Elevated levels of 3-nitrotyrosine early and throughout disease progression in transgenic mice expressing G37R SOD1 (line 42). Ratios of 3-nitrotyrosine to tyrosine were measured in cervical and lumbar spinal cord and brain stem of control mice, transgenic mice overexpressing wild-type human SOD1 (hSOD76), and transgenic mice expressing human mutant G37R SOD1 (line 42). (A) At 6 weeks of age [n = 12, 10, 11 (lumbar spinal cord); n = 13, 11, 11 (cervical spinal cord); n = 13, 6, 6 (brain stem)]. (B) At 20 weeks of age [n = 7, 3, 5 (lumbar spinal cord); n = 7, 3, 5 (cervical spinal cord); n = 7, 3, 5 (brainstem)]. Values are expressed as ratios (3-nitrotyrosine/tyrosine) × 1000.