Imaging Spreading Depression and Associated Intracellular Calcium Waves in Brain Slices

Abstract

Spreading depression (SD) was analyzed in hippocampal and neocortical brain slices by imaging intrinsic optical signals in combination with either simultaneous electrophysiological recordings or imaging of intracellular calcium dynamics. The goal was to determine the roles of intracellular calcium (Ca2+int) waves in the generation and propagation of SD. Imaging of intrinsic optical signals in the hippocampus showed that ouabain consistently induced SD, which characteristically started in the CA1 region, propagated at 15-35 micrometer/sec, and traversed across the hippocampal fissure to the dentate gyrus. In the dendritic regions of both CA1 and the dentate gyrus, SD caused a transient increase in light transmittance, characterized by both a rapid onset and a rapid recovery. In contrast, in the cell body regions the transmittance increase was prolonged. Simultaneous imaging of intracellular calcium and intrinsic optical signals revealed that a slow Ca2+int increase preceded any change in transmittance. Additionally, a wave of increased Ca2+int typically propagated many seconds ahead of the change in transmittance. These calcium increases were also observed in individual astrocytes injected with calcium orange, indicating that Ca2+int waves were normally associated with SD. However, when hippocampal slices were incubated in calcium-free/EGTA external solutions, SD was still observed, although Ca2+int waves were completely abolished. Under these conditions SD had a comparable peak increase in transmittance but a slower onset and a faster recovery. These results demonstrate that although there are calcium dynamics associated with SD, these increases are not necessary for the initiation or propagation of spreading depression.

Target cell-specific modulation of neuronal activity by astrocytes

“…Astrocytes, the predominant type of glial cells in the central nervous system, form a highly organized multicellular syncytium extending throughout the gray matter (3,4). Calcium imaging in acute brain slices and in vivo has demonstrated that astrocytes can generate various patterns of activity, either local and spatially restricted to processes of individual cells or coordinated between adjacent cells and propagating across the brain tissue (5)(6)(7)(8)(9)(10)(11)(12). Modeling indicates that coupling of astrocytic and neuronal activities may give rise to membrane potential instability and oscillations (13).…”

ET-1 induces cortical spreading depression via activation of the ETAreceptor/phospholipase C pathway in vivo

“…56). Thus Basarsky et al (2) showed that CSDs in calcium-free medium also occurred in the absence of intercellular calcium waves. In addition, metabolic poisons for astroglial cells, fluoroacetate and fluorocitrate, did not prevent CSDs but rather facilitated their onset (37).…”

Large-Scale Calcium Waves Traveling through Astrocytic NetworksIn Vivo

“…Several forms of astrocytic calcium waves have been described under artificial or pathological conditions, such as in cultured astrocytes (Cornell-Bell et al, 1990;Charles et al, 1991;Finkbeiner, 1992) and in spreading depression (SD) (Basarsky et al, 1998;Kunkler and Kraig, 1998;Peters et al, 2003;Chuquet et al, 2007). Glissandi differ in several respects from these previously known waves.…”