Recently, the journal Science showed in its cover an amazing image of a close up into the fly brain. This is the result of the combined effort of two research groups working on imaging. The first one (Boyden’s) had developed a way to increase the size of preserved samples, like a brain slice, up to 4 times by using an absorbable polymer similar to the one used in baby diapers and dosing it with water while at the same time making them transparent. The second technique, lattice light-sheet microscope from the Betzig lab 1, is based on an ultrathin sheet of light which illuminates only the part in the microscope’s plane of focus. That helps out-of-focus areas stay dark, keeping a specimen’s fluorescence from being extinguished.
This characteristic, together with its speed, made it a plausible ideal choice for the microscope to image huge chunks of expanded brains, and so it was. Even though the samples had to be repositioned and the image data acquired repositioned and stitched so as to rebuild the whole 3D data set (with the huge amount of data that implies), the whole acquisition time was relatively short: 62 hours.
If acquiring the data was a relatively “easy” step, making sense of it was anything but. However, after reconstructing the whole picture, the analysis made possible to count the synapses across the entire fly brain — roughly 40 million— and show how variable the density of those synapses is in different areas. They traced proteins, tiny cellular protrusions known as dendritic spines, and dopaminergic neurons. And that is just an example of the range of possibly interesting things to investigate with such a technique. Depending on labelling, in the future, it would be possible to track neuron connections, examine neurotransmitter or neuron type distribution…
The images are astonishing, the detail never saw before, the potential of the technique for brain research: gigantic. The authors are, however, not totally satisfied with it and they claim they will keep on working on improving it, since there are molecules that cannot be labelled with the available dyes and antibodies used so far (like lipids), or structures and/or tissues which do not swell well (like connective tissue).
Let’s hope about a future where these issues are resolved and this technique brings us a step further in better understanding the brain in health and disease.