Nerve Gas (IMAGE) Rockefeller University Caption Carbon dioxide-sensitive neurons expressing Gr21a (green) and Gr63a (red), proteins that together (white) are necessary for carbon dioxide detection. The neurons target a specific region of the fly brain, which is dedicated to processing the smell of carbon dioxide. Credit Vosshall Laboratory Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.