Responses of a population of antennal olfactory receptor cells in the female moth Manduca sexta to plant-associated volatile organic compounds

Extracellular electrophysiological recordings were made from individual typ e-A trichoid sensilla on the antenna of the female sphinx moth Manduca sext a. A single annulus of the antenna bears about 1,100 of these sensilla. and each is innervated by two olfactory receptor cells. We tested the response s of these receptor cells to a panel of 102 volatile compounds, as well as three plant-derived odor mixtures. and could discern three different functi onal types of type-A trichoid sensilla. One subset of receptor cells exhibi ted an apparently narrow molecular receptive range, responding strongly to only one or two terpenoid odorants. The second subset was activated exclusi vely by aromatics and responded strongly to two to seven odorants. The thir d subset had a broad molecular receptive range and responded strongly to od orants: belonging to several chemical classes. We also found receptor cells that did not respond to any of the odorants tested but were spontaneously active. Certain odorants elicited excitatory responses in some sensilla but inhibitory responses in others, and some receptor cells were strongly exci ted by certain odorants but inhibited by others. Impregnation of groups of receptor cells in type-A trichoid sensilla with rhodamine-dextran demonstra ted that their axons project mainly to the large female glomeruli of the an tennal lobe.