NK1, NK2 and NK3 tachykinin receptor localization and tachykinin distribution in the ileum of the mouse.

Tachykinin receptors NK1r, NK2r and NK3r bind tachykinins with different affinities and share pharmacological and molecular differences among animal species. NK1r, NK2r, NK3r and tachykinin (SP/NKA) distribution was studied by immunohistochemistry in the ileum of mouse since no data are available for this species. The results were then compared to those obtained in the rat and guinea pig either by us or by others to ascertain interspecies similarities and/or differences. NK1r- and NK3r-immunoreactivity (IR) were detected in neurons and NK1r-IR in the interstitial cells of Cajal at the deep muscular plexus. At variance with rat and guinea pig, NK1r-IR was also found in the myoid cells of the villi, while NK2r-IR was never detected in nerve varicosities. This latter datum suggests that the NK2r does not play a presynaptic role in the mouse. Unexpectedly, a high NK2r-IR and the presence of NK3r-IR were observed at the inner portion of the circular muscle layer in the mouse as well as in the rat and guinea pig, demonstrating a subregional distribution of these receptors. Tachykinin distribution did not show noticeable species-related differences. The present findings show species-related differences in the tachykinin receptor distribution that might be related to a different tachykinin control of intestinal motility.