The serotonin system was evaluated by Western blot analysis by determining the content of 5-HT3B, 5-HT4, and SERT proteins expressed as relative intensity (mean ± SEM) of the immunoreactive band in colon and brain tissue samples of Ctrl-Std, Ctrl-KD, IBS-Std, and IBS-KD rats. The gene discussed is SLC6A4; the disease is irritable bowel syndrome.