カプサイシンが脳幹味覚ニューロンの味応答に与える影響

抄録

In the present study, we investigated whether oral capsaicin affects the taste-evoked neuronal activities in the brainstem gustatory centers, the nucleus of the solitary tract of the medulla (NTS) and parabrachial nucleus of the pons (PBN), in the rat by using c-fos immunohistochemistry. Taste stimuli used were as follows: 0.2 M NaCl, 2 mM quinine-HCl, 0.2 M NaCl mixed with 330 μM capsaicin, and 2 mM quinine-HCl mixed with 330 μM capsaicin. Rats were chronically implanted with oral cannula and presented with these test stimuli for 10 minutes (500 μl/min). Application of either NaCl or quinine alone induced significant Fos-like immunoreacitivity (FLI) both in the waist and lateral areas of PBN. It has been reported that the neurons are responsive to NaCl or quinine in the waist and lateral areas, respectively. Combined application of capsaicin with NaCl or quinine, however, significantly reduced FLI in the waist area in PBN compared with FLI induced by NaCl or quinine by itself, whereas addition of capsaicin did not affect FLI in the lateral area of PBN. Furthermore, combined application of capsaicin with quinine reduced FLI in the gustatory portion of NTS compared with the FLI evoked by quinine alone. These results suggest that Capsaicin affects neuronal activity in subnuclei of the PBN differentially. These inhibitory effects of capsaicin on taste neuron can correlate with capsaicin-induced suppression of taste perception in humans. [J Physiol Sci. 2006;56 Suppl:S182]