Sensing the Smell of Attraction

Science's STKE  25 Jan 2005:
Vol. 2005, Issue 268, pp. tw35
DOI: 10.1126/stke.2682005tw35

In insects, behaviors--including those of agricultural pests and organisms that carry human diseases--are often triggered through the insect's sense of smell. Specific pheromones are detected by structures known as chemosensory sensilla on the antenna. Within these hairlike structures, several olfactory neurons are exposed to a fluid, sensillum lymph. Odorant-binding proteins (OBPs) are secreted specifically into certain sensillae. The function of the OBPs has been unclear, with some suggestion that they may function as carriers to either protect, degrade, or concentrate odorant molecules near sensitive neurons. Xu et al. studied odorant responses in Drosophila mutants lacking an OBP known as LUSH and concluded that OBPs may in fact have a more active role in odorant signaling. The authors made electrophysiological recordings from single sensillae to show that response of T1 neurons, which normally sense the pheromone 11-cis vaccenyl acetate (VA), was lost in lush mutants. However, there was also an effect on the T1 neurons themselves, which essentially lost their usual spontaneous action potentials, which normally occur about once per second. The authors note that this result could be explained if the OBP was working as a sensor, which was activated by a conformational change in response to odorant binding and then stimulated a receptor on the T1 neuron. If the activating conformation of the OBP was reached occasionally in the absence of odorant, it could account for the basal activity and explain the lack of activity in lush mutants. Consistent with such a role, addition of recombinant LUSH protein directly to T1 neurons rapidly restored sensitivity to VA. This intriguing hypothesis, if confirmed by further study, would substantially change our understanding of insect olfaction and open the way for new strategies aimed at modulating associated insect behaviors.

P.-X. Xu, R. Atkinson, D. N. M. Jones, D. P. Smith, Drosophila OBP LUSH is required for activity of pheromone-sensitive neurons. Neuron 45, 193-200 (2005). [PubMed]