Fig. 4.

Hyposmotic solutions cause swelling of astrocytes but not neurons. Two photon laser scanning microscopy of green fluorescent labeled (GFP) neurons and GFP astrocytes in cortical brain slices showed that osmotic changes in solution caused IOSs (intrinsic optical signals) that were not associated with any changes in neuronal volume but were associated with astrocytic swelling. The panels in column (A) show the changes in light transmittance as hippocampal brain slices swell or shrink in changing osmolarity. The GFP-labeled (B) soma, (C) dendrites, and (D) axon terminals of CA1 pyramidal neurons did not change their volume. In contrast (E) astrocytes showed swelling in hypo-osmotic solution and shrinkage in hyper-osmotic solution. The light transmittance and fluorescence images were obtained at 10 min after beginning perfusion with the solutions of different osmolarities, to ensure that a complete change had occurred in the slice (from Andrew et al., 2006).