Patterns of innervation of vasoactive intestinal polypeptide, neuropeptide Y, and gastrin-releasing peptide immunoreactive nerves in the feline pancreas

In this study, we performed a detailed analysis of the immunoreactive (IR) patterns and tissue distribution of vasoactive intestinal polypeptide (VIP), neuropeptide Y (NPY), and gastrin-releasing peptide (GRP) in the feline pancreas by means of immunohistochemical and radioimmunological techniques. Immunoreactivity for each peptide is localized to varicose nerve fibers distributed throughout the exocrine and endocrine pancreas, with some differences in the density and pattern of fiber distribution. In the acinar and stromal compartments, VIP-IR processes have a higher density than NPY-and GRP-containing fibers, the latter being the least abundant. The vasculature receives a particularly prominent NPY innervation, while GRP-and VIP-IR fibers are found occasionally in association with blood vessels. Around ducts, NPY-and VIP-IR nerves are more numerous than those positive for GRP-IR, which are quite sparse. One of the most interesting findings of the present work is the visualization of all peptide-IRs both in neuronal cell bodies and fibers within the intrapancreatic ganglia. VIP-IR is observed in virtually all ganglion cells, while GRP-and NPY-IRs are seen in a few neuronal cells. VIP and NPY tissue levels are much higher than GRP concentrations in all regions of the pancreas. VIP content in the head and body is greater than in the tail. The morphological relationship of VIP-, NPY-, and GRP-IR fibers with different pancreatic structures is consistent with specific peptidergic neural inputs in the regulation of pancreatic functions.