Senile plaques accumulate over the course of decades in the brains of patients with Alzheimer's disease. A fundamental tenet of the amyloid hypothesis of Alzheimer's disease is that the deposition of amyloid-β precedes and induces the neuronal abnormalities that underlie dementia 1 . This idea has been challenged, however, by the suggestion that alterations in axonal trafficking and morphological abnormalities precede and lead to senile plaques 2 . The role of microglia in accelerating or retarding these processes has been uncertain. To investigate the temporal relation between plaque formation and the changes in local neuritic architecture, we used longitudinal in vivo multiphoton microscopy to sequentially image young APPswe/PS1d9xYFP (B6C3-YFP) transgenic mice 3 . Here we show that plaques form extraordinarily quickly, over 24 h. Within 1-2 days of a new plaque's appearance, microglia are activated and recruited to the site. Progressive neuritic changes ensue, leading to increasingly dysmorphic neurites over the next days to weeks. These data establish plaques as a critical mediator of neuritic pathology.To explore the formation of amyloid plaques and to determine the effects of newly formed dense-cored plaques on the microarchitecture of the brain, we have developed a novel in vivo multiphoton imaging technique. This recognizes newly formed plaques and allows monitoring of their immediate vicinity thereafter to determine the rate of their formation and the temporal sequence of pathophysiological events. We imaged young (5-to 6-month-old) B6C3-YFP mice, an age when plaques begin to appear 4 (Fig. 1). We used three-colour imaging to establish fiduciary markers for repeated imaging: YFP positive neurons, dendrites and axons in the cortex, methoxy-XO4-labelled fibrillar amyloid-β deposits in the parenchyma and on vessel walls, and a fluorescent angiogram with Texas red dextran to image blood vessels. A volume of cortex (lamina I-III) that initially did not contain plaques was re-imaged until repeat imaging detected a new plaque, establishing its 'birthday'. To ensure that the appearance of a new plaque did not simply reflect a greater depth of imaging or a slightly different imaging volume, we went through each image stack and compared NIH Public Access Author ManuscriptNature. Author manuscript; available in PMC 2012 January 23. We postulated that we would occasionally observe the appearance and growth of new plaques within an imaging volume if the time interval between imaging sessions was long enough. From one weekly imaging session to the next, most of the sites remained unchanged ( Supplementary Fig. 1a-c). However, we identified 14 new plaques: instances in which a plaque appeared in a second imaging session in a volume that had clearly been unoccupied in the first images one week earlier (Fig. 1a-c).We examined the spatial relation between newly identified plaques and blood vessels. Measurements of the distance between vessel wall and the edge of a plaque confirmed that dense-core plaques develop...

Alzheimer's disease (AD) is characterized by senile plaques and neurodegeneration although the neurotoxic mechanisms have not been completely elucidated. It is clear that both oxidative stress and inflammation play an important role in the illness. The compound curcumin, with a broad spectrum of anti-oxidant, anti-inflammatory, and anti-fibrilogenic activities may represent a promising approach for preventing or treating AD. Curcumin is a small fluorescent compound that binds to amyloid deposits. In the present work we used in vivo multiphoton microscopy (MPM) to demonstrate that curcumin crosses the blood-brain barrier and labels senile plaques and cerebrovascular amyloid angiopathy (CAA) in APPswe/ PS1dE9 mice. Moreover, systemic treatment of mice with curcumin for 7 days clears and reduces existing plaques, as monitored with longitudinal imaging, suggesting a potent disaggregation effect. Curcumin also led to a limited, but significant reversal of structural changes in dystrophic dendrites, including abnormal curvature and dystrophy size. Together, these data suggest that curcumin reverses existing amyloid pathology and associated neurotoxicity in a mouse model of AD. This approach could lead to more effective clinical therapies for the prevention of oxidative stress, inflammation and neurotoxicity associated with AD.

Amyloid ␤ (A␤)-containing plaques are surrounded by dystrophic neurites in the Alzheimer's disease (AD) brain, but whether and how plaques induce these neuritic abnormalities remain unknown. We tested the hypothesis that soluble oligomeric assemblies of A␤, which surround plaques, induce calcium-mediated secondary cascades that lead to dystrophic changes in local neurites. We show that soluble A␤ oligomers lead to activation of the calcium-dependent phosphatase calcineurin (CaN) (PP2B), which in turn activates the transcriptional factor nuclear factor of activated T cells (NFAT). Activation of these signaling pathways, even in the absence of A␤, is sufficient to produce a virtual phenocopy of A␤-induced dystrophic neurites, dendritic simplification, and dendritic spine loss in both neurons in culture and in the adult mouse brain. Importantly, the morphological deficits in the vicinity of A␤ deposits in a mouse model of AD are ameliorated by CaN inhibition, supporting the hypothesis that CaN-NFAT are aberrantly activated by A␤ and that CaN-NFAT activation is responsible for disruption of neuronal structure near plaques. In accord with this, we also detect increased levels of an active form of CaN and NFATc4 in the nuclear fraction from the cortex of patients with AD. Thus, A␤ appears to mediate the neurodegeneration of AD, at least in part, by activation of CaN and subsequent NFAT-mediated downstream cascades.