Please cite only the published version using the reference above.See http://opus.bath.ac.uk/ for usage policies.Please scroll down to view the document. In the conditioned place preference extinction and reinstatement method, a combination of 0.3 mg/kg buprenorphine and 1.0 mg/kg naltrexone completely blocked drug-primed reinstatement in cocaine-conditioned rats (conditioned with 3 mg/kg cocaine, drug prime was 3 mg/kg cocaine), and attenuated drug-primed reinstatement in morphine-conditioned rats (conditioned with 5 mg/kg morphine, drug prime was 1.25 mg/kg morphine). These data add to the growing evidence that a buprenorphine/naltrexone combination may be protective against relapse in a polydrug abuse situation.

Emerging clinical and preclinical evidence suggests that a compound displaying high affinity for μ, κ, and δ opioid (MOP, KOP, and DOP) receptors and antagonist activity at each, coupled with moderate affinity and efficacy at nociceptin opioid peptide (NOP) receptors will have utility as a relapse prevention agent for multiple types of drug abuse. Members of the orvinol family of opioid ligands have the desired affinity profile but have typically displayed substantial efficacy at MOP and or KOP receptors. In this study it is shown that a phenyl ring analogue (1d) of buprenorphine displays the desired profile in vitro with high, nonselective affinity for the MOP, KOP, and DOP receptors coupled with moderate affinity for NOP receptors. In vivo, 1d lacked any opioid agonist activity and was an antagonist of both the MOP receptor agonist morphine and the KOP receptor agonist ethylketocyclazocine, confirming the desired opioid receptor profile in vivo.

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A BSTRACT Introduction: κ-opioid receptor (KOPr) system has been linked to relapse to many substances, especially opioids. Positive responses were recently reported in morphine and methamphetamine (polydrug)-dependent mice treated with buprenorphine and naltrexone, a functional κ antagonist. Objectives: This study aimed to determine the specific brain region that is responsive to KOPr treatment following polydrug dependence. Materials and Methods: The polydrug-dependent mice model was developed using conditioned place preference (CPP) method. Following successful withdrawal phase, the mice were treated with 0.3 mg/kg buprenorphine and 1.0 mg/kg naltrexone. Four brain regions (hippocampus, prefrontal cortex, amygdala, and striatum) were investigated using immunohistochemistry technique. This is to quantify the changes in KOPr expression in each major brain region that was primarily involved in addiction neurocircuits of many substances. Unpaired Student’s t test was used to analyze all results, where P < 0.05 is considered significant. Results: The results showed that treatment with buprenorphine and naltrexone successfully attenuated relapse in 60% of mice ( n = 14). A significant upregulation of KOPr was detected in striatum at the end of post-withdrawal phase ( P < 0.01, n = 12). This treatment successfully suppressed KOPr in striatum ( P < 0.001, n = 12), which supports the positive results seen in the CPP setting. No significant changes were observed in other brain regions studied. Conclusion: The hyperactivity of striatum suggests that the affected brain region following KOPr antagonist treatment is the region that primarily controls the drug rewarding activity, in which nucleus accumbens is located. This indicates that manipulation of KOPr system is one of the potential targets to treat morphine- or methamphetamine-dependence problem.

Introduction: An upregulation of the kappa opioid receptor (KOR) system during drug preoccupation stage in addiction cycle will cause dysphoria among addicts which can lead to relapse. Therefore, KOR antagonism treatment might hold the key to prevent relapse. In this study, we aim to identify the exact addiction’s stage in which KOR antagonist can be given. Methods: Using a conditioned place preference (CPP) model, adult male Swiss albino mice were divided into two major groups. The first group received treatment at the initial stage of morphine withdrawal (7.5 mg/kg, i.p) while the second group received treatment after complete abstinence was achieved. Each major groups were further divided into two treatment groups (n=8-12), either received a functional KOR antagonist (0.3 mg/kg buprenorphine/ 1 mg/kg naltrexone combination, i.p) or a selective KOR antagonist (10 mg/kg nor-BNI, i.p) prior to morphine priming (2.5 mg/kg, i.p). All data were analyzed using paired sample t-test. Results: The results showed that relapse was successfully attenuated in the groups that received KOR antagonists only after complete abstinence was successfully achieved (not significantly different from their baseline). However, the mice developed unusual sign of behavior sensitization (intermittent freezing, licking) when buprenorphine/naltrexone combination was given at initial stage of withdrawal. Conclusions: Our initial findings suggest that KOR antagonism might be beneficial only after the addicts achieved complete abstinence to prevent future druginduced relapse. Brain study should be conducted to explain the unusual behavior seen when the drug intervention is given at an earlier stage of withdrawal.