Summary α6-containing (α6*) nicotinic ACh receptors (nAChRs) are selectively expressed in dopamine (DA) neurons and participate in cholinergic transmission. We generated and studied mice with gain-of-function α6* nAChRs, which isolate and amplify cholinergic control of DA transmission. In contrast to gene knockouts or pharmacological blockers, which show necessity, we show that activating α6* nAChRs and DA neurons is sufficient to cause locomotor hyperactivity. α6L9’S mice are hyperactive in their home cage and fail to habituate to a novel environment. Selective activation of α6* nAChRs with low doses of nicotine, by stimulating DA but not GABA neurons, exaggerates these phenotypes and produces a hyperdopaminergic state in vivo. Experiments with additional nicotinic drugs show that altering agonist efficacy at α6* provides fine-tuning of DA release and locomotor responses. α6*-specific agonists or antagonists may, by targeting endogenous cholinergic mechanisms, provide a new method for manipulating DA transmission in Parkinson’s disease, nicotine dependence, or attention deficit hyperactivity disorder.

The molecular mechanisms of ␣7 nicotinic acetylcholine receptor (nAChR)-mediated neuroprotection remain unclear. In this study we provide evidence that nicotine stimulation of ␣7 nAChR transduces signals to phosphatidylinositol 3-kinase and Akt via Janus kinase 2 (JAK2) in a cascade, which results in neuroprotection. Exposure to ␤-amyloid results in the activation of the apoptotic enzyme caspase-3 and cleavage of the DNA-repairing enzyme poly-(ADP-ribose) polymerase. This cascade is inhibited by nicotine through JAK2 activation, and these effects are blocked by preincubation with the JAK2-specific inhibitor AG-490. We also found that pretreatment of cells with angiotensin II blocks the nicotine-induced activation of JAK2 via the AT 2 receptor and completely prevents ␣7 nAChR-mediated neuroprotective effects further suggesting a pivotal role for JAK2. These findings identify novel mechanisms of receptor interactions relevant to neuronal viability and suggest novel therapeutic strategies to optimize neuroprotection.The cholinergic deficit in Alzheimer's disease (AD) 1 has been clearly established and is the basis for the current symptomatic strategy. There is an early and significant depletion of high affinity nicotinic receptors in the brains of Alzheimer's patients (1), and a number of studies have shown cognitive improvement in rodent and primates including humans following administration of ligands targeting nicotinic acetylcholine receptor (nAChR) (2). In addition to their known symptomatic effects, neuronal nicotinic ligands have shown neuroprotective activity in vitro (3) and in vivo (4) suggesting an additional potential for disease modification.The ␣7 nAChR forms functional homomeric ligand-gated ion channels that promote rapidly desensitizing Ca 2ϩ influx, is widely expressed throughout the mammalian brain, and has been implicated in sensory gating, cognition, and neuroprotection (5). In addition, nicotine-induced neuroprotection against ␤-amyloid-induced toxicity is suppressed by ␣-bungarotoxin (␣-Bgt), and the selective ␣7 nAChR agonist, anabasine-derived 3-(4)-dimethylaminocinnamylidine, exerts cytoprotective effects (6, 7). Furthermore, a recent study (8), has reported that the levels of phosphorylated Akt, an effector of phosphatidylinositol 3-kinase (PI-3-K), are increased by nicotine and that the nicotine-induced cytoprotective effects are suppressed by the PI-3-K inhibitors (LY294002 and wortmannin). These findings suggest that the ␣7 nAChR transduces signals to PI-3-K in a cascade, which ultimately contributes to a neuroprotective effect against A␤-(1-42).In comparison to the findings above, another study (9) has shown that whereas nicotine activates the PI-3-K neuroprotective cascade, A␤-(1-42) chronically activates the mitogen-activated protein kinase (MAPK) cascade via the hippocampal ␣7 nAChR. The investigators suggest that this chronic activation of the MAPK pathway by A␤-(1-42) eventually leads to the down-regulation of MAPK which then sets up a positive feedback for A␤ accumulation and de...

In recent years the etiopathology of a number of debilitating diseases such as type 2 diabetes, arthritis, atherosclerosis, psoriasis, asthma, cystic fibrosis, sepsis, and ulcerative colitis has increasingly been linked to runaway cytokine-mediated inflammation. Cytokine-based therapeutic agents play a major role in the treatment of these diseases. However, the temporospatial changes in various cytokines are still poorly understood and attempts to date have focused on the inhibition of specific cytokines such as TNF-α. As an alternative approach, a number of preclinical studies have confirmed the therapeutic potential of targeting alpha7 nicotinic acetylcholine receptor-mediated anti-inflammatory effects through modulation of proinflammatory cytokines. This “cholinergic anti-inflammatory pathway” modulates the immune system through cholinergic mechanisms that act on alpha7 receptors expressed on macrophages and immune cells. If the preclinical findings translate into human efficacy this approach could potentially provide new therapies for treating a broad array of intractable diseases and conditions with inflammatory components.

Mammalian brain expresses multiple nicotinic acetylcholine receptor (nAChR) subtypes that differ in subunit composition, sites of expression and pharmacological and functional properties. Among known subtypes of receptors, α4β2* and α6β2*-nAChR have the highest affinity for nicotine (where * indicates possibility of other subunits). The α4β2*-nAChRs are widely distributed, while α6β2*-nAChR are restricted to a few regions. Both subtypes modulate release of dopamine from the dopaminergic neurons of the meso-accumbens pathway thought to be essential for reward and addiction. α4β2*-nAChR also modulate GABA release in these areas.Identification of selective compounds would facilitate study of nAChR subtypes. An improved understanding of the role of nAChR subtypes may help in developing more effective smoking cessation aids with fewer side effects than current therapeutics. We have screened a series of nicotinic compounds that vary in the distance between the pyridine and the cationic center, in steric bulk, and in flexibility of the molecule. These compounds were screened using membrane binding and synaptosomal function assays, or recordings from GH4C1 cells expressing hα7, to determine affinity, potency and efficacy at four subtypes of nAChRs found in brain, α4β2*, α6β2*, α7 and α3β4*. In addition, physiological assays in gain-of-function mutant mice were used to assess in vivo activity at α4β2* and α6β2*-nAChRs. This approach has identified several compounds with agonist or partial agonist activity that display improved selectivity for α6β2*-nAChR.

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