Surgical injury-induced early neocortical microvascular changes and characteristics of the cells populating the peri-lesion zone

Abstract

Adult mammalian brain contains a number of specialized neurovascular structures termed "niches" that act as sources of neuronal cells throughout the individual's life. Some of the niches generate neurons to satisfy the need for 'replacement' neurons within the same or closely located brain structures, whereas the other can provide such cells for more distant destinations in the brain. A common characteristic of known neurovascular niches is the presence of a complex 3-dimensional network of basal lamina processes, called fractones. It apparently plays a major role in communication between the various niche-populating cell types as well as in niche activity and output. We hypothesized that similar niches may form ad hoc after a mechanical brain trauma, and tested this possibility in a rat model of surgical brain injury. Four days after removing a small fragment of sensorimotor cortex, the peri-wound region showed numerous symptoms of active repair and remodeling of brain parenchyma, including the presence of multiple cell types of immature phenotypes. The latter, as shown by a variety of light and electron microscopy techniques, included endothelial cell precursors as well as nestin-positive immature neural cells of astrocytic or non-glial characteristics. However, there was no evidence of in situ neurogenesis or a considerable migration of cells from SVZ. The centers of the said repair processes were capillary blood vessels connected with basal lamina-formed fractones. These results indicate that surgical brain trauma causes the formation of a vascular niche with no apparent neurogenic potential.