Thy-1 in hippocampus: normal anatomy and neuritic growth in Alzheimer's disease.

Abnormal neuritic sprouting is a prominent feature of Alzheimer's disease (AD), and the Thy-1 glycoprotein has a role in neurite growth in culture. We therefore investigated the distribution of Thy-1 immunoreactivity in the hippocampus of normal elderly patients and of AD patients. Normally, Thy-1 immunoreactivity, which was more prominent in CA1 than elsewhere in the hippocampus, was located mainly in irregular patches on the perikarya of pyramidal cells, their dendrites and axons. In AD, Thy-1-immunoreactive neurons were reduced in number in CA1, and there was diffuse staining of neurofibrillary tangle-bearing pyramidal cells, but neurofibrillary tangles themselves were not immunoreactive. There was also staining of disorganized arrays of dystrophic neurites, some with spiny processes and bizarre filopodial endings. Some Thy-1-immunoreactive dystrophic neurites entered senile plaques. The data confirm that there is extensive growth of abnormal neurites in AD and suggest that Thy-1 is involved in this process.