Number and Distribution of Intraganglionic Laminar Endings in the Mouse Esophagus as Demonstrated with Two Different Immunohistochemical Markers

Intraganglionic laminar endings (IGLEs) represent the only vagal mechanosensory terminals in the tunica muscularis of the esophagus. Two specific markers for IGLEs were recently described in mouse: the purinergic P2X2 receptor and the vesicular glutamate transporter 2 (VGLUT2). This study aimed at comparing both markers with respect to their suitability for quantitative analysis. We counted IGLEs immunostained for VGLUT2 and P2X2, respectively, and mapped their distribution in esophageal wholemounts of C57Bl/6 mice. Numbers and distribution of IGLEs were compared with those of myenteric ganglia as demonstrated by cuprolinic blue histochemistry. Whereas the distribution of VGLUT2-immunopositive IGLEs closely matched that of myenteric ganglia, P2X2-immunopositive IGLEs were rarely found in upper and middle esophagus but increasingly in its lower parts. P2X2 stained only half the number of IGLEs found with VGLUT2 immunostaining. We also investigated the correlation between anterograde tracing and immunohistochemistry for identifying IGLEs. Confocal microscopy revealed colocalization of all three markers in ∼50% of IGLEs. The remaining IGLEs showed only tracer and VGLUT2 labeling but no P2X2 immunoreactivity. Thus, VGLUT2 and P2X2 represent two specific markers for qualitative demonstration of esophageal IGLEs. However, VGLUT2 may be superior to P2X2 as a quantitative marker for IGLEs in the esophagus of C57Bl/6 mice.