Alterations in Neuronal Nicotinic Acetylcholine Receptors in the Pathogenesis of Various Cognitive Impairments.

Cognitive impairment is a typical symptom of both neurodegenerative and certain other diseases. In connection with these different pathologies, the etiology and neurological and metabolic changes associated with cognitive impairment must differ. Until these characteristics and differences are understood in greater detail, pharmacological treatment of the different forms of cognitive impairment remains suboptimal. Neurotransmitter receptors, including neuronal nicotinic acetylcholine receptors (nAChRs), dopamine receptors, and glutamine receptors, play key roles in the functions and metabolisms of the brain. Among these, the role of nAChRs in the development of cognitive impairment has attracted more and more attention. The present review summarizes what is presently known concerning the structure, distribution, metabolism, and function of nAChRs, as well as their involvement in major cognitive disorders such as Alzheimer's disease, Parkinson's disease, vascular dementia, schizophrenia, and diabetes mellitus. As will be discussed, the relevant scientific literature reveals clearly that the α4ß2 and α7 nAChR subtypes and/or subunits of the receptors play major roles in maintaining cognitive function and in neuroprotection of the brain. Accordingly, focusing on these as targets of drug therapy can be expected to lead to breakthroughs in the treatment of cognitive disorders such as AD and schizophrenia.

SR9883 is a novel small-molecule enhancer of α4ß2* nicotinic acetylcholine receptor signaling that decreases intravenous nicotine self-administration in rats.

Background: Most smokers attempting to quit will quickly relapse to tobacco use even when treated with the most efficacious smoking cessation agents currently available. This highlights the need to develop effective new smoking cessation medications. Evidence suggests that positive allosteric modulators (PAM) and other enhancers of nicotinic acetylcholine receptor (nAChR) signaling could have therapeutic utility as smoking cessation agents. Methods: 3-[3-(3-pyridyl)-1,2,4-oxadiazol-5-yl]benzonitrile (NS9283) was used as a starting point for medical chemistry efforts to develop novel small molecule enhancers of α4ß2* nAChR stoichiometries containing a low-affinity agonist binding site at the interface of α4/α4 and α4/α5 subunits. Results: The NS9283 derivative SR9883 enhanced the effect of nicotine on α4ß2* nAChR stoichiometries containing low-affinity agonist binding sites, with EC50 values from 0.2-0.4 µM. SR9883 had no effect on α3ß2* or α3ß4* nAChRs. SR9883 was bioavailable after intravenous (1 mg kg-1) and oral (10-20 mg kg-1) administration and penetrated into the brain. When administered alone, SR9883 (5-10 mg kg-1) had no effect on locomotor activity or intracranial self-stimulation (ICSS) thresholds in mice. When co-administered with nicotine, SR9883 enhanced locomotor suppression and elevations of ICSS thresholds induced by nicotine. SR9883 (5 and 10 mg kg-1) decreased responding for intravenous nicotine infusions (0.03 mg kg-1 per infusion) but had no effect on responding for food rewards in rats. Conclusions: These data suggest that SR9883 is useful for investigating behavioral processes regulated by certain α4ß2* nAChR stoichiometries. SR9883 and related compounds with favorable drug-like physiochemical and pharmacological properties hold promise as novel treatments of tobacco use disorder.

Nicotine as a female reproductive toxicant-A review.

The preceding decades have seen an extensive emergence of the harmful effects of tobacco smoke on systemic health. Among the various compounds of tobacco, nicotine is one of the principal, potentially hazardous, and toxic components which is an oxidant agent that can affect both men's and women's fertility. Nicotine exerts its effect by modulating the expression of transmembrane ligand-gated ion channels called nicotinic acetylcholine receptors. The activities of female reproduction might be disrupted by exposure to nicotine at various sites, such as the ovary or reproductive tract. It's been demonstrated that nicotine might cause oxidative stress, apoptosis, hormonal imbalance, abnormalities in chromosomal segregation, impact oocyte development, and disruption in ovarian morphology and functions. This review paper summarizes the findings and provides an updated overview of the evidence on the harmful effects of nicotine use on women's reproductive health and the resulting detrimental impacts on the body. Additionally, it provides the detailed possible mechanisms involved in impairing reproductive processes like folliculogenesis, oocyte maturation, steroidogenesis, and pregnancy in different animal species.

Neuroactive Kynurenines as Pharmacological Targets: New Experimental Tools and Exciting Therapeutic Opportunities.

Both pre-clinical and clinical studies implicate functional impairments of several neuroactive metabolites of the kynurenine pathway (KP), the major degradative cascade of the essential amino acid tryptophan in mammals, in the pathophysiology of neurological and psychiatric diseases. A number of KP enzymes, such as tryptophan 2,3-dioxygenase (TDO2), indoleamine 2,3-dioxygenases (IDO1 and IDO2), kynurenine aminotransferases (KATs), kynurenine 3-monooxygenase (KMO), 3-hydroxyanthranilate oxidase (3-HAO), and quinolinic acid phosphoribosyltransferase (QPRT), control brain KP metabolism in health and disease and are therefore increasingly considered to be promising targets for the treatment of disorders of the nervous system. Understanding the distribution, cellular expression, and regulation of KP enzymes and KP metabolites in the brain is therefore critical for the conceptualization and implementation of successful therapeutic strategies. Significance Statement Studies have implicated the kynurenine pathway of tryptophan in the pathophysiology of neurological and psychiatric diseases. Key enzymes of the kynurenine pathway regulate brain metabolism in both health and disease, making them promising targets for treating these disorders. Therefore, understanding the distribution, cellular expression, and regulation of these enzymes and metabolites in the brain is critical for developing effective therapeutic strategies. In this review, we endeavor to describe these processes in detail.

Central nervous system disturbances by thiamethoxam in Japanese quail (Coturnix japonica): In vivo, ex vivo, and in silico study.

The neurotoxic effects of neonicotinoids (NEOs) have been widely reported in relation to the poisoning of wild birds, yet the underlying molecular mechanism has remained elusive. This study employed Japanese quails (Coturnix japonica) and primary quail embryonic neurons as in vivo and ex vivo models, respectively, to investigate the neurotoxic effects and mechanism of thiamethoxam (TMX), a representative neonicotinoid insecticide, at environmentally relevant concentrations. Following a 28-day exposure to TMX, metabolomic analysis of quail brain revealed TMX-induced changes in glutamatergic, GABA-ergic, and dopaminergic function. Subsequent ex vivo and in silico experimentation revealed that the activation of nicotinic acetylcholine receptors and calcium signaling, induced by clothianidin (CLO), the primary metabolite of TMX, served as upstream events for the alterations in neurotransmitter synthesis, metabolism, release, and uptake. Our findings propose that the disruption of the central nervous system, caused by environmentally significant concentrations of NEOs, may account for the avian poisoning events induced by NEOs.

Impact of a worker bee thoracic ganglion RIC-3 variant on the actions of acetylcholine and neonicotinoids on nicotinic receptors in Apis mellifera.

A transmembrane thioredoxin (TMX3) enables the functional expression of insect nicotinic acetylcholine receptors (nAChRs) in Xenopus laevis oocytes, while co-factors RIC-3 and UNC-50 regulate the receptor expression level. RIC-3 (resistant to inhibitors of cholinesterase 3) has been shown to diversify by its differential mRNA splicing patterns. How such diversity influences neonicotinoid sensitivity of nAChRs of beneficial insect species remains poorly understood. We have identified a RIC-3 variant expressed most abundantly in the thoracic ganglia of honeybee (Apis mellifera) workers and investigated its effects on the functional expression and pharmacology of Amα1/Amα8/Amß1 and Amα1/Amα2/Amα8/Amß1 nAChRs expressed in X. laevis oocytes. The AmRIC-3 enhanced the response amplitude to the acetylcholine (ACh) of these A. mellifera nAChRs when its cRNA was injected into oocytes at low concentrations but suppressed the ACh response amplitude at high concentrations. Co-expression of the AmRIC-3 had a minimal impact on the affinity of ACh, but changed the efficacy of imidacloprid and clothianidin, suggesting that the presence and the level of RIC-3 expression can affect the nAChR responses to ACh and neonicotinoids, depending on nAChR subunit composition in honeybees. © 2024 Society of Chemical Industry.

The angiogenic role of the alpha 9-nicotinic acetylcholine receptor in triple-negative breast cancers.

Nicotine acts as an angiogenic factor by stimulating endogenous cholinergic pathways. Several subtypes of nicotinic acetylcholine receptors (nAChRs) have been demonstrated to be closely correlated to the formation and progression of different types of cancers. Recently, several studies have found that nicotinic acetylcholine receptors α9 (α9-nAChRs) are highly expressed in breast tumors, especially in tumors derived from patients diagnosed at advanced stages. In vitro studies have demonstrated that activation of α9-nAChRs is associated with increased proliferation and migration of breast cancer. To study the tumor-promoting role of α9-nAChRs in breast cancers, we generated a novel anti-α9-nAChR and methoxy-polyethylene glycol (mPEG) bispecific antibody (α9 BsAb) for dissecting the molecular mechanism on α9-nAChR-mediated tumor progression. Unexpectedly, we discovered the angiogenic role of α9-nAChR in nicotine-induced neovascularization of tumors. It revealed α9 BsAbs reduced nicotine-induced endothelial cell tube formation, blood vessel development in Matrigel plug assay and angiogenesis in microtube array membrane murine model (MTAMs). To unbraid the molecular mechanism of α9-nAChR in nicotine-mediated angiogenesis, the α9 BsAbs were applied and revealed the inhibitory roles in nicotine-induced production of hypoxia-inducible factor-2 alpha (HIF-2α), vascular endothelial growth factor A (VEGF-A), phosphorylated vascular endothelial growth factor receptor 2 (p-VEGFR2), vascular endothelial growth factor receptor 2 (VEGFR2) and matrix metalloproteinase-9 (MMP9) from triple-negative breast cancer cells (MDA-MB-231), suggesting α9-nAChRs played an important role in nicotine-induced angiogenesis. To confirm our results, the shRNA targeting α9-nAChRs was designed and used to silence α9-nAChR expression and then evaluated the angiogenic role of α9-nAChRs. The results showed α9 shRNA also played an inhibitory effect in blocking the nicotine-induced angiogenic signaling. Taken together, α9-nAChR played a critical role in nicotine-induced angiogenesis and this bispecific antibody (α9 BsAb) may serve as a potential therapeutic candidate for treatments of the α9 positive cancers.

New insights into the effects of organometallic ruthenium complexes on nicotinic acetylcholine receptors.

Nicotinic acetylcholine receptors (nAChRs) are expressed in excitable and non-excitable cells of the organism. Extensive studies suggest that nAChR ligands have therapeutic potential, notably for neurological and psychiatric disorders. Organometallic ruthenium complexes are known to inhibit several medically important enzymes such as cholinesterases. In addition, they can also interact with muscle- and neuronal-subtype nAChRs. The present study aimed to investigate the direct effects of three organometallic ruthenium complexes, [(η6-p-cymene)Ru(II)(5-nitro-1,10-phenanthroline)Cl]Cl (C1-Cl), [(η6-p-cymene)Ru(II)(1-hydroxypyridine-2(1H)-thionato)Cl] (C1a) and [(η6-p-cymene)Ru(II)(1-hydroxy-3-methoxypyridine-2(1H)-thionato)pta]PF6 (C1), on muscle-subtype (Torpedo) nAChRs and on the two most abundant human neuronal-subtype nAChRs in the CNS (α4ß2 and α7) expressed in Xenopus laevis oocytes, using the two-electrode voltage-clamp. The results show that none of the three compounds had agonistic activity on any of the nAChR subtypes studied. In contrast, C1-Cl reversibly blocked Torpedo nAChR (half-reduction of ACh-evoked peak current amplitude by 332 nM of compound). When tested at 10 µM, C1-Cl was statistically more potent to inhibit TorpedonAChR than α4ß2 and α7 nAChRs. Similar results of C1 effects were obtained on Torpedo and α4ß2 nAChRs, while no action of the compound was detected on α7 nAChRs. Finally, the effects of C1a were statistically similar on the three nAChR subtypes but, in contrast to C1-Cl and C1, the inhibition was hardly reversible. These results, together with our previous studies on isolated mouse neuromuscular preparations, strongly suggest that C1-Cl is, among the three compounds studied, the only molecule that could be used as a potential myorelaxant drug.

Unravelling nicotinic receptor and ligand features underlying neonicotinoid knockdown actions on the malaria vector mosquito Anopheles gambiae.

With the spread of resistance to long-established insecticides targeting Anopheles malaria vectors, understanding the actions of compounds newly identified for vector control is essential. With new commercial vector-control products containing neonicotinoids under development, we investigate the actions of 6 neonicotinoids (imidacloprid, thiacloprid, clothianidin, dinotefuran, nitenpyram and acetamiprid) on 13 Anopheles gambiae nicotinic acetylcholine receptor (nAChR) subtypes produced by expression of combinations of the Agα1, Agα2, Agα3, Agα8 and Agß1 subunits in Xenopus laevis oocytes, the Drosophila melanogaster orthologues of which we have previously shown to be important in neonicotinoid actions. The presence of the Agα2 subunit reduces neonicotinoid affinity for the mosquito nAChRs, whereas the Agα3 subunit increases it. Crystal structures of the acetylcholine binding protein (AChBP), an established surrogate for the ligand-binding domain, with dinotefuran bound, shows a unique target site interaction through hydrogen bond formation and CH-N interaction at the tetrahydrofuran ring. This is of interest as dinotefuran is also under trial as the toxic element in baited traps. Multiple regression analyses show a correlation between the efficacy of neonicotinoids for the Agα1/Agα2/Agα8/Agß1 nAChR, their hydrophobicity and their rate of knockdown of adult female An. gambiae, providing new insights into neonicotinoid features important for malaria vector control.

Swift regulation of nicotinic acetylcholine receptors (nAChRs) and glutathione S-transferase (GST) enables the rapid detoxification of thiacloprid in pine sawyer beetles.

Thiacloprid, a neonicotinoid insecticide, has become one of the major control agents for the pine sawyer beetle, Monochamus alternatus Hope, however, the mechanism of detoxification is unknown. We demonstrate that glutathione S-transferases (GSTs) and nicotinic acetylcholine receptors (nAChRs) are involved in the rapid detoxification of thiacloprid in M. alternatus larvae. The activity of detoxification enzyme GSTs was significantly higher, while the activity of acetylcholinesterase (AChE) was inhibited under thiacloprid exposure. The inhibition of AChE activity led to lethal over-stimulation of the cholinergic synapse, which was then released by the rapid downregulation of nAChRs. Meanwhile, GSTs were overexpressed to detoxify thiacloprid accordingly. A total of 3 nAChR and 12 GST genes were identified from M. alternatus, among which ManAChRα2 and MaGSTs1 were predicted to confer thiacloprid tolerance. RNA interference (RNAi) was subsequently conducted to confirm the function of ManAChRα2 and MaGSTs1 genes in thiacloprid detoxification. The successful knock-down of the ManAChRα2 gene led to lower mortality of M. alternatus under LC30 thiacloprid treatment, and the suppression of the MaGSTs1 gene increased the mortality rate of M. alternatus. However, the mortality rate has no significant difference with controls when thiacloprid was fed together with both dsMaGSTs1 and dsManAChRα2. Molecular docking modeled the molecular basis for interaction between MaGSTs1/ManAChR and thiacloprid. This study highlights the important roles that ManAChRα2 and MaGSTs1 genes play in thiacloprid detoxification through transcriptional regulation and enzymatic metabolization, and proposes a new avenue for integrated pest management that combines pesticides and RNAi technology as an efficient strategy for M. alternatus control.

Role of medial prefrontal cortex voltage-dependent potassium 4.3 channels in nicotine-induced enhancement of object recognition memory in male mice.

Nicotine has been shown to enhance object recognition memory in the novel object recognition (NOR) test by activating excitatory neurons in the medial prefrontal cortex (mPFC). However, the exact neuronal mechanisms underlying the nicotine-induced activation of mPFC neurons and the resultant memory enhancement remain poorly understood. To address this issue, we performed brain-slice electrophysiology and the NOR test in male C57BL/6J mice. Whole-cell patch-clamp recordings from layer V pyramidal neurons in the mPFC revealed that nicotine augments the summation of evoked excitatory postsynaptic potentials (eEPSPs) and that this effect was suppressed by N-[3,5-Bis(trifluoromethyl)phenyl]-N'-[2,4-dibromo-6-(2H-tetrazol-5-yl)phenyl]urea (NS5806), a voltage-dependent potassium (Kv) 4.3 channel activator. In line with these findings, intra-mPFC infusion of NS5806 suppressed systemically administered nicotine-induced memory enhancement in the NOR test. Additionally, miRNA-mediated knockdown of Kv4.3 channels in mPFC pyramidal neurons enhanced object recognition memory. Furthermore, inhibition of A-type Kv channels by intra-mPFC infusion of 4-aminopyridine was found to enhance object recognition memory, while this effect was abrogated by prior intra-mPFC NS5806 infusion. These results suggest that nicotine augments the summation of eEPSPs via the inhibition of Kv4.3 channels in mPFC layer V pyramidal neurons, resulting in the enhancement of object recognition memory.

α7 nicotinic receptor activation mitigates herpes simplex virus type 1 infection in microglia cells.

Herpes simplex virus type 1 (HSV-1), a neurotropic DNA virus, establishes latency in neural tissues, with reactivation causing severe consequences like encephalitis. Emerging evidence links HSV-1 infection to chronic neuroinflammation and neurodegenerative diseases. Microglia, the central nervous system's (CNS) immune sentinels, express diverse receptors, including α7 nicotinic acetylcholine receptors (α7 nAChRs), critical for immune regulation. Recent studies suggest α7 nAChR activation protects against viral infections. Here, we show that α7 nAChR agonists, choline and PNU-282987, significantly inhibit HSV-1 replication in microglial BV2 cells. Notably, this inhibition is independent of the traditional ionotropic nAChR signaling pathway. mRNA profiling revealed that choline stimulates the expression of antiviral factors, IL-1ß and Nos2, and down-regulates the apoptosis genes and type A Lamins in BV2 cells. These findings suggest a novel mechanism by which microglial α7 nAChRs restrict viral infections by regulating innate immune responses.

Nicotine promotes development of bile duct ligation-induced liver fibrosis by increasing expression of nicotinic acetylcholine receptors in rats.

Aim of the study: Liver fibrosis and cigarette smoking seem to be directly linked. Nicotine, as an agonist of nicotinic acetylcholine receptors (nAChRs), induces many downstream signaling pathways. The pathways through which nicotine affects the process of liver fibrosis have not been clarified. The present study aimed to investigate the nicotine-induced effects on fibrosis progression in cholestatic rats. Material and methods: First, the Wistar rats were subjected to sham or bile duct ligation (BDL) surgery. The rats were treated with low and high doses of nicotine (1 or 10 mg/kg) for three weeks. They were monitored for their body weights before and 21 days after BDL. Also, spleens were weighed to calculate the spleen/body weight ratio. Ductular proliferation and fibrosis were evaluated using hematoxylin and eosin (H&E) as well as Masson's trichrome staining. The mRNA expression of α4nAChR, α7nAChR, and fibrosis gene α-smooth muscle actin (α-SMA) was measured by real-time PCR. Results: The findings showed that nicotine promotes the development of BDL-induced liver fibrosis. The ratio of spleen/body weight was significantly affected by nicotine exposure. H&E and Masson's trichrome staining showed that the level of liver fibrosis was higher in the cholestatic BDL groups, and this effect was significantly augmented in the nicotine-treated rats. Also, α4nAChR, α7nAChR, and α-SMA expression was observed in the BDL rats and increased following nicotine treatment. Conclusions: The activation of nAChR triggers biliary proliferation and liver fibrosis. Studying the intracellular mechanism of nicotine and alteration in the expression of nicotinic receptors following nicotine exposure can be useful both in diagnosing nicotine-related diseases and finding new treatment strategies.

The Role of Alpha-7 Nicotinic Acetylcholine Receptors in Pain: Potential Therapeutic Implications.

Chronic pain represents a prevalent and costly medical challenge globally. Nicotinic acetylcholine receptors (nAChRs), one type of ligand-gated ion channels found extensively in both the central and peripheral nervous systems, have emerged as promising therapeutic targets for chronic pain. Although there are currently no FDA-approved analgesics specifically targeting nAChRs, accumulating preclinical and clinical evidence suggest that selective ligands for alpha 7 (α7) nAChRs show potential for treating chronic pain, boasting a reduced incidence of side effects compared with other nicotinic receptor types. The recent structural resolution of human α7 nAChRs has confirmed their negative association with heightened pain, providing a valuable foundation for the development of targeted medications. This review presents a comprehensive overview, encompassing insights into the roles of α7 nAChRs derived from structural and functional studies, recent advancements in pharmacology, and investigations into their involvement in the pathophysiology of chronic pain. Moreover, the review addresses the variability in analgesic effects based on the type of receptor agonist and highlights the current research limitations. As such, this review offers potential therapeutic approaches for the development of innovative strategies for chronic pain management.

Expression and function of nicotinic acetylcholine receptors in specific neuronal populations: Focus on striatal and prefrontal circuits.

Nicotinic acetylcholine receptors (nAChRs) are widely expressed in the central nervous system and play an important role in the control of neural functions including neuronal activity, transmitter release and synaptic plasticity. Although the common subtypes of nAChRs are abundantly expressed throughout the brain, their expression in different brain regions and by individual neuronal types is not homogeneous or incidental. In recent years, several studies have emerged showing that particular subtypes of nAChRs are expressed by specific neuronal populations in which they have major influence on the activity of local circuits and behavior. It has been demonstrated that even nAChRs expressed by relatively rare neuronal types can induce significant changes in behavior and contribute to pathological processes. Depending on the identity and connectivity of the particular nAChRs-expressing neuronal populations, the activation of nAChRs can have distinct or even opposing effects on local neuronal signaling. In this review, we will summarize the available literature describing the expression of individual nicotinic subunits by different neuronal types in two crucial brain regions, the striatum and the prefrontal cortex. The review will also briefly discuss nicotinic expression in non-neuronal, glial cells, as they cannot be ignored as potential targets of nAChRs-modulating drugs. The final section will discuss options that could allow us to target nAChRs in a neuronal-type-specific manner, not only in the experimental field, but also eventually in clinical practice.

Nicotinic Acetylcholine Receptor Alpha6 Contributes to Antiviral Immunity via IMD Pathway in Drosophila melanogaster.

Currently, insecticides that target nicotinic acetylcholine receptors (nAChR) are widely used. Studies on the sublethal effects of insecticides have found that they can affect the amount of virus in insects. The mechanism by which insecticides affect insect virus load remain unclear. Here, we show that nAChR targeting insecticide can affect viral replication through the immune deficiency (IMD) pathway. We demonstrate that a low dose of spinosad (6.8 ng/mL), acting as an antagonist to Drosophila melanogaster nicotinic acetylcholine receptor α6 (Dα6), significantly elevates Drosophila melanogaster sigmavirus (DMelSV) virus titers in adults of Drosophila melanogaster. Conversely, a high dose of spinosad (50 ng/mL), acting as an agonist to Dα6, substantially decreases viral load. This bidirectional regulation of virus levels is absent in Dα6-knockout flies, signifying the specificity of spinosad's action through Dα6. Furthermore, the knockdown of Dα6 results in decreased expression of genes in the IMD pathway, including dredd, imd, relish, and downstream antimicrobial peptide genes AttA and AttB, indicating a reduced innate immune response. Subsequent investigations reveal no significant difference in viral titers between relish mutant flies and Dα6-relish double mutants, suggesting that the IMD pathway's role in antiviral defense is dependent on Dα6. Collectively, our findings shed light on the intricate interplay between nAChR signaling and the IMD pathway in mediating antiviral immunity, highlighting the potential for nAChR-targeting compounds to inadvertently influence viral dynamics in insect hosts. This knowledge may inform the development of integrated pest management strategies that consider the broader ecological impact of insecticide use.

Catharanthine Modulates Mesolimbic Dopamine Transmission and Nicotine Psychomotor Effects via Inhibition of α6-Nicotinic Receptors and Dopamine Transporters.

Iboga alkaloids, also known as coronaridine congeners, have shown promise in the treatment of alcohol and opioid use disorders. The objective of this study was to evaluate the effects of catharanthine and 18-methoxycoronaridine (18-MC) on dopamine (DA) transmission and cholinergic interneurons in the mesolimbic DA system, nicotine-induced locomotor activity, and nicotine-taking behavior. Utilizing ex vivo fast-scan cyclic voltammetry (FSCV) in the nucleus accumbens core of male mice, we found that catharanthine or 18-MC differentially inhibited evoked DA release. Catharanthine inhibition of evoked DA release was significantly reduced by both α4 and α6 nicotinic acetylcholine receptors (nAChRs) antagonists. Additionally, catharanthine substantially increased DA release more than vehicle during high-frequency stimulation, although less potently than an α4 nAChR antagonist, which confirms previous work with nAChR antagonists. Interestingly, while catharanthine slowed DA reuptake measured via FSCV ex vivo, it also increased extracellular DA in striatal dialysate from anesthetized mice in vivo in a dose-dependent manner. Superfusion of catharanthine or 18-MC inhibited the firing rate of striatal cholinergic interneurons in a concentration dependent manner, which are known to potently modulate presynaptic DA release. Catharanthine or 18-MC suppressed acetylcholine currents in oocytes expressing recombinant rat α6/α3ß2ß3 or α6/α3ß4 nAChRs. In behavioral experiments using male Sprague-Dawley rats, systemic administration of catharanthine or 18-MC blocked nicotine enhancement of locomotor activity. Importantly, catharanthine attenuated nicotine self-administration in a dose-dependent manner while having no effect on food reinforcement. Lastly, administration of catharanthine and nicotine together greatly increased head twitch responses, indicating a potential synergistic hallucinogenic effect. These findings demonstrate that catharanthine and 18-MC have similar, but not identical effects on striatal DA dynamics, striatal cholinergic interneuron activity and nicotine psychomotor effects.

Characterizing the binding of TC-5619 and encenicline on the alpha7 nicotinic acetylcholine receptor using PET imaging in the pig.

The alpha7 nicotinic acetylcholine receptor (α7-nAChR) has has long been considered a promising therapeutic target for addressing cognitive impairments associated with a spectrum of neurological and psychiatric disorders, including Alzheimer's disease and schizophrenia. However, despite this potential, clinical trials employing α7-nAChR (partial) agonists such as TC-5619 and encenicline (EVP-6124) have fallen short in demonstrating sufficient efficacy. We here investigate the target engagement of TC-5619 and encenicline in the pig brain by use of the α7-nAChR radioligand 11C-NS14492 to characterize binding both with in vitro autoradiography and in vivo occupancy using positron emission tomography (PET). In vitro autoradiography demonstrates significant concentration-dependent binding of 11C-NS14492, and both TC-5619 and encenicline can block this binding. Of particular significance, our in vivo investigations demonstrate that TC-5619 achieves substantial α7-nAChR occupancy, effectively blocking approximately 40% of α7-nAChR binding, whereas encenicline exhibits more limited α7-nAChR occupancy. This study underscores the importance of preclinical PET imaging and target engagement analysis in informing clinical trial strategies, including dosing decisions.

The α4 Nicotinic Acetylcholine Receptor Is Necessary for the Initiation of Organophosphate-Induced Neuronal Hyperexcitability.

Acute intoxication with organophosphorus (OP) cholinesterase inhibitors can produce seizures that rapidly progress to life-threatening status epilepticus. Significant research effort has been focused on investigating the involvement of muscarinic acetylcholine receptors (mAChRs) in OP-induced seizure activity. In contrast, there has been far less attention on nicotinic AChRs (nAChRs) in this context. Here, we address this data gap using a combination of in vitro and in vivo models. Pharmacological antagonism and genetic deletion of α4, but not α7, nAChR subunits prevented or significantly attenuated OP-induced electrical spike activity in acute hippocampal slices and seizure activity in mice, indicating that α4 nAChR activation is necessary for neuronal hyperexcitability triggered by acute OP exposures. These findings not only suggest that therapeutic strategies for inhibiting the α4 nAChR subunit warrant further investigation as prophylactic and immediate treatments for acute OP-induced seizures, but also provide mechanistic insight into the role of the nicotinic cholinergic system in seizure generation.

Unraveling the molecular interactions between α7 nicotinic receptor and a RIC3 variant associated with backward speech.

Recent work putatively linked a rare genetic variant of the chaperone Resistant to Inhibitors of acetylcholinesterase (RIC3) (NM_024557.4:c.262G > A, NP_078833.3:p.G88R) to a unique ability to speak backwards, a language skill that is associated with exceptional working memory capacity. RIC3 is important for the folding, maturation, and functional expression of α7 nicotinic acetylcholine receptors (nAChR). We compared and contrasted the effects of RIC3G88R on assembly, cell surface expression, and function of human α7 receptors using fluorescent protein tagged α7 nAChR and Förster resonance energy transfer (FRET) microscopy imaging in combination with functional assays and 125I-α-bungarotoxin binding. As expected, the wild-type RIC3 protein was found to increase both cell surface and functional expression of α7 receptors. In contrast, the variant form of RIC3 decreased both. FRET analysis showed that RICG88R increased the interactions between RIC3 and α7 protein in the endoplasmic reticulum. These results provide interesting and novel data to show that a RIC3 variant alters the interaction of RIC3 and α7, which translates to decreased cell surface and functional expression of α7 nAChR.