Transplantation of Central and Peripheral Monoamine Neurons to the Adult Rat Brain: Techniques and Conditions for Survival

The conditions for survival of transplants of peripheral and central monoamine neurons in the adult rat brain were studied using fluorescence histochemistry. Pieces of the superior cervical ganglion from newborn and adult rats and CNS tissue containing noradrenaline (NA), dopamine (DA) and indolamine (IA) neurons from embryonic, newborn and adult rats were transplanted to various brain sites using different techniques: insertion of the graft by means of a glass rod, by "injection", or by direct implantation of the graft in a resection cavity. Three principally different locations for the graft were tested: within the brain parenchyma in the caudal diencephalon and the caudate nucleus; onto the dorsal surface of the caudate nucleus; and onto the pial covering in the choroidal fissure after removal of the overlying cortex and parts of the hippocampal formation. Attempts were also made to transplant to the dorsal surface of the caudate nucleus or the hippocampus with the aid of an "artificial" vascular bed, achieved by previous transplantation of an iris. Consistent survival of the transplanted central and peripheral neurons was obtained only when the transplant was placed in contact with a vessel-rich tissue, such as the pia in the choroidal fissure or the "artificial" vascular bed. While the majority of the monoamine-containing neurons in the transplants died within the first month after transplantation, a significant number of neurons (up to about 150 in the ganglionic pieces and up to about 500 in the embryonic or newborn CNS pieces) survived for at least half a year in the brain. Survival of transplanted adult central monoamine neurons was not observed. A substantial outgrowth of axons was observed from all types of neurons in their new location. These newly formed fibers formed extensive fiber patterns within the transplant itself, around pia vessels, and within the adjacent brain tissue, above all in the hippocampal formation. The usefulness of the present transplantation technique for the exploration of mechanisms underlying reformation of axonal connections in the adult mammalian CNS is discussed.