Histologic study of age-related change in the posterior pituitary gland focusing on abnormal deposition of tau protein.

We studied histologic findings of age-related change in the posterior pituitary gland focusing specifically on abnormal deposition of tau protein. Posterior pituitary glands from a total of 201 patients with mean age of 72, range 15 to 100 years, were dissected at autopsy, and semiquantitative analysis of tau protein deposition in the posterior pituitaries was performed. We confirmed that tau protein deposition in the posterior pituitary appears histologically as either a 'thread-like' or 'dot' form. In double staining using an anti-neurofilament antibody and Gallyas-Braak staining, Gallyas-Braak-positive structures were located in the neurite. The grade and the frequency of tau protein deposition were increased in accord with aging. An interrelation was observed between tau protein deposition in the brain and that in the posterior pituitary. In tauopathy diseases, tau protein deposition in the posterior lobe is advanced compared to that in non-tauopathy diseases. The level of tau protein deposition in the hypothalamus was compared semi-quantitatively with that in the posterior pituitary, and the levels correlated well. We suggest that in the posterior pituitary of elderly people, high frequency of occurrence of deposition of abnormal tau protein in the neurites may cause dysfunction of the pituitary gland.