Recent findings suggest that 5-HT may be considered as a key element in bidirectional communication between brain and gut, modulating brain development and behavioral responses [43-46]. Interestingly, it was shown that alteration of this two-way serotoninergic system of communication between brain and gut may play a role in the pathogenesis of various diseases, including autism spectrum disorders [47] and depression [48]. The 5-HT effects in this gut-brain axis are mediated by 5-HT receptors and, among them, the 5-HT7R is a very interesting target, being expressed both in the gut and in the brain. More studies will allow to better understand the therapeutic potential of 5-HT7R ligands as well as peripheral 5-HT in inflammatory and fibrotic diseases of gut in relationship with brain inflammatory diseases.