Intra-oral pre-treatment with capsaicin increases consumption of sweet solutions in rats

Sprague-Dawley rats received preference tests for sucrose or saccharin daily following oral treatment with 0.02% capsaicin. Consumed sweet solutions and preference scores increased in capsaicin-treated rats, compared to control rats on the second to fifth exposure period for sucrose and all exposure periods for saccharin. Chow intake was not affected by repeated treatment with capsaicin. Real-time RT-PCR analysis revealed decreased expression of sweet receptors T1R2 and T1R3 as well as capsaicin receptor VR1 in the circumvallate after this repeated oral exposure to capsaicin. VR1 immunoreactivities were also localized in the vallate taste cells by fluorescence immunohistochemistry. Results suggest that decreased expression of sweet receptors in the circumvallate may be related to increased sweet consumption in capsaicin-treated rats; any causal relationship should be further studied. Also, these data suggest that capsaicin may interact with a sweet transduction pathway in the mediation of its receptor VR1 that are located in the vallate taste cells.