OLFACTORY CONVERGENCE IN THE RODENT AMYGDALA: ELECTROPHYSIOLOGICAL CELL TYPES AND CONNECTIVITY IN BAOT AND AVMEA

In most mammals, olfaction is mediated via at least two parallel sensory systems, the main and the accessory olfactory system. Traditionally, both are believed to engage separate sensory pathways. In the periphery, specialized sensory organs transduce chemical stimuli into neuronal signals, which are relayed to and processed by the main and accessory olfactory bulbs, respectively. In this study, we investigate the anatomical and cellular components underlying potential integration of main and accessory olfactory information in downstream nuclei. Using stereotactic viral transduction and genetically targeted expression of recombinant adeno-associated viruses, we trace projection neurons of the main and accessory olfactory bulbs and identify both unimodal and shared downstream targets. Notably, we identify convergent projections from both pathways to two amygdaloid nuclei, the bed nucleus of the accessory olfactory tract (BAOT) and the anteroventral medial amygdala (avMeA). Next, we use single-cell patch-clamp recordings in acute brain slices to characterize the electrophysiological and morphological properties of individual neurons within these nuclei. We combine these electrophysiological and morphological features to reveal distinct cell types in BAOT and avMeA. Next, we interrogate the functional connectivity between olfactory bulb projections and defined amygdaloid cell types using optogenetic activation of axon terminals within BAOT and avMeA. In summary, we identify BAOT and avMeA as key sites of main and accessory olfactory pathway convergence. In addition, we provide anatomical and functional characterization of neurons potentially involved in olfactory information integration.