Gary Plummer has done the math.

If a 'Grade 1' concussion means you see stars after a hit, Plummer says he's had 1,000 in his career, and his ex-teammate, Junior Seau, had 1,500.

That's one thousand, five hundred concussions.

Seau died of a self-inflicted gunshot wound to the chest Wednesday. Plummer played beside Seau at linebacker in four years with the San Diego Chargers, retiring in 1997 as a San Francisco 49er.

PHOTOS: Seau's career in pictures

"In the 1990s, I did a concussion seminar. They said a Grade 3 concussion meant you were knocked out, and a Grade 1 meant you were seeing stars after a hit, which made me burst out in laughter," Plummer told the San Jose Mercury News. "As a middle linebacker in the NFL, if you don't have five of these (Grade 1 effects) each game, you were inactive the next game.

"Junior played for 20 years. That's five concussions a game, easily. How many in his career then? That's over 1,500 concussions. I know that's startling, but I know it's true. I had over 1,000 in my 15 years. I felt the effects of it. I felt depression going on throughout my divorce. Junior went through it with his divorce."

Seau's family has agreed to have his brain studied for the effects of concussions. Former Chicago Bears safety Dave Duerson last year also died of a self-inflicted gunshot wound to the chest. He left a suicide note asking his family to donate his brain to Boston University, where researchers learned he suffered from a neurodegenerative disease linked to concussions.