Retrograde axonal transport in rat ileal mesenteric nerves. Characterization using intravenously administered 125I-nerve growth factor and effect of chemical sympathectomy

Abstract

We have previously demonstrated the reproducible occurrence of dystrophic axonopathy and a defect in the retrograde axonal transport of 125I-nerve growth factor (125I-NGF) involving postganglionic sympathetic axons in the alimentary tract of rats with chronic streptozocin (STZ)-induced diabetes. To avoid complexities inherent in monitoring the accumulation of 125I-NGF in the superior mesenteric ganglion as a measure of retrograde transport in the peripheral axons of the extensive alimentary territory, we have examined retrograde axonal transport of 125I-NGF directly in ileal mesenteric nerves. 125I-NGF was injected systemically, and 2-2.5 h later ileal mesenteric nerve pedicles were ligated in vivo for various intervals. Retrogradely transported 125I-NGF in rat mesenteric nerves was measured distal to a ligature placed on the ileal mesenteric pedicle. Transport-unrelated processes, such as mechanical compression or bleeding at the site of ligation, did not contribute significantly to accumulation measured in this fashion. Accumulation of retrogradely transported 125I-NGF at the ligature began 4 h after ligation and remained linear for approximately 12 h. The amount of retrogradely transported 125I-NGF accumulating distal to the ligature reflected the length of the ileal segment served by the pedicle, which allowed the standardization of accumulation based on length of ileum innervated. The results of several experiments showed that 125I-NGF transport originated largely from nerve terminals within the ileal wall with a smaller component from extramural sites, probably terminals within the walls of blood vessels. Accumulation at a ligature was greatly reduced in animals sympathectomized with guanethidine or 6-hydroxydopamine, indicating that at least 60-80% of axonal transport of 125I-NGF in ileal mesenteric nerves represented transport in postganglionic sympathetic axons. These results establish the feasibility of measurements of 125I-NGF transport in the minute fascicles of ileal mesenteric nerves serving the alimentary tract of the rat as a method to study retrograde axonal transport in sympathetic axons in pathologic processes such as diabetes.