Unlocking the DOR Code

of the retina. At first glance, it would seem improbable studies that have revealed the basic mechanisms by that full-fledged sodium action potentials would play a which odorant information in the periphery is reliably major role. Thus, the first stages of retinal processing transferred to the brain for higher order processing. are likely to remain analog rather than digital. However, The initial step in odorant recognition is the interaction subthreshold regenerative sodium currents might pro-between an odorant and a distinct subpopulation of ORs vide a small boost in signal processing. present on the dendritic membrane of OSNs. Several studies indicate that insect and vertebrate OSNs express only one or a few ORs, which thereby defines the David Copenhagen functional phenotype of the OSN. Independent of their Departments of Ophthalmology and Physiology physical location in the sensory epithelium, all neurons University of California, San Francisco expressing a given OR project to one of many function-School of Medicine ally distinct and spatially invariant neuropil conglomer-San Francisco, California 94143 ates in the brain called glomeruli. This topographical Selected Reading correspondence between neurons of the olfactory epi-thelium and their projections to olfactory glomeruli vation in the brain that is likely to be the first level of 91, 4564–4568. activity have been proposed to intersect with these spa-438, 8–14.a complete topographic map of the olfactory system, of mammalian olfactory systems and the presence of approximately 1000 ORs and 1800 glomeruli in these animals. In contrast, the fruit fly olfactory system is a much simpler system (approximately 61 ORs and 43 glomeruli) and, as such, affords a unique opportunity to understand the complete underpinnings of the olfactory process in a single organism. A recent study by Vosshall Olfactory systems possess the remarkable power to dis-et al. (2000) has provided the first look at the map of criminate between tens of thousands of distinct odors, receptor activation in the Drosophila brain. Building on covering a wide range of chemical types. How can olfac-this work, along with the current knowledge of Drosoph-tory systems distinguish the fragrance of a rose from ila odorant receptor (" DOR ") expression patterns in the the odor of garlic or a pine forest? The first step in antenna (Clyne et al., 1999; Gao and Chess, 1999; Voss-odorant discrimination takes place in the olfactory epi-hall et al., 1999), it may soon be possible to construct thelium (i.e., the nose). Olfactory epithelia of higher or-a …