When selenium is scarce, brain battles testes for it

Faced with a shortage of the essential nutrient selenium, the brain and the testes duke it out. In selenium-depleted male mice, testes hog the trace element, leaving the brain in the lurch, scientists report in the Nov. 18 Journal of Neuroscience.

The results are some of the first to show competition between two organs for trace nutrients, says analytical neurochemist Dominic Hare of the University of Technology Sydney and the Florey Institute of Neuroscience and Mental Health in Melbourne. In addition to uncovering this brain-testes scuffle, the study “highlights that selenium in the brain is something we can’t continue to ignore,” he says. 

About two dozen proteins in the body contain selenium, a nonmetallic chemical element. Some of these proteins are antioxidants that keep harmful molecules called free radicals from causing trouble.

Male mice without enough selenium have brain abnormalities that lead to movement problems and seizures, neuroscientist Matthew Pitts of the University of Hawaii at Manoa and colleagues found. In some experiments, Pitts and his colleagues depleted selenium by interfering with genes. Male mice engineered to lack two genes that produce proteins required for the body to properly use selenium had trouble balancing on a rotating rod and moving in an open field. In their brains, a particular group of nerve cells called parvalbumin interneurons didn’t mature normally.

But removing the selenium-hungry testes via castration before puberty improved these symptoms, leaving more selenium for the brain, the team found.  Selenium levels in the brains of these castrated mice were higher than those in uncastrated mice (though not as high as in females). The results “really suggest that there is some competition going on” in the males, Pitts says.

Because selenium is known to be important for both fertility and the brain, the results make sense, says biochemist Lutz Schomburg of Charité-University Medical School Berlin. “Taking out the brain or the testes will likely benefit the other organ,” he says. “The former experiment is impossible to do but the latter has now nicely been conducted.”

Schomburg cautions that the results aren’t necessarily relevant for people, who aren’t likely to be as selenium-deprived as the mice in the experiment. “Under normal conditions, the competition between testes and brain is not existent,” he says.

That’s in part because most people’s diets contain plenty of selenium. The nutrient is found in crops grown in soil with plentiful selenium, such as in the Great Plains in the United States. Brazil nuts are packed with selenium, as are tuna, halibut and sardines.

Yet some people in parts of China, New Zealand and Europe have low selenium intake, Pitts says. Differences in selenium levels in the body, either due to diet or genetic traits, may play a role in psychiatric disorders such as schizophrenia, he speculates. While that idea is unconfirmed, a hint comes from an earlier study that found that people with schizophrenia had reduced activity of the gene that encodes a protein that helps deliver selenium to where it is needed. Early-onset schizophrenia is also more prevalent in males. “In this way, males could be more at risk, because they have an additional organ sucking up resources that could be going to the brain,” Pitts says.