Differential involvement of amyloidogenic evolvability in oligodendropathies; Multiple Sclerosis and Multiple System Atrophy

Although multiple sclerosis (MS) and multiple system atrophy (MSA) are both characterized by impaired oligodendrocytes (OLs), the aetiological relevance remains obscure. Given inherent stressors affecting OLs, the objective of the present study was to discuss the possible role of amyloidogenic evolvability (aEVO) in these conditions. Hypothetically, in aEVO, protofibrils of amyloidogenic proteins (APs), including β-synuclein and β-amyloid, might form in response to diverse stressors in parental brain. Subsequently, the AP protofibrils might be transmitted to offspring via germ cells in a prion-like fashion. By virtue of the stress information conferred by protofibrillar APs, the OLs in offspring's brain might be more resilient to forthcoming stressors, perhaps reducing MS risk. aEVO could be comparable to a gene for the inheritance of acquired characteristics. On the contrary, during ageing, MSA risk is increased through antagonistic pleiotropy. Consistently, the expression levels of APs are reduced in MS, but are increased in MSA compared to controls. Furthermore, β-synuclein, the non-amyloidogenic homologue of β-synuclein, might exert a buffering effect on aEVO, and abnormal β-synuclein could also increase MS and MSA disease activity. Collectively, a better understanding of the role of aEVO in the OL diseases might lead to novel interventions for such chronic degenerative conditions.

Neurotrophins in carotid atherosclerosis and stenting

INTRODUCTION

Carotid stenting is used with an expanding indications. The neurotrophins are a family of proteins that induce the survival, development, and function of neurons. Carotid stenting alters cerebral blood flow and can affect neurotrophins' levels.

MATERIAL AND METHODS

We included 78 people: 39 with significant carotid stenoses (CS) referred for carotid stenting (mean age 67.79 ± 10.53 years) and relatively healthy control group of 39 people without carotid and vertebral artery disease (mean age 57.42 ± 15.77 years). Brain derived reurotrophic factor (BDNF) and neuronal growth factor (NGF) concentrations were evaluated with ELISA method from venous blood - once for the control group; and for the carotid stenting group: before (n33), 24 h after (n22) and at least 1 month after (n18) carotid stenting.

RESULTS

There was a difference between the mean neurotrophins' concentration of patients with significant carotid stenoses and the group without: BDNF p = 0.001, CI (-5.11 to -1.44) (3.10 ± 3.10 ng/ml in CS vs. 6.37 ± 4.67 ng/ml in controls); NGF p = 0.049, CI (0.64-347.75), 195.67 ± 495.34 pg/ml in CS vs. 21.48 ± 52.81 pg/ml in controls. BDNF levels before carotid stenting (3.10 ± 3.10 ng/ml) were significantly lower than the postprocedural (4.99 ± 2.57 ng/ml) - p < 0.0001, CI (-2.86 to -0.99). For NGF there was a tendency for lower values after stenting: 195.67 ± 495.34 pg/ml before vs. 94.92 ± 120.06 pg/ml after, but the result did not reach statistical significance. The neurotrophins levels one month after carotid stenting and controls' were not significantly different p < 0.01 (BDNF 5.03 ± 4.75 ng/ml vs. 6.37 ± 4.67 ng/min; NGF 47.89 ± 54.68 pg/ml vs. 21.48 pg/ml).

DISCUSSION AND CONCLUSION

Periprocedural and mid-term concentrations of neurotrophins after carotid stenting change in non-linear model. This may be due to changes in cerebral perfusion and also might be involved in neuronal recovery and reparation after reperfusion.KEY MESSAGESPeriprocedural and mid-term concentrations of neurotrophins after carotid stenting change in non-linear model.As the majority of them are not specific, their periprocedural change can be used as a clinical correlate to guide changes or even success in carotid stenting.Changes in neutrophins' concentrations may be due to changes in cerebral perfusion and also might be involved in neuronal recovery and reparation after reperfusion.This goes in analogy with cardiac high-sensitive troponin, used as procedural guidance in coronary interventions.

Fibroblast exosomal TFAP2C induced by chitosan oligosaccharides promotes peripheral axon regeneration via the miR-132-5p/CAMKK1 axis

Chitosan and its degradation product, oligosaccharides, have been shown to facilitate peripheral nerve regeneration. However, the underlying mechanisms are not well understood. In this study, we analyzed the protein expression profiles in sciatic nerves after injury using proteomics. A group of proteins related to exosome packaging and transport is up-regulated by chitosan oligosaccharides (COS), implying that exosomes are involved in COS-induced peripheral nerve regeneration. In fact, exosomes derived from fibroblasts (f-EXOs) treated with COS significantly promoted axon extension and regeneration. Exosomal protein identification and functional studies, revealed that TFAP2C is a key factor in neurite outgrowth induced by COS-f-EXOs. Furthermore, we showed that TFAP2C targets the pri-miRNA-132 gene and represses miR-132-5p expression in dorsal root ganglion neurons. Camkk1 is a downstream substrate of miR-132-5p that positively affects axon extension. In rats, miR-132-5p antagomir stimulates CAMKK1 expression and improves axon regeneration and functional recovery in sciatic nerves after injury. Our data reveal the mechanism for COS in axon regeneration, that is COS induce fibroblasts to produce TFAP2C-enriched EXOs, which are then transferred into axons to promote axon regeneration via miR-132-5p/CAMKK1. Moreover, these results show a new facet of fibroblasts in axon regeneration in peripheral nerves.

Engineered macrophage-biomimetic versatile nanoantidotes for inflammation-targeted therapy against Alzheimer's disease by neurotoxin neutralization and immune recognition suppression

Immune recognition of excessive neurotoxins by microglia is a trigger for the onset of neuroinflammation in the brain, leading to neurodegeneration in Alzheimer's disease (AD). Blocking active recognition of microglia while removing neurotoxins holds promise for fundamentally alleviating neurotoxin-induced immune responses, but is very challenging. Herein, an engineered macrophage-biomimetic versatile nanoantidote (OT-Lipo@M) is developed for inflammation-targeted therapy against AD by neurotoxin neutralization and immune recognition suppression. Coating macrophage membranes can not only endow OT-Lipo@M with anti-phagocytic and inflammation-tropism capabilities to target inflammatory lesions in AD brain, but also efficiently reduce neurotoxin levels to prevent them from activating microglia. The loaded oxytocin (OT) can be slowly released to downregulate the expression of immune recognition site Toll-like receptor 4 (TLR4) on microglia, inhibiting TLR4-mediated pro-inflammatory signalling cascade. Benefiting from this two-pronged immunosuppressive strategy, OT-Lipo@M exhibits outstanding therapeutic effects on ameliorating cognitive deficits, inhibiting neuronal apoptosis, and enhancing synaptic plasticity in AD mice, accompanied by the delayed hippocampal atrophy and brain microstructural disruption by in vivo 9.4T MR imaging. This work provides new insights into potential AD therapeutics targeting microglia-mediated neuroinflammation at the source.

Risk Factors in Depression and Anxiety Disorders from the Framework of Developmental Psychopathology

Depression and anxiety disorders are among the most prevalent psychiatric disorders that negatively affect individuals’ life in many ways. Understanding how these highly comorbid emotional disorders develop and persist might guide prevention, intervention, and treatment studies. Some common vulnerability factors underlie depression and anxiety disorders. Developmental psychopathology deals with these vulnerabilities and risk factors from a lifetime perspective. The aim of this review is to present the risk factors associated with depression and anxiety from the perspective of developmental psychopathology. For this purpose, we discussed genetic and biological factors, temperament, negative childhood experiences, family and peer relationships, and some cognitive and emotional factors as risk factors. Also, we discussed how these risk factors lead to depression and anxiety disorders. This review emphasizes that some common transdiagnostic risk factors underlie emotional disorders and highlights the importance of a developmental psychopathology perspective to understand the developmental pathways of depression and anxiety disorders.

On Language Cognition Relations and Evolution of Language

One can understand the importance of language with its relation to mental activities such as memory and thinking. Language, a crucial human ability, has long attracted the attention of various theorists and philosophers. Language, by its nature, interacts with many biological, cultural and psychological factors. This article has drawn a general framework by bringing together the views from disciplines such as linguistics, psychology, anthropology, biology and neuroscience. On the one hand, while the theoretical opinions about language are included, on the other hand, language is discussed in the context of the changes we went through by separating from our common ancestor in the evolution process. When dealing with language, it is possible to talk about our differences from animals, the interaction of language with our cognitive processes and its organization in the brain. The views put forward by philosophers such as Plato and Descartes about the relationship between language and cognitions have expanded by Chomsky, Pinker, Dunbar and others on the evolution of language. In this article, evolutionary psychology, which strives to understand language and its relationship with cognitions, is emphasized by combining the data of modern evolutionary biology and cognitive psychology. Language is acquired quickly and without the intense need for learning experiences, thanks to innate schemas, suggests that evolution formed these schemas. According to another view, the influence of the environment and culture gains importance instead of innatism. In addition, different opinions on the evolution of language are briefly discussed. Discussion topics include triggers of language development in evolution. These are related to biological and cultural influences, influences of vocalization and hand gestures on language. When thinking about language and its evolution, it is inevitable to observe and examine cognitive processes and thought. Multidisciplinary studies can also provide important information about the evolution of language while trying to understand the complex relationship between language and cognition.

Nicotine's effect on cognition, a friend or foe?

Tobacco smoking is a preventable cause of morbidity and mortality throughout the world. Smoking comes in form of absorption of many compounds, among which nicotine is the main psychoactive component of tobacco and its positive and negative reinforcement effects are proposed to be the key mechanism for the initiation and maintenance of smoking. Growing evidence suggests that the cognitive enhancement effects of nicotine may also contribute to the difficulty of quitting smoking, especially in individuals with psychiatric disorders. In this review, we first introduce the beneficial effect of nicotine on cognition including attention, short-term memory and long-term memory. We next summarize the beneficial effect of nicotine on cognition under pathological conditions, including Alzheimer's disease, Parkinson's disease, Schizophrenia, Stress-induced Anxiety, Depression, and drug-induced memory impairment. The possible mechanism underlying nicotine's effect is also explored. Finally, nicotine's detrimental effect on cognition is discussed, including in the prenatal and adolescent periods, and high-dose nicotine- and withdrawal-induced memory impairment is emphasized. Therefore, nicotine serves as both a friend and foe. Nicotine-derived compounds could be a promising strategy to alleviate neurological disease-associated cognitive deficit, however, due to nicotine's detrimental effect, continued educational programs and public awareness campaigns are needed to reduce tobacco use among pregnant women and smoking should be quitted even if it is e-cigarette, especially for the adolescents.

Chronic unilateral inhibition of GABA synthesis in the amygdala increases specificity of conditioned fear in a discriminative fear conditioning paradigm in rats

Neural activity in the amygdala is critical for fear learning. In anxiety disorder patients, bilateral hyperactivity of the amygdala can be observed. This hyperactivation is often associated with the facilitation of fear learning and/or over-generalization of conditioned fear. In contrast, hypoactivity of the amygdala, e.g. by pharmacological interventions, attenuates or blocks fear learning. To date, little is known about how neural excitability of the amygdala affects specificity or generalization of fear. Therefore, the present study utilized chronic inhibition of GABA synthesis in the amygdala to increase excitability and investigated the effect on the specificity of fear learning. In rats, unilateral cannulas aiming at the amygdala were implanted. The cannulas were connected to subcutaneously implanted osmotic mini pumps that delivered either the GABA synthesis inhibitor L-allylglycine or its inactive enantiomer D-allylglycine. Following one week of chronic GABA synthesis manipulation, the rats were submitted to a discriminative fear conditioning protocol. In addition, anxiety-like behavior in the light-dark box was measured. Our data show that chronic unilateral L-AG infusions into the amygdala improve the specificity of learned fear, support safety learning, and reduce fear generalization and anxiety. This data demonstrates that moderately increased amygdala excitability can be beneficial for the specificity of fear learning and highlights the potential application for therapeutic interventions.

Corticotropin-releasing factor potentiates glutamatergic input and excitability of presympathetic neurons in the hypothalamus in spontaneously hypertensive rats

Hyperactivity of presympathetic neurons in the hypothalamic paraventricular nucleus (PVN) plays a key role in generating excess sympathetic output in hypertension. However, the mechanisms driving hyperactivity of PVN presympathetic neurons in hypertension are unclear. In this study, we determined the role of corticotropin-releasing factor (CRF) in the PVN in augmented glutamatergic input, neuronal excitability and sympathetic outflow in hypertension. The number of CRF or c-Fos immunoreactive neurons and CRF/c-Fos double-labeled neurons in the PVN was significantly greater in spontaneously hypertensive rats (SHRs) than in normotensive Wistar-Kyoto (WKY) rats. Blocking glutamatergic input reduced the CRF-potentiated excitability of spinally projecting PVN neurons. Furthermore, CRF knockdown via Crispr/Cas9 in the PVN decreased the frequencies of spontaneous firing and miniature excitatory postsynaptic currents (mEPSCs) in spinally projecting PVN neurons in SHRs. In addition, the mRNA and protein levels of CRFR1, but not CRFR2, in the PVN were significantly higher in SHRs than in WKY rats. Blocking CRFR1 with NBI-35965, but not blocking CRFR2 with Antisauvagine-30, reduced the frequencies of spontaneous firing and mEPSCs of spinally projecting PVN neurons in SHRs. Also, microinjection of NBI-35965 into the PVN significantly reduced arterial blood pressure (ABP) and renal sympathetic nerve activity (RSNA) in anesthetized SHRs, but not in WKY rats. However, microinjection of Antisauvagine-30 into the PVN had no effect on ABP or RSNA in WKY rats and SHRs. Our findings suggest that endogenous CRF in the PVN potentiates glutamatergic input and firing activity of PVN presympathetic neurons via CRFR1, resulting in augmented sympathetic outflow in hypertension.

6- to 10-year-old children do not show race-based orienting biases to faces during an online attention capture task

Research has established that frequency of exposure to own- and other-race faces shapes the development of face processing biases characterized by enhanced attention to and recognition of more familiar own-race faces, that is, the other-race effect (ORE). The ORE is first evident during infancy based on differences in looking to own- versus other-race faces and is later assessed based on recognition memory task performance during childhood and adulthood. Using these measures, researchers have found that race-based face processing biases initially develop during infancy but remain sensitive to experiences with own- and other-race faces through childhood. In contrast, limited work suggests that infants' attention orienting may be less affected by frequency of exposure to own- and other-race faces. However, the plasticity of race-based face processing biases during childhood suggests that biased orienting to own-race faces may develop at later ages following continued exposure to these faces. We addressed this question by examining 6- to 10-year-old children's attention capture by own- and other-race faces during an online task. Children searched for a target among multiple distractors. During some trials, either an own- or other-race face appeared as one of the distractors. Children showed similar target detection performance (omission errors, accuracy, and response times) regardless of whether an own- or other-race face appeared as a distractor. These results differ from research demonstrating race-based biases in attention holding and recognition memory but converge with previous infant research suggesting that attention orienting might not be as strongly affected by frequency of exposure to race-based information during development.

Diet as a modifiable factor in tumorigenesis: Focus on microbiome-derived bile acid metabolites and short-chain fatty acids

Several lines of evidences have implicated the resident microbiome as a key factor in the modulation of host physiology and pathophysiology; including the resistance to cancers. Gut microbiome heavily influences host lipid homeostasis by their modulatory effects on the metabolism of bile acids (BAs). Microbiota-derived BA metabolites such as deoxycholic acid (DCA), lithocholic acid (LCA), and ursodeoxycholic acid (UDCA) are implicated in the pathogeneses of various cancer types. The pathogenic mechanisms are multimodal in nature, with widespread influences on the host immunes system, cell survival and growth signalling and DNA damage. On the other hand, short-chain fatty acids (SCFAs) produced by the resident microbial activity on indigestible dietary fibres as well as during intermittent fasting regimens (such as the Ramazan fasting) elicit upregulation of the beneficial anti-inflammatory and anticancer pathways in the host. The present review first provides a brief overview of the molecular mechanisms of microbiota-derived lipid metabolites in promotion of tumour development. The authors then discuss the potential of diet as a therapeutic route for beneficial alteration of microbiota and the consequent changes in the production of SCFAs, particularly butyrate, in relation to the cancer prevention and treatment.

The Drivers of Diversity: Integrated genetic and hormonal cues regulate neural diversity

Proper functioning of the nervous system relies not only on the generation of a vast repertoire of distinct neural cell types but also on the precise neural circuitry within them. How the generation of highly diverse neural populations is regulated during development remains a topic of interest. Landmark studies in Drosophila have identified the genetic and temporal cues regulating neural diversity and thus have provided valuable insights into our understanding of temporal patterning of the central nervous system. The development of the Drosophila central complex, which is mostly derived from type II neural stem cell (NSC) lineages, showcases how a small pool of NSCs can give rise to vast and distinct progeny. Similar to the human outer subventricular zone (OSVZ) neural progenitors, type II NSCs generate intermediate neural progenitors (INPs) to expand and diversify lineages that populate higher brain centers. Each type II NSC has a distinct spatial identity and timely regulated expression of many transcription factors and mRNA binding proteins. Additionally, INPs derived from them show differential expression of genes depending on their birth order. Together type II NSCs and INPs display a combinatorial temporal patterning that expands neural diversity of the central brain lineages. We cover advances in current understanding of type II NSC temporal patterning and discuss similarities and differences in temporal patterning mechanisms of various NSCs with a focus on how cell-intrinsic and extrinsic hormonal cues regulate temporal transitions in NSCs during larval development. Cell extrinsic ligands activate conserved signaling pathways and extrinsic hormonal cues act as a temporal switch that regulate temporal progression of the NSCs. We conclude by elaborating on how a progenitor's temporal code regulates the fate specification and identity of distinct neural types. At the end, we also discuss open questions in linking developmental cues to neural identity, circuits, and underlying behaviors in the adult fly.

Interaction of magnetic fields with biogenic magnetic nanoparticles on cell membranes: Physiological consequences for organisms in health and disease

The interaction mechanisms between magnetic fields (MFs) and living systems, which remained hidden for more than a hundred years, continue to attract the attention of researchers from various disciplines: physics, biology, medicine, and life sciences. Revealing these mechanisms at the cellular level would allow to understand complex cell systems and could help to explain and predict cell responses to MFs, intervene in organisms' reactions to MFs of different strengths, directions, and spatial distributions. We suggest several new physical mechanisms of the MF impacts on endothelial and cancer cells by the MF interaction with chains of biogenic and non-biogenic magnetic nanoparticles on cell membranes. The revealed mechanisms can play a hitherto unexpected role in creating physiological responses of organisms to externally applied MFs. We have also a set of theoretical models that can predict how cells will individually and collectively respond to a MF exposure. The physiological sequences of the MF - cell interactions for organisms in health and disease are discussed. The described effects and their underlying mechanisms are general and should take place in a large family of biological effects of MFs. The results are of great importance for further developing novel approaches in cell biology, cell therapy and medicine.

The crosstalk between 5-HT(2A)R and mGluR2 in schizophrenia

Schizophrenia is a severe brain disorder that usually produces a lifetime of disability. First generation or typical antipsychotics such as haloperidol and second generation or atypical antipsychotics such as clozapine and risperidone remain the current standard for schizophrenia treatment. In some patients with schizophrenia, antipsychotics produce complete remission of positive symptoms, such as hallucinations and delusions. However, antipsychotic drugs are ineffective against cognitive deficits and indeed treated schizophrenia patients have small improvements or even deterioration in several cognitive domains. This underlines the need for novel and more efficient therapeutic targets for schizophrenia treatment. Serotonin and glutamate have been identified as key parts of two neurotransmitter systems involved in fundamental brain processes. Serotonin (or 5-hydroxytryptamine) 5-HT_2A receptor (5-HT_2AR) and metabotropic glutamate 2 receptor (mGluR2) are G protein-coupled receptors (GPCRs) that interact at epigenetic and functional levels. These two receptors can form GPCR heteromeric complexes through which their pharmacology, function and trafficking becomes affected. Here we review past and current research on the 5-HT_2AR-mGluR2 heterocomplex and its potential implication in schizophrenia and antipsychotic drug action. This article is part of the Special Issue on "The receptor-receptor interaction as a new target for therapy".

Community-Derived Core Concepts for Neuroscience Higher Education

Core concepts provide a framework for organizing facts and understanding in neuroscience higher education curricula. Core concepts are overarching principles that identify patterns in neuroscience processes and phenomena and can be used as a foundational scaffold for neuroscience knowledge. The need for community-derived core concepts is pressing, because both the pace of research and number of neuroscience programs are rapidly expanding. While general biology and many subdisciplines within biology have identified core concepts, neuroscience has yet to establish a community-derived set of core concepts for neuroscience higher education. We used an empirical approach involving more than 100 neuroscience educators to identify a list of core concepts. The process of identifying neuroscience core concepts was modeled after the process used to develop physiology core concepts and involved a nationwide survey and a working session of 103 neuroscience educators. The iterative process identified eight core concepts and accompanying explanatory paragraphs. The eight core concepts are abbreviated as communication modalities, emergence, evolution, gene-environment interactions, information processing, nervous system functions, plasticity, and structure-function. Here, we describe the pedagogical research process used to establish core concepts for the neuroscience field and provide examples on how the core concepts can be embedded in neuroscience education.

Temporal regulation of neural diversity in Drosophila and vertebrates

The generation of neuronal diversity involves temporal patterning mechanisms by which a given progenitor sequentially produces multiple cell types. Several parallels are evident between the brain development programs of Drosophila and vertebrates, such as the successive emergence of specific cell types and the use of combinations of transcription factors to specify cell fates. Furthermore, cell-extrinsic cues such as hormones and signaling pathways have also been shown to be regulatory modules of temporal patterning. Recently, transcriptomic and epigenomic studies using large single-cell sequencing datasets have provided insights into the transcriptional dynamics of neurogenesis in the Drosophila and mammalian central nervous systems. We review these commonalities in the specification of neuronal identity and highlight the conserved or convergent strategies of brain development by discussing temporal patterning mechanisms found in flies and vertebrates.

Effects of emotional working memory training on problematic internet use, inhibition, attention, and working memory among young problematic internet users: A randomized control study

Problematic internet use (PIU) has been defined as an inability to control impulses to use the internet, and is associated with psychological, social, educational, and/or occupational problems. Considering the harmful effects of PIU, the present study evaluated a treatment intervention aimed at controlling PIU. A randomized control study investigated the effectiveness of emotional working memory training (eWMT) in improving inhibition, attention, and working memory among individuals with PIU in comparison with a placebo group. Young adults (N = 36) with PIU were either trained for 20 sessions in an n-back dual emotional task (eWMT; n = 18) or a feature matching task (placebo; n = 18). Results showed that 20 continuous sessions of eWMT significantly reduced the symptoms of PIU and improved participants' working memory, attention, and inhibition (compared to the placebo group). These preliminary findings suggest that eWMT can be considered a promising treatment to reduce PIU by improving individuals' cognitive and emotional functioning.

Generating neural diversity through spatial and temporal patterning

The nervous system consists of a vast diversity of neurons and glia that are accurately assembled into functional circuits. What are the mechanisms that generate these diverse cell types? During development, an epithelial sheet with neurogenic potential is initially regionalised into spatially restricted domains of gene expression. From this, pools of neural stem cells (NSCs) with distinct molecular profiles and the potential to generate different neuron types, are specified. These NSCs then divide asymmetrically to self-renew and generate post-mitotic neurons or glia. As NSCs age, they experience transitions in gene expression, which further allows them to generate different neurons or glia over time. Versions of this general template of spatial and temporal patterning operate during the development of different parts of different nervous systems. Here, I cover our current knowledge of Drosophila brain and optic lobe development as well as the development of the vertebrate cortex and spinal cord within the framework of this above template. I highlight where our knowledge is lacking, where mechanisms beyond these might operate, and how the emergence of new technologies might help address unanswered questions.

The involvement of dopamine and D2 receptor-mediated transmission in effects of cotinine in male rats

Previous studies indicated that cotinine, the major metabolite of nicotine, supported intravenous self-administration and exhibited relapse-like drug-seeking behaviors in rats. Subsequent studies started to reveal an important role of the mesolimbic dopamine system in cotinine's effects. Passive administration of cotinine elevated extracellular dopamine levels in the nucleus accumbens (NAC) and the D1 receptor antagonist SCH23390 attenuated cotinine self-administration. The objective of the current study was to further investigate the role of mesolimbic dopamine system in mediating cotinine's effects in male rats. Conventional microdialysis was conducted to examine NAC dopamine changes during active self-administration. Quantitative microdialysis and Western blot were used to determine cotinine-induced neuroadaptations within the NAC. Behavioral pharmacology was performed to investigate potential involvement of D2-like receptors in cotinine self-administration and relapse-like behaviors. NAC extracellular dopamine levels increased during active self-administration of cotinine and nicotine with less robust increase during cotinine self-administration. Repeated subcutaneous injections of cotinine reduced basal extracellular dopamine concentrations without altering dopamine reuptake in the NAC. Chronic self-administration of cotinine led to reduced protein expression of D2 receptors within the core but not shell subregion of the NAC, but did not change either D1 receptors or tyrosine hydroxylase in either subregion. On the other hand, chronic nicotine self-administration had no significant effect on any of these proteins. Systemic administration of eticlopride, a D2-like receptor antagonist attenuated both cotinine self-administration and cue-induced reinstatement of cotinine seeking. These results further support the hypothesis that the mesolimbic dopamine transmission plays a critical role in mediating reinforcing effects of cotinine.

G-quadruplex-hemin DNAzyme functionalized nanopipettes: Fabrication and sensing application

Solid-nanopores/nanopipettes have the exquisite ability to reveal the changes in molecular volume due to the advantages of adjustable size, good rigidity and low noise. Herein, a new platform for sensing application was established based on G-quadruplex-hemin DNAzyme (GQH) functionalized gold-coated nanopipettes. In this method, GQH was immobilized on gold-coated nanopipette, which could be used as a catalyst for the reaction of H₂O₂ with 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) to promote the conversion of ABTS to ABTS⁺ ions inside gold-coated nanopipette, and the change of transmembrane ion current could be monitored in real time. At the optimal conditions, there was a correlation between the ion current and the concentration of H₂O₂ in a certain range, which could be used for the hydrogen peroxide sensing. The GQH immobilized nanopipette provides a useful platform to investigate enzymatic catalysis in confined environment, which can be used in electrocatalysis, sensing and fundamental electrochemistry.

Mechanical regulation of synapse formation and plasticity

Dendritic spines are small protrusions arising from dendrites and constitute the major compartment of excitatory post-synapses. They change in number, shape, and size throughout life; these changes are thought to be associated with formation and reorganization of neuronal networks underlying learning and memory. As spines in the brain are surrounded by the microenvironment including neighboring cells and the extracellular matrix, their protrusion requires generation of force to push against these structures. In turn, neighboring cells receive force from protruding spines. Recent studies have identified BAR-domain proteins as being involved in membrane deformation to initiate spine formation. In addition, forces for dendritic filopodium extension and activity-induced spine expansion are generated through cooperation between actin polymerization and clutch coupling. On the other hand, force from expanding spines affects neurotransmitter release from presynaptic terminals. Here, we review recent advances in our understanding of the physical aspects of synapse formation and plasticity, mainly focusing on spine dynamics.

Biomechanical models and mechanisms of cellular morphogenesis and cerebral cortical expansion and folding

Morphogenesis of the nervous system involves a highly complex spatio-temporal pattern of physical forces (mainly tension and pressure) acting on cells and tissues that are pliable but have an intricately organized cytoskeletal infrastructure. This review begins by covering basic principles of biomechanics and the core cytoskeletal toolkit used to regulate the shapes of cells and tissues during embryogenesis and neural development. It illustrates how the principle of 'tensegrity' provides a useful conceptual framework for understanding how cells dynamically respond to forces that are generated internally or applied externally. The latter part of the review builds on this foundation in considering the development of mammalian cerebral cortex. The main focus is on cortical expansion and folding - processes that take place over an extended period of prenatal and postnatal development. Cortical expansion and folding are likely to involve many complementary mechanisms, some related to regulating cell proliferation and migration and others related to specific types and patterns of mechanical tension and pressure. Three distinct multi-mechanism models are evaluated in relation to a set of 18 key experimental observations and findings. The Composite Tension Plus (CT+) model is introduced as an updated version of a previous multi-component Differential Expansion Sandwich Plus (DES+) model (Van Essen, 2020); the new CT+ model includes 10 distinct mechanisms and has the greatest explanatory power among published models to date. Much needs to be done in order to validate specific mechanistic components and to assess their relative importance in different species, and important directions for future research are suggested.

Unbalanced amygdala communication in major depressive disorder

BACKGROUND

Previous studies suggested an association between functional alteration of the amygdala and typical major depressive disorder (MDD) symptoms. Examining whether and how the interaction between the amygdala and regions/functional networks is altered in patients with MDD is important for understanding its neural basis.

METHODS

Resting-state functional magnetic resonance imaging data were recorded from 67 patients with MDD and 74 age- and sex-matched healthy controls (HCs). A framework for large-scale network analysis based on seed mappings of amygdala sub-regions, using a multi-connectivity-indicator strategy (cross-correlation, total interdependencies (TI), Granger causality (GC), and machine learning), was employed. Multiple indicators were compared between the two groups. The altered indicators were ranked in a supporting-vector machine-based procedure and associated with the Hamilton Rating Scale for Depression scores.

RESULTS

The amygdala connectivity with the default mode network and ventral attention network regions was enhanced and that with the somatomotor network, dorsal frontoparietal network, and putamen regions in patients with MDD was reduced. The machine learning analysis highlighted altered indicators that were most conducive to the classification between the two groups.

LIMITATIONS

Most patients with MDD received different pharmacological treatments. It is difficult to illustrate the medication state's effect on the alteration model because of its complex situation.

CONCLUSION

The results indicate an unbalanced interaction model between the amygdala and functional networks and regions essential for various emotional and cognitive functions. The model can help explain potential aberrancy in the neural mechanisms that underlie the functional impairments observed across various domains in patients with MDD.

Failure of deactivation in bipolar disorder during performance of an fMRI adapted version of the Stroop task

INTRODUCTION

Few studies have examined the functional brain correlates of the performance of the Stroop task in bipolar disorder (BD). It is also not known whether it is associated with failure of de-activation in the default mode network, as has been found in studies using other tasks.

METHODS

Twenty-four BD patients and 48 age, sex and educationally estimated intellectual quotient (IQ) matched healthy subjects (HS) underwent a functional MRI during performance of the counting Stroop task. Task-related activations (incongruent versus congruent condition) and de-activations (incongruent versus fixation) were examined using whole-brain, voxel-based methodology.

RESULTS

Both the BD patients and the HS showed activation in a cluster encompassing the left dorsolateral and ventrolateral prefrontal cortex and the rostral anterior cingulate cortex and supplementary motor area, with no differences between them. The BD patients, however, showed significant failure of de-activation in the medial frontal cortex and the posterior cingulate cortex/precuneus.

CONCLUSIONS

The failure to find activation differences between BD patients and controls suggests that the 'regulative' component of cognitive control remains intact in the disorder, at least outside episodes of illness. The failure of de-activation found adds to evidence documenting trait-like default mode network dysfunction in the disorder.

The anatomical networks based on probabilistic structurally connectivity in bipolar disorder across mania, depression, and euthymic states

BACKGROUNDS

There have pieces of evidence of the distinct aberrant functional network topology profile in bipolar disorder (BD) across mania, depression, and euthymic episodes. However, the underlying anatomical network topology pattern in BD across different episodes is unclear.

METHODS

We calculated the whole-brain probabilistic structurally connectivity across 143 subjects (72 with BD [34 depression; 13 mania; 25 euthymic] and 53 healthy controls), and used graph theory to examine the trait- and state-related topology alterations of the structural connectome in BD. The correlation analysis was further conducted to explore the relationship between detected network measures and clinical symptoms.

RESULTS

There no omnibus alteration of any global network metrics were observed across all diagnostic groups. In the regional network metrics level, bipolar depression showed increased clustering coefficient in the right lingual gyrus compared with all other groups, and the increased clustering coefficient in the right lingual gyrus positively correlated with depression, anxiety, and illness burden symptoms but negatively correlated with mania symptoms; manic and euthymic patients showed decreased clustering coefficient in the left inferior occipital gyrus compared with HCs.

LIMITATIONS

The moderate sample size of all patient groups (especially for subjects with mania) might have contributed to the negative findings of the trait feature in this study.

CONCLUSIONS

We demonstrated the altered regional connectivity pattern in the occipital lobe of the bipolar depression and mania episode, especially the lingual gyrus. The association of the clustering coefficient in the lingual gyrus with clinical symptoms helps monitor the state of BD.

Regulation of neural stem cell self-renewal, proliferation and differentiation by the RhoA guanine nucleotide exchange factor Arhgef 1

The role of the Arhgef1 as a RhoA-specific guanine nucleotide exchange factor has been widely investigated in the immune system. Our previous findings reveal that Arhgef 1 is highly expressed in neural stem cells (NSCs) and controls the process of neurite formation. However, the functional role of Arhgef 1 in NSCs remains poorly understood. In order to investigate the role of Arhgef 1 in NSCs, Arhgef 1 expression in NSCs was reduced by using lentivirus-mediated short hairpin RNA interference. Our results indicate that down-regulated expression of Arhgef 1 reduced the self-renewal, proliferation capacity of NSCs and affect cell fate determination. In addition, the comparative transcriptome analysis from RNA-seq data determines the mechanisms of deficits in Arhgef 1 knockdown NSCs. Altogether, our present studies show that Arhgef 1 down-regulation leads to interruption of the cell cycle procession. The importance of Arhgef 1 for regulating self-renewal, proliferation and differentiation in NSCs is reported for the first time.

Deubiquitinase CYLD regulates excitatory synaptic transmission and short-term plasticity in the hippocampus

The fate of proteins is determined by the addition of various forms of polyubiquitin during ubiquitin-mediated proteasomal degradation. Cylindromatosis (CYLD), a K63-specific deubiquitinase, is enriched in postsynaptic density fractions of the rodent central nervous system (CNS), but the synaptic role of CYLD in the CNS is poorly understand. Here we show that CYLD deficiency (Cyld^-/-) results in reduced intrinsic hippocampal neuronal firing, a decrease in the frequency of spontaneous excitatory postsynaptic currents and a decrease in the amplitude of field excitatory postsynaptic potentials. Moreover, Cyld^-/- hippocampus shows downregulated levels of presynaptic vesicular glutamate transporter 1 (vGlut1) and upregulated levels of postsynaptic GluA1, a subunit of the AMPA receptor, together with an altered paired-pulse ratio (PPR). We also found increased activation of astrocytes and microglia in the hippocampus of Cyld^-/- mice. The present study suggests a critical role for CYLD in mediating hippocampal neuronal and synaptic activity.

Distinct populations of corticotropin-releasing factor (CRF) neurons mediate divergent yet complementary defensive behaviors in response to a threat

Defensive behaviors in response to a threat are shared across the animal kingdom. Active (fleeing, sheltering) or passive (freezing, avoiding) defensive responses are adaptive and facilitate survival. Selecting appropriate defensive strategy depends on intensity, proximity, temporal threat threshold, and past experiences. Hypothalamic corticotropin-releasing factor (CRF) is a major driver of an acute stress response, whereas extrahypothalamic CRF mediates stress-related affective behaviors. In this review, we shift the focus from a monolithic role of CRF as an anxiogenic peptide to comprehensively dissecting contributions of distinct populations of CRF neurons in mediating defensive behaviors. Direct interrogation of CRF neurons of the central amygdala (CeA) or the bed nucleus of the stria terminalis (BNST) show they drive unconditioned defensive responses, such as vigilance and avoidance of open spaces. Although both populations also contribute to learned fear responses in familiar, threatening contexts, CeA-CRF neurons are particularly attuned to the ever-changing environment. Depending on threat intensities, they facilitate discrimination of salient stimuli predicting manageable threats, and prevent their generalization. Finally, hypothalamic CRF neurons mediate initial threat assessment and active defense such as escape to shelter. Overall, these three major populations of CRF neurons demonstrate divergent, yet complementary contributions to the versatile defense system: heightened vigilance, discriminating salient threats, and active escape, representing three legs of the defense tripod. Despite the 'CRF exhaustion' in the field of affective neuroscience, understanding contributions of specific CRF neurons during adaptive defensive behaviors is needed in order to understand the implications of their dysregulation in fear- and anxiety-related psychiatric disorders. This article is part of the Special Issue on "Fear, Anxiety and PTSD".

Salience to remember: VTA-IC dopaminergic pathway activity is necessary for object recognition memory formation

Previous studies have shown that dopaminergic activity modulates the salience of novel stimuli enabling the formation of recognition memories. In this work, we hypothesize that dopamine released into the insular cortex (IC) from the ventral tegmental area (VTA) inputs enables the acquisition to consolidate object recognition memory. It has been reported that short training produces weak recognition memories; on the contrary, longer training produces lasting and robust recognition memories. Using a Cre-recombinase under the tyrosine hydroxylase (TH+) promoter mouse model, we photostimulated the VTA-IC dopaminergic pathway during short training or photoinhibited the same pathway during long training while mice explored objects. Our results showed that the photostimulation of the VTA-IC pathway during a short training enables the acquisition of recognition memory. Conversely, photoinhibition of the same pathway during a long training prevents the acquisition of recognition memory. Interestingly, the exploration time of the objects under photoinhibition or photostimulation of the dopaminergic VTA-IC pathway was not altered. Significantly, this enhancement of acquisition of the object recognition memory through the photostimulation of the VTA dopaminergic neurons could be impaired by the blockage of the D1-like receptors into the IC, either before or after the photostimulation. Altogether, our results suggest that dopamine released by the VTA is required during the acquisition to consolidate the object recognition memory through D1-like receptors into the IC without affecting the activity or the motivation to explore objects.

Controlled light exposure and intermittent fasting as treatment strategies for metabolic syndrome and gut microbiome dysregulation in night shift workers

The mammalian circadian clocks are entrained by environmental time cues, such as the light-dark cycle and the feeding-fasting cycle. In modern society, circadian misalignment is increasingly more common under the guise of shift work. Shift workers, accounting for roughly 20% of the workforce population, are more susceptible to metabolic disease. Exposure to artificial light at night and eating at inappropriate times of the day uncouples the central and peripheral circadian clocks. This internal circadian desynchrony is believed to be one of the culprits leading to metabolic disease. In this review, we discuss how alterations in the rhythm of gut microbiota and their metabolites during chronodisruption send conflicting signals to the host, which may ultimately contribute to disturbed metabolic processes. We propose two behavioral interventions to improve health in shift workers. Firstly, by carefully timing the moments of exposure to blue light, and hence shifting the melatonin peak, to improve sleep quality of daytime sleeping episodes. Secondly, by timing the daily time window of caloric intake to the biological morning, to properly align the feeding-fasting cycle with the light-dark cycle and to reduce the risk of metabolic disease. These interventions can be a first step in reducing the worldwide burden of health problems associated with shift work.

MicroRNA-650 Regulates the Pathogenesis of Alzheimer's Disease Through Targeting Cyclin-Dependent Kinase 5

Alzheimer's disease (AD) pathogenesis feature progressive neurodegeneration, amyloid-β plaque formation, and neurofibrillary tangles. Ample evidence has indicated the involvement of epigenetic pathways in AD pathogenesis. Here, we show that the expression of microRNA 650 (miR-650) is altered in brains from AD patients. Furthermore, we found that the processing of primary miR-650 to mature miR-650 is misregulated. Bioinformatic analysis predicted that miR-650 targets the expression of three AD-associated components: Apolipoprotein E (APOE), Presenilin 1 (PSEN1), and Cyclin-Dependent Kinase 5 (CDK5), and we have experimentally confirmed that miR-650 is able to significantly reduce the expression of APOE, PSEN1, and CDK5 in vitro. Importantly, the overexpression of miR-650 was further shown to significantly alter the CDK5 level and ameliorate AD pathologies in APP-PSEN1 transgenic mice. Overall, our results indicate that miR-650 influences AD pathogenesis through regulation of CDK5.

The Current State of Functional MR Imaging for Trauma Prognostication

In this review, we discuss the basics of functional MRI (fMRI) techniques including task-based and resting state fMRI, and overview the major findings in patients with traumatic brain injury. We summarize the studies that have longitudinally evaluated the changes in brain connectivity and task-related activation in trauma patients during different phases of trauma. We discuss how these data may potentially be used for prognostication, treatment planning, or monitoring and management of trauma patients.

Changes in neural activity during the combining affect labeling and reappraisal

Reappraisal, an emotion regulation strategy, is an effective way of controlling negative emotions. Conversely, it is known that affect labeling regulates negative emotions using a different process from reappraisal, and it is possible that the combined use of affect labeling and reappraisal might enhance the control of negative emotion. In this study, we compared the brain activity during combined use of affect labeling and reappraisal to negative emotion with the sole use of reappraisal by using fMRI. The participants performed a reappraisal after affect labeling to negative emotion which induced by negative image. In comparison to the sole use of reappraisal, increased activity was found in the bilateral inferior frontal gyrus and medial frontal gyrus, whereas decreased activity in the right amygdala. Furthermore, based on the results of a functional connectivity analysis using the seed region of the right amygdala, it was determined that coupling with the right amygdala increases due to the combined use of affect labeling and reappraisal. The results reveal that affect labeling of negative emotion potentially effects on reappraisal, which has implications for the more effective use of reappraisal.

Adolescent non-suicidal self-injury during the COVID-19 pandemic: A prospective longitudinal study of biological predictors of maladaptive emotion regulation

BACKGROUND

Non-suicidal self-injury (NSSI) in adolescence is thought to stem from interactions between vulnerability in developing biological systems and experience of stressors. The current study assesses whether multiple levels of the stress system's response to threat could prospectively predict NSSI engagement during the COVID-19 pandemic, a shared, time-locked stressor.

METHODS

Participants were 64 female adolescents (ages 12-16) from community and clinical settings who were oversampled for NSSI histories. Prior to the onset of the COVID-19 pandemic, adolescents completed a protocol that measured hypothalamic-pituitary-adrenal axis response to a social stressor (via salivary cortisol), amygdala volume, amygdala emotion-evoked activation, and frontolimbic resting-state functional connectivity. During early months of the pandemic (Summer 2020), measures of NSSI behavior (Inventory of Statements About Self-Injury), emotion regulation difficulties (Difficulties in Emotion Regulation Scale), perceived stress (Perceived Stress Scale), and pandemic-related stressors (Epidemic Pandemic Impacts Inventory) were collected. Multinomial logistic regression was used to assess if pre-pandemic biomarkers predicted mid-pandemic NSSI engagement: persistence of NSSI (Persist; N = 21), cessation of NSSI (Desist; N = 26), and no history of NSSI (Never; N = 17). Linear regressions explored if pre-pandemic biomarkers predicted mid-pandemic difficulties in emotion regulation and perceived stress.

RESULTS

Higher pre-pandemic overall cortisol response to stress and amygdala emotion-evoked activation characterized adolescents who persisted in NSSI, compared to those who desisted. These findings remained significant when controlling for pandemic related stressors. Lower prepandemic cortisol reactivity predicted more difficulties in emotion regulation during the pandemic. This finding did not remain significant after controlling for pandemic related stressors.

CONCLUSIONS

Findings suggest that patterns in key biological threat response systems may confer vulnerability for risk outcomes including NSSI engagement in adolescent females in the context of a shared, novel, naturally-occurring stressor. The results point to the importance of multi-level, longitudinal approaches for understanding the interface between developing neurobiological systems and experiential stress in at-risk adolescents. Identified patterns give insight into potential risk assessment strategies based on an understanding of the multi-level threat response.

Computational models of behavioral addictions: State of the art and future directions

Non-pharmacological behavioral addictions, such as pathological gambling, videogaming, social networking, or internet use, are becoming major public health concerns. It is not yet clear how behavioral addictions could share many major neurobiological and behavioral characteristics with substance use disorders, despite the absence of direct pharmacological influences. A deeper understanding of the neurocognitive mechanisms of addictive behavior is needed, and computational modeling could be one promising approach to explain intricately entwined cognitive and neural dynamics. This review describes computational models of addiction based on reinforcement learning algorithms, Bayesian inference, and biophysical neural simulations. We discuss whether computational frameworks originally conceived to explain maladaptive behavior in substance use disorders can be effectively extended to non-substance-related behavioral addictions. Moreover, we introduce recent studies on behavioral addictions that exemplify the possibility of such extension and propose future directions.

Neuroimmune interactions with binge alcohol drinking in the cerebellum of IL-6 transgenic mice

The neuroimmune system of the brain, which is comprised primarily of astrocytes and microglia, regulates a variety of homeostatic mechanisms that underlie normal brain function. Numerous conditions, including alcohol consumption, can disrupt this regulatory process by altering brain levels of neuroimmune factors. Alcohol and neuroimmune factors, such as proinflammatory cytokines IL-6 and TNF-alpha, act at similar targets in the brain, including excitatory and inhibitory synaptic transmission. Thus, alcohol-induced production of IL-6 and/or TNF-alpha could be important contributing factors to the effects of alcohol on the brain. Recent studies indicate that IL-6 plays a role in alcohol drinking and the effects of alcohol on the brain activity following the cessation of alcohol consumption (post-alcohol period), however information on these topics is limited. Here we used homozygous and heterozygous female and male transgenic mice with increased astrocyte expression of IL-6 to examined further the interactions between alcohol and IL-6 with respect to voluntary alcohol drinking, brain activity during the post-alcohol period, IL-6 signal transduction, and expression of synaptic proteins. Wildtype littermates (WT) served as controls. The transgenic mice model brain neuroimmune status with respect to IL-6 in subjects with a history of persistent alcohol use. Results showed a genotype dependent reduction in voluntary alcohol consumption in the Drinking in the Dark protocol and in frequency-dependent relationships between brain activity in EEG recordings during the post-alcohol period and alcohol consumption. IL-6, TNF-alpha, IL-6 signal transduction partners pSTAT3 and c/EBP beta, and synaptic proteins were shown to play a role in these genotypic effects.

[Formula: see text] Higher access to screens is related to decreased functional connectivity between neural networks associated with basic attention skills and cognitive control in children

Screen-based media has become a prevailing part of children's lives. Different technologies provide limitless access to a wide range of content. This accessibility has immensely increased screen exposure among children, showing that this exposure is associated with decreased cognitive abilities. This study was designed to evaluate how the neurobiological correlates for different sub-components of screen exposure, such as level of access, content, and frequency, are related to different cognitive abilities. Resting-state functional MRI data were collected in 29 native English-speaking children (8-12 years old), in addition to cognitive-behavioral measures. Functional connectivity measures within and between several networks related to cognitive control and attention were calculated [fronto-parietal (FP), cingulo-opercular (CO), dorsal attention (DAN), ventral attention (VAN), salience, default mode (DMN), cerebellar networks]. Sub-components of screen exposure were measured using the Screen-Q questionnaire. Higher access to screens was related to lower functional connectivity between neural networks associated with basic attention skills and cognitive control (i.e., DAN and salience). In addition, higher levels of parent-child interaction during screen exposure were related to increased functional connectivity between networks related to cognitive control and learning (i.e., CO and cerebellar). These findings suggest that screen exposure may reduce the engagement of basic attention and modulation of cognitive control networks and that higher levels of parent-child interaction engage cognitive control networks. An enhanced understanding of these processes can provide an important scientific basis for future educational and medical approaches regarding screen exposure.

Microscopic mechanism of PIEZO1 activation by pressure-induced membrane stretch

Mechanosensitive PIEZO1 ion channels open in response to membrane stretch. Yet, the underlying microscopic mechanism of this activation remains unknown. To probe this mechanism, we used cell-attached pressure-clamp recordings to measure single channel currents at different steady-state negative pipette pressures, spanning the full range of the channel's pressure sensitivity. Pressure-dependent activation occurs through a sharp reduction of the mean shut duration and through a moderate increase of the mean open duration. Across all tested pressures, the distribution of open and shut dwell times best follows sums of two and three exponential components, respectively. As the magnitude of the pressure stimulus increases, the time constants of most of these exponential components gradually change, in opposite directions for open and shut dwell times, and to a similar extent. In addition, while the relative amplitudes of fast and slow components remain unchanged for open intervals, they fully reverse for shut intervals, further reducing the mean shut duration. Using two-dimensional dwell time analysis, Markov-chain modeling, and simulations, we identified a minimal five-states model which recapitulates essential characteristics of single channel data, including microscopic reversibility, correlations between adjacent open and shut intervals, and asymmetric modulation of dwell times by pressure. This study identifies a microscopic mechanism for the activation of PIEZO1 channels by pressure-induced membrane stretch and deepens our fundamental understanding of mechanotransduction by a vertebrate member of the PIEZO channel family.

Taste arbor structural variability analyzed across taste regions

Taste ganglion neurons are functionally and molecularly diverse, but until recently morphological diversity was completely unexplored. Specifically, taste arbors (the portion of the neuron within the taste bud) vary in structure, but the reason for this variability is unclear. Here, we analyzed structural variability in taste arbors to determine which factors determine their morphological diversity. To characterize arbor morphology and its relationship to taste bud cells capable of transducing taste stimuli (taste-transducing cell) number and type, we utilized sparse cell genetic labeling of taste ganglion neurons in combination with whole-mount immunohistochemistry. Reconstruction of 151 taste arbors revealed variation in arbor size, complexity, and symmetry. Overall, taste arbors exist on a continuum of complexity, cannot be categorized into discrete morphological groups, and do not have stereotyped endings. Arbor size/complexity was not related to the size of the taste bud in which it was located or the type of taste-transducing cell contacted (membranes within 180 nm). Instead, arbors could be broadly categorized into three groups: large asymmetrical arbors contacting many taste-transducing cells, small symmetrical arbors contacting one or two taste-transducing cells, and unbranched arbors. Neurons with multiple arbors had arbors in more than one of these categories, indicating that this variability is not an intrinsic feature of neuron type. Instead, we speculate that arbor structure is determined primarily by nerve fiber remodeling in response to cell turnover and that large asymmetrical arbors represent a particularly plastic state.