ABSTRACT
Symptoms of PD develop after the reserve capacity of dopaminergic neurones is exhausted. Recent [18F] fluorodopa PET studies suggest that this probably occurs after at least 50% of dopaminergic neurones have degenerated, lower than previous estimates of 60-80%. However enhanced synthesis of dopamine in surviving neurones (upregulation of striatal dopa decarboxylase activity) and increased dopaminergic stimulation of the striatum may underestimate the true proportion of cell loss.
