NEW YORK - Ludacris will make a cartoon cameo in the 400th episode of "The Simpsons" as a tube of toothpaste that raps, of all things.

The 29-year-old rapper-actor, whose real name is Chris Bridges, portrays "Luda-Crest" in an informational video that brainy Lisa watches during the Simpsons' annual dental checkup. The episode airs tomorrow night on Fox.

The central story line, though, features the family taking in a dejected news anchor who was fired for using a shocking expletive while interviewing Homer on his nightly program. Lisa helps him devise a scheme to stage a comeback.

"The Simpsons," created by Matt Groening, is now in its 18th season.

Ludacris has taken up acting in recent years. He generated strong buzz for his performances in the films "Crash" and "Hustle & Flow," and recently guest-starred on NBC's "Law & Order: Special Victims Unit." *