Biology subjects

Contractor, A.

Publications and source records attributed to Contractor, A..

16 recordsLinked to original sources

bioRxiv2026

Movement refinement and cholinergic regulation of outcome-dependent updating during skilled reaching.

Motor skill learning transforms initially variable actions into precise and reproducible movements, yet conventional measures of task success can obscure the distinct processes through which this refinement occurs. We combined detailed outcome scoring and kinematic analysis of single-pellet reaching in mice to resolve how individual components of the action change with practice. Decomposing reaching into successive stages revealed improvements in targeting and retrieval, while grasp success after pellet contact did not change detectably. Paw trajectories became more consistent across both successful and unsuccessful reaches, whereas changes in the mean speed profile were detected in successful reaches. To examine how striatal cholinergic signaling contributes to movement refinement and the influence of recent outcomes on subsequent actions, we monitored acetylcholine (ACh) in vivo and inhibited cholinergic interneurons (CINs) during training. ACh was elevated before reach onset and declined during execution across all reach outcomes, with no detectable change between early and late training. CIN inhibition had little effect on movement refinement across days, but altered how recent outcomes influenced the next reach, most clearly following attempts in which the pellet was grasped and then lost. These findings distinguish refinement of the practiced movement from outcome-dependent adjustments to its execution. Together, they raise the possibility that the pre-reach ACh elevation plays a role in enabling the evaluation of recent outcomes to update the execution of the next reach.

neuroscience↗

bioRxiv2026

Brain Landscape In Situ Crosslinking Mass Spectrometry (BLIS-XL-MS) Enables Global Analysis of Protein Structural Remodeling in the Brain

Pathological protein conformational remodeling is a key molecular feature of brain disorders. However, conventional approaches to understand the changes in potein conformation are targeted and difficult to scale proteome-wide analysis. Emerging mass spectrometry-based structural proteomic methods broaden coverage but often involve complex workflows and trade-offs between labeling efficiency and preservation of the in vivo molecular state. Thus, quantitative analysis of proteome-wide structural remodeling remains limited. Here we present Brain Landscape In Situ Crosslinking Mass Spectrometry (BLIS-XL-MS), an experimental and computational framework for analyzing protein and protein-complex remodeling in brain tissue. BLIS-XL-MS stabilizes the molecular state before secondary crosslinking, improves reagent accessibility through sectioning and permeabilization, and integrates quantitative crosslink analysis with structural and protein-interaction-network interpretation. Applied to brains from GluA1A636T knock-in mice, modeling a neurodevelopmental disorder, BLIS-XL-MS revealed coordinated remodeling of protein systems involved in AMPA receptor-trafficking, mitochondrial function and cell-death pathways. We demonstrate that BLIS-XL-MS provides a scalable framework for mapping disease-associated structural remodeling across the brain proteome.

neuroscience↗

bioRxiv2026

A pathogenic AMPA receptor gating mutation disrupts synapse-mitochondrion axis and stalls synapse maturation

AMPA receptors (AMPARs) are central regulators of excitatory synaptic transmission and play critical roles in activity-dependent synapse maturation and circuit development. De novo missense mutations in AMPAR subunits have been widely linked to neurodevelopmental disorders (NDDs). Despite this, how these variants lead to neuronal dysfunction remain poorly understood. Here, we investigate the consequences of a recurrent pathogenic mutation in the GluA1 subunit (GRIA1 p.A636T), which alters AMPAR gating properties and is associated with autism spectrum disorder and intellectual disability. We developed a GluA1A636T knock-in mouse model, we show that GluA1A636T mice exhibit impairments in hippocampal-dependent learning and working memory accompanied by reduced baseline activity of CA1 neurons in vivo. Mass spectrometry-based quantitative proteomic analyses of juvenile and adult hippocampal samples revealed that the A636T mutation significantly alters synaptic protein expression at both ages. Notably, the mutation drives a robust upregulation of mitochondrial proteins specifically in adult mice. Consistent with this, dendritic mitochondria in adult GluA1A636T mice exhibited altered morphology and increased oxidative stress. Electrophysiological analyses further revealed abnormalities in synaptic function, including reduced basal excitatory transmission, persistence of functionally silent synapses in adulthood, and altered synaptic plasticity consistent with impaired synapse maturation. Together, these findings demonstrate that a pathogenic AMPAR gating mutation disrupts the coordinated development of synaptic and metabolic programs in the hippocampus, linking altered excitatory signaling to delayed mitochondrial stress and enduring circuit dysfunction. Our study provides a developmental framework for understanding how disease-associated AMPAR variants impair brain function and highlights synapse-mitochondria coupling as a critical axis in glutamate receptor ionotropic (GRI) disorders.

neuroscience↗

bioRxiv2026

Autism associated mutation in Cacna1d causes perseverative behavioral phenotype in mice

Behavioral inflexibility and perseveration are core features of autism spectrum disorder and are frequently modeled in mice using reversal learning and repetitive behavior assays. Mutations in CACNA1D, which encodes the L-type calcium channel Cav1.3, have been linked to autism, yet their behavioral consequences remain incompletely characterized. We examined mice carrying the autism-associated Cacna1dG407R gain-of-function mutation across a battery of assays assessing learning, flexibility, and repetitive behavior. Mutant mice learned spatial discriminations and instrumental contingencies at rates comparable to wild-type controls but exhibited deficits during reversal learning following intermediate and extended overtraining, as well as under probabilistic reinforcement. Across ethological assays, mutant mice showed increased grooming, marble burying, and nestlet shredding, consistent with enhanced perseverative behavior. Anxiety-related measures and general locomotion were largely unaffected. These results identify Cav1.3 gain-of-function as a selective regulator of behavioral flexibility and support a role for calcium-dependent corticostriatal plasticity in autism-associated perseveration.

neuroscience↗

bioRxiv2025

Exaggerated NMDA Receptor-Primed Metaplasticity via SK Channel Dysregulation in Fmr1 Knockout Mice

Fragile X syndrome (FXS), the most common monogenic neurodevelopmental disorder associated with autism and intellectual disability, results from the loss of expression of the FMR1 gene. Synaptic and circuit-level abnormalities are well documented in FXS and extensively studied in the Fmr1 KO mouse model. In CA1 hippocampal neurons functional, molecular and structural synaptic changes have been described yet the canonical form of Hebbian CA1 long term potentiation (LTP) remains intact in Fmr1 KO mice. Here we examined whether state-dependent synaptic plasticity in CA1, in which prior "priming" activity modulates subsequent synaptic plasticity, was affected in Fmr1 KO mice. We found that NMDA receptor activation prior to LTP induction produced metaplastic inhibition of LTP, which was exaggerated in Fmr1 KO mice. This effect was mediated by the activity of small conductance calcium-activated potassium (SK) channels which was enhanced after NMDA priming, and dampened dendritic excitability. Blocking SK channels during NMDA-primed LTP induction eliminated the abnormal metaplasticity in Fmr1 KO slices, implicating altered SK activity in the exaggerated LTP inhibition in Fmr1 KO mice. These finding reveal a disrupted coupling between NMDA receptors and SK channels in Fmr1 KO mice, which alters the impact of priming on LTP expression in the CA1. Altered metaplasticity may represent a neural correlate of impaired adaptive hippocampal learning in Fmr1 KO mice. Significance StatementWhile conventional synaptic plasticity (LTP and LTD) has been extensively examined in Fmr1 KO mice, evidence about the integrity of metaplasticity in these mice has been limited. This study provides a characterization of alterations in NMDA receptor mediated metaplasticity in the hippocampus in Fmr1 KO mice. The question of whether hippocampal LTP is altered in these mice remains unresolved, and changes in metaplasticity may partly explain the discrepancies across studies. Our findings not only identify novel synaptic phenotypes and their underlying mechanisms in the FXS mouse model, but also highlight potential therapeutic targets for FXS.

neuroscience↗

bioRxiv2025

Operant House: A Versatile Open-Source Platform for Automated Operant Conditioning Testing of Mice in Home Cages

Operant conditioning is a valuable method for studying cognitive functions, yet its adoption is limited by low throughput, labor intensity, and high costs. Here, we developed "Operant House," a low-cost, programmable device featuring a touchscreen, retractable levers, and a water reward port, designed for flexible, automated operant conditioning tasks. To validate its utility, we implemented two protocols to assess working memory in mice: a delayed non-match-to-position test and a two-choice spatial discrimination test. Using these protocols, we examined a mouse model of Alzheimers disease carrying familial Alzheimers disease-associated amyloid precursor protein mutations. Results revealed significant working memory deficits as early as 5 months of age. These findings highlight the Operant House as a cost-effective, high-throughput platform for evaluating higher cognitive functions in mice, offering an accessible tool for investigating models of neurological and neuropsychiatric disorders.

neuroscience↗

bioRxiv2024

Subregional activity in the dentate gyrus is amplified during elevated cognitive demands

Neural activity in the dentate gyrus (DG) supports the detection and discrimination of novelty, context, and patterns. Granule cell activation differs between the supra- and infrapyramidal blades across hippocampal-dependent tasks, yet how excitatory dynamics shape this blade-specific bias under varying cognitive demands remains unclear. Here, we combined an automated touchscreen pattern separation task in mice with temporally controlled tagging of active neurons to determine how increasing cognitive demand influences spatial activity patterns in the DG. As task difficulty increased, activation became progressively biased toward the suprapyramidal blade and was accompanied by structured distributions of active mature granule cells (mGCs) along both the radial and transverse axes. Selective inhibition of mGCs did not alter these spatial patterns but profoundly impaired performance, as mice were no longer able to discriminate between closely spaced locations. In contrast, chemogenetic inhibition of adult-born granule cells (abDGCs) beyond a critical maturation window impaired performance under high-demand conditions, increased overall mGC activity, and disrupted blade-specific organization even in animals that successfully completed the task. These findings demonstrate that high cognitive demand recruits spatially organized mGC activity and support a modulatory role for abDGCs in shaping dentate circuit dynamics.

neuroscience↗

bioRxiv2024

Levetiracetam prevents Aβ42 production through SV2a-dependent modulation of App processing in Alzheimer's disease models

In Alzheimers disease (AD), amyloid-beta (A{beta}) peptides are produced by proteolytic cleavage of the amyloid precursor protein (APP), which can occur during synaptic vesicle (SV) cycling at presynapses. Precisely how amyloidogenic APP processing may impair presynaptic proteostasis and how to therapeutically target this process remains poorly understood. Using App knock-in mouse models of early A{beta} pathology, we found proteins with hampered degradation accumulate at presynaptic sites. At this mild pathological stage, amyloidogenic processing leads to accumulation of A{beta}42 inside SVs. To explore if targeting SVs modulates A{beta} accumulation, we investigated levetiracetam (Lev), a SV-binding small molecule drug that has shown promise in mitigating AD-related pathologies despite its mechanism of action being unclear. We discovered Lev reduces A{beta}42 levels by decreasing amyloidogenic processing of APP in a SV2a-dependent manner. Lev corrects SV protein levels and cycling, which results in increased surface localization of APP, where it favors processing via the non-amyloidogenic pathway. Using metabolic stable isotopes and mass spectrometry we confirmed that Lev prevents the production of A{beta}42 in vivo. In transgenic mice with aggressive pathology, electrophysiological and immunofluorescent microscopy analyses revealed that Lev treatment reduces SV cycling and minimizes synapse loss. Finally, we found that human Down syndrome brains with early A{beta} pathology, have elevated levels of presynaptic proteins, confirming a comparable presynaptic deficit in human brains. Taken together, we report a mechanism that highlights the therapeutic potential of Lev to modify the early stages of AD and represent a promising strategy to prevent A{beta}42 pathology before irreversible damage occurs. One Sentence SummaryWe discovered that the SV-binding drug levetiracetam prevents A{beta}42 production by modulating SV cycling which alters APP localization and thus proteolytic processing, highlighting its therapeutic potential for AD.

neuroscience↗

bioRxiv2024

Human and Mouse Models for Kabuki Syndrome Reveal Increase in Inhibitory Synapse Development.

Intellectual disability, affecting 2-3% of the general population, often co-occurs with neurodevelopmental disorders and is frequently caused by mutations that impair synaptic function. Kabuki syndrome (KS), a rare multisystem disorder associated with developmental delay and intellectual disability, results from mutations in either KMT2D (KS1) or KDM6A (KS2), encoding a histone methyltransferase and demethylase, respectively. The mechanisms underlying intellectual disability in KS remain poorly understood. Here, we generated human iPS cells carrying conditional Cre/lox-dependent loss-of-function mutations in KMT2D or KDM6A and differentiated them into excitatory or inhibitory neurons. Analysis revealed that KS1 and KS2 inhibitory neurons unexpectedly showed increased GABAergic synapse formation, whereas excitatory neurons displayed reduced synapse development and impaired synaptic transmission. We confirmed these findings in hippocampal neurons in vitro and in vivo using a mouse model for KS1 demonstrating a bidirectional shift: increase in inhibition and decrease in excitation. Synapse numbers and synaptic transmission in brain slices were shifted to increased inhibition/excitation ratio. Mechanistically, KS1 mutations activated neuroinflammatory signaling, impaired astrocytic function, and promoted glia-driven inhibitory synapse formation in human neurons. By integrating human neuron models with conditional KMT2D/KDM6A deletions and a Kmt2d-mutant mouse model, we identify a novel synaptic disease mechanism in KS that links chromatin remodeling defects to disrupted information transfer in neural circuits, providing a mechanistic explanation for intellectual disability. Significance StatementKabuki syndrome, a rare disorder with intellectual disability, is caused by mutations in the chromatin regulators KMT2D and KDM6A, yet its cellular pathophysiology has remained unclear. Using new Cre/lox-inducible human neuron models together with a mouse model, we reveal a conserved excitation-inhibition imbalance characterized by increased inhibitory and decreased excitatory synapse formation. Our findings establish the first mechanistic framework linking KMT2D/KDM6A mutations to synaptic dysfunction, uncover glial contributions to disease pathogenesis, and suggest potential therapeutic avenues for restoring synaptic balance. HighlightsO_LIKS1 and KS2 mutations cause decrease in excitatory synapses in human neurons C_LIO_LIKS1 and KS2 mutations cause increase in inhibitory synapses in human neurons C_LIO_LIKS1 mutation causes decrease in excitatory and increase in inhibitory synapses in mice C_LIO_LIKS1 mutant mouse astrocytes facilitate increase in inhibitory synapses in human neurons C_LI

neuroscience↗

bioRxiv2024

Ca2+-dependent phosphodiesterase 1 regulates the plasticity of striatal spiny projection neuron glutamatergic synapses

Long-term synaptic plasticity at glutamatergic synapses on striatal spiny projection neurons (SPNs) is central to learning goal-directed behaviors and habits. Although considerable attention has been paid to the mechanisms underlying synaptic strengthening and new learning, little scrutiny has been given to those involved in the attenuation of synaptic strength that attends suppression of a previously learned association. Our studies revealed a novel, non-Hebbian, long-term, postsynaptic depression of glutamatergic SPN synapses induced by interneuronal nitric oxide (NO) signaling (NO-LTD) that was preferentially engaged at quiescent synapses. This form of plasticity was gated by local Ca2+ influx through CaV1.3 Ca2+ channels and stimulation of phosphodiesterase 1 (PDE1), which degraded cyclic guanosine monophosphate (cGMP) and blunted NO signaling. Consistent with this model, mice harboring a gain-of-function mutation in the gene coding for the pore-forming subunit of CaV1.3 channels had elevated depolarization-induced dendritic Ca2+ entry and impaired NO-LTD. Extracellular uncaging of glutamate and intracellular uncaging of cGMP suggested that this Ca2+-dependent regulation of PDE1 activity allowed for local regulation of dendritic NO signaling. This inference was supported by simulation of SPN dendritic integration, which revealed that dendritic spikes engaged PDE1 in a branch-specific manner. In a mouse model of Parkinsons disease (PD), NO-LTD was absent not because of a postsynaptic deficit in NO signaling machinery, but rather due to impaired interneuronal NO release. Re-balancing intrastriatal neuromodulatory signaling in the PD model restored NO release and NO-LTD. Taken together, these studies provide novel insights into the mechanisms governing NO-LTD in SPN and its role in psychomotor disorders, like PD.

neuroscience↗

bioRxiv2023

Modulation of the spatiotemporal dynamics of striatal direct pathway neurons and motor output by mGluR5

Striatal spiny-projection neurons (SPNs) integrate glutamatergic inputs from the motor cortex and thalamus with neuromodulatory signals to regulate motor output. In vivo Ca2+ imaging has demonstrated that spatially overlapping ensembles of direct and indirect pathway SPNs (dSPNs, iSPNs) are co-active during spontaneous movement. This co-activity is statistically greater among nearby neurons, correlates with behavioral state, and changes in an SPN-type-specific manner under pathological conditions. How this co-activity arises and whether is important for movement are not well understood. Co-activity likely arises from shared excitatory inputs, the strength of which are scaled by well-characterized mechanisms of synaptic plasticity. Here, we show that the Group I metabotropic glutamate receptor 5 (mGluR5), which regulates the strength of corticostriatal synapses, is a key mediator of behaviorally relevant SPN co-activity. Pharmacological modulation of mGluR5 signaling bidirectionally altered movement and co-activity, but not the absolute level of activity in dSPNs. Targeted deletion of mGluR5 in dSPNs recapitulated the effects on spatiotemporal neural dynamics and movement, consistent with a striatum-specific effect of mGluR5 modulation. Targeted deletion of mGluR5 also produced changes in the synaptic properties of dSPNs. Separate from any effects on overall activity, our results show that excitatory synaptic modulation influences motor function by coordinating the spatial co-activation of dSPNs in vivo.

neuroscience↗

bioRxiv2023

A pathogenic missense mutation in kainate receptors elevates dendritic excitability and synaptic integration through dysregulation of SK channels

Numerous rare de novo variants that cause neurodevelopmental disorders (NDDs) occur within genes encoding synaptic proteins, including ionotropic glutamate receptors (iGluRs). However, in many cases it remains unclear how damaging missense variants affect brain function. Here we determined the physiological consequences of an NDD causing missense mutation in the GRIK2 kainate receptor (KAR) gene, that results in a single amino acid change p.Ala657Thr in the GluK2 receptor subunit. We engineered the equivalent mutation in the mouse Grik2 gene, yielding a GluK2(A657T) mouse, to better understand the human disorder and determine how hippocampal neuronal function is disrupted. Synaptic KAR currents in hippocampal CA3 pyramidal neurons from heterozygous A657T mice exhibited slow decay kinetics, consistent with incorporation of the mutant subunit into functional receptors. Unexpectedly, CA3 neurons demonstrated elevated action potential spiking due to down-regulation of the small conductance Ca2+ activated K+ channel (SK), which mediates the post-spike afterhyperpolarization (AHP). The reduction in SK activity resulted in increased CA3 dendritic excitability, increased EPSP-spike coupling and lowered the threshold for the induction of LTP of the associational commissural (AC) synapses in the distal dendrites of CA3 neurons. Pharmacological inhibition of SK channels in wild-type (WT) mice increased dendritic excitability and EPSP-spike coupling, mimicking the phenotype in A657T mice and suggesting a causative role for attenuated SK activity in aberrant excitability observed in the mutant mice. These findings demonstrate that a disease-associated missense mutation in GRIK2 leads to altered signaling through neuronal KARs, pleiotropic effects on neuronal and dendritic excitability, and implicate these processes in neuropathology in patients with genetic NDDs.

neuroscience↗

bioRxiv2021

Modulating D1 rather than D2 receptor-expressing spiny-projection neurons corresponds to optimal antipsychotic effect

Overactive dopamine transmission in psychosis is predicted to unbalance striatal output via D1- and D2-dopamine receptor-expressing spiny-projection neurons (SPNs). Antipsychotic drugs are thought to re-balance this output by blocking D2-receptor signaling. Here we imaged D1- and D2-SPN Ca2+ dynamics in mice to determine the neural signatures of antipsychotic effect. Initially we compared effective (clozapine and haloperidol) antipsychotics to a candidate drug that failed in clinical trials (MP-10). Clozapine and haloperidol normalized hyperdopaminergic D1-SPN dynamics, while MP-10 only normalized D2-SPN activity. Clozapine, haloperidol or chemogenetic manipulations of D1-SPNs also normalized sensorimotor gating. Given the surprising correlation between clinical efficacy and D1-SPN modulation, we evaluated compounds that selectively target D1-SPNs. D1R partial agonism, antagonism, or positive M4 cholinergic receptor modulation all normalized the levels of D1-SPN activity, locomotion, and sensorimotor gating. Our results suggest that D1-SPN activity is a more relevant therapeutic target than D2-SPN activity for the development of effective antipsychotics.

neuroscience↗

bioRxiv2020

Gabra2 is a genetic modifier of Dravet syndrome in mice

Pathogenic variants in epilepsy genes result in a spectrum of clinical presentation, ranging from benign phenotypes to intractable epilepsies with significant co-morbidities and increased risk of sudden unexpected death in epilepsy (SUDEP). One source of this phenotypic heterogeneity is modifier genes that affect penetrance, dominance or expressivity of a primary pathogenic variant. Mouse models of epilepsy also display varying degrees of clinical severity on different genetic backgrounds. Mice with heterozygous deletion of Scn1a (Scn1a+/-) model Dravet syndrome, a severe epilepsy most often caused by SCN1A haploinsufficiency. Scn1a+/- heterozygous mice recapitulate key features of Dravet syndrome, including febrile and afebrile spontaneous seizures, SUDEP, and cognitive and behavioral deficits. The Scn1a+/- mouse model also exhibits strain-dependent phenotype severity. Scn1a+/- mice maintained on the 129S6/SvEvTac (129) strain have normal lifespan and no overt seizures. In contrast, admixture with C57BL/6J (B6) results in severe epilepsy and premature lethality in [B6x129]F1.Scn1a+/- mice. In previous work, we identified Dravet Survival Modifier loci (Dsm1-Dsm5) responsible for strain-dependent differences in survival. Gabra2, encoding the GABAA 2 subunit, was nominated as the top candidate modifier at the Dsm1 locus on chromosome 5. Direct measurement of GABAA receptors found lower abundance of 2-containing receptors in hippocampal synapses of B6 mice relative to 129. We also identified a B6-specific single nucleotide intronic deletion within Gabra2 that lowers mRNA and protein by nearly 50%. Repair of this de novo deletion reestablished normal levels of Gabra2 transcript and protein expression. In the current study, we used B6 mice with the repaired Gabra2 allele to validate it as a modifier of phenotype severity in Scn1a+/- mice. Repair of Gabra2 restored transcript and protein expression, increased abundance of 2-containing GABAA receptors in hippocampal synapses, and improved seizure and survival phenotypes of Scn1a+/- mice. These findings validate Gabra2 as a genetic modifier of Dravet syndrome.

genetics↗

bioRxiv2018

Potentiating α2 subunit containing perisomatic GABAA receptors protects against seizures in a mouse model of Dravet Syndrome

GABAA receptor potentiators are commonly used for the treatment of epilepsy, but it is not clear whether distinct GABAA receptor subtypes contribute to seizure activity, and whether targeting receptor subtypes will have disproportionate benefit over adverse effects. Here we demonstrate that the 2 / 3 selective positive allosteric modulator (PAM) AZD7325 preferentially potentiates hippocampal inhibitory responses at synapses proximal to the soma of CA1 neurons. The effect of AZD7325 on synaptic responses was more prominent in mice on the 129S6/SvEvTac background strain that has been demonstrated to be seizure resistant in the model of Dravet syndrome (Scn1a+/-) and in which the 2 GABAA receptor subunits are higher relative to in the C57BL/6J strain. Consistent with this, treatment of mice with AZD7325 is associated with a higher temperature threshold for hyperthermia-induced seizures in Scn1a+/- mice without apparent sedative effects. Our results in a model system indicate that selective targeting 2 is a potential therapeutic option for Dravet syndrome.

neuroscience↗

bioRxiv2018

Development of photoactivatable drugs enables nicotinic optopharmacology

Photoactivatable ( caged) pharmacological agents have revolutionized neuroscience but the palette of available ligands is limited. We describe a general method for caging tertiary amines using an unconventional quaternary ammonium linkage that is chemically stable and elicits a desirable red-shift in activation wavelength. A photoactivatable nicotine (PA-Nic) prepared using this strategy could be uncaged via 1- or 2-photon excitation, making it useful for optopharmacology experiments to study nicotinic acetylcholine receptors (nAChRs) in different experimental preparations and spatiotemporal scales.

neuroscience↗