Herein we describe a novel series of compounds from which varenicline (1, 6,7,8,9-tetrahydro-6,10-methano-6H-pyrazino[2,3-h][3]benzazepine) has been identified for smoking cessation. Neuronal nicotinic acetylcholine receptors (nAChRs) mediate the dependence-producing effects of nicotine. We have pursued alpha4beta2 nicotinic receptor partial agonists to inhibit dopaminergic activation produced by smoking while simultaneously providing relief from the craving and withdrawal syndrome that accompanies cessation attempts. Varenicline displays high alpha4beta2 nAChR affinity and the desired in vivo dopaminergic profile.

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Casein kinase I (CKI) is an essential component of the biological clock, phosphorylating PER proteins, and in doing so regulating their turnover and nuclear entry in oscillator cells of the suprachiasmatic nucleus (SCN). Although hereditary decreases in PER phosphorylation have been well characterized, little is known about the consequences of acute enzyme inhibition by pharmacological means. A novel reagent, 4-[3-cyclohexyl-5-(4-fluoro-phenyl)-3H-imidazol-4-yl]-pyrimidin-2-ylamine (PF-670462), proved to be both a potent (IC 50 ϭ 7.7 Ϯ 2.2 nM) and selective (Ͼ30-fold with respect to 42 additional kinases) inhibitor of CKI in isolated enzyme preparations; in transfected whole cell assays, it caused a concentrationrelated redistribution of nuclear versus cytosolic PER. When tested in free-running animals, 50 mg/kg s.c. PF-670462 produced robust phase delays when dosed at circadian time (CT)9 (Ϫ1.97 Ϯ 0.17 h). Entrained rats dosed in normal light-dark (LD) and then released to constant darkness also experienced phase delays that were dose-and time of dosing-dependent. PF-670462 yielded only phase delays across the circadian cycle with the most sensitive time at CT12 when PER levels are near their peak in the SCN. Most importantly, these druginduced phase delays persisted in animals entrained and maintained in LD throughout the entire experiment; re-entrainment to the prevailing LD required days in contrast to the rapid elimination of the drug (t 1/2 ϭ 0.46 Ϯ 0.04 h). Together, these results suggest that inhibition of CKI yields a perturbation of oscillator function that forestalls light as a zeitgeber, and they demonstrate that pharmacological tools such as PF-670462 may yield valuable insight into clock function.Circadian behavior is mediated by a timed sequence of intracellular events, genomic in nature, occurring in mammals within so-called pacemaker cells of the suprachiasmatic nucleus (SCN) (Antle and Silver, 2005). Here, rhythmicity relies on a common theme of precisely regulated gene transcription and translation as a means to perpetuate cycling, and in doing so, to dictate the timing of downstream events (Reppert and Weaver, 2001; for review, see Schibler, 2006, among others). Clock-related proteins rise and fall in concentration as a consequence of nuclear and cytosolic feedback loops, adjusted daily to maintain reproducible cycling timed at roughly 24-h intervals. Light is the primary zeitgeber, or "time-giver", in this process, and its actions on loop dynamics are thought to comprise the most important external influence on pacemaker function.In its simplest conception, the oscillations of the clock can run using four genes, Period (Per1, Per2) and Cryptochrome (Cry1, Cry2), that are activated in early circadian day by heterodimeric complexes of CLOCK and BMAL1 (Griffin et al., 1999;Kume et al., 1999;Cermakian and Boivin, 2003). Translated PER partners in the cytoplasm with CRY, the resultant heterodimer, readily gaining nuclear entry and opposing activation by Clock and BMAL1. A feedback loop is...

Several drugs have recently been reported to induce rapid antidepressant effects in clinical trials and rodent models. Although the cellular mechanisms involved remain unclear, reports suggest that increased glutamate transmission contributes to these effects. Here, we demonstrate that the antidepressant-like efficacy of three unique drugs, with reported rapid onset antidepressant properties, is coupled with a rapid transient rise in glutamate cycling in medial prefronal cortex (mPFC) of awake rats as measured by ex vivo 1H-[13C]-nuclear magnetic resonance spectroscopy. Rats were acutely pre-treated by intraperitoneal injection with a single dose of ketamine (1,3,10,30,80mg/kg), Ro 25-6981 (1,3,10mg/kg), scopolamine (5,25,100μg/kg) or vehicle (controls). At fixed times after drug injection animals received an intravenous infusion of [1,6-13C2]glucose for 8 min to enrich brain amino acid pools with 13C, followed by rapid euthanasia. The mPFC was dissected, extracted with ethanol and metabolite 13C enrichments measured. We found a clear dose dependent effect of ketamine and Ro 25-6981 on behavior and the percent of 13C-enrichment of glutamate, glutamine and GABA. Further, we also found an effect of scopolamine on both cycling and behavior. These studies demonstrate that three pharmacologically distinct classes of drugs, clinically related through their reported rapid antidepressant actions, share the common ability to rapidly stimulate glutamate cycling at doses pertinent for their antidepressant-like efficacy. We conclude that increased cycling precedes the antidepressant action at behaviorally effective doses and suggests the rapid change in cycling could be used to predict efficacy of novel agents or identify doses with antidepressant activity.

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