Chemosensation olfaction

Consideration of the origins and evolution of chemosensation can help one to begin to understand the themes of olfaction and chemical communication that are common to diverse phyletic groups. This section emphasizes ideas that were propounded with characteristic clarity and elegance by the late Vincent Dethier in his 1990 R. H. Wright Lectures on Olfaction. Because the published version of those lectures (1) may not be widely accessible, some of Dethier s main points are restated here. 

The sensitivity and selectivity of olfaction and contact chemosensation are due (1) in the brain, to the existence of a neuronal network of neurons tuned to a specific chemical stimulus, and (2) in the periphery, to the existence of olfactory/ chemosensory receptor neurons housed in sensory microorgans called sensilla. The sensilla can best be viewed as simple cuticular porous extrusions that increase the surface that captures airborne odorants or chemicals dissolved in water droplets. They contain the receptive olfactory or chemosensory structures (Schneider, 1969). The olfactory sensilla are most numerous on the antennae and mediate the reception of sex pheromones and plant volatiles, as well as other odorants. Low volatility pheromones may also be detected by contact chemoreceptors on... 

In the context of evolution of pheromone olfaction and general chemosensation, we can speculate that general chemosensory proteins may be more highly conserved than olfactory PBPs when compared across species. Indeed, little sequence diversification would be expected to occur among genes encoding chemosensory proteins tuned to bind chemicals of common importance to all species. 

Gavillet B. and Picimbon J. F. (2002) Endocrine regulation of olfaction and chemosensation. Proc. Eur. Comp. Endocrinol. C826, 463 -68. 

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