Diffusion Barriers of the Lateral Ventricular System

Adult neurogenesis in mammalian brain has become a well-accepted phenomenon. The neural stem cells in the sub ventricular zone (SVZ) along the lateral wall of the lateral ventricle, the largest germinal center of adult neurogenesis, are maintained by the neural stem cell niche. One prominent feature of the niche is its close proximity to the cerebral spinal fluid (CSF). The role of micromolecules (such as ions, water and gases) present in the CSF and diffusing through the lateral ventricular wall and how the stem cell micro-environment is maintained is poorly understood. The cytoarchitecture of the lateral ventricular wall with a pinwheel organization of ependymal cells around astrocyte processes gives uniqueness to the lateral wall of the lateral ventricles versus other ventricle walls. The possibility of different cell junctional protein interactions that could take place here may provide us with some cues that may indictate a preferentially diffusion taking place through the lateral walls in comparison with the medial wall of the lateral ventricles or other ventricle walls. To test this hypothesis we injected the tracer BDA (3 kDa) and NaFl (0.376 kDa) into lateral ventricles and studied the diffusion pattern. The diffusion curves generated from the injection of the two different sized tracers did not show any significant difference in signal intensities obtained from the medial and lateral regions of the lateral ventricles or between the lateral and medial walls, indicating the possibility of similar tight junctional protein complexes present along both the walls. With the help of EM, we observed the presence of tight junctions between all the cell types of the lateral and medial wall. The organization of peripheral membrane tight junction protein (ZO-1) also showed similar expression patterns between the cells of both walls of lateral ventricles. The result from the localization of tight junction proteins was consistent with diffusion analysis. Thereby, I found that despite the presence of astrocyte processes at the ventricle walls; the barrier role of the SVZ is still maintained