Rationale-Opioid receptor agonists can enhance some effects of cannabinoid receptor agonists and cannabinoid receptor agonists can enhance some effects of opioid receptor agonists; however, the generality of these interactions is not established.Objective-This study examined interactions between the discriminative stimulus and antinociceptive effects of μ opioid receptor agonists and Δ 9 -tetrahydrocannabinol (THC) in rhesus monkeys.Results-Neither heroin nor morphine (i.v. or s.c.) altered the discriminative stimulus effects of THC in monkeys (n=5) discriminating 0.1 mg/kg THC i.v. In contrast, THC (s.c.) markedly attenuated the discriminative stimulus effect of morphine and heroin in non-dependent monkeys (n=4) discriminating 1.78 mg/kg morphine s.c. Doses of THC that attenuated the discriminative stimulus effects of morphine in non-dependent monkeys failed to modify the discriminative stimulus effects of morphine in morphine-dependent (5.6 mg/kg/12 hr) monkeys (n=4) discriminating 0.0178 mg/kg naltrexone s.c. THC also failed to modify the discriminative stimulus effects of naltrexone in morphine-dependent monkeys or the effects of midazolam in monkeys (n=4) discriminating 0.32 mg/kg midazolam s.c. Doses of THC (s.c.) that attenuated the discriminative stimulus effects of morphine in non-dependent monkeys enhanced the antinociceptive effects of morphine (s.c.) in non-dependent monkeys. While μ receptor agonists did not alter the discriminative stimulus effects of THC, in a context-dependent manner THC altered the effects of μ receptor agonists.Conclusion-That the same doses of THC enhance, attenuate, or do not affect morphine, depending on the condition, suggests that attenuation of morphine by THC can result from perceptual masking rather than common pharmacodynamic mechanisms or pharmacokinetic interactions. Keywordsopioid; THC; drug discrimination; rhesus monkey; perceptual masking; morphine; heroin; midazolam; naltrexone; antinociception Cannabinoid receptor agonists and μ opioid receptor agonists have some effects in common (e.g. antinociception): drugs from both classes have important therapeutic effects and some are abused (e.g., marijuana and heroin). Cannabinoid and opioid systems and drugs interact under a broad range of conditions, from cellular (Rios et al. 2006) to behavioral (e.g. Haney NIH Public AccessAuthor Manuscript Psychopharmacology (Berl). Author manuscript; available in PMC 2012 October 24.Published in final edited form as:Psychopharmacology (Berl). 2008 August ; 199(2): 199-208. doi:10.1007/s00213-008-1157-0. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript2007) measures of drug action. Understanding these interactions could be especially important for developing novel medications that might comprise both cannabinoid and opioid mechanisms and for understanding the factors that contribute to polydrug abuse.Especially relevant to polydrug abuse are studies on the combined effects of opioids and cannabinoids on behavioral measures that are related to and p...

Cocaine abuse and obesity are serious public health problems, and studies suggest that both dopamine and serotonin systems are involved in regulating the consumption of drugs and food. Lorcaserin has serotonin (5-HT) 2C receptor agonist actions, is approved by the U.S. Food and Drug Administration for treating obesity, and might be effective for treating cocaine abuse. These studies characterized the pharmacokinetic and behavioral profiles of lorcaserin (intragastric administration) and determined the effectiveness of lorcaserin to alter discriminative stimulus and reinforcing effects of cocaine (intravenous administration) in rhesus monkeys. Administered acutely, lorcaserin dosedependently increased the occurrence of yawning while decreasing spontaneous activity and operant responding for food. These effects appeared within 30-60 minutes of administration and began to dissipate by 240 minutes, a time course closely matching plasma concentrations of lorcaserin. In monkeys discriminating cocaine from saline, lorcaserin alone did not occasion cocaine-appropriate responding but shifted the cocaine dose-response curve to the right and down in two of three monkeys. When administered acutely, lorcaserin dosedependently decreased the rate at which monkeys responded for infusions of cocaine. When administered chronically, 3.2 mg/kg lorcaserin reduced the rate of cocaine-maintained responding by 50% for the duration of a 14-day treatment period. Together, these results show that lorcaserin attenuates the discriminative stimulus effects of cocaine after acute administration and the reinforcing effects of cocaine after acute and repeated administration, consistent with the view that it might have utility in treating cocaine abuse.

Opioid abuse remains a serious public health challenge, despite the availability of medications that are effective in some patients (naltrexone, buprenorphine, and methadone). This study explored the potential of a pseudoirreversible mu-opioid receptor antagonist [methocinnamox (MCAM)] as a treatment for opioid abuse by examining its capacity to attenuate the reinforcing effects of mu-opioid receptor agonists in rhesus monkeys. In one experiment, monkeys responded for heroin (n 5 5) or cocaine (n 5 4) under a fixed-ratio schedule. Another group (n 5 3) worked under a choice procedure with one alternative delivering food and the other alternative delivering the mu-opioid receptor agonist remifentanil. A third group (n 5 4) responded for food and physiologic parameters were measured via telemetry. The effects of MCAM were determined in all experiments and, in some cases, were compared with those of naltrexone.When given immediately before sessions, naltrexone dosedependently decreased responding for heroin and decreased choice of remifentanil while increasing choice of food, with responding returning to baseline levels 1 day after naltrexone injection. MCAM also decreased responding for heroin and decreased choice of remifentanil while increasing choice of food; however, opioid-maintained responding remained decreased for several days after treatment. Doses of MCAM that significantly decreased opioid-maintained responding did not decrease responding for cocaine or food. MCAM did not impact heart rate, blood pressure, body temperature, or activity at doses that decreased opioid self-administration. Because MCAM selectively attenuates opioid self-administration for prolonged periods, this novel drug could be a safe and effective alternative to currently available treatments for opioid abuse.

One consequence of the ongoing opioid epidemic is a large number of overdose deaths. Naloxone reverses opioid-induced respiratory depression; however, its short duration of action limits the protection it can provide. Methocinnamox (MCAM) is a novel opioid receptor antagonist with a long duration of action. This study examined the ability of MCAM to prevent and reverse the respiratory-depressant effects (minute volume [V E ]) of heroin in five monkeys. MCAM (0.32 mg/kg) was given before heroin to determine whether it prevents respiratory depression; heroin dose-effect curves were generated 1, 2, 4, and 8 days later, and these effects were compared with those of naltrexone (0.032 mg/kg). Heroin dose dependently decreased V E . MCAM and naltrexone prevented respiratory depression, shifting the heroin dose-effect curve rightward at least 10-fold. MCAM, but not naltrexone, attenuated these effects of heroin for 4 days. MCAM (0.1-0.32 mg/kg) was given 30 minutes after heroin to determine whether it reverses respiratory depression; heroin dose-effect curves were generated 1, 2, 4, 8, and 16 days later, and these effects were compared with those of naloxone (0.0032-0.1 mg/kg). MCAM and naloxone reversed respiratory depression within 30 minutes, although only MCAM antagonized heroin on subsequent days. Thus, MCAM prevents and reverses respiratory depression, the potentially lethal effect of heroin, longer than opioid receptor antagonists currently in use. Because of its sustained effects, MCAM might provide more effective rescue from and protection against the fatal respiratorydepressant effects of opioids, thereby improving treatment of opioid overdose.