Integration of CO2 and odorant signals in the mouse olfactory bulb

Carbon dioxide (CO(2)) is an important environmental cue for many animal species. In both vertebrates and invertebrates, CO(2) is detected by a specialized subset of olfactory sensory neurons (OSNs) and mediates several stereotypical behaviors. It remains unknown how CO(2) cues are integrated with other olfactory signals in the mammalian olfactory bulb, the first stage of central olfactory processing. By recording from the mouse olfactory bulb in vivo, we found that CO(2)-activating neurons also respond selectively to odorants, many of which are putative mouse pheromones and natural odorants. In addition, many odorant-responsive bulbar neurons are inhibited by CO(2). For a substantial number of CO(2)-activating neurons, binary mixtures of CO(2) and a specific odorant produce responses that are distinct from those evoked by either CO(2) or the odorant alone. In addition, for a substantial number of CO(2)-inhibiting neurons, CO(2) addition can completely block the action potential firing of the cells to the odorants. These results indicate strong interaction between CO(2) signals and odorant signals in the olfactory bulb, suggesting important roles for the integration of these two signals in CO(2)-mediated behavioral responses.