receptor. Immunoreaction for the 5-HT2A receptor in the prefrontal cortex of a normal aging (a, c) and an Alzheimer patient (b, d), cresyl violet counterstain. Both large pyramidal cells (arrowheads) and small interneurons (arrows) are stained. Note the reduction in labeled cells in the cortex of the Alzheimer patient (b, d). a, b: x200; c, d; x400.