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Neuron Jun 2024NMDA receptors (NMDARs) are ionotropic receptors crucial for brain information processing. Yet, evidence also supports an ion-flux-independent signaling mode mediating...
NMDA receptors (NMDARs) are ionotropic receptors crucial for brain information processing. Yet, evidence also supports an ion-flux-independent signaling mode mediating synaptic long-term depression (LTD) and spine shrinkage. Here, we identify AETA (Aη), an amyloid-β precursor protein (APP) cleavage product, as an NMDAR modulator with the unique dual regulatory capacity to impact both signaling modes. AETA inhibits ionotropic NMDAR activity by competing with the co-agonist and induces an intracellular conformational modification of GluN1 subunits. This favors non-ionotropic NMDAR signaling leading to enhanced LTD and favors spine shrinkage. Endogenously, AETA production is increased by in vivo chemogenetically induced neuronal activity. Genetic deletion of AETA production alters NMDAR transmission and prevents LTD, phenotypes rescued by acute exogenous AETA application. This genetic deletion also impairs contextual fear memory. Our findings demonstrate AETA-dependent NMDAR activation (ADNA), characterizing AETA as a unique type of endogenous NMDAR modulator that exerts bidirectional control over NMDAR signaling and associated information processing.
PubMed: 38878768
DOI: 10.1016/j.neuron.2024.05.027 -
Molecular Autism Jun 2024Mutations in the X-linked gene cyclin-dependent kinase-like 5 (CDKL5) cause a severe neurological disorder characterised by early-onset epileptic seizures, autism and...
BACKGROUND
Mutations in the X-linked gene cyclin-dependent kinase-like 5 (CDKL5) cause a severe neurological disorder characterised by early-onset epileptic seizures, autism and intellectual disability (ID). Impaired hippocampal function has been implicated in other models of monogenic forms of autism spectrum disorders and ID and is often linked to epilepsy and behavioural abnormalities. Many individuals with CDKL5 deficiency disorder (CDD) have null mutations and complete loss of CDKL5 protein, therefore in the current study we used a Cdkl5 rat model to elucidate the impact of CDKL5 loss on cellular excitability and synaptic function of CA1 pyramidal cells (PCs). We hypothesised abnormal pre and/or post synaptic function and plasticity would be observed in the hippocampus of Cdkl5 rats.
METHODS
To allow cross-species comparisons of phenotypes associated with the loss of CDKL5, we generated a loss of function mutation in exon 8 of the rat Cdkl5 gene and assessed the impact of the loss of CDLK5 using a combination of extracellular and whole-cell electrophysiological recordings, biochemistry, and histology.
RESULTS
Our results indicate that CA1 hippocampal long-term potentiation (LTP) is enhanced in slices prepared from juvenile, but not adult, Cdkl5 rats. Enhanced LTP does not result from changes in NMDA receptor function or subunit expression as these remain unaltered throughout development. Furthermore, Ca permeable AMPA receptor mediated currents are unchanged in Cdkl5 rats. We observe reduced mEPSC frequency accompanied by increased spine density in basal dendrites of CA1 PCs, however we find no evidence supporting an increase in silent synapses when assessed using a minimal stimulation protocol in slices. Additionally, we found no change in paired-pulse ratio, consistent with normal release probability at Schaffer collateral to CA1 PC synapses.
CONCLUSIONS
Our data indicate a role for CDKL5 in hippocampal synaptic function and raise the possibility that altered intracellular signalling rather than synaptic deficits contribute to the altered plasticity.
LIMITATIONS
This study has focussed on the electrophysiological and anatomical properties of hippocampal CA1 PCs across early postnatal development. Studies involving other brain regions, older animals and behavioural phenotypes associated with the loss of CDKL5 are needed to understand the pathophysiology of CDD.
Topics: Animals; Long-Term Potentiation; Receptors, N-Methyl-D-Aspartate; Receptors, AMPA; Spasms, Infantile; Disease Models, Animal; Rats; Protein Serine-Threonine Kinases; Hippocampus; Pyramidal Cells; Male; CA1 Region, Hippocampal; Epileptic Syndromes; Genetic Diseases, X-Linked; Synapses; Excitatory Postsynaptic Potentials
PubMed: 38877552
DOI: 10.1186/s13229-024-00601-9 -
Frontiers in Neuroscience 2024Abnormal hippocampal neurodevelopment, particularly in the dentate gyrus region, may be a key mechanism of attention-deficit/hyperactivity disorder (ADHD). In this...
OBJECTIVES
Abnormal hippocampal neurodevelopment, particularly in the dentate gyrus region, may be a key mechanism of attention-deficit/hyperactivity disorder (ADHD). In this study, we investigate the effect of the most commonly used Chinese herb for the treatment of ADHD, Rehmanniae Radix Preparata (RRP), on behavior and hippocampal neurodevelopment in spontaneously hypertensive rats (SHR).
METHODS
Behavior tests, including Morris water maze (MWM) test, open field test (OFT) and elevated plus maze (EPM) test were performed to assess the effect of RRP on hyperactive and impulsive behavior. Hippocampal neurodevelopment was characterized by transmission electron microscopy, immunofluorescence, Golgi staining and Nissl staining approaches. Regulatory proteins such as Trkb, CDK5, FGF2/FGFR1 were examined by Western blot analysis.
RESULTS
The results showed that RRP could effectively control the impulsive and spontaneous behavior and improve the spatial learning and memory ability. RRP significantly reduced neuronal loss and increased the number of hippocampal stem cells, and promoted synaptic plasticity. In addition, FGF/FGFR signaling was upregulated after RRP treatment.
CONCLUSION
RRP can effectively reduce impulsive and spontaneous behavior and ameliorate hippocampal neurodevelopmental abnormalities in ADHD rat model.
PubMed: 38872946
DOI: 10.3389/fnins.2024.1402056 -
ENeuro Jun 2024Glutamatergic synapses exhibit significant molecular diversity but circuit-specific mechanisms that underlie synaptic regulation are not well characterized. Prior...
Glutamatergic synapses exhibit significant molecular diversity but circuit-specific mechanisms that underlie synaptic regulation are not well characterized. Prior reports show that RhoGEF Tiam1 regulates perforant path-dentate gyrus (DG) granule neuron synapses. In the present study, we report Tiam1's homolog Tiam2 is implicated in glutamatergic neurotransmission at CA1 pyramidal neurons. We find that Tiam2 regulates evoked excitatory glutamatergic currents via a post-synaptic mechanism mediated by the catalytic Dbl-homology domain. Overall, we present evidence for RhoGEF Tiam2's role in glutamatergic synapse function at Schaffer-collateral-CA1 pyramidal neuron synapses. Glutamatergic synapses are known to vary in composition and function but how this heterogeneity is established to create input-specific synaptic diversity is not well understood. In the present study we show Tiam2 regulates glutamatergic neurotransmission at Schaffer-collateral-CA1 pyramidal neuron synapses. We find that this function is dependent on its catalytic domain. By contrast we did not observe a role for Tiam2 in synaptic transmission at perforant path-DG granule neuron synapses. We also find that Tiam1 and Tiam2 are individually dispensable for functional synaptic plasticity in CA1 pyramidal neurons. To our knowledge, this is the first evidence of the RhoGEF Tiam2's role in regulating glutamatergic synapses.
PubMed: 38871458
DOI: 10.1523/ENEURO.0500-21.2024 -
ENeuro Jun 2024CRISPR/Cas9 gene editing represents an exciting avenue to study genes of unknown function, and can be combined with genetically-encoded tools such as fluorescent...
CRISPR/Cas9 gene editing represents an exciting avenue to study genes of unknown function, and can be combined with genetically-encoded tools such as fluorescent proteins, channelrhodopsins, DREADDs, and various biosensors to more deeply probe the function of these genes in different cell types. However, current strategies to also manipulate or visualize edited cells are challenging due to the large size of Cas9 proteins and the limited packaging capacity of adeno-associated viruses (AAVs). To overcome these constraints, we developed an alternative gene editing strategy using a single AAV vector and mouse lines that express Cre-dependent Cas9 to achieve efficient cell-type specific editing across the nervous system. Expressing Cre-dependent Cas9 from a genomic locus affords space to package guide RNAs for gene editing together with Cre-dependent, genetically encoded tools to manipulate, map, or monitor neurons using a single virus.We validated this strategy with three common tools in neuroscience: ChRonos, a channelrhodopsin, for studying synaptic transmission using optogenetics; GCaMP8f for recording Ca2+ transients using photometry, and mCherry for tracing axonal projections. We tested these tools in multiple brain regions and cell types, including GABAergic neurons in the nucleus accumbens, glutamatergic neurons projecting from the ventral pallidum to the lateral habenula, dopaminergic neurons in the ventral tegmental area, and proprioceptive neurons in the periphery. This flexible approach could help identify and test the function of novel genes affecting synaptic transmission, circuit activity, or morphology with a single viral injection. Our CRISPR/Cas9 approach is the first to use a single vector to both knock-down genes of interest and express tools to monitor, map, and manipulate neurons. We demonstrate its utility in the central nervous system and describe the first systemic CRISPR/Cas9 gene editing with co-expressed reporters in the peripheral nervous system. Our approach fills a significant gap in the neuronal gene editing toolkit, allowing high-throughput study of genes of unknown function in the nervous system, and has broad utility for loss-of-function studies in other biological fields. This tool has great translational potential: it can be used to screen risk factor genes identified through genome-wide association studies, or knock-down native gene expression and reintroduce mutant variants identified in clinical settings.
PubMed: 38871457
DOI: 10.1523/ENEURO.0438-23.2024 -
Biological Research Jun 2024Spreading depression (SD) is an intriguing phenomenon characterized by massive slow brain depolarizations that affect neurons and glial cells. This phenomenon is...
BACKGROUND
Spreading depression (SD) is an intriguing phenomenon characterized by massive slow brain depolarizations that affect neurons and glial cells. This phenomenon is repetitive and produces a metabolic overload that increases secondary damage. However, the mechanisms associated with the initiation and propagation of SD are unknown. Multiple lines of evidence indicate that persistent and uncontrolled opening of hemichannels could participate in the pathogenesis and progression of several neurological disorders including acute brain injuries. Here, we explored the contribution of astroglial hemichannels composed of connexin-43 (Cx43) or pannexin-1 (Panx1) to SD evoked by high-K stimulation in brain slices.
RESULTS
Focal high-K stimulation rapidly evoked a wave of SD linked to increased activity of the Cx43 and Panx1 hemichannels in the brain cortex, as measured by light transmittance and dye uptake analysis, respectively. The activation of these channels occurs mainly in astrocytes but also in neurons. More importantly, the inhibition of both the Cx43 and Panx1 hemichannels completely prevented high K-induced SD in the brain cortex. Electrophysiological recordings also revealed that Cx43 and Panx1 hemichannels critically contribute to the SD-induced decrease in synaptic transmission in the brain cortex and hippocampus.
CONCLUSIONS
Targeting Cx43 and Panx1 hemichannels could serve as a new therapeutic strategy to prevent the initiation and propagation of SD in several acute brain injuries.
Topics: Animals; Astrocytes; Connexins; Cortical Spreading Depression; Synaptic Transmission; Connexin 43; Male; Nerve Tissue Proteins; Cerebral Cortex; Neurons; Hippocampus; Rats, Sprague-Dawley; Rats; Potassium
PubMed: 38867288
DOI: 10.1186/s40659-024-00519-9 -
ENeuro Jun 2024Synapsins are highly abundant presynaptic proteins that play a crucial role in neurotransmission and plasticity via the clustering of synaptic vesicles. The synapsin III...
Synapsins are highly abundant presynaptic proteins that play a crucial role in neurotransmission and plasticity via the clustering of synaptic vesicles. The synapsin III isoform is usually downregulated after development, but in hippocampal mossy fiber boutons it persists in adulthood. Mossy fiber boutons express presynaptic forms of short- and long-term plasticity, which are thought to underlie different forms of learning. Previous research on synapsins at this synapse focused on synapsin isoforms I and II. Thus, a complete picture regarding the role of synapsins in mossy fiber plasticity is still missing. Here, we investigated presynaptic plasticity at hippocampal mossy fiber boutons by combining electrophysiological field recordings and transmission electron microscopy in a mouse model lacking all synapsin isoforms. We found decreased short-term plasticity - i.e. decreased facilitation and post-tetanic potentiation - but increased long-term potentiation in male synapsin triple knockout mice. At the ultrastructural level, we observed more dispersed vesicles and a higher density of active zones in mossy fiber boutons from knockout animals. Our results indicate that all synapsin isoforms are required for fine regulation of short- and long-term presynaptic plasticity at the mossy fiber synapse. Synapsins cluster vesicles at presynaptic terminals and shape presynaptic plasticity at giant hippocampal mossy fiber boutons. Deletion of all synapsin isoforms results in decreased short- but increased long-term plasticity.
PubMed: 38866497
DOI: 10.1523/ENEURO.0330-23.2024 -
Cell Reports Jun 2024Activation of prepronociceptin (PNOC)-expressing neurons in the arcuate nucleus (ARC) promotes high-fat-diet (HFD)-induced hyperphagia. In turn, PNOC neurons can inhibit...
Activation of prepronociceptin (PNOC)-expressing neurons in the arcuate nucleus (ARC) promotes high-fat-diet (HFD)-induced hyperphagia. In turn, PNOC neurons can inhibit the anorexic response of proopiomelanocortin (POMC) neurons. Here, we validate the necessity of PNOC activity for HFD-induced inhibition of POMC neurons in mice and find that PNOC-neuron-dependent inhibition of POMC neurons is mediated by gamma-aminobutyric acid (GABA) release. When monitoring individual PNOC neuron activity via Ca imaging, we find a subpopulation of PNOC neurons that is inhibited upon gastrointestinal calorie sensing and disinhibited upon HFD feeding. Combining retrograde rabies tracing and circuit mapping, we find that PNOC neurons from the bed nucleus of the stria terminalis (PNOC) provide inhibitory input to PNOC neurons, and this inhibitory input is blunted upon HFD feeding. This work sheds light on how an increase in caloric content of the diet can rewire a neuronal circuit, paving the way to overconsumption and obesity development.
PubMed: 38865247
DOI: 10.1016/j.celrep.2024.114343 -
Neuromolecular Medicine Jun 2024Depression frequently occurs following traumatic brain injury (TBI). However, the role of Fibromodulin (FMOD) in TBI-related depression is not yet clear. Previous...
Depression frequently occurs following traumatic brain injury (TBI). However, the role of Fibromodulin (FMOD) in TBI-related depression is not yet clear. Previous studies have suggested FMOD as a potential key factor in TBI, yet its association with depression post-TBI and underlying mechanisms are not well understood. Serum levels of FMOD were measured in patients with traumatic brain injury using qPCR. The severity of depression was assessed using the self-depression scale (SDS). Neurological function, depressive state, and cognitive function in mice were assessed using the modified Neurological Severity Score (mNSS), forced swimming test (FST), tail suspension test (TST), Sucrose Preference Test (SPT), and morris water maze (MWM). The morphological features of mouse hippocampal synapses and neuronal dendritic spines were revealed through immunofluorescence, transmission electron microscopy, and Golgi-Cox staining. The protein expression levels of FMOD, MAP2, SYP, and PSD95, as well as the phosphorylation levels of the PI3K/AKT/mTOR signaling pathway, were detected through Western blotting. FMOD levels were decreased in TBI patients' serum. Overexpression of FMOD preserved neuronal function and alleviated depression-like behaviour, increased synaptic protein expression, and induced ultrastructural changes in hippocampal neurons. The increased phosphorylation of PI3K, AKT, and mTOR suggested the involvement of the PI3K/AKT/mTOR signaling pathway in FMOD's protective effects. FMOD exhibits potential as a therapeutic target for depression related to TBI, with its protective effects potentially mediated through the PI3K/AKT/mTOR signaling pathway.
Topics: Animals; TOR Serine-Threonine Kinases; Brain Injuries, Traumatic; Mice; Signal Transduction; Male; Proto-Oncogene Proteins c-akt; Phosphatidylinositol 3-Kinases; Hippocampus; Depression; Humans; Adult; Female; Middle Aged; Mice, Inbred C57BL; Synapses; Disease Models, Animal; Dendritic Spines; Disks Large Homolog 4 Protein
PubMed: 38864941
DOI: 10.1007/s12017-024-08793-2 -
Nature Communications Jun 2024Impairment of the central nervous system (CNS) poses a significant health risk for astronauts during long-duration space missions. In this study, we employed an...
Impairment of the central nervous system (CNS) poses a significant health risk for astronauts during long-duration space missions. In this study, we employed an innovative approach by integrating single-cell multiomics (transcriptomics and chromatin accessibility) with spatial transcriptomics to elucidate the impact of spaceflight on the mouse brain in female mice. Our comparative analysis between ground control and spaceflight-exposed animals revealed significant alterations in essential brain processes including neurogenesis, synaptogenesis and synaptic transmission, particularly affecting the cortex, hippocampus, striatum and neuroendocrine structures. Additionally, we observed astrocyte activation and signs of immune dysfunction. At the pathway level, some spaceflight-induced changes in the brain exhibit similarities with neurodegenerative disorders, marked by oxidative stress and protein misfolding. Our integrated spatial multiomics approach serves as a stepping stone towards understanding spaceflight-induced CNS impairments at the level of individual brain regions and cell types, and provides a basis for comparison in future spaceflight studies. For broader scientific impact, all datasets from this study are available through an interactive data portal, as well as the National Aeronautics and Space Administration (NASA) Open Science Data Repository (OSDR).
Topics: Animals; Space Flight; Mice; Female; Brain; Neurons; Transcriptome; Neurogenesis; Single-Cell Analysis; Mice, Inbred C57BL; Synaptic Transmission; Weightlessness; Astrocytes; Oxidative Stress; Gene Expression Profiling; Multiomics
PubMed: 38862479
DOI: 10.1038/s41467-024-48916-8