VAGAL AND SPINAL AFFERENT INNERVATION OF THE RAT ESOPHAGUS - A COMBINED RETROGRADE TRACING AND IMMUNOCYTOCHEMICAL STUDY WITH SPECIAL EMPHASIS ON CALCIUM-BINDING PROTEINS

Vagal afferent neurons contain a variety of neurochemical markers and neuroactive substances, most of which are present also in dorsal root ganglion cells. To test for the suitability of the calcium-binding pro tein calretinin as a specific marker for vagal afferent fibers in the periphery, immunocytochemistry for this protein was combined with retr ograde tracing. Nerve fibers in the rat esophagus, as well as vagal an d spinal sensory neurons innervating the esophagus, were investigated for co-localization of calretinin with calbindin, calcitonin gene-rela ted peptide, and NADPH diaphorase. The results indicated that calretin in immunocytochemistry demonstrates neuronal structures known as vagal afferent from other studies, in particular intraganglionic laminar en dings. A few enteric neurons whose distribution was unrelated to intra ganglionic laminar endings also stained for calretinin. Strikingly, ca lretinin immunoreactivity was absent from spinal afferent neurons inne rvating the rat esophagus. In intraganglionic laminar endings and nodo se ganglion cells calretinin was highly co-localized with calbindin bu t not with calcitonin gene-related peptide. On the other hand, calbind in was also found in spinal afferents to the esophagus where it was co -localized with calcitonin gene-related peptide. Vagal afferent neuron s innervating the esophagus were never positive for NADPH diaphorase. Thus, calretinin appears to be a more specific marker for vagal affere nt structures in the esophagus than calbindin, which is expressed by b oth vagal and spinal sensory neurons. Calretinin immunocytochemistry m ay be utilized as a valuable tool for investigations of subpopulations of vagal afferents in certain viscera. J. Comp. Neurol. 398:289-307, 1998. (C) 1998 Wiley-Liss, Inc.