RESEARCH ARTICLE Direct Behavioral and Neurophysiological Evidence for Retronasal Olfaction in Mice

The neuroscience of flavor perception is hence becoming increasingly important to under-stand food flavor perception that guides food selection, ingestion and appreciation. We re-cently provided evidence that rats can use the retronasal mode of olfaction, an essential element of human flavor perception. We showed that in rats, like humans, odors can acquire a taste. We and others also defined how the input of the olfactory bulb (OB)-not functionally imageable in humans- codes retronasal smell in anesthetized rat. The powerful awake transgenic mouse, however, would be a valuable additional model in the study of flavor neu-roscience. We used a go/no-go behavioral task to test the mouse's ability to detect and dis-criminate the retronasal odor amyl acetate. In this paradigm a tasteless aqueous odor solution was licked by water-restricted head-fixed mice from a lick spout. Orthonasal con-tamination was avoided. The retronasal odor was successfully discriminated by mice against pure distilled water in a concentration-dependent manner. Bulbectomy removed the mice's ability to discriminate the retronasal odor but not tastants. The OB showed robust op-tical calcium responses to retronasal odorants in these awake mice. These results suggest that mice, like rats, are capable of smelling retronasally. This direct neuro-behavioral evi-dence establishes the mouse as a useful additional animal model for flavor research