On the question of the origin of macrophages in the retina and the vitreous following photocoagulation (autoradiographic investigations by means of 3H-thymidine).

Abstract

The question of the origin of the macrophages in the retina and in the vitreous following photocoagulation was investigated in fourteen albino rabbits by means of 3H-thymidine. A group of seven animals were photocoagulated, the others served as controls. Prior to photocoagulation all fourteen rabbits received intravenous injections of 3H-thymidine three times at intervals of twelve hours to label all hematogenous macrophages then being formed in the bone marrow. Cells of the pigment epithelium and of the neurosensory retina on the other hand, normally being in the Go-phase, remain unlabeled. The animals were sacrificed at one hour, 24 hours and thereafter at daily intervals till the sixth day following photocoagulation. Five hours before death they received colchicine. In this way one was able to determine, wether previously labeled cells of the bone marrow undergo further mitosis following release into the tissues. Twentysix hours following photocoagulation one finds in photocoagulated animals numerous labeled cells in the area of the lesion at the walls of choroidal vessels, further immediately inside Bruch's membrane in between the photoreceptors, later even in the inner retinal layers and the adjoining vitreous, contrasting with the findings in the controls. In the ciliary region in both groups labeled cells occur in the stroma, between the epithelial cells and in the vitreous. These labeled cells in the coagulated animals increase with time more than in the controls. Numerous such labeled cells are arrested in metaphase by the colchicine. Our experiments show that at least the greater part of the macrophages appearing in and about retinal lesions following photocoagulation are of hematogenous origin. Continual immigration of hematogenous macrophages through the ciliary region, which is increased following photocoagulation, also seems most likely to take place, though this is not completely proven by this study.