ABSTRACT
This chapter focuses on an analysis of the extrinsic afferent innervation of the upper gastrointestinal tract and pancreas and includes a description of the origin, peripheral distribution and neurochemistry of afferent fibers as visualized by combining retrograde tracing approaches and immunohistochemistry, with a particular emphasis on vagal afferents. calcitonin gene-related peptide (CGRP) and tachykinins (TKs) are widely distributed throughout the enteric nervous system where they are present in nerve fibers innervating the layers of the gut, the pancreas and hepatobiliary tract in several species. The percentages of CGRP/TK-containing vagal neurons supplying the upper gastrointestinal tract and pancreas were even lower, ranging from 1% to 7%. The contribution of vagal or spinal peptidergic neurons, as visualized by immunohistochemical labeling for CGRP and TKs in combination with retrograde tracing axonal techniques, to the total afferent innervation of different viscera varies depending on the viscus. The major source for the peptidergic afferent innervation of abdominal viscera, including the alimentary tract, is the dorsal root ganglia.
