Morphological and histological features of the vomeronasal organ in the brown bear

Jumpei Tomiyasu; Daisuke Kondoh; Hideyuki Sakamoto; Naoya Matsumoto; Motoki Sasaki; Nobuo Kitamura; Shingo Haneda; Motozumi Matsui

doi:10.1111/joa.12673

Morphological and histological features of the vomeronasal organ in the brown bear

J Anat. 2017 Nov;231(5):749-757. doi: 10.1111/joa.12673. Epub 2017 Aug 8.

Authors

Jumpei Tomiyasu^{1

2}, Daisuke Kondoh³, Hideyuki Sakamoto⁴, Naoya Matsumoto⁴, Motoki Sasaki^{2

3}, Nobuo Kitamura^{2

3}, Shingo Haneda¹, Motozumi Matsui^{1

2}

Affiliations

¹ Laboratory of Theriogenology, Department of Applied Veterinary Medicine, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Hokkaido, Japan.
² The United Graduate School of Veterinary Sciences, Gifu University, Gifu, Japan.
³ Laboratory of Veterinary Anatomy, Department of Basic Veterinary Medicine, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Hokkaido, Japan.
⁴ Noboribetsu Bear Park, Noboribetsu, Hokkaido, Japan.

Abstract

The vomeronasal organ (VNO) is a peripheral receptor structure that is involved in reproductive behavior and is part of the vomeronasal system. Male bears exhibit flehmen behavior that is regarded as the uptake of pheromones into the VNO to detect estrus in females. However, the morphological and histological features of the VNO in bears have not been comprehensively studied. The present study investigated the properties and degree of development of the VNO of the brown bear by histological, histochemical and ultrastructural methods. The VNO of bears was located at the same position as that of many other mammals, and it opened to the mouth like the VNO of most carnivores. The shape of the vomeronasal cartilages and the histological features of the sensory epithelium in the bear VNO were essentially similar to those of dogs. Receptor cells in the VNO of the bear possessed both cilia and microvilli like those of dogs. The dendritic knobs of receptor cells were positive for anti-G protein alpha-i2 subunit (G_αi2 ) but negative for anti-G protein alpha-o subunit_, indicating preferential use of the V1R-G_αi2 pathway in the vomeronasal system of bears, as in other carnivores. The VNO of the bear possessed three types of secretory cells (secretory cells of the vomeronasal gland, multicellular intraepithelial gland cells and goblet cells), and the present findings showed that the secretory granules in these cells also had various properties. The vomeronasal lumen at the middle region of the VNO invaginated toward the ventral region, and this invagination contained tightly packed multicellular intraepithelial gland cells. To our knowledge, this invagination and intraepithelial gland masses in the VNO are unique features of brown bears. The VNO in the brown bear, especially the secretory system, is morphologically well-developed, suggesting that this organ is significant for information transmission in this species.

Keywords: olfactory communication; pheromones; reproductive behavior; vomeronasal glands.

MeSH terms

Animals
Female
Male
Ursidae / anatomy & histology*
Vomeronasal Organ / anatomy & histology*