Incorporation of the ␣5 nicotinic acetylcholine receptor (nAChR) subunit can greatly influence nAChR function without altering receptor number. Although few animal studies have assessed the role of the ␣5 nAChR in nicotine-mediated behaviors, recent evidence suggests an association between polymorphisms in the ␣5 nAChR gene and nicotine dependence phenotypes in humans. Thus, additional studies are imperative to elucidate the role and function of the ␣5 nAChR subunit in nicotine dependence. Using ␣5(Ϫ/Ϫ) mice, the current study aimed to examine the role of ␣5 nAChRs in the initial pharmacological effects of nicotine, nicotine reward using the conditioned place preference model, and the discriminative effects of nicotine using a two-lever drug discrimination model. 86 Rb ϩ efflux and 125 I-epibatidine binding assays were conducted to examine the effect of ␣5 nAChR subunit deletion on expression and activity of functional nAChRs. Results show that ␣5(Ϫ/Ϫ) mice are less sensitive to the initial effects of nicotine in antinociception, locomotor activity, and hypothermia measures and that the ␣5 nAChR is involved in nicotine reward. Alternatively, ␣5(Ϫ/Ϫ) mice did not differ from wild-type littermates in sensitivity to the discriminative stimulus effects of nicotine. Furthermore, deletion of the ␣5 nAChR subunit resulted in a statistically significant decrease in function in the thalamus and hindbrain, but the decreases noted in spinal cord were not statistically significant. Receptor number was unaltered in all areas tested. Taken together, results of the study suggest that ␣5 nAChRs are involved in nicotine-mediated behaviors relevant to development of nicotine dependence.

Cannabis sativa (marijuana plant) contains myriad cannabinoid compounds; yet, investigative attention has focused almost exclusively on Δ 9 -tetrahydrocannabinol (THC), its primary psychoactive substituent. Interest in modulation of THC's effects by these other cannabinoids [e.g., cannabidiol (CBD)] has been stimulated anew by recent approval by Canada of Sativex (a 1:1 dose ratio combination of CBD:THC) for the treatment of multiple sclerosis. The goal of this study was to determine the degree to which THC's abuse-related effects were altered by co-administration of CBD. To this end, CBD and THC were assessed alone and in combination in a two-lever THC discrimination procedure in Long-Evans rats and in a conditioned place preference/aversion (CPP/ A) model in ICR mice. CBD did not alter the discriminative stimulus effects of THC at any CBD:THC dose ratio tested. In contrast, CBD, at CBD:THC dose ratios of 1:1 and 1:10, reversed CPA produced by acute injection with 10 mg/kg THC. When administered alone, CBD did not produce effects in either procedure. These results suggest that CBD, when administered with THC at therapeutically relevant ratios, may ameliorate aversive effects (e.g., dysphoria) often associated with initial use of THC alone. While this effect may be beneficial for therapeutic usage of a CBD:THC combination medication, our discrimination results showing that CBD did not alter THC's discriminative stimulus effects suggest that CBD:THC combination medications may also produce THC-like subjective effects at these dose ratios.

Primarily, rats have served as subjects in Δ 9 -tetrahydrocannabinol's (THC) discrimination studies although other species such as monkeys and pigeons have been used. While the introduction of the knockout and transgenic mice has vastly stimulated the study of the discriminative stimulus effects of drugs there is only a single published report of mice trained to discriminate THC. Thus, this study extended those results by providing a systematic replication that THC serves as an effective discriminative stimulus in mice and by further investigating the mechanisms of action involved in the THC discrimination model in the mouse. Male C57BL/6J mice were trained to discriminate 10 mg/kg THC from vehicle in 2-lever drug discrimination. THC fully and dose dependently substituted for itself. Cannabinoid indoles, except one with low cannabinoid CB 1 receptor affinity, substituted for THC. Anandamide failed to substitute for THC when administered alone but completely substituted when administered with the non-specific fatty acid amide hydrolase inhibitor, phenylmethylsulphonyl fluoride. As expected, nicotine failed to substitute for THC. Lastly, the cannabinoid CB 1 receptor antagonist rimonabant blocked THC's discriminative stimulus effects.Taken together these studies demonstrate THC's ability to produce discriminative stimulus effects as well as demonstrate its pharmacological specificity and mechanism of action in a two-lever drug discrimination mouse model.

Bupropion is an atypical antidepressant that also has utility as a smoking cessation aid. Hydroxybupropions are major metabolites of bupropion and are believed to contribute to antidepressant and perhaps smoking cessation activities. Because bupropion metabolism is more similar in humans and mice than in humans and rats, the present study investigated effects of hydroxybupropion enantiomers in mouse behavioral models measuring various aspects of nicotine dependence. Bupropion and (2S,3S)-hydroxybupropion, but not (2R,3R)-hydroxybupropion, significantly decreased the development of nicotine reward as measured in the conditioned place preference and withdrawal paradigm in mice. Bupropion and both of its metabolites reversed affective and somatic withdrawal signs in nicotine-dependent mice, but the (2S,3S)-hydroxymetabolite had higher potency. Bupropion and (2S,3S)-, but not (2R,3R)-hydroxybupropion, produced partial substitution for nicotine in drug discrimination tests. Our findings support the hypothesis that the effects of bupropion on measures of nicotine dependence reflect actions of bupropion itself, its hydroxymetabolites, or a combination and suggest that the (2S,3S)-hydroxy isomer is the most active principle, making it a potentially better drug candidate for smoking cessation than bupropion.

Rationale Salvinorin A, the primary psychoactive derivative of the hallucinogenic herb Salvia divinorum, is a potent and highly selective kappa-opioid receptor (KOR) agonist. Several recent studies, however, have suggested endocannabinoid system mediation of some of its effects. Objectives This study represents a systematic examination of this hypothesis. Methods Salvinorin A was isolated from S. divinorum and was evaluated in a battery of in vitro and in vivo procedures designed to detect cannabinoid activity, including CB1 receptor radioligand and [35S]GTPγS binding, calcium flux assay, in vivo cannabinoid screening tests, and drug discrimination. Results Salvinorin A did not bind to nor activate CB1 receptors. In vivo salvinorin A produced pronounced hypolocomotion and antinociception (and to a lesser extent, hypothermia). These effects were blocked by the selective KOR antagonist, JDTic, but not by the CB1 receptor antagonist rimonabant. Interestingly, however, rimonabant attenuated KOR activation stimulated by U69,593 in a [35S]GTPγS assay. Salvinorin A did not substitute for Δ9-tetrahydrocannabinol (THC) in mice trained to discriminate THC. Conclusions These findings suggest that similarities in the pharmacological effects of salvinorin A and those of cannabinoids are mediated by its activation of KOR rather than by any direct action of salvinorin A on the endocannabinoid system. Further, the results suggest that rimonabant reversal of salvinorin A effects in previous studies may be explained in part by rimonabant attenuation of KOR activation.

The endogenous cannabinoid system has been noted for its therapeutic potential, as well as the psychoactivity of cannabinoids such as Δ9-tetrahydrocannabinol (THC). However, less is known about the psychoactivity of anandamide (AEA), an endocannabinoid ligand. Thus, the goals of this study were to establish AEA as a discriminative stimulus in transgenic mice lacking fatty acid amide hydrolase (i.e., FAAH −/− mice unable to rapidly metabolize AEA), evaluate whether THC or oleamide, a fatty acid amide, produced AEA-like responding, and assess for CB1 mediation of AEA’s discriminative stimulus. Mice readily discriminated between 6 mg/kg AEA and vehicle in a two-lever drug discrimination task. AEA dose-dependently generalized to itself. THC elicited full AEA-like responding, whereas oleamide failed to substitute. The CB1 antagonist rimonabant attenuated AEA- and THC-induced AEA-appropriate responding, demonstrating CB1 mediation of AEA’s discriminative stimulus. These findings suggest that, in the absence of FAAH, AEA produces intoxication comparable to THC, and consequently to marijuana.

Anandamide (AEA), an endocannabinoid (eCB), shares some, but not all, pharmacological properties with THC. This pharmacological dissociation is in part due to the rapid catabolism of AEA by fatty acid amide hydrolase (FAAH). With inhibitors of FAAH, studies have demonstrated that AEA shares THC's discriminative stimulus (DS) properties providing the leading evidence for the involvement of the eCB system in the subjective effects of marijuana. However, this remains to be fully elucidated without demonstrating that these DS effects are cross symmetrical. Thus, the current study investigated whether FAAH (−/−) mice, those lacking the ability to breakdown AEA, could be trained to discriminate AEA (6 mg/kg) versus VEH in a 2‐lever discrimination. AEA was successfully trained and dose dependently generalized. THC fully and dose dependently substituted whereas oleamide, another FAA, failed to substitute. THC's and AEA's DS effects were blocked by SR141716. This study demonstrates that: AEA's DS can be trained in FAAH (−/−) mice, THC and AEA cross generalize, and these effects are CB1 receptor mediated. Oleamide's lack of AEA‐like DS effects provides further support for the specificity of this model. Taken together, this research demonstrates that THC or AEA activation of the eCB system results in similar DS effects. Research supported by NIH grant DA‐09789.