Alzheimer’s disease (AD) is a fast growing global problem. AD is a form of dementia characterised by the progressive loss of cognitive abilities. Pathologically, the disease is defined by two neuropathological hallmarks: neurofibrillary tangles and amyloid-β plaques. Plaques appear to be toxic to brain tissue and are surrounded by activated microglia and astrocytes, dystrophic neurites and neurons under oxidative stress. When plaques first develop, they are generally small, but in advanced AD, plaques can be much larger. How small plaques may develop into large plaques is still unclear. A number of studies have shown that small plaques grow uniformly over time to give rise to larger plaques. However, this study investigates an alternative hypothesis: that clusters of multiple small plaques merge over time to form large plaques. This hypothesis was inspired by a study that showed that plaques do not deposit in random locations within the brain parenchyma, but rather form in clusters and that these plaque clusters get bigger over time. The aim was to investigate the clustering of plaques in vivo, and follow these clusters over time to see whether they merge together to form a single, larger plaque. This study employed a 2-stage staining technique to follow individual plaques in APPPS1 transgenic mice over time. The fluorescent, amyloid-binding dye Methoxy-X04 was injected into the mice at Day 0 of the experiment. Methoxy-X04 crosses the blood brain barrier and binds stably to plaques for several months and thus labelled the original plaque population. Following 1 day, 1 month or 4 month incubation periods, acute in vivo plaque imaging was performed or the mice sacrificed for post mortem analysis. Antibodies against amyloid-β labelled the state of the plaques at these later time points. Hence this procedure enabled comparison of individual plaque status at different time points and the identification of new plaques that had developed over the incubation time. Detailed analysis of the new and pre-existing plaques revealed two key results. Firstly, that new plaques are more likely to form very close (< 40 µm) to a pre-existing plaque than at further distances. New plaques depositing very close to other plaques formed clusters of plaques in the tissue. Secondly, that clusters of close plaques can fuse over time to form a single large plaque. These two key results provide compelling evidence for a clustering hypothesis of large plaque formation and growth. Together, these data provide in vivo support for the clustering hypothesis by which clusters of small plaques merge together to form single plaques over time. This work expands our understanding of how plaques form and develop in AD and could inform the understanding of plaque clearance strategies to combat AD pathological changes in the brains of patients.

No description available.

No description available.

The present work examines top-down shielding from distraction in visual attention; that is, under which circumstances can the intentions and goals of an observer counteract the bottom-up salience of irrelevant distractors. Several factors of influence will be considered: First, prior experience with distractors, i.e. did observers previously acquire an effective distractor shielding strategy; second, intra- vs. cross-dimensionality of distractors, i.e. are irrelevant distractors defined in the same feature dimension (e.g., shape, color) as the target or in a different feature dimension; third, time, i.e. how effective is distractor shielding early vs. later in processing; and finally, the incentive for effective distractor shielding.

Abnormalities in social behavior are found in almost all psychiatric disorders, such as anxiety, depression, autism and schizophrenia. Thus, comprehension of the neurobiological basis of social interaction is important to better understand numerous pathologies and improve treatments. Several evidences suggest that an alteration of cannabinoid CB1 receptor function could be involved in the pathophysiology of such disorders. However, the role of CB1 receptor is still unclear and its localization on different neuronal subpopulations may produce distinct outcomes. To dissect the role of CB1 receptor on different neuronal population, male mice were used – knockout mice and their respective control littermates [total deletion (CB1-/-); specific deletion on cortical glutamatergic neurons (GluCB1-/-); on GABAergic neurons of the forebrain (GABACB1-/-); or on dopaminergic D1 receptor expressing neurons (D1CB1-/-)], and wild-type (WT) mice treated with CB1 antagonist/inverse agonist SR141716A (3mg/kg). To elucidate the behavioral effects of specific CB1 receptor deficiency, D1CB1-/- mice were submitted to a battery of behavioral tests which included exploration-based tests, depressive-like behavioral tests, and fear-related memory paradigms. It was demonstrated that D1CB1-/- mice exhibited significantly increased contextual and auditory-cued fear, with attenuated within-session extinction. Also, when all mice lines were submitted to different social tasks, involving male or female as the stimulus subject, GluCB1-/- mice showed reduced interest for the social stimulus, as CB1-/- or WT treated with SR141716A mice. D1CB1-/- showed moderate changes in social interest, and GABACB1-/- mice showed the opposite phenotype by spending more time investigating the social stimulus. In conclusion, specific reduction of endocannabinoid signaling in D1-expressing neurons is able to affect acute fear adaptation. Moreover, CB1 receptors specifically modulate social investigation of female mice in a cell-specific manner. These findings support the involvement of cannabinoid signaling in social alterations in psychiatry disorders.

No description available.

No description available.

No description available.

No description available.

Fibronectin-leucine-rich-repeat-transmembrane proteins (FLRTs) are a family of three single pass transmembrane proteins with extracellular leucine rich repeats and a short intracellular domain of largely unknown function. They are broadly expressed in the developing and adult nervous system as well as in other tissues. FLRTs have been implicated in a variety of different developmental processes mainly via two functions: as homophilic cell adhesion molecules, and as repulsive ligands for Unc5-positive cells. Furthermore, they can regulate cell adhesion via control of surface expression of C Cadherin and are involved in FGF signaling. Previously we found that all FLRTs are localized to synapses in the mouse brain and thus investigated a potential involvement of FLRTs in synapse formation. However, using different in vitro and in vivo approaches ranging from HEK293 cell-neuron coculture assays to ultrastructural analysis of synapse density in FLRT3 knock-out mouse brains, I did not find any evidence for an involvement of FLRTs in synapse development. This is in contrast to published results but can be explained by differences in the experimental approaches and timing of the experiments. In collaboration with structural biologists we solved the crystal structure of the FLRT and Unc5 extracellular domains and a complex of both, to gain insight into the structural basis of the adhesive and repulsive functions of FLRTs. We found that homophilic FLRT FLRT and heterophilic FLRT-Unc5 interactions both occur via the FLRT LRR domain but at distinct structural surfaces. Thus, the interactions can be uncoupled. Based on the structural results we developed FLRT and Unc5 glycosylation mutants that specifically inhibit FLRT-FLRT or FLRT-Unc5 interaction and validated them in vitro. I then used these mutants in in utero electroporation experiments to prove that the repulsive effect of Unc5D overexpression in radially migrating neurons that was discovered previously is indeed, at least partially, mediated by FLRT2. Furthermore I found that overexpression of FLRTs inhibits radial migration of cortical pyramidal neurons and this effect is dependent on FLRT-FLRT homophilic interaction and the FLRT intracellular domain but independent of FLRT-Unc5 binding. In summary, the work presented here provides new insights into adhesive and repulsive functions of the FLRT family of proteins in the regulation of cell migration during cortical development.