Studies on the permeability of the blood-retinal barrier. I. On the existence, development, and site of a blood-retinal barrier.

Abstract

THE concept of a blood-brain barrier has gradually evolved from a large number of different observations concerning the peculiar impermeability of the central nervous system to a wide range of substances.The original observations (Ehrlich, 1885) and much of the subsequent work (Goldmann, 1913; Spatz, 1933; Broman, 1949; Jeppsson, 1962; Bakay and Haque,' 1964; and many others) dealt with the behaviour of acid dyes, notably trypan blue which has been extensively used to demonstrate the presence or absence of this barrier.Two problems of the blood-brain barrier, its development and its site, have been' the subject of considerable discussion.If the first of these seems to have been settled by the works of Grontoft (1954) and Grazer and Clemente (1957), who demonstrated complete impermeability to trypan blue in brains at various stages of development, the second, and most controversial problem, is still unsolved.Numerous hypotheses for the site of the barrier have been proposed, and to-day there are two main schools of thought: those who believe that the blood-brain barrier is located in the endo- thelium of the vessels of the central nervous system (Spatz, 1933; Krogh, 1946; Broman, 1949; Grontoft, 1954; Rodriguez, 1955; Crone, 1960; and others) and those who believe it is located in the glial membrane facing the basement membrane of the cerebral capillaries (Gaitner, 1927; Walter, 1933; De'Robertis and Gerschenfeld, 1961; and others).In the retina of the rabbit, a similar barrier to trypan blue has been described by Schnaudigel (1913), Palm (1947), and Ashton (1965), and to the fluorescent dyes- diaminoacridines-by Rodriguez-Peralta (1962), but surprisingly there is otherwise little information in the literature regarding the permeability of the retinal vessels.Adler (1959), in his descriptive textbook of the physiology of the eye, refers only briefly to a possible difference in permeability between the choriocapillaris and the retinal capillaries.Recently Ashton and Cunha-Vaz (1965), studying the effect of histamine on the permeability of the ocular vessels, found that the retinal and cerebral vessels shared the common property of being resistant to histamine, in sharp contrast to the other vessels of the eye which behave similarly to vessels elsewhere in the body (Majno and