Astrocytic gliosis in the amygdala in Down's syndrome and Alzheimer's disease

Astrocytic gliosis is an important neuropathologic change in Alzheimer's disease (AD). It is unclear whether reactive gliosis is an early or a late change in AD. It is also not known if reactive astrocytosis is related to the appearance of deposits of the β-amyloid peptide (βAP). This is important because βAP deposition is thought to be one of the earliest pathologic changes in AD brain and might induce gliosis, since βAP is thought to have trophic properties. An important approach to identifying early pathologic changes in AD was to examine young cases with Down's syndrome (DS), since persons with DS invariably developed the neuropathologic changes of AD, prematurely. It seemed that numerous astrocytes could be detected in DS brains from the second and third decade, but they did not show the hypertrophy seen in older DS and in AD brain. Further, astrocytes and βAP deposits showed no consistent spatial relationship, although occasional colocalization occurs. Even when colocalized with βAP deposits, astrocytes in young DS cases showed no evidence of morphologic change. These findings suggested that astrocytosis is a late change in DS and possibly in AD.