Fatty Acid Taste Quality Information via GPR40 and CD36 in the Posterior Tongue of Mice

Aim

Taste cells expressing GPR120 and connected chorda tympani nerve (CT) fibers are necessary for obtaining specific information on long-chain fatty acids (FA) in mice. However, the functions of GPR40, GPR120, and CD36 in the posterior part of the tongue remain unclear. Therefore, the present study has examined the neuron types coding for FA information in the glossopharyngeal (GL) nerve and their functions.

Methods

We performed single-fiber recordings in the GL nerve from GPR120-knockout (KO) and wild-type (WT) mice and behavioral preference tests based on five-minute intake using WT mice after the CT (and greater petrosal) nerves were sectioned bilaterally.

Results

Single fibers were classified into FA-(F), S-, M-, electrolyte-(E), Q-type, and N-best groups, based on their maximal responses to oleic acid (OA), sucrose, monopotassium glutamate, HCl, quinine hydrochloride, and NaCl. Among the GL fibers, 3.8% of GPR120-KO and 11.8% of WT mice were F-type. Furthermore, 81.8% or more of the S- and M-type fibers showed responses to FAs in both mouse genotypes. Residual responses to FAs were substantially suppressed by GPR40 and CD36 antagonists in GPR120-KO mice. Preference scores for OA decreased significantly with the addition of CD36 or GPR40 antagonists. Additionally, the preference scores for monopotassium glutamate and sucrose decreased when the mice were conditioned to avoid OA.

Conclusion

These results suggest that GPR120 contributes only to the existence of F-type fibers and that CD36 and GPR40 mediate the palatable umami or sweet taste of FAs via the activation of S- and M-type fibers in the GL nerve.