Co-localization of two-color rAAV2-retro confirms the dispersion characteristics of efferent projections of mitral cells in mouse accessory olfactory bulb.

Zheng Ning,Wang Zhi-Zhong,Yang Fang-Jia,Xu Fu-Qiang,Manyande Anne,Rao Xiao-Ping,Zhu Xu-Tao,Wang Song-Wei,Lu Chen

doi:10.24272/j.issn.2095-8137.2020.020

Zheng Ning, Wang Zhi-Zhong + Show 7 more

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https://doi.org/10.24272/j.issn.2095-8137.2020.020

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Abstract

The accessory olfactory bulb (AOB), located at the posterior dorsal aspect of the main olfactory bulb (MOB), is the first brain relay of the accessory olfactory system (AOS), which can parallelly detect and process volatile and nonvolatile social chemosignals and mediate different sexual and social behaviors with the main olfactory system (MOS). However, due to its anatomical location and absence of specific markers, there is a lack of research on the internal and external neural circuits of the AOB. This issue was addressed by single-color labeling and fluorescent double labeling using retrograde rAAVs injected into the bed nucleus of the stria terminalis (BST), anterior cortical amygdalar area (ACo), medial amygdaloid nucleus (MeA), and posteromedial cortical amygdaloid area (PMCo) in mice. We demonstrated the effectiveness of this AOB projection neuron labeling method and showed that the mitral cells of the AOB exhibited efferent projection dispersion characteristics similar to those of the MOB. Moreover, there were significant differences in the number of neurons projected to different brain regions, which indicated that each mitral cell in the AOB could project to a different number of neurons in different cortices. These results provide a circuitry basis to help understand the mechanism by which pheromone information is encoded and decoded in the AOS.

Highlights

Most animals rely heavily on their chemosensory perception to interact with their surroundings, with a variety of odor molecules carrying a wealth of information
accessory olfactory bulb (AOB) projects to bed nucleus of the stria terminalis (BST), ACo, medial amygdaloid nucleus (MeA), and posteromedial cortical amygdaloid area (PMCo) To verify the effectiveness of labeling the mitral cells of the AOB, we injected retrograde tracers into different accessory olfactory cortices of mice
These results indicate that the dispersion characteristics of efferent projections of mitral cells in the AOB are similar to those of the main olfactory bulb (MOB), that is, the axonal branches of individual mitral cells can reach all olfactory cortices (Nagayama et al, 2010)

Summary

Introduction

Most animals rely heavily on their chemosensory perception to interact with their surroundings, with a variety of odor molecules carrying a wealth of information. The vomeronasal organ (VNO), which comprises the peripheral sensory structure of the AOS, plays a major role in detecting both hetero- and con-specific social cues that convey information about identity, gender, social rank, and sexual state (Ackels et al, 2016). The VNO is a bilaterally symmetrical, cylindrical organ encased in a bony capsule on the anterior nasal septum. It is blind posteriorly with a crescent-shaped sensory epithelium located at the medial wall of the organ and a large blood vessel running laterally to the lumen. Cells in the basal layer expressing type-II vomeronasal receptors (V2Rs) and Go proteins project to the posterior part of the AOB (pAOB) (Dulac & Torello, 2003; Riviere et al, 2009). The sensory neurons expressing V2Rs, which contain a large Nterminal domain and form ligand binding sites, respond to proteinaceous components (Breer et al, 2006; Krieger et al, 1999; Leinders-Zufall et al, 2004)

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