The expression of serotonin receptors in the gastrointestinal tract of healthy and fat necrosis-affected Japanese Black cattle.

Serotonin (5-HT) regulates gastrointestinal (GI) motility by activating various 5-HT receptor (5-HTR) subtypes. However, the expression and distribution of 5-HTR subtypes in the GI tract of Japanese Black cattle under both healthy and diseased conditions remain largely unknown. This study examined the expression of seven-transmembrane 5-HTR subtypes in healthy and fat necrosis (FN)-affected Japanese Black cattle. We found clear expression of 5-HT1BR, 5-HT2BR, 5-HT4R, and 5-HT7R mRNAs in the GI tract, in both young and adult groups. Expression of 5-HT4R and 5-HT7R was higher at most sites in adult cattle than in young cattle. The highest 5-HT4R expression was observed in the colon of adult cattle. Given the availability of antibodies and use of 5-HT4R agonists in therapy, we further examined the localization of 5-HT4R. We detected 5-HT4R mRNA and protein in neurons of the myenteric and submucosal plexuses. In FN-affected cattle, expression of 5-HT1BR, 5-HT2BR, and 5-HT7R mRNAs tended to decrease in the GI tract, while 5-HT4R mRNA remained unchanged, in comparison with healthy adult cattle. Our results show that 5-HT1BR, 5-HT2BR, 5-HT4R, and 5-HT7R mRNAs are obviously expressed in the GI tracts of Japanese Black cattle. Because 5-HT4R mRNA expression did not differ between healthy and FN-affected cattle, 5-HT4R agonists may offer therapeutic benefits for both groups, suggesting potential for clinical application in Japanese Black cattle.