Rationale Alleviating addiction to tobacco products could prevent millions of deaths. Investigating novel compounds selectively targeting α4β2 nAChRs hypothesized to have a key role in the rewarding effects of nicotine may be a useful approach for future treatment. Objectives The present study was designed to evaluate 2-fluoro-3-(4-nitrophenyl) deschloroepibatidine (4-nitro-PFEB), a potent competitive antagonist of neuronal α4β2 nAChRs, in several animal models related to nicotine reward: drug discrimination, intracranial self-stimulation (ICSS), conditioned place preference, and limited access to self-administration. Methods Long Evans rats were trained in a two-lever discrimination procedure to discriminate 0.4 mg/kg nicotine (s.c.) from saline. Male Sprague–Dawley rats were stereotaxically implanted with electrodes and trained to respond for direct electrical stimulation of the medial forebrain bundle. ICR mice were evaluated using an unbiased place preference paradigm, and finally, male Wistar rats were implanted with intrajugular catheters and tested for nicotine self-administration under limited access (1 h/day). Results 4-Nitro-PFEB attenuated the discriminative stimulus effects of nicotine, but alone did not produce nicotine-like discriminative stimulus effects. Nicotine-induced facilitation of ICSS reward thresholds was reversed by 4-nitro-PFEB, which alone had no effect on thresholds. 4-Nitro-PFEB also blocked the conditioned place preference produced by nicotine, but alone had no effect on conditioned place preference. Finally, 4-nitro-PFEB dose-dependently decreased nicotine self-administration. Conclusions These results support the hypothesis that neuronal α4β2 nAChRs play a key role in mediating the rewarding effects of nicotine and further suggest that targeting α4β2 nAChRs may yield a potential candidate for the treatment of nicotine dependence.

Marijuana’s effects in humans are most often reported as intoxicating or therapeutic; yet, some humans report dysphoria or other negative affects. To evaluate whether differences in endocannabinoid levels might account for this variability, the present study examined whether sensitivity to cannabinoids changed when anandamide (AEA) metabolism was inhibited through administration of phenylmethyl sulfonyl fluoride (PMSF) a nonspecific irreversible amidase inhibitor. Male Long Evans rats were trained to discriminate 3 mg/kg Δ9-tetrahydrocannabinol (THC) versus vehicle in 2-lever drug discrimination procedure. ED50s for THC and CP 55,940 were lower when administered with PMSF than alone. PMSF administration also potentiated characteristic cannabimimetic effects of THC in ICR mice. Potentiation of AEA’s in vivo effects by PMSF were also observed, primarily a consequence of PMSF inhibition of the enzyme fatty acid amide hydrolase. Enhancement of the effects of THC and CP55,940 through this mechanism is unlikely, as these cannabinoids are predominantly metabolized through the P450 system. Mass spectrometry revealed that, in the presence of THC, endogenous AEA levels in the brain decreased and that this decrease was prevented by PMSF, suggesting that increased AEA levels may have acted additively with exogenously administered cannabinoids to increase cannabimimetic effects. These findings may account for the varying affect in response to marijuana in humans or cannabinoids in animals while also suggesting that metabolic inhibitors of AEA may potentiate marijuana’s intoxicating effects in humans.

The partial a4b2 nicotinic acetylcholine receptor (nAChR) agonist, varenicline, shares some but not all preclinical effects of nicotine. This unique profile may be crucial to its effectiveness as a therapeutic aid for smoking cessation. The present study evaluated the ability of varenicline to alter brain stimulation reward (BSR) and to alter nicotine facilitation of BSR in a rate-independent intracranial selfstimulation discrete trial procedure. Male Sprague-Dawley rats were stereotaxically implanted with electrodes and trained to respond for direct electrical stimulation aimed at the medial forebrain bundle. Once stable thresholds were established, nicotine, varenicline, and mecamylamine were tested alone to determine their effects on BSR. Subsequently, challenge tests for nicotine facilitation of BSR with nonthreshold altering doses of varenicline and mecamylamine were conducted. This study demonstrated that nicotine dose-dependently facilitated BSR, whereas varenicline did not. Similarly to mecamylamine, varenicline reversed nicotine facilitation of BSR, suggesting that nAChRs mediate the effects of nicotine on BSR. Thus, specifically targeting a4b2 nAChRs inhibits the ability of nicotine to facilitate BSR. The efficacy of varenicline as a treatment for smoking cessation may be related to its unique ability to reduce the rewarding effects of nicotine while not producing rewarding effects alone, a critical consideration in effective drug replacement therapies. Drug Dev Res, 72:310-314, 2011.

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