Characterization of oligomeric forms of Aβ1-42 peptide. (a) Representative Western blot showing a broad range of molecular weight protein markers (lane 1), Aβ monomers (lane 2), and Aβ oligomers incubated at 4°C for 24 h (lane 3). Aβ was detected using the monoclonal 6E10 anti-Aβ antibody. Arrows show monomers and oligomers migrating at ~18 kDa. (b) Characterization of Aβ preparation (4°C for 24 h) by TEM showed mainly Aβ oligomers (white arrowheads) and very few protofibrils (black arrow). (c) Ca2+ recordings of cultured neurons showed a robust increase in the cytosolic Ca2+ concentration induced by Aβ oligomers, but not monomers, both at 5 μM, which is reduced by the NMDA antagonist MK801 (50 μM).