Days after Canadian actor Michael J. Fox appeared in a TV ad urging Missouri voters to support stem cell research, opponents will unveil their own commercial during the World Series Wednesday night.

The Cardinals' starting pitcher for Game 4, Jeff Suppan, is among several celebrities who appear in the minute-long ad.

Others include Arizona Cardinals quarterback Kurt Warner, Kansas City Royals first baseman Mark Sweeney and two actors, Patricia Heaton of TV's Everybody Loves Raymond and Jim Caviezel, who portrayed Jesus in The Passion of the Christ.

"Amendment 2 claims it bans human cloning, but in the 2,000 words you don't read, it makes cloning a constitutional right," Suppan says in the commercial. "Don't be deceived."

Amendment 2 would provide constitutional protections for embryonic stem cell research in Missouri. The 30-second spot featuring Fox, 45, who sways uncontrollably in the ad because of his Parkinson's disease, is actually a commercial for Democratic U.S. Senate candidate Claire McCaskill.

But the Senate race and stem cell issue are intertwined — McCaskill's Republican opponent, Sen. Jim Talent, opposes the stem cell measure.

Loaning his celebrity

Fox also has lent his celebrity to Democrats Rep. Benjamin L. Cardin, running for the Senate in Maryland, and Wisconsin Gov. Jim Doyle, who is seeking re-election. Both politicians also back stem cell research.

"They say all politics is local, but it's not always the case," Fox says in the ad that began airing Saturday during Game 1 of the World Series. "What you do in Missouri matters to millions of Americans — Americans like me."

The Fox ad has triggered a backlash, with some criticizing it as exploitive. Conservative radio commentator Rush Limbaugh claimed Fox was "either off his medication or acting," though he later apologized.

Dr. John Boockvar, a neurosurgeon and assistant professor at Weill Cornell Medical Center at New York's Presbyterian Hospital, called Limbaugh's claim "ludicrous." Boockvar said those with Parkinson's have "on" and "off" spells.

"If there is one single disease that has the highest potential for benefit from stem cell research," Boockvar said Tuesday, "it's Parkinson's."

The Missouri ad opposing Amendment 2 was finished Tuesday and was immediately available on the internet. Missourians Against Human Cloning spokeswoman Cathy Ruse said the ad was already in the works, "but we sped up production after the Michael J. Fox ad came out.

"That ad claims opponents want to criminalize research and prevent the expansion of stem cell research. Those claims are just false and misleading," Ruse said. "Our gripe with Amendment 2 is it creates a right to do human cloning and it creates the right to human egg trafficking for cloning research."

'Pathetic attempt' to distort facts

Connie Farrow, a spokeswoman for Missouri Coalition for Lifesaving Cures, a supporter of the amendment, called the ad "a pathetic attempt to distort the facts and mislead voters."

"To believe the claims made in their ad you'd have to believe that over 100 nonprofit patient and medical organizations, including the Missouri State Medical Association, the Juvenile Diabetes Research Foundation and the Muscular Dystrophy Association, just to name a few, are conspiring to mislead voters," Farrow said. "And that defies commonsense."

Celebrities have a long history of supporting political candidates. But there's no question that Fox, who campaigned for John Kerry in the 2004 presidential race, is uniquely suited as a spokesman for stem cell research.

Fox, who starred on TV's Family Ties and Spin City plus the Back to the Future films, shakes and rocks as he directly addresses the camera, the effects of his disease clearly apparent.

Parkinson's disease is a chronic, progressive disorder of the central nervous system that leaves patients increasingly unable to control their movements.

Fox was diagnosed with Parkinson's in 1991 and revealed his condition publicly in 1998. In 2000, he quit full-time acting because of his symptoms and founded the Michael J. Fox Foundation for Parkinson's Research, which has raised millions of dollars.