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Neurobiology of Disease Aug 2024Periventricular nodular heterotopia (PNH), the most common brain malformation diagnosed in adulthood, is characterized by the presence of neuronal nodules along the...
Periventricular nodular heterotopia (PNH), the most common brain malformation diagnosed in adulthood, is characterized by the presence of neuronal nodules along the ventricular walls. PNH is mainly associated with mutations in the FLNA gene - encoding an actin-binding protein - and patients often develop epilepsy. However, the molecular mechanisms underlying the neuronal failure still remain elusive. It has been hypothesized that dysfunctional cortical circuitry, rather than ectopic neurons, may explain the clinical manifestations. To address this issue, we depleted FLNA from cortical pyramidal neurons of a conditional Flna mice by timed in utero electroporation of Cre recombinase. We found that FLNA regulates dendritogenesis and spinogenesis thus promoting an appropriate excitatory/inhibitory inputs balance. We demonstrated that FLNA modulates RAC1 and cofilin activity through its interaction with the Rho-GTPase Activating Protein 24 (ARHGAP24). Collectively, we disclose an uncharacterized role of FLNA and provide strong support for neural circuit dysfunction being a consequence of FLNA mutations.
Topics: Animals; Filamins; rac1 GTP-Binding Protein; Mice; Cerebral Cortex; Actin Depolymerizing Factors; Pyramidal Cells; Neurogenesis; GTPase-Activating Proteins; Neurons; Mice, Transgenic; Periventricular Nodular Heterotopia; Neuropeptides
PubMed: 38852754
DOI: 10.1016/j.nbd.2024.106558 -
Translational Pediatrics May 2024The calcium-binding protein 4 () gene is a newly identified epilepsy-related gene that might be associated with a rare type of genetic focal epilepsy; that is, autosomal...
BACKGROUND
The calcium-binding protein 4 () gene is a newly identified epilepsy-related gene that might be associated with a rare type of genetic focal epilepsy; that is, autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE). , mutant CABP4 causes an increased inward flow voltage of calcium ions and a significant increase in the electrical signal discharge in hippocampus neurons; however, the role of in epilepsy has not yet been specifically described, and there is not yet a CABP4 mutant animal model recapitulating the epilepsy phenotype.
METHODS
We introduced a human missense mutation into the C57BL/6J mouse genome and generated a knock-in strain carrying a glycine-to-aspartic acid mutation in the gene. Quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot were performed to evaluate the expression level. Slice patch-clamp recording was carried out on pyramidal cells of prefrontal cortex layers II and III.
RESULTS
The mutant mice were viable and born at an expected Mendelian ratio. Surprisingly, the heterozygous (HE) mice did not display either an abnormal appearance or an overt seizure phenotype, and there was no statistically significant difference between the HE and wild-type (WT) mice in terms of overall messenger RNA (mRNA) and protein expression. However, the HE mutant mice showed an imbalance in the amount of protein expressed in the brain regions. Additionally, the patch-clamp recordings from the HE mouse layer II/III cortical pyramidal cells revealed an increase in the frequency of micro-excitatory post-synaptic currents (mEPSCs) but no change in the amplitude was observed.
CONCLUSIONS
The findings of this study suggest that the p.G155D mutation might be one of the mechanisms underlying seizure onset.
PubMed: 38840676
DOI: 10.21037/tp-23-484 -
Molecular Brain Jun 2024Loss-of-function mutations in the progranulin (GRN) gene are an autosomal dominant cause of Frontotemporal Dementia (FTD). These mutations typically result in...
Loss-of-function mutations in the progranulin (GRN) gene are an autosomal dominant cause of Frontotemporal Dementia (FTD). These mutations typically result in haploinsufficiency of the progranulin protein. Grn mice provide a model for progranulin haploinsufficiency and develop FTD-like behavioral abnormalities by 9-10 months of age. In previous work, we demonstrated that Grn mice develop a low dominance phenotype in the tube test that is associated with reduced dendritic arborization of layer II/III pyramidal neurons in the prelimbic region of the medial prefrontal cortex (mPFC), a region key for social dominance behavior in the tube test assay. In this study, we investigated whether progranulin haploinsufficiency induced changes in dendritic spine density and morphology. Individual layer II/III pyramidal neurons in the prelimbic mPFC of 9-10 month old wild-type or Grn mice were targeted for iontophoretic microinjection of fluorescent dye, followed by high-resolution confocal microscopy and 3D reconstruction for morphometry analysis. Dendritic spine density in Grn mice was comparable to wild-type littermates, but the apical dendrites in Grn mice had a shift in the proportion of spine types, with fewer stubby spines and more thin spines. Additionally, apical dendrites of Grn mice had longer spines and smaller thin spine head diameter in comparison to wild-type littermates. These changes in spine morphology may contribute to altered circuit-level activity and social dominance deficits in Grn mice.
Topics: Animals; Dendritic Spines; Prefrontal Cortex; Haploinsufficiency; Progranulins; Mice; Pyramidal Cells; Male; Mice, Inbred C57BL
PubMed: 38840181
DOI: 10.1186/s13041-024-01095-5 -
Neuron May 2024Electric fields affect the activity of neurons and brain circuits, yet how this happens at the cellular level remains enigmatic. Lack of understanding of how to...
Electric fields affect the activity of neurons and brain circuits, yet how this happens at the cellular level remains enigmatic. Lack of understanding of how to stimulate the brain to promote or suppress specific activity significantly limits basic research and clinical applications. Here, we study how electric fields impact subthreshold and spiking properties of major cortical neuronal classes. We find that neurons in the rodent and human cortex exhibit strong, cell-class-dependent entrainment that depends on stimulation frequency. Excitatory pyramidal neurons, with their slower spike rate, entrain to both slow and fast electric fields, while inhibitory classes like Pvalb and Sst (with their fast spiking) predominantly phase-lock to fast fields. We show that this spike-field entrainment is the result of two effects: non-specific membrane polarization occurring across classes and class-specific excitability properties. Importantly, these properties are present across cortical areas and species. These findings allow for the design of selective and class-specific neuromodulation.
PubMed: 38838670
DOI: 10.1016/j.neuron.2024.05.009 -
ENeuro Jun 2024In the rodent whisker system, active sensing and sensorimotor integration are mediated in part by the dynamic interactions between the motor cortex (M1) and...
In the rodent whisker system, active sensing and sensorimotor integration are mediated in part by the dynamic interactions between the motor cortex (M1) and somatosensory cortex (S1). However, understanding these dynamic interactions requires knowledge about the synapses and how specific neurons respond to their input. Here, we combined optogenetics, retrograde labeling, and electrophysiology to characterize the synaptic connections between M1 and layer 5 (L5) intratelencephalic (IT) and pyramidal tract (PT) neurons in S1 of mice (both sexes). We found that M1 synapses onto IT cells displayed modest short-term depression, whereas synapses onto PT neurons showed robust short-term facilitation. Despite M1 inputs to IT cells depressing, their slower kinetics resulted in summation and a response that increased during short trains. In contrast, summation was minimal in PT neurons due to the fast time course of their M1 responses. The functional consequences of this reduced summation, however, were outweighed by the strong facilitation at these M1 synapses, resulting in larger response amplitudes in PT neurons than IT cells during repetitive stimulation. To understand the impact of facilitating M1 inputs on PT output, we paired trains of inputs with single backpropagating action potentials, finding that repetitive M1 activation increased the probability of bursts in PT cells without impacting the time dependence of this coupling. Thus, there are two parallel but dynamically distinct systems of M1 synaptic excitation in L5 of S1, each defined by the short-term dynamics of its synapses, the class of postsynaptic neurons, and how the neurons respond to those inputs.
Topics: Animals; Somatosensory Cortex; Motor Cortex; Male; Female; Optogenetics; Neural Pathways; Synapses; Mice; Neurons; Mice, Inbred C57BL; Vibrissae; Pyramidal Tracts; Mice, Transgenic; Excitatory Postsynaptic Potentials
PubMed: 38834298
DOI: 10.1523/ENEURO.0154-24.2024 -
Animal Cells and Systems 2024The cytoplasmic FMR1-interacting protein 2 (CYFIP2) have diverse molecular functions in neurons, including the regulation of actin polymerization, mRNA translation, and...
Cell-autonomous reduction of CYFIP2 changes dendrite length, dendritic protrusion morphology, and inhibitory synapse density in the hippocampal CA1 pyramidal neurons of 17-month-old mice.
The cytoplasmic FMR1-interacting protein 2 (CYFIP2) have diverse molecular functions in neurons, including the regulation of actin polymerization, mRNA translation, and mitochondrial morphology and function. Mutations in the gene are associated with early-onset epilepsy and neurodevelopmental disorders, while decreases in its protein levels are linked to Alzheimer's disease (AD). Notably, previous research has revealed AD-like phenotypes, such as dendritic spine loss, in the hippocampal CA1 pyramidal neurons of 12-month-old heterozygous mice but not of age-matched CA1 pyramidal neuron-specific conditional knock-out (cKO) mice. This study aims to investigate whether dendritic spine loss in cKO mice is merely delayed compared to heterozygous mice, and to explore further neuronal phenotypes regulated by CYFIP2 in aged mice. We characterized dendrite and dendritic protrusion morphologies, along with excitatory/inhibitory synapse densities in CA1 pyramidal neurons of 17-month-old cKO mice. Overall dendritic branching was normal, with a reduction in the length of basal, not apical, dendrites in CA1 pyramidal neurons of cKO mice. Furthermore, while dendritic protrusion density remained normal, alterations were observed in the length of mushroom spines and the head volume of stubby spines in basal, not apical, dendrites of cKO mice. Although excitatory synapse density remained unchanged, inhibitory synapse density increased in apical, not basal, dendrites of cKO mice. Consequently, a cell-autonomous reduction of CYFIP2 appears insufficient to induce dendritic spine loss in CA1 pyramidal neurons of aged mice. However, CYFIP2 is required to maintain normal dendritic length, dendritic protrusion morphology, and inhibitory synapse density.
PubMed: 38832126
DOI: 10.1080/19768354.2024.2360740 -
Frontiers in Aging Neuroscience 2024Studies in rodent models have revealed that oligomeric beta-amyloid protein [Aβ (1-42)] plays an important role in the pathogenesis of Alzheimer's disease. Early...
GluN2A or GluN2B subunits of the NMDA receptor contribute to changes in neuronal excitability and impairments in LTP in the hippocampus of aging mice but do not mediate detrimental effects of oligomeric Aβ (1-42).
Studies in rodent models have revealed that oligomeric beta-amyloid protein [Aβ (1-42)] plays an important role in the pathogenesis of Alzheimer's disease. Early elevations in hippocampal neuronal excitability caused by Aβ (1-42) have been proposed to be mediated via enhanced activation of GluN2B-containing N-methyl-D-aspartate receptors (NMDAR). To what extent GluN2A or GluN2B-containing NMDAR contribute to Aβ (1-42)-mediated impairments of hippocampal function in advanced rodent age is unclear. Here, we assessed hippocampal long-term potentiation (LTP) and neuronal responses 4-5 weeks after bilateral intracerebral inoculation of 8-15 month old GluN2A or GluN2B transgenic mice with oligomeric Aβ (1-42), or control peptide. Whole-cell patch-clamp recordings in CA1 pyramidal neurons revealed a more positive resting membrane potential and increased total spike time in GluN2A, but not GluN2B-hippocampi following treatment with Aβ (1-42) compared to controls. Action potential 20%-width was increased, and the descending slope was reduced, in Aβ-treated GluN2A, but not GluN2B hippocampi. Sag ratio was increased in Aβ-treated GluN2B-mice. Firing frequency was unchanged in wt, GluN2A, and GluN2Bhippocampi after Aβ-treatment. Effects were not significantly different from responses detected under the same conditions in wt littermates, however. LTP that lasted for over 2 h in wt hippocampal slices was significantly reduced in GluN2A and was impaired for 15 min in GluN2B-hippocampi compared to wt littermates. Furthermore, LTP (>2 h) was significantly impaired in Aβ-treated hippocampi of wt littermates compared to wt treated with control peptide. LTP induced in Aβ-treated GluN2A and GluN2B-hippocampi was equivalent to LTP in control peptide-treated transgenic and Aβ-treated wt animals. Taken together, our data indicate that knockdown of GluN2A subunits subtly alters membrane properties of hippocampal neurons and reduces the magnitude of LTP. GluN2B knockdown reduces the early phase of LTP but leaves later phases intact. Aβ (1-42)-treatment slightly exacerbates changes in action potential properties in GluN2A-mice. However, the vulnerability of the aging hippocampus to Aβ-mediated impairments of LTP is not mediated by GluN2A or GluN2B-containing NMDAR.
PubMed: 38832073
DOI: 10.3389/fnagi.2024.1377085 -
Communications Biology Jun 2024Deciphering the functional organization of large biological networks is a major challenge for current mathematical methods. A common approach is to decompose networks...
Deciphering the functional organization of large biological networks is a major challenge for current mathematical methods. A common approach is to decompose networks into largely independent functional modules, but inferring these modules and their organization from network activity is difficult, given the uncertainties and incompleteness of measurements. Typically, some parts of the overall functional organization, such as intermediate processing steps, are latent. We show that the hidden structure can be determined from the statistical moments of observable network components alone, as long as the functional relevance of the network components lies in their mean values and the mean of each latent variable maps onto a scaled expectation of a binary variable. Whether the function of biological networks permits a hierarchical modularization can be falsified by a correlation-based statistical test that we derive. We apply the test to gene regulatory networks, dendrites of pyramidal neurons, and networks of spiking neurons.
Topics: Gene Regulatory Networks; Humans; Animals; Pyramidal Cells
PubMed: 38831002
DOI: 10.1038/s42003-024-06342-y -
Experimental & Molecular Medicine Jun 2024Cortical neuromodulation (CNM) is widely used to promote recovery after stroke. Despite the beneficial results of CNM, the roles played by different neuron types in the...
Cortical neuromodulation (CNM) is widely used to promote recovery after stroke. Despite the beneficial results of CNM, the roles played by different neuron types in the effects of current CNM techniques are unable to be differentiated. Our aim was to use selective optogenetic cortical stimulation to explore how different subpopulations of neuronal cells contribute to poststroke recovery. We transduced the sensory-parietal cortex (SPC) of rats with CamKII-ChR2 (pyramidal neurons), PV-ChR2 (parvalbumin-expressing inhibitory neurons), or hSyn-ChR2 (pan-neuronal population) before inducing photothrombotic capsular infarct lesions. We found that selective stimulation of inhibitory neurons resulted in significantly greater motor recovery than stimulation of excitatory neurons or the pan-neuronal population. Furthermore, 2-deoxy-2-[F] fluoro-D-glucose microPET (FDG-microPET) imaging revealed a significant reduction in cortical diaschisis and activation of the corticostriatal neural circuit, which were correlated with behavioral recovery in the PV-ChR2 group. The spatial pattern of brain-derived neurotrophic factor (BDNF) expression was evident in the stimulated cortex and underlying cortico-subcortical circuit. Our results indicate that the plasticity of inhibitory neurons is crucial for functional recovery after capsular infarct. Modifying CNM parameters to potentiate the stimulation of inhibitory neurons could improve poststroke outcomes.
PubMed: 38825647
DOI: 10.1038/s12276-024-01253-8 -
Molecular Pharmacology May 2024Bipolar disorder impacts millions of patients in the United States but the mechanistic understanding of its pathophysiology and therapeutics is incomplete. Atypical...
Bipolar disorder impacts millions of patients in the United States but the mechanistic understanding of its pathophysiology and therapeutics is incomplete. Atypical antipsychotic serotonin (5-HT) receptor antagonists, such as quetiapine and olanzapine, and mood-stabilizing voltage-gated sodium channel (VGSC) blockers, such as lamotrigine, carbamazepine, and valproate, show therapeutic synergy and are often prescribed in combination for the treatment of bipolar disorder. Combination therapy is a complex task for clinicians and patients, often resulting in unexpected difficulties with dosing, drug tolerances, and decreased patient compliance. Thus, an unmet need for bipolar disorder treatment is to develop a therapeutic agent that targets both 5-HT receptors and VGSCs. Towards this goal, we developed a novel small molecule that simultaneously antagonizes 5-HT receptors and blocks sodium current. The new compound, -(4-bromo-2,5-dimethoxyphenethyl)-6-(4-phenylbutoxy)hexan-1-amine (XOB) antagonizes 5-HT-stimulated, G-mediated, calcium flux at 5-HT receptors at low micromolar concentrations while displaying negligible affinity and activity at 5-HT, 5-HT, and 5-HT receptors. At similar concentrations, XOB administration inhibits sodium current in heterologous cells and results in reduced action potential (AP) firing and VGSC-related AP properties in mouse prefrontal cortex layer V pyramidal neurons. Thus, XOB represents a new, proof-of-principle tool that can be used for future preclinical investigations and therapeutic development. This polypharmacology approach of developing a single molecule to act upon two targets, which are currently independently targeted by combination therapies, may lead to safer alternatives for the treatment of psychiatric disorders that are increasingly being found to benefit from the simultaneous targeting of multiple receptors. We synthesized a novel small molecule (XOB) that simultaneously antagonizes two key therapeutic targets of bipolar disorder, 5-HT receptors and voltage-gated sodium channels (VGSCs), in heterologous cells, and inhibits the intrinsic excitability of mouse prefrontal cortex layer V pyramidal neurons in brain slices. XOB represents a valuable new proof-of-principle tool for future preclinical investigations and provides a novel molecular approach to the pharmacological treatment of complex neuropsychiatric disease, which often requires a combination of therapeutics for sufficient patient benefit.
PubMed: 38821630
DOI: 10.1124/molpharm.123.000837