Morphology of axons in the human lateral geniculate nucleus: a Golgi study in prenatal and postnatal material

A study was made of rapid Golgi preparations from the lateral geniculate nucleus in humans aged from 28 weeks gestation to 70 years in order to identify axon terminals of afferent fibre systems. We describe three main axonal types using, as far as possible, nomenclature already adopted for other species. Type I axons were found only rarely. They are relatively straight with short, stalked side-branches and may represent cortico-geniculate fibres. Type II axons have complex, ball-like arborizations with large, irregular varicosities. They are common at all ages from gestation to maturity and are probably retinal in origin. Type IV axons (Type III was not used as no unequivocally intrinsic axons, for which the term has been used in the past, were identified) are branched, meandering and characterized by many, regular varicosities. Their origin is unclear, but may be related to non-specific brainstem sources. The basic morphology of Type II axons varies little between late gestation and adulthood, but Types I and IV seem to evolve during the perinatal period, perhaps from primitive forms that have similar morphological features. We conclude that the morphology of afferent axons to the human lateral geniculate nucleus is basically similar to that of lower mammalian species.