IDENTIFICATION OF THE POPULATIONS OF ENTERIC NEURONS THAT HAVE NK1 TACHYKININ RECEPTORS IN THE GUINEA-PIG SMALL-INTESTINE

Simultaneous immunofluorescence labelling was used to investigate the patterns of colocalisation of the NK1 tachykinin receptor with other n euronal markers, and hence determine the functional classes of neuron that bear the NK1 receptor in the guinea-pig ileum. In the myenteric p lexus, 85% of NK1 receptor-immunoreactive (NK1r-IR) nerve cells had ni tric oxide synthase (NOS) immunoreactivity and the remaining 15% were immunoreactive for choline acetyltransferase (ChAT). Of the latter gro up, about 50% were immunoreactive for both neuropeptide Y (NPY) and so matostatin (SOM), and had the morphologies of secretomotor neurons. Ma ny of the remaining ChAT neurons were immunoreactive for calbindin or tachykinins (TK), but not both. These calbindin immunoreactive neurons had Dogiel type II morphology. No NK1r-IR nerve cells in the myenteri c plexus had serotonin or calretinin immunoreactivity. In the submucos al ganglia, 84% of NK1r-IR nerve cells had neuropeptide Y immunoreacti vity and 16% were immunoreactive for TK. It is concluded that NK1r-IR occurs in five classes of neuron; namely, in the majority of NOS-immun oreactive inhibitory motor neurons, in ChAT/TK-immunoreactive excitato ry neurons to the circular muscle, in all ChAT/NPY/SOM-immunoreactive secretomotor neurons, in a small proportion of ChAT/calbindin myenteri c neurons, and in about 50% of ChAT/TK submucosal neurons.