The vomeronasal system of the Japanese raccoon dog, <i>Nyctereutes viverrinus</i>

The vomeronasal system consists of a vomeronasal organ (VNO) and an accessory olfactory bulb (AOB) that act together to detect specific substances such as pheromones. The degree to which this system has developed varies among carnivorans. Raccoon dogs (Nyctereutes viverrinus) communicate using feces and urine, suggesting a significant role of the vomeronasal system. Here, we histologically detail the VNO and AOB of raccoon dogs. The VNO had a J-shaped cartilage and opened anteriorly into the incisive duct. Numerous blood vessels surrounded the vomeronasal lumen, which was medially lined by sensory epithelium. The VNO contained secretory vomeronasal glands in the submucosa, multicellular intraepithelial glands in non-sensory epithelium, and goblet cells. Submucosal glands were periodic acid-Schiff (PAS) positive and negative for Alcian blue (pH 2.5). Multicellular intraepithelial glands positive for PAS were observed in three of the six raccoon dogs analyzed herein; the glands were AB-negative and positive in one and two, respectively. The vomeronasal nerve and glomerular layers were histologically distinguishable in the AOB, but deeper layers comprised a single plexiform-granule layer with intermingled mitral/tufted and granular cells. These characteristics of raccoon dog AOBs resembled those of domesticated dogs rather than wild red foxes and gray wolves. The vomeronasal nerve and glomerular layers were positive for anti-Gαi2 and negative for anti-Gαo, suggesting that vomeronasal type 1 receptors are functionally expressed in the vomeronasal system of raccoon dogs. Overall, our findings morphologically indicated that raccoon dogs communicate using the vomeronasal system.