Quantification of astrocyte volume changes during ischemia in situ reveals two populations of astrocytes in the cortex of GFAP/EGFP mice

Abstract

Energy depletion during ischemia leads to disturbed ionic homeostasis and accumulation of neuroactive substances in the extracellular space, subsequently leading to volume changes in astrocytes. Confocal microscopy combined with 3D reconstruction was used to quantify ischemia-induced astrocyte volume changes in cortical slices of GFAP/EGFP transgenic mice. Twenty-minutes of oxygen-glucose deprivation (OGD) or oxygen-glucose deprivation combined with acidification (OGD(pH 6.8)) revealed the presence of two distinct astrocytic populations, the first showing a large volume increase (HR astrocytes) and the second displaying a small volume increase (LR astrocytes). In addition, changes in resting membrane potential (V(m)), measured by the patch-clamp technique, supported the existence of two astrocytic populations responding differently to ischemia. Although one group markedly depolarized during OGD or OGD(pH 6.8), only small changes in V(m) toward more negative values were observed in the second group. Conversely, acidification (ACF(pH 6.8)) led to a uniform volume decrease in all astrocytes, accompanied by only a small depolarization. Interestingly, two differently responding populations were not detected during acidification. Differences in the expression of inwardly rectifying potassium channels (Kir4.1), glial fibrillary acidic protein (GFAP), and taurine levels in cortical astrocytes were detected using immunohistochemical methods. We conclude that two distinct populations of astrocytes are present in the cortex of GFAP/EGFP mice, based on volume and V(m) changes during exposure to OGD or OGD(pH 6.8). Immunohistochemical analysis suggests that the diverse expression of Kir4.1 channels and GFAP as well as differences in the accumulation of taurine might contribute to the distinct ability of astrocytes to regulate their volume.

Structural remodeling of gray matter astrocytes in the neonatal pig brain after hypoxia/ischemia

“…Astrocyte swelling has been reported in numerous in vitro and in vivo studies (Benesova et al, 2009;Chv atal et al, 2007;Nagelhus et al, 1996;Risher et al, 2009). In recent in vivo studies, Risher et al (2009) reported swelling of the astrocyte cell body and processes within 6 min of hypo-osmotic stress or during 6-12 min following cardiac arrest; however, the overall astrocyte territory remained constant.…”

Taurine Release by Astrocytes Modulates Osmosensitive Glycine Receptor Tone and Excitability in the Adult Supraoptic Nucleus

“…Indeed, taurine has been suggested to play a protective role during brain pathologies associated with swelling, such as ischemia (Benesova et al, 2009) and hyponatremia (Chvátal et al, 2007). In addition, neuronal hyperactivity can significantly increase extracellular [K ϩ ] (Gutnick et al, 1979), and elevated levels of extracellular [K ϩ ] can promote swelling-induced taurine release by surrounding glial cells (Pasantes-Morales and Schousboe, 1989).…”

The inhibitor of volume‐regulated anion channels DCPIB activates TREK potassium channels in cultured astrocytes

“…In vivo, they are endowed with a variety of potassium (K + ) and chloride (Cl -) ion channels that differently contribute to cell volume regulation (Benesova et al, 2012). There is clear evidence that as a result of ischaemia and oxygen glucose deprivation astrocytes swell (Benesova et al, 2009) and release high amount of glutamate/aspartate (Phillis and O'Regan, 2003). Because these processes play a pivotal role in the pathogenetic mechanisms of the ischemic damage , a great effort is currently made to identify pharmacological agents able to interfere with the underlying molecular mechanisms.…”