What the Frog's Nose Tells the Frog's Brain

The olfactory system has the challenging task of responding to thousands of structurally dissimilar odors. In the last decade, advances in molecular biology and genomics have made it possible to obtain an understanding of the diversity of olfactory receptors (Mombaerts, 1999; Buck, 2000). In the mouse, for example, there are over 1,000 different olfactory receptor genes (Zhang and Firestein, 2002), and each olfactory receptor neuron (ORN) expresses only one of these olfactory receptors through a remarkable mechanism that includes feedback by the olfactory receptor protein excluding expression of all other olfactory receptor genes (Serizawa et al., 2003). Therefore, it is thought that each ORN will respond to a set of structurally related odors that stimulate the particular olfactory receptor expressed in that cell (Bozza et al., 2002). Thus, the information on odor stimuli that is sent...