Increased cell death in hippocampal slice cultures from trkB (−/−) mice. A, B, Cresyl violet-stained sections show the normal structure of hippocampal slices in both control (A, C) and trkB (−/−) mice (B, D) after 3 d in culture. C, D, Higher-magnification micrographs show an increase in pyknotic nuclei in the CA3 region of trkB (−/−) mutant mice (D) when compared with control mice (C). CA1, Pyramidal layer CA1;CA3, pyramidal layer CA3; DG, dentate gyrus; SB, subiculum. Magnification: A, B, 10×; C, D, 40×.