Neuronal Death Occurs In Different Forms

Neurons can die in different ways (Fig. 9). The death of cells has been classified generally as two distinct types: apoptosis and necrosis. These two forms of cellular degeneration are classified differently because they are believed to differ structurally and biochemically. Apoptosis is generally regarded as physiological cell death and is considered to be an organized PCD that is mediated by active, intrinsic mechanisms through which certain molecular pathways are activated to initiate apoptosis (Table VI). In contrast, necrosis is cell death resulting from a failure to sustain home-ostasis due to extrinsic insults to the cell (e.g., osmotic, thermal, toxic, traumatic). The process of cellular necrosis involves damage to the structural and functional integrity of the cell plasma membrane, a rapid influx of ions and H2O, and, subsequently, dissolution c

Figure 9 Neuronal cell death occurs as an apoptosis-necrosis continuum. According to the traditional binary scheme for cell death, a neuron (A) can die by either necrosis (B) or apoptosis (C). These forms of cell death were thought to be structurally distinct (representative images of cells are shown) and mutually exclusive. With cellular necrosis (B), which occurs as groups of cells, massive damage to organelles and the plasma membrane occurs with the release of cellular constituents. The nucleus (Nu) undergoes fragmentation, with the condensation of nuclear material being irregular and distinct from that occurring in apoptosis. In necrotic neurons the nucleolus can remain intact. In contrast, apoptosis (C) is an organized form of cell death that occurs generally as isolated cells within groups of cells. The nucleus containing the DNA is packaged into uniformly condensed masses (shown by the round or elliptical black structures), and the surrounding cytoplasm becomes shrunken and condensed (shown by the gray) with the organelles generally preserved until end stage apoptosis. Small fragments of cell cytoplasm surrounding packaged chromatin bud from the dying cell and are engulfed by glial cells. The concept of the apoptosis-necrosis continuum is based on the observation that neurons can die with a structure that is a hybrid of apoptosis and necrosis (D). The nuclear (Nu) and cytoplasmic changes are intermediate between those occurring in apoptosis and necrosis. The packaging of the chromatin occurs as large irregular masses in the nucleus. In the cytoplasm, some mitochondria remain intact whereas others are swollen.

Figure 9 Neuronal cell death occurs as an apoptosis-necrosis continuum. According to the traditional binary scheme for cell death, a neuron (A) can die by either necrosis (B) or apoptosis (C). These forms of cell death were thought to be structurally distinct (representative images of cells are shown) and mutually exclusive. With cellular necrosis (B), which occurs as groups of cells, massive damage to organelles and the plasma membrane occurs with the release of cellular constituents. The nucleus (Nu) undergoes fragmentation, with the condensation of nuclear material being irregular and distinct from that occurring in apoptosis. In necrotic neurons the nucleolus can remain intact. In contrast, apoptosis (C) is an organized form of cell death that occurs generally as isolated cells within groups of cells. The nucleus containing the DNA is packaged into uniformly condensed masses (shown by the round or elliptical black structures), and the surrounding cytoplasm becomes shrunken and condensed (shown by the gray) with the organelles generally preserved until end stage apoptosis. Small fragments of cell cytoplasm surrounding packaged chromatin bud from the dying cell and are engulfed by glial cells. The concept of the apoptosis-necrosis continuum is based on the observation that neurons can die with a structure that is a hybrid of apoptosis and necrosis (D). The nuclear (Nu) and cytoplasmic changes are intermediate between those occurring in apoptosis and necrosis. The packaging of the chromatin occurs as large irregular masses in the nucleus. In the cytoplasm, some mitochondria remain intact whereas others are swollen.

of the cell. Thus, cellular necrosis is induced not by an intrinsic program within the cell per se (as in PCD) but by abrupt or slow homeostatic perturbations and departures from physiological conditions. It has been realized that an abnormal activation of PCD in brain and spinal cord neurons may also play a role in the disease process in humans with neurodegenerative disorders; therefore, deciphering of the contributions of the different types of cell death in degenerative diseases of the human CNS could help to develop treatments for these diseases. These treatments could possibly be drugs that inhibit the actions of key enzymes, ion channels in cell membranes, or numerous other proteins, as well as drugs (e.g., antioxidants) that block or inactivate the production of toxic chemicals (e.g., free oxygen radicals) that are generated during the process of neuronal death.

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Understanding And Treating Autism

Understanding And Treating Autism

Whenever a doctor informs the parents that their child is suffering with Autism, the first & foremost question that is thrown over him is - How did it happen? How did my child get this disease? Well, there is no definite answer to what are the exact causes of Autism.

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