ANATOMICAL RELATIONSHIP BETWEEN VAGAL AFFERENT-FIBERS AND CCK-IMMUNOREACTIVE ENTERO-ENDOCRINE CELLS IN THE RAT SMALL-INTESTINAL MUCOSA

There is evidence for a pathway involving small intestinal CCK-produci ng entero-endocrine cells and visceral afferent nerve fibers in signal ing the effect of luminal nutrients on gastrointestinal and food intak e regulation. In order to investigate the type of anatomical appositio n that exists between CCK cells and vagal afferents, CCK immunocytoche mistry was performed on tissue from rats whose vagal afferent fibers t o the abdomen had previously been labeled in vivo by injecting the flu orescent carbocyanine dye DiI into the nodose ganglia. CCK immunoreact ive (CCK-IR) cells were more abundant than vagal afferent fibers, but both were present throughout the small intestine as well as in crypts and villi. Few CCK-IR cells were in close (<5 mu m) anatomical contact with vagal afferent axons, and the latter did not produce suspicious terminal specializations near CCK-IR cells. Most labeled vagal afferen t axons, which distributed strictly within the crypt and villous lamin a propria, were at distances of tens to hundreds of microns to the nea rest CCK-LR cell. These findings strongly support the idea that CCK re leased from entero-endocrine cells acts on vagal sensory fibers in a p aracrine fashion, but do not rule out the presence of a few very close , neurocrine-like contacts or a humoral mode of action. Possible impli cations of such an arrangement on CCK-mediated satiety are discussed.