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Fig. 1. Perfusion defi cits after SAH: ( a ) Representative coronal brain sections from FITC-
dextran injected animals sacrifi ced at 3 h after sham or SAH surgery. FITC-dextran was
circulated for 10 s only. Note uniform labeling of vessels with FITC-dextran in sham and
partial, incomplete labeling in SAH animals. ( b ) Representative high magnifi cation images
of FITC-dextran labeling in right striatum after sham and SAH surgery. Note partial fi lled
vessels in striatum of SAH animal. Also note the clear back ground. Scale: 20 μ m .
Fixing the tracer injected brain so that tracer does not leak out of
the vessels can be challenging. In addition, if fi xation is not com-
plete tracer leakage can also occur during brain sectioning and give
faulty results. Perfusion fi xation is not an option as this procedure
will clear the tracer out instead of fi xing it within the vessel. Snap
freezing works well but can cause tracer diffusion during section-
ing which appears as small fl uorescent streaks around the vessels.
We and others have found that immersion fi xation is the best way
to preserve the tracer in a vessel (see Procedures) ( 17, 21 ).
Moreover, since immersion fi xation is performed in 4% paraform-
aldehyde with increasing sucrose (10, 20, and 30%) gradients, ice
crystals that can form during freezing process and damage the tis-
sue are avoided.
2.2.3. Brain Processing
Cerebral blood fl ow (CBF) measurement using laser Doppler fl ow-
metry is yet another method of studying cerebral perfusion after
SAH ( 12, 22-25 ).
2.2.4. Alternative Methods
for Examining Perfusion
Defi cits
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