Radial glia express aromatase in the injured zebra finch brain

Estrogens have neurotrophic and neuroprotective properties. The synthesis of estrogen occurs via the expression of aromatase. Previous studies have shown that injury to the vertebrate brain results in a rapid and dramatic up-regulation of aromatase expression in astrocytes around the lesion. As part of experiments examining injury-induced glial aromatization, we identified aromatase in radial glia of the zebra finch brain. Adult female zebra finches received a penetrating injury to the right hippocampus. Twenty-four hours after lesioning, birds were administered bromodeoxyuridine (BrdU) and sacrificed 2 hours, 1 day, or 7 days later. We determined the distribution of aromatase and BrdU labeling by using immunocytochemistry. Radial aromatase was localized to cells lining the lateral ventricle adjacent to the lesioned hippocampus. Injury also induced a dramatic accumulation of newly generated cells labeled with BrdU around the lesion. BrdU labeling was strongly associated with aromatase-positive radial fibers, suggesting the migration of newly generated cells along these fibers. In the songbird brain, estrogen supports neuronal recruitment and promotes the survival and addition of new neurons. The presence of aromatase in radial glia provides a mechanism of estrogen delivery to postmitotic cells. Radial aromatization may be a key feature in the repair of the vertebrate brain following neural injury.