P1‐029: A comparison of conventional versus push‐pull microdialysis for the detection of amyloid β in the mouse brain

Strong evidence supports a central role for beta-amyloid protein (Aß) in the pathogenesis of Alzheimer's disease (AD). Much attention has been focused on toxic forms of soluble and insoluble Aß. Gaining an understanding of the soluble species of Aß that are released from neurons may provide greater insight into the pathophysiology of AD. Previous work has demonstrated the ability to measure extracellular concentrations of soluble Aß in the brains of freely moving animals using in vivo microdialysis (Cirrito et al., 2003). We have compared two distinct microdialysis methods, conventional microdialysis and push-pull microdialysis, to monitor Aß levels in the brain interstitial fluid (ISF) of AD transgenic animals. In addition, we examined the effects of gamma secretase inhibition with ELN44989 on the levels of Aß (1-x) and Aß (1-40). Conventional microdialysis is limited by the membrane cut-off size and generally allows measurement of molecules smaller than 30-60 KDa. Conversely, push-pull microdialysis allows for detection of molecules up to 1-3 MDa offering the advantage of detecting a broader range of soluble oligomeric Aß species. Both methods were employed in this study, followed by ELISA measurement of Aß (1-x) and Aß (1-40). Aß (1-x) and Aß (1-40) in dialysates from conventional microdialysis were 243 pg/ml and 125 pg/ml, respectively. Using push pull microdialysis, levels of Aß (1-x) and Aß (1-40) were notably higher. In both cases, ISF Aß levels were significantly reduced following systemic administration of ELN44989. We conclude that push-pull microdialysis provides distinct advantages over conventional microdialysis for the detection of Aß species in the rodent brain, and can provide greater insight into role of multiple Abeta species (including high molecular weight) to pathological and functional endpoints.