Cheng Wang, Ph.D, is a senior scientist at the National Center for Toxicological Research, U.S. Food and Drug Administration, Jefferson, Arkansas. He also is an adjunct faculty memberof the Department of Pharmacology and Toxicology at the University of Arkansas for Medical Sciences (UAMS), Little Rock, USA. Dr. William Slikker is a recognized expert in neurotoxicology and the director of the National Center for Toxicological Research, U.S. Food and Drug Administration, Jefferson, Arkansas.