Biology subjects

Maskos, U.

Publications and source records attributed to Maskos, U..

15 recordsLinked to original sources

bioRxiv2024

Nicotine engages a VTA-NAc feedback loop to inhibit amygdala-projecting dopamine neurons and induce anxiety.

Nicotine activates ventral tegmental area (VTA) dopaminergic (DA) neurons projecting to the nucleus accumbens (NAc) to drive its reinforcing effects. Simultaneously, it inhibits those projecting to the amygdala (Amg) to mediate anxiety through a process that remains unknown. Here we show that NAc- and Amg-projecting DA neurons respond with similar polarities to ethanol and nicotine, suggesting a shared network-based mechanism underlying the inhibitory effect of these otherwise pharmacologically-distinct drugs. Selective activation of NAc-projecting DA neurons, using genetic or optogenetic strategies, produced inhibition of Amg-projecting DA neurons, through a GABAergic feedback loop. Furthermore, optogenetically silencing this feedback loop prevented nicotine from inducing both inhibition of DA neurons and anxiety-like behavior. Therefore, nicotine-induced inhibition of the VTA-Amg DA pathway results from a VTA-NAc inhibitory feedback loop, mediating anxiety.

neuroscience↗

bioRxiv2024

CHRFAM7A overexpression in human iPSC-derived Interneurons dysregulates α7-nAChR surface expression and alters response to oligomeric β-amyloid peptide

The 7 neuronal nicotinic receptor (7-nAChR) gene, CHRNA7, is widely expressed within the brain and at the periphery. It plays various important roles in cognition and immune functions. Decreased expression of 7-nAChR has been associated with Alzheimers disease (AD) triggered by the accumulation of the 42-amino acid beta-amyloid peptide (A{beta}1-42). The interactions of this peptide with 7-nAChR may represent a pivotal mechanism that is involved in pathogenesis of AD. The regulation of CHRNA7 is a complex process. Normal function of 7-nAChR in mammalian cells requires the co-expression of chaperone proteins such as RIC3 and NACHO which facilitate the formation of cell surface receptors. In humans, CHRNA7 regulation also involves the specific chimeric CHRFAM7A gene product dup7, which may assemble with 7 subunits and lead to dominant negative regulation of 7-nAChR function. To further elucidate the complex interplay between CHRFAM7A gene product (dup7), 7-nAChRs and A{beta}1-42, we used human induced pluripotent stem cells (iPSC)-derived interneurons (INs). Four iPSC lines were analyzed for the presence of CHRFAM7A copies. Among them, a cell line with a null genotype was selected for the lentiviral overexpression of CHRFAM7A. Our data show that overexpression of CHRFAM7A led to a reduction in the surface detection of 7-nAChR ligand binding sites in iPSC-derived INs. INs expressing the 7-dup7 subunit (7-dup7-INs) exhibited lower levels of RIC3 and NACHO. Upon agonist treatment by nicotine, an up-regulation of 7-nAChR ligand binding sites was observed in 7-dup7-INs as compared to non-transduced INs (7-INs). At low levels of A{beta} treatment, 7-INs displayed a significant reduction in production of reactive oxygen species (ROS), while high levels resulted in a slight increase. In contrast, 7-dup7-INs exhibited lower baseline levels of ROS that remained unaltered by A{beta} treatment. ROS are known to exacerbate AD pathogenesis. We hypothesize that such effects may also be triggered by 7-dup7-INs in the brain of patients. Further investigations are currently undertaken to confirm this hypothesis.

neuroscience↗

bioRxiv2024

Linking Altered Neuronal and Synaptic Properties to Nicotinic Receptor Alpha5 Subunit Gene Dysfunction: A Translational Investigation in Rat mPFC and Human Cortical Layer 6

BackgroundGenetic variation in the 5 nicotinic acetylcholine receptor (nAChR) subunit of mice results in behavioral deficits linked to the prefrontal cortex (PFC). A Single Nucleotide Polymorphisms (SNP) in CHRNA5 imparts a partial loss of function to the 5 subunit-containing (5*) nAChRs and have been demonstrated to be associated with psychiatric disorders in humans, including schizophrenia, nicotine dependence, cocaine and alcohol addiction. MethodsWe performed single cell-electrophysiology combined with morphological reconstructions on layer 6 (L6) excitatory neurons in the medial PFC (mPFC) of wild type (WT) rats (n = 25), rats carrying the human coding polymorphism rs16969968 in Chrna5 (n = 11) and 5 knockout (KO) rats (n = 28). Neuronal and synaptic properties were compared among three rat genotypes. Galantamine was applied to identified L6 neuron populations to specifically boost the nicotinic responses mediated by 5*nAChRs in the rat mPFC and human neocortex (n = 6 patients). ResultsCompared with neurons in WT rats, L6 regular spiking (RS) neurons in the 5KO group exhibited altered electrophysiological properties, while those in 5SNP rats remained unchanged. L6 RS neurons in mPFC of 5SNP and 5KO rats differed from WT rats in dendritic morphology, spine density and spontaneous synaptic activity. Galantamine acted as a positive allosteric modulator of 5*nAChRs in RS but not burst spiking (BS) neurons in both rat and human cortical L6. ConclusionOur findings suggest that dysfunction in the 5 subunit gene leads to aberrant neuronal and synaptic properties, shedding light on the underlying mechanisms of cognitive deficits observed in human populations carrying 5SNPs. They highlight a potential pharmacological target for restoring the relevant behavioral output.

neuroscience↗

bioRxiv2023

Generation of nanobodies acting as silent and positive allosteric modulators of the α7 nicotinic acetylcholine receptor

The 7 nicotinic acetylcholine receptor (nAChR), a potential drug target for treating cognitive disorders, mediates communication between neuronal and non-neuronal cells. Although many competitive antagonists, agonists, and partial-agonists have been found and synthesized, they have not led to effective therapeutic treatments. In this context, small molecules acting as positive allosteric modulators binding outside the orthosteric, acetylcholine, site have attracted considerable interest. Two single-domain antibody fragments, C4 and E3, against the extracellular domain of the human 7-nAChR were generated through alpaca immunization with cells expressing a human 7-nAChR/mouse 5-HT3A chimera, and are herein described. They bind to the 7-nAChR but not to the other major nAChR subtypes, 4{beta}2 and 3{beta}4. E3 acts as a slowly associating positive allosteric modulator, strongly potentiating the acetylcholine-elicited currents, while not precluding the desensitization of the receptor. An E3-E3 bivalent construct shows similar potentiating properties but displays very slow dissociation kinetics conferring quasi-irreversible properties. Whereas, C4 does not alter the receptor function, but fully inhibits the E3-evoked potentiation, showing it is a silent allosteric modulator competing with E3 binding. Both nanobodies do not compete with -bungarotoxin, localizing at an allosteric extracellular binding site away from the orthosteric site. The functional differences of each nanobody, as well as the alteration of functional properties through nanobody modifications indicate the importance of this extracellular site. The nanobodies will be useful for pharmacological and structural investigations; moreover, they, along with the extracellular site, have a direct potential for clinical applications.

neuroscience↗

bioRxiv2023

An original potentiating mechanism revealed by the cryoEM structures of the human α7 nicotinic receptor in complex with nanobodies

The human 7 nicotinic receptor is a pentameric channel mediating cellular and neuronal communication. It has attracted considerable interest to design ligands for the treatment of neurological and psychiatric disorders. To develop a novel class of 7 ligands, we recently generated two nanobodies named E3 and C4 acting as positive and silent allosteric modulators respectively. Here, we solved the cryo-EM structures of the nanobody-receptor complexes. E3 and C4 bind to a common epitope involving two subunits at the apex of the receptor. They form by themselves a symmetric pentameric assembly that extends the extracellular domain. Unlike C4, the binding of E3 drives an active or desensitized conformation in the absence of orthosteric agonist, and mutational analysis shows a key contribution of a N-linked sugar moiety in mediating E3 potentiation. The nanobody E3, by remotely controlling the global allosteric conformation of the receptor, implements an original mechanism of regulation which opens new avenues for drug design.

neuroscience↗

bioRxiv2022

Poor sensitivity of iPSC-derived neural progenitors and glutamatergic neurons to SARS-CoV-2

COVID-19 is a respiratory disease affecting multiple organs including the central nervous system (CNS), with a characteristic loss of smell and taste. Although frequently reported, the neurological symptoms remain enigmatic. There is no consensus on the extent of CNS infection. Here, we derived human induced pluripotent stem cells (hiPSC) into neural progenitor cells (NPCs) and cortical excitatory neurons to study their permissiveness to SARS-CoV-2 infection. Flow cytometry and western blot analysis indicated that NPCs and neurons do not express detectable levels of the SARS-CoV-2 receptor ACE2. We thus generated cells expressing ACE2 by lentiviral transduction to analyze in a controlled manner the properties of SARS-CoV-2 infection relative to ACE2 expression. Sensitivity of parental and ACE2 expressing cells was assessed with GFP- or luciferase-carrying pseudoviruses and with authentic SARS-CoV-2 Wuhan, D614G, Alpha or Delta variants. SARS-CoV-2 replication was assessed by microscopy, RT-qPCR and infectivity assays. Pseudoviruses infected only cells overexpressing ACE2. Neurons and NPCs were unable to efficiently replicate SARS-CoV-2, whereas ACE2 overexpressing neurons were highly sensitive to productive infection. Altogether, our results indicate that primary NPCs and cortical neurons remain poorly permissive to SARS-CoV-2 across the variants spectrum, in the absence of ACE2 expression.

neuroscience↗

bioRxiv2021

Prolonged nicotine exposure reduces aversion to the drug in mice by altering nicotinic transmission in the interpeduncular nucleus.

Nicotine intake is likely to result from a balance between the rewarding and aversive properties of the drug, yet the individual differences in neural activity that control aversion to nicotine and their adaptation during the addiction process remain largely unknown. Using a two-bottle choice experiment, we observed a high heterogeneity in nicotine-drinking profiles in isogenic adult male mice, with about half of the mice persisting in consuming nicotine even at high concentrations, whereas the other half stopped consuming. We found that nicotine intake was negatively correlated with nicotine-evoked currents in the interpeduncular nucleus (IPN), and that prolonged exposure to nicotine, by weakening this response, decreased aversion to the drug, and hence boosted consumption. Lastly, using knock-out mice and local gene re-expression, we identified {beta}4-containing nicotinic acetylcholine receptors of IPN neurons as the molecular and cellular correlates of nicotine aversion. Collectively, our results identify the IPN as a substrate of individual variabilities and adaptations in nicotine consumption.

neuroscience↗

bioRxiv2021

Inhibitory control of synaptic signals preceding motor action in mouse frontal cortex

Preparatory activity in the frontal cortex preceding movement onset is thought to represent a neuronal signature of motor planning. However, how excitatory and inhibitory synaptic inputs to frontal neurons are integrated during movement preparation remains unclear. Here we address this question by performing in vivo whole-cell patch-clamp recordings in the secondary motor cortex (MOs) of head-fixed mice moving on a treadmill. We find that both superficial and deep principal neurons show slowly increasing (~10 s) membrane potential and spike rate ramps preceding the onset of spontaneous, self-paced running periods. By contrast, in animals trained to perform a goal-directed task, both membrane potential and spike ramps are characterized by larger amplitudes and accelerated kinetics during preparation of goal-driven movement. To determine the role of local inhibitory neurons in shaping these task-dependent preparatory signals, we chemogenetically suppressed the activity of specific interneuron subpopulations in untrained animals. Inactivation of parvalbumin-positive (PV+) interneurons leads to depolarized membrane potential ramps with increased amplitudes during preparation of movement, while inactivation of somatostatin-positive (SOM+) interneurons abolishes membrane potential ramps. A computational model of the local MOs circuit shows that SOM+-mediated inhibition of PV+ interneurons in conjunction with recurrent connectivity among the principal neurons can reproduce slow ramping signals, while plasticity of excitatory synapses on SOM+ interneurons can explain the acceleration of these signals in trained animals. Together, our data reveal that local inhibitory neurons play distinct roles in controlling task-dependent preparatory ramping signals when MOs neurons integrate external inputs during motor planning. HighlightsO_LIPrincipal neurons in MOs show slow preparatory membrane potential and firing rate ramps preceding the onset of spontaneous, self-paced running periods. C_LIO_LIIn animals trained to perform a goal-directed task, both membrane potential and spike ramps are faster and larger in amplitude. C_LIO_LIInactivation of PV+ interneurons disinhibits MOs principal neurons and increases the amplitude of membrane potential ramps, while inactivation of SOM+ interneurons abolishes membrane potential ramps. C_LIO_LIOur modeling results suggest that the concerted action of external inputs and local inactivation shapes task-dependent preparatory motor signals in MOs neurons. C_LI

neuroscience↗

bioRxiv2020

Distinct dopamine circuits transmit the reinforcing and anxiogenic effects of nicotine

Nicotine, the addictive component of tobacco, stimulates dopamine (DA) neurons of the ventral tegmental area (VTA) to establish and maintain reinforcement. Nicotine also induces negative emotional states such as anxiety, yet through an unknown circuitry. Here we show that nicotine at reinforcing doses drives opposite functional responses on two distinct populations of VTA DA neurons with anatomically segregated projections: it activates those that project to the nucleus accumbens (NAc) while it inhibits those that project to the amygdala nuclei (Amg). We further show that nicotine, by acting on {beta}2 subunit-containing nicotinic acetylcholine receptors of the VTA, mediates both reinforcement and anxiety. Finally, using optogenetic experiments we dissociate the roles of the VTA-NAc excitation and VTA-Amg inhibition in reinforcement and anxiety-like behavior, respectively. We thus propose that the positive and negative behavioral outcomes of nicotine consumption involve distinct subpopulations of VTA DA neurons with opposite responses to nicotine.

neuroscience↗

bioRxiv2020

Nicotinic receptors atlas in the adult human lung

Nicotinic acetylcholine receptors (nAChRs) are pentameric ligand-gated ion channels responsible for the rapid neural and neuromuscular signal transmission. Although it is well documented that 16 subunits are encoded by the human genome, their presence in airway epithelial cells (AEC) remains poorly understood, and contribution to pathology is mainly discussed in the context of cancer. We analysed nAChR subunit expression in the human lung of smokers and non-smokers using transcriptomic data for whole lung tissues, isolated large AEC, and isolated small AEC. We identified differential expressions of nAChRs in terms of detection and repartition in the three modalities. Smoking-associated alterations were also unveiled. Then, we identified a nAChR transcriptomic print at a single cell level. Finally, we reported the localizations of detectable nAChRs in bronchi and large bronchioles. Thus, we compiled the first complete atlas of pulmonary nAChRs to open new avenues to further unravel the involvement of these receptors in lung homeostasis and respiratory diseases.

cell biology↗

bioRxiv2019

Gene-Gene interactions and pleiotropy in the brain nicotinic pathway associated with the heaviness and precocity of tobacco smoking among outpatients with multiple substance use disorders

IntroductionTobacco smoking is a major health burden worldwide, especially in populations suffering from other substance use disorders (SUDs). Several smoking phenotypes have been associated with single nucleotide polymorphisms (SNPs) of nicotinic acetylcholine receptors (nAChRs). Yet, little is known about the genetics of tobacco smoking in populations with other SUDs, particularly regarding gene-gene interactions and pleiotropy, which are likely involved in the polygenic architecture of SUDs. Thus, we undertook a candidate pathway association study of nAChR-related genes and smoking phenotypes in a sample of SUD patients.\n\nMethods493 patients with genetically-verified Caucasian ancestry were characterized extensively regarding patterns of tobacco smoking, other SUDs, and 83 SNPs from the nicotinic pathway, encompassing all brain nAChR subunits and metabolic/chaperone/trafficking proteins. Single-SNP, gene-based and SNP x SNP interactions analyses were performed to investigate associations with relevant tobacco smoking phenotypes. This included Bayesian analyses to detect pleiotropy, and adjustment on clinical and sociodemographic confounders.\n\nResultsAfter multiple adjustment, we found independent associations between CHRNA3 rs8040868 and a higher number of cigarettes per day (CPD), and between RIC3 rs11826236 and a lower age at smoking initiation. Two SNP x SNP interactions were associated with age at onset (AAO) of daily smoking. There was pleiotropy regarding three SNPs in CHRNA3 (CPD, AAO daily smoking), ACHE (CPD, HSI) and CHRNB4 (CPD, both AAOs).\n\nDiscussionDespite limitations, the present study shows that the genetics of tobacco smoking in SUD patients are both distinct and partially shared across smoking phenotypes, and involve metabolic and chaperone effectors of the nicotinic pathway.

genetics↗

bioRxiv2018

Mammalian vesicular glutamate transporter VGLUT1 reduces synaptic vesicle superpool size and spontaneous release frequency.

Glutamate secretion at excitatory synapses is tightly regulated to allow for the precise tuning of synaptic strength. Vesicular Glutamate Transporters (VGLUT) accumulate glutamate into synaptic vesicles (SV) and thereby regulate quantal size. Further, the number of release sites and the release probability of SVs maybe regulated by the organization of active zone proteins and SV clusters. In the present work, we uncover a mechanism mediating an increased SV clustering through a tripartite interaction of VGLUT1, endophilinA1 and intersectin1. This strengthening of SV clusters results in a combined reduction of axonal SV super-pool size and miniature excitatory events frequency. Our findings support a model in which clustered vesicles are held together through multiple weak interactions between SH3 domains and proline rich sequences of synaptic proteins. In mammals, VGLUT1 gained a poly-proline sequence that recruits endophilinA1 and turns the transporter into a dual regulator of quantal release parameters at excitatory synapses.

neuroscience↗

bioRxiv2018

Nicotinic modulation of hierarchal inhibitory control over prefrontal cortex resting state dynamics: modeling of genetic modification and schizophrenia-related pathology

Nicotinic acetylcholine receptors (nAChRs) strongly modulate the cholinergic drive to a hierarchy of inhibitory neurons in the superficial layers of the PFC, critical to cognitive processes. Genetic deletion of various types of nAChRs, located on specific interneurons, impacts the properties of ultra-slow transitions between high and low activity states (H-states and L-states, respectively), recorded in mice during quiet wakefulness. In addition, recent data indicate that a genetic mutation of the 5 nAChR subunit located on vasoactive intestinal polypeptide (VIP) inhibitory neurons, the rs16969968 single nucleotide polymorphism (5 SNP), appears to be responsible for \"hypofrontality\" observed in schizophrenia. Chronic nicotine application to 5 SNP mice restores neural activity to control levels. Using firing rate models of hierarchically organized neural populations, we showed that the change of activity patterns recorded in the genetically modified mice can be explained by a change of activity state stability, differentially modulated by cholinergic inputs to parvalbumin (PV), somatostatin (SOM) or VIP inhibitory populations. A change in amplitude, but not duration of H-states fully account for the lowered pyramidal (PYR) firing rates recorded in 5 SNP mice. We demonstrate that desensitization and upregulation of {beta}2 nAChRs located on SOM interneurons, but not activation of 5 nAChRs located on VIP interneurons, by chronic nicotine application could account for activity normalization recorded in 5 SNP mice. The model implies that subsequent nicotine withdrawal should lead to PYR activity depression more severe than the original hypofrontality caused by SNP mutation.

systems biology↗

bioRxiv2018

Somatic nicotinic acetylcholine receptors control the activity of dopamine neurons and reward-related behaviors.

Dopamine (DA) neurons of the ventral tegmental area (VTA) integrate cholinergic inputs to regulate key functions such as motivation and goal-directed behaviors. Yet the temporal dynamic range and mechanism of action of acetylcholine (ACh) on the modulation of VTA circuits and reward-related behaviors are not known. Here we used a chemical-genetic approach for rapid and precise optical manipulation of nicotinic neurotransmission in VTA neurons in vivo. We provide direct evidence that the ACh tone fine-tunes the firing properties of VTA DA neurons through somatic {beta}2-containing ({beta}2*) nicotinic ACh receptors (nAChRs). Furthermore, locally photo-antagonizing these receptors in the VTA was sufficient to reversibly switch nicotine reinforcement on and off. By enabling control of nicotinic transmission in targeted brain circuits, this technology will help unravel the various physiological functions of nAChRs and may assist in the design of novel therapies relevant to neuropsychiatric disorders.

neuroscience↗

bioRxiv2018

Acetylcholine-dependent phasic dopamine activity signals exploratory locomotion and choices

Dopamine neurons from the Ventral Tegmental Area (VTA) switch from tonic to phasic burst firing in response to reward-predictive cues and actions. Bursting is influenced by nicotinic acetylcholine receptors (nAChRs), which are not implicated in reinforcement learning, but rather in exploration and uncertainty-seeking. The leading model assigns these functions to tonic dopamine firing. To investigate this paradox, we recorded the activity of VTA dopamine neurons during a spatial decision-making task. When reward was certain, mice adopted a stereotyped behavior, and dopamine neurons signaled reward. When confronted with uncertain rewards or a novel environment, mice exhibited exploration. Modulation of phasic, but not tonic, dopamine activity predicted uncertainty-seeking and locomotor exploration. Deletion of nAChRs disrupted the influence of uncertainty and novelty on dopamine firing and behavior, sparing reward signaling and learning. Hence, nAChR modulation of dopamine neurons can influence cognitive functions on a short timescale, through the modulation of phasic, synchronous bursting.

neuroscience↗