Biology Reference
In-Depth Information
4.3. Gliosis
The central nervous system is composed primarily of post-mitotic
cell populations and is therefore largely incapable of repopulation.
The induction of scarring, termed astrogliosis, following neurotoxic
insults (
43, 44
), trauma, and stroke (
45
) is well documented. This
is mediated by activated astrocytes and microglia. Proinfl ammatory
cytokines in the IL-6 family, also known as neuropoietic cytokines
(
46
), preferentially activate janus kinases (JAK) and the signal
transducers and activators of transcription (STAT) pathways
(
47, 48
) (Fig.
3
). Through JAK2/STAT3 signaling, these cytok-
ines activate target genes involved in immune responses,
differentiation, survival, apoptosis, and proliferation.
5. Imaging
Advanced imaging modalities have changed the scope of clinical
practice, allowing physicians to obtain detailed anatomic informa-
tion. The application of magnetic resonance spectroscopy (MRS)
has opened the door to noninvasive, in vivo investigation of the
human brain. Evaluation of acute SAH with contrast enhanced CT
was fi rst reported in 1984, demonstrating contrast extravasation in
the subarachnoid space and suggesting BBB disruption correlating
with poor outcomes (
38
). Recent evidence has shown acute diffu-
sion weighted MRI (DWI) changes in 82% of SAH victims within
24 h of symptom onset. Furthermore, when separated on the basis
of lesional area, those with no or spotty lesions less than 10 mm
2
in
size had favorable outcomes in 100% and 54% of cases, respectively,
when treated aggressively; while those with areal lesions >10 mm
2
always suffered poor outcomes and severe disability (
49
). These
territorial infarct patterns can be attributed to spasm of proximal
vessels, which is visible on cerebral angiography. New evidence,
however, suggests spasm in the distal microcirculation of paren-
chyma underlying sulcal clots may lead to “focal laminar” cortical
infarcts seen on DWI (
50
).
MRS can be utilized to study in vivo neurochemical events and
detects specifi c molecules,
1
H,
7
Li,
13
C,
19
F, and
31
P, with a resolu-
tion of millimol/L.
1
H MRS spectra allows for detection of lactate,
NAA, Cho, Cr+, and PCr, and has been utilized in traumatic brain
injury to infer damage patterns and provide prognostic informa-
tion. The concentrations of metabolites
N
-acetyl aspartate (NAA),
creatine, choline, and lactate can be measured within the brain and
mapped to T2 weighted images. The amino acid NAA is a marker
of functioning neurons, and its concentration has been shown
decrease in the setting of neuronal ischemia (
51
). Production of
choline can be utilized as an indirect measure of cell membrane
disruption, resulting from catabolism of phosphorylcholines (
52, 53
).
Creatine levels are not thought to change during injury, and can
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