Biology Reference
In-Depth Information
Chapter 23
Spreading Depolarization
Clemens Reiffurth , Sergei A. Kirov , and Jens P. Dreier
Abstract
The term spreading depolarization (SD) describes a wave of profound cellular depolarization in the brain's
gray matter. The hallmark of SD is the breakdown of ion homeostasis. Among the ionic changes, the net
infl ux of calcium into neurons is of importance since it is assumed to induce the cascades leading to neu-
ronal death. While short-lasting SDs are survived, long-lasting SDs are detrimental. SD has been studied
extensively in animal models in vivo and in vitro for decades and has been shown lately to occur frequently
in the early and delayed time period in patients with SAH. In this chapter, electrophysiological and imag-
ing methods are described to record SD.
Key words:
Spreading depolarization, Spreading depression, Nonspreading depression, Brain slice,
Intrinsic optical signal, Extracellular recording, Two-photon laser scanning microscopy
1. Introduction
Spreading depolarization (SD) is characterized by near-complete
sustained depolarization of neurons to almost 0 mV associated
with a substantial redistribution of ions between intra- and extra-
cellular compartments; e.g., the extracellular calcium concentra-
tion falls from 1.3 to 0.1 mM (
1, 2
) and the intracellular calcium
concentration increases from 60 nM to 25
M (
3
). The extracel-
lular negative direct current (DC) shift between −5 and −30 mV
serves as a robust measure of SD since it refl ects the depolarization
of a sizable number of brain cells. SD slowly progresses in the gray
matter of the central nervous system at a rate of ~3 mm/min.
However, of note, propagation is not the essential feature of the
process. If synaptic activity is present when SD starts, SD is fol-
lowed by sustained suppression of synaptic activity which causes
the phenomenon of spreading depression of electrocorticographic
activity. However, if synaptic activity has been already ceased by
μ
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