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Why is it, in PD, that the cells (neurons) known to be affected are confined to a very specific class, namely those neurons which emit and employ the neurotransmitter dopamine, mainly in the substantia nigra, while other parts of the vastly complex nervous system are exempt? If the effect is due to some exogenous poison, as many suspect, why does this poison, for example an oxidizing free radical, affect only the substantia nigra? I think it is because the neurons in question aren't killed by some external influence, they commit suicide. The process is called apoptosis. As the brain develops in childhood, neurons proliferate and differentiate into a multitude of specific functions, greatly in excess of what is actually needed in the adult brain and nervous system. Surplus neurons receive a signal, presumably specific to each particular type of neuron, that tells them to die, or at least to atrophy and become inactive. Researchers are exploring the action of certain proteins called kinases, which are activated by various extracellular stimuli, to regulate the process of apoptosis. One kinase promotes apoptosis, another inhibits it, and normally the two effects are kept in balance. The bottom line? When science learns what the stimuli in question are (e.g., an excess of dopamine) and how to control them, it should then be possible to halt the onset and progression of PD, as well as other degenerative diseases. Further reading? Science, 24 November 1995: 1277, 1326ff. J. R. Bruman (818) 789-3694 3527 Cody Road Sherman Oaks CA 91403