Localization of Taurine and Glial Fibrillary Acidic Protein in Human Optic Nerve Using Immunocytochemical Techniques

Abstract

The well-known findings that taurine deficiency is associated with photoreceptor cell degeneration and loss of retinal function in cats, monkeys, rats, and humans, has focused attention on the role of taurine in photoreceptors (reviewed in Cocker and Lake, 1989). Although receptor cell degeneration is certainly a major effect, we have in addition observed shrinkage and cell loss in the inner retina (Lake and Malik, 1987; Lake et al., 1986) and fiber loss in the optic nerve of taurine-deleted adult rats (Lake et al., 1988). Morphometric studies of optic nerves from mother rats that had just raised a litter of pups have shown that in comparison to controls, in taurine-deleted dams there is a reduction of axon diameters and thinning of myelin sheaths, and a shift in the distributions of fiber size and myelin thickness (See Table 1). This thinning of myelin that we have observed, implicates optic nerve oligodendrocytes as targets of taurine deficiency; however, whether they are affected before, with, or secondary to axonal changes, remains to be established. It is also unknown whether the changes in the optic nerve axons occur secondary to the degeneration of photoreceptors, or are a primary effect. Hence, as a first step in resolving these questions, it is of obvious importance to determine the cytochemical location of the relatively high levels of taurine found in the nerve (e.g. Sturman et al., 1986; Ross et al., 1989). This we have done for the rat (Lake and Verdone-Smith, 1990a,b) and the micrographs which follow show the localization of taurine in human optic nerve tissue.