Anis Contractor

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.

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 GluA1 ^A636T 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.

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 dentate 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.

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.

Fragile X syndrome (FXS), the most common monogenic neurodevelopmental disorder associated with autism and intellectual disability, results from the loss of expression of the X-linked FMR1 gene. Synaptic and circuit-level abnormalities in the brain 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 altered in male 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 functional coupling between NMDA receptors and SK channels in Fmr1 KO mice, altering the impact of priming on LTP expression in the CA1. Altered metaplasticity may represent a neural correlate of impaired hippocampal function in Fmr1 KO mice and potentially contribute to clinical manifestations in FXS individuals.

Amyloid-β (Aβ) peptides are a defining feature of Alzheimer’s disease (AD). These peptides are produced by the proteolytic processing of the amyloid precursor protein (APP), which can occur through the synaptic vesicle (SV) cycle. However, how amyloidogenic APP processing alters SV composition and presynaptic function is poorly understood. Using App knock-in mouse models of amyloid pathology, we found that proteins with impaired degradation accumulate at presynaptic sites together with Aβ ₄₂ in the SV lumen. Levetiracetam (Lev) is a US Food and Drug Administration–approved antiepileptic that targets SVs and has shown therapeutic potential to reduce AD phenotypes through an undefined mechanism. We found that Lev lowers Aβ ₄₂ levels by reducing amyloidogenic APP processing in an SV2a-dependent manner. Lev modified SV cycling and increased APP cell surface expression, which promoted its preferential processing through the nonamyloidogenic pathway. Stable isotope labeling combined with mass spectrometry confirmed that Lev prevents Aβ ₄₂ production in vivo. In transgenic mice with aggressive amyloid pathology, electrophysiology and immunofluorescence confirmed that Lev restores SV cycling abnormalities and reduces synapse loss. Last, early Aβ pathology in brains from donors with Down syndrome was characterized by elevated presynaptic proteins. Together, these findings highlight the potential to prevent Aβ pathology before irreversible damage occurs.

Striatal spiny-projection neurons (SPNs) integrate glutamatergic inputs from the motor cortex and thalamus with neuromodulatory signals to regulate motor output. In vivo Ca ²⁺ 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 it 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.

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 GluA1 ^A636T knock-in mouse model, we show that GluA1 ^A636T 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 GluA1 ^A636T 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.

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 Cacna1d ^G407R 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.