Neurochemical identification of enteric neurons expressing P2X₃ receptors in the guinea-pig ileum

Abstract.

It was hypothesised that P2X₃ receptors, predominantly labelling spinal and cranial sensory ganglionic neurons, are also expressed in intrinsic sensory enteric neurons, although direct evidence is lacking. The aim of this study was to localise P2X₃ receptors in the enteric nervous system of the guinea-pig ileum, and to neurochemically identify the P2X₃-expressing neurons. In the submucous plexus, cholinergic neurons expressing calretinin (CRT), were immunostained for P2X₃. These neurons made up about 12% of the submucous neurons. In the myenteric plexus, approximately 36% of the neurons expressed P2X₃. Half of the latter neurons were immunoreactive for CRT, whereas about 20% were immunoreactive for nitric oxide synthase (NOS). Based on earlier neurochemical analysis of enteric neurons in the guinea-pig, the myenteric neurons exhibiting P2X₃/CRT immunoreactivity were identified as longitudinal muscle motor neurons, and those expressing P2X₃/NOS immunoreactivity as short inhibitory circular muscle motor neurons. In both plexuses, no colocalisation was observed between P2X₃ and calbindin, a marker for intrinsic sensory neurons. Multiple staining with antisera raised against somatostatin, neuropeptide Y, substance P or neurofilament protein did not reveal any costaining. It can be concluded that in the guinea-pig ileum, intrinsic sensory neurons do not express P2X₃ receptors. However, this does not negate the possibility that extrinsic sensory nerves expressing P2X₃ are involved in a purinergic mechanosensory transduction pathway as demonstrated in other organs.