A novel peptide derived from vascular endothelial growth factor prevents amyloid beta aggregation and toxicity.

Amyloid-ß oligomers (Aßo) are the most pathologically relevant Aß species in Alzheimer's disease (AD), because they induce early synaptic dysfunction that leads to learning and memory impairments. In contrast, increasing VEGF (Vascular Endothelial Growth Factor) brain levels have been shown to improve learning and memory processes, and to alleviate Aß-mediated synapse dysfunction. Here, we designed a new peptide, the blocking peptide (BP), which is derived from an Aßo-targeted domain of the VEGF protein, and investigated its effect on Aß-associated toxicity. Using a combination of biochemical, 3D and ultrastructural imaging, and electrophysiological approaches, we demonstrated that BP strongly interacts with Aßo and blocks Aß fibrillar aggregation process, leading to the formation of Aß amorphous aggregates. BP further impedes the formation of structured Aßo and prevents their pathogenic binding to synapses. Importantly, acute BP treatment successfully rescues long-term potentiation (LTP) in the APP/PS1 mouse model of AD, at an age when LTP is highly impaired in hippocampal slices. Moreover, BP is also able to block the interaction between Aßo and VEGF, which suggests a dual mechanism aimed at both trapping Aßo and releasing VEGF to alleviate Aßo-induced synaptic damage. Our findings provide evidence for a neutralizing effect of the BP on Aß aggregation process and pathogenic action, highlighting a potential new therapeutic strategy.

A critical role for VEGF and VEGFR2 in NMDA receptor synaptic function and fear-related behavior.

Vascular endothelial growth factor (VEGF) is known to be required for the action of antidepressant therapies but its impact on brain synaptic function is poorly characterized. Using a combination of electrophysiological, single-molecule imaging and conditional transgenic approaches, we identified the molecular basis of the VEGF effect on synaptic transmission and plasticity. VEGF increases the postsynaptic responses mediated by the N-methyl-D-aspartate type of glutamate receptors (GluNRs) in hippocampal neurons. This is concurrent with the formation of new synapses and with the synaptic recruitment of GluNR expressing the GluN2B subunit (GluNR-2B). VEGF induces a rapid redistribution of GluNR-2B at synaptic sites by increasing the surface dynamics of these receptors within the membrane. Consistently, silencing the expression of the VEGF receptor 2 (VEGFR2) in neural cells impairs hippocampal-dependent synaptic plasticity and consolidation of emotional memory. These findings demonstrated the direct implication of VEGF signaling in neurons via VEGFR2 in proper synaptic function. They highlight the potential of VEGF as a key regulator of GluNR synaptic function and suggest a role for VEGF in new therapeutic approaches targeting GluNR in depression.

Characterization of calbindin-positive cones in primates.

The aim of this study is to characterize calbindin-positive photoreceptors and their opsin content in the retina of nocturnal prosimians (Microcebus murinus), New World monkeys (Callithrix jacchus), Old World monkeys (Macaca fascicularis), and humans. To identify the calbindin and opsin content of cones, combined multiple labeling with different fluorescent probes, antibodies directed against calbindin, short, and mid-long wavelength opsins, and lectin peanut agglutinin cytochemistry were used. With the exception of Microcebus, calbindin is present in the cones of all primates but is absent from rods. The distribution of calbindin is similar in human and macaque cones, with dense label in the inner segment, cell body, axon and cone pedicle. Cones in marmoset also show dense staining in the cell body, axon and pedicle but only light label in the inner segment. Primate cone outer segments do not contain calbindin. In the primates studied, three patterns of calbindin and opsin localization are observed. In macaque and marmoset all short and mid-long wavelength cones contain calbindin. In humans, all mid-long wavelength cones contain calbindin whereas all short wavelength cones are devoid of calbindin as confirmed by confocal microscopy. In the nocturnal prosimian Microcebus none of the mid-long or short wavelength cones contain calbindin. In addition to primates, calbindin is absent in cones of other nocturnal species but is present in cones of diurnal species suggesting a difference in the role of calbindin possibly related to the adaptational states or other photoreceptor properties.

Analysis of immunohistochemical label of Fos protein in the suprachiasmatic nucleus: comparison of different methods of quantification.

The induction of the proto-oncogene c-fos, and its phosphoprotein product Fos, has been extensively used to study the effects of light on the circadian pacemaker in the suprachiasmatic nucleus (SCN). Experimental approaches to the quantification of Fos induction have mainly been based on immunohistochemistry and subsequent measure of Fos immunoreactivity (IR) in sections of the SCN. In this study, the authors compare several methods of quantification using optical density image analysis or counts of Fos-IR labeled cells. To assess whether optical density measures using image analysis reflect the amount of Fos in brain tissue, the authors developed standards of known concentrations of Fos protein in an agar matrix. The agar standards were sectioned and treated simultaneously with sections of the SCN from animals exposed to different levels of irradiance. Optical density was found to be proportional to the quantity of Fos in the sections, indicating that this measure accurately reflects relative levels of Fos protein induction. Quantification by optical density analysis allows an objective measure in which the various parameters, conditions of illumination, and threshold can be maintained constant throughout the analysis. Counting cells by visual observation is more subjective because threshold values cannot be precisely defined and can vary according to the observer, illumination, degree of label, and other factors. In addition, cell counts involving direct visual observation, automated cell counts, or stereological methods do not take into account the difference in the density of label between cells, thus giving equal weight to lightly or densely stained cells. These measures are more or less weakly correlated with measures of optical density and thus do not accurately reflect the amount of bound Fos protein in the tissue sections. In contrast, labeled surface area as measured by image analysis shows a linear relationship with optical density. The main outcome of this study is that computer-assisted image analysis provides an accurate and rapid method to determine the relative amount of Fos protein in the SCN and the effects of light on intracellular signaling mechanisms involved in the circadian clock.

Axonal surface molecules act in combination with semaphorin 3a during the establishment of corticothalamic projections.

Interactions between growing axons are considered to play important roles for the establishment of precise neuronal connections during the development of the nervous system. Here we used time-lapse imaging techniques to examine the behavior of neocortical and thalamic axons when they encounter each other in vitro. Results indicate that axonal growth cones are able to respond to specific cues expressed on the surface of fibers. Thalamic growth cones often extended along the surface of other thalamic axons and, likewise, cortical growth cones formed fascicles with cortical axons. In contrast, after contacts between cortical and thalamic fibers, in most cases growth cones collapsed and retracted from the axons. Collapse assays using membrane preparations from cortical or thalamic explants demonstrated the existence of cell-type specific collapsing factors whose activity was enhanced by a member of the semaphorin protein family, Sema3A (expressed in the thalamocortical pathway), as it increased the rate of homotypic fasciculations and at the same time amplified the segregation between cortical and thalamic axons. The interaction between axonal surface molecules and environmental cues might mediate the segregation of afferent and efferent fiber tracts in the neocortical white matter.

Visual latencies in cytochrome oxidase bands of macaque area V2.

Cytochrome oxidase bands in area V2 of the primate visual cortex constitute separate relays for parallel channels relaying information from area V1 to other extrastriate cortical areas. We investigated whether information is transferred at the same speed in the different channels by measuring the latencies of neurons in different cytochrome oxidase bands identified by the presence or absence of retrogradely labeled cells from injections in area V4. Results show that neurons in the thick and pale bands respond 20 msec earlier than those in the thin bands. We also found that color-selective neurons respond later than neurons with no selectivity for color and that direction-selective neurons have shorter latencies than neurons with no selectivity for the direction of stimulus movement.