Assessments of Reactive Astrogliosis Following CNS Injuries - Animal Models of Acute Neurological Injuries: Injury and Mechanistic Assessments - page 50

Chapter 4
Assessments of Reactive Astrogliosis Following CNS Injuries
Candace L. Floyd
Abstract
The term “gliosis” is generally defi ned as the cellular process by which glial cells in the CNS respond to
insult and is used to describe the functional, morphological, biochemical, and molecular changes that
occur in response to injury or disease. However, gliosis is most associated with the activation of astrocytes
in response to CNS insults and is therefore discussed here as reactive astrogliosis. Although the molecular,
biochemical, and functional changes associated with reactive astrogliosis are not fully elucidated, the mor-
phological changes are better described. One morphological hallmark is the up-regulation of the interme-
diate fi lament protein glial fi brillary acidic protein (GFAP) which is often accompanied by a thickening of
the main astrocyte processes, or hypertrophy. In healthy tissue, GFAP is the main intermediate fi lament
expressed and the expression depends upon the subpopulation of astrocytes examined. After CNS injury,
the expression of GFAP is signifi cantly increased albeit heterogeneity and regional differences remain. It is
important to note that in both nonreactive and reactive astrocytes, the expression of GFAP protein that
can be detected by immunohistochemistry (IHC) is limited to the proximal portions of cell processes
which means that the complexity of the fi ne distal processes and their associated volume cannot be visual-
ized with GFAP-IHC. Techniques for evaluating GFAP-IHC in brain and spinal cord tissue from rodents
are discussed.
It recently has been discovered that in healthy tissue, cortical, and hippocampal astrocytes are orga-
nized into adjacent, but nonoverlapping domains and that under some conditions of reactive astrogliosis
this “tiling” of astrocyte processes can be lost. Astrocyte domain organization has been evaluated using
diolistic labeling of cells in fi xed slices and techniques for diolistic labeling to determine the domain organi-
zation of astrocytes using a gene gun system are detailed. Other techniques to measure reactive astrogliosis,
including bioluminescence imaging, manganese-enhanced magnetic resonance imaging, electrophysiology
of astrocyte inwardly rectifying potassium (Kir4.1) currents, evaluation of transcriptional control of the
GFAP gene, and selective ablation of reactive astrocytes in a transgenic mouse model are overviewed.
Key words: GFAP-immunohistochemistry, Diolistic labeling, Astrocyte, Gliosis, Bioluminescence,
Manganese-enhanced magnetic resonance imaging, Kir4.1, Transgenic mouse models