Olfaction influences food choice and intake. Conversely, the nutritional and metabolic status modifies odour detection. In an effort to understand the olfactory-metabolic crosstalk, we have localized orexigenic and anorexigenic hormones and their receptors in the olfactory epithelium and bulb of rats, and looked for their effect on the olfactory signal. 1) Concerning the orexigenic hormones: - in fasted rats, transcription of orexins (A & B) and their receptors (1 & 2) increased in the olfactory epithelium and, in the bulb, in mitral, periglomerular and granular cells. An orexin antagonist decreased locomotor activity of fasted animals, their time spent sniffing and bulb cells c-Fos response. Orexins also enhanced the amplitude of the olfactory epithelium electroolfactogram. - similarly, NPY enhanced the electroolfactogram amplitude (30%) in fasted rats, mainly through Y1 receptors and less through Y5. 2) Concerning the anorexigenic hormones: - in the olfactory epithelium, the transcription of leptin and its receptor (long and short forms) were enhanced by fasting. In fasted rats, leptin decreased locomotor activity, time spent sniffing and bulb cells c-Fos response, as well as electroolfactogram amplitude. - fasting induced an increase in the number of receptors in the olfactory epithelium, together with an increase in local insulin production. Interestingly, insulin decreased the electroolfactogram amplitude of the olfactory epithelium by 30%. These results are consistent with an enhanced interest, especially for food odours, in fasted animals, in contrast to decreased odour stimulation in satiated ones. Endly, we analyzed the olfactory epithelium transcriptome of fasted vs satiated rats. Fasting decreased transcription of immunity-related genes, perhaps in connection with stress, while it increased some transcripts related to cell-dynamics or signal transduction. Thus transcriptomic data were largely correlated with enhanced olfactory activity upon fasting