Selective pathological changes of the periaqueductal gray matter in Alzheimer's disease

The periaqueductal gray matter (PAG) is a major neuroanatomical component of the brainstem and has pivotal roles in autonomic functions, behavior, and cognition, most notably in the processing of emotions and feelings. In a study of 32 brains obtained from patients with Alzheimer's disease (AD), thioflavin S-stained sections from the PAG contained major pathological changes in 81% of cases. These changes were absent in all 26 control brains (13 from normal subjects and 13 from non-AD patients). In the AD cases, both sides of the PAG were affected symmetrically; in 72%, there were only senile plaques, but there were both senile plaques and neurofibrillary tangles in 9%. Using immunohistochemical methods with 10D5, ALZ-50, and AT8 antibodies, we also established the presence of beta-amyloid peptide and abnormally phosphorylated tau protein in the PAG. Furthermore, we found that the type and density of pathological changes were expressed differently in different PAG regions and correlated with gender and the duration of dementia. These findings constitute a first step in documenting the selective changes of PAG in AD. The compartmentalized pattern of AD changes in PAG also reveals for the first time the columnar organization of PAG in human subjects.