-penetrant NOP small molecule agonist (SR-8993), and using this compound, we previously showed that nociceptin receptor activation attenuated consolidation of fear-related memories. Here, we sought to determine whether SR-8993 also affects the rewarding properties of cocaine. Using a conditioned place preference (CPP) procedure, we show that SR-8993 (3 or 10 mg/kg) failed to disrupt acquisition or expression of cocaine CPP (7.5 or 15 mg/kg) in C57BL/6 mice. Additionally, SR-8993 did not affect rate of extinction or reinstatement (yohimbine- and cocaine-induced) of cocaine CPP. These studies indicate that selective activation of NOP may not be sufficient in reducing behavioral responses to cocaine.

The opioid receptors as targets for drug abuse medication

The endogenous opioid system is largely expressed in the brain, and both endogenous opioid peptides and receptors are present in areas associated with reward and motivation. It is well known that this endogenous system plays a key role in many aspects of addictive behaviours. The present review summarizes the modifications of the opioid system induced by chronic treatment with drugs of abuse reported in preclinical and clinical studies, as well as the action of opioid antagonists and agonists on the reinforcing effects of drugs of abuse, with therapeutic perspectives. We have focused on the effects of chronic psychostimulants, alcohol and nicotine exposure. Taken together, the changes in both opioid peptides and opioid receptors in different brain structures following acute or chronic exposure to these drugs of abuse clearly identify the opioid system as a potential target for the development of effective pharmacotherapy for the treatment of addiction and the prevention of relapse.

AMN082, a metabotropic glutamate receptor 7 allosteric agonist, attenuates locomotor sensitization and cross-sensitization induced by cocaine and morphine in mice

Previous studies have indicated that metabotropic glutamate receptors 7 (mGluR7s) are involved in drug addiction. However, the role of these receptors in drug-induced behavioral sensitization is unknown. The aim of the present study was to determine whether systemic injection of AMN082, a selective mGluR7 allosteric agonist, reduces the cocaine- and morphine-induced hyperactivity and the development and expression of locomotor sensitization, and also affects the reciprocal cross-sensitization to the stimulant effect of cocaine and morphine in mice. AMN082 (1.25-10.0 mg/kg, i.p.) did not have an impact on locomotion of naive mice and did not affect the acute cocaine- or morphine-induced hyperactivity, except the dose of 10 mg/kg that suppressed the locomotor effect of both drugs. Repeated exposure to cocaine or morphine (10 mg/kg, 5× every 3 days) gradually increased locomotion during induction of sensitization and after 4 (cocaine) or 7 day (morphine) withdrawal phase when challenged with cocaine (10 mg/kg, i.p.) or morphine (10 mg/kg, i.p.) on day 17 or 20, respectively. Pretreatment of animals with the lower doses of AMN082 (1.25-5.0 mg/kg, i.p.), 30 min before every cocaine or morphine injection during repeated drug administration or before cocaine or morphine challenge, dose-dependently attenuated the development, as well as the expression of cocaine or morphine locomotor sensitization. AMN082 also inhibited the reciprocal cross-sensitization between these drugs. Prior to administration of MMPIP (10 mg/kg, i.p.), a selective mGluR7 antagonist reversed the inhibitory effect of AMN082 on the development or expression of cocaine or morphine sensitization. These data indicate that AMN082 attenuated the development and expression of cocaine and morphine sensitization, and the reciprocal cross-sensitization via a mechanism that involves mGluR7s. Thus, AMN082 might have therapeutic implications not only in the treatment of cocaine or opioid addiction but also in the treatment of cocaine/opioid polydrug-abusers.

Region-specific effects of isoflurane anesthesia on Fos immunoreactivity in response to intravenous cocaine challenge in rats with a history of repeated cocaine administration

We have previously shown that acute intravenous (i.v.) administration of cocaine increases Fos immunoreactivity in rats under isoflurane anesthesia. Given that Fos expression is a marker of neural activation, the results suggested that isoflurane is appropriate for imaging cocaine effects under anesthesia. However, most imaging research in this area utilizes subjects with a history of repeated cocaine exposure and this drug history may interact with anesthetic use differently from acute cocaine exposure. Thus, this study further examined Fos expression under isoflurane in rats with a history of repeated i.v. cocaine administration. Rats received daily injections of either saline or cocaine (2mg/kg, i.v.) across 7 consecutive days, followed by 5 days of no drug exposure. On the test day, rats were either nonanesthetized or anesthetized under isoflurane and were given an acute challenge of cocaine (2mg/kg, i.v.). Additional saline-exposed controls received a saline challenge. Ninety min after the drug challenge, the rats were perfused under isoflurane anesthesia and their brains were processed for Fos protein immunohistochemistry. We found that challenge injections of cocaine following a regimen of repeated cocaine exposure resulted in Fos expression in the prefrontal cortex and striatum roughly equivalent to that found in rats who had received the cocaine challenge after a history of vehicle injections. Additionally, isoflurane anesthesia resulted in a heterogeneous attenuation of cocaine-induced Fos expression, with the most robust effect in the orbital cortex but no effect in the nucleus accumbens core (NAcC). These results indicate that cocaine-induced Fos is preserved in the NAcC under isoflurane, suggesting that isoflurane can be used in imaging studies involving cocaine effects in this region.

Topiramate for cocaine dependence during methadone maintenance treatment: a randomized controlled trial

BACKGROUND

Dual dependence on opiate and cocaine occurs in about 60% of patients admitted to methadone maintenance and negatively impacts prognosis (Kosten et al. 2003. Drug Alcohol Depend. 70, 315). Topiramate (TOP) is an antiepileptic drug that may have utility in the treatment of cocaine dependence because it enhances the GABAergic system, antagonizes the glutamatergic system, and has been identified by NIDA as one of only a few medications providing a "positive signal" warranting further clinical investigation. (Vocci and Ling, 2005. Pharmacol. Ther. 108, 94).

METHOD

In this double-blind controlled clinical trial, cocaine dependent methadone maintenance patients (N=171) were randomly assigned to one of four groups. Under a factorial design, participants received either TOP or placebo, and monetary voucher incentives that were either contingent (CM) or non-contingent (Non-CM) on drug abstinence. TOP participants were inducted onto TOP over 7 weeks, stabilized for 8 weeks at 300 mg daily then tapered over 3 weeks. Voucher incentives were supplied for 12 weeks, starting during the fourth week of TOP induction. Primary outcome measures were cocaine abstinence (Y/N) as measured by thrice weekly urinalysis and analyzed using Generalized Estimating Equations (GEE) and treatment retention. All analyses were intent to treat and included the 12-week evaluation phase of combined TOP/P treatment and voucher intervention period.

RESULTS

There was no significant difference in cocaine abstinence between the TOP vs. P conditions nor between the CM vs. Non-CM conditions. There was no significant TOP/CM interaction. Retention was not significantly different between the groups.

CONCLUSION

Topiramate is not efficacious for increasing cocaine abstinence in methadone patients.

The biology of Nociceptin/Orphanin FQ (N/OFQ) related to obesity, stress, anxiety, mood, and drug dependence

Nociceptin/Orphanin FQ (N/OFQ) is a 17 amino acid peptide that was deorphanized in 1995. The generation of specific agonists, antagonists and receptor deficient mice and rats has enabled progress in elucidating the biological functions of N/OFQ. Additionally, radio-imaging technologies have been advanced for investigation of this system in animals and humans. Together with traditional neurobehavioral techniques, these tools have been utilized to identify the biological significance of the N/OFQ system and its interacting partners. The present review focuses on the role of N/OFQ in the regulation of feeding, body weight homeostasis, stress, the stress-related psychiatric disorders of depression and anxiety, and in drug and alcohol dependence. Critical evaluation of the current scientific preclinical literature suggests that small molecule modulators of nociceptin opioid peptide receptors (NOP) might be useful in the treatment of diseases related to these biological functions. In particular, the literature data suggest that antagonism of NOP receptors will produce anti-obesity and antidepressant activities in humans. However, there are also contradictory data discussed. The current literature on the role of N/OFQ in anxiety and addiction, on the other hand points primarily to a role of agonist modulation being potentially therapeutic. Some drug-like molecules that function either as agonists or antagonists of NOP receptors have been optimized for human clinical study to test some of these hypotheses. The discovery of PET ligands for NOP receptors, combined with the pharmacological tools and burgeoning preclinical data set discussed here bodes well for a rapid advancement of clinical understanding and potential therapeutic benefit.

Treatment-like steady-state methadone in rats interferes with incubation of cocaine sensitization and associated alterations in gene expression

In a previous study, steady-state methadone treatment was found to prevent associative cocaine learning, as well as related decreases in mRNA expression of preprohypocretin/preproorexin (ppHcrt) in the lateral hypothalamus (LH) and dopamine D2 receptor (DR2) in the caudate-putamen (CP), and increases in mu-opioid receptor in the ventral striatum of rats. To investigate whether the same regimen of methadone exposure could prevent the incubation of cocaine sensitization and related alterations in gene expression, male Sprague-Dawley rats received 45 mg/kg/day steady-dose "binge" cocaine administration (IP) for 14 days followed by mini-pumps releasing 30 mg/kg/day methadone (SC). After 14 days of methadone, and a subsequent 10-day drug-free period, all rats were tested for sensitization (cocaine test dose: 15 mg/kg) and brain tissue was collected to quantify mRNA expression. Rats exposed to cocaine displayed cocaine-induced stereotypy at test, as well as enhanced ppHcrt mRNA in the LH and reduced DR2 mRNA in the CP. Importantly, these alterations were significantly reduced in rats treated with methadone following cocaine. These results suggest that steady-state methadone can interfere with the incubation of neuroadaptations underlying changes in behavioral responses to cocaine and cocaine-associated stimuli, and that these effects can be observed even after withdrawal from methadone.

Different physiological properties of spontaneous excitatory postsynaptic currents in nucleus accumbens shell neurons between adult and juvenile rats

Studies have demonstrated the changes of the physiological characteristics of nucleus accumbens (NAc) neurons with the postnatal development of rats. In the present study, spontaneous excitatory postsynaptic currents (sEPSCs) were recorded in the slices of NAc shell (NAcS) of adult and juvenile rats. Our results demonstrate that both the average amplitude of sEPSCs and the average frequency of sEPSCs in the NAcS slices of adult rats decreased significantly than that in juvenile rats. The average half width of sEPSCs in the NAcS slices in adult rats increased significantly than that in juvenile rats. The rise time of sEPSCs, the rise 50 time of sEPSCs and the 10-90 rise time of sEPSCs in the NAcS slices increased significantly in adult rats than that in juvenile rats. The decay time of sEPSCs in the NAcS slices also increased significantly in adult rats than that in juvenile rats. The above results strongly indicate that there are marked changes in the electrophysiological properties of single sEPSC in the NAcS slices of juvenile and adult rats.

The first universal opioid ligand, (2S)-2-[(5R,6R,7R,14S)-N-cyclopropylmethyl-4,5-epoxy-6,14-ethano-3-hydroxy-6-methoxymorphinan-7-yl]-3,3-dimethylpentan-2-ol (BU08028): characterization of the in vitro profile and in vivo behavioral effects in mouse models of acute pain and cocaine-induced reward

Certain behavioral features of buprenorphine, including a bell-shaped curve for antinociception and attenuation of alcohol consumption, are thought to be mediated by activation of nociceptin/orphanin FQ peptide (NOP) receptors, despite moderate affinity and low efficacy at NOP receptors. We hypothesized that ligands with buprenorphine's physical properties, but possessing increased NOP receptor affinity and efficacy, would improve the profile as a drug abuse medication and reduce addiction liability. Using this strategy, we designed several compounds with universally high affinity, i.e., less than 10 nM at μ, δ, κ, and NOP receptors. Among these, (2S)-2-[(5R,6R,7R,14S)-N-cyclopropylmethyl-4,5-epoxy-6,14-ethano-3-hydroxy-6-methoxymorphinan-7-yl]-3,3-dimethylpentan-2-ol (BU08028) has high affinity at all opioid receptors and increased NOP receptor efficacy in vitro in the [³⁵S]GTPγS binding assay, however, while still being a partial agonist. In vivo, BU08028 was evaluated in an acute thermal antinociception assay, for its ability to induce conditioned place preference (CPP), and for its effect on cocaine-induced CPP. BU08028 is a very potent long-lasting analgesic. It produces an increase in locomotor activity and a significant CPP. As a pretreatment to cocaine, BU08028 does not alter cocaine CPP but causes a further increase in cocaine-induced locomotor activity. The analgesic, rewarding, and stimulant effects are probably caused by μ receptor stimulation. It is likely that with BU08028, a partial agonist at both NOP and μ receptors, μ-mediated activity overpowers NOP-mediated effects. Thus, it is possible that a different buprenorphine analog that is a universal high-affinity opioid ligand but with "full agonist" activity at NOP may counteract traditional opioid-mediated effects such as antinociception and reward.

Preclinical evidence of new opioid modulators for the treatment of addiction

IMPORTANCE OF THE FIELD

Addiction to opiates is one of the most severe forms of substance dependence, and despite a variety of pharmacological approaches to treat it, relapse is observed in a high percentage of subjects. New pharmacological compounds are necessary to improve the outcome of treatments and reduce adverse side effects. Moreover, drugs that act on the opioid system can also be of benefit in the treatment of alcohol or cocaine addiction. AREA COVERED BY THIS REVIEW: Recent preclinical studies of pharmacological agents for the treatment of opiate addiction (2008 to the present date).

WHAT THE READER WILL GAIN

The reader will be informed of the latest drugs shown in animal models to modify dependence on opiates and the reinforcing effects of these drugs. In addition, reports of the latest studies to test these compounds in models of other drug addictions are reviewed.

TAKE HOME MESSAGE

The classic clinical pharmacotherapy for opiate dependence, involving mu-opioid receptor agonists or antagonists, has not yielded a high success rate in humans. In pharmacotherapy for opioid dependence, new options are emerging and different pharmacological strategies are now being tested.

Steady-state methadone blocks cocaine seeking and cocaine-induced gene expression alterations in the rat brain

To elucidate the effects of steady-state methadone exposure on responding to cocaine conditioned stimuli and on cocaine-induced alterations in central opioid, hypocretin/orexin, and D2 receptor systems, male Sprague-Dawley rats received intravenous infusions of 1 mg/kg/inf cocaine paired with an audiovisual stimulus over three days of conditioning. Then, mini pumps releasing vehicle or 30 mg/kg/day methadone were implanted (SC), and lever pressing for the stimulus was assessed in the absence of cocaine and after a cocaine prime (20 mg/kg, IP). It was found that rats treated with vehicle, but not methadone, responded for the cocaine conditioned stimulus and displayed elevated mu-opioid receptor mRNA expression in the nucleus accumbens core and basolateral amygdala, reduced hypocretin/orexin mRNA in the lateral hypothalamus, and reduced D2 receptor mRNA in the caudate-putamen. This is the first demonstration that steady-state methadone administered after cocaine exposure blocks cocaine-induced behavioral and neural adaptations.

Review. Psychological and neural mechanisms of relapse

Relapse, the resumption of drug taking after periods of abstinence, remains the major problem for the treatment of addiction. Even when drugs are unavailable for long periods or when users are successful in curbing their drug use for extended periods, individuals remain vulnerable to events that precipitate relapse. Behavioural studies in humans and laboratory animals show that drug-related stimuli, drugs themselves and stressors are powerful events for the precipitation of relapse. Molecular, neurochemical and anatomical studies have identified lasting neural changes that arise from mere exposure to drugs and other enduring changes that arise from learning about the relationship between drug-related stimuli and drug effects. Chronic drug exposure increases sensitivity of some systems of the brain to the effects of drugs and stressful events. These changes, combined with those underlying conditioning and learning, perpetuate vulnerability to drug-related stimuli. Circuits of the brain involved are those of the mesocorticolimbic dopaminergic system and its glutamatergic connections, and the corticotropin-releasing factor and noradrenergic systems of the limbic brain. This paper reviews advances in our understanding of how these systems mediate the effects of events that precipitate relapse and of how lasting changes in these systems can perpetuate vulnerability to relapse.