Aβ40, Aβ42, and oAβ ELISAs

hAβ₄₀ and hAβ₄₂ levels in conditioned media from primary neuronal cultures as well as soluble and insoluble Aβ₄₀ and Aβ₄₂ tissue homogenates from biochemically fractionated mouse brains were measured using human Aβ₄₀ and Aβ₄₂ ELISA kits according to the manufacturer’s protocols (Biosource, Invitrogen). Insoluble amyloid fractions from mouse tissue homogenates containing 70% formic acid were first neutralized by performing a 1:100 dilution in a solution of 1.0 M Tris (pH 11) prior to performing dilution series in ELISA diluent buffer supplied with ELISA kits. Soluble amyloid fractions were diluted as normal directly in ELISA diluent buffer. Plates were read at 450 nm using a Spectra Max Plus plate reader (Molecular Devices, Sunnyvale, CA). ELISA-based detection of oAβ was performed as described previously.⁵⁹ For detection of oAβ, total tissue homogenates in PBS were utilized for oAβ ELISAs, as the addition of detergent is known to induce artifactual Aβ oligomerization. Moreover, albuminized tubes were used for the handling of total tissue homogenates to block nonspecific oAβ binding sites on the plastic tubes.