Ultrastructure of spinal cord grafts with and without cografts of locus coeruleus in oculo.

The ultrastructure of spinal cord and spinal cord-locus coeruleus double grafts transplanted to the anterior chamber of the eye of adult rats was studied. The present results show that single spinal cord grafts express several morphologically organotypical characteristics of normal spinal cord at the ultrastructural level. Thus, the parenchyma was divided into a cell-rich layer corresponding to the normal gray matter and an axonal layer with a large amount of myelinated fibers and immature oligodendrocytes. In the cellular layer, a variety of cell types of different sizes were observed. The neurons had different patterns of cytoplasmic organelles, including Nissl bodies, Golgi apparatus, mitochondria, and polysomes. The Nissl substance was variable and some neurons appeared to be immature. Although the spinal cord grafts are in a state of relative gliosis, surrounded by a glial barrier, cografted fetal locus coeruleus catecholamine neurons are able to innervate the spinal cord grafts and form anatomically relevant synapses with the spinal cord neuronal elements as revealed by TH-immunoelectron microscopy. In conclusion, several organotypical features of normal spinal cord are found. Examples also were found, however, of a disturbed and delayed development that have to be considered when evaluating the functional potential of grafted cells.