QUADRUPLE COLOCALIZATION OF CALRETININ, CALCITONIN-GENE-RELATED PEPTIDE, VASOACTIVE-INTESTINAL-PEPTIDE, AND SUBSTANCE-P IN FIBERS WITHIN THE VILLI OF THE RAT INTESTINE

Double-labeling immunofluorescent histochemistry demonstrates that cal retinin, a calcium-binding protein, coexists with calcitonin gene-rela ted peptide, vasoactive intestinal peptide, and substance P in the fib ers innervating the lamina propria of the rat intestinal villi. An ace tylcholinesterase histochemical stain revealed that the majority of ca lretinin-containing cells in the myenteric ganglia were cholinergic an d that about one half of the submucosal calretinin-containing cells co localized with acetylcholinesterase. In situ hybridization studies con firmed the presence of calretinin mRNA in the dorsal root ganglia, and a ribonuclease protection assay verified the presence of calretinin m essage in the intestine. The coexistence of calretinin in calcitoninge ne-related-peptide-containing cells that also contained substance P an d vasoactive intestinal polypeptide in the dorsal root ganglia suggest that these ganglia are the source of the quadruple colocalization wit hin the sensory fibers of the villi. Although the function of calretin in in these nerves is unknown, it is hypothesized that the coexistence of three potent vasodilatory peptides influences the uptake of metabo lized food products within the vasculature of the villi.