Anterior olfactory nucleus mediates parallel inter-bulbar pathways in rodents

Background: Interhemispheric communication of olfactory information is crucial for accurate odor perception and odor source localization in animals. However, the underlying structural basis for this communication in mammals remains poorly understood. Using electrophysiological recordings and virus-mediated tracing, we systematically dissected the neural circuits involved in interhemispheric transmission between the bilateral olfactory bulbs (OBs). Results: We identified the anterior olfactory nucleus (AON) as a central hub that facilitates direct communication between the OBs via three distinct pathways: the excitatory inter-bulbar pathway, the inhibitory inter-bulbar pathway, and the bi-bulbar co-innervation pathway. Notably, our results highlight the differential roles of AON subregions in these pathways: the pars externa (AONpE) primarily mediates the inhibitory pathway, while the pars principalis (AONpP) participates in all three pathways. These pathways recruit CaMKIIα-positive neurons in specific AON regions, which in turn project to distinct neuronal populations within the OBs. Conclusions: This study provides novel anatomical insights into the neural circuits underlying interhemispheric olfactory communication. The differential connectivity patterns of AON subregions contribute to a better understanding of how bilateral olfactory information is processed and transferred between the two OBs.