Age, and not the tongue, influences our changing tastes, a new study conducted by a team of Japanese researchers reveals.
In humans and animals aging decreases dietary and energy requirements and it is generally believed that reduced consumption is related to alterations in taste preference.
However, the mechanisms underlying an age-induced shift in taste preference remain unclear.
Thus, the researchers investigated differences in fluid intake and taste nerve responses across different age groups of rats.
The researchers initially measured the intake of sweet, salty, umami, sour or bitter taste solutions in 5 age groups; juvenile, young-adult, adult, middle-aged and old-aged male rats.
The result showed that older animals exhibit a decreased preference for sweet and umami taste and a reduced aversion to bitter taste.
Additional behavioral studies examined whether aging alters taste thresholds by measuring the consumption of simultaneously presented high- and low-concentrated taste solutions.
This work revealed that taste sensitivity is lower in older rats.
To elucidate the neural mechanisms of such age-related changes in taste preference and sensitivity, electrophysiological experiments examined taste response characteristics of chorda tympani nerves.
These nerves mediate gustatory information from the tongue to the brainstem. The researchers observed no significant differences in activity of the chorda tympani nerves by taste stimuli across the different age groups.
Overall, these behavioral and electrophysiological studies demonstrate that age-related changes in taste preference and sensitivity are independent of the peripheral gustatory system.
Chizuko Inui-Yamamoto, Ph.D., the lead author of the study, stated that to their knowledge, this is the first report demonstrating a reduced aversion to bitter taste in aged rats.
She said that her team had expected that these changes were due to the peripheral taste system.
However, differences in electrophysiological recording of taste responses of the chorda tympani nerves across age groups were not observed.
Inui-Yamamoto asserted that their studies showed that aging elicited no changes in transmission of taste information from the tongue to the central nervous system.