Motor neuron disease and model systems: aetiologies, mechanisms and therapies.

The phenotypes of many neurological diseases, including motor neuron disease (amyotrophic lateral sclerosis; ALS) and Alzheimer's disease (AD), are determined by the vulnerabilities of populations of nerve cells and the character/ evolution of cellular abnormalities. Because different cell types respond selectively to individual trophic factors, these factors may be useful in ameliorating pathology in cells that express their cognate receptors. To test therapies for ALS and AD, investigators require model systems. Although there are a variety of models of ALS, two models are particularly attractive: transgenic mice that express human superoxide dismutase 1 (SOD-1) mutations linked to familial ALS develop paralysis associated with a gain of adverse property of the mutant SOD; and axotomy of facial axons in neonatal rats, a manipulation that causes retrograde cell degeneration, which can be ameliorated by several trophic factors.