Imaging dynamic volume changes in astrocytes
Florence, Clare Margaret
Astrocytes, the major type of non-neuronal cells in the brain, play an important functional role in the brain’s extracellular potassium (K+) and pH homeostasis. Pathological brain states have been shown to cause astrocyte swelling. However, these volume changes have never before been verified to occur in response to physiological activity. In the present thesis, two-photon laser scanning microscopy was used to visualize real-time astrocyte volume changes in the stratum radiatum of the CA1 region of the hippocampus. Astrocyte somas and primary processes were observed to swell by 19.0±0.9% in response to a physiological (3 mM) increase in the concentration of extracellular K+. Astrocyte swelling was partially mediated by K+ influx through inwardly rectifying K+ channels (Kir), as their inhibition resulted in a significant decrease of the increased K+ induced astrocyte swelling (13.9±0.9%). In addition, the bicarbonate ion (HCO3-) was found to play a significant role in the increased K+ induced astrocyte swelling. The astrocyte swelling was significantly decreased when the influx of HCO3- was decreased in 1) a HCO3- free extracellular solution (5.4±0.7%), 2) in the presence of an extracellular carbonic anhydrase inhibitor (11.4±0.6% ), and 3) when the activity of the sodium-bicarbonate cotransporter (NBC) was blocked (8.3±0.7%) . Conversely, astrocytes were found to shrink by 7.7±0.5% in response to ã-Amino-butyric Acid (GABA) receptor activation. GABAA receptor mediated astrocyte shrinkage was significantly decreased to 5.0±0.6% when HCO3- efflux was reduced. Furthermore, in this thesis it was shown for the first time that astrocytes swell in response to neuronal stimulation (4.0±0.4%). This activity induced astrocyte swelling was significantly decreased to 1.5±0.2% in a HCO3- free extracellular solution. These astrocyte volume changes may have important implications for the regulation of brain activity under both physiological and pathological brain states.
DegreeMaster of Science (M.Sc.)
CommitteeHowland, John; Fisher, Thomas; Desautels, Michel; Gray, Jack
Copyright DateDecember 2010