Antisense oligonucleotide therapeutic approach for Timothy syndrome.

Timothy syndrome (TS) is a severe, multisystem disorder characterized by autism, epilepsy, long-QT syndrome and other neuropsychiatric conditions1. TS type 1 (TS1) is caused by a gain-of-function variant in the alternatively spliced and developmentally enriched CACNA1C exon 8A, as opposed to its counterpart exon 8. We previously uncovered several phenotypes in neurons derived from patients with TS1, including delayed channel inactivation, prolonged depolarization-induced calcium rise, impaired interneuron migration, activity-dependent dendrite retraction and an unanticipated persistent expression of exon 8A2-6. We reasoned that switching CACNA1C exon utilization from 8A to 8 would represent a potential therapeutic strategy. Here we developed antisense oligonucleotides (ASOs) to effectively decrease the inclusion of exon 8A in human cells both in vitro and, following transplantation, in vivo. We discovered that the ASO-mediated switch from exon 8A to 8 robustly rescued defects in patient-derived cortical organoids and migration in forebrain assembloids. Leveraging a transplantation platform previously developed7, we found that a single intrathecal ASO administration rescued calcium changes and in vivo dendrite retraction of patient neurons, suggesting that suppression of CACNA1C exon 8A expression is a potential treatment for TS1. Broadly, these experiments illustrate how a multilevel, in vivo and in vitro stem cell model-based approach can identify strategies to reverse disease-relevant neural pathophysiology.

Granulocyte macrophage colony-stimulating factor-induced macrophages of individuals with autism spectrum disorder adversely affect neuronal dendrites through the secretion of pro-inflammatory cytokines.

BACKGROUND: A growing body of evidence suggests that immune dysfunction and inflammation in the peripheral tissues as well as the central nervous system are associated with the neurodevelopmental deficits observed in autism spectrum disorder (ASD). Elevated expression of pro-inflammatory cytokines in the plasma, serum, and peripheral blood mononuclear cells of ASD has been reported. These cytokine expression levels are associated with the severity of behavioral impairments and symptoms in ASD. In a prior study, our group reported that tumor necrosis factor-α (TNF-α) expression in granulocyte-macrophage colony-stimulating factor-induced macrophages (GM-CSF MΦ) and the TNF-α expression ratio in GM-CSF MΦ/M-CSF MΦ (macrophage colony-stimulating factor-induced macrophages) was markedly higher in individuals with ASD than in typically developed (TD) individuals. However, the mechanisms of how the macrophages and the highly expressed cytokines affect neurons remain to be addressed. METHODS: To elucidate the effect of macrophages on human neurons, we used a co-culture system of control human-induced pluripotent stem cell-derived neurons and differentiated macrophages obtained from the peripheral blood mononuclear cells of five TD individuals and five individuals with ASD. All participants were male and ethnically Japanese. RESULTS: Our results of co-culture experiments showed that GM-CSF MΦ affect the dendritic outgrowth of neurons through the secretion of pro-inflammatory cytokines, interleukin-1α and TNF-α. Macrophages derived from individuals with ASD exerted more severe effects than those derived from TD individuals. LIMITATIONS: The main limitations of our study were the small sample size with a gender bias toward males, the use of artificially polarized macrophages, and the inability to directly observe the interaction between neurons and macrophages from the same individuals. CONCLUSIONS: Our co-culture system revealed the non-cell autonomous adverse effects of GM-CSF MΦ in individuals with ASD on neurons, mediated by interleukin-1α and TNF-α. These results may support the immune dysfunction hypothesis of ASD, providing new insights into its pathology.

Interplay between autophagy and CncC regulates dendrite pruning in Drosophila.

Autophagy is essential for the turnover of damaged organelles and long-lived proteins. It is responsible for many biological processes such as maintaining brain functions and aging. Impaired autophagy is often linked to neurodevelopmental and neurodegenerative diseases in humans. However, the role of autophagy in neuronal pruning during development remains poorly understood. Here, we report that autophagy regulates dendrite-specific pruning of ddaC sensory neurons in parallel to local caspase activation. Impaired autophagy causes the formation of ubiquitinated protein aggregates in ddaC neurons, dependent on the autophagic receptor Ref(2)P. Furthermore, the metabolic regulator AMP-activated protein kinase and the insulin-target of rapamycin pathway act upstream to regulate autophagy during dendrite pruning. Importantly, autophagy is required to activate the transcription factor CncC (Cap "n" collar isoform C), thereby promoting dendrite pruning. Conversely, CncC also indirectly affects autophagic activity via proteasomal degradation, as impaired CncC results in the inhibition of autophagy through sequestration of Atg8a into ubiquitinated protein aggregates. Thus, this study demonstrates the important role of autophagy in activating CncC prior to dendrite pruning, and further reveals an interplay between autophagy and CncC in neuronal pruning.

SARM1 is responsible for calpain-dependent dendrite degeneration in mouse hippocampal neurons.

Sterile alpha and toll/interleukin receptor motif-containing 1 (SARM1) is a critical regulator of axon degeneration that acts through hydrolysis of NAD+ following injury. Recent work has defined the mechanisms underlying SARM1's catalytic activity and advanced our understanding of SARM1 function in axons, yet the role of SARM1 signaling in other compartments of neurons is still not well understood. Here, we show in cultured hippocampal neurons that endogenous SARM1 is present in axons, dendrites, and cell bodies and that direct activation of SARM1 by the neurotoxin Vacor causes not just axon degeneration, but degeneration of all neuronal compartments. In contrast to the axon degeneration pathway defined in dorsal root ganglia, SARM1-dependent hippocampal axon degeneration in vitro is not sensitive to inhibition of calpain proteases. Dendrite degeneration downstream of SARM1 in hippocampal neurons is dependent on calpain 2, a calpain protease isotype enriched in dendrites in this cell type. In summary, these data indicate SARM1 plays a critical role in neurodegeneration outside of axons and elucidates divergent pathways leading to degeneration in hippocampal axons and dendrites.

Balancing act of small GTPases downstream of plexin-A4 signaling motifs promotes dendrite elaboration in mammalian cortical neurons.

The precise development of neuronal morphologies is crucial to the establishment of synaptic circuits and, ultimately, proper brain function. Signaling by the axon guidance cue semaphorin 3A (Sema3A) and its receptor complex of neuropilin-1 and plexin-A4 has multifunctional outcomes in neuronal morphogenesis. Downstream activation of the RhoGEF FARP2 through interaction with the lysine-arginine-lysine motif of plexin-A4 and consequent activation of the small GTPase Rac1 promotes dendrite arborization, but this pathway is dispensable for axon repulsion. Here, we investigated the interplay of small GTPase signaling mechanisms underlying Sema3A-mediated dendritic elaboration in mouse layer V cortical neurons in vitro and in vivo. Sema3A promoted the binding of the small GTPase Rnd1 to the amino acid motif lysine-valine-serine (LVS) in the cytoplasmic domain of plexin-A4. Rnd1 inhibited the activity of the small GTPase RhoA and the kinase ROCK, thus supporting the activity of the GTPase Rac1, which permitted the growth and branching of dendrites. Overexpression of a dominant-negative RhoA, a constitutively active Rac1, or the pharmacological inhibition of ROCK activity rescued defects in dendritic elaboration in neurons expressing a plexin-A4 mutant lacking the LVS motif. Our findings provide insights into the previously unappreciated balancing act between Rho and Rac signaling downstream of specific motifs in plexin-A4 to mediate Sema3A-dependent dendritic elaboration in mammalian cortical neuron development.

Anti-SFT2D2 autoantibodies alter dendrite spine and cause psychotic behavior in mice.

BACKGROUND: Autoimmunity plays an important role in schizophrenia (SCZ). Autoantibodies against SFT2D2 have been reported in patients with SCZ; however, the specific mechanism remains unclear. This study aimed to describe an autoimmune model, namely, mice immunized against SFT2D2-peptides. METHODS: ApoE-/- and WT mice (C57BL/6) were immunized four times (day 0, day 14, day 21, day 35) with SFT2D2 peptide or KLH via subcutaneous injection. Behavioral tests were conducted after the third immunization, and immunochemistry of brain tissue were performed after the sacrifice of the mice. RESULTS: Active immunization with KLH-coupled SFT2D2-derived peptides in both WT and ApoE-/- (compromised blood-brain barrier) mice led to high circulating levels of anti-SFT2D2 IgG. While there was no detectable deficit in WT mice, impaired pre-pulse inhibition, motor impairments, and reduced cognition in ApoE-/- mice, without signs of anxiety and depression were observed. In addition, immunohistochemical assays demonstrated that activated microglia and astrocytes were increased but neuronal dendritic spine densities were decreased, accompanied by increased expression of complement molecule C4 across brain regions in ApoE-/- mice. CONCLUSIONS: In model mice with compromised blood-brain barrier, endogenous anti-SFT2D2 IgG can activate glial cells and modulate synaptic plasticity, and induce a series of psychosis-like changes. These antibodies may reveal valuable therapeutic targets, which may improve the treatment strategies for a subgroup of SCZ patients.

Sumoylation in astrocytes induces changes in the proteome of the derived small extracellular vesicles which change protein synthesis and dendrite morphology in target neurons.

Emerging evidence highlights the relevance of the protein post-translational modification by SUMO (Small Ubiquitin-like Modifier) in the central nervous system for modulating cognition and plasticity in health and disease. In these processes, astrocyte-to-neuron crosstalk mediated by extracellular vesicles (EVs) plays a yet poorly understood role. Small EVs (sEVs), including microvesicles and exosomes, contain a molecular cargo of lipids, proteins, and nucleic acids that define their biological effect on target cells. Here, we investigated whether SUMOylation globally impacts the sEV protein cargo. For this, sEVs were isolated from primary cultures of astrocytes by ultracentrifugation or using a commercial sEV isolation kit. SUMO levels were regulated: 1) via plasmids that over-express SUMO, or 2) via experimental conditions that increase SUMOylation, i.e., by using the stress hormone corticosterone, or 3) via the SUMOylation inhibitor 2-D08 (2',3',4'-trihydroxy-flavone, 2-(2,3,4-Trihydroxyphenyl)-4H-1-Benzopyran-4-one). Corticosterone and 2-D08 had opposing effects on the number of sEVs and on their protein cargo. Proteomic analysis showed that increased SUMOylation in corticosterone-treated or plasmid-transfected astrocytes increased the presence of proteins related to cell division, transcription, and protein translation in the derived sEVs. When sEVs derived from corticosterone-treated astrocytes were transferred to neurons to assess their impact on protein synthesis using the fluorescence non-canonical amino acid tagging assay (FUNCAT), we detected an increase in protein synthesis, while sEVs from 2-D08-treated astrocytes had no effect. Our results show that SUMO conjugation plays an important role in the modulation of the proteome of astrocyte-derived sEVs with a potential functional impact on neurons.

Super-resolution imaging reveals the relationship between CaMKIIß and drebrin within dendritic spines.

Dendritic spines are unique postsynaptic structures that emerge from the dendrites of neurons. They undergo activity-dependent morphological changes known as structural plasticity. The changes involve actin cytoskeletal remodeling, which is regulated by actin-binding proteins. CaMKII is a crucial molecule in synaptic plasticity. Notably, CaMKIIß subtype is known to bind to filamentous-actin and is closely involved in structural plasticity. We have shown that CaMKIIß binds to drebrin, and is localized in spines as both drebrin-dependent and drebrin-independent pools. However, the nanoscale relationship between drebrin and CaMKIIß within dendritic spines has not been clarified. In this study, we used stochastic optical reconstruction microscopy (STORM) to examine the detailed localization of these proteins. STORM imaging showed that CaMKIIß co-localized with drebrin in the core region of spines, and localized in the submembrane region of spines without drebrin. Interestingly, the dissociation of CaMKIIß and drebrin in the core region was induced by NMDA receptor activation. In drebrin knockdown neurons, CaMKIIß was decreased in the core region but not in the submembrane region. Together it indicates that the clustering of CaMKIIß in the spine core region is dependent on drebrin. These findings suggest that drebrin-dependent CaMKIIß is in a standby state before its activation.

Control of hippocampal synaptic plasticity by microglia-dendrite interactions depends on genetic context in mouse models of Alzheimer's disease.

INTRODUCTION: Human data suggest susceptibility and resilience to features of Alzheimer's disease (AD) such as microglia activation and synaptic dysfunction are under genetic control. However, causal relationships between these processes, and how genomic diversity modulates them remain systemically underexplored in mouse models. METHODS: AD-vulnerable hippocampal neurons were virally labeled in inbred (C57BL/6J) and wild-derived (PWK/PhJ) APP/PS1 and wild-type mice, and brain microglia depleted from 4 to 8 months of age. Dendrites were assessed for synapse plasticity changes by evaluating spine densities and morphologies. RESULTS: In C57BL/6J, microglia depletion blocked amyloid-induced synaptic density and morphology changes. At a finer scale, synaptic morphology on individual branches was dependent on microglia-dendrite physical interactions. Conversely, synapses from PWK/PhJ mice showed remarkable stability in response to amyloid, and no evidence of microglia contact-dependent changes on dendrites. DISCUSSION: These results demonstrate that microglia-dependent synaptic alterations in specific AD-vulnerable projection pathways are differentially controlled by genetic context.

Topology recapitulates morphogenesis of neuronal dendrites.

Branching allows neurons to make synaptic contacts with large numbers of other neurons, facilitating the high connectivity of nervous systems. Neuronal arbors have geometric properties such as branch lengths and diameters that are optimal in that they maximize signaling speeds while minimizing construction costs. In this work, we asked whether neuronal arbors have topological properties that may also optimize their growth or function. We discovered that for a wide range of invertebrate and vertebrate neurons the distributions of their subtree sizes follow power laws, implying that they are scale invariant. The power-law exponent distinguishes different neuronal cell types. Postsynaptic spines and branchlets perturb scale invariance. Through simulations, we show that the subtree-size distribution depends on the symmetry of the branching rules governing arbor growth and that optimal morphologies are scale invariant. Thus, the subtree-size distribution is a topological property that recapitulates the functional morphology of dendrites.

Aberrant DJ-1 expression underlies L-type calcium channel hypoactivity in dendrites in tuberous sclerosis complex and Alzheimer's disease.

L-type voltage-gated calcium (Ca2+) channels (L-VGCC) dysfunction is implicated in several neurological and psychiatric diseases. While a popular therapeutic target, it is unknown whether molecular mechanisms leading to disrupted L-VGCC across neurodegenerative disorders are conserved. Importantly, L-VGCC integrate synaptic signals to facilitate a plethora of cellular mechanisms; however, mechanisms that regulate L-VGCC channel density and subcellular compartmentalization are understudied. Herein, we report that in disease models with overactive mammalian target of rapamycin complex 1 (mTORC1) signaling (or mTORopathies), deficits in dendritic L-VGCC activity are associated with increased expression of the RNA-binding protein (RBP) Parkinsonism-associated deglycase (DJ-1). DJ-1 binds the mRNA coding for the alpha and auxiliary Ca2+ channel subunits CaV1.2 and α2δ2, and represses their mRNA translation, only in the disease states, specifically preclinical models of tuberous sclerosis complex (TSC) and Alzheimer's disease (AD). In agreement, DJ-1-mediated repression of CaV1.2/α2δ2 protein synthesis in dendrites is exaggerated in mouse models of AD and TSC, resulting in deficits in dendritic L-VGCC calcium activity. Finding of DJ-1-regulated L-VGCC activity in dendrites in TSC and AD provides a unique signaling pathway that can be targeted in clinical mTORopathies.

Calcium signals tune AMPK activity and mitochondrial homeostasis in dendrites of developing neurons.

Dendritic outgrowth in immature neurons is enhanced by neuronal activity and is considered one of the mechanisms of neural circuit optimization. It is known that calcium signals affect transcriptional regulation and cytoskeletal remodeling necessary for dendritic outgrowth. Here, we demonstrate that activity-dependent calcium signaling also controls mitochondrial homeostasis via AMP-activated protein kinase (AMPK) in growing dendrites of differentiating mouse hippocampal neurons. We found that the inhibition of neuronal activity induced dendritic hypotrophy with abnormally elongated mitochondria. In growing dendrites, AMPK is activated by neuronal activity and dynamically oscillates in synchrony with calcium spikes, and this AMPK oscillation was inhibited by CaMKK2 knockdown. AMPK activation led to phosphorylation of MFF and ULK1, which initiate mitochondrial fission and mitophagy, respectively. Dendritic mitochondria in AMPK-depleted neurons exhibited impaired fission and mitophagy and displayed multiple signs of dysfunction. Genetic inhibition of fission led to dendritic hypoplasia that was reminiscent of AMPK-deficient neurons. Thus, AMPK activity is finely tuned by the calcium-CaMKK2 pathway and regulates mitochondrial homeostasis by facilitating removal of damaged components of mitochondria in growing neurons during normal brain development.

Short-chain fatty acids stimulate dendrite elongation in dendritic cells by inhibiting histone deacetylase.

Dendritic cells activate immune responses by presenting pathogen-derived molecules. The dendrites of dendritic cells contribute to the incorporation of foreign antigens or presenting antigens to T cells. Short-chain fatty acids (SCFAs), such as acetic, propionic, butyric and valeric acids, have many effects on immune responses by activating specific receptors or inhibiting a histone deacetylase (HDAC), although their effect on dendrite formation in dendritic cells is unknown. In the present study, we aimed to investigate the effect of SCFAs on dendrite elongation using a dendritic cell line (DC2.4 cells) and mouse bone marrow-derived dendritic cells. We found that SCFAs induced dendrite elongation. The elongation was reduced by inhibitors of Src family kinase (SFK), phosphatidylinositol-3 kinase (PI3K), Rho family GTPases (Cdc42, Rac1) or actin polymerization, indicating that SCFAs promote dendrite elongation by activating actin polymerization via the SFK/PI3K/Rho family GTPase signaling pathway. We showed that agonists for SCFA receptors GPR43 and GPR109a did not promote dendrite elongation. By contrast, HDAC inhibitors, including trichostatin A, promoted dendrite elongation in DC2.4 cells, and the promoting activity of trichostatin A was decreased by inhibiting the SFK/PI3K/Rho family GTPase signaling pathway or actin polymerization. Furthermore, DC2.4 cells treated with valeric acid showed enhanced uptake of soluble proteins, insoluble beads and Staphylococcus aureus. We also found that treatment with valeric acid enhanced major histocompatibility complex class II-mediated antigen presentation in bone marrow-derived dendritic cells. These results suggest that SCFAs promote dendrite elongation by inhibiting HDAC, stimulating the SFK/PI3K/Rho family pathway and activating actin polymerization, resulting in increased antigen uptake and presentation in dendritic cells.

Statistical modeling of mRNP transport in dendrites: A comparative analysis of ß-actin and Arc mRNP dynamics.

Localization of messenger RNA (mRNA) in dendrites is crucial for regulating gene expression during long-term memory formation. mRNA binds to RNA-binding proteins (RBPs) to form messenger ribonucleoprotein (mRNP) complexes that are transported by motor proteins along microtubules to their target synapses. However, the dynamics by which mRNPs find their target locations in the dendrite have not been well understood. Here, we investigated the motion of endogenous ß-actin and Arc mRNPs in dissociated mouse hippocampal neurons using the MS2 and PP7 stem-loop systems, respectively. By evaluating the statistical properties of mRNP movement, we found that the aging Lévy walk model effectively describes both ß-actin and Arc mRNP transport in proximal dendrites. A critical difference between ß-actin and Arc mRNPs was the aging time, the time lag between transport initiation and measurement initiation. The longer mean aging time of ß-actin mRNP (~100 s) compared with that of Arc mRNP (~30 s) reflects the longer half-life of constitutively expressed ß-actin mRNP. Furthermore, our model also permitted us to estimate the ratio of newly generated and pre-existing ß-actin mRNPs in the dendrites. This study offers a robust theoretical framework for mRNP transport, which provides insight into how mRNPs locate their targets in neurons.

The intrinsically disordered cytoplasmic tail of a dendrite branching receptor uses two distinct mechanisms to regulate the actin cytoskeleton.

Dendrite morphogenesis is essential for neural circuit formation, yet the molecular mechanisms underlying complex dendrite branching remain elusive. Previous studies on the highly branched Caenorhabditis elegans PVD sensory neuron identified a membrane co-receptor complex that links extracellular signals to intracellular actin remodeling machinery, promoting high-order dendrite branching. In this complex, the claudin-like transmembrane protein HPO-30 recruits the WAVE regulatory complex (WRC) to dendrite branching sites, stimulating the Arp2/3 complex to polymerize actin. We report here our biochemical and structural analysis of this interaction, revealing that the intracellular domain (ICD) of HPO-30 is intrinsically disordered and employs two distinct mechanisms to regulate the actin cytoskeleton. First, HPO-30 ICD binding to the WRC requires dimerization and involves the entire ICD sequence, rather than a short linear peptide motif. This interaction enhances WRC activation by the GTPase Rac1. Second, HPO-30 ICD directly binds to the sides and barbed end of actin filaments. Binding to the barbed end requires ICD dimerization and inhibits both actin polymerization and depolymerization, resembling the actin capping protein CapZ. These dual functions provide an intriguing model of how membrane proteins can integrate distinct mechanisms to fine-tune local actin dynamics.

Endoplasmic Reticulum Exit Sites scale with somato-dendritic size in neurons.

Nervous systems exhibit dramatic diversity in cell morphology and size. How neurons regulate their biosynthetic and secretory machinery to support such diversity is not well understood. Endoplasmic reticulum exit sites (ERESs) are essential for maintaining secretory flux, and are required for normal dendrite development, but how neurons of different size regulate secretory capacity remains unknown. In Caenorhabditis elegans, we find that the ERES number is strongly correlated with the size of a neuron's dendritic arbor. The elaborately branched sensory neuron, PVD, has especially high ERES numbers. Asymmetric cell division provides PVD with a large initial cell size critical for rapid establishment of PVD's high ERES number before neurite outgrowth, and these ERESs are maintained throughout development. Maintenance of ERES number requires the cell fate transcription factor MEC-3, C. elegans TOR (ceTOR/let-363), and nutrient availability, with mec-3 and ceTOR/let-363 mutant PVDs both displaying reductions in ERES number, soma size, and dendrite size. Notably, mec-3 mutant animals exhibit reduced expression of a ceTOR/let-363 reporter in PVD, and starvation reduces ERES number and somato-dendritic size in a manner genetically redundant with ceTOR/let-363 perturbation. Our data suggest that both asymmetric cell division and nutrient sensing pathways regulate secretory capacities to support elaborate dendritic arbors.

Organelle mapping in dendrites of human iPSC-derived neurons reveals dynamic functional dendritic Golgi structures.

Secretory pathways within dendrites of neurons have been proposed for local transport of newly synthesized proteins. However, little is known about the dynamics of the local secretory system and whether the organelles are transient or stable structures. Here, we quantify the spatial and dynamic behavior of dendritic Golgi and endosomes during differentiation of human neurons generated from induced pluripotent stem cells (iPSCs). In early neuronal development, before and during migration, the entire Golgi apparatus transiently translocates from the soma into dendrites. In mature neurons, dynamic Golgi elements, containing cis and trans cisternae, are transported from the soma along dendrites, in an actin-dependent process. Dendritic Golgi outposts are dynamic and display bidirectional movement. Similar structures were observed in cerebral organoids. Using the retention using selective hooks (RUSH) system, Golgi resident proteins are transported efficiently into Golgi outposts from the endoplasmic reticulum. This study reveals dynamic, functional Golgi structures in dendrites and a spatial map for investigating dendrite trafficking in human neurons.

Golgi polarity shift instructs dendritic refinement in the neonatal cortex by mediating NMDA receptor signaling.

Dendritic refinement is a critical component of activity-dependent neuronal circuit maturation, through which individual neurons establish specific connectivity with their target axons. Here, we demonstrate that the developmental shift of Golgi polarity is a key process in dendritic refinement. During neonatal development, the Golgi apparatus in layer 4 spiny stellate (SS) neurons in the mouse barrel cortex lose their original apical positioning and acquire laterally polarized distributions. This lateral Golgi polarity, which is oriented toward the barrel center, peaks on postnatal days 5-7 (P5-P7) and disappears by P15, which aligns with the developmental time course of SS neuron dendritic refinement. Genetic ablation of N-methyl-D-aspartate (NMDA) receptors, key players in dendritic refinement, disturbs the lateral Golgi polarity. Golgi polarity manipulation disrupts the asymmetric dendritic projection pattern and the primary-whisker-specific response of SS neurons. Our results elucidate activity-dependent Golgi dynamics and their critical role in developmental neuronal circuit refinement.

Asymmetric Voltage Attenuation in Dendrites Can Enable Hierarchical Heterosynaptic Plasticity.

Long-term synaptic plasticity is mediated via cytosolic calcium concentrations ([Ca2+]). Using a synaptic model that implements calcium-based long-term plasticity via two sources of Ca2+ - NMDA receptors and voltage-gated calcium channels (VGCCs) - we show in dendritic cable simulations that the interplay between these two calcium sources can result in a diverse array of heterosynaptic effects. When spatially clustered synaptic input produces a local NMDA spike, the resulting dendritic depolarization can activate VGCCs at nonactivated spines, resulting in heterosynaptic plasticity. NMDA spike activation at a given dendritic location will tend to depolarize dendritic regions that are located distally to the input site more than dendritic sites that are proximal to it. This asymmetry can produce a hierarchical effect in branching dendrites, where an NMDA spike at a proximal branch can induce heterosynaptic plasticity primarily at branches that are distal to it. We also explored how simultaneously activated synaptic clusters located at different dendritic locations synergistically affect the plasticity at the active synapses, as well as the heterosynaptic plasticity of an inactive synapse "sandwiched" between them. We conclude that the inherent electrical asymmetry of dendritic trees enables sophisticated schemes for spatially targeted supervision of heterosynaptic plasticity.

The Voltage-Gated Sodium Channel in Drosophila, Para, Localizes to Dendrites As Well As Axons in Mechanosensitive Chordotonal Neurons.

The fruit fly Drosophila melanogaster has provided important insights into how sensory information is transduced by transient receptor potential (TRP) channels in the peripheral nervous system (PNS). However, TRP channels alone have not been able to completely model mechanosensitive transduction in mechanoreceptive chordotonal neurons (CNs). Here, we show that, in addition to TRP channels, the sole voltage-gated sodium channel (NaV) in Drosophila, Para, is localized to the dendrites of CNs. Para is localized to the distal tip of the dendrites in all CNs, from embryos to adults, and is colocalized with the mechanosensitive TRP channels No mechanoreceptor potential C (NompC) and Inactive/Nanchung (Iav/Nan). Para localization also demarcates spike initiation zones (SIZs) in axons and the dendritic localization of Para is indicative of a likely dendritic SIZ in fly CNs. Para is not present in the dendrites of other peripheral sensory neurons. In both multipolar and bipolar neurons in the PNS, Para is present in a proximal region of the axon, comparable to the axonal initial segment (AIS) in vertebrates, 40-60 µm from the soma in multipolar neurons and 20-40 µm in bipolar neurons. Whole-cell reduction of para expression using RNAi in CNs of the adult Johnston's organ (JO) severely affects sound-evoked potentials (SEPs). However, the duality of Para localization in the CN dendrites and axons identifies a need to develop resources to study compartment-specific roles of proteins that will enable us to better understand Para's role in mechanosensitive transduction.