| The odor responses of olfactory receptor neurons (ORNs) are conferred by odorant receptors, and odor coding is based on the activities of a population of odorant receptors. I have undertaken a functional analysis of the Drosophila antennal repertoire of odorant receptors using a mutant ab3A neuron as an in vivo expression system. I have identified the odor response spectrum of individual odorant receptors, and have mapped many of these receptors to the functional classes of neurons from which they are derived. By comparing the odor response spectra of these receptors, I have found that receptors vary in their breadth of tuning with respect to a diverse odorant panel, and also that odorants vary in the number of receptors they activate. This analysis revealed that the odorant receptor is the primary determinant of the odor response spectrum of the ORN. The odorant receptor was also found to determine the spontaneous firing rate, response dynamics, and signaling mode (i.e. excitation or inhibition) of the ORN. Finally, antennal receptors were found to function normally in multiple neuron classes, including those of the maxillary palp, suggesting that most, if not all, receptors can function normally in the absence of sensillum-specific or neuron-specific perireceptor molecules such as odorant binding proteins. This analysis was then extended to two receptors from the malaria vector mosquito Anopheles gambiae. One of these receptors was found to respond to 4-methylphenol, a human sweat component, suggesting that it may be involved in the human host-seeking behavior of the female mosquito. In addition, these results raise the possibility that the expression system provided by the mutant ab3A neuron can be used to identify ligands for large numbers of receptors from other insect species, such as disease vectors and agricultural pests, and also to screen for compounds that activate or block these receptors. |
