Characterization of RNA - Animal Models of Acute Neurological Injuries: Injury and Mechanistic Assessments - page 133

freezing and thawing, it is not necessary to repeat the incubation
at 65°C. If using the RNA samples in a diagnostic assay, follow
the instructions supplied by the manufacturer.

Variations of this procedure have been used to extract RNA from
fi ngerstick blood samples ( 26 ), and microliter volumes of blood
( 27 ) as well as microRNA (mRNA) and DNA from a single Paxgene
blood RNA tube ( 28 ).

PreAnalytix Paxgene Blood
RNA Kit Handbook
(cat#762164)

The analysis of gene transcript levels in brain is a valuable tool for
the study of neurological and psychiatric diseases. Due to the low
availability of human brain tissue samples, gene expression experi-
ments have initially been performed in lymphocytes or immortal-
ized lymphoblastoid cell lines obtained via peripheral blood.
Although there is some congruence between brain and blood gene
expression profi les, there are differential spatial and temporal
expression patterns of gene expression between brain and blood, as
some genes are only expressed in the brain and many diseases
manifest their phenotype in certain tissues and not in others. For
these reasons, comparing expression results to disease phenotypes
will be informative only if expression measurements are carried out
in tissue types relevant to the disease of interest. For example, brain
ischemia is thought to be regulated by more genes than any other
brain insult possibly because ischemia damages all cellular elements,
including neurons, glia, axons/white matter, and the vessels ( 29 ).
A recent study examined the effect of tissue type (blood and
brain) on gene expression in human and rat and as expected found
a signifi cant effect of tissue specifi city on gene expression. The per-
centage of differentially expressed transcripts in brain and blood
(69.7% rat) was comparable to the percentage of differentially
expressed transcripts in humans (72.4%). The study also found that
human data may have a larger noise associated with postmortem
artifact, and thus not detect differences between tissue types as
accurately as in animal models ( 11 ).
Clearly, expression profi ling of brain tissue has the potential to
identify complex patterns of expression, such as those that might
not necessarily be found by examining the transcriptome from
other sources and has become a widely used strategy for inves-
tigating the molecular mechanisms underlying many complex
human diseases. However, studies of human disease have some
limitations, such as the inability to manipulate and examine specifi c
pathways, and the limited ability to safely acquire samples from
affected tissues. Studies using animal models may not entirely
refl ect the pathophysiological process through which some diseases
evolve in humans, however, they represent a very useful tool for
evaluating the therapeutic effi cacy of pharmacologic therapy (e.g., to
study different responses to drug administration ( 30 )) or studying
the mechanisms underlying some biological processes that cannot

2.2. Total RNA
Extraction from Brain