Does the Environmental Air Impact the Condition of the Vomeronasal Organ? A Mouse Model for Intensive Farming

Abstract

Chemical communication in mammals is ensured by exchanging chemical signals through the vomeronasal organ (VNO) and its ability to detect pheromones. The alteration of this organ has been proven to impact animal life, participating in the onset of aggressive behaviors in social groups. To date, few studies have highlighted the possible causes leading to these alterations, and the farming environment has not been investigated, even though irritant substances such as ammonia are known to induce serious damage in the respiratory tract. The goal of this study was to investigate the environmental impact on the VNO structure. Thirty mice were split into three groups, one housed in normal laboratory conditions and the other two in confined environments, with or without the release of litter ammonia. VNOs were analyzed using histology and immunohistochemistry to evaluate the effect of different environments on their condition. Both restricted conditions induced VNO alterations (p = 0.0311), soft-tissue alteration (p = 0.0480), and nonsensory epithelium inflammation (p = 0.0024). There was glycogen accumulation (p < 0.0001), the olfactory marker protein was underexpressed (p < 0.0001), and Gαi2 positivity remained unchanged while Gαo expression was upregulated in confined conditions. VNO conditions seemed to worsen with ammonia, even if not always significantly. These murine model results suggest that the housing environment can strongly impact VNO conditions, providing novel insights for improving indoor farming systems.

Keywords: alteration; ammonia; environmental air; histology; vomeronasal organ.

Figure 1

Schematic of the plexiglass box setup used to obtain the confined conditions. O₂ = Dioxygen; NH₃ = Ammonia.

Figure 2

Daily levels of dioxygen (in green), and ammonia (in yellow), in the device during the experiment for the group exposed to ammonia.

Figure 3

Representative images of a score “2” in the tested parameters after hematoxylin and eosin staining. (A) Mouse VNO alterations, Scale bar = 200 µm. (B) Soft tissue alteration with a lymphocyte infiltration (red arrow). Scale bar = 50 µm; (C) NSE alteration, scale bar = 100 µm; (D) VNSE alteration, scale bar = 50 µm.

Figure 4

Distribution (%) of VNO alteration scores in the VNOs of mice in normal housing conditions, confined conditions, or confined conditions with natural ammonia exposure. Data are shown as the percentage of VNOs for each score in the three different groups, * p ≤ 0.05.

Figure 5

Distribution (%) of nonsensory epithelium inflammation scores comparing mouse NSEs after normal housing conditions, confined conditions, or confined conditions with natural ammonia exposure. Data are shown as the percentage of VNOs for each score, * p ≤ 0.05.

Figure 6

Distribution (%) of VNO soft tissue alteration scores of mice housed in normal housing conditions, confined conditions, or confined conditions with natural ammonia exposure. Data are shown as the percentage of VNOs for each score, *** p ≤ 0.001.

Figure 7

Distribution (%) of vomeronasal sensorial epithelium alteration scores comparing the VNSEs of mice housed in normal conditions, confined conditions, or confined conditions with natural ammonia exposure. Data are shown as the percentage of VNOs for each score.

Figure 8

Effects of environmental living conditions on glycogen accumulation. PAS staining was used to stain glycogen accumulation in the VNSEs of mice housed in normal conditions (A), confined conditions (B), or confined conditions with natural ammonia exposure (C). Data are shown (D) as the mean ± SD, *** p ≤ 0.001. Objective × 20, Scale bar = 200 µm.

Figure 9

Immunohistochemical staining of the OMP protein in the VNSEs of mice housed in normal conditions (A), confined conditions (B), or confined conditions with natural ammonia exposure (C). Data are shown (D) as the mean ± SD, *** p ≤ 0.001. Objective × 20, Scale bar = 200 µm.

Figure 10

Immunohistochemical staining of the Gαi2 protein in the VNSEs of mice housed in normal conditions (A), confined conditions (B), or confined conditions with natural ammonia exposure (C). Data are shown (D) as the mean ± SD. Objective × 20, Scale bar = 200 µm.

Figure 11

Immunohistochemical staining of the Gαo protein in the VNSEs of mice housed in normal conditions (A), confined conditions (B), or confined conditions with natural ammonia exposure (C). Data are shown (D) as the mean ± SD, ** p ≤ 0.01; *** p ≤ 0.001. Objective × 20, Scale bar = 200 µm.