Organization of the nervous tissue (hippocampus and septum) developing in the anterior eye chamber. I. General characteristic and non-neural elements.

Hippocampal and septal tissue of the rats' embryos was grafted into anterior eye chamber of the adult rats. After 3-4 months of survival the light and electron microscopy of the grafts was performed. Significant difference in development and organization of septal (SGs) and hippocampal (HGs) grafts was observed. Developed SGs had spherical shape, the area of their contact with host iris was limited, vascularization usually occurred through a narrow tissues talk. HGs often had elongated convex shape, resembling the hippocampus in situ. They contacted the iris by their ventral surface, through which multiple vessels ingrowed. HGs increased in volume significantly more, than SGs. SGs consisted of diffuse aggregates of multipolar neurons, while in HGs pyramidal neurons formed more or less organized layer. The apical dendrites of pyramidal cells were always oriented towards iris. Periferal areas with high number of glial cells and central areas, where nervous cells were concentrated, were distinguished in the grafts. Connective tissue cells were also present in them. Specific clusters of connective tissue cells with tight junctions between them were observed at the interface between a graft and iris. Their intracellular spaces formed tissue capillaries interconnected with perivascular space of blood vessels. Morphology of the clusters indicated that these connective tissue cells had some trophic functions. Two types of organization of limiting superficial glial sheath were observed. Multilayer capsula, consisting of modified oligodendrocytes and their processes was observed in SGs. This glial sheath could be perforated by nervous processes. Monolayer glial membrane formed by fibrous astrocytes was characteristic of HGs. This type of surface organization more closely resembled normal glial limiting membrane of the brain. The capillaries in the grafts were characterized by various degrees of permeability depending on their location. The capillaries of the central "neuronal" areas had all structural features of blood-brain barrier. The capillaries of periferal, "glial" areas had less prominent barrier characteristics. Endothelium of the capillaries in connective tissue aggregates had fenestrae and perforations, which indicates to a higher degree of permeability.