Intraganglionic laminar endings in the rat esophagus contain purinergic P2X(2) and P2X(3) receptor immunoreactivity

Intraganglionic laminar endings (IGLEs) represent the most prominent vagal afferent terminal structures throughout the gastrointestinal tract. They are most prominent in the esophagus and stomach, but can be found down to the distal colon. Their role as mechanosensors as proposed on anatomical grounds was recently substantiated in elegant functional experiments. There is evidence that vagal mechanosensors in the esophagus and stomach respond to ATP. Thus, the present study aimed at detecting purinergic receptors on IGLEs. IGLEs in the rat esophagus were identified by immunohistochemistry for calretinin and sections were co-incubated with antibodies directed against P2X(2) or P2X(3) receptors. Also, double label immunocytochemistry for purinergic receptors and calcitonin gene-related peptide as a marker for spinal afferents was performed. Terminal nerve fibers immunoreactive for P2X(2) and P2X(3), respectively, were observed between outer and inner layers of the tunica muscularis, covering myenteric ganglia totally or partly. Both P2X(2) and P2X(3) receptor immunoreactivities were highly co-localized with calretinin positive IGLEs as shown by confocal laser scanning microscopy. Numerous calcitonin gene-related peptide immunostained fibers were found to closely approach and intermingle with P2X immunopositive IGLEs. However, there was never co-staining for either of the purinergic receptors and calcitonin gene-related peptide within the same fibers. P2X(3) but not P2X(2) immunoreactivity was also observed within nerve fiber arborizations in the mucosa of the pharynx. In the nodose ganglion, 8.9+/-1.1% of P2X(2) and 7.2+/-1.3% of P2X(3) immunopositive neurons, respectively, co-stained for calretinin. On the other hand, 63.4+/-4.6% and 60.1+/-5.3% of calretinin positive cell bodies contained P2X(2) and P2X(3) receptor immunoreactivity, respectively. These results indicate that IGLEs are equipped with both P2X(2) and P2X(3) receptors. Thus, they may act as chemosensors or their mechanosensory properties may be modulated by ATP. It is also suggested that spinal afferents innervating the esophagus are equipped with neither P2X(2) nor P2X(3) purinergic receptors.