Microscope Peers Into A Mouse’s Brain

Researchers have used the superresolution fluorescence microscopy method known as STED, or stimulated emission depletion, to acquire images of a neuron inside the brain of a living adult mouse (Science, DOI: 10.1126/science.1215369). Katrin I. Willig and Stefan W. Hell at the Max Planck Institute for Biophysical Chemistry, in Göttingen, Germany, and coworkers used a STED microscope to shine beams of light through a glass-sealed hole made in a mouse’s skull. In the experiment, a beam of 488-nm light excites fluorescence from enhanced yellow fluorescent protein, and an overlapping, donut-shaped beam at 592 nm turns off that fluorescence everywhere except in a tightly defined spot. The team recorded images every few minutes and observed morphologic changes and movement in the dendritic spines of the neuron. Such movements, which might result from changes in connections in the neural network, have previously been seen in brain slices from young mice. But it was unclear before now whether the events could also happen in an adult brain. To obtain higher spatial resolution without risking photodamage, the researchers suggest using red fluorescent proteins that require STED beams with longer wavelengths or proteins with fluorescence that can be switched with a conformational transition at low light levels.