The development of peptide-containing neurons within neocortical transplants in adult mice

Transplantation of embryonic neocortex into adult host neocortex leads to the survival of many donor cells, with the subsequent differentiation of the cortical neurons within a loosely laminated cellular pattern. We wanted to know whether peptide-containing neurons that are known to exist in normal neocortex would survive in the transplants, and if so, whether they would differentiate into morphological cell types that normally contain these peptides in cortex. By 30 days after transplantation, the implants were well vascularized and the donor neurons appeared healthy in Nissl-stained preparations. AChE-positive axons grew across the interface and innervated the transplant in moderate densities. Immunocytochemical localization of peptides in the transplant revealed that processes containing the four peptides normally present in cortex also develop in the transplants. These were vasoactive intestinal polypeptide, cholecystokinin, pancreatic polypeptide and somatostatin. Other peptides not yet demonstrated in and presumably not present in neocortex, did not develop in the transplants. These included alpha-melanocyte stimulating hormone, arginine-vasopressin, corticotropin releasing factor, beta-endorphin and substance P. The results demonstrate that peptide-immunoreactive neurons survive in neural transplants, where they develop complicated patterns of axonal arborization. The conditions used in these experiments produced no evidence that peptidergic neurons within the transplant grow out of the transplant and into the host brain within six weeks. Similarly, host peptidergic axons were never seen crossing the interface zone and entering the transplant in any significant numbers.