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Bax‐dependent and ‐independent death of motoneurons after facial nerve injury in adult mice
Author(s) -
Park Okhee,
Lee Kea Joo,
Rhyu Im Joo,
Geum Dongho,
Kim Hyun,
Buss Robert,
Oppenheim Ronald W.,
Sun Woong
Publication year - 2007
Publication title -
european journal of neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.346
H-Index - 206
eISSN - 1460-9568
pISSN - 0953-816X
DOI - 10.1111/j.1460-9568.2007.05787.x
Subject(s) - axotomy , programmed cell death , avulsion , apoptosis , avulsion injury , medicine , microglia , necrosis , inflammation , nerve injury , pathology , biology , anatomy , endocrinology , anesthesia , central nervous system , biochemistry
Nerve injury‐induced neuronal death may occur after accidental trauma or nerve inflammation. Although the response to facial root avulsion has been examined in rodent models, there are conflicting results as to whether motoneuron (MN) death is mediated by apoptosis or necrosis. We examined the response of MNs and proximal nerves after facial nerve avulsion in adult mice. Following facial nerve avulsion in 4–5‐week‐old mice, we observed a progressive reduction of MNs such that by 4 weeks less than 10% of avulsed MNs remained compared with the control side. The profile of MN degeneration was distinct from axotomy‐induced responses. For example, the onset of MN death was more rapid, and the extent of MN loss was greater compared with axotomy. Furthermore, the degeneration of oligodendrocytes and the activation of microglia were increased in the proximal nerve after avulsion. Ultrastructural observations suggested that root avulsion mainly induces non‐apoptotic neuronal death, although a small subset of neurons appeared to die via apoptosis. To evaluate the contribution of apoptotic death, we evaluated MN responses in Bax‐knockout (KO) mice in which neurons are rescued from apoptotic death. Surprisingly, although the majority of Bax‐KO mice exhibited only a moderate MN loss after avulsion, a subset of Bax‐KO mice (25%) exhibited extensive MN death and injury‐induced changes in the nerve that were indistinguishable from events in wild‐type littermates. These results suggest that both Bax‐dependent and ‐independent forms of cell death are evoked by root avulsion, and that programmed cell death may be involved in triggering a robust necrotic response.