SAN DIEGO -- Junior Seau's family has donated some of his brain tissue for research amid questions about whether damage from his football career contributed to his decision to commit suicide, officials said Thursday.

The San Diego County medical examiner's office recently released preserved brain tissue to the National Institutes of Health, coroner's spokeswoman Sarah Gordon said.

"We have no information about the type of study that will be done," she said.

The tissue was released at the request of Seau's family, she added. She declined to disclose whether Seau's entire brain was released.

The 43-year-old former NFL linebacker shot himself in the chest at his Oceanside home in May, less than 2½ years after ending his Pro Bowl career.

Seau's death echoed last year's suicide of former Chicago Bears defensive back Dave Duerson. Duerson left a note asking for his brain to be studied for signs of brain trauma. That raised anew questions about whether brain damage from repeated concussions on the field lead to long-term problems such as depression.

To date, however, no link has been found between Seau's death and his football days. Although is death was ruled a suicide, a final autopsy report and results of drug-screening tests are pending.