Biology Reference
In-Depth Information
other processes such as nonspreading depression of activity under
severe energy depletion or spreading persistent depression by a
previous SD, SD is not associated with spreading depression.
Importantly, as explained in Chap.
29
,
the type of synaptic dys-
function associated with SD does not determine whether or not
SD causes neuronal death (
4-6
).
Studying characteristics and mechanisms of SD in vitro using
the acute slice preparation (
7, 8
) is perhaps the most popular
approach since it allows to study the neurophysiological funda-
mentals at cellular and simple circuit levels. Other advantages of
brain slice preparations are the ability to apply known concentra-
tions of drugs by superfusion, and the precise control of the envi-
ronment regarding pO
2
, pCO
2
, pH, and temperature. Moreover,
parenchymal effects of compounds can be tested in a system devoid
of a circulation and, thus, separated from the vascular effects of the
same compounds when the results obtained in vitro are compared
with those obtained in vivo (
9
). This has particular relevance for
compounds, such as the peptide endothelin-1 which is a strong
vasoconstrictor on the one hand and a neuronal and astroglial
modulator on the other. Acute brain slice preparations can be
maintained in a healthy state over extended periods of time (12 h
and more). Direct visualization of the slice structure allows accu-
rate placement of both recording and stimulating electrodes at the
desired sites as well as imaging of structures that are usually buried
deep within the brain. In this way, communication as well as patho-
logical interactions can be studied in detail between different struc-
tures that are diffi cult to access in vivo (
10
). In addition, human
tissue, mostly obtained from patients with intractable epilepsy or
specimens from tumor resections, is available to bridge the bench-
to-bedside gap (
11, 12
).
2. Preparation
of Brain Tissue
Slices
Suitable rodents (e.g., rat, mouse, guinea pig, and gerbil) have to
be deeply anesthetized using volatile or injectable anesthetics fol-
lowed by decapitation. Pups can be anesthetized by putting them
on dry ice. To minimize the ischemic neuronal damage due to
arrest of blood circulation, the brain has to be removed from the
skull as quickly as possible. Caution should be taken to completely
remove the dura mater so that the brain can be extracted without
damage using a scoop. The intact brain is then placed into a beaker
fi lled with cold (~4°C) oxygenated artifi cial cerebrospinal fl uid
(aCSF). Our laboratory uses the following aCSF composition (in
mM): 124 NaCl, 3 KCl, 1.8 MgSO
4
, 1.6 CaCl
2
, 1.25 NaH
2
PO
4
,
26 NaHCO
3
, and 10 glucose. The solution is saturated with a gas
mixture of 95% O
2
/5% CO
2
(often referred to as carbogen) to
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