Fig. 4. Bcl-xL overexpression protects motor neurons from axotomy-induced cell death. A, Ret-labeled motor neurons in the facial nucleus of a nonaxotomized wild-type mouse. Note the labeling in the medial and lateral (circled) portion of the nucleus. Inset, High-magnification view of Ret labeling in wild-type neurons. B, Ret-labeled motor neurons in the facial nucleus of an axotomized wild-type mouse. Cells in the lateral portion of the nucleus have degenerated (circled), and Ret is no longer detectable except in the medial portion of the nucleus, which is not affected by this lesion paradigm. C, Ret-labeled motor neurons in the facial nucleus of an axotomized transgenic Bcl-xL mouse (line 7193). Many lateral motor neurons survive axotomy (circled), although they are reduced in size.Inset, High-magnification view of Ret labeling in the rescued lateral lateral motor neurons. (Compare the size of motor neurons in the inset in C with the insetin A.) D, Cresyl violet-stained motor neurons in the facial nucleus of an axotomized transgenicBcl-xL mouse. E, High-magnification bright-field view of facial motor neurons 7 d after axotomy in transgenic line 7194. Arrows indicate rescued motor neurons. F, Dark-field view of the same section as in E, labeled with the SV40 probe to detect transgene-derived sequences. Note the high degree of correlation between the rescued motor neurons shown in E and the expression of transgene-derived Bcl-xL shown inF (arrows). Scale bars:A–D, 100 μm; E–F, insets, 25 μm.