Maldonado, T.M.*; Jones, R.E.; Norris, D.O.: Neurodegeneration and amyloidosis in the brain of kokanee salmon (Oncorhynchus nerka kennerlyi) during sexual maturation and senescence.

The brain of senescent kokanee salmon exhibits neuropathology similar to that of aging humans (Maldonado et al., Brain Research. 858, 237-251, 2000). Beta-amyloid (ABETA) is distributed regionally in the salmon brain and its extracellular presence correlates with senescence. Brains of kokanee from one of four reproductive stages (immature, maturing, mature and spawning) were stained with cresyl violet to visualize pyknotic neurons (neurodegeneration) in 24 specific regions of the brain. Brains of immature and maturing fish exhibited only low levels of neurodegeneration compared to sexually mature and spawning fish. Greatest neurodegeneration occurred in regions immunopositive for ABETA including those involved in gustation, olfaction, vision the stress response, reproductive behavior and coordination as well as in the suprachiasmatic nucleus and inferior lobe of the hypothalamus. Five regions showed neurodegeneration with no amyloidosis (ABETA deposition) whereas the nucleus lateralis tuberis and the Purkinje cells of the cerebellum showed neither neurodegeneration nor amyloidosis. In most regions, increased neurodegeneration preceded ABETA deposition while in some regions it could not be determined which appeared first.