Distribution and co-localization of calbindin D28k with VIP and neuropeptide Y but not somatostatin, galanin and substance P in the enteric nervous system of the rat.

Calbindin D28k, previously demonstrated in the mammalian central nervous system, has been localized to discrete neurons in the enteric nervous system of the rat. Calbindin D28k is present in cell bodies in both the myenteric and submucous plexi and in interganglionic nerve fibers in all regions of the gastrointestinal tract. Immunoreactive nerve fibers were also detected in the mucosal region, although none were observed in the pyloric sphincter, circular or longitudinal muscle layers. The highest concentration of immunoreactivity was present in the submucosal plexus and mucosa of the colon. Western blot analysis of the protein detected by the antiserum confirmed that it comigrated with purified calbindin D28k and the single immunoreactive band seen in extracts from rat brain. The colocalization of calbindin D28k with components of the peptidergic innervation was also investigated. Of the peptides studied the neurons containing both vasoactive intestinal polypeptide and neuropeptide Y in the submucous plexus were seen to exhibit calbindin D28k immunoreactivity. The neurons containing somatostatin, galanin and substance P did not demonstrate co-localization. In the stomach, calbindin D28k was detected within a small number of epithelial cells which were found to correspond to a sub-population of the somatostatin-immunoreactive endocrine cells.