Neuronal nicotinic ␣7 acetylcholine receptors (␣7nAChRs) are expressed primarily in the brain and are implicated in modulating many cognitive functions (e.g., attention, working and episodic memory). Not surprisingly, much effort has been committed to the development of molecules acting at ␣7nAChRs as potential therapies for a variety of central nervous system diseases (e.g., Alzheimer's). N-[(3S)-1-azabicyclo[2.2.2]oct-3-yl]-1H-indazole-3-carboxamide hydrochloride (RG3487) binds potently to the human ␣7nAChR (K i ϭ 6 nM), in which it acts as a partial agonist (63-69% of acetylcholine) as assessed by whole-cell patch-clamp recordings in both oocytes and QM7 cell lines. RG3487 activates human ␣7nAChRs with an EC 50 of 0.8 M (oocytes) and 7.7 M (QM7 cells). RG3487 also exhibits antagonist properties at the serotonin 3 receptor [IC 50 ϭ 2.8 nM (oocytes), 32.7 nM (N1E-115 cells)]. In vivo, RG3487 improved object recognition memory in rats after acute [minimally effective dose (MED) 1.0 mg/kg p.o.] or repeated (10 day) administration at brain and plasma concentrations in the low-nanomolar range. Spatial learning deficits in age-impaired rats were reversed after RG3487 administration (MED: 0.03 mg/kg i.p.) as evaluated in the Morris water maze task. In the prepulse inhibition (PPI) of startle model of sensorimotor gating, RG3487 improved apomorphine-induced deficits in PPI performance (MED: 0.03 mg/kg i.p.) and reversed phencyclidine-induced impairments in an attentional set-shifting model of executive function (MED: Յ0.03 mg/kg i.p.). Cumulative evidence from these studies indicates RG3487 is a novel and potent ␣7nAChR partial agonist that improves cognitive performance and sensorimotor gating.

An effective treatment for age-related cognitive deficits remains an unmet medical need. Currently available drugs for the symptomatic treatment of Alzheimer's disease or other dementias have limited efficacy. This may be due to their action at only one of the many neurotransmitter systems involved in the complex mechanisms that underlie cognition. An alternative approach would be to target second messenger systems that are utilized by multiple neurotransmitters. Cyclic adenosine monophosphate (cAMP) is a second messenger that plays a key role in biochemical processes that regulate the cognitive process of memory consolidation. Prolongation of cAMP signals can be accomplished by inhibiting phosphodiesterases (PDEs). Eleven PDE families, comprised of more than 50 distinct members, are currently known. This review summarizes the evidence demonstrating that rolipram, a selective inhibitor of cAMP-selective PDE4 enzymes, has positive effects on learning and memory in animal models. These data provide support for the general approach of second messenger modulation as a potential therapy for cognitive dysfunction, and specifically suggest that PDE4 inhibitors may have utility for improving the symptoms of cognitive decline associated with neurodegenerative and psychiatric diseases.

Varenicline, a partial α4β2 and full α7 nicotinic receptor agonist, has been shown to inhibit nicotine self-administration and nicotine-induced increases in extracellular dopamine in the nucleus accumbens. In the present study, we investigated whether varenicline inhibits nicotine-enhanced electrical brain-stimulation reward (BSR), and if so, which receptor subtypes are involved. Systemic administration of nicotine (0.25–1.0 mg/kg, i.p.) or varenicline (0.03–3 mg/kg, i.p.) produced biphasic effects, with low doses producing enhancement (e.g., decreased BSR threshold), and high doses inhibiting BSR. Pretreatment with low dose (0.03–1.0 mg/kg) varenicline dose-dependently attenuated nicotine (0.25 or 0.5 mg/kg)-enhanced BSR. The BSR-enhancing effect produced by varenicline was blocked by mecamylamine (a high affinity nicotinic receptor antagonist) or dihydro-β-erythroidine (a relatively selective nicotinic α4-containing receptor antagonist), but not methyllycaconitine (a selective α7 receptor antagonist), suggesting an effect mediated by activation of α4β2 receptors. This suggestion is supported by findings that the α4β2 receptor agonist SIB-1765F produced a dose-dependent enhancement of BSR, while pretreatment with SIB-1765F attenuated nicotine (0.5 mg/kg)-enhanced BSR. In contrast, the selective α7 receptor agonist ARR-17779, altered neither BSR itself nor nicotine-enhanced BSR, at any dose tested. These findings suggest that: 1) varenicline inhibits nicotine-enhanced BSR, supporting its use as a smoking cessation aid; and 2) varenicline-enhanced BSR by itself and varenicline's anti-nicotine effects are mediated by activation of α4β2, but not α7, receptors.

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Rationale Disturbances in information processing and cognitive function are key features of schizophrenia. Nicotinic α7 acetylcholine receptors (α7-nAChR) are involved in sensory gating and cognition, thereby representing a viable therapeutic strategy. Objectives and methods We investigated the effects of GTS-21, an α7-nAChR partial agonist, on prepulse inhibition (PPI) of acoustic startle in two pharmacologic impairment models in Wistar male rats: NMDA-glutamate receptor antagonism by MK-801 and dopamine receptor agonism by apomorphine. The cognitive effects of GTS-21 were assessed using the object recognition task (ORT) at short (3 h) and long (48 h) delays in Sprague-Dawley male rats. Pharmacological specificity was assessed by methyllycaconitine (MLA) coadministration with GTS-21. Results In the PPI task, GTS-21 (1–10 mg/kg) alone did not alter the PPI response or startle amplitude. Coadministration of GTS-21 with MK-801 (0.1 mg/kg) or apomorphine (0.5 mg/kg) abolished the pharmacologic-induced PPI impairment as did the antipsychotics clozapine (5.0 mg/kg) and haloperidol (0.3 mg/kg). MK-801 alone increased startle amplitude which was blocked by GTS-21. In the ORT, GTS-21 (0.1–10 mg/kg) reversed the MK-801 (0.08 mg/kg)-induced memory deficit at the 3 h delay and enhanced memory at the 48 h delay, an effect abolished by MLA (0.313–5 mg/kg). Conclusions The results extend our preclinical pharmacological understanding of GTS-21 to include the ability of GTS-21 to modulate NMDA-glutamate receptor function, in vivo. Given the role of NMDA-glutamate receptor involvement in schizophrenia, α7-nAChR agonists may represent a novel treatment strategy for the pathophysiological deficits of schizophrenia and other psychiatric disorders.

The genotoxins ethyl chloride (EtCl) and methyl chloride (MeCl) were generated during the preparation of the hydrochloride salts of two tertiary amines in the presence of ethanol and methanol, respectively. In EtOH five batches of a tertiary amine hydrochloride were prepared on 0.3-18 kg scale using 37% aqueous HCl; residual EtCl was detected at less than 10 ppm in each batch. The preparation of the hydrochloride salt of another tertiary amine in MeOH on a 3 kg scale produced salt with 11-12 ppm of MeCl, and these higher levels precipitated investigations into controlling the levels of residual MeCl in batches of the HCl salt of the second amine. Four rework procedures were developed to reduce the level of MeCl in one batch of HCl salt. Generating the salts at a lower temperature (10 °C) was the key parameter to minimize the concentration of these impurities in this drug candidate when HCl was charged as 37% aqueous HCl. Control of the process was demonstrated by preparing a 30 kg batch containing 1 ppm of MeCl without rework processing; this level of MeCl is well within the guideline of e1.5 µg for the daily dosage of this drug candidate. The analytical methods to detect EtCl and MeCl, which were critical for the development of these processes, are also described.

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