Actin-dependent astrocytic infiltration is a key step for axon defasciculation during remodeling

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Transneuronal Dpr12/DIP‐δ interactions facilitate compartmentalized dopaminergic innervation of Drosophila mushroom body axons

The mechanisms controlling wiring of neuronal networks are not completely understood. The stereotypic architecture of the Drosophila mushroom body (MB) offers a unique system to study circuit assembly. The adult medial MB γ‐lobe is comprised of a long bundle of axons that wire with specific modulatory and output neurons in a tiled manner, defining five distinct zones. We found that the immunoglobulin superfamily protein Dpr12 is cell‐autonomously required in γ‐neurons for their developmental regrowth into the distal γ4/5 zones, where both Dpr12 and its interacting protein, DIP‐δ, are enriched. DIP‐δ functions in a subset of dopaminergic neurons that wire with γ‐neurons within the γ4/5 zone. During metamorphosis, these dopaminergic projections arrive to the γ4/5 zone prior to γ‐axons, suggesting that γ‐axons extend through a prepatterned region. Thus, Dpr12/DIP‐δ transneuronal interaction is required for γ4/5 zone formation. Our study sheds light onto molecular and cellular mechanisms underlying circuit formation within subcellular resolution.     

Visual experience affects both behavioral and neuronal aspects in the individual life history of the desert ant Cataglyphis fortis

The individual life history of the desert ant Cataglyphis fortis is characterized by a fast transition from interior tasks to mainly visually guided foraging. Previous studies revealed a remarkable structural synaptic plasticity in visual and olfactory input regions within the mushroom bodies of the ants' brain centers involved in learning and memory. Reorganization of synaptic complexes (microglomeruli) was shown to be triggered by sensory exposure rather than an internal program. Using video analyses at the natural nest site and activity recordings after artificial light treatments we investigated whether the ants get exposed to light before onset of foraging and whether this changes the ants' activity levels. We asked whether synaptic reorganization occurs in a similar time window by immunolabeling and quantification of pre- and postsynaptic compartments of visual and olfactory microglomeruli after periods of light-exposure. Ants reverted back to dark nest conditions were used to investigate whether synaptic reorganization is reversible. The behavior analyses revealed that late-interior ants (diggers) are exposed to light and perform exploration runs up to 2 days before they start foraging. This corresponds well with the result that artificial light treatment over more than 2-3 days significantly increased the ants' locomotor activities. At the neuronal level, visual exposure of more than 1 day was necessary to trigger reorganization of microglomeruli, and light-induced changes were only partly reversible in the dark. We conclude that visual preexposure is an important and flexible means to prepare the ants' visual pathway for orientation capabilities essential during foraging.     

Sonic hedgehog is a regulator of extracellular glutamate levels and epilepsy

Sonic hedgehog (Shh), both as a mitogen and as a morphogen, plays an important role in cell proliferation and differentiation during early development. Here, we show that Shh inhibits glutamate transporter activities in neurons, rapidly enhances extracellular glutamate levels, and affects the development of epilepsy. Shh is quickly released in response to epileptic, but not physiological, stimuli. Inhibition of neuronal glutamate transporters by Shh depends on heterotrimeric G protein subunit Gα_i and enhances extracellular glutamate levels. Inhibiting Shh signaling greatly reduces epileptiform activities in both cell cultures and hippocampal slices. Moreover, pharmacological or genetic inhibition of Shh signaling markedly suppresses epileptic phenotypes in kindling or pilocarpine models. Our results suggest that Shh contributes to the development of epilepsy and suppression of its signaling prevents the development of the disease. Thus, Shh can act as a modulator of neuronal activity, rapidly regulating glutamate levels and promoting epilepsy.     

Glial control of sphingolipid levels sculpts diurnal remodeling in a circadian circuit

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Neuronal Plasticity in the Mushroom‐Body Calyx of Bumble Bee Workers During Early Adult Development

Division of labor among workers is a key feature of social insects and frequently characterized by an age‐related transition between tasks, which is accompanied by considerable structural changes in higher brain centers. Bumble bees (Bombus terrestris), in contrast, exhibit a size‐related rather than an age‐related task allocation, and thus workers may already start foraging at two days of age. We ask how this early behavioral maturation and distinct size variation are represented at the neuronal level and focused our analysis on the mushroom bodies (MBs), brain centers associated with sensory integration, learning and memory. To test for structural neuronal changes related to age, light exposure, and body size, whole‐mount brains of age‐marked workers were dissected for synapsin immunolabeling. MB calyx volumes, densities, and absolute numbers of olfactory and visual projection neuron (PN) boutons were determined by confocal laser scanning microscopy and three‐dimensional image analyses. Dark‐reared bumble bee workers showed an early age‐related volume increase in olfactory and visual calyx subcompartments together with a decrease in PN‐bouton density during the first three days of adult life. A 12:12  h light‐dark cycle did not affect structural organization of the MB calyces compared to dark‐reared individuals. MB calyx volumes and bouton numbers positively correlated with body size, whereas bouton density was lower in larger workers. We conclude that, in comparison to the closely related honey bees, neuronal maturation in bumble bees is completed at a much earlier stage, suggesting a strong correlation between neuronal maturation time and lifestyle in both species.     

Polysialytation as a regulator of neural plasticity in rodent learning and aging

Although generally accepted to play an important role in development, the precise functional significance of NCAM remains to be elucidated. Correlative and interventive studies suggest a role for polysialylated NCAM in neurite elaboration. In the adult NCAM polysialylation continues to be expressed in regions of the central nervous system which retain neuroplastic potential. During memory formation modulation of polysialylation on the synapse-enriched isoform of NCAM occurs in the hippocampus. The polysialylated neurons of this structure have been located at the border of the granule cell layer and hilar region of the dentate and their number increases dramatically during memory consolidation. The converse is also true for a profound decline in the basal number of polysialylated neurons occurs with ageing when neural plasticity becomes attenuated. In conclusion, it is suggested that NCAM polysialylation regulates ultrastructural plasticity associated with synaptic elaboration.Abbreviations PSA polysialic acid - NCAM neural cell adhesion molecule - SGL sub-granular cell layer - MF mossy fibers Special issue dedicated to Dr. Robert Balazs.     

Identification of a crown-gall tumor growth factor as GABA

A crown-gall tumor growth factor (TGF-II) isolated from bean leaves inoculated with Agrobacterium tumefaciens strain 13333 is shown to be γ-aminobutyric acid (GABA). This identification is based on the comparative behavior of purified TGF-II and authentic GABA with respect to elution from preparative ion exchange and molecular sieve columns, ninhydrin reaction, TLC, co-chromatography on an automated amino acid analyzer, MS analysis and biological activity. GABA is detected by bioassay only in bean leaves infected with the bacterium and is in growth limiting supply when only a few tumors are present per leaf. GABA promotes tumor growth when as little as 1 ng is applied per leaf.     

Neuronal differentiation of PC12 cells as a result of prevention of cell death by bcl-2

Rat pheochromocytoma PC12 cells die when cultured in serum-free medium. Neurotrophic factors can rescue PC12 cells from cell death, and induce neuronal differentiation. To further investigation the relationship among cell death, survival, and differentiation, the bcl-2 cDNA, which is known to prevent apoptosis in various types of cells, was transfected into PC12 cells. Six monoclonal bcl-2-transfected cell lines were isolated and confirmed to express mRNA and protein product of bcl-2. The wild-type and bcl-2-transfected PC12 cells were kept to adhere to collagen-coated dishes at the inintiation of serum-free experiments to avoid cellular damage due to detachment of the cells by triturtion. Even under the conditions, the control PC12 cells mostly died within 24 h, when cultured in serum-free medium whereas those expressing Bcl-2 survived even for 7 days in serum-free medium. Moreover, outgrowth of long processes in thebcl-2-transfected cells was only observed under the condition to keep the cells attached to the dishes in serum-free medium without any additive neurotrophic or growth factors. Neurofilament medium protein, which is a neuron-specific cytoskeletal component, was also expressed in the differentited cells, suggesting that the long processes in bcl-2-transfected PC12 cells are neurites. However, neuronal differentiation of PC12 cells expressing Bcl-2 was not observed when cultured in serum-containing medium. Accordingly, survival of PC12 cells expressing Bcl-2 under the condition which cells usually die may be accompanied with neuronal differentiation. 1994 John Wiley & Sons, Inc.     

Organization and emergence of a mixed GABA-glycine retinal circuit that provides inhibition to mouse ON-sustained alpha retinal ganglion cells

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Regulation of synaptic vesicle accumulation and axon terminal remodeling during synapse formation by distinct Ca2+ signaling

The synaptic vesicle accumulation and subsequent morphological remodeling of axon terminals are characteristic features of presynaptic differentiation of zebrafish olfactory sensory neurons. The synaptic vesicle accumulation and axon terminal remodeling are regulated by protein kinase A and calcineurin signaling, respectively. To investigate upstream signals of presynaptic differentiation, we focused on Ca²⁺ signaling as Ca²⁺/calmodulin is required for the activation of both calcineurin and some adenylyl cyclases. We here showed that application of Ca²⁺/calmodulin inhibitor or olfactory sensory neuron-specific expression of calmodulin inhibitory peptide suppressed both synaptic vesicle accumulation and axon terminal remodeling. Thus, the trigger of presynaptic differentiation could be Ca²⁺ release from intracellular stores or Ca²⁺ influx. Application of a phospholipase C inhibitor or olfactory sensory neuron-specific expression of inositol 1,4,5-trisphosphate (IP₃) 5-phosphatase suppressed synaptic vesicle accumulation, but not morphological remodeling. In contrast, application of a voltage-gated Ca²⁺ channel blocker or expression of Kir2.1 inward rectifying potassium channel prevented the morphological remodeling. We also provided evidence that IP₃ signaling acted upstream of protein kinase A signaling. Our results suggest that IP₃-mediated Ca²⁺/calmodulin signaling stimulates synaptic vesicle accumulation and subsequent neuronal activity-dependent Ca²⁺/calmodulin signaling induces the morphological remodeling of axon terminals.     

Neuronal hyperexcitability and seizures are associated with changes in glial-neuronal interactions in the hippocampus of a mouse model of epilepsy with mental retardation

Hippocampal excitability and the metabolic glial-neuronal interactions were investigated in 22-week-old mice with motor neuron degeneration (mnd), a model of progressive epilepsy with mental retardation. Mnd mice developed spontaneous spikes in the hippocampus and were more susceptible to kainate-induced seizures compared with control mice. Neuronal hyperexcitability in their hippocampus was confirmed by the selective increase of c-Fos positive nuclei. Glial activation and pro-inflammatory cytokines over-expression were observed in the hippocampus of mnd mice, even in the absence of marked hippocampal neurodegeneration, as suggested by unchanged amounts of neuroactive amino acids and N-acetyl aspartate. Concentration of other amino acids, including GABA and glutamate, was not changed as well. However, ex vivo(13) C magnetic resonance spectroscopy, after simultaneous injection of [1-(13) C]glucose and [1,2-(13) C]acetate, followed by decapitation, showed decreased [1,2-(13) C]GABA formation from hippocampal astrocytic precursors and a marked reduction in [4,5-(13) C]glutamate derived from glutamine. We suggest that astrocyte dysfunction plays a primary role in the pathology and that mnd mice are of value to investigate early pathogenetic mechanism of progressive epilepsy with mental retardation.     

The remodeling index as a practical tool for predicting progression rate during early stages of chronic liver disease

Chronic liver disease (CLD) constitutes a major cause of morbidity and mortality worldwide. Follow-up studies have documented that the majority of patients with CLD never reach the cirrhotic stage, while others display a higher progression rate leading to liver failure at relatively short intervals. This phenomenon has never been adequately explained. Recent evidence suggests that the renin-angiotensin system (RAS) is a major coordinator of chronic liver inflammation and subsequent fibrosis development, a process often termed hepatic remodeling. Combining these data with the “natural neutralizing antibodies theory” led us to the assumption that there could be an intrinsic anti-remodeling mechanism consisted of natural antibodies against components of the RAS. Varying degrees of activation of this defense mechanism could account for the variability in disease progression rate among patients with CLD. Identifying the main components of this mechanism allowed us to develop a ratio, designated remodeling index, as a measure of an individual's predilection towards cirrhosis. We believe that this index could be used as a safe, non-invasive and cost effective tool for assessing progression rate in normotensive patients with early CLD, thus alleviating the need for repeated liver biopsies.     

GTRAP3-18 serves as a negative regulator of Rab1 in protein transport and neuronal differentiation

Glutamate transporter associated protein 3–18 (GTRAP3-18) is an endoplasmic reticulum (ER)-localized protein belonging to the prenylated rab-acceptor-family interacting with small Rab GTPases, which regulate intracellular trafficking events. Its impact on secretory trafficking has not been investigated. We report here that GTRAP3-18 has an inhibitory effect on Rab1, which is involved in ER-to-Golg trafficking. The effects on the early secretory pathway in HEK293 cells were: reduction of the rate of ER-to-Golgi transport of the vesicular stomatitis virus glycoprotein (VSVG), slowed accumulation of a Golgi marker plasmid in pre-Golgi structures after Brefeldin A treatment and inhibition of cargo concentration of the neuronal glutamate transporter excitatory amino-acid carrier 1 (EAAC1) into transpor complexes in HEK293 cells, an effect that could be completely reversed in the presence of an excess of Rab1. In accordance with the known role of Rab1 in neurite formation, overexpression of GTRAP3-18 significantly inhibited the length of outgrowing neurites in differentiated CAD cells. The inhibitory effect of GTRAP3-18 on neurite growth was rescued by co-expression with Rab1, supporting the conclusion that GTRAP 3-18 acted by inhibiting Rab1 action. Finally, we hypothesized that expression of GTRAP3-18 in the brain shoul be lower at stages of active synaptogenesis compared to early developmental stages. This was the case as expression of GTRAP3-18 declined from E17 to P0 and adult rat brains. Thus, we propose a model where protein trafficking and neuronal differentiation are directly linked by the interaction of Rab1 and its regulator GTRAP3-18.     

Transcriptional networks identify synaptotagmin-like 3 as a regulator of cortical neuronal migration during early neurodevelopment

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Gaseous NO2 as a regulator for ammonia oxidation of Nitrosomonas eutropha

Cells of Nitrosomonas eutropha strain N904 that were denitrifying under anoxic conditions with hydrogen as electron donor and nitrite as electron acceptor were unable to utilize ammonium (ammonia) as an energy source. The recovery of ammonia oxidation activity was dependent on the presence of NO₂. Anaerobic ammonia oxidation activity was observed in a helium atmosphere supplemented with 25 ppm NO₂ after 20 h. Ammonia oxidation activity was detected after 2–3 days using an oxic atmosphere with 25 ppm NO₂. In contrast, ammonia consumption started after 8–9 days under oxic conditions without the addition of NO₂; in this case, small amounts of NO and NO₂ were detected and their concentrations increased with increasing ammonia oxidation activities. Hardly any ammonia oxidation was detected when nitrogen oxides were removed by intensive aeration. It would seem, therefore, that NO₂ is the master regulatory signal for ammonia oxidation in Nitrosomonas eutropha. Anaerobic ammonia oxidation activity was inhibited by the addition of NO. This inhibition was partly compensated by either increasing the NO₂ concentration or by using 2,3-dimercapto-1-propane-sulfonic acid as a NO binding substrate. DMPS was inhibitory to nitrification under oxic conditions, while increased amounts of NO or NO₂ led to increased oxidation activities.     

B7-DC induced by IL-13 works as a feedback regulator in the effector phase of allergic asthma

B7-DC is a costimulatory molecule belonging to the B7 family. We previously found that treatment with anti-B7-DC mAb during the effector phase enhances asthma phenotypes in mice. We investigated the mechanisms of B7-DC induction and how B7-DC regulates asthma phenotypes. In allergen-challenged IFN-γ-deficient mice, anti-B7-DC mAb failed to enhance the asthma phenotypes although the induction of B7-DC on dendritic cells of the mice was comparable with that on dendritic cells of wild-type mice. B7-DC on dendritic cells was up-regulated by IL-13 in vitro. The induction of B7-DC on dendritic cells after allergen challenge was attenuated by blockade of IL-13 in vivo. The asthma phenotypes were enhanced in B7-DC-deficient mice, more than in wild-type mice. The enhancement was concurrent with the down-regulation of IFN-γ and up-regulation of IL-13. These results suggest that B7-DC induced by IL-13 works as a feedback regulator by up-regulating IFN-γ production during the effector phase of allergic asthma.