Search

Background and Purpose: Traumatic brain injury (TBI) is a complex medical condition affecting people globally. Hydrogen sulfide (H 2 S) is a recently discovered gaseous mediator and is dysregulated in the brain after TBI. Sodium hydrogen sulfide (NaHS), a known donor of H 2 S, is beneficial in various biological processes involving aging and diseases, including injury. It is neuroprotective against oxidative stress, neuroinflammation, and other secondary injury processes. However, the NaHS-H 2 S system has not been investigated as a regulator of injury-mediated synaptic plasticity proteins and the underlying mechanisms after TBI., Experimental Approach: We developed a model of TBI in Swiss albino mice to study the effects of exogenous H 2 S, administered as NaHS. We assessed cognitive function (Barnes maze and novel object recognition) and motor function (rotarod). Brain tissue was analysed with ELISA, qRT-PCR, immunoblotting, Golgi-cox staining, and immunofluorescence., Key Results: NaHS administration restored the injury-caused decline in H 2 S levels. Injury-mediated oxidative stress parameters were improved following NaHS. It down-regulated TBI biomarkers, ameliorated the synaptic marker proteins, and improved cognitive and motor deficits. These changes were accompanied by enhanced dendritic arborization and spine number. Restoration of N-methyl D-aspartate receptor subunits and diminished glutamate and calcium levels, along with marked changes in microtubule-associated protein 2 A and calcium/calmodulin-dependent protein kinase II, formed the basis of the underlying mechanism(s)., Conclusion and Implications: Our findings suggest that NaHS could have therapeutic activity against TBI, as it ameliorated cognitive and motor deficits caused by changes in synaptic plasticity proteins and dendritic arborisation, in our model., (© 2024 British Pharmacological Society.)

Dendrites are crucial for receiving information into neurons. Sensory experience affects the structure of these tree-like neurites, which, it is assumed, modifies neuronal function, yet the evidence is scarce, and the mechanisms are unknown. To study whether sensory experience affects dendritic morphology, we use the Caenorhabditis elegans ' arborized nociceptor PVD neurons, under natural mechanical stimulation induced by physical contacts between individuals. We found that mechanosensory signals induced by conspecifics and by glass beads affect the dendritic structure of the PVD. Moreover, developmentally isolated animals show a decrease in their ability to respond to harsh touch. The structural and behavioral plasticity following sensory deprivation are functionally independent of each other and are mediated by an array of evolutionarily conserved mechanosensory amiloride-sensitive epithelial sodium channels (degenerins). Calcium imaging of the PVD neurons in a micromechanical device revealed that controlled mechanical stimulation of the body wall produces similar calcium dynamics in both isolated and crowded animals. Our genetic results, supported by optogenetic, behavioral, and pharmacological evidence, suggest an activity-dependent homeostatic mechanism for dendritic structural plasticity, that in parallel controls escape response to noxious mechanosensory stimuli., Competing Interests: SI, YI, AC, HS, MO, MK, BP No competing interests declared, (© 2025, Inberg et al.)

RAC1 encodes a Rho family small GTPase that regulates actin cytoskeletal reorganization and intracellular signaling pathways. Pathogenic RAC1 variants lead to a neurodevelopmental disorder with diverse phenotypic manifestations, including abnormalities in brain size and facial dysmorphism. However, the underlying pathophysiological mechanisms have yet to be elucidated. Here, we present the case of a school-aged male who exhibited global developmental delay, intellectual disability, and acquired microcephaly. Through whole exome sequencing, we identified a novel de novo variant in RAC1, (NM_006908.5): c.92 A > G,p.(E31G). We then examined the pathophysiological significance of the p.E31G variant by focusing on brain development. Biochemical analyses revealed that the recombinant RAC1-E31G had no discernible impact on the intrinsic GDP/GTP exchange activity. However, it exhibited a slight inhibitory effect on GTP hydrolysis. Conversely, it demonstrated a typical response to both a guanine-nucleotide exchange factor and a GTPase-activating protein. In transient expression analyses using COS7 cells, RAC1-E31G exhibited minimal interaction with the downstream effector PAK1, even in its GTP-bound state. Additionally, overexpression of RAC1-E31G was observed to exert a weak inhibitory effect on the differentiation of primary cultured hippocampal neurons. Moreover, in vivo studies employing in utero electroporation revealed that acute expression of RAC1-E31G resulted in impairments in axonal elongation and dendritic arborization in the young adult stage. These findings suggest that the p.E31G variant functions as a dominant-negative version in the PAK1-mediated signaling pathway and is responsible for the clinical features observed in the patient under investigation, namely microcephaly and intellectual disability., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Traumatic brain injury is a highly irreversible process that consists of primary as well as secondary injury which develops and progresses over months to years, leading to cognitive dysfunctions. Vitamin B 12 received considerable interest due to its potential therapeutic properties. The pathways of vitamin B 12 are closely related to neuronal survival but its effects on the pathophysiology of injury with respect to cognition is a relatively unexplored area of research. In this study, we investigated, the effect of vitamin B 12 and its involvement in neuroprotection on TBI-induced pathophysiology in male Swiss albino mice. Our findings suggested that vitamin B 12 supplementation improves TBI-mediated neurological impairments, spatial and recognition memory, and anxiety-like behavior. Furthermore, the oxidative stress was reduced by declined homocysteine level with vitamin B 12 supplementation validating declined expression of astrocytes and TBI biomarkers. The studies on neuronal morphology revealed that vitamin B 12 supplementation increases the dendritic arborization and density of mushroom and filopodia-shaped spines and further increases the expression of synaptic plasticity-related genes and proteins. Taken together, our findings reveal that, supplementation of vitamin B 12 restored the TBI-induced downregulation of dendritic arborization, and spine density which ultimately increases synaptic plasticity, cell survival, and recovery of cognitive dysfunctions., Competing Interests: Declaration of competing interest The authors declare that there is no conflict of interest., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The WW and C2 domain-containing protein (WWC2) is implicated in several neurological disorders. Here, we demonstrate that WWC2 interacts with inhibitory, but not excitatory, postsynaptic scaffolds, consistent with prior proteomic identification of WWC2 as a putative component of the inhibitory postsynaptic density. Using mice lacking WWC2 expression in excitatory forebrain neurons, we show that WWC2 suppresses γ-aminobutyric acid type-A receptor (GABA A R) incorporation into the plasma membrane and regulates HAP1 and GRIP1, which form a complex promoting GABA A R recycling to the membrane. Inhibitory synaptic transmission is increased in CA1 pyramidal cells lacking WWC2. Furthermore, unlike the WWC2 homolog KIBRA (kidney/brain protein; WWC1), a key regulator of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) trafficking at excitatory synapses, the deletion of WWC2 does not affect synaptic AMPAR expression. In contrast, loss of KIBRA does not affect GABA A R membrane expression. These data reveal synapse class-selective functions for WWC proteins as regulators of ionotropic neurotransmitter receptors and provide insight into mechanisms regulating GABA A R membrane expression., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

Objective: The aim of this study is to elucidate the underlying mechanism through which glial cell line-derived neurotrophic factor (GDNF) improves cognitive deficits in adults resulting from neonatal surgical interventions., Methods: Newborn Sprague-Dawley rats, regardless of gender, were randomly allocated into seven groups on postnatal day 7 as follows (n=15): (1) Control group (not subjected to anesthesia, surgery, or any pharmaceutical interventions); (2) GDNF group (received intracerebroventricular injection of GDNF); (3) Surgery group (underwent right carotid artery exposure under anesthesia with 3 % sevoflurane); (4) Surgery plus GDNF group; (5) Surgery plus GDNF and type II JAK inhibitor NVP-BBT594 (BBT594) group (administered intraperitoneal injection of BBT594); (6) BBT group; and (7) Surgery plus BBT group. Starting from postnatal day 33, all rats underwent Barnes maze and fear conditioning tests, followed by decapitation under sevoflurane anesthesia for subsequent analyses. The left hemibrains underwent Golgi staining, while the right hemibrains were used for hippocampal protein extraction to assess Protein kinase Mζ (PKMζ) and Kalirin expression through western blotting., Results: GDNF demonstrated a mitigating effect on spatial learning and memory impairment, as well as context-related fear memory impairment, reductions in dendritic total lengths, and spinal density within the hippocampus induced by surgical intervention. Notably, all of these ameliorative effects of GDNF were reversed upon administration of the RET inhibitor BBT594. Additionally, GDNF alleviated the downregulation of protein expression of PKMζ and Kalirin in the hippocampus of rats subjected to surgery, subsequently reversed by BBT594., Conclusion: The effective impact of GDNF on learning and memory impairment caused by surgical intervention appears to be mediated through the RET pathway. Moreover, GDNF may exert its influence by upregulating the expression of PKMζ and Kalirin, consequently enhancing the development of dendrites and dendritic spines., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Human cortical neurons (hCNs) exhibit high dendritic complexity and synaptic density, and the maturation process is greatly protracted. However, the molecular mechanism governing these specific features remains unclear. Here, we report that the hominoid-specific gene TBC1D3 promotes dendritic arborization and protracts the pace of synaptogenesis. Ablation of TBC1D3 in induced hCNs causes reduction of dendritic growth and precocious synaptic maturation. Forced expression of TBC1D3 in the mouse cortex protracts synaptic maturation while increasing dendritic growth. Mechanistically, TBC1D3 functions via interaction with MICAL1, a monooxygenase that mediates oxidation of actin filament. At the early stage of differentiation, the TBC1D3/MICAL1 interaction in the cytosol promotes dendritic growth via F-actin oxidation and enhanced actin dynamics. At late stages, TBC1D3 escorts MICAL1 into the nucleus and downregulates the expression of genes related with synaptic maturation through interaction with the chromatin remodeling factor ATRX. Thus, this study delineates the molecular mechanisms underlying human neuron development., Competing Interests: Declaration of interests The authors have no competing financial interests., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

The Pcdhg gene cluster encodes 22 γ-Protocadherin (γ-Pcdh) cell adhesion molecules that critically regulate multiple aspects of neural development, including neuronal survival, dendritic and axonal arborization, and synapse formation and maturation. Each γ-Pcdh isoform has unique protein domains-a homophilically interacting extracellular domain and a juxtamembrane cytoplasmic domain-as well as a C-terminal cytoplasmic domain shared by all isoforms. The extent to which isoform-specific versus shared domains regulate distinct γ-Pcdh functions remains incompletely understood. Our previous in vitro studies identified protein kinase C (PKC) phosphorylation of a serine residue within a shared C-terminal motif as a mechanism through which γ-Pcdh promotion of dendrite arborization via myristoylated alanine-rich C-kinase substrate (MARCKS) is abrogated. Here, we used CRISPR/Cas9 genome editing to generate two new mouse lines expressing only non-phosphorylatable γ-Pcdhs, due either to a serine-to-alanine mutation (Pcdhg S/A ) or to a 15-amino acid C-terminal deletion resulting from insertion of an early stop codon (Pcdhg CTD ). Both lines are viable and fertile, and the density and maturation of dendritic spines remain unchanged in both Pcdhg S/A and Pcdhg CTD cortex. Dendrite arborization of cortical pyramidal neurons, however, is significantly increased in both lines, as are levels of active MARCKS. Intriguingly, despite having significantly reduced levels of γ-Pcdh proteins, the Pcdhg CTD mutation yields the strongest phenotype, with even heterozygous mutants exhibiting increased arborization. The present study confirms that phosphorylation of a shared C-terminal motif is a key γ-Pcdh negative regulation point and contributes to a converging understanding of γ-Pcdh family function in which distinct roles are played by both individual isoforms and discrete protein domains., (© 2024 The Author(s). Developmental Neurobiology published by Wiley Periodicals LLC.)

Gulf War Illness (GWI) is a multi-symptom disorder that manifests with fatigue, sleep disturbances, mood-cognition pathologies, and musculoskeletal symptoms. GWI affects at least 25% of the military personnel that served in Operations Desert Shield and Desert Storm from 1990 to 1991. We modeled Gulf War toxicant exposure in C57BL/6J mice by combined exposure to pyridostigmine bromide (an anti-sarin drug), chlorpyrifos (an organophosphate insecticide), and DEET (an insect repellent) for 10 days followed by oral treatment with Withania somnifera root extract for 21 days beginning at 12 weeks post-exposure. W. somnifera , commonly referred to as ashwagandha, has been used in traditional Ayurvedic medicine for centuries to improve memory and reduce inflammation, and its roots contain bioactive molecules which share functional groups with modern pain, cancer, and anti-inflammatory drugs. Previously, we observed that GWI mice displayed chronic reductions in dendritic arbor and loss of spines in granule cells of the dentate gyrus of the hippocampus at 14 weeks post-exposure. Here, we examined the effects of treatment with W. somnifera root extract on chronic dendrite and spine morphology in dentate granule cells of the mouse hippocampus following Gulf War toxicant exposure. GWI mice showed approximately 25% decreases in dendritic length ( p < 0.0001) and overall dendritic spine density with significant reductions in thin and mushroom spines. GWI mice treated with the Ayurvedic W. somnifera extract exhibited dendritic lengths and spine densities near normal levels. These findings demonstrate the efficacy of the Ayurvedic treatment for neuroprotection following these toxic exposures. We hope that the extract and the neuronal processes influenced will open new avenues of research regarding treatment of Gulf War Illness and neurodegenerative disorders., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Shaikh, Murray, Ravindranath and Citron.)

Gulf War Illness (GWI) is a chronic multi-symptom disorder affecting approximately 30 % of Veterans deployed to the Persian Gulf from 1990 to 91. GWI encompasses a wide spectrum of symptoms which frequently include neurological problems such as learning and memory impairments, mood disorders, and an increased incidence of neurodegenerative disorders. Combined exposure to both reversible and irreversible acetylcholinesterase (AChE) inhibitors has been identified as a likely risk factor for GWI. It is possible that the exposures affected connectivity in the brain, and it was also unknown whether this could benefit from treatment. We assessed chronic changes in dendritic architecture in granule cells of the dentate gyrus following exposure to pyridostigmine bromide (PB, 0.7 mg/kg), chlorpyrifos (CPF, 12.5 mg/kg), and N,N-diethyl-m-toluamide (DEET, 7.5 mg/kg) in male C57Bl/6J mice. We also evaluated the therapeutic effects of dietary administration for eight weeks of 1 % tert-butylhydroquinone (tBHQ), a Nrf2 activator, on long-term neuronal morphology. We found that Gulf War toxicant exposure resulted in reduced dendritic length and branching as well as overall spine density in dentate granule cells at 14 weeks post-exposure and that these effects were ameliorated by treatment with tBHQ. These findings indicate that Gulf War toxicant exposure results in chronic changes to dentate granule cell morphology and that modulation of neuroprotective transcription factors such as Nrf2 may improve long-term neuronal health in the hippocampus., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Published by Elsevier B.V.)

Dendrites of neurons receive synaptic or sensory inputs and are important sites of neuronal computation. The morphological features of dendrites not only are hallmarks of the neuronal type but also largely determine a neuron's function. Thus, dendrite morphogenesis has been a subject of intensive study in neuroscience. Quantification of dendritic morphology, which is required for accurate assessment of phenotypes, can often be a challenging task, especially for complex neurons. Because manual tracing of dendritic branches is labor-intensive and time-consuming, automated or semiautomated methods are required for efficient analysis of a large number of samples. A popular in vivo model system for studying the mechanisms of dendrite morphogenesis is dendritic arborization (da) neurons in the Drosophila larval peripheral nervous system. In this chapter, we introduce methods for visualizing and measuring the dendritic arbors of these neurons. We begin with an introduction of da neurons and an overview of the methods that have been used for measuring da neuron dendrites. We then discuss the techniques and detailed steps of neuron visualization and image acquisition. Finally, we provide example steps for dendrite tracing and measurement., (© 2024. The Author(s), under exclusive license to Springer Science+Business Media, LLC, part of Springer Nature.)

Dendritic arborization is a critical determinant of neuronal connectivity. The structure of a neuron's dendritic arbor determines the number of synaptic inputs a neuron can receive and how it processes synaptic input from other neurons. Here, we describe methods for visualizing and quantifying the dendritic arbor in primary cell cultures and in the intact rodent brain. These techniques can be used to answer significant scientific questions, such as the effects of disease processes, drugs, growth factors, and diverse environmental stressors on dendritogenesis in both in vitro and in vivo rodent models., (© 2024. The Author(s), under exclusive license to Springer Science+Business Media, LLC, part of Springer Nature.)

Autism spectrum disorder (ASD) is a neurodevelopmental disorder affecting over 1% of the global population. Individuals with ASD often exhibit complex behavioral conditions, including significant social difficulties and repetitive behaviors. Moreover, ASD often co-occurs with several other conditions, including intellectual disabilities and anxiety disorders. The etiology of ASD remains largely unknown owing to its complex genetic variations and associated environmental risks. Ultimately, this poses a fundamental challenge for the development of effective ASD treatment strategies. Previously, we demonstrated that daily supplementation with the probiotic Lactiplantibacillus plantarum PS128 (PS128) alleviates ASD symptoms in children. However, the mechanism underlying this improvement in ASD-associated behaviors remains unclear. Here, we used a well-established ASD mouse model, induced by prenatal exposure to valproic acid (VPA), to study the physiological roles of PS128 in vivo . Overall, we showed that PS128 selectively ameliorates behavioral abnormalities in social and spatial memory in VPA-induced ASD mice. Morphological examination of dendritic architecture further revealed that PS128 facilitated the restoration of dendritic arborization and spine density in the hippocampus and prefrontal cortex of ASD mice. Notably, PS128 was crucial for restoring oxytocin levels in the paraventricular nucleus and oxytocin receptor signaling in the hippocampus. Moreover, PS128 alters the gut microbiota composition and increases the abundance of Bifidobacterium spp. and PS128-induced changes in Bifidobacterium abundance positively correlated with PS128-induced behavioral improvements. Together, our results show that PS128 treatment can effectively ameliorate ASD-associated behaviors and reinstate oxytocin levels in VPA-induced mice, thereby providing a promising strategy for the future development of ASD therapeutics.

Background: Stroke remains the leading cause of death and disability in the world. A new potential treatment for stroke is the granulocyte colony-stimulating factor (G-CSF), which exerts neuroprotective effects through multiple mechanisms. Memory impairment is the most common cognitive problem after a stroke. The suggested treatment for memory impairments is cognitive rehabilitation, which is often ineffective. The hippocampus plays an important role in memory formation. This project aimed to study the effect of G-CSF on memory and dendritic morphology of hippocampal CA1 pyramidal neurons after middle cerebral artery occlusion (MCAO)in rats., Methods: Male Sprague-Dawley rats were divided into three groups: the sham, control (MCAO + Vehicle), and treatment (MCAO + G-CSF) groups. G-CSF (50 µg/kg S.C) was administered at 6, 24, and 48 h after brain ischemia induction. The passive avoidance task to evaluate learning and memory was performed on days 6 and 7 post-ischemia. Seven days after MCAO, the brain was removed and the hippocampal slices were stained with Golgi. After that, the neurons were analyzed for dendritic morphology and maturity., Outcomes: The data showed that stroke was associated with a significant impairment in the acquisition and retention of passive avoidance tasks, while the G-CSF improved learning and memory loss. The dendritic length, arborization, spine density, and mature spines of the hippocampus CA1 neurons were significantly reduced in the control group, and treatment with G-CSF significantly increased these parameters., Conclusion: G-CSF, even with three doses, improved learning and memory deficits, and dendritic morphological changes in the CA1 hippocampal neurons resulted from brain ischemia., (© 2023. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Neural stem cells (NSCs) in the adult hippocampus are composed of multiple subpopulations. However, their origin and functional heterogeneity are still unclear. Here, we found that the contribution of murine Wnt-responsive (Axin2 + ) and Hedgehog-responsive (Gli1 + ) embryonic neural progenitors to adult NSCs started from early and late postnatal stages, respectively. Axin2 + adult NSCs were intended to actively proliferate, whereas Gli1 + adult NSCs were relatively quiescent and responsive to external stimuli. Moreover, Gli1 + NSC-derived adult-born neurons exhibited more complex dendritic arborization and connectivity than Axin2 + NSC-derived ones. Importantly, genetic cell ablation analysis identified that Axin2 + and Gli1 + adult NSCs were involved in hippocampus-dependent learning, but only Axin2 + adult NSCs were engaged in buffering stress responses and depressive behavior. Together, our study not only defined the heterogeneous multiple origins of adult NSCs but also advanced the concept that different subpopulations of adult NSCs may function differently., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2023 Elsevier Inc. All rights reserved.)

In this study we investigated the effects of a neonatal handling protocol that mimics the handling of sham control pups in protocols of neonatal exposure to brain insults on dendritic arborization and glycosaminoglycan (GAG) levels in the developing brain. GAGs are long, unbranched polysaccharides, consisting of repeating disaccharide units that can be modified by sulfation at specific sites and are involved in modulating neuronal plasticity during brain development. In this study, male and female Sprague-Dawley rats underwent neonatal handling daily between post-natal day (PD)4 and PD9, with brains analyzed on PD9. Neuronal morphology and morphometric analysis of the apical and basal dendritic trees of CA1 hippocampal pyramidal neurons were carried out by Golgi-Cox staining followed by neuron tracing and analysis with the software Neurolucida. Chondroitin sulfate (CS)-, Hyaluronic Acid (HA)-, and Heparan Sulfate (HS)-GAG disaccharide levels were quantified in the hippocampus by Liquid Chromatography/Mass Spectrometry analyses. We found sex by neonatal handling interactions on several parameters of CA1 pyramidal neuron morphology and in the levels of HS-GAGs, with females, but not males, showing an increase in both dendritic arborization and HS-GAG levels. We also observed increased expression of glucocorticoid receptor gene Nr3c1 in the hippocampus of both males and females following neonatal handling suggesting that both sexes experienced a similar stress during the handling procedure. This is the first study to show sex differences in two parameters of brain plasticity, CA1 neuron morphology and HS-GAG levels, following handling stress in neonatal rats., Competing Interests: Declaration of Competing Interest None., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Linoleic acid (LA, 18:2n-6) is an essential nutrient for optimal infant growth and brain development. The effects of LA in the brain are thought to be mediated by oxygenated metabolites of LA known as oxidized LA metabolites (OXLAMs), but evidence is lacking to directly support this hypothesis. This study investigated whether OXLAMs modulate key neurodevelopmental processes including axon outgrowth, dendritic arborization, cell viability and synaptic connectivity. Primary cortical neuron-glia co-cultures from postnatal day 0-1 male and female rats were exposed for 48h to the following OXLAMs: 1) 13-hydroxyoctadecadienoic acid (13-HODE); 2) 9-hydroxyoctadecadienoic acid (9-HODE); 3) 9,10-dihydroxyoctadecenoic acid (9,10-DiHOME); 4) 12(13)-epoxyoctadecenoic acid (12(13)-EpOME); 5) 9,10,13-trihydroxyoctadecenoic acid (9,10,13-TriHOME); 6) 9-oxo-octadecadienoic acid (9-OxoODE); and 7) 12,13-dihydroxyoctadecenoic acid (12,13-DiHOME). Axonal outgrowth, evaluated by Tau-1 immunostaining, was increased by 9-HODE, but decreased by 12,13-DiHOME in male but not female neurons. Dendrite arborization, evaluated by MAP2B-eGFP expression, was affected by 9-HODE, 9-OxoODE, and 12(13)-EpOME in male neurons and, by 12(13)-EpOME in female neurons. Neither cell viability nor synaptic connectivity were significantly altered by OXLAMs. Overall, this study shows select OXLAMs modulate neuron morphology in a sex-dependent manner, with male neurons being more susceptible., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Pamela J. Lein reports financial support was provided by National Institute of Child Health and Human Development., (Copyright © 2023 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Brain-derived neurotrophic factor (BDNF) and its receptors tropomyosin kinase receptor B (TrkB) and the p75 neurotrophin receptor (p75) are the primary regulators of dendritic growth in the CNS. After being bound by BDNF, TrkB and p75 are endocytosed into endosomes and continue signaling within the cell soma, dendrites, and axons. We studied the functional role of BDNF axonal signaling in cortical neurons derived from different transgenic mice using compartmentalized cultures in microfluidic devices. We found that axonal BDNF increased dendritic growth from the neuronal cell body in a cAMP response element-binding protein (CREB)-dependent manner. These effects were dependent on axonal TrkB but not p75 activity. Dynein-dependent BDNF-TrkB-containing endosome transport was required for long-distance induction of dendritic growth. Axonal signaling endosomes increased CREB and mTOR kinase activity in the cell body, and this increase in the activity of both proteins was required for general protein translation and the expression of Arc, a plasticity-associated gene, indicating a role for BDNF-TrkB axonal signaling endosomes in coordinating the transcription and translation of genes whose products contribute to learning and memory regulation., Competing Interests: GM, RT, MI, AA, MG, CW, WM, EP, FB No competing interests declared, (© 2023, Moya-Alvarado et al.)

The establishment of a functional cerebral cortex depends on the proper execution of multiple developmental steps, culminating in dendritic and axonal outgrowth and the formation and maturation of synaptic connections. Dysregulation of these processes can result in improper neuronal connectivity, including that associated with various neurodevelopmental disorders. The γ-Protocadherins (γ-Pcdhs), a family of 22 distinct cell adhesion molecules that share a C-terminal cytoplasmic domain, are involved in multiple aspects of neurodevelopment including neuronal survival, dendrite arborization, and synapse development. The extent to which individual γ-Pcdh family members play unique versus common roles remains unclear. We demonstrated previously that the γ-Pcdh-C3 isoform (γC3), via its unique "variable" cytoplasmic domain (VCD), interacts in cultured cells with Axin1, a Wnt-pathway scaffold protein that regulates the differentiation and morphology of neurons. Here, we confirm that γC3 and Axin1 interact in the cortex in vivo and show that both male and female mice specifically lacking γC3 exhibit disrupted Axin1 localization to synaptic fractions, without obvious changes in dendritic spine density or morphology. However, both male and female γC3 knock-out mice exhibit severely decreased dendritic complexity of cortical pyramidal neurons that is not observed in mouse lines lacking several other γ-Pcdh isoforms. Combining knock-out with rescue constructs in cultured cortical neurons pooled from both male and female mice, we show that γC3 promotes dendritic arborization through an Axin1-dependent mechanism mediated through its VCD. Together, these data identify a novel mechanism through which γC3 uniquely regulates the formation of cortical circuitry. SIGNIFICANCE STATEMENT The complexity of a neuron's dendritic arbor is critical for its function. We showed previously that the γ-Protocadherin (γ-Pcdh) family of 22 cell adhesion molecules promotes arborization during development; it remained unclear whether individual family members played unique roles. Here, we show that one γ-Pcdh isoform, γC3, interacts in the brain with Axin1, a scaffolding protein known to influence dendrite development. A CRISPR/Cas9-generated mutant mouse line lacking γC3 (but not lines lacking other γ-Pcdhs) exhibits severely reduced dendritic complexity of cerebral cortex neurons. Using cultured γC3 knock-out neurons and a variety of rescue constructs, we confirm that the γC3 cytoplasmic domain promotes arborization through an Axin1-dependent mechanism. Thus, γ-Pcdh isoforms are not interchangeable, but rather can play unique neurodevelopmental roles., (Copyright © 2023 the authors.)

Background: The accumulation of α-synuclein (α-syn) fibrils in intraneuronal inclusions called Lewy bodies and Lewy neurites is a pathological signature of Parkinson's disease (PD). Although several aspects linked to α-syn-dependent pathology (concerning its spreading, aggregation, and activation of inflammatory and neurodegenerative processes) have been under intense investigation, less attention has been devoted to the real impact of α-syn overexpression on structural and functional properties of substantia nigra pars compacta (SNpc) dopamine (DA) neurons, particularly at tardive stages of α-syn buildup, despite this has obvious relevance to comprehending mechanisms beyond PD progression., Objectives: We aimed to determine the consequences of a prolonged α-syn overexpression on somatodendritic morphology and functions of SNpc DA neurons., Methods: We performed immunohistochemistry, stereological DA cell counts, analyses of dendritic arborization, ex vivo patch-clamp recordings, and in vivo DA microdialysis measurements in a 12- to 13-month-old transgenic rat model overexpressing the full-length human α-syn (Snca +/+ ) and age-matched wild-type rats., Results: Aged Snca +/+ rats have mild loss of SNpc DA neurons and decreased basal DA levels in the SN. Residual nigral DA neurons display smaller soma and compromised dendritic arborization and, in parallel, increased firing activity, switch in firing mode, and hyperexcitability associated with hypofunction of fast activating/inactivating voltage-gated K + channels and Ca 2+ - and voltage-activated large conductance K + channels. These intrinsic currents underlie the repolarization/afterhyperpolarization phase of action potentials, thus affecting neuronal excitability., Conclusions: Besides clarifying α-syn-induced pathological landmarks, such evidence reveals compensatory functional mechanisms that nigral DA neurons could adopt during PD progression to counteract neurodegeneration. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society., (© 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.)

Brain-derived neurotrophic factor (BDNF) induces activation of the TrkB receptor and several downstream pathways (MAPK, PI3K, PLC-γ), leading to neuronal survival, growth, and plasticity. It has been well established that TrkB signaling regulation is required for neurite formation and dendritic arborization, but the specific mechanism is not fully understood. The non-receptor tyrosine kinase c-Abl is a possible candidate regulator of this process, as it has been implicated in tyrosine kinase receptors' signaling and trafficking, as well as regulation of neuronal morphogenesis. To assess the role of c-Abl in BDNF-induced dendritic arborization, wild-type and c-Abl-KO neurons were stimulated with BDNF, and diverse strategies were employed to probe the function of c-Abl, including the use of pharmacological inhibitors, an allosteric c-Abl activator, and shRNA to downregulates c-Abl expression. Surprisingly, BDNF promoted c-Abl activation and interaction with TrkB receptors. Furthermore, pharmacological c-Abl inhibition and genetic ablation abolished BDNF-induced dendritic arborization and increased the availability of TrkB in the cell membrane. Interestingly, inhibition or genetic ablation of c-Abl had no effect on the classic TrkB downstream pathways. Together, our results suggest that BDNF/TrkB-dependent c-Abl activation is a novel and essential mechanism in TrkB signaling., Competing Interests: The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

Major depressive disorder (MDD) is a severe mental illness. Decreased brain plasticity and dendritic fields have been consistently found in MDD patients and animal models; however, the underlying molecular mechanisms remain to be clarified. Here, we demonstrate that the deletion of cancerous inhibitor of PP2A (CIP2A), an endogenous inhibitor of protein phosphatase 2A (PP2A), leads to depression-like behaviors in mice. Hippocampal RNA sequencing analysis of CIP2A knockout mice shows alterations in the PI3K-AKT pathway and central nervous system development. In primary neurons, CIP2A stimulates AKT activity and promotes dendritic development. Further analysis reveals that the effect of CIP2A in promoting dendritic development is dependent on PP2A-AKT signaling. In vivo, CIP2A deficiency-induced depression-like behaviors and impaired dendritic arborization are rescued by AKT activation. Decreased CIP2A expression and impaired dendrite branching are observed in a mouse model of chronic unpredictable mild stress (CUMS). Indicative of clinical relevance to humans, CIP2A expression is found decreased in transcriptomes from MDD patients. In conclusion, we discover a novel mechanism that CIP2A deficiency promotes depression through the regulation of PP2A-AKT signaling and dendritic arborization., (© 2022 The Authors.)

MicroRNAs are enriched in neurons and play important roles in dendritic spine development and synaptic plasticity. MicroRNA activity is controlled by a wide range of RNA-binding proteins. FMRP, a highly conserved RNA-binding protein, has been linked to microRNA-mediated gene regulation in axonal development and dendritic spine formation. FMRP also participates in dendritic arbor morphogenesis, but whether and how microRNAs contribute to its function in this process remains to be elucidated. Here, using Drosophila larval sensory neurons, we show that a FMRP-associated microRNA, miR-276, functions in FMRP-mediated space-filling dendrite morphogenesis. Using EGFP microRNA sensors, we demonstrate that FMRP likely acts by regulating miR-276a RNA targeting rather than by modulating microRNA levels. Supporting this conclusion, miR-276a coimmunoprecipitated with FMRP and this association was dependent on the FMRP KH domains. By testing putative targets of the FMRP-miR-276a regulatory axis, we identified nejire as a FMRP-associated mRNA and, using EGFP reporters, showed that the nejire 3' untranslated region is a target of miR-276a in vivo. Genetic analysis places nejire downstream of the FMRP-miR-276a pathway in regulating dendrite patterning. Together, our findings support a model in which FMRP facilitates miR-276a-mediated control of nejire for proper dendrite space-filling morphology and shed light on microRNA-dependent dendrite developmental pathology of fragile X syndrome., (© The Author(s) 2022. Published by Oxford University Press on behalf of Genetics Society of America.)

N-methyl-D-aspartate (NMDA) receptors play a critical role in activity-dependent dendritic arborization, spinogenesis, and synapse formation by stimulating calcium-dependent signaling pathways. Previously, we have shown that brevetoxin 2 (PbTx-2), a voltage-gated sodium channel (VGSC) activator, produces a concentration-dependent increase in intracellular sodium [Na + ] I and increases NMDA receptor (NMDAR) open probabilities and NMDA-induced calcium (Ca 2+ ) influxes. The objective of this study is to elucidate the downstream signaling mechanisms by which the sodium channel activator PbTx-2 influences neuronal morphology in murine cerebrocortical neurons. PbTx-2 and NMDA triggered distinct Ca 2+ -influx pathways, both of which involved the NMDA receptor 2B (GluN2B). PbTx-2-induced neurite outgrowth in day in vitro 1 (DIV-1) neurons required the small Rho GTPase Rac1 and was inhibited by both a PAK1 inhibitor and a PAK1 siRNA. PbTx-2 exposure increased the phosphorylation of PAK1 at Thr-212. At DIV-5, PbTx-2 induced increases in dendritic protrusion density, p-cofilin levels, and F-actin throughout the dendritic arbor and soma. Moreover, PbTx-2 increased miniature excitatory post-synaptic currents (mEPSCs). These data suggest that the stimulation of neurite outgrowth, spinogenesis, and synapse formation produced by PbTx-2 are mediated by GluN2B and PAK1 signaling.

Stress represents a major risk factor for psychiatric disorders, including post-traumatic stress disorder (PTSD). Recently, we dissected the destabilizing effects of acute stress on the excitatory glutamate system in the prefrontal cortex (PFC). Here, we assessed the effects of single subanesthetic administration of ketamine (10 mg/kg) on glutamate transmission and dendritic arborization in the PFC of footshock (FS)-stressed rats, along with changes in depressive, anxious, and fear extinction behaviors. We found that ketamine, while inducing a mild increase of glutamate release in the PFC of naïve rats, blocked the acute stress-induced enhancement of glutamate release when administered 24 or 72 h before or 6 h after FS. Accordingly, the treatment with ketamine 6 h after FS also reduced the stress-dependent increase of spontaneous excitatory postsynaptic current (sEPSC) amplitude in prelimbic (PL)-PFC. At the same time, ketamine injection 6 h after FS was found to rescue apical dendritic retraction of pyramidal neurons induced by acute stress in PL-PFC and facilitated contextual fear extinction. These results show rapid effects of ketamine in animals subjected to acute FS, in line with previous studies suggesting a therapeutic action of the drug in PTSD models. Our data are consistent with a mechanism of ketamine involving re-establishment of synaptic homeostasis, through restoration of glutamate release, and structural remodeling of dendrites., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Sala, Paoli, Bonifacino, Mingardi, Schiavon, La Via, Milanese, Tornese, Datusalia, Rosa, Facchinetti, Frumento, Carini, Salerno Scarzella, Scuderi, Forti, Barbon, Bonanno, Popoli and Musazzi.)

Many studies on neuronal plasticity have been conducted in the hippocampus and sensory cortices. In female rats in the estrus phase, when there is a low concentration of estradiol in the blood, there is a reduction in the dendritic spine density of CA1 neurons, while an increase in dendritic spines has been observed during metestrus, when progesterone levels are high. In comparison with the hippocampus, less information is known about dendritic remodeling of the motor cortex. Thus, the objective of the present study was to evaluate the neuronal morphology of pyramidal cells of layer V of the motor cortex in each phase of the estrous cycle. For this, we used Long-Evans strain rats and formed 4 experimental groups according to the phase of the estrous cycle at the moment of sacrifice: proestrus, estrus, metestrus, or diestrus. All animals were gently monitored regarding the expression of one estrous cycle in order to determine the regularity of the cycle. We obtained the brains in order to evaluate the neuronal morphology of neurons of layer V of the primary motor cortex following the Golgi-Cox method and Sholl analysis. Our results show that the dendritic arborization of neurons of rats sacrificed in the metestrus phase is reduced compared to the other phases of the estrous cycle. However, we did not find changes in dendritic spine density between experimental groups. When comparing our results with previous data, we can suggest that estrogens and progesterone differentially promote plasticity events in pyramidal neurons between different brain regions., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Sleep deprivation-induced degenerative changes in the brain lead to the impairment of memory, anxiety, and quality of life. Several studies have reported the effects of sleep deprivation on CA1 and dentate gyrus regions of the hippocampus; in contrast, there is less known about the impact of chronic sleep deprivation (CSD) and sleep recovery on CA3 neurons and behavior. Hence, the present study aimed to understand the effect of CSD and sleep recovery on hippocampal CA3 neurons and spatial memory, and anxiety-like behavior in rats. Sixty male rats (Sprague Dawley) were grouped as control, environmental control (EC), CSD, 5 days sleep recovery (CSD + 5D SR), and 21 days sleep recovery (CSD + 21D SR). CSD, CSD + 5D SR and, CSD + 21D SR group rats were sleep deprived for 21 days (18 h/day). After CSD, the CSD + 5D SR and CSD + 21D SR rats were sleep recovered for 5- and 21-days respectively. Oxidative stress, dendritic arborization of CA3 neurons, spatial memory, and anxiety-like behavior was assessed. Spatial memory, basal, and apical dendritic branching points/intersections in hippocampal CA3 neurons were reduced, and anxiety-like behavior and oxidative stress increased significantly in the CSD group compared to control (p < 0.001). The CSD + 21D SR showed a significant improvement in spatial memory, reduction in anxiety-like behavior, and oxidative stress when compared to the CSD group (p < 0.05). The basal and apical dendritic branching points/intersections in hippocampal CA3 neurons were increased after CSD + 21D SR, however, it was not significant (p > 0.05). Even though the CSD + 21D SR showed a significant improvement in all the parameters, it did not reach the control level. There was an improvement in all the parameters after CSD + 5D SR but this was not significant compared to the CSD group (p > 0.05). Overall results indicate that the CSD-induced impairment of spatial memory and anxiety-like behavior was associated with oxidative stress and reduced dendritic arborization of hippocampal CA3 neurons. The CSD + 21D SR significantly reduced the damage caused by CSD, but it was not sufficient to reach the control level., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Neurite atrophy with loss of neuronal polarity is a pathological hallmark of Alzheimer's disease (AD) and other neurological disorders. While there is substantial agreement that disruption of intracellular vesicle trafficking is associated with axonal pathology in AD, comparatively less is known regarding its role in dendritic atrophy. This is a significant gap of knowledge because, unlike axons, dendrites are endowed with the complete endomembrane system comprising endoplasmic reticulum (ER), ER-Golgi intermediate compartment (ERGIC), Golgi apparatus, post-Golgi vesicles, and a recycling-degradative route. In this study, using live-imaging of pGOLT-expressing vesicles, indicative of Golgi outposts and satellites, we investigate how amyloid-β (Aβ) oligomers affect the trafficking of Golgi-like organelles in the different dendritic compartments of cultured rat hippocampal neurons. We found that short-term (4 h) treatment with Aβ led to a decrease in anterograde trafficking of Golgi vesicles in dendrites of both resting and stimulated (with 50 mM KCl) neurons. We also characterized the ability of mirtazapine, a noradrenergic and specific serotonergic tetracyclic antidepressant (NaSSA), to rescue Golgi dynamics in dendrites. Mirtazapine treatment (10 μM) increased the number and both anterograde and retrograde motility, reducing the percentage of static Golgi vesicles. Finally, mirtazapine reverted the neurite atrophy induced by 24 h treatment with Aβ oligomers, suggesting that this drug is able to counteract the effects of Aβ by improving the dendritic trafficking of Golgi-related vesicles., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Fabbretti, Antognolli and Tongiorgi.)

Cognitive impairment due to natural or surgical menopause is always associated with estrogen deficiency leading to reduced brain-derived neurotrophic factor (BDNF). Reduced BDNF levels in menopause affect neuronal maturation, survival, axonal and dendritic arborization and the maintenance of dendritic spine density. Conventional long-term estrogen replacement therapy reported causing the risk of venous thromboembolism and breast cancer. To overcome these undesirable effects, phytoestrogens have been used in menopause-induced condition without the risk of side effects. Therefore, the aim of the present study was to investigate the effect of dietary supplementation of fenugreek seed extract (FG) either alone or in combination with choline-DHA on BDNF and dendritic arborization of pyramidal neurons in CA1 and CA3 regions of the hippocampus in ovariectomized rats. Female Wistar rats of 9-10 months old were divided into six groups as normal control (NC); ovariectomy (OVX); OVX + FG; OVX + choline-DHA; OVX + FG + choline-DHA; and OVX + estradiol. All the groups, except NC, were ovariectomized. After 2 weeks of ovariectomy, dietary supplementation was initiated for a period of 30 days. After supplementation, behavioral studies, BDNF levels and dendritic arborization were estimated. Ovariectomized (OVX) rats showed reduced BDNF levels, dendritic branching points and dendritic intersections of pyramidal neurons in CA1 and CA3 regions of the hippocampus. OVX rats supplemented with FG with choline-DHA showed significantly improved BDNF levels, dendritic branching points and dendritic intersections. These results are demonstrating that FG with choline-DHA supplementation can be an alternative for estrogen replacement therapy to modulate menopause-induced learning and memory deficits.

The Wnt signaling pathway plays key roles in various developmental processes. Wnt5a, which activates the non-canonical pathway, has been shown to be particularly important for axon guidance and outgrowth as well as dendrite morphogenesis. However, the mechanism underlying the regulation of Wnt5a remains unclear. Here, through conditional disruption of Foxg1 in hippocampal progenitors and postmitotic neurons achieved by crossing Foxg1 fl/fl with Emx1-Cre and Nex-Cre, respectively, we found that Wnt5a rather than Wnt3a/Wnt2b was markedly upregulated. Overexpression of Foxg1 had the opposite effects along with decreased dendritic complexity and reduced mossy fibers in the hippocampus. We further demonstrated that FOXG1 directly repressed Wnt5a by binding to its promoter and one enhancer site. These results expand our knowledge of the interaction between Foxg1 and Wnt signaling and help elucidate the mechanisms underlying hippocampal development.

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 Author(s) 2020. Published by Oxford University Press on behalf of the American Society for Nutrition.)

The abnormal function of the voltage-gated potassium channel Kv10.2 can induce epilepsy. However, the physiological function of Kv10.2 in the central nervous system remains unclear. In this study, we found that Kv10.2 knockout (KO) increased the complexity of neurons in the CA3 subarea of hippocampus. Kv10.2 KO led to enlarged somata, elongated dendritic length, and increased the number of dendritic tips in cultured rat hippocampus neurons. Kv10.2 KO also increased Synapsin I and PSD95 protein density in cultured rat hippocampal neurons. Whole cell patch-clamp recordings of brain slices in the CA3 subarea of hippocampus revealed that Kv10.2 KO increased the amplitude of spontaneous excitatory postsynaptic currents (sEPSC) and miniature excitatory postsynaptic currents (mEPSC), depolarized the resting membrane potential and increased the action potential firing, reduced the rheobase and increased the input resistance, which results in enhanced neuronal excitability. Furthermore, we made electroencephalogram (EEG) recordings of brain activity in freely moving rats before and after inducing seizures by pentylenetetrazole (PTZ) injection. Kv10.2 KO rats dramatically increased the EEG amplitude during epilepsy. Behavioral observation after seizure induction revealed that Kv10.2 KO rats demonstrated shortened onset latency, prolonged duration, and increased seizure severity when compared with wild type rats. Therefore, this study provides a new link between Kv10.2 and neuronal morphology and higher intrinsic excitability.

Objectives: Amantadine has been shown to attenuate postoperative learning and memory dysfunction in young adult rats. However, postoperative cognitive dysfunction often occurs in elderly patients. We aimed to determine whether amantadine attenuated postoperative learning and memory dysfunction and whether these effects were associated with improved dendritic arborization in old rodents., Methods: Eighteen-month old male C57BL/6J mice or Fischer 344 rats were subjected to right carotid artery exposure (surgery) under isoflurane anesthesia. This age represents an early old stage in rodents. Carotid artery exposure was used to simulate commonly performed carotid endarterectomy in elderly patients. Amantadine was injected intraperitoneally at 25 μg/g once a day for 3 days with the first dose at 15 min before surgery. The animals were tested by Barnes maze and fear conditioning starting one week after the surgery. Hippocampus was harvested for Western blotting and Golgi staining., Results: Surgery and anesthesia impaired the learning and memory in old mice and rats. Surgery reduced the expression of brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF), dendritic arborization and spine density in the hippocampus of old rats. These effects were attenuated by amantadine. The effects of amantadine were blocked by intracerebroventricular injection of anti-BDNF antibody or anti-GDNF antibody., Conclusion: Surgery and anesthesia impaired learning, memory and dendritic arborization in old rodents that are age relevant to postoperative cognitive dysfunction. These effects may be attenuated by amantadine via preserving the expression of neurotrophic factors., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2020 Zhong, Li, Ni and Zuo.)

Neurons require a well-coordinated intercellular transport system to maintain their normal cellular function and morphology. The kinesin family of proteins (KIFs) fills this role by regulating the transport of a diverse array of cargos in post-mitotic cells. On the other hand, in mitotic cells, KIFs facilitate the fidelity of the cellular division machinery. Though certain mitotic KIFs function in post-mitotic neurons, little is known about them. We studied the role of a mitotic KIF (KIF3B) in neuronal architecture. We find that the RNAi mediated knockdown of KIF3B in primary cortical neurons resulted in an increase in spine density; the number of thin and mushroom spines; and dendritic branching. Consistent with the change in spine density, we observed a specific increase in the distribution of the excitatory post-synaptic protein, PSD-95 in KIF3B knockdown neurons. Interestingly, overexpression of KIF3B produced a reduction in spine density, in particular mushroom spines, and a decrease in dendritic branching. These studies suggest that KIF3B is a key determinant of cortical neuron morphology and that it functions as an inhibitory constraint on structural plasticity, further illuminating the significance of mitotic KIFs in post-mitotic neurons., (Copyright © 2020 Joseph, Grinman, Swarnkar and Puthanveettil.)

Neuroregeneration is a dynamic process synergizing the functional outcomes of multiple signaling circuits. Channelrhodopsin-based optogenetics shows the feasibility of stimulating neural repair but does not pin down specific signaling cascades. Here, we utilized optogenetic systems, optoRaf and optoAKT, to delineate the contribution of the ERK and AKT signaling pathways to neuroregeneration in live Drosophila larvae. We showed that optoRaf or optoAKT activation not only enhanced axon regeneration in both regeneration-competent and -incompetent sensory neurons in the peripheral nervous system but also allowed temporal tuning and proper guidance of axon regrowth. Furthermore, optoRaf and optoAKT differ in their signaling kinetics during regeneration, showing a gated versus graded response, respectively. Importantly in the central nervous system, their activation promotes axon regrowth and functional recovery of the thermonociceptive behavior. We conclude that non-neuronal optogenetics targets damaged neurons and signaling subcircuits, providing a novel strategy in the intervention of neural damage with improved precision., Competing Interests: QW, HF, FL, SS, VK, YS, KZ No competing interests declared, (© 2020, Wang et al.)

The main lysosomal protease cathepsin D (cathD) is essential for maintaining tissue homeostasis via its degradative function, and its loss leads to ceroid accumulation in the mammalian nervous system, which results in progressive neurodegeneration. Increasing evidence implies non-proteolytic roles of cathD in regulating various biological processes such as apoptosis, cell proliferation, and migration. Along these lines, we here showed that cathD is required for modulating dendritic architecture in the nervous system independent of its traditional degradative function. Upon cathD depletion, class I and class III arborization (da) neurons in Drosophila larvae exhibited aberrant dendritic morphology, including over-branching, aberrant turning, and elongation defects. Re-introduction of wild-type cathD or its proteolytically-inactive mutant dramatically abolished these morphological defects. Moreover, cathD knockdown also led to dendritic defects in the adult mushroom bodies, suggesting that cathD-mediated processes are required in both the peripheral and central nervous systems. Taken together, our results demonstrate a critical role of cathD in shaping dendritic architecture independent of its proteolytic function.

Autism spectrum disorder (ASD) includes a group of multifactorial neurodevelopmental disorders defined clinically by core deficits in social reciprocity and communication, restrictive interests and repetitive behaviors. ASD affects one in 54 children in the United States, one in 89 children in Europe, and one in 277 children in Asia, with an estimated worldwide prevalence of 1-2%. While there is increasing consensus that ASD results from complex gene x environment interactions, the identity of specific environmental risk factors and the mechanisms by which environmental and genetic factors interact to determine individual risk remain critical gaps in our understanding of ASD etiology. Polychlorinated biphenyls (PCBs) are ubiquitous environmental contaminants that have been linked to altered neurodevelopment in humans. Preclinical studies demonstrate that PCBs modulate signaling pathways implicated in ASD and phenocopy the effects of ASD risk genes on critical morphometric determinants of neuronal connectivity, such as dendritic arborization. Here, we review human and experimental evidence identifying PCBs as potential risk factors for ASD and discuss the potential for PCBs to influence not only core symptoms of ASD, but also comorbidities commonly associated with ASD, via effects on the central and peripheral nervous systems, and/or peripheral target tissues, using bladder dysfunction as an example. We also discuss critical data gaps in the literature implicating PCBs as ASD risk factors. Unlike genetic factors, which are currently irreversible, environmental factors are modifiable risks. Therefore, data confirming PCBs as risk factors for ASD may suggest rational approaches for the primary prevention of ASD in genetically susceptible individuals.

Postoperative cognitive dysfunction (POCD) affects millions of patients each year in the USA and has been recognized as a significant complication after surgery. Epigenetic regulation of learning and memory has been shown. For example, an increase of histone deacetylases (HDACs), especially HDAC2, which epigenetically regulates gene expression, impairs learning and memory. However, the epigenetic contribution to the development of POCD is not known. Also, the effects of living situation on POCD have not been investigated. Here, we showed that mice that lived alone before the surgery and lived in a group after the surgery and mice that lived in a group before surgery and lived alone after surgery had impairment of learning and memory compared with the corresponding control mice without surgery. Surgery increased the activity of HDACs including HDAC2 but not HDAC1 and decreased brain-derived neurotrophic factor (BDNF), dendritic arborization, and spine density in the hippocampus. Suberanilohydroxamic acid (SAHA), a relatively specific inhibitor of HDAC2, attenuated these surgery effects. SAHA did not change BDNF expression, dendritic arborization, and spine density in mice without surgery. Surgery also reduced the activity of nuclear histone acetyltransferases (HATs). This effect was not affected by SAHA. Our results suggest that surgery activates HDACs, which then reduces BDNF and dendritic arborization to develop POCD. Thus, epigenetic change contributes to the occurrence of POCD.

Background: Primary neuronal cell cultures are useful for studying mechanisms that influence dendritic morphology during normal development and in response to various stressors. However, analyzing dendritic morphology is challenging, particularly in cultures with high cell density, and manual methods of selecting neurons and tracing dendritic arbors can introduce significant bias, and are labor-intensive. To overcome these challenges, semi-automated and automated methods are being developed, with most software solutions requiring computer-assisted dendrite tracing with subsequent quantification of various parameters of dendritic morphology, such as Sholl analysis. However fully automated approaches for classic Sholl analysis of dendritic complexity are not currently available., New Method: The previously described Omnisphero software, was extended by adding new functions to automatically assess dendritic mass, total length of the dendritic arbor and the number of primary dendrites, branch points, and terminal tips, and to perform Sholl analysis., Results: The new functions for assessing dendritic morphology were validated using primary mouse hippocampal and rat cortical neurons transfected with a fluorescently tagged MAP2 cDNA construct. These functions allow users to select specific populations of neurons as a training set for subsequent automated selection of labeled neurons in high-density cultures., Comparison With Existing Semi-Automated Methods: Compared to manual or semi-automated analyses of dendritic arborization, the new functions increase throughput while significantly decreasing researcher bias associated with neuron selection, tracing, and thresholding., Conclusion: These results demonstrate the importance of using unbiased automated methods to mitigate experimenter-dependent bias in analyzing dendritic morphology., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Memory transience is essential to gain cognitive flexibility. Recently, hippocampal neurogenesis is emerging as one of the mechanisms involved in the balance between persistence and forgetting. Social recognition memory (SRM) has its duration prolonged by neurogenesis. However, it is still to be determined whether boosting neurogenesis in distinct phases of SRM may favor forgetting over persistence. In the present study, we used enriched environment (EE) and memantine (MEM) to increase neurogenesis. SRM was ubiquitously prolonged by both, while EE after the memory acquisition did not favor forgetting. Interestingly, the proportion of newborn neurons with mature morphology in the dorsal hippocampus was higher in animals where persistence prevailed. Finally, one of the main factors for dendritic growth is the formation of cytoskeleton. We found that Latrunculin A, an inhibitor of actin polymerization, blunted the promnesic effect of EE. Altogether, our results indicate that the mechanisms triggered by EE to improve SRM are not limited to increasing the number of newborn neurons., Competing Interests: Declaration of competing interest The authors declared no competing interests., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Nucleoporins (NUPs) are an essential component of the nuclear-pore complex, which regulates nucleocytoplasmic transport of macromolecules. Pathogenic variants in NUP genes have been linked to several inherited human diseases, including a number with progressive neurological degeneration. We present six affected individuals with bi-allelic truncating variants in NUP188 and strikingly similar phenotypes and clinical courses, representing a recognizable genetic syndrome; the individuals are from four unrelated families. Key clinical features include congenital cataracts, hypotonia, prenatal-onset ventriculomegaly, white-matter abnormalities, hypoplastic corpus callosum, congenital heart defects, and central hypoventilation. Characteristic dysmorphic features include small palpebral fissures, a wide nasal bridge and nose, micrognathia, and digital anomalies. All affected individuals died as a result of respiratory failure, and five of them died within the first year of life. Nuclear import of proteins was decreased in affected individuals' fibroblasts, supporting a possible disease mechanism. CRISPR-mediated knockout of NUP188 in Drosophila revealed motor deficits and seizure susceptibility, partially recapitulating the neurological phenotype seen in affected individuals. Removal of NUP188 also resulted in aberrant dendrite tiling, suggesting a potential role of NUP188 in dendritic development. Two of the NUP188 pathogenic variants are enriched in the Ashkenazi Jewish population in gnomAD, a finding we confirmed with a separate targeted population screen of an international sampling of 3,225 healthy Ashkenazi Jewish individuals. Taken together, our results implicate bi-allelic loss-of-function NUP188 variants in a recessive syndrome characterized by a distinct neurologic, ophthalmologic, and facial phenotype., (Copyright © 2020 American Society of Human Genetics. Published by Elsevier Inc. All rights reserved.)

Analysis of patient-derived DNA samples has identified hundreds of variants that are likely involved in neuropsychiatric diseases such as autism spectrum disorder (ASD) and schizophrenia (SCZ). While these studies couple behavioral phenotypes to individual genotypes, the number and diversity of candidate genes implicated in these disorders highlights the fact that the mechanistic underpinnings of these disorders are largely unknown. Here, we describe a RNAi-based screening platform that uses C. elegans to screen candidate neuropsychiatric risk genes (NRGs) for roles in controlling dendritic arborization. To benchmark this approach, we queried published lists of NRGs whose variants in ASD and SCZ are predicted to result in complete or partial loss of gene function. We found that a significant fraction (>16%) of these candidate NRGs are essential for dendritic development. Furthermore, these gene sets are enriched for dendritic arbor phenotypes (>14 fold) when compared to control RNAi datasets of over 500 human orthologs. The diversity of PVD structural abnormalities observed in these assays suggests that the functions of diverse NRGs (encoding transcription factors, chromatin remodelers, molecular chaperones and cytoskeleton-related proteins) converge to regulate neuronal morphology and that individual NRGs may play distinct roles in dendritic branching. We also demonstrate that the experimental value of this platform by providing additional insights into the molecular frameworks of candidate NRGs. Specifically, we show that ANK2/UNC-44 function is directly integrated with known regulators of dendritic arborization and suggest that altering the dosage of ARID1B/LET-526 expression during development affects neuronal morphology without diminishing aspects of cell fate specification., (Copyright © 2020 Aguirre-Chen et al.)

Although banned from production for decades, PCBs remain a significant risk to human health. A primary target of concern is the developing brain. Epidemiological studies link PCB exposures in utero or during infancy to increased risk of neuropsychiatric deficits in children. Nonclinical studies of legacy congeners found in PCB mixtures synthesized prior to the ban on PCB production suggest that non-dioxin-like (NDL) congeners are predominantly responsible for the developmental neurotoxicity associated with PCB exposures. Mechanistic studies suggest that NDL PCBs alter neurodevelopment via ryanodine receptor-dependent effects on dendritic arborization. Lightly chlorinated congeners, which were not present in the industrial mixtures synthesized prior to the ban on PCB production, have emerged as contemporary environmental contaminants, but there is a paucity of data regarding their potential developmental neurotoxicity. PCB 11, a prevalent contemporary congener, is found in the serum of children and their mothers, as well as in the serum of pregnant women at increased risk for having a child diagnosed with a neurodevelopmental disorder (NDD). Recent data demonstrates that PCB 11 modulates neuronal morphogenesis via mechanisms that are convergent with and divergent from those implicated in the developmental neurotoxicity of legacy NDL PCBs. This review summarizes these data and discusses their relevance to adverse neurodevelopmental outcomes in humans.

Dendritic arborization is highly regulated and requires tight control of dendritic growth, branching, cytoskeletal dynamics, and ion channel expression to ensure proper function. Abnormal dendritic development can result in altered network connectivity, which has been linked to neurodevelopmental disorders, including autism spectrum disorders (ASDs). How neuronal growth control programs tune dendritic arborization to ensure function is still not fully understood. Using Drosophila dendritic arborization (da) neurons as a model, we identified the conserved Ste20-like kinase Tao as a negative regulator of dendritic arborization. We show that Tao kinase activity regulates cytoskeletal dynamics and sensory channel localization required for proper sensory function in both male and female flies. We further provide evidence for functional conservation of Tao kinase, showing that its ASD-linked human ortholog, Tao kinase 2 (Taok2), could replace Drosophila Tao and rescue dendritic branching, dynamic microtubule alterations, and behavioral defects. However, several ASD-linked Taok2 variants displayed impaired rescue activity, suggesting that Tao/Taok2 mutations can disrupt sensory neuron development and function. Consistently, we show that Tao kinase activity is required in developing and as well as adult stages for maintaining normal dendritic arborization and sensory function to regulate escape and social behavior. Our data suggest an important role for Tao kinase signaling in cytoskeletal organization to maintain proper dendritic arborization and sensory function, providing a strong link between developmental sensory aberrations and behavioral abnormalities relevant for Taok2-dependent ASDs. SIGNIFICANCE STATEMENT Autism spectrum disorders (ASDs) are linked to abnormal dendritic arbors. However, the mechanisms of how dendritic arbors develop to promote functional and proper behavior are unclear. We identified Drosophila Tao kinase, the ortholog of the ASD risk gene Taok2, as a regulator of dendritic arborization in sensory neurons. We show that Tao kinase regulates cytoskeletal dynamics, controls sensory ion channel localization, and is required to maintain somatosensory function in vivo Interestingly, ASD-linked human Taok2 mutations rendered it nonfunctional, whereas its WT form could restore neuronal morphology and function in Drosophila lacking endogenous Tao. Our findings provide evidence for a conserved role of Tao kinase in dendritic development and function of sensory neurons, suggesting that aberrant sensory function might be a common feature of ASDs., (Copyright © 2020 the authors.)

Despite being banned from production for decades, polychlorinated biphenyls (PCBs) continue to pose a significant risk to human health. This is due to not only the continued release of legacy PCBs from PCB-containing equipment and materials manufactured prior to the ban on PCB production, but also the inadvertent production of PCBs as byproducts of contemporary pigment and dye production. Evidence from human and animal studies clearly identifies developmental neurotoxicity as a primary endpoint of concern associated with PCB exposures. However, the relative role(s) of specific PCB congeners in mediating the adverse effects of PCBs on the developing nervous system, and the mechanism(s) by which PCBs disrupt typical neurodevelopment remain outstanding questions. New questions are also emerging regarding the potential developmental neurotoxicity of lower chlorinated PCBs that were not present in the legacy commercial PCB mixtures, but constitute a significant proportion of contemporary human PCB exposures. Here, we review behavioral and mechanistic data obtained from experimental models as well as recent epidemiological studies that suggest the non-dioxin-like (NDL) PCBs are primarily responsible for the developmental neurotoxicity associated with PCBs. We also discuss emerging data demonstrating the potential for non-legacy, lower chlorinated PCBs to cause adverse neurodevelopmental outcomes. Molecular targets, the relevance of PCB interactions with these targets to neurodevelopmental disorders, and critical data gaps are addressed as well., Competing Interests: The authors declare no conflicts of interest.

Fragile X-associated tremor ataxia syndrome (FXTAS) is a rare disorder associated to the presence of the fragile X premutation, a 55-200 CGG repeat expansion in the 5' UTR of the FMR1 gene. Two main neurological phenotypes have been described in carriers of the CGG premutation: (1) neurodevelopmental disorders characterized by anxiety, attention deficit hyperactivity disorder (ADHD), social deficits, or autism spectrum disorder (ASD); and (2) after 50 years old, the FXTAS phenotype. This neurodegenerative disorder is characterized by ataxia and a form of parkinsonism. The molecular pathology of this disorder is characterized by the presence of elevated levels of Fragile X Mental Retardation 1 (FMR1) mRNA, presence of a repeat-associated non-AUG (RAN) translated peptide, and FMR1 mRNA-containing nuclear inclusions. Whereas in the past FXTAS was mainly considered as a late-onset disorder, some phenotypes of patients and altered learning and memory behavior of a mouse model of FXTAS suggested that this disorder involves neurodevelopment. To better understand the physiopathological role of the increased levels of Fmr1 mRNA during neuronal differentiation, we used a small interfering RNA (siRNA) approach to reduce the abundance of this mRNA in cultured cortical neurons from the FXTAS mouse model. Morphological alterations of neurons were rescued by this approach. This cellular phenotype is associated to differentially expressed proteins that we identified by mass spectrometry analysis. Interestingly, phenotype rescue is also associated to the rescue of the abundance of 29 proteins that are involved in various pathways, which represent putative targets for early therapeutic approaches., (Copyright © 2019 The Authors. Published by Elsevier Inc. All rights reserved.)

The Ring Finger Protein 10 [RNF10] is a novel synapse-to-nucleus signaling protein that specifically links activation of synaptic NMDA receptors to modulation of gene expression. RNF10 dissociation from the GluN2A subunit of the NMDA receptor represents the first step of its synaptonuclear transport and it is followed by an importin-dependent translocation into the nucleus. Here, we have identified protein kinase C [PKC]-dependent phosphorylation of RNF10 Ser31 as a key step for RNF10 detachment from NMDA receptor and its subsequent trafficking to the nucleus. We show that pSer31-RNF10 plays a role both in synaptonuclear signaling and in neuronal morphology. In particular, the prevention of Ser31 RNF10 phosphorylation induces a decrease in spine density, neuronal branching, and CREB signaling, while opposite effects are obtained by mimicking a stable RNF10 phosphorylation at Ser31. Overall, these results add novel information about the functional and structural role of synaptonuclear protein messengers in shaping dendritic architecture in hippocampal neurons.

Higher brain function relies on proper development of the cerebral cortex, including correct positioning of neurons and dendrite morphology. Disruptions in these processes may result in various neurocognitive disorders. Mutations in the CPE gene, which encodes carboxypeptidase E (CPE), have been linked to depression and intellectual disability. However, it remains unclear whether CPE is involved in early brain development and in turn contributes to the pathophysiology of neurocognitive disorders. Here, we investigate the effects of CPE knockdown on early brain development and explore the functional significance of the interaction between CPE and its binding partner p150Glued. We demonstrate that CPE is required for cortical neuron migration and dendrite arborization. Furthermore, we show that expression of CPE-C10 redistributes p150Glued from the centrosome and that disruption of CPE interaction with p150Glued leads to abnormal neuronal migration and dendrite morphology, suggesting that a complex between CPE and p150Glued is necessary for proper neurodevelopment., (© The Author(s) 2018. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.)

EPAC2 is a guanine nucleotide exchange factor that regulates GTPase activity of the small GTPase Rap and Ras and is highly enriched at synapses. Activation of EPAC2 has been shown to induce dendritic spine shrinkage and increase spine motility, effects that are necessary for synaptic plasticity. These morphological effects are dysregulated by rare mutations of Epac2 associated with autism spectrum disorders. In addition, EPAC2 destabilizes synapses through the removal of synaptic GluA2/3-containing AMPA receptors. Previous work has shown that Epac2 knockout mice (Epac2 -/- ) display abnormal social interactions, as well as gross disorganization of the frontal cortex and abnormal spine motility in vivo. In this study we sought to further understand the cellular consequences of knocking out Epac2 on the development of neuronal and synaptic structure and organization of cortical neurons. Using primary cortical neurons generated from Epac2 +/+ or Epac2 -/- mice, we confirm that EPAC2 is required for cAMP-dependent spine shrinkage. Neurons from Epac2 -/- mice also displayed increased synaptic expression of GluA2/3-containing AMPA receptors, as well as of the adhesion protein N-cadherin. Intriguingly, analysis of excitatory and inhibitory synaptic proteins revealed that loss of EPAC2 resulted in altered expression of vesicular GABA transporter (VGAT) but not vesicular glutamate transporter 1 (VGluT1), indicating an altered ratio of excitatory and inhibitory synapses onto neurons. Finally, examination of cortical neurons located within the anterior cingulate cortex further revealed subtle deficits in the establishment of dendritic arborization in vivo. These data provide evidence that loss of EPAC2 enhances the stability of excitatory synapses and increases the number of inhibitory inputs., (Copyright © 2019 The Authors. Published by Elsevier Inc. All rights reserved.)

The transcription factor Foxg1 is known to be continuously expressed at a high level in mature neurons in the telencephalon, but little is known about its role in neural plasticity. Mutations in human FOXG1 cause deficiencies in learning and memory and limit social ability, which is defined as FOXG1 syndrome, but its pathogenic mechanism remains unclear. To examine the role of Foxg1 in adults, we crossed Camk2a-Cre ER with Foxg1 fl/fl mice and conditionally disrupted Foxg1 with tamoxifen in mature neurons. We found that spatial learning and memory were significantly impaired when examined by the Morris water maze test. The cKO mice also showed a significant reduction in freezing time during the contextual and cued fear conditioning test, indicating that fear conditioning memory was affected. A remarkable reduction in Schaffer-collateral long-term potentiation was also recorded. Morphologically, the dendritic arborization and spine densities of hippocampal pyramidal neurons were significantly reduced. Primary cell culture further confirmed altered dendritic complexity after Foxg1 deletion. Our results indicated that Foxg1 plays an important role in maintaining the neural plasticity, which is vital to high-grade function.