In one or a plurality of embodiments, there is provided a target molecule of amylospheroid, which is expressed in mature neurons and to which the amylospheroid binds to induce death of cells. Further, in one or a plurality of embodiments, there is provided a method and a substance for inhibiting death of mature neurons induced by the amylospheroid. In one aspect, the present disclosure relates to a use of Na+/K+-ATPase α3 as a binding target molecule of amylospheroid. In another aspect, the present disclosure relates to a method for suppressing death of mature neurons induced by the amylospheroid, including inhibiting protein-protein interaction between the amylospheroid and the Na+/K+-ATPase α3, and the like.