Figure 3. Tissue acetylcholine (ACh) and 5-hydroxytryptamine (5-HT) contents are increased in DIO mice, together with increased expression of tryptophan hydroxylase 1 (TPH1) and tryptophan hydroxylase 2 (TPH2), but not acetylcholine transferase (ChAT) or serotonin reuptake transporter (SERT) (12 weeks of feeding).

Colonic tissue content of 5-HT (A) and ACh (B) is significantly enhanced in DIO mice. These changes occurred without altered expression in ChAT (C, rate-limiting enzyme in the synthesis of ACh), but was associated with increased expression of TPH1 (D) and TPH2 (E), which are involved in the synthesis of 5-HT. SERT (F) expression was not changed in the colon of DIO mice. Images in (G) are representative examples of 5-HT immunoreactive enterochromaffin (EC) cells in the colonic mucosa of ND and DIO mice. Number of mucosal EC cells was similar in ND and DIO mice (H); note that 5-HT-positive mast cells in the lamina propria were not counted. Similar expression of paired box gene 4 (PAX4) in the colon of ND and DIO mice (I). Numbers in parentheses indicate number of animals. Asterisks mark significant changes, see text for P values. DIO, diet-induced obese mice; ND, mice receiving normal diet.