Nutritional impact on odor induced activity in the olfactory buld

National audienceThe detection of olfactory nutritive cues is crucial for survival and implies modifications of activities in the olfactory system. Odorants activate the olfactory receptor neurons (ORNs) of the mucosa which project to the olfactory bulb (OB). OSNs axons connect apical dendrites of mitral cells in olfactory glomeruli which are surrounded by juxtaglomerular cells. Then, after having interacted with granular cells in deeper layers of the OB, mitral cells send the information towards the cortex. In this context, we use c-fos immunodetection and optical imaging in vivo to question the impact of the nutritive state at the first stage of olfactory coding in the OB. Using fos activity, we first show that cellular responses to familiar odors (known isoamyl acetate and pellet odors) of juxtaglomerular, mitral and granular cells were significantly decreased in fed rats compared to 48-hrs fasted ones. We then demonstrate that orexins and leptin were partly responsible for this modulation: the administration of orexin receptors antagonist or of leptin per se in fasted rats led to OB responses to pellet odors similar to those observed in fed rats. In a second series of experiments, we are currently using Intrinsic optical signals (IOS) imaging to study specific glomerular activation patterns in response to a set of odorants in anesthetized rats. IOS are due to changes in blood oxygenation and flow and light scattering during activation and reliably map functional sensory modules. We are analyzing the intensity and time course of odor-evoked optical signals from each spot of the olfactory maps. To bring insights into the putative nutritional plasticity on odor-induced maps in the OB, we aim to apply this optical imaging technique to the same groups studied by c-fos