Parkinson's sufferer and actor Michael J. Fox has been mocked by rightwing host Rush Limbaugh after he appeared in a Missouri television ad urging viewers to vote yes for stem cell research and for a Democratic Senate candidate over the Republican incumbent. We look at one of the most hotly contested issues in the 2006 elections with Arthur Caplan of the Center for Bioethics at the University of Pennsylvania. [includes rush transcript]

In addition to electing candidates for the House and Senate, voters on November 7th will get to settle matters of public policy ranging from gay marriage to abortion and raising the minimum wage.

A near record number of ballot initiatives were proposed by citizens this year. Perhaps the most hotly contested issue this election season is embryonic stem cell research. Earlier this year, President Bush issued the first veto of his presidency in order to bar the expansion of federally funded stem cell research. Scientists have widely criticized Bush�s move to block the use of embryonic stem cells to find treatments or cures for many debilitating diseases. Polls show 70 percent of the country backs stem cell research.

One its most prominent backers is actor Michael J. Fox. Fox was diagnosed with Parkinson�s in 1991 and went public with his condition seven years later. Last week, he appeared in a television campaign ad urging viewers to vote yes for stem cell research and for a Democratic Senate candidate.

• Michael J. Fox TV commercial.

Soon after the TV ad ran, conservative talk show host Rush Limbaugh lashed out at Fox for his appearance in the ad where he is visibly shaking from the effects of the disease.

• Rush Limbaugh.

Fox responded to Rush Limbaugh's comments in an interview with Katie Couric on CBS Evening News

• Michael J. Fox on CBS Evening News.

Arthur Caplan is the director of the Center for Bioethics at the University of Pennsylvania. He joins us now from the Center in Philadelphia.

• Arthur Caplan. Director of the Center for Bioethics at the University of Pennsylvania.