The mouse mutant Motor neuron degeneration (Mnd) displays an adult-onset progressive degeneration of upper and lower motor neurons, with mild symptoms recognizable at 6 months, leading to spastic paralysis and premature death at 10-12 months on the C57B1/6 background. Despite this late onset, abnormally-accumulating autofluorescent material can be seen in both the spinal cord and other regions as early as the first month. This pigmented material is present in both increasing numbers of cells, and in increasing amounts within individual cells, as the animals age. Motor neurons then go on to degenerate, while most other cell types stabilize. The level of pathological involvement, well before the onset of clear clinical symptoms, suggests that the full degenerative process is an extremely gradual and protracted one with some selectivity for motor neurons.