The Effect of Ammonia on Olfactory Epithelium and Vomeronasal Organ Neuroepithelium of Rabbits

Abstract

In recent studies, the vomeronasal organ (VNO), although vestigial and with unknown function in humans, was reported to be present in almost every person examined. In rabbits, it is a well-developed organ, one lying on each side of the nasal septum. Histologically it was found to contain neuroepithelium which is considered an accessory olfactory system taking charge of an olfactory discrimination different from that of olfactory epithelium. Experimental removal of the VNO in male animals reduces reproductive performance and aggression. In this study, the effects of prolonged exposure to ammonia vapor on the histological pattern and enzymatic activity of the olfactory epithelium and the VNO neuroepithelium of 30 adult male rabbits were investigated and compared with a control group. In the exposed animals, the supporting cells in both types of epithelia showed hyperplasia which was more marked in the olfactory epithelium. Manifestations of cytotoxicity were found more in the bipolar cells of the olfactory epithelium than in the VNO neuroepithelium. The enzymatic activity in the exposed group supported the histological results. The presence of the VNO neuroepithelium of the rabbit in a narrow duct with a minute nasal orifice could have some protective effects on the cells.

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

“…Our study showed that compared to normal housing conditions, confined conditions induced more VNO changes, suggesting that the accumulation of pollutant gases and dust could be one of the causes of these changes in farm animals. These findings are in agreement with those reported in nasal mucosa studies, and alterations in the nasal mucosa have been previously linked to environmental contaminants such as organic dust and natural gases, including ammonia and hydrogen sulfide [ 14 , 15 , 16 ]. The olfactory epithelium and the sensory epithelium are physiologically and anatomically similar [ 25 ], and it is possible to draw a parallel between these two structures and their responses to environmental conditions.…”

“…The olfactory epithelium is strongly impacted by air pollutants in the closed housing environment of many farm species, such as pigs or rabbits [ 14 , 15 , 16 , 17 ]. The organic matter litter decomposition releases some pollutants, such as ammonia [ 18 , 19 , 20 ], responsible for nasal pathologies and contributes to the deterioration and inflammatory lesions of the nasal epithelium in mice [ 21 , 22 ].…”

“…Since the vomeronasal epithelium shares several anatomical and physiological similarities with the olfactory mucosa, these farm pollutants could also be presumed to be possible causes of inflammation of the VNO. A study by Gaafar showed that prolonged exposure to ammonia had a chronic irritative effect on the respiratory mucosa and the VNSE with a reduction in the number of neurons in rabbits [ 16 ].…”

Effects of CO2 inhalation exposure on mice vomeronasal epithelium

“…However, it is well-known that urine is able to activate the main olfactory system (CN I) in the nasal cavity. Possibly, CO 2 exposure can induce histopathological changes in the different nasal epitheliums, and comparative studies could be relevant to determine whether the VNO is more protected as suggested by Gaafar et al (1998).…”

“…Several inhalation studies have considered effects of toxic chemicals on olfactory functioning, but only one (Gaafar et al 1998) has examined the influence on the VNO. However, histopathological changes on the VNO in relation to toxic exposure could have a major ecological impact as intraspecies relationships can be disrupted.…”