Programmed Cell Death

Research into the biochemical basis of cell death began with cellular apoptosis, and in recent years, the programmed cell death (PCD) mechanisms contributing to cell death and apoptosis became synonymous, which has created confusion, because "apoptosis" refers to a particular morphology and not to a biochemical pathway (Fujikawa 2000, 2002). Cell death investigators with a simplistic view of morphology, for example, that cells with shrunken, condensed nuclei are apoptotic, created confusion because cells with shrunken, condensed but intact nuclei are necrotic, not apoptotic (Fujikawa et al. 1999, 2000, 2002, 2007; Fujikawa 2000, 2002).

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Fig. 4.2 Apoptosis and necrosis are morphologically distinct events (compare with Fig. 4.1). (a-d) are H&E-stained sections, (e-h) are TUNEL-stained sections with methyl green counterstain, (i-l) are lower magnification and (m-p) higher magnification electron photomicrographs. (a) and (e) show the left, and (i) and (m) the right piriform cortex of a control rat given normal saline, and (b) and (f) show the left, and (j) and (n) the right piriform cortex of a rat with 3-h kainic acid-induced SE (KASE) and a 24-h recovery period. (c) and (g) show the left, and (k) and (o) the right piriform cortex of a control rat given normal saline, and (d) and (h) show the left, and (l) and (p) the right piriform cortex of a rat with 3-h KASE and a 72-h recovery period. Control light-microscopic sections show round nuclei with nucleoli and reticular chromatin stained with H&E (a and c) and methyl green (e and g). SE light-microscopic sections show necrotic acidophilic neurons with pyknotic (shrunken), condensed nuclei and eosinophilic cytoplasm stained with H&E (b and d) and with TUNEL/methyl green (f and h). TUNEL positivity in the condensed nuclei of necrotic neurons appeared 72 h but not 24 h after SE. Arrows point to necrotic neurons and arrowheads in (h) point to some neurons with TUNEL-positive nuclei. (i) and (k) are electron photomicrographs showing normal nuclei and (m) and (o) normal mitochondria (arrows point to some) in control rats. (j) and (l) show the shrunken, electron-dense necrotic neurons with pyknotic nuclei containing scattered chromatin clumps (much smaller at 72 h recovery) and degenerating cytoplasm with many vacuoles and dilated mitochondria. At higher magnification (n and p) the swollen mitochondria are apparent, containing dark particles (flocculent densities) indicating irreversible damage (arrowheads). Scale bars are 20 |im (a-h), 4 |im (i-l) and 1 |im (m-p) (from Fujikawa et al. 2000, with permission from Elsevier)

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