Synaptophysin-Positive Neurons in External And Extreme Capsules in Human Brain

Purpose: Externaland extreme capsules are parts of cerebral white matter, and accordingto the classic knowledge they must have no neuronal cell bodies.This researchis designedto find neurons in the external and extreme capsules, and to determine that these neurons are functional or aberrant. Materitais and Methods: Ten adult normal human brains from both sexes were studied using 15,µm serial coronal sections after appropriate fixation in 4% formalin and processing. These sections were stained by Kluver-Barrera and immunohistochemical method for synaptophysin. External and extreme capsules in stained sections observed with an optic microscope to find and verify the presence or absence of neurons in these areas of white matter. Results: In the external capsule, some neurons with small to moderate size range were observed. They were spherical, ovoid, fusiform, polygonal, and pyramidal in shape. These neurons were scattered among delicated nerve fibers or were located in a chain-like manner. The long axis of the fusiform neurons was parallel to the nerve fibers of the external capsule. The apical process of the pyramidal neurons which moved upward disapeared within a short distance of the cell body. The neuronal content of the external capsule increased on passing laterally (toward the claustrum) and ventrally. These neurons were strongly synaptophysin - positive. The neurons in the extreme capsule tend to be more fusiform in shape, lying with their long axis parallel to the vertical fibers of this capsule. These neurons were also scattered among nerve fibers or were located in a chain-like manner. The neurons in the extreme capsule were strongly synaptophysin - positive. There was no accumulation of neurons (such as cellular bridges or islands) in these two capsules. The demarcation between claustrum and both capsules and between insular cortex and extreme capsule were less distinct than between putamen and external capsule. Conclusion: This study revealed that there are some synaptophysin -positive neurons in the external aI).d extreme capsules (as parts of white matter) of human brain. These neurons may have similar connections and functions to neurons of claustrum or insuia.