Frontiers in Synaptic Neuroscience最新文献

Introduction: Cancer patients treated with paclitaxel often develop chemotherapy-induced peripheral neuropathy, which has not been effectively treated with drugs. The anti-diabetic drug metformin is effective in the treatment of neuropathic pain. The aim of this study was to elucidate effect of metformin on paclitaxel-induced neuropathic pain and spinal synaptic transmission.

Methods: Electrophysiological experiments on rat spinal slices were performed in vitro and mechanical allodynia quantified in vitro.

Results: The present data demonstrated that intraperitoneal injection of paclitaxel produced mechanical allodynia and potentiated spinal synaptic transmission. Intrathecal injection of metformin significantly reversed the established mechanical allodynia induced by paclitaxel in rats. Either spinal or systemic administration of metformin significantly inhibited the increased frequency of spontaneous excitatory postsynaptic currents (sEPSCs) in spinal dorsal horn neurons from paclitaxel-treated rats. We found that 1 h incubation of metformin also reduced the frequency rather than the amplitude of sEPSCs in the spinal slices from paclitaxel-treated rats.

Discussion: These results suggested that metformin was able to depress the potentiated spinal synaptic transmission, which may contribute to alleviating the paclitaxel-induced neuropathic pain.

The synapse has consistently been considered a vulnerable and critical target within Alzheimer's disease, and synapse loss is, to date, one of the main biological correlates of cognitive decline within Alzheimer's disease. This occurs prior to neuronal loss with ample evidence that synaptic dysfunction precedes this, in support of the idea that synaptic failure is a crucial stage within disease pathogenesis. The two main pathological hallmarks of Alzheimer's disease, abnormal aggregates of amyloid or tau proteins, have had demonstrable effects on synaptic physiology in animal and cellular models of Alzheimer's disease. There is also growing evidence that these two proteins may have a synergistic effect on neurophysiological dysfunction. Here, we review some of the main findings of synaptic alterations in Alzheimer's disease, and what we know from Alzheimer's disease animal and cellular models. First, we briefly summarize some of the human evidence to suggest that synapses are altered, including how this relates to network activity. Subsequently, animal and cellular models of Alzheimer's disease are considered, highlighting mouse models of amyloid and tau pathology and the role these proteins may play in synaptic dysfunction, either in isolation or examining how the two pathologies may interact in dysfunction. This specifically focuses on neurophysiological function and dysfunction observed within these animal models, typically measured using electrophysiology or calcium imaging. Following synaptic dysfunction and loss, it would be impossible to imagine that this would not alter oscillatory activity within the brain. Therefore, this review also discusses how this may underpin some of the aberrant oscillatory patterns seen in animal models of Alzheimer's disease and human patients. Finally, an overview of some key directions and considerations in the field of synaptic dysfunction in Alzheimer's disease is covered. This includes current therapeutics that are targeted specifically at synaptic dysfunction, but also methods that modulate activity to rescue aberrant oscillatory patterns. Other important future avenues of note in this field include the role of non-neuronal cell types such as astrocytes and microglia, and mechanisms of dysfunction independent of amyloid and tau in Alzheimer's disease. The synapse will certainly continue to be an important target within Alzheimer's disease for the foreseeable future.

Since the discovery of neurexins (Nrxns) as essential and evolutionarily conserved synaptic adhesion molecules, focus has largely centered on their functional contributions to glutamatergic synapses. Recently, significant advances to our understanding of neurexin function at GABAergic synapses have revealed that neurexins can play pleiotropic roles in regulating inhibitory synapse maintenance and function in a brain-region and synapse-specific manner. GABAergic neurons are incredibly diverse, exhibiting distinct synaptic properties, sites of innervation, neuromodulation, and plasticity. Different classes of GABAergic neurons often express distinct repertoires of Nrxn isoforms that exhibit differential alternative exon usage. Further, Nrxn ligands can be differentially expressed and can display synapse-specific localization patterns, which may contribute to the formation of a complex trans-synaptic molecular code that establishes the properties of inhibitory synapse function and properties of local circuitry. In this review, we will discuss how Nrxns and their ligands sculpt synaptic inhibition in a brain-region, cell-type and synapse-specific manner.

Four modes of endocytosis and subsequent synaptic vesicle (SV) recycling have been described at the presynapse to ensure the availability of SVs for synaptic release. However, it is unclear to what extend these modes operate under physiological activity patterns in vivo. The coat protein clathrin can regenerate SVs either directly from the plasma membrane (PM) via clathrin-mediated endocytosis (CME), or indirectly from synaptic endosomes by SV budding. Here, we examined the role of clathrin in SV recycling under physiological conditions by applying the clathrin inhibitor Pitstop-2 to the calyx of Held, a synapse optimized for high frequency synaptic transmission in the auditory brainstem, in vivo. The effects of clathrin-inhibition on SV recycling were investigated by serial sectioning scanning electron microscopy (S³EM) and 3D reconstructions of endocytic structures labeled by the endocytosis marker horseradish peroxidase (HRP). We observed large endosomal compartments as well as HRP-filled, black SVs (bSVs) that have been recently recycled. The application of Pitstop-2 led to reduced bSV but not large endosome density, increased volumes of large endosomes and shifts in the localization of both types of endocytic compartments within the synapse. These changes after perturbation of clathrin function suggest that clathrin plays a role in SV recycling from both, the PM and large endosomes, under physiological activity patterns, in vivo.

Membrane lipid rafts are sphingolipids and cholesterol-enriched membrane microdomains, which form a center for the interaction or assembly of palmitoylated signaling molecules, including Src family non-receptor type protein tyrosine kinases. Lipid rafts abundantly exist in neurons and function in the maintenance of synapses. Excitatory synaptic strength is largely controlled by the surface expression of α-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptors in the mammalian brain. AMPA receptor endocytosis from the synaptic surface is regulated by phosphorylation of the GluA2 subunit at tyrosine 876 by Src family kinases. Here, I revealed that tyrosine phosphorylated GluA2 is concentrated in the lipid rafts fraction. Furthermore, stimulation-induced upregulation of GluA2 tyrosine phosphorylation is disrupted by the treatment of neurons with a cholesterol-depleting compound, filipin III. These results indicate the importance of lipid rafts as enzymatic reactive sites for AMPA receptor tyrosine phosphorylation and subsequent AMPA receptor internalization from the synaptic surface.

Layer 5 (L5) serves as the main output layer of cortical structures, where long-range projecting pyramidal neurons broadcast the columnar output to other cortical and extracortical regions of the brain. L5 pyramidal neurons are grouped into two subclasses based on their projection targets; while intratelencephalic (IT) neurons project to cortical areas and the striatum, extratelencephalic (ET) neurons project to subcortical areas such as the thalamus, midbrain, and brainstem. Each L5 subclass possesses distinct morphological and electrophysiological properties and is incorporated into a unique synaptic network. Thanks to recent advances in genetic tools and methodologies, it has now become possible to distinguish between the two subclasses in the living brain. There is increasing evidence indicating that each subclass plays a unique role in sensory processing, decision-making, and learning. This review first summarizes the anatomical and physiological properties as well as the neuromodulation of IT and ET neurons in the rodent neocortex, and then reviews recent literature on their roles in sensory processing and rodent behavior. Our ultimate goal is to provide a comprehensive understanding of the role of each subclass in cortical function by examining their operational regimes based on their cellular properties.

A-kinase anchoring protein 79-human/150-rodent (AKAP79/150) organizes signaling proteins to control synaptic plasticity. AKAP79/150 associates with the plasma membrane and endosomes through its N-terminal domain that contains three polybasic regions and two Cys residues that are reversibly palmitoylated. Mutations abolishing palmitoylation (AKAP79/150 CS) reduce its endosomal localization and association with the postsynaptic density (PSD). Here we combined advanced light and electron microscopy (EM) to characterize the effects of AKAP79/150 palmitoylation on its postsynaptic nanoscale organization, trafficking, and mobility in hippocampal neurons. Immunogold EM revealed prominent extrasynaptic membrane AKAP150 labeling with less labeling at the PSD. The label was at greater distances from the spine membrane for AKAP150 CS than WT in the PSD but not in extra-synaptic locations. Immunogold EM of GFP-tagged AKAP79 WT showed that AKAP79 adopts a vertical, extended conformation at the PSD with its N-terminus at the membrane, in contrast to extrasynaptic locations where it adopts a compact or open configurations of its N- and C-termini with parallel orientation to the membrane. In contrast, GFP-tagged AKAP79 CS was displaced from the PSD coincident with disruption of its vertical orientation, while proximity and orientation with respect to the extra-synaptic membrane was less impacted. Single-molecule localization microscopy (SMLM) revealed a heterogeneous distribution of AKAP150 with distinct high-density, nano-scale regions (HDRs) overlapping the PSD but more prominently located in the extrasynaptic membrane for WT and the CS mutant. Thick section scanning transmission electron microscopy (STEM) tomography revealed AKAP150 immunogold clusters similar in size to HDRs seen by SMLM and more AKAP150 labeled endosomes in spines for WT than for CS, consistent with the requirement for AKAP palmitoylation in endosomal trafficking. Hidden Markov modeling of single molecule tracking data revealed a bound/immobile fraction and two mobile fractions for AKAP79 in spines, with the CS mutant having shorter dwell times and faster transition rates between states than WT, suggesting that palmitoylation stabilizes individual AKAP molecules in various spine subpopulations. These data demonstrate that palmitoylation fine tunes the nanoscale localization, mobility, and trafficking of AKAP79/150 in dendritic spines, which might have profound effects on its regulation of synaptic plasticity.

Synapses are the basic units for information processing and storage in the nervous system. It is only when the synaptic connection is established, that it becomes meaningful to discuss the structure and function of a circuit. In humans, our unparalleled cognitive abilities are correlated with an increase in the number of synapses. Additionally, genes involved in synaptogenesis are also frequently associated with neurological or psychiatric disorders, suggesting a relationship between synaptogenesis and brain physiology and pathology. Thus, understanding the molecular mechanisms of synaptogenesis is the key to the mystery of circuit assembly and neural computation. Furthermore, it would provide therapeutic insights for the treatment of neurological and psychiatric disorders. Multiple molecular events must be precisely coordinated to generate a synapse. To understand the molecular mechanisms underlying synaptogenesis, we need to know the molecular components of synapses, how these molecular components are held together, and how the molecular networks are refined in response to neural activity to generate new synapses. Thanks to the intensive investigations in this field, our understanding of the process of synaptogenesis has progressed significantly. Here, we will review the molecular mechanisms of synaptogenesis by going over the studies on the identification of molecular components in synapses and their functions in synaptogenesis, how cell adhesion molecules connect these synaptic molecules together, and how neural activity mobilizes these molecules to generate new synapses. Finally, we will summarize the human-specific regulatory mechanisms in synaptogenesis and results from human genetics studies on synaptogenesis and brain disorders.