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Proceedings of the National Academy of... May 2024The muscle-type nicotinic acetylcholine receptor is a transmitter-gated ion channel residing in the plasma membrane of electrocytes and striated muscle cells. It is...
The muscle-type nicotinic acetylcholine receptor is a transmitter-gated ion channel residing in the plasma membrane of electrocytes and striated muscle cells. It is present predominantly at synaptic junctions, where it effects rapid depolarization of the postsynaptic membrane in response to acetylcholine released into the synaptic cleft. Previously, cryo-EM of intact membrane from revealed that the lipid bilayer surrounding the junctional receptor has a uniquely asymmetric and ordered structure, due to a high concentration of cholesterol. It is now shown that this special lipid environment influences the transmembrane (TM) folding of the protein. All five submembrane MX helices of the membrane-intact junctional receptor align parallel to the surface of the cholesterol-ordered lipids in the inner leaflet of the bilayer; also, the TM helices in the outer leaflet are splayed apart. However in the structure obtained from the same protein after extraction and incorporation in nanodiscs, the MX helices do not align to a planar surface, and the TM helices arrange compactly in the outer leaflet. Realignment of the MX helices of the nanodisc-solved structure to a planar surface converts their adjoining TM helices into an obligatory splayed configuration, characteristic of the junctional receptor. Thus, the form of the receptor sustained by the special lipid environment of the synaptic junction is the one that mediates fast synaptic transmission; whereas, the nanodisc-embedded protein may be like the extrajunctional form, existing in a disordered lipid environment.
Topics: Receptors, Nicotinic; Lipid Bilayers; Animals; Torpedo; Cryoelectron Microscopy; Cholesterol; Cell Membrane; Protein Folding; Models, Molecular
PubMed: 38683987
DOI: 10.1073/pnas.2319913121 -
Journal of Integrative Neuroscience Apr 2024Comorbid chronic neuropathic pain (NPP) and anxio-depressive disorders (ADD) have become a serious global public-health problem. The SLIT and NTRK-like 1 (SLITRK1)...
BACKGROUND
Comorbid chronic neuropathic pain (NPP) and anxio-depressive disorders (ADD) have become a serious global public-health problem. The SLIT and NTRK-like 1 (SLITRK1) protein is important for synaptic remodeling and is highly expressed in the amygdala, an important brain region involved in various emotional behaviors. We examined whether SLITRK1 protein in the amygdala participates in NPP and comorbid ADD.
METHODS
A chronic NPP mouse model was constructed by L5 spinal nerve ligation; changes in chronic pain and ADD-like behaviors were measured in behavioral tests. Changes in SLITRK1 protein and excitatory synaptic functional proteins in the amygdala were measured by immunofluorescence and Western blot. Adeno-associated virus was transfected into excitatory synaptic neurons in the amygdala to up-regulate the expression of SLITRK1.
RESULTS
Chronic NPP-related ADD-like behavior was successfully produced in mice by L5 ligation. We found that chronic NPP and related ADD decreased amygdalar expression of SLITRK1 and proteins important for excitatory synaptic function, including Homer1, postsynaptic density protein 95 (PSD95), and synaptophysin. Virally-mediated SLITRK1 overexpression in the amygdala produced a significant easing of chronic NPP and ADD, and restored the expression levels of Homer1, PSD95, and synaptophysin.
CONCLUSION
Our findings indicated that SLITRK1 in the amygdala plays an important role in chronic pain and related ADD, and may prove to be a potential therapeutic target for chronic NPP-ADD comorbidity.
Topics: Animals; Male; Mice; Amygdala; Anxiety; Anxiety Disorders; Behavior, Animal; Chronic Pain; Depression; Depressive Disorder; Disease Models, Animal; Disks Large Homolog 4 Protein; Homer Scaffolding Proteins; Membrane Proteins; Mice, Inbred C57BL; Nerve Tissue Proteins; Neuralgia; Synaptophysin
PubMed: 38682225
DOI: 10.31083/j.jin2304082 -
Antioxidants (Basel, Switzerland) Mar 2024Epilepsy, marked by abnormal and excessive brain neuronal activity, is linked to the activation of L-type voltage-gated calcium channels (LTCCs) in neuronal membranes....
Epilepsy, marked by abnormal and excessive brain neuronal activity, is linked to the activation of L-type voltage-gated calcium channels (LTCCs) in neuronal membranes. LTCCs facilitate the entry of calcium (Ca) and other metal ions, such as zinc (Zn) and magnesium (Mg), into the cytosol. This Ca influx at the presynaptic terminal triggers the release of Zn and glutamate to the postsynaptic terminal. Zn is then transported to the postsynaptic neuron via LTCCs. The resulting Zn accumulation in neurons significantly increases the expression of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase subunits, contributing to reactive oxygen species (ROS) generation and neuronal death. Amlodipine (AML), typically used for hypertension and coronary artery disease, works by inhibiting LTCCs. We explored whether AML could mitigate Zn translocation and accumulation in neurons, potentially offering protection against seizure-induced hippocampal neuronal death. We tested this by establishing a rat epilepsy model with pilocarpine and administering AML (10 mg/kg, orally, daily for 7 days) post-epilepsy onset. We assessed cognitive function through behavioral tests and conducted histological analyses for Zn accumulation, oxidative stress, and neuronal death. Our findings show that AML's LTCC inhibition decreased excessive Zn accumulation, reactive oxygen species (ROS) production, and hippocampal neuronal death following seizures. These results suggest amlodipine's potential as a therapeutic agent in seizure management and mitigating seizures' detrimental effects.
PubMed: 38671837
DOI: 10.3390/antiox13040389 -
Journal of Cell Science Apr 2024Amyloid β (Aβ) is a central contributor to neuronal damage and cognitive impairment in Alzheimer's disease (AD). Aβ disrupts AMPA receptor-mediated synaptic...
Amyloid β (Aβ) is a central contributor to neuronal damage and cognitive impairment in Alzheimer's disease (AD). Aβ disrupts AMPA receptor-mediated synaptic plasticity, a key factor in early AD progression. Numerous studies propose that Aβ oligomers hinder synaptic plasticity, particularly long-term potentiation (LTP), by disrupting GluA1 (encoded by GRIA1) function, although the precise mechanism remains unclear. In this study, we demonstrate that Aβ mediates the accumulation of GM1 ganglioside in lipid raft domains of cultured cells, and GluA1 exhibits preferential localization in lipid rafts via direct binding to GM1. Aβ enhances the raft localization of GluA1 by increasing GM1 in these areas. Additionally, chemical LTP stimulation induces lipid raft-dependent GluA1 internalization in Aβ-treated neurons, resulting in reduced cell surface and postsynaptic expression of GluA1. Consistent with this, disrupting lipid rafts and GluA1 localization in rafts rescues Aβ-mediated suppression of hippocampal LTP. These findings unveil a novel functional deficit in GluA1 trafficking induced by Aβ, providing new insights into the mechanism underlying AD-associated cognitive dysfunction.
Topics: Amyloid beta-Peptides; Long-Term Potentiation; Receptors, AMPA; Membrane Microdomains; Alzheimer Disease; Animals; Hippocampus; G(M1) Ganglioside; Humans; Neurons; Rats; Mice; Protein Transport
PubMed: 38668720
DOI: 10.1242/jcs.261281 -
Proceedings of the National Academy of... Apr 2024Pronounced differences in neurotransmitter release from a given presynaptic neuron, depending on the synaptic target, are among the most intriguing features of cortical...
Pronounced differences in neurotransmitter release from a given presynaptic neuron, depending on the synaptic target, are among the most intriguing features of cortical networks. Hippocampal pyramidal cells (PCs) release glutamate with low probability to somatostatin expressing oriens-lacunosum-moleculare (O-LM) interneurons (INs), and the postsynaptic responses show robust short-term facilitation, whereas the release from the same presynaptic axons onto fast-spiking INs (FSINs) is ~10-fold higher and the excitatory postsynaptic currents (EPSCs) display depression. The mechanisms underlying these vastly different synaptic behaviors have not been conclusively identified. Here, we applied a combined functional, pharmacological, and modeling approach to address whether the main difference lies in the action potential-evoked fusion or else in upstream priming processes of synaptic vesicles (SVs). A sequential two-step SV priming model was fitted to the peak amplitudes of unitary EPSCs recorded in response to complex trains of presynaptic stimuli in acute hippocampal slices of adult mice. At PC-FSIN connections, the fusion probability (P) of well-primed SVs is 0.6, and 44% of docked SVs are in a fusion-competent state. At PC-O-LM synapses, P is only 40% lower (0.36), whereas the fraction of well-primed SVs is 6.5-fold smaller. Pharmacological enhancement of fusion by 4-AP and priming by PDBU was recaptured by the model with a selective increase of P and the fraction of well-primed SVs, respectively. Our results demonstrate that the low fidelity of transmission at PC-O-LM synapses can be explained by a low occupancy of the release sites by well-primed SVs.
Topics: Animals; Synaptic Vesicles; Mice; Neurotransmitter Agents; Hippocampus; Excitatory Postsynaptic Potentials; Synaptic Transmission; Interneurons; Pyramidal Cells; Synapses; Models, Neurological
PubMed: 38657053
DOI: 10.1073/pnas.2322550121 -
The Journal of Physiology May 2024Training rodents in a particularly difficult olfactory-discrimination (OD) task results in the acquisition of the ability to perform the task well, termed 'rule...
Training rodents in a particularly difficult olfactory-discrimination (OD) task results in the acquisition of the ability to perform the task well, termed 'rule learning'. In addition to enhanced intrinsic excitability and synaptic excitation in piriform cortex pyramidal neurons, rule learning results in increased synaptic inhibition across the whole cortical network to the point where it precisely maintains the balance between inhibition and excitation. The mechanism underlying such precise inhibitory enhancement remains to be explored. Here, we use brain slices from transgenic mice (VGAT-ChR2-EYFP), enabling optogenetic stimulation of single GABAergic neurons and recordings of unitary synaptic events in pyramidal neurons. Quantal analysis revealed that learning-induced enhanced inhibition is mediated by increased quantal size of the evoked inhibitory events. Next, we examined the plasticity of synaptic inhibition induced by long-lasting, intrinsically evoked spike firing in post-synaptic neurons. Repetitive depolarizing current pulses from depolarized (-70 mV) or hyperpolarized (-90 mV) membrane potentials induced long-term depression (LTD) and long-term potentiation (LTP) of synaptic inhibition, respectively. We found a profound bidirectional increase in the ability to induce both LTD, mediated by L-type calcium channels, and LTP, mediated by R-type calcium channels after rule learning. Blocking the GABA receptor reversed the effect of intrinsic stimulation at -90 mV from LTP to LTD. We suggest that learning greatly enhances the ability to modify the strength of synaptic inhibition of principal neurons in both directions. Such plasticity of synaptic plasticity allows fine-tuning of inhibition on each particular neuron, thereby stabilizing the network while maintaining the memory of the rule. KEY POINTS: Olfactory discrimination rule learning results in long-lasting enhancement of synaptic inhibition on piriform cortex pyramidal neurons. Quantal analysis of unitary inhibitory synaptic events, evoked by optogenetic minimal stimulation, revealed that enhanced synaptic inhibition is mediated by increased quantal size. Surprisingly, metaplasticity of synaptic inhibition, induced by intrinsically evoked repetitive spike firing, is increased bidirectionally. The susceptibility to both long-term depression (LTD) and long-term potentiation (LTP) of inhibition is enhanced after learning. LTD of synaptic inhibition is mediated by L-type calcium channels and LTP by R-type calcium channels. LTP is also dependent on activation of GABA receptors. We suggest that learning-induced changes in the metaplasticity of synaptic inhibition enable the fine-tuning of inhibition on each particular neuron, thereby stabilizing the network while maintaining the memory of the rule.
Topics: Animals; Neuronal Plasticity; Mice; Mice, Transgenic; Pyramidal Cells; GABAergic Neurons; Learning; Long-Term Potentiation; Male; Synapses; Optogenetics; Neural Inhibition; Piriform Cortex; Mice, Inbred C57BL; Long-Term Synaptic Depression
PubMed: 38654583
DOI: 10.1113/JP284761 -
Frontiers in Neuroanatomy 2024The brain contains thousands of millions of synapses, exhibiting diverse structural, molecular, and functional characteristics. However, synapses can be classified into...
The brain contains thousands of millions of synapses, exhibiting diverse structural, molecular, and functional characteristics. However, synapses can be classified into two primary morphological types: Gray's type I and type II, corresponding to Colonnier's asymmetric (AS) and symmetric (SS) synapses, respectively. AS and SS have a thick and thin postsynaptic density, respectively. In the cerebral cortex, since most AS are excitatory (glutamatergic), and SS are inhibitory (GABAergic), determining the distribution, size, density, and proportion of the two major cortical types of synapses is critical, not only to better understand synaptic organization in terms of connectivity, but also from a functional perspective. However, several technical challenges complicate the study of synapses. Potassium ferrocyanide has been utilized in recent volume electron microscope studies to enhance electron density in cellular membranes. However, identifying synaptic junctions, especially SS, becomes more challenging as the postsynaptic densities become thinner with increasing concentrations of potassium ferrocyanide. Here we describe a protocol employing Focused Ion Beam Milling and Scanning Electron Microscopy for studying brain tissue. The focus is on the unequivocal identification of AS and SS types. To validate SS observed using this protocol as GABAergic, experiments with immunocytochemistry for the vesicular GABA transporter were conducted on fixed mouse brain tissue sections. This material was processed with different concentrations of potassium ferrocyanide, aiming to determine its optimal concentration. We demonstrate that using a low concentration of potassium ferrocyanide (0.1%) improves membrane visualization while allowing unequivocal identification of synapses as AS or SS.
PubMed: 38645671
DOI: 10.3389/fnana.2024.1348032 -
The Journal of Neuroscience : the... Jun 2024Vertebrate vision begins with light absorption by rod and cone photoreceptors, which transmit signals from their synaptic terminals to second-order neurons: bipolar and...
Vertebrate vision begins with light absorption by rod and cone photoreceptors, which transmit signals from their synaptic terminals to second-order neurons: bipolar and horizontal cells. In mouse rods, there is a single presynaptic ribbon-type active zone at which the release of glutamate occurs tonically in the dark. This tonic glutamatergic signaling requires continuous exo- and endocytosis of synaptic vesicles. At conventional synapses, endocytosis commonly requires dynamins: GTPases encoded by three genes (), which perform membrane scission. Disrupting endocytosis by dynamin deletions impairs transmission at conventional synapses, but the impact of disrupting endocytosis and the role(s) of specific dynamin isoforms at rod ribbon synapses are understood incompletely. Here, we used cell-specific knock-outs (KOs) of the neuron-specific and to investigate the functional roles of dynamin isoforms in rod photoreceptors in mice of either sex. Analysis of synaptic protein expression, synapse ultrastructure, and retinal function via electroretinograms (ERGs) showed that dynamins 1 and 3 act redundantly and are essential for supporting the structural and functional integrity of rod ribbon synapses. Single KO showed no phenotype, and single KO only modestly reduced synaptic vesicle density without affecting vesicle size and overall synapse integrity, whereas double KO impaired vesicle endocytosis profoundly, causing enlarged vesicles, reduced vesicle density, reduced ERG responses, synaptic terminal degeneration, and disassembly and degeneration of postsynaptic processes. Concurrently, cone function remained intact. These results show the fundamental redundancy of dynamins 1 and 3 in regulating the structure and function of rod ribbon synapses.
Topics: Animals; Retinal Rod Photoreceptor Cells; Mice; Synapses; Male; Female; Electroretinography; Dynamin I; Dynamin III; Mice, Knockout; Mice, Inbred C57BL
PubMed: 38641407
DOI: 10.1523/JNEUROSCI.1379-23.2024 -
Medicine Apr 2024Cerebral palsy (CP) is the most common disabling disease in children, and motor dysfunction is the core symptom of CP. Although relevant risk factors have been found to... (Observational Study)
Observational Study
Cerebral palsy (CP) is the most common disabling disease in children, and motor dysfunction is the core symptom of CP. Although relevant risk factors have been found to be closely associated with CP: congenital malformations, multiple gestation, prematurity, intrauterine inflammation and infection, birth asphyxia, thrombophilia, and perinatal stroke. Its important pathophysiological mechanism is amniotic fluid infection and intraamniotic inflammation leading to fetal developing brain damage, which may last for many years. However, the molecular mechanism of CP is still not well explained. This study aimed to use bioinformatics to identify key biomarker-related signaling pathways in CP. The expression profile of children with CP was selected from the Gene Expression Comprehensive Database, and the CP disease gene data set was obtained from GeneCards. A protein-protein interaction network was established and functional enrichment analysis was performed using Gene Ontology and Kyoto Encyclopedia of Genes and Genomes databases. A total of 144 differential key intersection genes and 10 hub genes were identified through molecular biology. Gene Ontology functional enrichment analysis results show that differentially expressed genes are mainly concentrated in biological processes, such as immune response and neurogenesis. The cellular components involved mainly include axons, postsynaptic membranes, etc, and their molecular functions mainly involve proteoglycan binding, collagen binding, etc. Kyoto Encyclopedia of Genes and Genomes analysis shows that the intersection genes are mainly in signaling pathways related to the immune system, inflammatory response, and nervous system, such as Th17 cell differentiation, Toll-like receptor signaling pathway, tumor necrosis factor signaling pathway, NF-κB signaling pathway, axon guidance, PI3K-Akt signaling pathway, HIF-1 signaling pathway, gap junction, etc. Jak-STAT signaling pathway, mTOR signaling pathway, and related hub genes regulate immune cells and inflammatory factors and play an important role in the development and progression of CP.
Topics: Child; Female; Pregnancy; Humans; Cerebral Palsy; Phosphatidylinositol 3-Kinases; Biomarkers; Brain Injuries; Computational Biology; Inflammation
PubMed: 38640267
DOI: 10.1097/MD.0000000000037828 -
Methods in Molecular Biology (Clifton,... 2024Postsynaptic density (PSD) is a morphologically and functionally specialized postsynaptic membrane structure of excitatory synapses. It contains hundreds of proteins...
Postsynaptic density (PSD) is a morphologically and functionally specialized postsynaptic membrane structure of excitatory synapses. It contains hundreds of proteins such as neurotransmitter receptors, adhesion molecules, cytoskeletal proteins, and signaling enzymes. The study of the molecular architecture of the PSD is one of the most intriguing issues in neuroscience research. The isolation of the PSD from the brain of an animal is necessary for subsequent biochemical and morphological analyses. Many laboratories have developed methods to isolate PSD from the animal brain. In this chapter, we present a simple method to isolate PSD from the mouse brain using sucrose density gradient-based purification of synaptosomes followed by detergent extraction.
Topics: Animals; Mice; Post-Synaptic Density; Synaptic Membranes; Brain; Cytoskeletal Proteins; Laboratories
PubMed: 38630221
DOI: 10.1007/978-1-0716-3810-1_7