The peptide content of colonic afferents decreases following colonic inflammation

Peripheral injury produces long term changes in peptide content in dorsal r oot ganglion (DRG) cells that contribute to the inflammatory process in the periphery and neuronal plasticity in the spinal cord. We report here the p roportion of colonic afferents labeled for calcitonin gene-related peptide (CGRP), substance P (SP) or somatostatin (Som) in the T13-L2 and L6-S2 DRG and changes in the percentage of SP or CGRP labeled afferents 6, 24, and 72 h following induction of experimental colitis. Following injection of fluo rogold (FG) into the descending colon, significantly more FG labeled DRG ce lls were observed in the T13-L2 than L6-S2 DRG. In noninflamed rats, in bot h spinal regions, 60-70% of the colonic afferents that were labeled with FG were double labeled for SP. Similar results were obtained when double labe ling for CGRP. Only 20-30% of the FG labeled afferents were double labeled for Som. Following experimental colitis induced by intracolonic zymosan, th ere was a significant decrease in the percentage of cells double labeled fo r SP in the T13-L2 and L6-S2 DRG at 6, 24, and 72 h. The percentage of CGRP double labeled cells was decreased in the T13-L2 DRG at all time points, b ut only at 24 h in the L6-S2 DRG. The cell bodies of CGRP labeled colonic a fferents were significantly larger than SP or Som in control rats. Inflamma tion did not affect the mean size of the double labeled cells. These result s suggest that colonic inflammation increases SP and CORP release in the sp inal cord and the colon that is manifest as a decrease in peptide content i n the cell bodies of the colonic afferents during the first 72 h following injury. (C) 1999 Elsevier Science Inc. All rights reserved.