Immunohistochemical and electron microscopic study of extrinsic hepatic reinnervation following orthotopic liver transplantation in rats.

Abstract

Because little has been known about the morphological and functional consequences of liver transplantation on hepatic autonomic nerves, we examined the time-course of extrinsic hepatic innervation at the level of the porta hepatis of liver allografts. Orthotopic liver transplantation was performed using male Lewis rats. Crosscut tissue specimens were obtained postoperatively for up to 6 months from the porta hepatis of transplanted livers, and processed for immunohistochemical staining for protein gene product 9.5 (PGP 9.5) and growth-associated protein 43 (GAP-43), and for transmission electron microscopy (TEM). Extrinsic nerve fibers at the porta hepatis stained positively for PGP 9.5 throughout the entire study period. In contrast, the immunoreactivity of GAP-43 was negative at postoperative day (POD) 1 and 2. GAP-43-positive nerves were first observed to appear in the porta hepatis at POD 3. The immunoreactivity of GAP-43 remained positive thereafter until 3 months post-OLT, and became negative in all the specimens at 4 months post-OLT. Transmission electron microscopy demonstrated a small number of regenerating axons existing among many degenerating axons at POD 3. At 3 months post-OLT, most regenerating axons had been fully ensheathed by the cytoplasm of Schwann cells, although their density remained at a lower level compared with normal. The results of this study suggest that liver allografts become extrinsically reinnervated, with the regenerating axons reaching the hepatic hilus 3 days after transplantation. The process of extrinsic hepatic reinnervation is considered to almost terminate 4 months after transplantation in rats.