Assessment of the Abuse Liability of Synthetic Cannabinoid Agonists JWH-030, JWH-175, and JWH-176.

The emergence and use of synthetic cannabinoids have greatly increased in recent years. These substances are easily dispensed over the internet and on the streets. Some synthetic cannabinoids were shown to have abuse liability and were subsequently regulated by authorities. However, there are compounds that are still not regulated probably due to the lack of abuse liability studies. In the present study, we assessed the abuse liability of three synthetic cannabinoids, namely JWH-030, JWH-175, and JWH-176. The abuse liability of these drugs was evaluated in two of the most widely used animal models for assessing the abuse potential of drugs, the conditioned place preference (CPP) and self-administration (SA) test. In addition, the open-field test was utilized to assess the effects of repeated (7 days) treatment and abrupt cessation of these drugs on the psychomotor activity of animals. Results showed that JWH-175 (0.5 mg/kg), but not JWH-030 or JWH-176 at any dose, significantly decreased the locomotor activity of mice. This alteration in locomotor activity was only evident during acute exposure to the drug and was not observed during repeated treatment and abstinence. Similarly, only JWH-175 (0.1 mg/kg) produced significant CPP in rats. On the other hand, none of the drugs tested was self-administered by rats. Taken together, the present results indicate that JWH-175, but not JWH-030 and JWH-176, may have abuse potential. More importantly, our findings indicate the complex psychopharmacological effects of synthetic cannabinoids and the need to closely monitor the production, dispensation, and use of these substances.

Evaluation of the abuse potential of AM281, a new synthetic cannabinoid CB1 receptor antagonist.

AM281 (1-(2,4-dichlorophenyl)-5-(4-iodophenyl)-4-methyl-N-4-morpholinyl-1H-pyrazole-3-carboxamide) is a new synthetic cannabinoid CB1 receptor antagonist. Similar to other cannabinoid antagonists, AM281 has been suggested to have therapeutic indications. However, recent reports have suggested that cannabinoid CB1 receptor antagonists may share similar behavioral effects with other drugs of abuse such as cocaine and amphetamine. These reports cast doubts on the safety profile of AM281. Thus, in the present study we evaluated the abuse potential (rewarding and reinforcing effects) of AM281 through two of the most widely used animal models for assessing the abuse potential of drugs: the conditioned place preference (CPP) and self-administration (SA) tests. Experiments were performed in Sprague-Dawley rats in various dosages [CPP (0.1, 0.5 or 2.5mg/kg), SA (0.005, 0.025 or 0.1mg/kg/infusion)]. We also delved into the consequences of repeated drug exposure on the subsequent response to the drug. Thus, parallel experiments were carried out in rats pretreated with AM281 for 7 or 14 days. Our findings indicated that AM281, at any dose, did not induce CPP and SA in drug-naïve rats. Interestingly, significant CPP (0.5mg/kg of AM281), but not SA, was observed in 14 days pretreated rats. These observations suggest that AM281 per se has no or minimal rewarding and reinforcing properties, but alterations in neuronal functions and behavior due to repeated AM281 exposure may contribute in part to the abuse potential of this drug. In view of this finding, we advocate the careful use, monitoring, and dispensation of AM281.

Cigarette smoke exposure during adolescence enhances sensitivity to the rewarding effects of nicotine in adulthood, even after a long period of abstinence.

Adolescence is a period of enhanced vulnerability to the motivational properties of tobacco/cigarette smoking. Several studies have suggested that smoking initiation during this period will more likely lead to long-lasting cigarette or nicotine addiction. In the present study, we investigated the influences of adolescent cigarette smoke or nicotine exposure on the rewarding effects of nicotine, particularly whether these influences persist even after a long period of abstinence. Towards this, adolescent and adult Sprague-Dawley rats were repeatedly exposed to cigarette smoke or nicotine, for 14 days, and then were subjected to a 1-month abstinence period. Thereafter, the rewarding effects of nicotine were evaluated through the conditioned place preference (CPP) and self-administration (SA) tests. Even after a 1-month abstinence period, rats pre-exposed to either nicotine or cigarette smoke demonstrated enhanced CPP for the higher dose (0.6 mg/kg) of nicotine. Notably, cigarette smoke-preexposed adolescent rats, now adults, showed CPP for both 0.2 and 0.6 mg/kg dose of nicotine. Moreover, only these rats (pre-exposed to cigarette smoke during adolescence) showed significant acquisition and maintenance of nicotine (0.03 mg/kg/infusion) SA. These results suggest that cigarette smoke exposure during adolescence enhances sensitivity to the rewarding effects of nicotine in adulthood, even after a long period of abstinence. This may be a factor in the high rates of nicotine addiction and dependence observed in smokers who started during adolescence. More importantly, our findings highlight the enduring consequences of adolescent-onset cigarette smoking and the need to protect this vulnerable population.

Methoxetamine, a ketamine derivative, produced conditioned place preference and was self-administered by rats: Evidence of its abuse potential.

Methoxetamine (MXE) is an N-methyl-d-aspartate (NMDA) receptor antagonist that is chemically and pharmacologically similar to ketamine. Recently, there have been many reports regarding its use/misuse in humans which have resulted in serious or even fatal outcomes. Despite these reports, MXE is not controlled or regulated in many countries which may be partly due to the lack of scientific evidence regarding its abuse potential. Thus, in the present study we evaluated the abuse potential (rewarding and reinforcing effects) of MXE through the conditioned place preference (CPP) and self-administration (SA) tests in Sprague-Dawley rats. In addition, locomotor activity during the conditioning phase of the CPP was also analyzed. Ketamine was used as a reference drug. MXE (2.5 and 5mg/kg) induced significant CPP in rats, an effect comparable to that of ketamine (5mg/kg). Interestingly, MXE did not produce any locomotor alterations while ketamine decreased the locomotor activity of rats. In the SA test, rats showed modest self-administration of MXE (0.25, 0.5, 1.0mg/kg/infusion), while ketamine (0.5mg/kg/infusion) was robustly self-administered. These results demonstrate that MXE, similar to ketamine, has rewarding and reinforcing effects in rats. The present study strongly suggests that MXE has a potential for human abuse. In addition, the discrepant effects of MXE and ketamine on locomotor activity and rate of self-administration propose that the psychopharmacological effects of these drugs may diverge in some aspects. More importantly, this study advocates the careful monitoring and prompt regulation of MXE and its related substances.