The Study Of Odor Representation By The Neurons In The Anterior Piriform Cortex Of Awake Mice

The mammalian piriform cortex receives direct synaptic input from the olfactory bulb and is likely the locus for the formation of odor percept. Although a lot of studies have been done in the olfactory bulb, little is known about the piriform cortex. It remains unclear how cortical neurons encode odor signals spatially and temporally. Most of previous data are acquired from anesthetized animals, whereas, anesthetic may cause some uncertain effect on the brain. How do cortical neurons encode olfactory information in unanesthetized animals?By single-cell recordings from head-restrained awake mice, we studied the odor response profiles of individual neurons in the anterior piriform cortex (aPCX). Neurons were juxtacellularly labeled, and their cell types were determined by their morphologies and neurotransmitter phenotypes. We found a considerable level of variability in selectivity patterns among pyramidal neurons (PNs). Approximately one-quarter of PNs were broadly activated by structurally dissimilar odorants, whereas the excitations to the rest of PNs were highly selective. Broad inhibition was only observed from a subpopulation of PNs. GABAergic neurons displayed nonselective excitatory responses to test odorants and rarely exhibited inhibition. In contrast, non-GABAergic nonpyramidal neurons in the deep layer tended to be strongly inhibited by multiple different odorants. Our findings suggest that odor representations are accomplished by both broadly tuned and narrow-tuned PNs in the aPCX of awake animals. In addition, various types of interneurons may play different roles in the intracortical processing of olfactory information.To answer whether there is specific spatial response pattern in the piriform cortex, we compared nearby cortical neurons'(<50μm) responses to odorants. Interestingly, we found that two nearby neurons seemed to share similar responsive properties, and this result suggests that there may be some spatial patterns in the piriform cortex.At last, we also found piriform neurons'firings relate to the behavior state of animals. When animals run, neurons kept quiet until animals stopped running. This result indicates that when the animals are in different behavior states and contexts, piriform neurons may exhibit different responsive patterns or tuning curves to odorants.