The aim of this thesis was to use MEMRI (manganese-enhanced magnetic resonance imaging) for studying the processing of behaviorally significant odors in the rat primary olfactory cortex, under conditions close to natural perception in awake animals. MEMRI is a method based on the detection of o functional and remanent contrast agent, manganese, which has proved to be valuable dor studying odor processing in the olfactory bulb. However , this method has mainly been used to trace neuronal pathways, but seldom to explore sensory functions. Here, we have conducted two studies to define the conditions of application of manganese and to optimize processing of MEMRI images. Based on these methodological developments, we have then used MEMRI to investigate the activation of central olfactory structures following exposure of awake rats to biologically relevant odors (food and predator odors compared to a control situation). MEMRI revealed that a predator is processed differently from the control situation in the primary olfactory cortex. Fos immunolabeling in the anterior piriform cortex corroborated this result. Altogether, MEMRI and Fos results suggest that olfactory processing may rely on both the intensity of activation and the size of neuronal populations recruited. Finally, MEMRI revealed that the olfactory message, crucial for survival, is asymmetrically processed in the brain. Methodological and scientific advances brought by this thesis will be useful for better understanding brain olfactory processing.
Central processing of behaviorally relevant odors in the awake rat, as revealed by Manganese-enhanced MRI