CD4(+) T cell-mediated facial motoneuron survival after injury: Distribution pattern of cell death and rescue throughout the extent of the facial motor nucleus.

We have previously demonstrated that CD4(+) T cells transiently rescue facial motoneurons (FMN) from axotomy-induced death in immunodeficient mice. Three subpopulations of motoneurons have been observed within the facial motor nucleus following axotomy: one that always survives axotomy (50%), one that is amenable to rescue from axotomy-induced death through the addition of neurotrophic factors or CD4(+) T cells (30-40%), and one that always dies after axotomy (10-15%). The objective of this study was to anatomically map the extent of axotomy-induced cell death and immune cell rescue in the facial nucleus to study the differential survival capabilities of each subpopulation. Wild-type (WT) mice, recombinase activating gene 2 knockout (RAG-2 KO) mice, and RAG-2 KO mice reconstituted with CD4(+) T cells were subjected to right facial nerve axotomy. At 4 weeks post-axotomy, topographical mapping of axotomy-induced cell death throughout the rostro-caudal extent of the facial nucleus was accomplished in accordance with previously published maps of the subnuclear arrangement of the facial neurons. The results indicate that all 3 subpopulations of FMN can be found in each of the subnuclear groups throughout the entire rostro-caudal extent of the facial nucleus. These data are discussed in context of recent work in amyotrophic lateral sclerosis, a fatal motoneuron disease.