Jones & Norris IBN 9603622 Pacific salmon, after being born in freshwater streams, migrate downstream to a lake or to the ocean. Then, after several years, they migrate upstream to their original place of birth. Pacific salmon are semelparous; i.e. they breed once and die soon thereafter. During this upstream breeding migration, blood levels of stress (glucocorticoids) and reproductive hormones (gonadotropins, estrogens and androgens) surge, and their reproductive organs mature. After spawning, they all die within 7 to 14 days. Before death, their bodies (e.g skin, muscle, heart) exhibit pathological changes that are remarkably similar to those seen in aging humans. Recently, Dr. Jones and Dr. Norris discovered that the brains of spawning salmon exhibit neuronal degeneration and beta-amyloid plaque deposition. They also found changes in glucocorticoid hormone receptor immunoreactivity in specific brain regions. The presence of amyloid-like plaques and dying neurons are very striking observations since this is also seen in older humans, especially those with Alzheimer's disease. Dr. Jones and Norris will now examine more precisely the timing of these changes in wild salmon and determine the role of steroid hormones. Greater understanding of salmon brain aging, especially the role of stress and reproductive hormones, could help in the management and conservation of Pacific salmon, some of which are endangered. Dr. Jones and Norris will also verify that salmon brain aging is similar to that in other species, including human. Thus, the synchronized, predictable, and rapid aging of salmon may serve as an ideal model system to help us understand normal aging processes in the brain, as well as in abnormal conditions such as Alzheimer's disease.
