In these models of PD the neurotoxin-induced degeneration of the A9 neurons appears to be dependent upon the activity of tumor necrosis factor alpha (TNF) which is elevated in the striatal tissue of mice and rats following the injection of MPTP or 6-hydroxydopamine (Mogi et al., 1999; Sriram et al., 2002). The gene discussed is TNF; the disease is Parkinson disease.