Neurodegeneration in the spinal cord of double knockout (DKO) mice. (A) Spinal cord sections of 44-week-old mice were stained with Klüver-Barrera (KB). Enlarged images indicated spinal lamina XI (motor neuronal region) in the spinal cord as shown by square. (B) The numbers of motor neuron in the spinal lamina XI of lumber spinal cord segments L3 were counted and presented as the number of motor neurons. (C) An enlarged anterior horn—spinal lamina I, II, and III indicated by dashed squares in (A)—of spinal cord sections stained with KB. (D) Thicknesses of spinal lamina II and III were measured in lumber spinal cord segments L3 in wild-type (WT) and DKO mice and presented as the thicknesses of spinal lamina II and III. (E) The numbers of spinal lamina II neurons and marginal cells in spinal lamina I were counted and presented as the number of neurons. The numbers of mice examined are as follows: 44-week-old WT (n = 4; open columns) and DKO (n = 4; closed columns); data are presented as mean ± standard deviation (SD) and were analyzed by Student t test (*P <0.05; **P <0.01; ***P <0.001). The thickness of sections was 5 μm.