No abstract

Xenogeneic donors, a largely untapped resource, would solve many of the problems associated with the limited availability of human donor tissue for neural transplantation. Previous work in our laboratory has revealed that xenografts of isolated bovine chromaffin cells survive transplantation into the periaqueductal gray (PAG) of immunosuppressed adult rats. Electron microscopic analysis reveals that graft sites contain healthy chromaffin cells, but do not contain host immune cells typical of graft rejection. The aim of the current study was to assess the necessary conditions for long-term survival of bovine chromaffin cell xenografts in the central nervous system (CNS). In particular, the need for short-course vs. permanent immunosuppressive therapy with cyclosporine A (CsA) for the long-term survival of grafted bovine chromaffin cells was addressed. Grafts from animals receiving continuous CsA treatment for either 3, 6, or 12 wk contained large clumps of dopamine-beta-hydroxylase (DBH) positive cells in contrast to the few surviving cells observed in nonimmunosuppressed animals. In addition, grafts from animals that had CsA treatment terminated at 3 or 6 wk contained similarly large clumps of DBH-positive cells. Furthermore, short-term immunosuppression (3 wk) appeared to enhance the long-term survival of grafted cells, since clumps of DBH staining cells could still be positively identified in the host PAG at least 1 yr after transplantation. Complete rejection of graft tissue depends on several factors, such as blood-brain barrier integrity, the presence of major histocompatibility complex (MHC) antigens in either the host or graft, and the status of the host immune system.(ABSTRACT TRUNCATED AT 250 WORDS)

Our previous studies have demonstrated that suspension grafts of isolated bovine chromaffin cells survive in the periaqueductal gray (PAG) of rat midbrain for up to 1 year after transplantation. The current study aimed to determine whether this type of graft could survive transplantation into sites other than the PAG that can benefit from chromaffin cell secretory products. In this study, electron microscope analysis showed that chromaffin cells implanted into the frontal neocortex, striatum, PAG, or the subarachnoid space overlying the spinal cord survived for at least 8 weeks without evidence of degeneration. Intraparenchymally placed grafts appeared relatively avascular and well integrated within the host parenchyma. When blood vessels were found, they were primarily at the host-graft border and were of the nonfenestrated central nervous system (CNS) type. Numerous synapses were present between the grafted cells and host neuronal processes. In addition, extensive intercommunication, via gap junction-like structures, was common in the grafts. Morphologic evidence of granular secretion was most commonly seen in striatal grafts. In contrast, subarachnoid grafts displayed minimal interaction with the host spinal tissue and were heavily vascularized with fenestrated capillaries. Despite morphologic differences between intra- and extraparenchymal grafts, this study demonstrates that isolated suspensions of bovine chromaffin cells survive transplantation into CNS sites without exogenous trophic factors and suggests that these cells are potential candidates for neural transplantation into these regions.

No abstract

A simple chamber and an inexpensive superfusion system for studying mammalian brain slices containing neural transplants is described. With this method, rat brain slices containing bovine chromaffin cell transplants can be maintained for several hours, allowing for the determination of neurochemical characteristics and pharmacologic responsiveness of the grafted cells. Using this technique, basal and nicotine-stimulated release of metenkephalin from rat periaqueductal gray slices containing bovine chromaffin cell transplants were measured. Results showed that met-enkephalin release can be increased by nicotinic stimulation in slices containing chromaffin cell, but not control implants, for at least 8 weeks postimplantation. Furthermore, this response was dose-related. These results are in good agreement with previous behavioral studies and provide corroborative evidence for the mechanism of pain reduction by the release of opioid peptides from chromaffin cell transplants in the periaqueductal gray. This study demonstrates that neurochemical and pharmacologic analyses of neural transplants using a superfused brain slice method can be a complementary approach in determining the underlying mechanisms of neural transplants in the central nervous system.