Sniffing and optical imaging of olfactory bulb responses

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DESCRIPTION (provided by applicant): The goal of this project is to understand how odorant representations by populations of olfactory receptor neurons at the level of their input to the olfactory bulb are modified by sniffing in awake rats. While population responses of the olfactory bulb and sniffing behavior have been explored to some degree in separation, and it has become clear that sniffing could have a major impact on odorant encoding, it is entirely unknown how sniffing actually affects odor encoding in the olfactory system. The transformation of odorant information from the spatially roughly organized olfactory epithelium to the spatially highly organized olfactory bulb, allowed by highly specific convergence of olfactory receptor neurons onto glomeruli, is a critical step in this encoding process. It is clear that airflow can modulate where odorants sorb to the olfactory epithelium, and it is clear that the spatial organization of receptor neurons is by no means random. The input of the olfactory bulb, which acts like a window on the olfactory receptor repertoire of odorants, is hence likely to be affected by sniffing. If so, this undoubtedly has major affects on higher order processing as well. Indeed, several important hypotheses rely on the assumption that sniffing is invariable. This study will focus on the impact of sniffing of odorants on the coding and processing of information about odors at this first level of the olfactory pathway by selectively imaging activity in olfactory receptor neuron terminals while rats are performing an olfactory discrimination task and sniffing activity is measured. Specifically, this study will: 1) determine to what extent sniffing modulates the neural odormaps in the olfactory bulb; 2) determine whether the phenomenon of enhanced sniffing in response to lower odorant concentrations leads to concentration-invariance of input odormaps to the bulb. Together, these experiments will constitute a significant step towards understanding how odor quality - encoding at a specific level of the olfactory pathway is affected by the ubiquitous and natural behavior of sniffing in rats. Understanding the basic functions of the olfactory system can potentially lead to improved diagnosis and treatment of diseases of the nervous system.