Excitotoxicity and Wallerian degeneration as a processes related to cell death in nervous system

Cell death is one of the processes that are currently extensively studied. Beside the commonly used terminology regarding cell death, i.e. apoptosis, autophagy, necrosis, and cornification, in recent years there has been a growing number of additional definitions of this process, such as mitotic catastrophe, anoikis, entosis, paraptosis, pyroptosis, pyronecrosis, excitotoxicity, and Wallerian degeneration, which are described in 2009 by the Nomenclature Committee on Cell Death as atypical. The recent report of that Committee significantly alter the classification and nomenclature of the cell death processes, in which excitotoxicity and Wallerian degeneration have not been taken into account. Thus the present review describes excitotoxicity, and Wallerian degeneration, as two processes associated to cell death phenomena characteristic for nervous system. Excitotoxicity is a neuronal death caused by excessive, or prolonged activation of receptors for the excitatory amino acids. Depending on the intensity of the initiating stimulus, the excitotoxicity may overlap with other types of cell death such as apoptosis and necrosis. Wallerian degeneration is a process that results when a nerve fiber is cut or crushed, in which the part of the axon separated from the neuron's cell body degenerates distal to the injury. Wallerian degeneration is not a typical cell death mechanism, since neurons undergoing this process remain alive.