Immunocytochemical identification of neural elements in the central nervous systems of a snail,some insects,a fish,and a mammal with an antiserum to the molluscan cardio-excitatory tetrapeptide FMRF-amide

Summary The choriocapillaris is the fenestrated capillary network that supplies a large portion of the nutrients required by the retinal pigment epithelium, photoreceptor cells, and other cells of the outer neural retina. The permeability of these capillaries was investigated in the rat by the use of ferritin (mol. wt. approx. 480,000; mol. diam. 110Å) as a tracer. Ninety minutes after intravascular ferritin administration, a high concentration of tracer particles was distributed uniformly in the capillary lumina but few particles were present in Bruch's membrane, the multilayered basement membrane that separates the choriocapillary endothelium from the retinal pigment epithelium. The bulk of the tracer remained in the capillary lumina with a definite blockage seen at fenestral, channel, and vesicle diaphragms. These results indicate that the rat choriocapillary endothelium, unlike the fenestrated endothelia lining other capillary beds, constitutes an important barrier to the passage of ferritin and presumably of circulating native molecules of similar size.Supported by NIH grants EY 01889 and EY 07034 from the National Eye Institute and a grant-in-aid from Fight for Sight, Inc., of New York City