Astroglial swelling in the neuronal depolarization ensemble

The coupling between neuronal depolarization and astroglial swelling was examined. First, previous in vitro data for the swelling of cultured neurons (N18; rat neuroblastoma) and astroglia (C6; rat astroglyoma) upon exposure to a hypoosmotic solution were reappraised. Neurons swelled rapidly, forming blisters, and easily burst. whereas astroglia resisted swelling and slowly assumed a large full-moon shape. The time constant of swelling was 35.2 +/- 7.8 s for N18 and 594.8 +/- 554.0 s for C6. The glial plasmic membrane was found to be much stronger than the neuronal one, presumably due to a well-developed cytoskeleton. To overcome such neuronal membranous weakness, strong astroglial processes need to cover the neurons including the cell body and synapses, as demonstrated electron-microscopically. Next, in situ astroglial swelling was investigated in rats. During K(+)-induced cortical spreading depression, increases or decreases of a wave-ring spread of light (550 nm) transmission through a 1 mm-thick cerebral cortical layer was observed. The moving local optical density decrease in the cortex was attributable to local vascular bed compression induced by astroglial swelling, since concomitant occurrence of colocated dynamic capillary flow stall was confirmed by a hemodilution technique. Astroglial swelling may occur in an ensemble acting during neuronal depolarization, suggesting that neurons and astroglia behave like a unit complex.