Increased hypothalamic c‐Fos expression and anxiety‐like behaviors by oral exposure to capsaicin in rats

Abstract

In this study, we examined the neurobehavioral outcome of repeated oral exposures to capsaicin in rats. Oral application of 0.02% capsaicin was performed once daily and the rats were subjected to the behavioral tests following 10 days of oral capsaicin or sacrificed for c‐Fos immunohistochemistry at 1 h after the first oral capsaicin. The control group received water orally instead of capsaicin, and for immunohistochemistry, rats were transcardially perfused with 4% paraformaldehyde. Total ambulatory counts and the distance travelled in the activity chamber did not differ between the capsaicin and the control groups; however, the central zone activities were decreased in the capsaicin group. In the elevated‐plus maze test, capsaicin rats spent more time in the closed arms than control rats. In Porsolt swim test, swimming duration was decreased, struggling increased, in capsaicin rats without statistical significance. Oral capsaicin exposure significantly increased c‐Fos expression not only in the nucleus tractus of solitarius but also in the paraventricular nucleus. Results suggest that a long‐term oral exposure to capsaicin may increase anxiety‐like behaviors, likely by affecting neural plasticity of the hypothalamic neurons. Supported by NRF(20100003642)