Alzheimer's disease (AD) and Parkinson's disease (PD), the two most common types of adult-onset chronic degenerative disorders of the CNS1,2 are characterized by degeneration of certain populations of neurons with relative sparing of other groups of nerve cells3,4. Dysfunction of at-risk neurons is associated with several types of cytoskeletal pathology. As these nerve cells degenerate alterations occur in neurotransmitter markers. Dysfunction/death of neurons in these systems result in the clinical syndromes of AD and PD. The bradykinesia and rigidity of PD are associated with lesions in the nigrostriatal dopaminergic system, whereas the dementia of AD is attributed to abnormalities of nerve cells in monoaminergic brainstem nuclei, in the basal forebrain cholinergic system, and in neuronal populations within the amygdala, hippocampus, and neocortex. On the basis of clinical and histopathological criteria, AD and PD are distinguished from other adult-onset degenerative neurological disorders, including Pick's disease, progressive supranuclear palsy, the Guamanian parkinsonism-dementia complex, etc. The present review describes the current status of our understanding of cellular abnormalities occurring in at-risk neuronal populations in AD and PD.
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