The UCLA Health System operates the Ronald Reagan UCLA Medical Center, a hospital in Santa Monica and twelve primary care clinics throughout Los Angeles County. In addition, the UCLA David Geffen School of Medicine uses two Los Angeles County public hospitals as teaching hospitals—Harbor–UCLA Medical Center and Olive View–UCLA Medical Center—as well as the largest private nonprofit hospital on the west coast, Cedars-Sinai Medical Center. The Greater Los Angeles VA Medical Center is also a major teaching and training site for the university. The UCLA Medical Center made history in 1981 when Assistant Professor Michael Gottlieb first diagnosed AIDS. UCLA medical researchers also pioneered the use of positron emission tomography (PET) scanning to study brain function. Professor of Pharmacology Louis Ignarro was one of the recipients of the 1998 Nobel Prize in Physiology or Medicine for discovering the signaling cascade of nitric oxide, one of the most important molecules in cardiopulmonary physiology.