Odorized air can enter the nose orthonasally through the external nares during inspiration or during sniffing. It can also enter retronasally during expiration or with swallowing and chewing movements. Human and some animal studies have indicated that there are differences in the sensations evoked between the orthonasal and retronasal routes. Retronasal olfaction is functionally important in appreciation of flavor and could well contribute to changes in flavor appreciation in aging and disease. Retronasal olfaction may also be differentially sensitive to the fat content of food thus contributing to food preferences that are very relevant to the issue of obesity. Some evidence from the literature suggests that physico-chemical properties of odorants may account for some of the differences in perception between orthonasal and retronasal stimulation, although very likely trigeminal sensation and/or coordinated activity in motor centers may also contribute. Air flow rate in the nose interacts with physicochemical properties of odorants (including mucosal solubility and diffusibility in air). Our recordings of rat electroolfactograms during orthonasal and retronasal stimulation show that the retronasal route gives a greatly reduced response for polar (hydrophilic) odorants with preserved responses to non-polar (hydrophobic) odorants. This investigation will utilize electroolfactogram recordings and recordings from the olfactory bulb to study how odorant properties interact with air flow parameters both orthonasally and retronasally. We will investigate whether this preparation can be used as a model of retronasal olfaction and will specifically include a range of flavor odorants. Retronasal inputs in the rat seem to preferentially activate the lateral recesses of the olfactory epithelium. This may also provide a useful tool for study of olfactory bulb physiology because a single stimulus can lead to very different patterns of action in the bulb depending on the route of presentation.