Section I. The cholinergic system

Physiological roles of CNS muscarinic receptors gained from knockout mice

Because the five muscarinic acetylcholine receptor subtypes have overlapping distributions in many CNS tissues, and because ligands with a high degree of selectivity for a given subtype long remained elusive, it has been difficult to determine the physiological functions of each receptor. Genetically engineered knockout mice, in which one or more muscarinic acetylcholine receptor subtype has been inactivated, have been instrumental in identifying muscarinic receptor functions in the CNS, at the neuronal, circuit, and behavioral level. These studies revealed important functions of muscarinic receptors modulating neuronal activity and neurotransmitter release in many brain regions, shaping neuronal plasticity, and affecting functions ranging from motor and sensory function to cognitive processes. As gene targeting technology evolves including the use of conditional, cell type specific strains, knockout mice are likely to continue to provide valuable insights into brain physiology and pathophysiology, and advance the development of new medications for a range of conditions such as Alzheimer's disease, Parkinson's disease, schizophrenia, and addictions, as well as non-opioid analgesics. This article is part of the Special Issue entitled 'Neuropharmacology on Muscarinic Receptors'.

Effect of Estradiol on Neurotrophin Receptors in Basal Forebrain Cholinergic Neurons: Relevance for Alzheimer's Disease

The basal forebrain is home to the largest population of cholinergic neurons in the brain. These neurons are involved in a number of cognitive functions including attention, learning and memory. Basal forebrain cholinergic neurons (BFCNs) are particularly vulnerable in a number of neurological diseases with the most notable being Alzheimer's disease, with evidence for a link between decreasing cholinergic markers and the degree of cognitive impairment. The neurotrophin growth factor system is present on these BFCNs and has been shown to promote survival and differentiation on these neurons. Clinical and animal model studies have demonstrated the neuroprotective effects of 17β-estradiol (E2) on neurodegeneration in BFCNs. It is believed that E2 interacts with neurotrophin signaling on cholinergic neurons to mediate these beneficial effects. Evidence presented in our recent study confirms that altering the levels of circulating E2 levels via ovariectomy and E2 replacement significantly affects the expression of the neurotrophin receptors on BFCN. However, we also showed that E2 differentially regulates neurotrophin receptor expression on BFCNs with effects depending on neurotrophin receptor type and neuroanatomical location. In this review, we aim to survey the current literature to understand the influence of E2 on the neurotrophin system, and the receptors and signaling pathways it mediates on BFCN. In addition, we summarize the physiological and pathophysiological significance of E2 actions on the neurotrophin system in BFCN, especially focusing on changes related to Alzheimer's disease.

Locus Ceruleus Norepinephrine Release: A Central Regulator of CNS Spatio-Temporal Activation?

Norepinephrine (NE) is synthesized in the Locus Coeruleus (LC) of the brainstem, from where it is released by axonal varicosities throughout the brain via volume transmission. A wealth of data from clinics and from animal models indicates that this catecholamine coordinates the activity of the central nervous system (CNS) and of the whole organism by modulating cell function in a vast number of brain areas in a coordinated manner. The ubiquity of NE receptors, the daunting number of cerebral areas regulated by the catecholamine, as well as the variety of cellular effects and of their timescales have contributed so far to defeat the attempts to integrate central adrenergic function into a unitary and coherent framework. Since three main families of NE receptors are represented-in order of decreasing affinity for the catecholamine-by: α2 adrenoceptors (α2Rs, high affinity), α1 adrenoceptors (α1Rs, intermediate affinity), and β adrenoceptors (βRs, low affinity), on a pharmacological basis, and on the ground of recent studies on cellular and systemic central noradrenergic effects, we propose that an increase in LC tonic activity promotes the emergence of four global states covering the whole spectrum of brain activation: (1) sleep: virtual absence of NE, (2) quiet wake: activation of α2Rs, (3) active wake/physiological stress: activation of α2- and α1-Rs, (4) distress: activation of α2-, α1-, and β-Rs. We postulate that excess intensity and/or duration of states (3) and (4) may lead to maladaptive plasticity, causing-in turn-a variety of neuropsychiatric illnesses including depression, schizophrenic psychoses, anxiety disorders, and attention deficit. The interplay between tonic and phasic LC activity identified in the LC in relationship with behavioral response is of critical importance in defining the short- and long-term biological mechanisms associated with the basic states postulated for the CNS. While the model has the potential to explain a large number of experimental and clinical findings, a major challenge will be to adapt this hypothesis to integrate the role of other neurotransmitters released during stress in a centralized fashion, like serotonin, acetylcholine, and histamine, as well as those released in a non-centralized fashion, like purines and cytokines.

Further optimization of the mGlu5 PAM clinical candidate VU0409551/JNJ-46778212: Progress and challenges towards a back-up compound

This Letter describes the progress and challenges in the continued optimization of the mGlu5 positive allosteric modulator (PAM) clinical candidate VU0490551/JNJ-46778212. While many analogs addressed key areas for improvement, no one compound possessed the amalgamation of improvements needed within the (2(phenoxymethyl)-6,7-dihydrooxazolo[5,4-c]pyridine-5(4H)-yl(aryl)methanone scaffold to advance as a back-up clinical candidate. However, many analogs displayed excellent solubility and physiochemical properties, and were active in the amphetamine-induced hyperlocomotion (AHL) model. Moreover, the SAR was robust for this series of PAMs, and both polar and hydrogen-bond donors were found to be tolerated, leading to analogs with overall attractive profiles and good ligand efficiencies.

Enhanced histamine H2 excitation of striatal cholinergic interneurons in L-DOPA-induced dyskinesia

Levodopa is the most effective therapy for the motor deficits of Parkinson's disease (PD), but long term treatment leads to the development of L-DOPA-induced dyskinesia (LID). Our previous studies indicate enhanced excitability of striatal cholinergic interneurons (ChIs) in mice expressing LID and reduction of LID when ChIs are selectively ablated. Recent gene expression analysis indicates that stimulatory H2 histamine receptors are prefentially expressed on ChIs at high levels in the striatum, and we tested whether a change in H2 receptor function might contribute to the elevated excitability in LID. Using two different mouse models of PD (6-hydroxydopamine lesion and Pitx3^ak/ak mutation), we chronically treated the animals with either vehicle or L-DOPA to induce dyskinesia. Electrophysiological recordings indicate that histamine H2 receptor-mediated excitation of striatal ChIs is enhanced in mice expressing LID. Additionally, H2 receptor blockade by systemic administration of famotidine decreases behavioral LID expression in dyskinetic animals. These findings suggest that ChIs undergo a pathological change in LID with respect to histaminergic neurotransmission. The hypercholinergic striatum associated with LID may be dampened by inhibition of H2 histaminergic neurotransmission. This study also provides a proof of principle of utilizing selective gene expression data for cell-type-specific modulation of neuronal activity.

Cholinergic modulation of stimulus-driven attentional capture

Distraction is one of the main problems encountered by people with degenerative diseases that are associated with reduced cortical cholinergic innervations. We examined the effects of donepezil, a cholinesterase inhibitor, on stimulus-driven attentional capture. Reflexive attention shifts to a distractor are usually elicited by abrupt peripheral changes. This bottom-up shift of attention to a salient item is thought to be the result of relatively inflexible hardwired mechanisms. Thirty young male participants were randomly allocated to one of two groups: placebo first/donepezil second session or the opposite. They were asked to locate a target appearing above and below fixation whilst a peripheral distractor moved abruptly (motion-jitter attentional capture condition) or not (baseline condition). A classical attentional capture effect was observed under placebo: moving distractors interfered with the task in slowing down response times as compared to the baseline condition with fixed distractors. Increased interference from moving distractors was found under donepezil. We suggest that attentional capture in our paradigm likely involved low level mechanisms such as automatic reflexive orienting. Peripheral motion-jitter elicited a rapid reflexive orienting response initiated by a cholinergic signal from the brainstem pedunculo-pontine nucleus that activates nicotinic receptors in the superior colliculus.

Further optimization of the M5 NAM MLPCN probe ML375: tactics and challenges

This Letter describes the continued optimization of the MLPCN probe ML375, a highly selective M5 negative allosteric modulator (NAM), through a combination of matrix libraries and iterative parallel synthesis. True to certain allosteric ligands, SAR was shallow, and the matrix library approach highlighted the challenges with M5 NAM SAR within in this chemotype. Once again, enantiospecific activity was noted, and potency at rat and human M5 were improved over ML375, along with slight enhancement in physiochemical properties, certain in vitro DMPK parameters and CNS distribution. Attempts to further enhance pharmacokinetics with deuterium incorporation afforded mixed results, but pretreatment with a pan-P450 inhibitor (1-aminobenzotriazole; ABT) provided increased plasma exposure.

Development of a highly potent, novel M5 positive allosteric modulator (PAM) demonstrating CNS exposure: 1-((1H-indazol-5-yl)sulfoneyl)-N-ethyl-N-(2-(trifluoromethyl)benzyl)piperidine-4-carboxamide (ML380)

A functional high throughput screen identified a novel chemotype for the positive allosteric modulation (PAM) of the muscarinic acetylcholine receptor (mAChR) subtype 5 (M₅). Application of rapid analog, iterative parallel synthesis efficiently optimized M₅ potency to arrive at the most potent M₅ PAMs prepared to date and provided tool compound 8n (ML380) demonstrating modest CNS penetration (human M₅ EC₅₀ = 190 nM, rat M₅ EC₅₀ = 610 nM, brain to plasma ratio (K_p) of 0.36).

Discovery, synthesis and characterization of a highly muscarinic acetylcholine receptor (mAChR)-selective M5-orthosteric antagonist, VU0488130 (ML381): a novel molecular probe

Of the five G-protein-coupled muscarinic acetylcholine receptors (mAChRs; M1-M5), M5 is the least explored and understood due to a lack of mAChR subtype-selective ligands. We recently performed a high-throughput functional screen and identified a number of weak antagonist hits that are selective for the M5 receptor. Here, we report an iterative parallel synthesis and detailed molecular pharmacologic profiling effort that led to the discovery of the first highly selective, central nervous system (CNS)-penetrant M5-orthosteric antagonist, with sub-micromolar potency (hM5 IC50=450 nM, hM5 Ki=340 nM, M1-M4 IC50>30 μM), enantiospecific inhibition, and an acceptable drug metabolism and pharmacokinetics (DMPK) profile for in vitro and electrophysiology studies. This compound will be a powerful tool and molecular probe for the further investigation into the role of M5 in addiction and other diseases.

Discovery of the first M5-selective and CNS penetrant negative allosteric modulator (NAM) of a muscarinic acetylcholine receptor: (S)-9b-(4-chlorophenyl)-1-(3,4-difluorobenzoyl)-2,3-dihydro-1H-imidazo[2,1-a]isoindol-5(9bH)-one (ML375)

A functional high throughput screen and subsequent multidimensional, iterative parallel synthesis effort identified the first muscarinic acetylcholine receptor (mAChR) negative allosteric modulator (NAM) selective for the M5 subtype. ML375 is a highly selective M5 NAM with submicromolar potency (human M5 IC50 = 300 nM, rat M5 IC50 = 790 nM, M1-M4 IC50 > 30 μM), excellent multispecies PK, high CNS penetration, and enantiospecific inhibition.

Discovery of novel N-substituted oxindoles as selective m1 and m4 muscarinic acetylcholine receptors partial agonists

Activation of the M1 and M4 muscarinic acetylcholine receptors is thought to play an important role in improving the symptoms of schizophrenia. However, discovery of selective agonists for these receptors has been a challenge, considering the high sequence homology and conservation of the orthosteric acetylcholine binding site among muscarinic acetylcholine receptor subtypes. We report in this study the discovery of novel N-substituted oxindoles as potent muscarinic acetylcholine receptor partial agonists selective for M1 and M4 over M2, M3, and M5. Among these oxindoles, compound 1 showed high selectivity for the M1 and M4 receptors with remarkable penetration into the central nervous system. Compound 1 reversed methamphetamine- and apomorphine-induced psychosis-like behaviors with low potency to extrapyramidical and peripheral side effects.

Inhibition of acetylcholinesterase activity in brain and behavioral analysis in adult rats after chronic administration of fenproporex

Fenproporex is an amphetamine-based anorectic and it is rapidly converted in vivo into amphetamine. It elevates the levels of extracellular dopamine in the brain. Acetylcholinesterase is a regulatory enzyme which is involved in cholinergic synapses and may indirectly modulate the release of dopamine. Thus, we investigated whether the effects of chronic administration of fenproporex in adult rats alters acquisition and retention of avoidance memory and acetylcholinesterase activity. Adult male Wistar rats received repeated (14 days) intraperitoneal injection of vehicle or fenproporex (6.25, 12.5 or 25 mg/kg i.p.). For behavioral assessment, animals were submitted to inhibitory avoidance (IA) tasks and continuous multiple trials step-down inhibitory avoidance (CMIA). Acetylcholinesterase activity was measured in the prefrontal cortex, hippocampus, hypothalamus and striatum. The administration of fenproporex (6.25, 12.5 and 25 mg/kg) did not induce impairment in short and long-term IA or CMIA retention memory in rats. In addition, longer periods of exposure to fenproporex administration decreased acetylcholinesterase activity in prefrontal cortex and striatum of rats, but no alteration was verified in the hippocampus and hypothalamus. In conclusion, the present study showed that chronic fenproporex administration decreased acetylcholinesterase activity in the rat brain. However, longer periods of exposure to fenproporex did not produce impairment in short and long-term IA or CMIA retention memory in rats.

Muscarinic Acetylcholine Receptor Subtypes as Potential Drug Targets for the Treatment of Schizophrenia, Drug Abuse and Parkinson's Disease

The neurotransmitter dopamine plays important roles in modulating cognitive, affective, and motor functions. Dysregulation of dopaminergic neurotransmission is thought to be involved in the pathophysiology of several psychiatric and neurological disorders, including schizophrenia, Parkinson's disease and drug abuse. Dopaminergic systems are regulated by cholinergic, especially muscarinic, input. Not surprisingly, increasing evidence implicates muscarinic acetylcholine receptor-mediated pathways as potential targets for the treatment of these disorders classically viewed as "dopamine based". There are five known muscarinic receptor subtypes (M(1) to M(5)). Due to their overlapping expression patterns and the lack of receptor subtype-specific ligands, the roles of the individual muscarinic receptors have long remained elusive. During the past decade, studies with knock-out mice lacking specific muscarinic receptor subtypes have greatly advanced our knowledge of the physiological roles of the M(1)-M(5) receptors. Recently, new ligands have been developed that can interact with allosteric sites on different muscarinic receptor subtypes, rather than the conventional (orthosteric) acetylcholine binding site. Such agents may lead to the development of novel classes of drugs useful for the treatment of psychosis, drug abuse and Parkinson's disease. The present review highlights recent studies carried out using muscarinic receptor knock-out mice and new subtype-selective allosteric ligands to assess the roles of M(1), M(4), and M(5) receptors in various central processes that are under strong dopaminergic control. The outcome of these studies opens new perspectives for the use of novel muscarinic drugs for several severe disorders of the CNS.

The effects of galantamine on nicotine withdrawal-induced deficits in contextual fear conditioning in C57BL/6 mice

Current smoking cessation aids are relatively ineffective at maintaining abstinence during withdrawal. Nicotine withdrawal is associated with a variety of symptoms including cognitive deficits and targeting these deficits may be a useful strategy for maintaining abstinence. Galantamine is an acetylcholinesterase inhibitor and allosteric modulator of nicotinic acetylcholine receptors (nAChRs) with cognitive enhancing effects that may alleviate cognitive deficits associated with nicotine withdrawal. The effects of galantamine on nicotine withdrawal-induced deficits in contextual fear conditioning in C57BL/6 mice were examined. An initial acute dose-response experiment revealed that 0.5 and 1mg/kg galantamine had no effect on fear conditioning. To determine if galantamine would reverse nicotine withdrawal-related deficits in contextual fear conditioning, mice were implanted with osmotic mini-pumps that delivered chronic saline or 6.3mg/kg/d nicotine for 12 days and then pumps were removed. Training and testing of fear conditioning occurred 24 and 48 h later, respectively. Nicotine withdrawal disrupted contextual fear conditioning, which was reversed with 1 but not 0.5mg/kg galantamine. Across all conditions in both studies 2mg/kg galantamine led to high levels of freezing that were likely due to nonspecific effects. The ability of galantamine to reverse nicotine withdrawal-deficits in contextual conditioning is likely mediated through enhanced levels of acetylcholine via inhibition of acetylcholinesterase, potentiation of hippocampal α4β2* nAChRs, or both. The present study suggests that acetylcholinesterase inhibitors and/or drugs that act as allosteric modulators of nAChRs might be targets for smoking cessation aids because they may alleviate withdrawal symptoms such as cognitive deficits that can lead to relapse.

Gene regulation in the rat prefrontal cortex after learning with or without cholinergic insult

The prefrontal cortex is essential for a wide variety of higher functions, including attention and memory. Cholinergic neurons are thought to be of prime importance in the modulation of these processes. Degeneration of forebrain cholinergic neurons has been linked to several neurological disorders. The present study was designed to identify genes and networks in rat prefrontal cortex that are associated with learning and cholinergic-loss-memory deficit. Affymetrix microarray technology was used to screen gene expression changes in rats submitted or not to 192 IgG-saporin immunolesion of cholinergic basal forebrain and trained in spatial/object novelty tasks. Results showed learning processes were associated with significant expression of genes, which were organized in several clusters of highly correlated genes and would be involved in biological processes such as intracellular signaling process, transcription regulation, and filament organization and axon guidance. Memory loss following cortical cholinergic deafferentation was associated with significant expression of genes belonging to only one clearly delineated cluster and would be involved in biological processes related to cytoskeleton organization and proliferation, and glial and vascular remodeling, i.e., in processes associated with brain repair after injury.

The mouse homeobox gene Gbx2 is required for the development of cholinergic interneurons in the striatum

Mammalian forebrain cholinergic neurons are composed of local circuit neurons in the striatum and projection neurons in the basal forebrain. These neurons are known to arise from a common pool of progenitors that primarily resides in the medial ganglionic eminence (MGE). However, little is known about the genetic programs that differentiate these two types of cholinergic neurons. Using inducible genetic fate mapping, here we examined the developmental fate of cells that express the homeodomain transcription factor Gbx2 in the MGE. We show that the Gbx2 lineage-derived cells that undergo tangential migration exclusively give rise to almost all cholinergic interneurons in the striatum, whereas those undergoing radial migration mainly produce noncholinergic neurons in the basal forebrain. Deletion of Gbx2 throughout the mouse embryo or specifically in the MGE results in abnormal distribution and significant reduction of cholinergic neurons in the striatum. We show that early-born (before embryonic day 12.5) cholinergic interneurons preferentially populate the lateral aspect of the striatum and mature earlier than late-born (after embryonic day 12.5) neurons, which normally reside in the medial part of the striatum. In the absence of Gbx2, early-born striatal cholinergic precursors display abnormal neurite outgrowth and increased complexity, and abnormally contribute to the medial part of the caudate-putamen, whereas late-born striatal cholinergic interneurons are mostly missing. Together, our data demonstrate that Gbx2 is required for the development of striatal cholinergic interneurons, perhaps by regulating tangential migration of the striatal cholinergic precursors.

Cognitive function as an emerging treatment target for marijuana addiction

Cannabis is the most widely used illicit substance in the world, and demand for effective treatment is increasing. However, abstinence rates following behavioral therapies have been modest, and there are no effective pharmacotherapies for the treatment of cannabis addiction. We propose a novel research agenda and a potential treatment strategy, based on observations that both acute and chronic exposure to cannabis are associated with dose-related cognitive impairments, most consistently in attention, working memory, verbal learning, and memory functions. These impairments are not completely reversible upon cessation of marijuana use, and moreover may interfere with the treatment of marijuana addiction. Therefore, targeting cognitive impairment associated with chronic marijuana use may be a promising novel strategy for the treatment of marijuana addiction. Preclinical studies suggest that medications enhancing the cholinergic transmission may attenuate cannabis-induced cognitive impairments, but these cognitive enhancing medications have not been examined in controlled human studies. Preliminary evidence from individuals addicted to other drugs suggests that computerized cognitive rehabilitation may also have utility to improve cognitive function in marijuana users. Future clinical studies optimally designed to measure cognitive function as well as drug use behavior would be needed to test the efficacy of these treatments for marijuana addiction.

Gene expression profile in rat hippocampus with and without memory deficit

The cholinergic neuronal system, through its projections to the hippocampus, plays an important role in learning and memory. The aim of the study was to identify genes and networks in rat hippocampus with and without memory deficit. Genome-scale screening was used to analyze gene expression changes in rats submitted or not to intraparenchymal injection of 192 IgG-saporin and trained in spatial/object novelty tasks. Results showed learning processes were associated with significant expression of genes that could be grouped into several clusters of similar expression profiles and that are involved in biological functions, namely lipid metabolism, signal transduction, protein metabolism and modification, and transcription regulation. Memory loss following hippocampal cholinergic deafferentation was associated with significant expression of genes that did not show similar cluster organization. Only one cluster of genes could be identified; it included genes that would be involved in tissue remodeling. More important, most of the genes significantly altered in lesioned rats were down-regulated.

Cognitive enhancement as a pharmacotherapy target for stimulant addiction

BACKGROUND

No medications have been proven to be effective for cocaine and methamphetamine addiction. Attenuation of drug reward has been the main strategy for medications development, but this approach has not led to effective treatments. Thus, there is a need to identify novel treatment targets in addition to the brain reward system.

AIM

To propose a novel treatment strategy for stimulant addiction that will focus on medications enhancing cognitive function and attenuating drug reward.

METHODS

Pre-clinical and clinical literature on potential use of cognitive enhancers for stimulant addiction pharmacotherapy was reviewed.

RESULTS AND CONCLUSIONS

Cocaine and methamphetamine users show significant cognitive impairments, especially in attention, working memory and response inhibition functions. The cognitive impairments seem to be predictive of poor treatment retention and outcome. Medications targeting acetylcholine and norepinephrine are particularly well suited for enhancing cognitive function in stimulant users. Many cholinergic and noradrenergic medications are on the market and have a good safety profile and low abuse potential. These include galantamine, donepezil and rivastigmine (cholinesterase inhibitors), varenicline (partial nicotine agonist), guanfacine (alpha(2)-adrenergic agonist) and atomoxetine (norepinephrine transporter inhibitor). Future clinical studies designed optimally to measure cognitive function as well as drug use behavior would be needed to test the efficacy of these cognitive enhancers for stimulant addiction.

Cholinergic functioning in stimulant addiction: implications for medications development

Acetylcholine, the first neurotransmitter discovered, participates in many CNS functions, including sensory and motor processing, sleep, nociception, mood, stress response, attention, arousal, memory, motivation and reward. These diverse cholinergic effects are mediated by nicotinic- and muscarinic-type cholinergic receptors (nAChR and mAChR, respectively). The goal of this review is to synthesize a growing literature that supports the potential role of acetylcholine as a treatment target for stimulant addiction. Acetylcholine interacts with the dopaminergic reward system in the ventral tegmental area, nucleus accumbens and prefrontal cortex. In the ventral tegmental area, both nAChR and mAChR stimulate the dopaminergic system. In the nucleus accumbens, cholinergic interneurons integrate cortical and subcortical information related to reward. In the prefrontal cortex, the cholinergic system contributes to the cognitive aspects of addiction. Preclinical studies support a facilitative role of nicotinic receptor agonists in the development of stimulant addiction. In contrast, nonselective muscarinic receptor agonists seem to have an inhibitory role. In human studies, acetylcholinesterase inhibitors, which increase synaptic acetylcholine levels, have shown promise for the treatment of stimulant addiction. Further studies testing the efficacy of cholinergic medications for stimulant addiction are warranted.

Combined scopolamine and ethanol treatment results in a locomotor stimulant response suggestive of synergism that is not blocked by dopamine receptor antagonists

BACKGROUND

Muscarinic acetylcholine receptors (mAChRs) are well positioned to mediate ethanol's stimulant effects. To investigate this possibility, we examined the effects of scopolamine, a receptor subtype nonselective mAChR antagonist, on ethanol-induced stimulation in genotypes highly sensitive to this effect of ethanol. We also investigated whether the dopamine D1-like receptor antagonist, SCH-23390 or the dopamine D2-like receptor antagonist, haloperidol, could block the extreme stimulant response found following co-administration of scopolamine and ethanol.

METHODS

Scopolamine (0, 0.0625, 0.125, 0.25, or 0.5 mg/kg) was given 10 minutes prior to saline or ethanol (0.75 to 2 g/kg) to female FAST (Experiment I) or DBA/2J (Experiment II) mice that were then tested for locomotion for 30 minutes. In Experiments III and IV, respectively, SCH-23390 (0, 0.015, or 0.03 mg/kg) was given 10 minutes prior, and haloperidol (0, 0.08, or 0.16 mg/kg) was given 2 minutes prior, to scopolamine (0 or 0.5 mg/kg), followed 10 minutes later by saline or ethanol (1.5 g/kg) and female DBA/2J mice were tested for locomotion for 30 minutes.

RESULTS

FAST and DBA/2J mice displayed a robust enhancement of the locomotor effects of ethanol following pretreatment with scopolamine that was suggestive of synergism. SCH-23390 had no effect on the response to the scopolamine + ethanol drug combination, nor did it attenuate ethanol- or scopolamine-induced locomotor activity. Haloperidol, while attenuating the effects of ethanol, was not able to block the effects of scopolamine or the robust response to the scopolamine-ethanol drug combination.

CONCLUSIONS

These results suggest that while muscarinic receptor antagonism robustly enhances acute locomotor stimulation to ethanol, dopamine receptors are not involved in the super-additive interaction of scopolamine and ethanol treatment. They also suggest that in addition to cautions regarding the use of alcohol when scopolamine is clinically prescribed due to enhanced sedative effects, enhanced stimulation may also be a concern.

Potentiation of the nicotinic acetylcholine receptor by aluminum in mammalian neurons

Aluminum (Al(3+)), a known neurotoxic substance, has long been implicated in the pathogenesis of Alzheimer's disease and other neurodegenerative diseases. Al(3+) targets many ligand-gated and voltage-gated ion channels and modulates their functions. In the present study, the actions of Al(3+) on the nicotinic acetylcholine receptor (nAChR) were investigated by whole-cell patch clamp technique in acutely isolated rat trigeminal ganglion neurons. We observed that Al(3+) potentiated nicotine-evoked inward currents in a concentration-dependent manner (10-1000 microM). The effects of Al(3+) on nicotine-evoked currents were voltage independent. Al(3+) appeared to increase the affinity of nicotine to nAChR but not the efficacy. Al(3+) reduced the agonist concentration producing a half-maximal response (EC(50)) for nicotine from 74.4+/-1.9 microM to 32.9+/-2.6 microM, but did not alter the threshold nor maximal response. On the contrary, another trivalent cation, Ga(3+), had little effect on nicotine-evoked currents. The present results indicated that Al(3+) enhanced the function of nAChR and this potentiation might underlie the neurological alteration induced by Al(3+).

Cholinergic circuits and signaling in the pathophysiology of schizophrenia

Central cholinergic signaling has long been associated with aspects of memory, motivation, and mood, each affected functions in neuropsychiatric disorders such as schizophrenia. In this chapter, we review evidence related to the core hypothesis that dysregulation of central cholinergic signaling contributes to the pathophysiology of schizophrenia. Although central cholinergic circuits are resistant to simplification-particularly when one tries to parse the contributions of various classes of cholinergic receptors to disease related phenomena--the potential role of ACh signaling in Schizophrenia pathophysiology deserves careful consideration for prospective therapeutics. The established role of cholinergic circuits in attentional tuning is considered along with recent work on how the patterning of cholinergic activity may modulate corticostriatal circuits affected in schizophrenia.

2-Fluoro-3-(4-nitro-phenyl)deschloroepibatidine is a novel potent competitive antagonist of human neuronal alpha4beta2 nAChRs

A patch-clamp technique in a whole-cell configuration was used to examine the functional activity of recently developed 2-fluoro-3-(substituted phenyl)deschloroepibatidine analogs on two major subtypes of neuronal nicotinic acetylcholine receptors (nAChRs), alpha4beta2 and alpha3beta4, that predominate in the central and peripheral nervous systems, respectively. These epibatidine analogs have been shown previously to possess high binding affinity to alpha4beta2 but not to alpha7 nAChRs and to inhibit nicotine-induced analgesia in behavioral pain tests. The 2-fluoro-3-(4-nitro-phenyl)deschloroepibatidine (4-nitro-PFEB) exhibited the most pronounced antagonist activity among these analogs when tested electrophysiologically on alpha4beta2 nAChRs. It inhibited acetylcholine (ACh)-induced currents in a concentration-dependent manner with an IC(50) value of 0.1 microM and produced complete inhibition at approximately 1 microM concentration. 4-Nitro-PFEB at 0.1 microM concentration produced a 4-fold rightward shift in the ACh concentration-response curve without altering maximum ACh-induced response. This inhibitory effect of 4-nitro-PFEB was voltage- and use-independent and was partially reversible at its 1 microM concentration. The rise and decay kinetics of ACh-induced currents was not altered in the presence of 4-nitro-PFEB. In contrast to alpha4beta2 nAChRs, this compound did not affect alpha3beta4 nAChR-mediated currents at < or =1 microM (IC(50) approximately 63.9 microM). Overall, these functional data agree with previous binding and behavioral findings and suggest collectively that 4-nitro-PFEB is the most effective and selective antagonist of alpha4beta2 versus alpha3beta4 and alpha7 nAChRs among the tested analogs, acting on alpha4beta2 nAChR through a competitive mechanism with a potency 17-fold higher than that of dihydro-beta-erythroidine.