Dehydration‐induced proliferation of identified pituicytes in fully adult rats

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Abstract
The mitotic activity astrocytes in the adult central nervous system (CNS) is of interest due to their roles in gliosis and tumorigenesis, and their potential in aiding recovery of function following injury or disease. The posterior pituitary offers a potentially powerful model to study proliferation in vivo, since its resident astrocytes, called pituicytes, have been reported to divide concurrently with hormone release from the neurosecretory terminals there. Our aim in this study was to confirm and characterize this proliferative response during dehydration and rehydration in fully adult animals, using contemporary techniques. Adult male rats were given 2% saline in substitution for water for 0–9 days. Proliferation of pituicytes was quantified in tissue sections triple-labeled with the proliferation marker, 5-bromodeoxyuridine (BrdU), the astrocyte marker glial fibrillary acidic protein (GFAP), and the DNA marker 4,6, diamidino-2-phenylindole, HC1 (DAPI). A robust proliferative response began within three days of dehydration and continued at a constant rate thereafter. In animals allowed to rehydrate, this response continued. After 9 days of dehydration, approximately 35% of pituicytes had participated in mitosis. While cell density remained constant across conditions, a reversible increase in posterior pituitary area was seen, suggesting that some cell death also occurs simultaneously. A significant proportion of non-pituicytes also underwent similar changes. These results indicate that pituicytes in the adult posterior pituitary retain characteristics necessary for reentering the cell cycle in response to local factors present during neurosecretory activity. We hypothesize that this proliferative response is directly related to the morphological changes previously reported for these cells under activating conditions.