Tyrosine-hydroxylase-immunoreactive neurons in retinal transplants in the rat

Embryonic rat retinae were transplanted to the brains of newborn rats, and the distribution of catecholaminergic neurons in the retinal tissue was studied 1-2 months after transplantation, using the tyrosine hydroxylase (TH) immunohistochemical method. The results showed that distinct TH-positive cells were identified in all retinal transplants examined. The somata of the majority of these TH-immunoreactive cells were located along the inner margin of the inner nuclear layer in the retinal transplants; the processes of these cells were distributed mainly in the outer portion of the inner plexiform layer. This pattern is comparable to that observed in retinae of normal and host rats, suggesting that the organization of the catecholaminergic neurons in the transplant is largely similar to that in the normal retina. However, a reduction of the immunoreactivity in the plexiform layers and subpopulations of TH-positive cells with somatic diameter smaller than 8 microns or larger than 18 microns was observed in most of the retinal transplants studied. This implies that the organization of the catecholaminergic system in the transplant may not be as intact as in the normal retina.