Brain-derived neurotrophic factor signaling in the HVC is required for testosterone-induced song of female canaries

Testosterone-induced singing in songbirds is thought to involve testosterone-dependent morphological changes that include angiogenesis and neuronal recruitment into the HVC, a central part of the song control circuit. Previous work showed that testosterone induces the production of vascular endothelial growth factor (VEGF) and its receptor (VEGFR2 tyrosine kinase), which in turn leads to an upregulation of brain-derived neurotrophic factor (BDNF) production in HVC endothelial cells. Here we report for the first time that systemic inhibition of the VEGFR2 tyrosine kinase is sufficient to block testosterone-induced song in adult female canaries, despite sustained androgen exposure and the persistence of the effects of testosterone on HVC morphology. Expression of exogenous BDNF in HVC, induced locally by in situ transfection, reversed the VEGFR2 inhibition-mediated blockade of song development, thereby restoring the behavioral phenotype associated with androgen-induced song. The VEGFR2-inhibited, BDNF-treated females developed elaborate malelike song that included large syllable repertoires and high syllable repetition rates, features known to attract females. Importantly, although functionally competent new neurons were recruited to HVC after testosterone treatment, the time course of neuronal addition appeared to follow BDNF-induced song development. These findings indicate that testosterone-associated VEGFR2 activity is required for androgen-induced song in adult songbirds and that the behavioral effects of VEGFR2 inhibition can be rescued by BDNF within the adult HVC. Copyright © 2009 Society for Neuroscience

Theory and Applications of X-ray Standing Waves in Real Crystals

Theoretical aspects of x-ray standing wave method for investigation of the real structure of crystals are considered in this review paper. Starting from the general approach of the secondary radiation yield from deformed crystals this theory is applied to different concreat cases. Various models of deformed crystals like: bicrystal model, multilayer model, crystals with extended deformation field are considered in detailes. Peculiarities of x-ray standing wave behavior in different scattering geometries (Bragg, Laue) are analysed in detailes. New possibilities to solve the phase problem with x-ray standing wave method are discussed in the review. General theoretical approaches are illustrated with a big number of experimental results.Comment: 101 pages, 43 figures, 3 table

A Metric Framework for quantifying Data Concentration

Poor performance of artificial neural nets when applied to credit-related classification problems is investigated and contrasted with logistic regression classification. We propose that artificial neural nets are less successful because of the inherent structure of credit data rather than any particular aspect of the neural net structure. Three metrics are developed to rationalise the result with such data. The metrics exploit the distributional properties of the data to rationalise neural net results. They are used in conjunction with a variant of an established concentration measure that differentiates between class characteristics. The results are contrasted with those obtained using random data, and are compared with results obtained using logistic regression. We find, in general agreement with previous studies, that logistic regressions out-perform neural nets in the majority of cases. An approximate decision criterion is developed in order to explain adverse results

Cytotoxic CD8+ T cell-neuron interactions: perforin-dependent electrical silencing precedes but is not causally linked to neuronal cell death

Cytotoxic CD8(+) T cells are considered important effector cells contributing to neuronal damage in inflammatory and degenerative CNS disorders. Using time-lapse video microscopy and two-photon imaging in combination with whole-cell patch-clamp recordings, we here show that major histocompatibility class I (MHC I)-restricted neuronal antigen presentation and T cell receptor specificity determine CD8(+) T-cell locomotion and neuronal damage in culture and hippocampal brain slices. Two separate functional consequences result from a direct cell-cell contact between antigen-presenting neurons and antigen-specific CD8(+) T cells. (1) An immediate impairment of electrical signaling in single neurons and neuronal networks occurs as a result of massive shunting of the membrane capacitance after insertion of channel-forming perforin (and probably activation of other transmembrane conductances), which is paralleled by an increase of intracellular Ca(2+) levels (within <10 min). (2) Antigen-dependent neuronal apoptosis may occur independently of perforin and members of the granzyme B cluster (within approximately 1 h), suggesting that extracellular effects can substitute for intracellular delivery of granzymes by perforin. Thus, electrical silencing is an immediate consequence of MHC I-restricted interaction of CD8(+) T cells with neurons. This mechanism is clearly perforin-dependent and precedes, but is not causally linked, to neuronal cell death

Relationships of peripheral IGF-1, VEGF and BDNF levels to exercise-related changes in memory, hippocampal perfusion and volumes in older adults

Animal models point towards a key role of brain-derived neurotrophic factor (BDNF), insulin-like growth factor-I (IGF-I) and vascular endothelial growth factor (VEGF) in mediating exercise-induced structural and functional changes in the hippocampus. Recently, also platelet derived growth factor-C (PDGF-C) has been shown to promote blood vessel growth and neuronal survival. Moreover, reductions of these neurotrophic and angiogenic factors in old age have been related to hippocampal atrophy, decreased vascularization and cognitive decline. In a 3-month aerobic exercise study, forty healthy older humans (60 to 77years) were pseudo-randomly assigned to either an aerobic exercise group (indoor treadmill, n=21) or to a control group (indoor progressive-muscle relaxation/stretching, n=19). As reported recently, we found evidence for fitness-related perfusion changes of the aged human hippocampus that were closely linked to changes in episodic memory function. Here, we test whether peripheral levels of BDNF, IGF-I, VEGF or PDGF-C are related to changes in hippocampal blood flow, volume and memory performance. Growth factor levels were not significantly affected by exercise, and their changes were not related to changes in fitness or perfusion. However, changes in IGF-I levels were positively correlated with hippocampal volume changes (derived by manual volumetry and voxel-based morphometry) and late verbal recall performance, a relationship that seemed to be independent of fitness, perfusion or their changes over time. These preliminary findings link IGF-I levels to hippocampal volume changes and putatively hippocampus-dependent memory changes that seem to occur over time independently of exercise. We discuss methodological shortcomings of our study and potential differences in the temporal dynamics of how IGF-1, VEGF and BDNF may be affected by exercise and to what extent these differences may have led to the negative findings reported here

Identification of a Novel Signaling Pathway and Its Relevance for GluA1 Recycling

We previously showed that the serum- and glucocorticoid-inducible kinase 3 (SGK3) increases the AMPA-type glutamate receptor GluA1 protein in the plasma membrane. The activation of AMPA receptors by NMDA-type glutamate receptors eventually leads to postsynaptic neuronal plasticity. Here, we show that SGK3 mRNA is upregulated in the hippocampus of new-born wild type Wistar rats after NMDA receptor activation. We further demonstrate in the Xenopus oocyte expression system that delivery of GluA1 protein to the plasma membrane depends on the small GTPase RAB11. This RAB-dependent GluA1 trafficking requires phosphorylation and activation of phosphoinositol-3-phosphate-5-kinase (PIKfyve) and the generation of PI(3,5)P2. In line with this mechanism we could show PIKfyve mRNA expression in the hippocampus of wild type C57/BL6 mice and phosphorylation of PIKfyve by SGK3. Incubation of hippocampal slices with the PIKfyve inhibitor YM201636 revealed reduced CA1 basal synaptic activity. Furthermore, treatment of primary hippocampal neurons with YM201636 altered the GluA1 expression pattern towards reduced synaptic expression of GluA1. Our findings demonstrate for the first time an involvement of PIKfyve and PI(3,5)P2 in NMDA receptor-triggered synaptic GluA1 trafficking. This new regulatory pathway of GluA1 may contribute to synaptic plasticity and memory