Parallel Neural Pathways Mediate CO2 Avoidance Responses in Drosophila

An important task of the nervous system is to distribute information appropriately throughout the brain. The olfactory and gustatory systems of Drosophila provide good models for understanding these processes and the underlying mechanisms (see the Perspective by [ Su and Carlson ][1]). Lin et al. (p. [1338][2]) mapped out the circuit that detects carbon dioxide (CO2), an important environmental and communication signal for fruit flies. Two distinct classes of projection neurons mediate avoidance of high and low concentrations of CO2, while a third class, comprising inhibitory neurons, shuts down the low-concentration pathway at high concentrations. In contrast to other basic taste qualities, salt is innately attractive at low concentrations, but aversive at high concentrations. The mechanisms underlying salt detection are poorly understood in any species mainly because of a lack of specific molecular tools. Zhang et al. (p. [1334][3]) discovered that Drosophila uses two types of gustatory receptor neurons to distinguish between high and low concentrations of salt. One type is activated maximally by low salt and induces attractive feeding behavior. The other class of receptors is activated primarily by high salt and leads to avoidance behavior. [1]: /lookup/doi/10.1126/science.1240139 [2]: /lookup/doi/10.1126/science.1236693 [3]: /lookup/doi/10.1126/science.1234133