1. BresaGen, Inc., Athens, GA 30605.
2. Cellular Neurobiology Branch, National Institute on Drug Abuse, Department of Health and Human Services, Baltimore, MD 21224.
3. Laboratory of Neuroscience, National Institute of Aging, Department of Health and Human Services, Baltimore, MD 21224.
4. Present address: Gibco/Invitrogen, Grand Island, NY 14072.