Abstract
BackgroundSo far, an overall view of olfactory structures activated by natural biologically relevant odors in the awake rat is not available. Manganese-enhanced MRI (MEMRI) is appropriate for this purpose. While MEMRI has been used for anatomical labeling of olfactory pathways, functional imaging analyses have not yet been performed beyond the olfactory bulb. Here, we have used MEMRI for functional imaging of rat central olfactory structures and for comparing activation maps obtained with odors conveying different biological messages.Methodology/Principal FindingsOdors of male fox feces and of chocolate flavored cereals were used to stimulate conscious rats previously treated by intranasal instillation of manganese (Mn). MEMRI activation maps showed Mn enhancement all along the primary olfactory cortex. Mn enhancement elicited by male fox feces odor and to a lesser extent that elicited by chocolate odor, differed from that elicited by deodorized air. This result was partly confirmed by c-Fos immunohistochemistry in the piriform cortex.Conclusion/SignificanceBy providing an overall image of brain structures activated in awake rats by odorous stimulation, and by showing that Mn enhancement is differently sensitive to different stimulating odors, the present results demonstrate the interest of MEMRI for functional studies of olfaction in the primary olfactory cortex of laboratory small animals, under conditions close to natural perception. Finally, the factors that may cause the variability of the MEMRI signal in response to different odor are discussed.
Highlights
In small animal models, an overall picture of the activation of the primary olfactory cortex following stimulation by natural biologically relevant odors has not yet been produced
Conclusion/Significance: By providing an overall image of brain structures activated in awake rats by odorous stimulation, and by showing that Mn enhancement is differently sensitive to different stimulating odors, the present results demonstrate the interest of Manganese-enhanced MRI (MEMRI) for functional studies of olfaction in the primary olfactory cortex of laboratory small animals, under conditions close to natural perception
In vivo calcium imaging [9,10,11] is limited to restricted brain surface regions and positron emission tomography (PET) scanning, which produces three-dimensional images of the whole brain, has a low spatial resolution that has largely limited its application to human studies [12,13,14,15]
Summary
An overall picture of the activation of the primary olfactory cortex following stimulation by natural biologically relevant odors has not yet been produced. This is likely due to the inadequacy of most functional imaging techniques to provide such global views. In vivo calcium imaging [9,10,11] is limited to restricted brain surface regions and PET scanning, which produces three-dimensional images of the whole brain, has a low spatial resolution that has largely limited its application to human studies [12,13,14,15]. We have used MEMRI for functional imaging of rat central olfactory structures and for comparing activation maps obtained with odors conveying different biological messages
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