Afferent innervation of the rat pancreas: retrograde tracing and immunohistochemistry in the dorsal root ganglia.

This study was undertaken to determine the segmental organization of the dorsal root ganglion (DRG) cells that give rise to pancreatic afferents containing a certain neuropeptide in the rat. These cells were examined using retrograde tracing combined with immunohistochemistry. Injection of horseradish peroxidase (HRP) into the pancreas resulted in the labeling of cells in bilateral T5-L2 DRGs, with most labeled cells lying at T10-T11. Injection into the duodenal (right), splenic (left), and entire lobes consistently produced more labeled cells significantly in the right, left, and right DRGs, respectively. Calcitonin gene-related peptide (CGRP)-, substance P (SP)-, somatostatin (SOM)-, and galanin (GAL)-immunoreactive (IR) cells in the DRGs (T9-T12) were found in -52, 17, 8, and 6%, respectively, but neuropeptide Y- and vasoactive intestinal polypeptide-IR cells were not found. About 88% of HRP-labeled cells in DRGs (T9-T12) contained CGRP, and approximately 16% of them contained SP. Although SOM- and GAL-IR cells were localized in the DRGs, these cells innervating the pancreas could not be found. In brief, these results show that bilateral (not similar in cell number on each side) DRG cells innervate the duodenal or splenic pancreas, and the majority of these cells that project to the pancreas contain CGRP and SP.