Posted on by Dr. Francis Collins
Credit: Gao et. al, Science
Researchers are making amazing progress in developing new imaging approaches. And they are now using one of their latest creations, called ExLLSM, to provide us with jaw-dropping views of a wide range of biological systems, including the incredibly complex neural networks within the mammalian brain.
In this video, ExLLSM takes us on a super-resolution, 3D voyage through a tiny sample (0.0030 inches thick) from the part of the mouse brain that processes sensation, the primary somatosensory cortex. The video zooms in and out of densely packed pyramidal neurons (large yellow cell bodies), each of which has about 7,000 synapses, or connections. You can also see presynapses (cyan), the part of the neuron that sends chemical signals; and postsynapes (magenta), the part of the neuron that receives chemical signals.
At 1:45, the video zooms in on dendritic spines, which are mushroom-like nubs on the neuronal branches (yellow). These structures, located on the tips of dendrites, receive incoming signals that are turned into electrical impulses. While dendritic spines have been imaged in black and white with electron microscopy, they’ve never been presented before on such a vast, colorful scale.
The video comes from a paper, published recently in the journal Science , from the labs of Ed Boyden, Massachusetts Institute of Technology, Cambridge, and the Nobel Prize-winning Eric Betzig, Janelia Research Campus of the Howard Hughes Medical Institute, Ashburn, VA. Like many collaborations, this one comes with a little story.
Four years ago, the Boyden lab developed expansion microscopy (ExM). The technique involves infusing cells with a hydrogel, made from a chemical used in disposable diapers. The hydrogel expands molecules within the cell away from each other, usually by about 4.5 times, but still locks them into place for remarkable imaging clarity. It makes structures visible by light microscopy that are normally below the resolution limit.
Though the expansion technique has worked well with a small number of cells under a standard light microscope, it hasn’t been as successful—until now—at imaging thicker tissue samples. That’s because thicker tissue is harder to illuminate, and flooding the specimen with light often bleaches out the fluorescent markers that scientists use to label proteins. The signal just fades away.
For Boyden, that was a problem that needed to be solved. Because his lab’s goal is to trace the inner workings of the brain in unprecedented detail, Boyden wants to image entire neural circuits in relatively thick swaths of tissue, not just look at individual cells in isolation.
After some discussion, Boyden’s team concluded that the best solution might be to swap out the light source for the standard microscope with a relatively new imaging tool developed in the Betzig lab. It’s called lattice light-sheet microscopy (LLSM), and the tool generates extremely thin sheets of light that illuminate tissue only in a very tightly defined plane, dramatically reducing light-related bleaching of fluorescent markers in the tissue sample. This allows LLSM to extend its range of image acquisition and quickly deliver stunningly vivid pictures.
Telephone calls were made, and the Betzig lab soon welcomed Ruixuan Gao, Shoh Asano, and colleagues from the Boyden lab to try their hand at combining the two techniques. As the video above shows, ExLLSM has proved to be a perfect technological match. In addition to the movie above, the team has used ExLLSM to provide unprecedented views of a range of samples—from human kidney to neuron bundles in the brain of the fruit fly.
Not only is ExLLSM super-resolution, it’s also super-fast. In fact, the team imaged the entire fruit fly brain in 2 1/2 days—an effort that would take years using an electron microscope.
ExLLSM will likely never supplant the power of electron microscopy or standard fluorescent light microscopy. Still, this new combo imaging approach shows much promise as a complementary tool for biological exploration. The more innovative imaging approaches that researchers have in their toolbox, the better for our ongoing efforts to unlock the mysteries of the brain and other complex biological systems. And yes, those systems are all complex. This is life we’re talking about!
 Cortical column and whole-brain imaging with molecular contrast and nanoscale resolution. Gao R, Asano SM, Upadhyayula S, Pisarev I, Milkie DE, Liu TL, Singh V, Graves A, Huynh GH, Zhao Y, Bogovic J, Colonell J, Ott CM, Zugates C, Tappan S, Rodriguez A, Mosaliganti KR, Sheu SH, Pasolli HA, Pang S, Xu CS, Megason SG, Hess H, Lippincott-Schwartz J, Hantman A, Rubin GM, Kirchhausen T, Saalfeld S, Aso Y, Boyden ES, Betzig E. Science. 2019 Jan 18;363(6424).
Video: Expansion Microscopy Explained (YouTube)
Video: Lattice Light-Sheet Microscopy (YouTube)
How to Rapidly Image Entire Brains at Nanoscale Resolution, Howard Hughes Medical Institute, January 17, 2019.
Synthetic Neurobiology Group (Massachusetts Institute of Technology, Cambridge)
Eric Betzig (Janelia Reseach Campus, Ashburn, VA)
NIH Support: National Institute of Neurological Disorders and Stroke; National Human Genome Research Institute; National Institute on Drug Abuse; National Institute of Mental Health; National Institute of Biomedical Imaging and Bioengineering
Posted on by Dr. Francis Collins
It’s a problem that parents know all too well: a child won’t eat because their oatmeal is too slimy or a slice of apple is too hard. Is the kid just being finicky? Or is there a biological basis for disliking food based on its texture? This image, showing the tongue (red) of a fruit fly (Drosophila melanogaster), provides some of the first evidence that biology could indeed play a role .
The image shows a newly discovered mechanosensory nerve cell (green), which is called md-L, short for multidendritic neuron in the labellum. When the fly extends its tongue to eat, the hair bristles (short red lines) on its surface bend in proportion to the consistency of the food. If a bristle is bent hard enough, the force is detected at its base by one of the arms of an md-L neuron. In response, the arm shoots off an electrical signal that’s relayed to the central part of the neuron and onward to the brain via the outgoing informational arm, or axon.
Posted on by Dr. Francis Collins
This colorful cylinder could pass for some sort of modern art sculpture, but it actually represents a sneak peak at some of the remarkable science that we can look forward to seeing from the Brain Research through Advancing Innovative Neurotechnologies (BRAIN) Initiative. In a recent study in the journal Cell , NIH grantee Jeff Lichtman of Harvard University, Cambridge, MA and his colleagues unveiled the first digitized reconstruction of tissue from the mammalian cerebral cortex—the outermost part of the brain, responsible for complex behaviors.
Specifically, Lichtman’s group mapped in exquisite detail a very small cube of a mouse’s cerebral cortex. In fact, the cube is so tiny (smaller than a grain of sand!) that it contained no whole cells, just a profoundly complex tangle of finger-like nerve cell extensions called axons and dendrites. And what you see in this video is just one cylindrical portion of that tissue sample, in which Licthtman and colleagues went full force to identify and label every single cellular and intracellular element. The message-sending axons are delineated in an array of pastel colors, while more vivid hues of red, green, and purple mark the message-receiving dendrites and bright yellow indicates the nerve-insulating glia. In total, the cylinder contains parts of about 600 axons, 40 different dendrites, and 500 synapses, where nerve impulses are transmitted between cells.