Page 52 - Read Online

Figure 5: Scanning electron micrograph of isolated microglia cells from brain tissue. (A) Microglia recovered from early embryonic developing brain show many of
them retain spines bearing surfaces which radiate out of the cell body ; (B) a few cells remain amoeboid in shape with a ruffled surface membrane and short stubby
projections in late embryo; (C) in neonates, the presence of both amoeboid cells with spines bearing surfaces and also extended structure of amoeboid microglia cell;
(D) ramified or “resting” microglia isolated from adult brain with extended pseudopodia are seen
RESULTS brain parenchyma with a blood vessel containing
leukocytes, many of which are present at the margin
Colonization pattern of neuroglial cells from embryo to of the capillary and tethered to the endothelium and
adult therefore extravaseting at the perivascular spaces, along
with other neuroglial cells in the matrix [Figure 2D].
Staining of brain tissue of different ages with normal HE Therefore, normal HE staining shows overall cellular
staining shows a changing cellular distribution in the distribution, colonization, and differentiation patterns
brain across time. In the early embryo, huge numbers of various brain cells that change remarkably from
of presumptive neuroglial and myeloid cells were embryo to adult.
found to migrate from the inner ventricular margin to
the outer cortex region. Different glial progenitor cells, Variable morphological forms of microglia in developing
along with neuronal precursor cells, colonize the brain through adult brain
parenchyma from the predictive neuroglial stem cell
line at the margin of the forming ventricle [Figure 2A]. Silver-gold staining of brain tissue, in situ, can
In the case of a late embryo, normal HE staining shows differentiate myeloid lineage cells, including microglia/
a remarkably different cellularity near the ventricle. A macrophages, from neuronal and glial populations by its
cellular band is distinct at the margin, but immediately characteristic dark staining relative to background. [28,29]
after that, a diffused cell matrix starts with scattered As a result, changes in shape from “amoeboid” in the
cells. Variations among the cells are more prominent, embryo to “ramified” in the adult, is documented.
indicating further differentiation occurring in the cells In early embryos, the developing brain is saturated
[Figure 2B]. An example of a section from a neonate with presumptive cells that stain darkly and are hard
of 4-5 days clearly shows perivascular monocyte to distinguish between neuro-glial and microglial
cells and a cell extravasating out of a blood capillary, precursors, and hence, were omitted. In late embryos
hence, across the blood brain barrier (BBB), indicating [Figure 3A], the deeply stained myelo-monocytic lineage
blood capillaries as important sources of myeloid/ cells, or presumptive microglia, appear prominently in
monocytic cells that colonize the brain [Figure 2C]. In comparison with other neuroglial cells. A distinct and
a section from an adult, normal HE staining reveals prominent neuronal cell body, along with a dendritic

Neuroimmunol Neuroinflammation | Volume 3 | Issue 2 | February 15, 2016 43