Proceedings of The Physiological Society

Future Physiology (Leeds, UK) (2017) Proc Physiol Soc 39, PC57

Poster Communications

Multi-sensory Integration in the olfactory bulb: the effect of metabolic state on the representation of odours

C. Stefens1, J. Johnston1

1. School of Biomedical Sciences, University of Leeds, Leeds, United Kingdom.

A feedback loop exists between the digestive and olfactory systems; the level of satiety regulates olfactory sensitivity (Tong et al. 2011, Cameron et al. 2012) and heightened olfactory sensitivity increases food intake (Soria-Gómez et al. 2014). Furthermore, the amount of food ingested is influenced by the hedonic value of its odour (Palouzier-Paulignan et al. 2012) which in turn is lowered by the level of satiety (Cameron et al. 2012). The olfactory bulb is the first brain structure to process odours and is also a key sensor of metabolic state (Palouzier-Paulignan et al. 2012; Soria-Gomez et al. 2014). How does satiety alter olfactory function? At least two mechanisms signal satiety; an increase in nutrients entering the blood and an expansion of the stomach. Increased insulin and glucose can decrease the sensitivity of mitral cells, the output neurons of the olfactory bulb (Tucker et al. 2013) but it is not yet known if satiety alters the representation of odours earlier in the circuitry of the olfactory bulb. We are using intrinsic signal optical imaging (ISOI) to measure the activity of the olfactory afferents that synapse in the glomeruli of the olfactory bulb (refs). An odour activates a specific pattern of glomeruli and we are therefore able to image the first representation of odours in the brain. Experiment: Mice will be fasted and then imaged before and after injection of glucose, to emulate hunger and satiated states. The responses to isoamyl acetate which acts as a food odour will be compared. One week prior to the experiment and for four successive days mice are exposed to isoamyl acetate with sugar in a petri dish in order to pair the odour with a food reward. During the experiment mice are anesthetised with an intraperitoneal injection of urethane (1.2-1.5 g/kg), and the olfactory bulbs are exposed with a craniotomy. Our preliminary results from 3 mice indicate that glucose induces a 42%, 59% and 71% decrease in the median glomerular response per animal. Interestingly the reduction of the glomerular response does not appear to be global as in each mouse between 10-30% of responding glomeruli were unaffected by the glucose administration, suggesting that glucose may act on subsets of glomeruli rather than reducing global sensitivity to odours.

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