Abstract
Research in the area of in vivo olfactory physiology benefits from having direct access to the nasal airways through which odorants can be presented. Ordinarily, the passage of odorants through the airways is controlled by respiratory rhythm. This fact makes it difficult to control the timing and strength of an olfactory stimulus, since animals must breathe regularly, and the act of breathing itself also controls odorant presentation. However, using an artificial inhalation preparation allows us to decouple breathing from olfaction. With this technique we present oxygen and anesthetic (if desired) to the lungs directly and independently control odorant access to the nasal passages. This technique allows for direct control of odorant presentation in vivo, enabling more precise control of parameters of stimulation when investigating olfactory processing. This technique may have additional applications, for example in aerosolized drug delivery.
Keywords: Inhalation, Olfaction, Nasopharynx, Respiration, Tracheotomy
Background
Olfaction, aerosolized drug delivery, and many facets of airway humidification and homeostasis are governed by active respiration through the nasal passages. Basic research into these areas benefits from being able to actively control respiration in an anesthetized preparation. Our lab focuses in part on how active respiration controls olfactory coding in the olfactory bulb, which is the site of the first synapse in the neurobiology of odor perception. To address questions along this front in anesthetized mice, we employ an artificial respiration strategy that decouples airflow through the nasal passages from gas exchange with the lungs. This type of preparation allows experimentally manipulating nasal airflow while simultaneously delivering oxygenated air (usually incorporating a dilute aerosolized general anesthetic) to the lungs, thus producing a stable in vivo preparation that can last for eight hours or more.This protocol is modified from an earlier form that has been briefly outlined in previous publications (Wachowiak and Cohen, 2001; Vučinić et al., 2006). Our lab and others have used this or a similar technique to investigate odor processing in the olfactory bulb of anesthetized rodents for several years (e.g., Sobel and Tank, 1993; Wachowiak and Cohen, 2001; Spors et al., 2006; Bathellier et al., 2008; Wachowiak et al., 2013; Rothermel et al., 2014; Economo et al., 2016). Here, we provide a detailed protocol for this method with the goal making it more easily adopted, and we expect that it may even find uses outside of the community working on olfactory physiology in rodents.
Materials and Reagents
Equipment
Procedure
Acknowledgments
We thank members of the Wachowiak laboratory, past and present, for improving on this technique over the years and for continuing to use it in many applications. We acknowledge funding support from several grants from the NIH, most recently R01DC006441 and R01DC013076 to MW and F32DC015389 to TPE.
Competing interests
We declare no conflict of interest or competing interests.
Ethics
All procedures have been approved by the Institutional Animal Care and Use Committee (IACUC) at the University of Utah (most recent IACUC approval #16-06018).
References
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