Biology subjects

Ramsey, A. J.

Publications and source records attributed to Ramsey, A. J..

10 recordsLinked to original sources

bioRxiv2026

Characterization of the Grin1Q536R/+ mouse: a preclinical model for GRIN1-related neurodevelopmental disorder

N-methyl-D-aspartate receptors (NMDARs) are ionotropic glutamate receptors playing critical roles in brain development, synaptic plasticity, and cognition. GRIN1-Related Neurodevelopmental Disorder (GRIN1-NDD) is a rare genetic condition caused by pathogenic variations in the GRIN1 gene, which encodes the obligatory subunit of NMDARs. The spectrum of GRIN1 clinical symptoms is hypothesized to result from the functional consequences that different missense variants have on NMDARs. To investigate the disease mechanism in vivo, we generated a novel heterozygous Grin1Q536R/+ knock-in mouse model that carries the identical variation as an adolescent male patient. We describe the clinical presentation of this patient and conduct comprehensive molecular, morphological, electrophysiological, and behavioural characterization in the juvenile, adult, and aging mice. Compared to wildtype littermates, Grin1Q536R/+ mice displayed reduced whole-cell NMDA-induced currents in cortical pyramidal neurons, and reduced NMDAR-mediated synaptic transmission, decreased long-term potentiation, but intact depotentiation at the hippocampal CA1 synapses. Morphological change was observed in the dentate gyrus region of the Grin1Q536R/+ mice. Behavioral phenotyping revealed age- and sex-dependent differences from controls, including hyperlocomotion, reduced muscle strength, and spatial learning deficits. These phenotypes are in line with the clinical manifestations and the relative disease severity of the male patient. The age-dependent phenotypic shift in Grin1Q536R/+ mice highlights the model's value for investigating GRIN1-NDD disease progression and informing longitudinal monitoring as well as potential therapeutic adjustments with age. Taken together, our findings establish a novel and robust in vivo model for studying NMDAR mechanisms and disease pathology in GRIN1-NDD, while supporting the preclinical development of new therapeutic strategies.

neuroscience↗

bioRxiv2025

Characterization of a novel mouse model of Dopamine Transporter Deficiency Syndrome and pharmacological therapeutic strategies

The dopamine transporter (DAT) is an essential protein in the maintenance of dopamine homeostasis in the brain. Thus, single amino acid changes in the gene that encodes for DAT can be sufficient to induce disease, such as Dopamine Transporter Deficiency Syndrome (DTDS). DTDS-associated variants are posited to cause DAT protein misfolding, retention in the endoplasmic reticulum, and a consequent depletion or loss of DAT at the cell surface. In turn, proper dopaminergic regulation is lost. Current treatments for DTDS are largely ineffective, and improved therapeutic options are greatly needed. To this end, we have created a novel mouse model of DTDS harboring the A313V knock-in DAT variant, a proxy for the DTDS-causing A314V variant in humans. We show that the A313V knock-in DAT mice are hyperactive, have increased striatal tissue content of dopamine and its metabolites homovanillic acid (HVA) and DOPAC, and impaired dopamine uptake. We demonstrate that FDA approved compounds alpha-methyl-para-tyrosine ([a]MPT) and amphetamine (AMPH) ameliorate hyperactivity in this mouse model. Moreover, [a]MPT may be a disease-modifying treatment by addressing the hyperdopaminergic tone underlying this hyperactivity. In contrast, noribogaine, a pharmacological chaperone for DAT, is unable to rescue DAT expression. Taken together, these findings show that the A313V knock-in DAT variant mice recapitulate several defining phenotypes seen in patients with DTDS, and provide evidence for two novel treatments for the disease.

pharmacology and toxicology↗

bioRxiv2025

Metaplastic priming enables non-ionotropic NMDA receptor-mediated synaptic depotentiation in the hippocampus

The reversal of learning-induced synaptic potentiation through depotentiation is thought to underlie forgetting and can be influenced by prior synaptic activity. Here, we evaluated how such metaplastic alterations manifest at the synaptic level. In hippocampal slices obtained from male and female mice, we artificially induced long-term potentiation (LTP) using either a temporally spaced or compressed stimulation pattern. Using a combination of electrophysiology and protein quantification approaches, we found divergent molecular pathways recruited during depotentiation of spaced and compressed LTP. Depotentiation of both forms of LTP required glutamatergic activation of the NMDA receptor (NMDAR). However, only depotentiation of spaced LTP required ionotropic NMDAR signaling, while ion flux-independent, or non-ionotropic, NMDAR signaling was necessary and sufficient for depotentiation of compressed LTP. Downstream of NMDAR signaling, AMPA receptor phosphorylation was also differentially modified during depotentiation of spaced and compressed LTP. Finally, we found that spaced but not compressed depotentiation required synaptic Arc. Together, our results reveal that the temporal pattern of prior LTP induction exerts a metaplastic influence on the molecular pathways recruited during the induction and expression of depotentiation. Our findings have important implications for the regulation of both physiological and pathological forgetting. Significance statementSynaptic depotentiation, the reversal of learning-associated synaptic potentiation, is an important mechanism of forgetting. This study uncovers how prior synaptic activity modifies the molecular mechanisms underlying depotentiation in the hippocampus in a metaplastic manner. We reveal that the mechanisms of NMDA-receptor depotentiation depend on the temporal spacing of long-term potentiation (LTP) induction. Specifically, we show that non-ionotropic NMDA receptor signaling is necessary and sufficient for the depotentiation of LTP induced using temporally compressed but not spaced patterned activity. Further, depotentiation of spaced and compressed LTP are associated with distinct downstream signaling pathways and AMPA receptor phosphorylation states during depotentiation. Our results illuminate fundamental mechanisms that govern plasticity associated with forgetting, with implications for memory preservation in disease states.

neuroscience↗

bioRxiv2024

Context matters: Integrative NMDA receptor dysfunction reveals effective seizure treatment in mice with a human patient GluN1 variant

Mutations in N-Methyl D-Aspartate receptors (NMDARs) cause epilepsy and profound cognitive impairment, though the underlying subunit-specific vulnerabilities remain unclear. We investigate the impact of a severe human variant in the lurcher motif of obligate GluN1 NMDAR subunit using transgenic mice, leveraging context-specific dysfunction to devise a surprising treatment. We show that the GluN1 Y647S variant significantly reduces current flow through isolated NMDARs in the mouse brain. However, this loss-of-function paradoxically extends NMDAR-dependent dendritic integration, causing prolonged circuit-wide excitation that promotes seizures. Mutant receptors fail to sufficiently engage opposing dendritic ion channels that normally prevent NMDAR overactivation. Boosting negative feedback restores normal dendritic integration and successfully treats seizures in vivo, despite loss-of-function of isolated NMDARs. We demonstrate how seizures arise from loss-of-function NMDARs and target the interaction between a GluN1 variants receptor-level effects and its dendritic environment to treat them effectively.

neuroscience↗

bioRxiv2024

Grin1Y647S/+ Mice: A Preclinical Model of GRIN1-Related Neurodevelopmental Disorder

GRIN1-related neurodevelopmental disorder (GRIN1-NDD) is characterized by clinically significant variation in the GRIN1 gene, which encodes the obligatory GluN1 subunit of N-methyl-D-aspartate receptors (NMDARs). The identified p.Tyr647Ser (Y647S) variant is carried by a 34-year-old female with seizures and intellectual disability. This study builds upon initial in vitro investigations of the functional impacts of this variant in the SYTANLAAF domain of the GluN1 M3 helix and examines its in vivo consequences in a mouse model. To investigate in vitro functional impacts of NMDARs containing GluN1-Y647S variant subunits, GluN1-Y647S was co-expressed with wildtype GluN2A or GluN2B subunits in Xenopus laevis oocytes and HEK cells. Grin1Y647S/+ mice were created by CRISPR-Cas9 endonuclease-mediated transgenesis and the molecular, electrophysiological, and behavioural consequences of the variant were examined. Additionally, de-identified patient data were collected to examine the representative nature of Grin1Y647S/+ mice in modelling specific aspects of patient symptomology. In vitro, NMDARs containing GluN1-Y647S showed altered sensitivity to endogenous agonists and negative allosteric modulators, and reduced cell surface trafficking. Ex vivo, Grin1Y647S/+ mice displayed a reduction in whole brain GluN1 levels and a deficiency in NMDAR-mediated synaptic transmission in the hippocampus. Behaviourally, Grin1Y647S/+ mice exhibited altered vocalizations, muscle strength, sociability, and problem-solving, as well as spontaneous convulsions that were ameliorated with supplementation of {beta}-hydroxybutyrate (BHB), an endogenously produced ketone body. The Y647S variant confers a complex in vivo phenotype, which reflects largely diminished properties of NMDAR function. As a result, Grin1Y647S/+ mice display atypical behaviour in domains relevant to the clinical characteristics of GRIN1-NDD and the individual carrying the variant, which allowed for the identification of BHB supplementation as a potential anti-convulsant treatment. Ultimately, the characterization of Grin1Y647S/+ mice accomplished in the present work, expands our understanding of the mechanisms underlying GRIN1-NDD and provides a foundation for the continued development of novel therapeutics.

neuroscience↗

bioRxiv2024

Combination of Haloperidol with UNC9994, β-arrestin-biased analog of Aripiprazole, ameliorates schizophrenia-related phenotypes induced by NMDAR deficit in mice.

BackgroundGlutamatergic system dysfunction, particularly involving the N-methyl-D-aspartate receptor (NMDAR), contributes to a full spectrum of schizophrenia-like symptoms, including the cognitive and negative symptoms that are resistant to treatment with antipsychotic drugs (APDs). Aripiprazole, an atypical antipsychotic drug (APD), acts as a dopamine partial agonist and its combination with haloperidol (a typical APD) has been suggested as a potential strategy to improve schizophrenia symptoms. Recently, an analog of aripiprazole - UNC9994 was developed. UNC9994 does not affect D2R-mediated Gi/o protein signaling but acts as a partial agonist for D2R/{beta}-arrestin interactions. Hence, our objective was to probe the effects of co-administrating haloperidol with UNC9994 in NMDAR mouse models of schizophrenia. MethodsNMDAR hypofunction was induced pharmacologically by acute injection of MK-801 (NMDAR pore blocker; 0.15 mg/kg) and genetically by knockdown of Grin1 gene expression in mice, which have a 90% reduction in NMDAR levels (Grin1-KD). After intraperitoneal injections of vehicle, haloperidol (0.15 mg/kg), UNC9994 (0.25 mg/kg) or their combination mice were tested in open field, Pre-Pulse inhibition (PPI), Y-maze and Puzzle box. ResultsOur findings indicate that low dose co-administration of UNC9994 and haloperidol reduces hyperactivity in MK-801-treated animals and in Grin1-KD mice. Furthermore, this dual administration effectively reverses PPI deficits, repetitive/rigid behavior in the Y-maze, and deficient executive function in the Puzzle box in both animal models. ConclusionsThe dual administration of haloperidol with UNC9994 at low doses represents a promising approach to ameliorate positive, negative, and cognitive symptoms of schizophrenia. Significance statementSchizophrenia is a devastating mental disorder and characterized by positive, negative, and cognitive symptoms. Cognitive and negative symptoms remain a focus of research dedicated to development of effective antipsychotic drugs (APDs). Aripiprazole, an atypical APD, acts as a dopamine partial agonist and its combination with haloperidol (a typical APD) has been suggested as a potential strategy to improve schizophrenia symptoms. An analog of aripiprazole - UNC9994 was recently developed, which does not affect D2R-mediated Gi/o protein signaling but acts as a partial agonist for D2R/{beta}-arrestin interactions. Our pre-clinical findings on pharmacological (MK-801, 0.15 mg/kg) and genetic (Grin1-KD) mouse models of NMDAR deficiency showed that the dual administration of UNC9994 (0.25 mg/kg) with haloperidol (0.15 mg/kg) at low doses reduces hyperactivity, corrects prepulse inhibition (PPI) deficits, rigid behavior in the Y-maze, and deficient executive function in the Puzzle box. Further studies of the polypharmacy of UNC9994 with APDs is essential to facilitate translational studies in clinics.

pharmacology and toxicology↗

bioRxiv2023

Tricyclic and tetracyclic antidepressants upregulate VMAT2 activity and rescue disease-causing VMAT2 variants

Vesicular monoamine transporter 2 (VMAT2) is an essential transporter that regulates brain monoamine transmission and is important for mood, cognition, motor activity, and stress regulation. However, VMAT2 remains underexplored as a pharmacological target. In this study, we report that tricyclic and tetracyclic antidepressants acutely inhibit, but persistently upregulate VMAT2 activity by promoting VMAT2 protein maturation. Importantly, the VMAT2 upregulation effect was greater in BE(2)-M17 cells that endogenously express VMAT2 as compared to a heterologous expression system (HEK293). The net sustained effect of tricyclics and tetracyclics is an upregulation of VMAT2 activity, despite their acute inhibitory effect. Furthermore, imipramine and mianserin, two representative compounds, also demonstrated rescue of nine VMAT2 variants that cause Brain Vesicular Monoamine Transport Disease (BVMTD). VMAT2 upregulation could be beneficial for disorders associated with reduced monoamine transmission, including mood disorders and BVMTD, a rare but often fatal condition caused by a lack of functional VMAT2. Our findings provide the first evidence that small molecules can upregulate VMAT2 and have potential therapeutic benefit for various neuropsychiatric conditions.

pharmacology and toxicology↗

bioRxiv2022

Deficits in integrative NMDA receptors caused by Grin1 disruption can be rescued in adulthood

Glutamatergic NMDA receptors (NMDAR) are critical for cognitive function, and their reduced expression leads to intellectual disability. Since subpopulations of NMDARs exist in distinct subcellular environments, their functioning may be unevenly vulnerable to genetic disruption. Here, we investigate synaptic and extrasynaptic NMDARs on the major output neurons of the prefrontal cortex in mice deficient for the obligate NMDAR subunit encoded by Grin1 and wild-type littermates. With whole-cell recording in brain slices, we find that single, low-intensity stimuli elicit surprisingly-similar glutamatergic synaptic currents in both genotypes. By contrast, clear genotype differences emerge with manipulations that recruit extrasynaptic NMDARs, including stronger, repetitive, or pharmacological stimulation. These results reveal a disproportionate functional deficit of extrasynaptic NMDARs compared to their synaptic counterparts. To probe the repercussions of this deficit, we examine an NMDAR-dependent phenomenon considered a building block of cognitive integration, basal dendrite plateau potentials. Since we find this phenomenon is readily evoked in wild-type but not in Grin1-deficient mice, we ask whether plateau potentials can be restored by an adult intervention to increase Grin1 expression. This genetic manipulation, previously shown to restore cognitive performance in adulthood, successfully rescues electrically-evoked basal dendrite plateau potentials after a lifetime of NMDAR compromise. Taken together, our work demonstrates NMDAR subpopulations are not uniformly vulnerable to the genetic disruption of their obligate subunit. Furthermore, the window for functional rescue of the more-sensitive integrative NMDARs remains open into adulthood.

neuroscience↗

bioRxiv2018

Restoring striatal WAVE-1 improves maze exploration performance of GluN1 knockdown mice

NMDA receptors are important for cognition and are implicated in neuropsychiatric disorders. GluN1 knockdown (GluN1KD) mice have reduced NMDA receptor levels, striatal spine density deficits, and cognitive impairments. However, how NMDA depletion leads to these effects is unclear. Since Rho GTPases are known to regulate spine density and cognition, we examined the levels of RhoA, Rac1, and Cdc42 signaling proteins. Striatal Rac1-pathway components are reduced in GluN1KD mice, with Rac1 and WAVE-1 deficits at 6 and 12 weeks of age. Concurrently, medium spiny neuron (MSN) spine density deficits are present in mice at these ages. To determine whether WAVE-1 deficits were causal or compensatory in relation to these phenotypes, we intercrossed GluN1KD mice with WAVE-1 overexpressing (WAVE-Tg) mice to restore WAVE-1 levels. GluN1KD-WAVE-Tg hybrids showed rescue of striatal WAVE-1 protein levels and MSN spine density, as well as selective behavioral rescue in the Y-maze and 8-arm radial maze tests. GluN1KD-WAVE-Tg mice expressed normalized WAVE-1 protein levels in the hippocampus, yet spine density of hippocampal CA1 pyramidal neurons was not significantly altered. Our data suggest a nuanced role for WAVE-1 effects on cognition and a delineation of specific cognitive domains served by the striatum. Rescue of striatal WAVE-1 and MSN spine density may be significant for goal-directed exploration and associated long-term memory in mice.

neuroscience↗

bioRxiv2018

Connectivity analyses of bioenergetic changes in schizophrenia: Identification of novel treatments

We utilized a cell-level approach to examine glycolytic pathways in the DLPFC of subjects with schizophrenia (n=16) and control (n=16) subjects and found decreased mRNA expression of glycolytic enzymes in pyramidal neurons, but not astrocytes. To replicate these novel bioenergetic findings, we probed independent datasets for bioenergetic targets and found similar abnormalities. Next, we used a novel strategy to build a schizophrenia bioenergetic profile by a tailored application of the Library of Integrated Network-Based Cellular Signatures data portal (iLINCS) and investigated connected cellular pathways, kinases, and transcription factors using Enrichr. Finally, with the goal of identifying drugs capable of \"reversing\" the bioenergetic schizophrenia signature, we performed a connectivity analysis with iLINCS and identified peroxisome proliferator-activated receptor (PPAR) agonists as promising therapeutic targets. We administered a PPAR agonist to the GluN1 knockdown model of schizophrenia and found it improved long-term memory. Taken together, our findings suggest that tailored bioinformatics approaches, coupled with the LINCS library of transcriptional signatures of chemical and genetic perturbagens may be employed to identify novel treatment strategies for schizophrenia and related diseases.

neuroscience↗