Neuronal Shape Research Articles

The great migration: How glial cells could regulate GnRH neuron development and shape adult reproductive life

In mammals, reproductive function is under the control of hypothalamic neurons named Gonadotropin-Releasing Hormone (GnRH) neurons. These neurons migrate from the olfactory placode to the brain, during embryonic development. For the past 40 years, these neurons have been considered an example of tangential migration, i.e., dependent on the olfactory/vomeronasal/terminal nerves. Numerous studies have highlighted the factors involved in the migration of these neurons but thus far overlooked the cellular microenvironment that produces them. Many of these factors are dysregulated in hypogonadotropic hypogonadism, resulting in subfertility/infertility. Nevertheless, over the past ten years, several papers have reported the influence of glial cells (named olfactory ensheathing cells [OECs]) in the migration and differentiation of GnRH neurons. This review will describe the atypical origins, migration, and differentiation of these neurons, focusing on the latest discoveries. There will be a more specific discussion on the involvement of OECs in the development of GnRH neurons, during embryonic and perinatal life; as well as on their potential implication in the development of congenital or idiopathic hypogonadotropic hypogonadism (such as Kallmann syndrome).

Local mRNA translation and cytoskeletal reorganization: Mechanisms that tune neuronal responses.

Neurons are highly polarized cells with significantly long axonal and dendritic extensions that can reach distances up to hundreds of centimeters away from the cell bodies in higher vertebrates. Their successful formation, maintenance, and proper function highly depend on the coordination of intricate molecular networks that allow axons and dendrites to quickly process information, and respond to a continuous and diverse cascade of environmental stimuli, often without enough time for communication with the soma. Two seemingly unrelated processes, essential for these rapid responses, and thus neuronal homeostasis and plasticity, are local mRNA translation and cytoskeletal reorganization. The axonal cytoskeleton is characterized by high stability and great plasticity; two contradictory attributes that emerge from the powerful cytoskeletal rearrangement dynamics. Cytoskeletal reorganization is crucial during nervous system development and in adulthood, ensuring the establishment of proper neuronal shape and polarity, as well as regulating intracellular transport and synaptic functions. Local mRNA translation is another mechanism with a well-established role in the developing and adult nervous system. It is pivotal for axonal guidance and arborization, synaptic formation, and function and seems to be a key player in processes activated after neuronal damage. Perturbations in the regulatory pathways of local translation and cytoskeletal reorganization contribute to various pathologies with diverse clinical manifestations, ranging from intellectual disabilities (ID) to autism spectrum disorders (ASD) and schizophrenia (SCZ). Despite the fact that both processes are essential for the orchestration of pathways critical for proper axonal and dendritic function, the interplay between them remains elusive. Here we review our current knowledge on the molecular mechanisms and specific interaction networks that regulate and potentially coordinate these interconnected processes.

Downregulation of Neurofilament Light Chain Expression in Human Neuronal-Glial Cell Co-Cultures by a Microbiome-Derived Lipopolysaccharide-Induced miRNA-30b-5p.

Microbiome-derived Gram-negative bacterial lipopolysaccharide (LPS) has been shown by multiple laboratories to reside within Alzheimer's disease (AD)-affected neocortical and hippocampal neurons. LPS and other pro-inflammatory stressors strongly induce a defined set of NF-kB (p50/p65)-sensitive human microRNAs, including a brain-enriched Homo sapien microRNA-30b-5p (hsa-miRNA-30b-5p; miRNA-30b). Here we provide evidence that this neuropathology-associated miRNA, known to be upregulated in AD brain and LPS-stressed human neuronal-glial (HNG) cells in primary culture targets the neurofilament light (NF-L) chain mRNA 3'-untranslated region (3'-UTR), which is conducive to the post-transcriptional downregulation of NF-L expression observed within both AD and LPS-treated HNG cells. A deficiency of NF-L is associated with consequent atrophy of the neuronal cytoskeleton and the disruption of synaptic organization. Interestingly, miRNA-30b has previously been shown to be highly expressed in amyloid-beta (Aβ) peptide-treated animal and cell models, and Aβ peptides promote LPS entry into neurons. Increased miRNA-30b expression induces neuronal injury, neuron loss, neuronal inflammation, impairment of synaptic transmission, and synaptic failure in neurodegenerative disease and transgenic murine models. This gut microbiota-derived LPS-NF-kB-miRNA-30b-NF-L pathological signaling network: (i) underscores a positive pathological link between the LPS of gastrointestinal (GI)-tract microbes and the inflammatory neuropathology, disordered cytoskeleton, and disrupted synaptic signaling of the AD brain and stressed brain cells; and (ii) is the first example of a microbiome-derived neurotoxic glycolipid having significant detrimental miRNA-30b-mediated actions on the expression of NF-L, an abundant neuron-specific filament protein known to be important in the maintenance of neuronal cell shape, axonal caliber, and synaptic homeostasis.

Neuronal Morphological Model-Driven Image Registration for Serial Electron Microscopy Sections.

Registration of a series of the two-dimensional electron microscope (EM) images of the brain tissue into volumetric form is an important technique that can be used for neuronal circuit reconstruction. However, complex appearance changes of neuronal morphology in adjacent sections bring difficulty in finding correct correspondences, making serial section neural image registration challenging. To solve this problem, we consider whether there are such stable "markers" in the neural images to alleviate registration difficulty. In this paper, we employ the spherical deformation model to simulate the local neuron structure and analyze the relationship between registration accuracy and neuronal structure shapes in two adjacent sections. The relevant analysis proves that regular circular structures in the section images are instrumental in seeking robust corresponding relationships. Then, we design a new serial section image registration framework driven by this neuronal morphological model, fully utilizing the characteristics of the anatomical structure of nerve tissue and obtaining more reasonable corresponding relationships. Specifically, we leverage a deep membrane segmentation network and neural morphological physical selection model to select the stable rounded regions in neural images. Then, we combine feature extraction and global optimization of correspondence position to obtain the deformation field of multiple images. Experiments on real and synthetic serial EM section neural image datasets have demonstrated that our proposed method could achieve more reasonable and reliable registration results, outperforming the state-of-the-art approaches in qualitative and quantitative analysis.

SRF depletion in early life contributes to social interaction deficits in the adulthood

Alterations in social behavior are core symptoms of major developmental neuropsychiatric diseases such as autism spectrum disorders or schizophrenia. Hence, understanding their molecular and cellular underpinnings constitutes the major research task. Dysregulation of the global gene expression program in the developing brain leads to modifications in a number of neuronal connections, synaptic strength and shape, causing unbalanced neuronal plasticity, which may be important substrate in the pathogenesis of neurodevelopmental disorders, contributing to their clinical outcome. Serum response factor (SRF) is a major transcription factor in the brain. The behavioral influence of SRF deletion during neuronal differentiation and maturation has never been studied because previous attempts to knock-out the gene caused premature death. Herein, we generated mice that lacked SRF from early postnatal development to precisely investigate the role of SRF starting in the specific time window before maturation of excitatory synapses that are located on dendritic spine occurs. We show that the time-controlled loss of SRF in neurons alters specific aspects of social behaviors in SRF knock-out mice, and causes deficits in developmental spine maturation at both the structural and functional levels, including downregulated expression of the AMPARs subunits GluA1 and GluA2, and increases the percentage of filopodial/immature dendritic spines. In aggregate, our study uncovers the consequences of postnatal SRF elimination for spine maturation and social interactions revealing novel mechanisms underlying developmental neuropsychiatric diseases.

DeepRayburst for Automatic Shape Analysis of Tree-Like Structures in Biomedical Images.

Precise quantification of tree-like structures from biomedical images, such as neuronal shape reconstruction and retinal blood vessel caliber estimation, is increasingly important in understanding normal function and pathologic processes in biology. Some handcrafted methods have been proposed for this purpose in recent years. However, they are designed only for a specific application. In this paper, we propose a shape analysis algorithm, DeepRayburst, that can be applied to many different applications based on a Multi-Feature Rayburst Sampling (MFRS) and a Dual Channel Temporal Convolutional Network (DC-TCN). Specifically, we first generate a Rayburst Sampling (RS) core containing a set of multidirectional rays. Then the MFRS is designed by extending each ray of the RS to multiple parallel rays which extract a set of feature sequences. A Gaussian kernel is then used to fuse these feature sequences and outputs one feature sequence. Furthermore, we design a DC-TCN to make the rays terminate on the surface of tree-like structures according to the fused feature sequence. Finally, by analyzing the distribution patterns of the terminated rays, the algorithm can serve multiple shape analysis applications of tree-like structures. Experiments on three different applications, including soma shape reconstruction, neuronal shape reconstruction, and vessel caliber estimation, confirm that the proposed method outperforms other state-of-the-art shape analysis methods, which demonstrate its flexibility and robustness.

Microtubule polarity is instructive for many aspects of neuronal polarity

Many neurons in bilaterian animals are polarized with functionally distinct axons and dendrites. Microtubule polarity, microtubule stability, and the axon initial segment (AIS) have all been shown to influence polarized transport in neurons. Each of these cytoskeletal cues could act independently to control axon and dendrite identity, or there could be a hierarchy in which one acts upstream of the others. Here we test the hypothesis that microtubule polarity acts as a master regulator of neuronal polarity by using a Drosophila genetic background in which some dendrites have normal minus-end-out microtubule polarity and others have the axonal plus-end-out polarity. In these mosaic dendrite arbors, we found that ribosomes, which are more abundant in dendrites than axons, were reduced in plus-end-out dendrites, while an axonal cargo was increased. In addition, we determined that microtubule stability was different in plus-end-out and minus-end-out dendrites, with plus-end-out ones having more stable microtubules like axons. Similarly, we found that ectopic diffusion barriers, like those at the AIS, formed at the base of dendrites with plus-end-out regions. Thus, changes in microtubule polarity were sufficient to rearrange other cytoskeletal features associated with neuronal polarization. However, overall neuron shape was maintained with only subtle changes in branching in mosaic arbors. We conclude that microtubule polarity can act upstream of many aspects of intracellular neuronal polarization, but shape is relatively resilient to changes in microtubule polarity in vivo.

Acetylated α-tubulin K394 regulates microtubule stability to shape the growth of axon terminals

Microtubules are essential to neuron shape and function. Acetylation of tubulin has the potential to directly tune the behavior and function of microtubules in cells. Although proteomic studies have identified several acetylation sites in α-tubulin, the effects of acetylation at these sites remains largely unknown. This includes the highly conserved residue lysine 394 (K394), which is located at the αβ-tubulin dimer interface. Using a fly model, we show that α-tubulin K394 is acetylated in the nervous system and is an essential residue. We found that an acetylation-blocking mutation in endogenous α-tubulin, K394R, perturbs the synaptic morphogenesis of motoneurons and reduces microtubule stability. Intriguingly, the K394R mutation has opposite effects on the growth of two functionally and morphologically distinct motoneurons, revealing neuron-type-specific responses when microtubule stability is altered. Eliminating the deacetylase HDAC6 increases K394 acetylation, and the over-expression of HDAC6 reduces microtubule stability similar to the K394R mutant. Thus, our findings implicate α-tubulin K394 and its acetylation in the regulation of microtubule stability and suggest that HDAC6 regulates K394 acetylation during synaptic morphogenesis.

Bok’s equi-volume principle: Translation, historical context, and a modern perspective

The human brain has a complex and unique structure, characterized by intricate three-dimensional folds. These folds, and the mechanisms for their formation, have been studied for over a hundred years. Here we offer a full translation of the pivotal (1929) work by Siegfried Bok, “Der Einflußder in den Furchen und Windungen auftretenden Krümmungen der Großhirnrinde auf die Rindenarchitektur” (“The Influence of the Curvature Occurring in the Folds and Turns of the Cerebral Cortex on Cortical Architecture”). This paper established the influential equi-volume principle, which stated that cortical and laminar thicknesses, along with neuronal shape and fiber orientation, change in order to preserve relative volume throughout the folds of the cortex. We also offer a commentary on the main points of the work, looking at Bok’s observations and predictions regarding the structure of neurons, cortical laminae, and the cortex itself, throughout the folds and curves of the brain. His equi-volume principle has held up to decades of experimentation and, even today, has important implications for the analysis of brain structure and function.Statement of Significance: This manuscript presents, for the first time, a full English translation of the foundational neuroanatomy article, “Der Einflußder in den Furchen und Windungen auftretenden Krümmungen der Großhirnrinde auf die Rindenarchitektur” (“The Influence of the Curvature Occurring in the Folds and Turns of the Cerebral Cortex on Cortical Architecture”), written over 90 years ago by Siegfried T. Bok and heavily cited since then. In addition, we provide an assessment of Bok’s main points, in light of his contemporaries in research at the time, as well as more recent work during the intervening decades.

HYPOXIC BRAIN DAMAGEIN PREMATURE INFANTS (MORPHOLOGICAL STUDY)

The aim of the study was to investigate the morphological signs of hypoxic damage to the central nervous system (CNS) in premature infants. Material and methods: The autopsy reports of 20 premature infants were analyzed. The mean gestational age was 25.9±3.7 weeks, median birth weight was 650 [535;940] grams, and height was 32.6±5.4 cm. We analyzed clinical assessment of the infant's condition at birth, the course of the neonatal period, blood gases and acid-base status, the mode and parameters of mechanical lung ventilation, as well as the oxygenation index (OI) and oxygen saturation index (OSI). Macroscopic and histological signs of damage to various brain structures were studied during pathological anatomical examination. Cortex, parietal subcortex, hippocampus, striatum, cerebellum, foci of hemorrhage were examined. Results: The main causes of mortality in premature infants were severe asphyxia and its sequelae such as combined ischemic and hemorrhagic brain and spinal cord damage (45%). Severe hypoxia was confirmed by laboratory investigations. Critical lactate and acid-base blood values corresponding to decompensated lactate acidosis were registered in newborns including hyperlactatemia up to 9±3.6 mmol/l, pH 7.01±0.21, BE (-12.3) [-30; -7.9] mmol/l. The OI and OSI, indicating severity of hypoxia, were significantly elevated with their medians being 13.7[9.6;19.8] and 31.8[9.6;16.2], respectively. All infants had central nervous system lesions of varying severity with the underlying morphological immaturity. Pericellular and perivascular cerebral edema, unilateral or bilateral subcortical and subependymal hemorrhages, intraventricular hemorrhages of various degrees, up to tamponade and blood leakage into the cisterna magna, and cerebral leukomalacia were the most frequent findings. In all patients, altered neuronal shape and size as well as hyperchromic nuclei were revealed in the subcortical zone. Changes in all cell structures (cytoplasm, nuclei, and nucleoli), as well as satellitosis and neuronophagy, were characteristic. Conclusion: Polymorphic morphological changes were observed in the brain structures of premature infants who died as a result of perinatal hypoxia. Along with signs of morphological immaturity, irreversible changes in cortical and subcortical neurons were found. The magnitude of changes is associated with the severity of perinatal hypoxia and decompensated lactate acidosis.

Effect of electroacupuncture of different acupoint groups on cerebral cortical neurovascular unit and PI3K/Akt signaling in rats with ischemic stroke

To observe the protective effect of electroacupuncture (EA) on neurovascular unit, neurological function in rats with cerebral ischemia (CI), so as to explore its mechanisms underlying improvement of ischemic cerebral tissue. Male SD rats, SPF grade, were randomly and equally divided into sham operation group, model group, EA group Ⅰ and EA group Ⅱ，27 rats in each group. The CI model was established by occlusion of the middle cerebral artery (MCAO). EA (2 Hz/20 Hz, 0.5 mA) was applied to "Quchi"(LI11), "Hegu"(LI4), "Zusanli"(ST36) and "Shuigou"(GV26) for rats of the EA group Ⅰ, and to "Baihui"(GV26), "Fengfu"(GV16), "Neiguan"(PC26) and "Xinshu"(BL15) for rats of the EA group Ⅱ for 20 min, once a day for 14 days. The modified neurologic severity score (mNSS) was calculated according to the state of locomotor, sensory, and reflex parameters. Transmission electron microscope (TEM) was used to observe the neuronal structure of the ischemic cerebral area. The CD34 positive cells (for microvessels) of the ischemic brain tissue were detected by using immunohistochemistry, and the expression levels of cerebral phosphatidylinositol-3 kinase (PI3K) and protein kinase B (Akt) mRNAs were detected by quantitative real-time-PCR, respectively. Along with the extension of time, the mNSS at 4 h, and 3, 7 and 14 d after CI were apparently decreased, and the number of CD34 positive cells from 3 d to 14 d after CI, and the expression of PI3K mRNA and Akt mRNA from 3 d to 7 d were significantly increased in the model，EAⅠand EA Ⅱ group （P<0.01, P<0.05）. Compared with the sham operation group, the mNSS at 4 h, and 3, 7 and 14 d, and CD34-positive number and PI3K mRNA and Akt mRNA expression levels at 3, 7 and 14 d were significantly increased in the model group (P<0.01, P>0.05). In comparison with the model group, the mNSS at 3, 7 and 14 d were obviously decreased (P<0.01), and the CD34-positive number and PI3K and Akt mRNA expression levels at 3, 7 and 14 d considerably increased in both EA group Ⅰ and Ⅱ (P<0.01, P<0.05). The therapeutic effect of EA group Ⅱ was significantly superior to that of EA group Ⅰ in lowering mNSS at 14 d, up-regulating the CD34-positive number at 7 and 14 d,and PI3K mRNA at 3, 7 and 14 d and Akt mRNA at 3 and 7 d (P<0.05, P<0.01). Results of TEM showed an irregular shape of neurons with nuclear pyknosis, non-uniform chromatin, more organelle loss, swollen mitochondrial Golgi complex and expansion of rough endoplasmic reticulum, being relatively milder in the EA group Ⅰ, particularly in the EA group Ⅱ. EA therapy can improve the neurological function in cerebral ischemia rats, which may be related to its effects in protecting the neurovascular unit and up-regulating PI3K/Akt signal pathway. The effects of EA at GV26, GV16, PC26 and BL15 are better than those of EA at LI11, LI4, ST36 and GV26.

Characterization of the Kisspeptin and GnRH expression in the hypothalamus of the male and female taiep rat, an animal model of demyelination.

Reproductive alterations have been reported in patients with demyelinating diseases, these alterations can lead to infertility. In the hypothalamus we can find two neuronal types that regulate reproductive function; kisspeptidergic and GnHergic neurons. At the present moment, the relation between demyelination and reproductive alterations it is yet unknown; in order to elucidate this relation, we used the taiep rat, an animal that presents demyelination of the central nervous system and that also shows reproductive issues. We characterized the immunofluorescent expression of kisspeptin and GnRH in the hypothalamus of the male and female taiep rats using Sprague-Dawley rats as control. We obtained the brains of the females during oestrous and adult males; the brains were cut at 10mm. Performed immunofluorescence of kisspeptin and GnRH (bs-0749r-cy5, bs-10369R-A488; Bioss Antibodies) and analysed the intensity of the fluorescence in the hypothalamus using the software ImageJ1.50i. Fluorescence is concentrated in fiber-like structures with neuron shape. An increment in the intensity of the fluorescence of kisspeptin was observed in said structures in male taiep rats compared with SD (0.37±0.02 vs 0.28±0.01, p< 0.001). Female taiep rats during oestrus showed a decrease in the intensity of the fluorescence of kisspeptin structures compared with SD (0.44±0.02 vs 0.57±0.03, p< 0.001). We could not observe any significant changes in the expression of GnRH fibers in the hypothalamus of the taiep rat compared with SD. Demyelination in the taiep rat affects kisspeptin expression at hypothalamic level, but this does not affect the expression of GnRH in either males or females, this effect is probably related with the availability of receptors in the GnRHergic neuron, we will evaluate this in the future. The decrease in kisspeptin expression in the female taiep rat, could be caused by previously reported low concentrations of oestrogen, given that it is capable of stimulating kisspeptin expression.

The Untouchable Ventral Nucleus of the Trapezoid Body: Preservation of a Nucleus in an Animal Model of Autism Spectrum Disorder.

Autism spectrum disorder (ASD) is a neurodevelopmental condition characterized by repetitive behaviors, poor social skills, and difficulties with communication and hearing. The hearing deficits in ASD range from deafness to extreme sensitivity to routine environmental sounds. Previous research from our lab has shown drastic hypoplasia in the superior olivary complex (SOC) in both human cases of ASD and in an animal model of autism. However, in our study of the human SOC, we failed to find any changes in the total number of neurons in the ventral nucleus of the trapezoid body (VNTB) or any changes in cell body size or shape. Similarly, in animals prenatally exposed to the antiepileptic valproic acid (VPA), we failed to find any changes in the total number, size or shape of VNTB neurons. Based on these findings, we hypothesized that the neurotransmitter profiles, ascending and descending axonal projections of the VNTB are also preserved in these neurodevelopmental conditions. We investigated this hypothesis using a combination of immunohistochemistry and retrograde tract tracing. We found no difference between control and VPA-exposed animals in the number of VNTB neurons immunoreactive for choline acetyltransferase (ChAT). Additionally, we investigated the ascending projections from the VNTB to both the central nucleus of the inferior colliculus (CNIC) and medial geniculate (MG) and descending projections to the cochlea. Our results indicate no significant differences in the ascending and descending projections from the VNTB between control and VPA-exposed animals despite drastic changes in these projections from surrounding nuclei. These findings provide evidence that certain neuronal populations and circuits may be protected against the effects of neurodevelopmental disorders.

A general principle of dendritic constancy: A neuron’s size- and shape-invariant excitability

Reducing neuronal size results in less membrane and therefore lower input conductance. Smaller neurons are thus more excitable, as seen in their responses to somatic current injections. However, the impact of a neuron's size and shape on its voltage responses to dendritic synaptic activation is much less understood. Here we use analytical cable theory to predict voltage responses to distributed synaptic inputs in unbranched cables, showing that these are entirely independent of dendritic length. For a given synaptic density, neuronal responses depend only on the average dendritic diameter and intrinsic conductivity. This remains valid for a wide range of morphologies irrespective of their arborization complexity. Spiking models indicate that morphology-invariant numbers of spikes approximate the percentage of active synapses. In contrast to spike rate, spike times do depend on dendrite morphology. In summary, neuronal excitability in response to distributed synaptic inputs is largely unaffected by dendrite length or complexity.

Urokinase plasminogen activator mediates changes in human astrocytes modeling fragile X syndrome.

The function of astrocytes intertwines with the extracellular matrix, whose neuron and glial cell-derived components shape neuronal plasticity. Astrocyte abnormalities have been reported in the brain of the mouse model for fragile X syndrome (FXS), the most common cause of inherited intellectual disability, and a monogenic cause of autism spectrum disorder. We compared human FXS and control astrocytes generated from human induced pluripotent stem cells and we found increased expression of urokinase plasminogen activator (uPA), which modulates degradation of extracellular matrix. Several pathways associated with uPA and its receptor function were activated in FXS astrocytes. Levels of uPA were also increased in conditioned medium collected from FXS hiPSC-derived astrocyte cultures and correlated inversely with intracellular Ca2+ responses to activation of L-type voltage-gated calcium channels in human astrocytes. Increased uPA augmented neuronal phosphorylation of TrkB within the docking site for the phospholipase-Cγ1 (PLCγ1), indicating effects of uPA on neuronal plasticity. Gene expression changes during neuronal differentiation preceding astrogenesis likely contributed to properties of astrocytes with FXS-specific alterations that showed specificity by not affecting differentiation of adenosine triphosphate (ATP)-responsive astrocyte population. To conclude, our studies identified uPA as an important regulator of astrocyte function and demonstrated that increased uPA in human FXS astrocytes modulated astrocytic responses and neuronal plasticity.

Systematic morphological and morphometric analysis of identified olfactory receptor neurons in Drosophila melanogaster.

The biophysical properties of sensory neurons are influenced by their morphometric and morphological features, whose precise measurements require high-quality volume electron microscopy (EM). However, systematic surveys of nanoscale characteristics for identified neurons are scarce. Here, we characterize the morphology of Drosophila olfactory receptor neurons (ORNs) across the majority of genetically identified sensory hairs. By analyzing serial block-face electron microscopy images of cryofixed antennal tissues, we compile an extensive morphometric data set based on 122 reconstructed 3D models for 33 of the 40 identified antennal ORN types. Additionally, we observe multiple novel features-including extracellular vacuoles within sensillum lumen, intricate dendritic branching, mitochondria enrichment in select ORNs, novel sensillum types, and empty sensilla containing no neurons-which raise new questions pertinent to cell biology and sensory neurobiology. Our systematic survey is critical for future investigations into how the size and shape of sensory neurons influence their responses, sensitivity, and circuit function.

P 25. Investigating cytoskeletal integrity in the sensory nerve fibers in healthy individuals

Introduction. Neurons with long neurites are physiologically remarkable, as they need to transport newly synthesized proteins and organelles (e.g. mitochondria) from the soma over long distances to the synapses, which is essential for neuronal homeostasis. Via adaptor proteins, which walk on microtubules, organelles find their target place. Next to microtubules, the neuronal cytoskeleton consists of neurofilaments, and actin: neurofilaments regulate axonal caliber, and actin is involved in the neuronal shape (Eira et al. 2016, Hoffman et al. 1984). A misbalance or dysfunction of cytoskeletal components might contribute to neurodegenerative diseases, such as amyotrophic lateral sclerosis (ALS). Neurofilament light chain (NfL) is an established biomarker for ALS (Bacioglu et al. 2016). Here, we study the human cytoskeletal components during aging . As a model we chose sensory neurons which possess long processes and axon endings can be accessed easily by skin biopsies. In this study we focus on the expression levels of microtubules, neurofilaments, and actin in skin biopsies of healthy individuals. Furthermore, we analyze the axonal diameter. Methods. Skin biopsies (thigh and ankle) of 27 men (mean age 54.2 ± 18.9 a, from 24 a to 79 a) were PFA-fixed and cut. Fluorescent immunostaining for non-phosphorylated neurofilament heavy chain (npNfH), betaIII-tubulin, and actin was performed. Images of the dermis were acquired by confocal microscopy. At least 20 axons per healthy individual were analyzed for the mean gray values and diameter. Statistics were calculated using GraphPad Prism (V9). This study was approved by the local ethics committee. Participants gave informed written consent. Results. Cytoskeletal components (npNfH, betaIII-tubulin, actin) drastically increased with age. NpNfH increased 2.7-fold from 24- to 75-year-old individuals. Actin showed a change of 3.8-fold from the youngest to the 62-year-old controls (peak, maximum values), whereas betaIII-tubulin levels increased 3.2-fold from the 24- to the 75-year-old healthy individuals. Sensory axon caliber increased 2.2-fold from the 29- (1.35 µm) to the 78/79-year old (2.97 µm) controls which results in a 4.9-fold increase of the cross-sectional area of the axons. Statistical analysis (Mann-Whitney U test) showed highly significant results between each staining/caliber and age ( p < 0.001). Discussion. Our results suggest an age-driven “ossification” of the axonal cytoskeleton in peripheral sensory axons, which might influence cytoskeletal functionality and axonal caliber. The age-dependent increase in caliber can be explained by the higher expression of neurofilaments, which mainly regulate the diameter of axons (Costa et al. 2018). These findings are in accordance with the increased susceptibility of aged individuals to neurodegenerative diseases. The results reported here will be validated in a second independent cohort (27 men, age 26 to 74). We further plan the analysis of length dependency as biopsies were obtained from thigh and ankle.

Administering crocin ameliorates anxiety-like behaviours and reduces the inflammatory response in amyloid-beta induced neurotoxicity in rat.

Anxiety, hippocampus synaptic plasticity deficit, as well as pro-inflammatory cytokines, are involved in Alzheimer's disease (AD). The present study is designed to evaluate the possible therapeutic effect of crocin on anxiety-like behaviours, hippocampal synaptic plasticity and neuronal shape, as well as pro-inflammatory cytokines in the hippocampus using in vivo amyloid-beta (Aβ) models of AD. The Aβ peptide (1-42) was bilaterally injected into the frontal-cortex. Five hours after the surgery, the rats were given intraperitoneal (IP) crocin (30mg/kg) daily up to 12days. Elevated plus maze results showed that crocin treatment after bilateral Aβ injection significantly increased the percentage of spent time into open arms, frequency of entries, and percentage of entries into open arms as compared with the Aβ group. In the open field test, the Aβ+crocin group showed a higher percentage of spent time in the centre and frequency of entries into central zone as compare with the Aβ treated animals. Administering crocin increased the number of soma, dendrites and axonal arbores in the CA1 neurons among the rats with Aβ neurotoxicity. Cresyl violet (CV) staining showed that crocin increased the number of CV-positive cells in the CA1 region of the hippocampus compared with the Aβ group. Silver-nitrate staining indicated that crocin reduced neurofibrillary tangle formation induced by Aβ. Crocin treatment attenuated the expression of TNF-α and IL-1β mRNA in the hippocampus compared with the Aβ group. Our results suggest that crocin attenuated Aβ-induced anxiety-like behaviours and neuronal damage, and synaptic plasticity loss in hippocampal CA1 neurons may via its anti-inflammatory effects.

Glia actively sculpt sensory neurons by controlled phagocytosis to tune animal behavior.

Glia in the central nervous system engulf neuron fragments to remodel synapses and recycle photoreceptor outer segments. Whether glia passively clear shed neuronal debris or actively prune neuron fragments is unknown. How pruning of single-neuron endings impacts animal behavior is also unclear. Here, we report our discovery of glia-directed neuron pruning in Caenorhabditis elegans. Adult C. elegans AMsh glia engulf sensory endings of the AFD thermosensory neuron by repurposing components of the conserved apoptotic corpse phagocytosis machinery. The phosphatidylserine (PS) flippase TAT-1/ATP8A functions with glial PS-receptor PSR-1/PSR and PAT-2/α-integrin to initiate engulfment. This activates glial CED-10/Rac1 GTPase through the ternary GEF complex of CED-2/CrkII, CED-5/DOCK180, CED-12/ELMO. Execution of phagocytosis uses the actin-remodeler WSP-1/nWASp. This process dynamically tracks AFD activity and is regulated by temperature, the AFD sensory input. Importantly, glial CED-10 levels regulate engulfment rates downstream of neuron activity, and engulfment-defective mutants exhibit altered AFD-ending shape and thermosensory behavior. Our findings reveal a molecular pathway underlying glia-dependent engulfment in a peripheral sense-organ and demonstrate that glia actively engulf neuron fragments, with profound consequences on neuron shape and animal sensory behavior.

Aging-related alteration of trigeminal ganglion structures; A histologic study of Neuronal population, Satellite Ganglionic Cells and Vascular bed

Background: Aging is associated with signs that are similar to peripheral neuropathy and age-related decline in the peripheral sensory system and proprioceptive functions. Trigeminal ganglion (TG) is one of the sensory ganglion providing sensory information from the orofacial region. Ultrastruchral alteration in neuronal population of TG has been reported.Aim of work: Examine the effects of aging on neuronal population, distribution, and satellite ganglionic cells (SGCs) and compare with the TG of young animal. Materials and Methods: Old male Wistar rats (32 weeks old) (250±20g) and young male (4weeks old) (150±20g) were deeply anesthetized with chloroform. To avoid inadvertent mechanical dark neuron formation, each animal was transcardially perfused with 500ml of 4% paraformaldehyde in0.1 M phosphate-buffered saline. The skull cap was cut open and the TG was exposed and removed carefully. The sections were selected according to the systematic random sampling(SRS) and stained with H&E. From each section 10 fields(200×160µm) were selected randomly and the profile of neurons, neuronal shapes, SGCs, and the number of capillary profiles were studied. Results: The measured profile of neurons in the TG of young (17.11± 4.8) and old animals (15.69±4.4) showed a meaningful level of differences(p 0.05). The number of capillary profiles in the TG of young animals (7±2.73) showed a meaningful difference with those of old animals (3.8±0.83) (p < 0.05). Conclusion: With aging neuro-glial population and vascular bed of TG undergo a series of quantitative and qualitative alterations. Precisely aging is associated with decrease in neuronal size and vascular bed while the number of SGCs remains without significant changes. Aging leads to changes in neuronal distribution and likely morphologic alterations in SGCs subpopulation.