Pancreatic tissue grafts are reinnervated by neuro-peptidergic and cholinergic nerves within five days of transplantation

The reinnervation process is crucial for the survival and functioning of cell, tissue or organ transplants. This study was designed to examine the exact time of reinnervation of intraocular pancreatic tissue transplants in rats. The rate of survival of neuropeptide-containing cells in pancreatic tissue grafts was also investigated. Calcitonin gene-related peptide (CGRP), galanin (GAL), neuropeptide Y (NPY) were observed in the surviving nerve cell bodies of the grafts. The iridal nerves reinnervating the pancreatic grafts expressed CGRP, GAL, NPY and choline-acetyl-transferase (ChAT) on day 5, and tyrosine hydroxylase (TH) and nitric oxide synthase (bNOS) on day 6 of the transplantation period. The expression of CGRP in the reinnervating nerves was more consistent when compared to GAL, NPY, ChAT, TH and bNOS. Although all of the three neuropeptides (CGRP, GAL, NPY) were present in the surviving nerve cell bodies of the pancreatic tissue graft up to the end (day 9) of the transplantation period, the number of CGRP-immunopositive cells was consistently higher throughout the transplantation period. Hence, the number of CGRP-positive cells in the pancreatic tissue graft was significantly (P<0.05) higher than that of GAL and NPY. In conclusion, pancreatic fragments were reinnervated by neuropeptidergic (CGRP, NPY) and cholinergic (ChAT) nerves within the first 5 days of transplantation. In addition to the reinnervation of pancreatic tissue grafts, the intrinsic neurones of the grafts also survived after transplantation. The rate of survival of CGRP-containing cells in the pancreatic tissue grafts was more consistent compared to that of NPY and GAL.