Taste preference changes throughout different life stages in male rats

<div><p>Taste preference, a key component of food choice, changes with aging. However, it remains unclear how this occurs. To determine differences in taste preference between rats in different life stages, we examined the consumption of taste solutions and water using a two-bottle test. Male Sprague-Dawley rats of different ages were used: juvenile (3–6 weeks), young adult (8–11 weeks), adult (17–20 weeks), middle-aged (34–37 weeks), and old-aged (69–72 weeks). The intakes of the high and low concentration solutions presented simultaneously were measured. We observed that the old-aged group had lower preference ratios for 0.3 M sucrose and 0.1 M MSG in comparison with other groups. The preference ratio for 0.03 mM QHCl was higher in the middle-aged group than in the three younger groups and higher in the old-aged group than the juvenile group. The taste preferences for HCl and NaCl did not significantly differ among the age groups. The old-aged group tended to prefer high concentrations of sucrose, QHCl, NaCl, and MSG to low concentrations, indicating age-related decline in taste sensitivity. We also aimed to investigate differences between life stages in the electrophysiological responses of the chorda tympani nerve, one of the peripheral gustatory nerves, to taste stimuli. The electrophysiological recordings showed that aging did not alter the function of the chorda tympani nerve. This study showed that aging induced alterations in taste preference. It is likely that these alterations are a result of functional changes in other peripheral taste nerves, the gastrointestinal system, or the central nervous system.</p></div

Age-related changes in taste preference for low or high concentrations of taste solutions.

<p>Mean preference ratios + SEM for taste solutions of higher concentrations. The old-aged group exhibited a significantly greater preference for the higher concentration solution of sucrose (*<i>P</i> < 0.05, vs. juvenile, adult, and middle-aged), QHCl (**<i>P</i> < 0.01, **<i>P</i> < 0.01, and *<i>P</i> < 0.05 vs. juvenile, adult, and young-adult, respectively), NaCl (**<i>P</i> < 0.01, **<i>P</i> < 0.01, and *<i>P</i> < 0.05 vs. juvenile, young-adult, and middle-aged, respectively), and MSG (** <i>P</i> < 0.01, *<i>P</i> < 0.05, and *<i>P</i> < 0.05 vs. juvenile, young-adult, and middle-aged, respectively). The dotted lines indicate chance level. The gray-colored bars indicate preference ratios significantly different from the chance level. The <i>P</i> value of the old-aged group in the 0.03 mM vs. 0.3 mM QHCl experiment was 0.08.</p

A representative integrated response of the chorda tympani nerve to 0.1 M NH₄Cl, 0.1 M NaCl, 0.1 M MSG, 50 mM saccharin, 0.3 M sucrose, 0.3 mM QHCl, 20 mM QHCl, and 50 mM HCl for each age group.

<p>The horizontal bar indicates a stimulus duration of 30 s.</p

The relative responses to 0.1 M NH₄Cl of the chorda tympani nerve to taste solutions.

<p>Mean relative responses of the chorda tympani nerve (+ SEM) to 0.1 M NaCl, 0.1 M MSG, 50 mM saccharin, 0.3 M sucrose, 0.3 mM QHCl, 20 mM QHCl, and 50 mM HCl. The responses to each taste solution did not significantly differ among age groups.</p

General index.

<p>(A) Body weight was greater in the old-aged group compared to other groups (*¹<i>P</i> < 0.05); (B) The young adult and adult groups had greater 24-h food intake than other groups (***¹ <i>P</i> < 0.001, adult vs. juvenile, middle-aged, and old-aged; ***² <i>P</i> < 0.001, young adult vs. juvenile, middle-aged, and old-aged; *²<i>P</i> < 0.05, juvenile vs. old-aged); (C) Food intake based on body weight (per 100 g) was greater in the juvenile group than in other groups (***³ <i>P</i> < 0.001). Food intakes based on body weight of the young adult or adult group was greater than those of the middle-aged and old-aged groups (***⁴ P <0.001). Data is presented as mean + SEM.</p

The 24-h intake for DW and each solution.

<p>Mean 24-h intake + SEM from the two-bottle preference test in which two solutions were presented simultaneously for 48 h. All asterisks indicate comparisons between the taste substance and DW. *<i>P</i> < 0.05, **<i>P</i> < 0.01, ***<i>P</i> < 0.01.</p

Age-related changes in taste preference using a 48-h two-bottle test.

<p>Mean preference ratios + SEM for each taste solution. The preference ratios for 0.3 M sucrose, 0.5 M sucrose, 0.03 mM QHCl, and 0.1 M MSG significantly differed among groups. *<i>P</i> < 0.05, young adult vs. old-aged (0.3 M sucrose), middle-aged vs. young adult and old-aged (0.5 M sucrose), juvenile vs. old-aged, middle-aged vs. young adult and adult (0.03 mM QHCl), juvenile vs. middle-aged and old-aged (0.1 M MSG); **<i>P</i> < 0.01, juvenile vs. middle-aged (0.03 mM QHCl). The dotted lines indicate chance level. The gray-colored bars indicate preference ratios significantly different from the chance level. The <i>P</i> value of the middle-aged group in the 0.03 mM QHCl experiment was 0.06.</p