Involvement of glucocorticoid in induction of lingual T1R3 in rodents

Taste receptors affect male reproduction by influencing steroid synthesis

For the male genetic materials to reach and fertilize the egg, spermatozoa must contend with numerous environmental changes in a complex and highly sophisticated process from generation in the testis, and maturation in the epididymis to capacitation and fertilization. Taste is an ancient chemical sense that has an essential role in the animal's response to carbohydrates in the external environment and is involved in the body's energy perception. In recent years, numerous studies have confirmed that taste signaling factors (taste receptor families 1, 2 and their downstream molecules, Gα and PLCβ2) are distributed in testes and epididymis tissues outside the oral cavity. Their functions are directly linked to spermatogenesis, maturation, and fertilization, which are potential targets for regulating male reproduction. However, the specific signaling mechanisms of the taste receptors during these processes remain unknown. Herein, we review published literature and experimental results from our group to establish the underlying signaling mechanism in which the taste receptor factors influence testosterone synthesis in the male reproduction.

What is the link between personality and food behavior?

A number of personality characteristics have been linked to various aspects of taste (gustation), trigeminal, and olfactory perception. In particular, personality traits have been linked to olfactory sensory thresholds and olfactory identification abilities, as well as to the sensory-discriminative aspects of taste/flavour perception. To date, much of the research in this area has focused on Sensation Seeking (including Experience Seeking, and Openness to Novel Experiences), with the latter being linked to a preference for spicy, and possibly also crunchy, sour, and bitter foods/drinks. Novelty-seeking has also been linked to a preference for salty foods, while anxious individuals appear to enjoy a much narrower range of foods. A bidirectional link has also been documented between taste and mood. Certain of the personality-based differences in taste/flavour perception and food behaviour have been linked to differences in circulating levels of neurotransmitters and hormones in both normal and clinical populations. Taken together, therefore, the evidence that has been published to date supports a number of intriguing connections between personality traits and taste perception/food behaviour.

Subchronic and mild social defeat stress downregulates peripheral expression of sweet and umami taste receptors in male mice

Depression is associated with taste disorders; however, the mechanisms by which mental stress affects taste perception are not well understood. This study aimed to elucidate the effects of psychosocial stress on peripheral taste-sensing systems using a mouse depression model. Male mice were subjected to subchronic and mild social defeat stress (sCSDS). Results showed that sCSDS significantly increased body weight, food and water intake, and social avoidance behavior and that sCSDS did not change reward-seeking behavior on sucrose preference but tended to decrease pheromonal preference for female urine. Furthermore, sCSDS downregulated the mRNA levels of sweet and umami taste receptor subunits, i.e., sweet taste receptor type 1 members 2 and 3 (T1R2 and T1R3), but not the umami taste receptor subunit, i.e., taste receptor type 1 member 1 (T1R1), in the circumvallate papillae of mice. It is known that sucrose preference is mediated by the gut-brain axis without taste perception; thus, it was considered that sCSDS affected the peripheral taste-sensing systems, rather than the central reward systems, which mediate sucrose preference. This is the first study to report that psychosocial stress affects peripheral sweet and umami taste-sensing systems.

The olfactory mucosa, first actor of olfactory detection, is sensitive to glucocorticoid hormone

The olfactory mucosa (OM) is the primary site of odorant detection, and its axonal projections relay information to brain structures for signal processing. We have previously observed that olfactory function can be affected during a prolonged stress challenge in Wistar rats. The stress response is a neuroendocrine retro-controlled loop allowing pleiotropic adaptive tissue alterations, which are partly mediated through the release of glucocorticoid hormones. We hypothesised that, as part of their wide-ranging pleiotropic effects, glucocorticoids might affect the first step of olfactory detection. To study this, we used a number of approaches ranging from the molecular detection and functional characterisation of glucocorticoid receptors (GRs) in OM cells, to the study of GR acute activation in vivo at the molecular, electrophysiological and behavioural levels. In contrast to previous reports, where GR was reported to be exclusive in olfactory sensory neurones, we located functional GR expression mostly in olfactory ensheathing cells. Dexamethasone (2 mg/kg) was injected intraperitoneally to activate GR in vivo, and this led to functional odorant electrophysiological response (electro-olfactogram) and OM gene expression changes. In a habituation/cross-habituation test of olfactory sensitivity, we observed that DEX-treated rats exhibited higher responsiveness to a complex odorant mixture. These findings support the idea that olfactory perception is altered in stressed animals, as glucocorticoids might enhance odour detection, starting at the first step of detection.