Implantation of the myenteric plexus into the corpus striatum of adult rats: survival of the neurons and glia and interactions with host brain.

Live or freeze-killed syngeneic adult muscularis externa, comprising myenteric plexus sandwiched between two layers of smooth muscle, was implanted into the corpus striatum of adult Fischer rats and examined electron microscopically 10 days to 6 weeks after operation. Living grafts contained healthy neurons and glial cells at all time-periods examined, although some areas of necrosis were observed. After 10 days, the glia limitans around the grafts were poorly developed and the adjacent brain tissue contained only a small number of small non-myelinated axons. After 3 and 6 weeks, the brain surrounding the living grafts contained many clusters of small non-myelinated axons. Bundles of putative central nervous system (CNS) axonal sprouts had invaded the grafts, making contact with enteric glia, despite the presence of a well-developed glia limitans at the interface with the brain. In the longer-term grafts some CNS axonal sprouts in the myenteric plexus enlarged and became myelinated. A few astrocyte processes but no axons were found in the freeze-kilied grafts. The brain surrounding the freeze-killed grafts appeared to contain fewer axonal sprouts than were present around the living grafts. The possibility that the living grafts may promote both the sprouting and the elongation of CNS axons is discussed.