All regions of mouse brain are dependent on selenoprotein P for maintenance of selenium.

The brain and testis retain selenium better than other tissues during selenium deficiency. Studies of mice with selenoprotein P (Sepp1) deleted (Sepp1(-/-) mice) showed that brain and testis selenium levels are largely dependent on Sepp1. Therefore, we examined tissue selenium in mice fed varying amounts of selenium and in Sepp1(-/-) mice to characterize better the role(s) of Sepp1. Mice were fed a selenium-deficient diet for 8 wk supplemented with selenium as selenite from none to 0.25 mg/kg diet and tissue selenium was measured. Brain and testis maintained their selenium better than did liver, kidney, and muscle when dietary selenium was limiting but testis selenium fell sharply in the group fed the deficient diet. Brain retained its selenium well, even in the group fed the deficient diet. After intravenous injection of (75)Se-Sepp1 into Sepp1(-/-) and Sepp1(+/+) mice, qualitative differences between brain and testis (75)Se uptake were noted, further suggesting differences in their uptake of selenium from Sepp1. Finally, selenium was measured in brain regions of Sepp1(-/-) and Sepp1(+/+) mice fed the diet supplemented with 1 mg selenium/kg and Sepp1(+/+) mice fed the deficient diet. Deletion of Sepp1 and selenium deficiency each lowered selenium a similar amount in cortex, midbrain, brainstem, and cerebellum. Selenium in the hippocampus was lowered by deletion of Sepp1 but not by selenium deficiency. These results suggest that Sepp1 is more important for maintaining selenium in the hippocampus than in other brain regions. They also confirm the position of the brain at the apex of the organ selenium hierarchy.