Exploring the effects of aging on olfactory and gustatory senses in Nothobranchius furzeri and Mus musculus

Taste and smell allow vertebrates to detect and distinguish chemicals in their surroundings, such as food, predators or sexual partners. Sensory perception changes over the course of aging. Animals can perceive different scents and flavors, which may indicate the presence of nutrients or toxic substances. The aim of our research is to broaden knowledge on the interplay of chemical senses in the metabolic control via nutrient-sensing mechanism in vertebrate aging. We will try to achieve this objective through in vivo (behavioural tests) and ex vivo studies in two different species: Mus musculus outbred strain CD1 and Nothobranchius furzeri strain MZM0410 (Autoriz. n° 291/2022-PR + 1177/2020-PR). In particular, the study aims to i) analyze the differences in olfactory and gustatory responses in vivo among young, adult and elderly individuals; ii) investigate the morphological and molecular changes in smell and taste associated with aging; iii) examine the possible correlations between olfactory and taste abilities over aging. We considered three age points, corresponding to 1) young animals at sexual maturity, 2) adults in full reproductive activity, 3) reproductive and phenotypic senescence. For behavioural analyses, we tested CD1 mice in the habituation/dishabituation test (smell) and the preference 2 bottle test (taste). These tests were adapted for aquatic environment [1], in which the fishes were subjected to a preference test for 2 different types of food. From the two species, olfactory epithelium (OE) and taste buds (TBs) were collected as target tissues for ex vivo analyses. CD1 mice at all ages showed habituation to the odors presented and were able to discriminate a new odor, geraniol or citralva, presented to them after the last trial of mineral oil or geraniol, respectively (dishabituation). However, we observed an age-dependent reduction in the total time spent sniffing. In the taste preference test, CD1 mice at all ages preferred saccharin and umami over water and avoided citric acid and quinine solutions, while NaCl solution was equally preferred as water. With aging we also observed an increase of total (water+taste solution) fluid intake and a slight change of preference. In fish, Chironomus spp. is confirmed as the preferred food choice at all ages compared to dry food, although slight differences in food nibbling were observed over the three age stages. Old animals swam less and only for feeding. Histological analyses revealed differences in the morphology and distribution of olfactory and gustatory receptors [2], suggesting evolutionary adaptations to optimize sensory perception and food assimilation [3]. This study provides important insights into the relationship between smell, taste, feeding behavior, and sensory perception in both models, highlighting the importance of integrated approaches to understand the complexity of sensory and behavioral systems in phylogenetically distant species. Financial support was provided by PRIN 2022LYPBCT Notho-Diet: from chemosensory perception to husbandry standardization.