Inter-organ Wingless/Ror/Akt signaling regulates nutrient-dependent hyperarborization of somatosensory neurons.

Nutrition in early life has profound effects on an organism, altering processes such as organogenesis. However, little is known about how specific nutrients affect neuronal development. Dendrites of class IV dendritic arborization neurons in Drosophila larvae become more complex when the larvae are reared on a low-yeast diet compared to a high-yeast diet. Our systematic search for key nutrients revealed that the neurons increase their dendritic terminal densities in response to a combined deficiency in vitamins, metal ions, and cholesterol. The deficiency of these nutrients upregulates Wingless in a closely located tissue, body wall muscle. Muscle-derived Wingless activates Akt in the neurons through the receptor tyrosine kinase Ror, which promotes the dendrite branching. In larval muscles, the expression of wingless is regulated not only in this key nutrient-dependent manner, but also by the JAK/STAT signaling pathway. Additionally, the low-yeast diet blunts neuronal light responsiveness and light avoidance behavior, which may help larvae optimize their survival strategies under low-nutritional conditions. Together, our studies illustrate how the availability of specific nutrients affects neuronal development through inter-organ signaling.

Human cortical amygdala dendrites and spines morphology under open-source three-dimensional reconstruction procedures.

Visualizing nerve cells has been fundamental for the systematic description of brain structure and function in humans and other species. Different approaches aimed to unravel the morphological features of neuron types and diversity. The inherent complexity of the human nervous tissue and the need for proper histological processing have made studying human dendrites and spines challenging in postmortem samples. In this study, we used Golgi data and open-source software for 3D image reconstruction of human neurons from the cortical amygdaloid nucleus to show different dendrites and pleomorphic spines at different angles. Procedures required minimal equipment and generated high-quality images for differently shaped cells. We used the "single-section" Golgi method adapted for the human brain to engender 3D reconstructed images of the neuronal cell body and the dendritic ramification by adopting a neuronal tracing procedure. In addition, we elaborated 3D reconstructions to visualize heterogeneous dendritic spines using a supervised machine learning-based algorithm for image segmentation. These tools provided an additional upgrade and enhanced visual display of information related to the spatial orientation of dendritic branches and for dendritic spines of varied sizes and shapes in these human subcortical neurons. This same approach can be adapted for other techniques, areas of the central or peripheral nervous system, and comparative analysis between species.

Non-uniform distribution of dendritic nonlinearities differentially engages thalamostriatal and corticostriatal inputs onto cholinergic interneurons.

The tonic activity of striatal cholinergic interneurons (CINs) is modified differentially by their afferent inputs. Although their unitary synaptic currents are identical, in most CINs cortical inputs onto distal dendrites only weakly entrain them, whereas proximal thalamic inputs trigger abrupt pauses in discharge in response to salient external stimuli. To test whether the dendritic expression of the active conductances that drive autonomous discharge contribute to the CINs' capacity to dissociate cortical from thalamic inputs, we used an optogenetics-based method to quantify dendritic excitability in mouse CINs. We found that the persistent sodium (NaP) current gave rise to dendritic boosting, and that the hyperpolarization-activated cyclic nucleotide-gated (HCN) current gave rise to a subhertz membrane resonance. This resonance may underlie our novel finding of an association between CIN pauses and internally-generated slow wave events in sleeping non-human primates. Moreover, our method indicated that dendritic NaP and HCN currents were preferentially expressed in proximal dendrites. We validated the non-uniform distribution of NaP currents: pharmacologically; with two-photon imaging of dendritic back-propagating action potentials; and by demonstrating boosting of thalamic, but not cortical, inputs by NaP currents. Thus, the localization of active dendritic conductances in CIN dendrites mirrors the spatial distribution of afferent terminals and may promote their differential responses to thalamic vs. cortical inputs.

Regional Variation of Gap Junctional Connections in the Mammalian Inner Retina.

The retinas of many species show regional specialisations that are evident in the differences in the processing of visual input from different parts of the visual field. Regional specialisation is thought to reflect an adaptation to the natural visual environment, optical constraints, and lifestyle of the species. Yet, little is known about regional differences in synaptic circuitry. Here, we were interested in the topographical distribution of connexin-36 (Cx36), the major constituent of electrical synapses in the retina. We compared the retinas of mice, rats, and cats to include species with different patterns of regional specialisations in the analysis. First, we used the density of Prox1-immunoreactive amacrine cells as a marker of any regional specialisation, with higher cell density signifying more central regions. Double-labelling experiments showed that Prox1 is expressed in AII amacrine cells in all three species. Interestingly, large Cx36 plaques were attached to about 8-10% of Prox1-positive amacrine cell somata, suggesting the strong electrical coupling of pairs or small clusters of cell bodies. When analysing the regional changes in the volumetric density of Cx36-immunoreactive plaques, we found a tight correlation with the density of Prox1-expressing amacrine cells in the ON, but not in the OFF sublamina in all three species. The results suggest that the relative contribution of electrical synapses to the ON- and OFF-pathways of the retina changes with retinal location, which may contribute to functional ON/OFF asymmetries across the visual field.

The CATP-8/P5A-type ATPase functions in multiple pathways during neuronal patterning.

The assembly of neuronal circuits involves the migrations of neurons from their place of birth to their final location in the nervous system, as well as the coordinated growth and patterning of axons and dendrites. In screens for genes required for patterning of the nervous system, we identified the catp-8/P5A-ATPase as an important regulator of neural patterning. P5A-ATPases are part of the P-type ATPases, a family of proteins known to serve a conserved function as transporters of ions, lipids and polyamines in unicellular eukaryotes, plants, and humans. While the function of many P-type ATPases is relatively well understood, the function of P5A-ATPases in metazoans remained elusive. We show here, that the Caenorhabditis elegans ortholog catp-8/P5A-ATPase is required for defined aspects of nervous system development. Specifically, the catp-8/P5A-ATPase serves functions in shaping the elaborately sculpted dendritic trees of somatosensory PVD neurons. Moreover, catp-8/P5A-ATPase is required for axonal guidance and repulsion at the midline, as well as embryonic and postembryonic neuronal migrations. Interestingly, not all axons at the midline require catp-8/P5A-ATPase, although the axons run in the same fascicles and navigate the same space. Similarly, not all neuronal migrations require catp-8/P5A-ATPase. A CATP-8/P5A-ATPase reporter is localized to the ER in most, if not all, tissues and catp-8/P5A-ATPase can function both cell-autonomously and non-autonomously to regulate neuronal development. Genetic analyses establish that catp-8/P5A-ATPase can function in multiple pathways, including the Menorin pathway, previously shown to control dendritic patterning in PVD, and Wnt signaling, which functions to control neuronal migrations. Lastly, we show that catp-8/P5A-ATPase is required for localizing select transmembrane proteins necessary for dendrite morphogenesis. Collectively, our studies suggest that catp-8/P5A-ATPase serves diverse, yet specific, roles in different genetic pathways and may be involved in the regulation or localization of transmembrane and secreted proteins to specific subcellular compartments.

Neuropeptide Modulation Increases Dendritic Electrical Spread to Restore Neuronal Activity Disrupted by Temperature.

Peptide neuromodulation has been implicated to shield neuronal activity from acute temperature changes that can otherwise lead to loss of motor control or failure of vital behaviors. However, the cellular actions neuropeptides elicit to support temperature-robust activity remain unknown. Here, we find that peptide neuromodulation restores rhythmic bursting in temperature-compromised central pattern generator (CPG) neurons by counteracting membrane shunt and increasing dendritic electrical spread. We show that acutely rising temperatures reduced spike generation and interrupted ongoing rhythmic motor activity in the crustacean gastric mill CPG. Neuronal release and extrinsic application of Cancer borealis tachykinin-related peptide Ia (CabTRP Ia), a substance-P-related peptide, restored rhythmic activity. Warming led to a significant decrease in membrane resistance and a shunting of the dendritic signals in the main gastric mill CPG neuron. Using a combination of fluorescent calcium imaging and electrophysiology, we observed that postsynaptic potentials and antidromic action potentials propagated less far within the dendritic neuropil as the system warmed. In the presence of CabTRP Ia, membrane shunt decreased and both postsynaptic potentials and antidromic action potentials propagated farther. At elevated temperatures, CabTRP Ia restored dendritic electrical spread or extended it beyond that at cold temperatures. Selective introduction of the CabTRP Ia conductance using a dynamic clamp demonstrated that the CabTRP Ia voltage-dependent conductance was sufficient to restore rhythmic bursting. Our findings demonstrate that a substance-P-related neuropeptide can boost dendritic electrical spread to maintain neuronal activity when perturbed and reveals key neurophysiological components of neuropeptide actions that support pattern generation in temperature-compromised conditions.SIGNIFICANCE STATEMENT Changes in body temperature can have detrimental consequences for the well-being of an organism. Temperature-dependent changes in neuronal activity can be especially dangerous if they affect vital behaviors. Understanding how temperature changes disrupt neuronal activity and identifying how to ameliorate such effects is critically important. Our study of a crustacean circuit shows that warming disrupts rhythmic neuronal activity by increasing membrane shunt and reducing dendritic electrical spread in a key circuit neuron. Through the ionic conductance activated by it, substance-P-related peptide modulation restored electrical spread and counteracted the detrimental temperature effects on rhythmic activity. Because neuropeptides are commonly implicated in sustaining neuronal activity during perturbation, our results provide a promising mechanism to support temperature-robust activity.

Treadmill Exercise Reverses the Change of Dendritic Morphology and Activates BNDF-mTOR Signaling Pathway in the Hippocampus and Cerebral Cortex of Ovariectomized Mice.

A decline of estrogen level leads to spatial learning and memory impairments, which mediated by hippocampus and cortex. Accumulating evidences demonstrated that aerobic exercise improved memory of postmenopausal women and ovariectomized (OVX) mice. However, the molecular mechanisms for this protection of exercise are not completely clear. Accordingly, the present study was designed to examine the effect of aerobic exercise on the dendritic morphology in the hippocampus and cerebral cortex, as well as the BNDF-mTOR signaling pathway of OVX mice. Adult female C57BL/6 mice were divided into four groups (n = 10/group): sham-operated (SHAM/CON), sham-operated with 8-week treadmill exercise (SHAM/EX), ovariectomized operated (OVX/CON), and ovariectomized operated with exercise (OVX/EX). Aerobic exercise improved the impairment of dendritic morphology significantly induced by OVX that was tested by Golgi staining, and it also upregulated the synaptic plasticity-related protein expression of PSD95 and GluR1 as well as activated BDNF-mTOR signaling pathway in the hippocampus and cerebral cortex. In conclusion, aerobic exercise reversed the change of dendritic morphology and increased the synaptic plasticity-related protein expression in the hippocampus and cerebral cortex of OVX mice. The positive effects induced by exercise might be mediated through the BDNF-mTOR signaling pathway.

Time-Lapse Imaging of Neuronal Arborization using Sparse Adeno-Associated Virus Labeling of Genetically Targeted Retinal Cell Populations.

Discovering mechanisms that pattern dendritic arbors requires methods to visualize, image, and analyze dendrites during development. The mouse retina is a powerful model system for the investigation of cell type-specific mechanisms of neuronal morphogenesis and connectivity. The organization and composition of retinal subtypes are well-defined, and genetic tools are available to access specific types during development. Many retinal cell types also constrain their dendrites and/or axons to narrow layers, which facilitates time-lapse imaging. Mouse retina explant cultures are well suited for live-cell imaging using confocal or multiphoton microscopy, but methods optimized for imaging dendrite dynamics with temporal and structural resolution are lacking. Presented here is a method to sparsely label and image the development of specific retinal populations marked by the Cre-Lox system. Commercially available adeno-associated viruses (AAVs) used here expressed membrane-targeted fluorescent proteins in a Cre-dependent manner. Intraocular delivery of AAVs in neonatal mice produces fluorescent labeling of targeted cell types by 4-5 days post-injection (dpi). The membrane fluorescent signals are detectable by confocal imaging and resolve fine branch structures and dynamics. High-quality videos spanning 2-4 h are acquired from imaging retinal flat-mounts perfused with oxygenated artificial cerebrospinal fluid (aCSF). Also provided is an image postprocessing pipeline for deconvolution and three-dimensional (3D) drift correction. This protocol can be used to capture several cellular behaviors in the intact retina and to identify novel factors controlling neurite morphogenesis. Many developmental strategies learned in the retina will be relevant for understanding the formation of neural circuits elsewhere in the central nervous system.

Disabling VEGF-Response of Purkinje Cells by Downregulation of KDR via miRNA-204-5p.

The vascular endothelial growth factor (VEGF) is well known for its wide-ranging functions, not only in the vascular system, but also in the central (CNS) and peripheral nervous system (PNS). To study the role of VEGF in neuronal protection, growth and maturation processes have recently attracted much interest. These effects are mainly mediated by VEGF receptor 2 (VEGFR-2). Current studies have shown the age-dependent expression of VEGFR-2 in Purkinje cells (PC), promoting dendritogenesis in neonatal, but not in mature stages. We hypothesize that microRNAs (miRNA/miR) might be involved in the regulation of VEGFR-2 expression during the development of PC. In preliminary studies, we performed a miRNA profiling and identified miR204-5p as a potential regulator of VEGFR-2 expression. In the recent study, organotypic slice cultures of rat cerebella (postnatal day (p) 1 and 9) were cultivated and VEGFR-2 expression in PC was verified via immunohistochemistry. Additionally, PC at age p9 and p30 were isolated from cryosections by laser microdissection (LMD) to analyse VEGFR-2 expression by quantitative RT-PCR. To investigate the influence of miR204-5p on VEGFR-2 levels in PC, synthetic constructs including short hairpin (sh)-miR204-5p cassettes (miRNA-mimics), were microinjected into PC. The effects were analysed by confocal laser scanning microscopy (CLSM) and morphometric analysis. For the first time, we could show that miR204-5p has a negative effect on VEGF sensitivity in juvenile PC, resulting in a significant decrease of dendritic growth compared to untreated juvenile PC. In mature PC, the overexpression of miR204-5p leads to a shrinkage of dendrites despite VEGF treatment. The results of this study illustrate, for the first time, which miR204-5p expression has the potential to play a key role in cerebellar development by inhibiting VEGFR-2 expression in PC.

Frequency-Dependent Energy Demand of Dendritic Responses to Deep Brain Stimulation in Thalamic Neurons: A Model-Based Study.

Thalamic deep brain stimulation (DBS) generates excitatory postsynaptic currents and action potentials (APs) by triggering large numbers of synaptic inputs to local cells, which also activates axonal spikes to antidromically invade the soma and dendrites. To maintain signaling, the evoked dendritic responses require metabolic energy to restore ion gradients in each dendrite. The objective of this study is to estimate the energy demand associated with dendritic responses to thalamic DBS. We use a morphologically realistic computational model to simulate dendritic activity in thalamocortical (TC) relay neurons with axonal intracellular stimulation or DBS-like extracellular stimulation. We determine the metabolic cost by calculating the number of adenosine triphosphate (ATP) expended to pump Na+ and Ca2+ ions out of each dendrite. The ATP demand of dendritic activity exhibits frequency dependence, which is determined by the number of spikes in the dendrites. Each backpropagating AP from the soma activates a spike in the dendrites, and the dendritic firing is dominated by antidromic activation of the soma. High stimulus frequencies decrease dendritic ATP cost by reducing the fidelity of antidromic activation. Synaptic inputs and stimulus-induced polarization govern the ATP cost of dendritic responses by facilitating/suppressing antidromic activation, which also influences the ATP cost by depolarizing/hyperpolarizing each dendrite. These findings are important for understanding the synaptic signaling energy in TC relay neurons and metabolism-dependent functional imaging data of thalamic DBS.

How CD40L reverse signaling regulates axon and dendrite growth.

CD40-activated CD40L reverse signaling is a major physiological regulator of axon and dendrite growth from developing hippocampal pyramidal neurons. Here we have studied how CD40L-mediated reverse signaling promotes the growth of these processes. Cultures of hippocampal pyramidal neurons were established from Cd40-/- mouse embryos to eliminate endogenous CD40/CD40L signaling, and CD40L reverse signaling was stimulated by a CD40-Fc chimera. CD40L reverse signaling increased phosphorylation and hence activation of proteins in the PKC, ERK, and JNK signaling pathways. Pharmacological activators and inhibitors of these pathways revealed that whereas activation of JNK inhibited growth, activation of PKC and ERK1/ERK2 enhanced growth. Experiments using combinations of pharmacological reagents revealed that these signaling pathways regulate growth by functioning as an interconnected and interdependent network rather than acting in a simple linear sequence. Immunoprecipitation studies suggested that stimulation of CD40L reverse signaling generated a receptor complex comprising CD40L, PKCß, and the Syk tyrosine kinase. Our studies have begun to elucidate the molecular network and interactions that promote axon and dendrite growth from developing hippocampal neurons following activation of CD40L reverse signaling.

Iron Deficiency and Iron Excess Differently Affect Dendritic Architecture of Pyramidal Neurons in the Hippocampus of Piglets.

BACKGROUND: Both iron deficiency and overload may adversely affect neurodevelopment. OBJECTIVES: The study assessed how changes in early-life iron status affect iron homeostasis and cytoarchitecture of hippocampal neurons in a piglet model. METHODS: On postnatal day (PD) 1, 30 Hampshire × Yorkshire crossbreed piglets (n = 15/sex) were stratified by sex and litter and randomly assigned to experimental groups receiving low (L-Fe), adequate (A-Fe), or high (H-Fe) levels of iron supplement during the pre- (PD1-21) and postweaning periods (PD22-35). Pigs in the L-Fe, A-Fe, and H-Fe groups orally received 0, 1, and 30 mg Fe · kg weight-1 · d-1 preweaning and were fed a diet containing 30, 125, and 1000 mg Fe/kg postweaning, respectively. Heme indexes were analyzed weekly, and gene and protein expressions of iron regulatory proteins in duodenal mucosa, liver, and hippocampus were analyzed through qRT-PCR and western blot, respectively, on PD35. Hippocampal neurons stained using the Golgi-Cox method were traced and their dendritic arbors reconstructed in 3-D using Neurolucida. Dendritic complexity was quantified using Sholl and branch order analyses. RESULTS: Pigs in the L-Fe group developed iron deficiency anemia (hemoglobin = 8.2 g/dL, hematocrit = 20.1%) on PD35 and became stunted during week 5 with lower final body weight than H-Fe group pigs (6.6 compared with 9.6 kg, P < 0.05). In comparison with A-Fe, H-Fe increased hippocampal ferritin expression by 38% and L-Fe decreased its expression by 52% (P < 0.05), suggesting altered hippocampal iron stores. Pigs in the H-Fe group had greater dendritic complexity in CA1/3 pyramidal neurons than L-Fe group pigs as shown by more dendritic intersections with Sholl rings (P ≤ 0.04) and a greater number of dendrites (P ≤ 0.016). CONCLUSIONS: In piglets, the developing hippocampus is susceptible to perturbations by dietary iron, with deficiency and overload differentially affecting dendritic arborization.

The ELAV/Hu protein Found in neurons regulates cytoskeletal and ECM adhesion inputs for space-filling dendrite growth.

Dendritic arbor morphology influences how neurons receive and integrate extracellular signals. We show that the ELAV/Hu family RNA-binding protein Found in neurons (Fne) is required for space-filling dendrite growth to generate highly branched arbors of Drosophila larval class IV dendritic arborization neurons. Dendrites of fne mutant neurons are shorter and more dynamic than in wild-type, leading to decreased arbor coverage. These defects result from both a decrease in stable microtubules and loss of dendrite-substrate interactions within the arbor. Identification of transcripts encoding cytoskeletal regulators and cell-cell and cell-ECM interacting proteins as Fne targets using TRIBE further supports these results. Analysis of one target, encoding the cell adhesion protein Basigin, indicates that the cytoskeletal defects contributing to branch instability in fne mutant neurons are due in part to decreased Basigin expression. The ability of Fne to coordinately regulate the cytoskeleton and dendrite-substrate interactions in neurons may shed light on the behavior of cancer cells ectopically expressing ELAV/Hu proteins.

Identification of novel regulators of dendrite arborization using cell type-specific RNA metabolic labeling.

Obtaining neuron transcriptomes is challenging; their complex morphology and interconnected microenvironments make it difficult to isolate neurons without potentially altering gene expression. Multidendritic sensory neurons (md neurons) of Drosophila larvae are commonly used to study peripheral nervous system biology, particularly dendrite arborization. We sought to test if EC-tagging, a biosynthetic RNA tagging and purification method that avoids the caveats of physical isolation, would enable discovery of novel regulators of md neuron dendrite arborization. Our aims were twofold: discover novel md neuron transcripts and test the sensitivity of EC-tagging. RNAs were biosynthetically tagged by expressing CD:UPRT (a nucleobase-converting fusion enzyme) in md neurons and feeding 5-ethynylcytosine (EC) to larvae. Only CD:UPRT-expressing cells are competent to convert EC into 5-ethynyluridine-monophosphate which is subsequently incorporated into nascent RNA transcripts. Tagged RNAs were purified and used for RNA-sequencing. Reference RNA was prepared in a similar manner using 5-ethynyluridine (EUd) to tag RNA in all cells and negative control RNA-seq was performed on "mock tagged" samples to identify non-specifically purified transcripts. Differential expression analysis identified md neuron enriched and depleted transcripts. Three candidate genes encoding RNA-binding proteins (RBPs) were tested for a role in md neuron dendrite arborization. Loss-of-function for the m6A-binding factor Ythdc1 did not cause any dendrite arborization defects while RNAi of the other two candidates, the poly(A) polymerase Hiiragi and the translation regulator Hephaestus, caused significant defects in dendrite arborization. This work provides an expanded view of transcription in md neurons and a technical framework for combining EC-tagging with RNA-seq to profile transcription in cells that may not be amenable to physical isolation.

Statistical Laws of Protein Motion in Neuronal Dendritic Trees.

Across their dendritic trees, neurons distribute thousands of protein species that are necessary for maintaining synaptic function and plasticity and that need to be produced continuously and trafficked to their final destination. As each dendritic branchpoint splits the protein flow, increasing branchpoints decreases the total protein number downstream. Consequently, a neuron needs to produce more proteins to maintain a minimal protein number at distal synapses. Combining in vitro experiments and a theoretical framework, we show that proteins that diffuse within the cell plasma membrane are, on average, 35% more effective at reaching downstream locations than proteins that diffuse in the cytoplasm. This advantage emerges from a bias for forward motion at branchpoints when proteins diffuse within the plasma membrane. Using 3D electron microscopy (EM) data, we show that pyramidal branching statistics and the diffusion lengths of common proteins fall into a region that minimizes the overall protein need.

Suppression of DNA Double-Strand Break Formation by DNA Polymerase ß in Active DNA Demethylation Is Required for Development of Hippocampal Pyramidal Neurons.

Genome stability is essential for brain development and function, as de novo mutations during neuronal development cause psychiatric disorders. However, the contribution of DNA repair to genome stability in neurons remains elusive. Here, we demonstrate that the base excision repair protein DNA polymerase ß (Polß) is involved in hippocampal pyramidal neuron differentiation via a TET-mediated active DNA demethylation during early postnatal stages using Nex-Cre/Polß fl/fl mice of either sex, in which forebrain postmitotic excitatory neurons lack Polß expression. Polß deficiency induced extensive DNA double-strand breaks (DSBs) in hippocampal pyramidal neurons, but not dentate gyrus granule cells, and to a lesser extent in neocortical neurons, during a period in which decreased levels of 5-methylcytosine and 5-hydroxymethylcytosine were observed in genomic DNA. Inhibition of the hydroxylation of 5-methylcytosine by expression of microRNAs miR-29a/b-1 diminished DSB formation. Conversely, its induction by TET1 catalytic domain overexpression increased DSBs in neocortical neurons. Furthermore, the damaged hippocampal neurons exhibited aberrant neuronal gene expression profiles and dendrite formation, but not apoptosis. Comprehensive behavioral analyses revealed impaired spatial reference memory and contextual fear memory in adulthood. Thus, Polß maintains genome stability in the active DNA demethylation that occurs during early postnatal neuronal development, thereby contributing to differentiation and subsequent learning and memory.SIGNIFICANCE STATEMENT Increasing evidence suggests that de novo mutations during neuronal development cause psychiatric disorders. However, strikingly little is known about how DNA repair is involved in neuronal differentiation. We found that Polß, a component of base excision repair, is required for differentiation of hippocampal pyramidal neurons in mice. Polß deficiency transiently led to increased DNA double-strand breaks, but not apoptosis, in early postnatal hippocampal pyramidal neurons. This aberrant double-strand break formation was attributed to active DNA demethylation as an epigenetic regulation. Furthermore, the damaged neurons exhibited aberrant gene expression profiles and dendrite formation, resulting in impaired learning and memory in adulthood. Thus, these findings provide new insight into the contribution of DNA repair to the neuronal genome in early brain development.

Different dendritic domains of the GnRH neuron underlie the pulse and surge modes of GnRH secretion in female mice.

The gonadotropin-releasing hormone (GnRH) neurons exhibit pulse and surge modes of activity to control fertility. They also exhibit an unusual bipolar morphology comprised of a classical soma-proximal dendritic zone and an elongated secretory process that can operate as both a dendrite and an axon, termed a 'dendron'. We show using expansion microscopy that the highest density of synaptic inputs to a GnRH neuron exists at its distal dendron. In vivo, selective chemogenetic inhibition of the GnRH neuron distal dendron abolishes the luteinizing hormone (LH) surge and markedly dampens LH pulses. In contrast, inhibitory chemogenetic and optogenetic strategies targeting the GnRH neuron soma-proximal dendritic zone abolish the LH surge but have no effect upon LH pulsatility. These observations indicate that electrical activity at the soma-proximal dendrites of the GnRH neuron is only essential for the LH surge while the distal dendron represents an autonomous zone where synaptic integration drives pulsatile GnRH secretion.

An important role of PHRF1 in dendritic architecture and memory formation by modulating TGF-ß signaling.

PHRF1 is involved in transforming growth factor ß (TGF-ß) signaling to constrain the formation of acute promyelocytic leukemia (APL) in mouse APL models. PHRF1 also participates in modulating non-homologous end-joining. However, the role of PHRF1 in mammalian dendrite architecture and synaptic plasticity is unclear. Here, we investigated the role of PHRF1 in dendritic formation in the murine hippocampus using Camk2a promoter driven-iCre recombinase to conduct a PHRF1 conditional knockout, namely PHRF1Δ/Δ, in the forebrain region. PHRF1Δ/Δ mice developed normally, but exhibited anxiety-like behaviors and displayed defective spatial memory. Alterations of dendritic complexity in apical and basal dendrites of pyramidal neurons were noticed in PHRF1Δ/Δ mutants. Furthermore, electrical stimulation in the hippocampal CA1 region after the TGF-ß1 treatment showed a reduced synaptic plasticity in PHRF1Δ/Δ mice. Immunoblotting analysis indicated that PHRF1 ablation affected the TGF-ß signaling. Collectively, our results demonstrate that PHRF1 is important for the dendritic architecture and required for spatial memory formation in the hippocampus.

Signaling models for dopamine-dependent temporal contiguity in striatal synaptic plasticity.

Animals remember temporal links between their actions and subsequent rewards. We previously discovered a synaptic mechanism underlying such reward learning in D1 receptor (D1R)-expressing spiny projection neurons (D1 SPN) of the striatum. Dopamine (DA) bursts promote dendritic spine enlargement in a time window of only a few seconds after paired pre- and post-synaptic spiking (pre-post pairing), which is termed as reinforcement plasticity (RP). The previous study has also identified underlying signaling pathways; however, it still remains unclear how the signaling dynamics results in RP. In the present study, we first developed a computational model of signaling dynamics of D1 SPNs. The D1 RP model successfully reproduced experimentally observed protein kinase A (PKA) activity, including its critical time window. In this model, adenylate cyclase type 1 (AC1) in the spines/thin dendrites played a pivotal role as a coincidence detector against pre-post pairing and DA burst. In particular, pre-post pairing (Ca2+ signal) stimulated AC1 with a delay, and the Ca2+-stimulated AC1 was activated by the DA burst for the asymmetric time window. Moreover, the smallness of the spines/thin dendrites is crucial to the short time window for the PKA activity. We then developed a RP model for D2 SPNs, which also predicted the critical time window for RP that depended on the timing of pre-post pairing and phasic DA dip. AC1 worked for the coincidence detector in the D2 RP model as well. We further simulated the signaling pathway leading to Ca2+/calmodulin-dependent protein kinase II (CaMKII) activation and clarified the role of the downstream molecules of AC1 as the integrators that turn transient input signals into persistent spine enlargement. Finally, we discuss how such timing windows guide animals' reward learning.

Efficient Coding by Midget and Parasol Ganglion Cells in the Human Retina.

In humans, midget and parasol ganglion cells account for most of the input from the eyes to the brain. Yet, how they encode visual information is unknown. Here, we perform large-scale multi-electrode array recordings from retinas of treatment-naive patients who underwent enucleation surgery for choroidal malignant melanomas. We identify robust differences in the function of midget and parasol ganglion cells, consistent asymmetries between their ON and OFF types (that signal light increments and decrements, respectively) and divergence in the function of human versus non-human primate retinas. Our computational analyses reveal that the receptive fields of human midget and parasol ganglion cells divide naturalistic movies into adjacent spatiotemporal frequency domains with equal stimulus power, while the asymmetric response functions of their ON and OFF types simultaneously maximize stimulus coverage and information transmission and minimize metabolic cost. Thus, midget and parasol ganglion cells in the human retina efficiently encode our visual environment.