Abstract
The mammalian olfactory system processes odorants presented orthonasally (inhalation through the nose) and also retronasally (exhalation), enabling identification of both external as well as internal objects during food consumption. There are distinct differences between ortho- and retronasal air flow patterns, psychophysics, multimodal integration, and glomerular responses. Recent work indicates that rats can also detect odors retronasally, that rats can associate retronasal odors with tastes, and that their olfactory bulbs (OBs) can respond to retronasal odorants but differently than to orthonasal odors. To further characterize retronasal OB input activity patterns, experiments here focus on determining the effects of odor concentration on glomerular activity by monitoring calcium activity in the dorsal OB of rats using a dextran-conjugated calcium-sensitive dye in vivo. Results showed reliable concentration-response curves that differed between odorants, and recruitment of additional glomeruli, as odor concentration increased. We found evidence of different concentration-response functions between glomeruli, that in turn depended on odor. Further, the relation between dynamics and concentration differed remarkably among retronasal odorants. These dynamics are suggested to reduce the odor map ambiguity based on response amplitude. Elucidating the coding of retronasal odor intensity is fundamental to the understanding of feeding behavior and the neural basis of flavor. These data further establish and refine the rodent model of flavor neuroscience.
Highlights
Retronasal smell pertains to volatile stimuli released from food in the mouth while eating
RETRONASAL ODOR INTENSITY We first sought to determine the effect of retronasal odor concentration on glomerular responses of the olfactory bulbs (OBs)
Figures 1C1–F1 are examples of OB response maps for one rat presented with retronasal Ethyl butyrate (EB) at 0.3, 1, 3, and 10% VP
Summary
Retronasal smell pertains to volatile stimuli released from food in the mouth while eating. Studies further indicate that retronasal smell, at both threshold and suprathreshold odor concentrations, is less sensitive than orthonasal smell in humans (Heilmann and Hummel, 2004; Hummel et al, 2006; Furudono et al, 2013). These sensitivity differences may in part be explained by difference in direction-dependent flow patterns across the olfactory epithelium (Zhao et al, 2006) in interaction with flow rate and non-uniform receptor distributions (Schoenfeld and Cleland, 2006), in addition to differences in higher level mechanisms as learning (Bender et al, 2009)
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