Muscarinic Agonist Research Articles

Plant & Its Derivative Shows Therapeutic Activity on Neuroprotective Effect

In most cases, the death of neurons in certain parts of the brain is the defining feature of a condition that is classified as neurodegenerative. There have been studies conducted on both conventional and innovative drugs, however the results have shown that they only offer symptomatic advantages and come with a number of undesirable side effects. The finding of more potent compounds that can stop the pathophysiology of these diseases will be seen as a miracle in the present day. There is a wide variety of synthetic compounds accessible; nevertheless, these drugs may also create a broad range of additional health issues. As a consequence of this, scientists are looking to plants and other natural sources for the development of new medicines. In the practise of conventional medicine, it has been discovered that certain plants possess healing powers. The use of phytochemicals, which are produced from medicinal plants, may eventually replace the need for synthetic molecules. Numerous phytochemicals have been shown to be effective in the treatment of a wide range of diseases. This article discusses the potential therapeutic applications of plant-derived alkaloids for a number of neurodegenerative disorders (NDDs), including Alzheimer's disease (AD), Huntington's disease (HD), Parkinson's disease (PD), epilepsy, schizophrenia, and stroke. There are many different types of alkaloids that can be found in the plant kingdom. Some of these alkaloids include isoquinoline, indole, pyrroloindole, oxindole, piperidine, pyridine, aporphine, vinca, -carboline, methylxanthene, lycopodium, and erythrine byproducts. Alkaloids have a beneficial effect on the pathophysiology of these diseases because of their ability to act as muscarinic and adenosine receptor agonists, anti-oxidants, anti-amyloid and MAO inhibitors, acetylcholinestrase and butyrylcholinesterase inhibitors, an inhibitor of synuclein aggregation, dopaminergic and nicotine agonists, and NMDA antagonists.

Muscarinic Acetylcholine Receptor Agonists as Novel Treatments for Schizophrenia

Schizophrenia remains a challenging disease to treat effectively with current antipsychotic medications due to their limited efficacy across the entire spectrum of core symptoms as well as their often burdensome side-effect profiles and poor tolerability. An unmet need remains for novel, mechanistically unique, and better tolerated therapeutic agents for treating schizophrenia, especially those that treat not only positive symptoms but also the negative and cognitive symptoms of the disease. Almost 25 years ago, the muscarinic acetylcholine receptor (mAChR) agonist xanomeline was reported to reduce psychotic symptoms and improve cognition in patients with Alzheimer's disease. The antipsychotic and procognitive properties of xanomeline were subsequently confirmed in a small study of acutely psychotic patients with chronic schizophrenia. These unexpected clinical findings have prompted considerable efforts across academia and industry to target mAChRs as a new approach to potentially treat schizophrenia and other psychotic disorders. The authors discuss recent advances in mAChR biology and pharmacology and the current understanding of the relative roles of the various mAChR subtypes, their downstream cellular effectors, and key neural circuits mediating the reduction in the core symptoms of schizophrenia in patients treated with xanomeline. They also provide an update on the status of novel mAChR agonists currently in development for potential treatment of schizophrenia and other neuropsychiatric disorders.

Role of SERCA3-dependent calcium signaling in mouse aortic function

Calcium homeostasis has a major role in vascular reactivity. The Sarco/Endoplasmic Reticulum Ca2+-ATPases (SERCAs) contribute to generate intracellular Ca2+-stores that are mobilized during functional responses. The SERCA2 family is described as the most important in vascular cells, but SERCA3 has been reported to be co-expressed, with SERCA3a mainly at the endothelial level and SERCA3b at the smooth muscle level. Our objective is to evaluate the role of the SERCA3-dependent calcium pathway in vascular reactivity. For experiments, aortic rings were collected from wild-type (WT) and SERCA3-deficient (SERCA3-KO) mice (2–3 month-old male) and mounted in an organ bath system. Contractile and relaxant agents were applied to compare the in vitro aortic reactivity in both animal groups. The contractile responses to a depolarizing high-potassium solution or to cumulative increasing concentrations of serotonin (a 5-HT agonist, 10-9 to 10-5 M) or U46619 (a TXA2 analog, 10-10 to 3.10-6 M) were similar in SERCA3-KO and WT aorta. By contrast the response to phenylephrine (an α1-adrenergic agonist, 10-9 to 3.10-5 M) was significantly decreased in SERCA3-KO compared to WT aorta (N = 8-8; P < 0.05, 2-way ANOVA). However, in aorta denuded from endothelium, the contractile response to phenylephrine was similar in SERCA3-KO and WT vessels. In phenylephrine-precontracted aorta, the relaxant responses to acetylcholine (a muscarinic agonist, 10-9 to 3.10-5 M) or to isoproterenol (a b-adrenergic agonist, 10-10 to 10-5 M) were similar in both groups. The concentration-response curve to DEA-NOate (a NO donor, 10-11 to 10-5 M) was shifted to the right in SERCA3-KO compared to WT aortas, with a slight increase in EC50 (N = 9-8; P < 0.05, t -test). When the endothelium was removed, the effect to DEA-NOate was similar in both groups. We observed that SERCA3-KO aorta exhibit a major decrease in the amplitude of the α1-adrenergic contractile response, and in the sensitivity to the relaxant NO donor. These alterations are abolished in the absence of a functional endothelium. These preliminary data suggest that there is an influence of SERCA3 protein on the NO signaling pathway in mouse aorta.

Microbial regulation of intestinal motility provides resistance against helminth infection

Soil-transmitted helminths cause widespread disease, infecting ~1.5 billion people living within poverty-stricken regions of tropical and subtropical countries. As adult worms inhabit the intestine alongside bacterial communities, we determined whether the bacterial microbiota impacted on host resistance against intestinal helminth infection. We infected germ-free, antibiotic-treated and specific pathogen-free mice, with the intestinal helminth Heligmosomoides polygyrus bakeri. Mice harboured increased parasite numbers in the absence of a bacterial microbiota, despite mounting a robust helminth-induced type 2 immune response. Alterations to parasite behaviour could already be observed at early time points following infection, including more proximal distribution of infective larvae along the intestinal tract and increased migration in a Baermann assay. Mice lacking a complex bacterial microbiota exhibited reduced levels of intestinal acetylcholine, a major excitatory intestinal neurotransmitter that promotes intestinal transit by activating muscarinic receptors. Both intestinal motility and host resistance against larval infection were restored by treatment with the muscarinic agonist bethanechol. These data provide evidence that a complex bacterial microbiota provides the host with resistance against intestinal helminths via its ability to regulate intestinal motility.

Comparative Study on the effectiveness of Glycopyrrolate/Formoterol versus Tiotropium/Formoterol in patients with Chronic Obstructive Pulmonary Disease

BackgroundChronic Obstructive Pulmonary Disease (COPD) has several implications on health, lifestyle, and economic burden. Combinational therapy using muscarinic antagonists and beta-2 agonists has long been warranted for use as maintenance therapy. A lack of studies directly comparing Glycopyrrolate/Formoterol (GFF) versus Tiotropium/Formoterol (TFF) was observed which led us to analyze the effectiveness of these combinations. MethodsIn this pilot, prospective, randomized, open-label, parallel-arm, 12-week period study, 60 patients with COPD (moderate-severe) were randomized in a 1:1 ratio to receive either GFF or TFF (n = 30 each). The primary outcome was to demonstrate non-inferiority between the two groups concerning FEV1 for 12 weeks. The secondary outcome was the assessment of the ratio of FEV1/FVC and state of health evaluation by St. George's Respiratory Questionnaire (SGRQ). ResultsOut of 60 participants, 58 subjects completed the study. At week 12, the mean and standard deviation value of FEV1 between groups were 1.49 ± 0.38 and 1.38 ± 0.30 (p > 0.05) and FEV1/FVC ratio were 0.67 ± 0.09 and 0.74 ± 0.08 (p < 0.01) respectively. A significant difference was observed in the FEV1 and FEV1/FVC values in comparison with baseline versus last follow up in both the groups (p < 0.01). However, no remarkable variation was identified in the FEV1 values over the two groups. The health status assessment by SGRQ showed significant improvement in both groups after the treatment. ConclusionNon-inferiority of GFF when compared to TFF was established along with good tolerability and comparable adverse effect profile.

Xanomeline and Trospium: Potential substitute for conventional antipsychotics.

Dear Madam, Schizophrenia is a chronic mental illness with a global prevalence of 24 million people (1). With paucity of researches mounting the exact prevalence of schizophrenia in Pakistan, the treatment of this illness becomes even harder to combat. This condition is typically managed with antipsychotics, which work by blocking the D2 dopamine receptors but recent advances in research also suggest that the muscarinic cholinergic system is also involved in its pathophysiology (2). The drug Xanomeline is an oral muscarinic cholinergic receptor agonist that activates M1 and M4 receptors. Xanomeline however causes side effects like vomiting, nausea, diarrhoea, sweating and hypersalivation. To bypass these effects, Trospium was added, which acts by blocking peripheral muscarinic cholinergic receptors. (3, 4). To observe the reduction of psychosis in schizophrenics, a double-blinded clinical trial was done with promising results: reduction of both, positive and negative symptoms of Schizophrenia, good tolerance and no evidence of weight gain (4). Side effects included constipation, nausea, dry mouth, dyspepsia, and vomiting although the incidence of these effects reduced over the course of the trial. However, there is a dearth of research when it comes to comparison of this combination drug (called KARXT) with the usual antipsychotics. Therefore, further research regarding the safety of KARXT, and its efficacy needs to be explored for potential amelioration of symptoms. Moreover, studies comparing the efficacy of this drug with the commonly used antipsychotics need to be explored in order to effectively assess the advantage and potential replacement benefits of this drug.

Existence of a Long-Range Caudo-Rostral Sensory Influence in Terrestrial Locomotion.

In multisegmented locomotion, coordination of all appendages is crucial for the generation of a proper motor output. In running for example, leg coordination is mainly based on the central interaction of rhythm generating networks, called central pattern generators (CPGs). In slower forms of locomotion, however, sensory feedback, which originates from sensory organs that detect changes in position, velocity and load of the legs' segments, has been shown to play a more crucial role. How exactly sensory feedback influences the activity of the CPGs to establish functional neuronal connectivity is not yet fully understood. Using the female stick insect Carausius morosus, we show for the first time that a long-range caudo-rostral sensory connection exists and highlight that load as sensory signal is sufficient to entrain rhythmic motoneuron (MN) activity in the most rostral segment. So far, mainly rostro-caudal influencing pathways have been investigated where the strength of activation, expressed by the MN activity in the thoracic ganglia, decreases with the distance from the stepping leg to these ganglia. Here, we activated CPGs, producing rhythmic neuronal activity in the thoracic ganglia by using the muscarinic agonist pilocarpine and enforced the stepping of a single, remaining leg. This enabled us to study sensory influences on the CPGs' oscillatory activity. Using this approach, we show that, in contrast to the distance-dependent activation of the protractor-retractor CPGs in different thoracic ganglia, there is no such dependence for the entrainment of the rhythmic activity of active protractor-retractor CPG networks by individual stepping legs.SIGNIFICANCE STATEMENT We show for the first time that sensory information is transferred not only to the immediate adjacent segmental ganglia but also to those farther away, indicating the existence of a long-range caudo-rostral sensory influence. This influence is dependent on stepping direction but independent of whether the leg is actively or passively moved. We suggest that the sensory information comes from unspecific load signals sensed by cuticle mechanoreceptors (campaniform sensilla) of a leg. Our results provide a neuronal basis for the long-established behavioral rules of insect leg coordination. We thus provide a breakthrough in understanding the neuronal networks underlying multilegged locomotion and open new vistas into the neuronal functional connectivity of multisegmented locomotion systems across the animal kingdom.

Muscarinic Receptors Associated with Cancer.

Simple SummaryRecently, cancer research has described the presence of the cholinergic machinery, specifically muscarinic receptors, in a wide variety of cancers due to their activation and signaling pathways associated with tumor progression and metastasis, providing a wide overview of their contribution to different cancer formation and development for new antitumor targets. This review focused on determining the molecular signatures associated with muscarinic receptors in breast and other cancers and the need for pharmacological, molecular, biochemical, technological, and clinical approaches to improve new therapeutic targets.Cancer has been considered the pathology of the century and factors such as the environment may play an important etiological role. The ability of muscarinic agonists to stimulate growth and muscarinic receptor antagonists to inhibit tumor growth has been demonstrated for breast, melanoma, lung, gastric, colon, pancreatic, ovarian, prostate, and brain cancer. This work aimed to study the correlation between epidermal growth factor receptors and cholinergic muscarinic receptors, the survival differences adjusted by the stage clinical factor, and the association between gene expression and immune infiltration level in breast, lung, stomach, colon, liver, prostate, and glioblastoma human cancers. Thus, targeting cholinergic muscarinic receptors appears to be an attractive therapeutic alternative due to the complex signaling pathways involved.

Characterizing the Contribution of Muscarinic Receptor Subtypes to Inspiratory Bursting Activity at Hypoglossal Motor Neurons of CD1 Mice

Obstructive sleep apnea (OSA) is characterized by cessation of breathing during sleep, due to repetitive episodic collapse of the airway or increased airway resistance. This loss of airway patency during sleeping conditions is controlled in part by the tongue, innervated by the hypoglossal (XII) motor nucleus. Decreased excitability of XII motor neurons (MNs) that innervate the tongue may occur due to activation of muscarinic acetylcholine receptors acting through G‐protein coupled signal transduction pathways. The five types of muscarinic acetylcholine receptors can be broadly categorized as excitatory or inhibitory. M1, M3, and M5 receptors are excitatory receptors coupled to Gq, whereas M2 and M4 receptors are inhibitory receptors coupled to Gi. XII MNs express M1, M2, M3, and M5 subtypes of muscarinic receptors, but the specific mechanisms of how cholinergic signaling modulates excitability of XII MNs are not well understood. The objective of this study was to investigate how the muscarinic receptor subtypes individually contribute to inspiratory activity at XII MNs. We tested the hypothesis that activation of M1 and M5 receptors potentiate, whereas activation of M2 receptors inhibit inspiratory bursting in XII MNs. Using medullary rhythmic slice preparations from neonatal CD1 mice (postnatal day P0‐5) local application of muscarine (30s, 100 μM) to the XII motor nucleus increased inspiratory burst amplitude to 180 ± 7% [n = 23]. Blocking M1 receptors locally with pirenzepine (10 μM &amp; 100 μM) decreased the muscarine‐mediated potentiation of inspiratory bursting to 94 ± 15% and 72 ± 14% of control muscarine response [n = 9]. Activating M1 receptors locally with cevimeline (1 mM) for 30s and 60s increased burst amplitude to 116 ± 7% and 117 ± 7% of control muscarine response [n = 6]. Blocking M2 receptors locally with AF‐DX 116 (1 μM &amp; 10 μM), the muscarine‐mediated effect was 101 ± 10% [n = 3] and 95 ± 10% [n = 3] of control muscarine‐mediated excitation. M2 receptor blockade was also tested by application of the M2 receptor antagonist, methoctramine (MTH). Local application of MTH (2 μM) had no effect on muscarine‐mediated potentiation of inspiratory bursting (171 ± 15% compared to control muscarine response of 177 ± 14% [n = 10]). Similarly, blocking M2 receptors with bath application of MTH (200 nM) had no effect on muscarine‐mediated potentiation of inspiratory bursting (166 ± 20% compared to 161 ± 14% control muscarine response) or on inspiratory burst period (10 ± 0.3% compared to 10 ± 0.4% control muscarine response) [n = 5]. Modulating M5 receptors locally with VU 0238429 (20 μM and 1000 μM) increased burst amplitude to 116% ± 5% and 119 ± 4% of control muscarine‐mediated excitation [n = 3]. Our data partially support a role of M1 receptors contributing to the muscarinic potentiation of inspiratory bursting in XII MNs. Future research will evaluate other muscarinic receptor agonists and antagonists, as well as determine how the muscarinic modulation of inspiratory bursting changes with postnatal maturation.

Ca2+ entry through reverse Na+/Ca2+ exchanger in NCI-H716, glucagon-like peptide-1 secreting cells.

Glucagon like peptide-1 (GLP-1) released from enteroendocine L-cells in the intestine has incretin effects due to its ability to amplify glucose-dependent insulin secretion. Promotion of an endogenous release of GLP-1 is one of therapeutic targets for type 2 diabetes mellitus. Although the secretion of GLP-1 in response to nutrient or neural stimuli can be triggered by cytosolic Ca2+ elevation, the stimulus-secretion pathway is not completely understood yet. Therefore, the aim of this study was to investigate the role of reverse Na+/Ca2+ exchanger (rNCX) in Ca2+ entry induced by muscarinic stimulation in NCI-H716 cells, a human enteroendocrine GLP-1 secreting cell line. Intracellular Ca2+ was repetitively oscillated by the perfusion of carbamylcholine (CCh), a muscarinic agonist. The oscillation of cytosolic Ca2+ was ceased by substituting extracellular Na+ with Li+ or NMG+. KB-R7943, a specific rNCX blocker, completely diminished CCh-induced cytosolic Ca2+ oscillation. Type 1 Na+/Ca2+ exchanger (NCX1) proteins were expressed in NCI-H716 cells. These results suggest that rNCX might play a crucial role in Ca2+ entry induced by cholinergic stimulation in NCI-H716 cells, a GLP-1 secreting cell line.

5‐HT7 Receptors Mediate Dilation of Rat Cremaster Muscle Arterioles in vivo

Serotonin (5‐HT) infusion in vivo causes hypotension and a fall in total peripheral resistance (TPR) that is mediated by 5‐HT7 receptors. 5‐HT dilates small arterioles in skeletal muscle, a microcirculation that importantly contributes to TPR. However, the receptors that mediate this dilation have not been established. Therefore, we tested the hypothesis that 5‐HT7 receptors mediate the arteriolar dilation in the skeletal muscle microcirculation. Cremaster muscles of isoflurane‐anesthetized male Sprague‐Dawley rats were prepared for digital in vivo microscopy and superfused with physiological salt solution (PSS) at 34 °C. Bolus (1‐10 nmols) application of 5‐HT into the superfusate caused substantial dilation of 3rd to 5th order arterioles from 10 ± 1 to 27 ± 1 μm (n = 10 arterioles from 4 rats, p &lt;0.0001) that recovered within 2‐3 min. Dilation to bolus application of 5‐HT was inhibited by superfusion with 1 μM SB269970, a selective 5‐HT7 receptor antagonist (diameter in SB = 9 ± 1 μm; diameter in SB + 5‐HT = 10 ± 1 μm; n = 10 arterioles from 4 rats; p = 0.8763). Similarly, steady‐state superfusion with 10‐30 nM of the 5‐HT1/7 receptor agonist 5‐carboxamidotryptamine (5‐CT) dilated 3rd‐5th‐order arterioles from 16 ± 3 to 37 ± 5 μm (n = 7 arterioles from 3 rats, p = 0.0004). This dilation was reversed (diameter in 1 μM SB269970 = 13 ± 2 μm, n = 7, p = 0.1479 vs. baseline) or blocked (diameter in 1 μM SB269970 + 10‐30 nM 5‐CT = 10 ± 2 μm, n = 7, p = 0.0005 vs. 5‐CT alone) by 1 μM SB269970. Dilation of arterioles to the muscarinic agonist, methacholine (MCH) was not inhibited by SB269970 verifying the specificity of the antagonist; arterioles dilated from 13 ± 2 μm to 25 ± 2 μm to 100 nmols MCH and dilated from 9 ± 2 μm to 32 ± 2 μm in response to MCH in the presence of 1 μM SB269970; n = 10 arterioles from 4 rats; p = 0.7232 vs. dilation in the absence of SB269970. Consistent with these data, pooled samples (4‐5 rats) of 1st and 2nd – order cremaster arterioles expressed message for 5‐HT7 receptors by quantitative real‐time PCR (CT = 36.4 ± 0.74, n = 3 pooled samples, p = 0.039 vs CT = 40). These data support our hypothesis that 5‐HT7 receptors mediate dilation of small arterioles in skeletal muscle and likely contribute to the observed hypotension when these receptors are engaged in vivo.

P491. Rationale for Selective Muscarinic Receptor Agonists as Candidates for Antipsychotic Drug Development

Clinical trials of muscarinic receptor agonists for schizophrenia are underway and, if successful, hold the potential to change the current treatment landscape of therapies that directly interact with dopamine (DA) receptors. Muscarinic acetylcholine receptors (mAChRs) have important regulatory effects on dysfunctional DA circuits associated with psychosis and may provide an indirect way to normalize these circuits.

P599. The Muscarinic Agonist Xanomeline Demonstrates Standalone Activity and Augments Clinical Antipsychotics in Rodent Behavioral Models of Psychosis

Evidence indicates that muscarinic acetylcholine receptor agonists exhibit antipsychotic properties. Xanomeline, a centrally active M1 and M4 receptor agonist, is devoid of any direct dopamine receptor affinity or activity. An important question is whether xanomeline can also augment the effects of existing antipsychotics. Two rodent behavioral models were used to test combinations of xanomeline and either risperidone or aripiprazole. The conditioned avoidance response (CAR) and psychostimulant-induced locomotor activity (LMA) assays are commonly used behavioral tests in rodents that have good predictive validity for detecting antipsychotic activity.

P598. Exploring the Molecular Determinants for Functional Selectivity of the Antipsychotic Xanomeline at Muscarinic Acetylcholine Receptors

Xanomeline (formulated as KarXT) is a selective M1/M4 muscarinic acetylcholine receptor (mAChR) agonist being developed for the treatment of symptoms associated with schizophrenia and Alzheimer’s disease (AD). Questions remain regarding the mechanisms of xanomeline’s selectivity. Therefore, we specifically investigated molecular determinants of xanomeline binding and functional selectivity using two of the most highly homologous Gi-coupled mAChR subtypes (M2/M4).

Oscillatory calcium release and sustained store-operated oscillatory calcium signaling prevents differentiation of human oligodendrocyte progenitor cells

Endogenous remyelination in demyelinating diseases such as multiple sclerosis is contingent upon the successful differentiation of oligodendrocyte progenitor cells (OPCs). Signaling via the Gαq-coupled muscarinic receptor (M1/3R) inhibits human OPC differentiation and impairs endogenous remyelination in experimental models. We hypothesized that calcium release following Gαq-coupled receptor (GqR) activation directly regulates human OPC (hOPC) cell fate. In this study, we show that specific GqR agonists activating muscarinic and metabotropic glutamate receptors induce characteristic oscillatory calcium release in hOPCs and that these agonists similarly block hOPC maturation in vitro. Both agonists induce calcium release from endoplasmic reticulum (ER) stores and store operated calcium entry (SOCE) likely via STIM/ORAI-based channels. siRNA mediated knockdown (KD) of obligate calcium sensors STIM1 and STIM2 decreased the magnitude of muscarinic agonist induced oscillatory calcium release and attenuated SOCE in hOPCs. In addition, STIM2 expression was necessary to maintain the frequency of calcium oscillations and STIM2 KD reduced spontaneous OPC differentiation. Furthermore, STIM2 siRNA prevented the effects of muscarinic agonist treatment on OPC differentiation suggesting that SOCE is necessary for the anti-differentiative action of muscarinic receptor-dependent signaling. Finally, using a gain-of-function approach with an optogenetic STIM lentivirus, we demonstrate that independent activation of SOCE was sufficient to significantly block hOPC differentiation and this occurred in a frequency dependent manner while increasing hOPC proliferation. These findings suggest that intracellular calcium oscillations directly regulate hOPC fate and that modulation of calcium oscillation frequency may overcome inhibitory Gαq-coupled signaling that impairs myelin repair.

Development of VU6019650: A Potent, Highly Selective, and Systemically Active Orthosteric Antagonist of the M5 Muscarinic Acetylcholine Receptor for the Treatment of Opioid Use Disorder.

The muscarinic acetylcholine receptor (mAChR) subtype 5 (M5) represents a novel potential target for the treatment of multiple addictive disorders, including opioid use disorder. Through chemical optimization of several functional high-throughput screening hits, VU6019650 (27b) was identified as a novel M5 orthosteric antagonist with high potency (human M5 IC50 = 36 nM), M5 subtype selectivity (>100-fold selectivity against human M1-4) and favorable physicochemical properties for systemic dosing in preclinical addiction models. In acute brain slice electrophysiology studies, 27b blocked the nonselective muscarinic agonist oxotremorine-M-induced increases in neuronal firing rates of midbrain dopamine neurons in the ventral tegmental area, a part of the mesolimbic dopaminergic reward circuitry. Moreover, 27b also inhibited oxycodone self-administration in male Sprague-Dawley rats within a dose range that did not impair general motor output.

Pharmacological and molecular characterization of the A-type muscarinic acetylcholine receptor from Anopheles gambiae.

Muscarinic acetylcholine receptors (mAChRs) which are G protein-coupled receptors play key roles in insect physiology. Whereas vertebrate mAChRs are important targets for pharmaceutical drugs, insect mAChRs are under-exploited by the agro-chemical industry. Moreover, insect mAChRs have been less well studied than their vertebrate counterparts. Their critical functions mean that a better knowledge of the insect mAChRs is crucial for the effort to develop a new molecular-level strategy for insect pest management. Almost all insects possess three mAChRs named A, B and C which differ according to their coupling effector systems and their pharmacological profile. The aim of this study was to characterize the A-type mAChR (mAChR-A) from Anopheles gambiae which is the major vector of malaria in order to develop new strategies in pest management. In this paper, we reported that mAChR-A is more expressed in adult mosquitoes than in larvae. Furthermore, using calcium imaging recordings, we found that the An. gambiae mAChR-A expressed in Sf9 cells is activated by specific muscarinic agonists acetylcholine, muscarine and oxotremorine M and blocked by several mAChR antagonists. Moreover, using inhibitors of phosphoinositide pathway such as Gαq/11 protein blocker, we have shown that an increased intracellular calcium concentration elicited by the acetylcholine application was mediated by PLC/IP3R pathway. As a rise in intracellular calcium concentration could lead to an increase in the insecticide target sensitivity, these results suggest that An. gambiae mAChR-A should not be only considered as a potential target for new molecules but also as a key element to optimize the efficacy of insecticide in vector control.

Biased Profile of Xanomeline at the Recombinant Human M4 Muscarinic Acetylcholine Receptor.

Many Food and Drug Administration (FDA)-approved drugs are structural analogues of the endogenous (natural) ligands of G protein-coupled receptors (GPCRs). However, it is becoming appreciated that chemically distinct ligands can bind to GPCRs in conformations that lead to different cellular signaling events, a phenomenon termed biased agonism. Despite this, the rigorous experimentation and analysis required to identify biased agonism are often not undertaken in most clinical candidates and go unrealized. Recently, xanomeline, a muscarinic acetylcholine receptor (mAChR) agonist, has entered phase III clinical trials for the treatment of schizophrenia. If successful, xanomeline will be the first novel FDA-approved antipsychotic drug in almost 50 years. Intriguingly, xanomeline's potential for biased agonism at the mAChRs and, in particular, the M4 mAChR, the most promising receptor target for schizophrenia, has not been assessed. Here, we quantify the biased agonism profile of xanomeline and three other mAChR agonists in Chinese hamster ovary cells recombinantly expressing the M4 mAChR. Agonist activity was examined across nine distinct signaling readouts, including the activation of five different G protein subtypes, ERK1/2 phosphorylation, β-arrestin recruitment, calcium mobilization, and cAMP regulation. Relative to acetylcholine (ACh), xanomeline was biased away from ERK1/2 phosphorylation and calcium mobilization compared to Gαi2 protein activation. These findings likely have important implications for our understanding of the therapeutic action of xanomeline and call for further investigation into the in vivo consequences of biased agonism in drugs targeting the M4 mAChR for the treatment of schizophrenia.

Understanding Why Muscarinic Receptor Agonists Have Antipsychotic Properties

All current antipsychotics have direct dopamine (DA) D2 receptor activity, which is associated with problems such as dysphoria, EPS, or prolactin elevation. Muscarinic receptor agonists have shown antipsychotic-like activity across preclinical models and clinical trials. This poster reviews preclinical evidence as to how muscarinic receptor agonists, such as the M1/M4 preferring agonist xanomeline, might have clinically relevant antipsychotic effects. Highlight the novel mechanisms through which muscarinic receptor agonists are associated with antipsychotic effects without having any direct dopaminergic D2 receptor activity. The muscarinic receptor family is composed of 5 G protein-coupled receptors (GPCRs). One of the leading hypotheses explaining the antipsychotic activity of muscarinic receptor agonists is preclinical studies of muscarinic receptor modulation of those DA circuits associated with psychosis. Both M1 and M4 receptors are expressed in DA neural circuits implicated in psychosis, and provide unique regulation of these circuits. Xanomeline has both functional M1 and M4 receptor agonist activity, and shows robust antipsychotic-like effects in several animal models that require the presence of functional M1 and M4 receptors. M4 receptors are autoreceptors on cholinergic neurons that regulate DA circuits in two locations: ventral tegmental area (VTA) and nucleus accumbens (NAc). Cholinergic-rich neurons from the hindbrain at the VTA, where they release acetylcholine (ACh) into DA-rich synaptic spaces. M4 autoreceptors are present on these neurons, and their activation reduces ACh release and lowers ambient synaptic ACh concentrations, leading to reduced DA cell firing. Cholinergic interneurons residing in the NAc also express M4 autoreceptors. These ACh interneurons regulate ACh release with M4 activation also turning off ACh release. Therefore, M4 receptors serve as DA regulators at VTA and NAc, both key sites for dopamine's role in psychotic processes. M1 receptors regulate DA circuits in a different, "top down" manner. M1 receptors are found on cortical inhibitory interneurons. When activated, inhibitory drive onto excitatory output neurons is enhanced, which leads to reduced excitatory tone to VTA DA neurons. Over the last 25years, a growing body of evidence has shown potential for muscarinic receptor agonists to become a new class of medicines with potent antipsychotic activity. Preclinical data at micro-and macro-circuit levels suggest that the M1 and M4 receptor subtypes are most relevant in the regulation of DA circuits. The antipsychotic effects of muscarinic agonists effects may arise from influencing these key muscarinic receptor subtypes that are integral to the regulation of DA neural circuits. In summary, there has been great progress in understanding the potential for muscarinic receptor agonists for the treatment of psychosis. Karuna Therapeutics.

Biphasic reward effects are characteristic of both lorcaserin and drugs of abuse: implications for treatment of substance use disorders.

Lorcaserin is a modestly selective agonist for 2C serotonin receptors (5-HT2CR). Despite early promising data, it recently failed to facilitate cocaine abstinence in patients and has been compared with dopamine antagonist medications (antipsychotics). Here, we review the effects of both classes on drug reinforcement. In addition to not being effective treatments for cocaine use disorder, both dopamine antagonists and lorcaserin can have biphasic effects on dopamine and reward behavior. Lower doses can cause enhanced drug taking with higher doses causing reductions. This biphasic pattern is shared with certain stimulants, opioids, and sedative-hypnotics, as well as compounds without abuse potential that include agonists for muscarinic and melatonin receptors. Additional factors associated with decreased drug taking include intermittent dosing for dopamine antagonists and use of progressive-ratio schedules for lorcaserin. Clinically relevant doses of lorcaserin were much lower than those that inhibited cocaine-reinforced behavior and can also augment this same behavior in different species. Diminished drug-reinforced behavior only occurred in animals after higher doses that are not suitable for use in patients. In conclusion, drugs of abuse and related compounds often act as biphasic modifiers of reward behavior, especially when evaluated over a broad range of doses. This property may reflect the underlying physiology of the reward system, allowing homeostatic influences on behavior.