Olfactory epithelium changes in germfree mice

Abstract

Intestinal epithelium development is dramatically impaired in germfree rodents, but the consequences of the absence of microbiota have been overlooked in other epithelia. In the present study, we present the first description of the bacterial communities associated with the olfactory epithelium and explored differences in olfactory epithelium characteristics between germfree and conventional, specific pathogen-free, mice. While the anatomy of the olfactory epithelium was not significantly different, we observed a thinner olfactory cilia layer along with a decreased cellular turn-over in germfree mice. Using electro-olfactogram, we recorded the responses of olfactory sensitive neuronal populations to various odorant stimulations. We observed a global increase in the amplitude of responses to odorants in germfree mice as well as altered responses kinetics. These changes were associated with a decreased transcription of most olfactory transduction actors and of olfactory xenobiotic metabolising enzymes. Overall, we present here the first evidence that the microbiota modulates the physiology of olfactory epithelium. As olfaction is a major sensory modality for most animal species, the microbiota may have an important impact on animal physiology and behaviour through olfaction alteration.

Olfactory dysfunction in the pathophysiological continuum of dementia

“…The mucus secretions produced by the interlining Bowman's glands are rich in glycoproteins and contain odorantbinding proteins, growth-and immune-factors supporting the integrity and the odorant response of the olfactory sensory neurons (OSN) (Federico et al, 1999). Furthermore, the mucus creates a barrier to xenobiotics favoring the colonization of resident microbial species, which are involved in OE turnover and the efficiency of the odorant responses (François et al, 2016). Cholinergic and adrenergic efferents innervate the OE and regulate the secretory activity of Bowman's gland (Zielinski et al, 1989).…”

Disruptive physiology: olfaction and the microbiome–gut–brain axis

“…Scant information exists as to the normal nasal microbial composition or that seen in disease (Costello et al ., ; Yan et al ., ), although some information is emerging in rodents (Francois et al ., ). However, olfactory malfunction in the form of hyposmia has long been described as associated with neurodegenerative disorders such as Alzheimer's disease (Thompson, Knee & Golden, ).…”

“…It is well established that gut integrity to passage of macromolecules and particles is maintained by luminal microbes (Bischoff et al ., ). Recently, GF mouse olfactory epithelium was shown to be structurally abnormal and evidence adduced that microbiota ‘modulates the physiology’ (Francois et al ., , p. 1). The structural alterations were associated with functional abnormalities involving ‘a global increase in the amplitude of responses to odorants in GF mice as well as altered response kinetics.…”

“…Thus the perception of odorants and their production may well play a major role in the interpretation of the results of experiments involving the microbiome–gut–brain axis (MGBA). Furthermore, gut microbiota are responsible for the synthesis of many odorants, and experiments in germ‐free (GF) mice have shown that they may influence the very structure of the olfactory epithelium (Francois et al ., ). Lastly, a recent publication (Goodrich et al ., ) has shown in a human twin study that an olfactory gene, OR6A2 , is significantly associated with the presence of certain heritable microbe populations.…”

At the Intersection of Microbiota and Circadian Clock: Are Sexual Dimorphism and Growth Hormones the Missing Link to Pathology?

“…Indeed, raising rats under GF conditions impedes their capacity to generate specific odors involved in recognition that are genetically determined . In addition, the microbiome also contributes to a normal maturation of the olfactory system . This could contribute to the poor reproductive capacity of GF mice …”