October 8th, 2008
Watching brain cells in action
A Stanford University team has developed a microscope weighing only 1.1 grams. It is so small that it can be mounted to the head of a freely moving mouse to watch its brain cell activity. According to what said the lead researcher to New Scientist, ‘A lot of work has been done using brain slices, or anaesthetised animals — even using animals that are awake but restrained. But so far it has been impossible to image cellular-level activity in a freely moving mouse.’ Not anymore. And as mice are the ‘preferred’ animals in medical labs, this new kind of microscope could lead to new ways to study human diseases. [(Update: October, 2008) One of my alert readers told me that the caption of the diagram below mentioned 'the three sizes of microendoscopes used: 1,000, 500 and 350 mm in diameter.' In fact, these are microns, not millimeters. This is fixed below.] But read more…
You can see above several images related to this minimally invasive microendoscopy system which has also been used to watch muscles in action. “a, Schematic of the laser-scanning imaging system used to visualize sarcomeres in live subjects. A microscope objective focuses ultrashort pulsed laser illumination onto the face of a gradient refractive index microendoscope. The microendoscope demagnifies and refocuses the laser beam within the muscle and returns emitted light signals, which reflect off a dichroic mirror before detection by a photomultiplier tube (PMT). b, Shown are the three sizes of microendoscopes used: 1,000, 500 and 350 μm in diameter. c, 350-μm diameter microendoscope clad in stainless steel for minimally invasive imaging in the arm of a human subject. Scale bars are 1 cm.” (Credit: Schnitzer et al., Stanford University)
This research work has been led by Mark Schnitzer, an assistant professor of biology at Stanford University with the help of the members of
his research group. In this page, Schnitzer describes his fiber optic fluorescence microendoscopy project. “The Schnitzer group has recently invented two forms of fiber optic fluorescence imaging, respectively termed one- and two-photon fluorescence microendoscopy, which enable minimally invasive in vivo imaging of cells in deep (brain) areas that have been inaccessible to conventional microscopy. Such areas that the group has studied include the hippocampus, thalamus, and inner ear. The group has developed the capability for repeated microendoscopy imaging of hippocampal neurons and dendrites over the long-term using a chronic mouse preparation. This preparation has proved highly applicable for extended imaging studies over the progression of brain disease in animal model systems.”
Here are some applications of this research work. “Such ability to image cells deep within the live mammalian brain also promises to permit studies of how cellular properties are impacted by environment, training, or life experience. Moreover, the Schnitzer group has created portable, miniaturized microendoscopy devices based on flexible fiber optics for use in freely moving mice. The Schnitzer group now seeks to develop and apply these microendoscopy techniques to applications in both basic neurobiology and clinical settings, and has begun to examine human nervous tissues. For example, microendoscopy has recently provided the first images of sarcomeres in live human subjects, and we are now working with collaborators to bring this imaging capability into the neurology clinic for applications regarding neuromuscular disorders.”
Now, here is a description of this mini microscope picked from the New Scientist article mentioned in the introduction. “The device has already been used to study the circulation of blood through the one-cell-wide capillaries in the brain of active mice. The microscope is attached to the head of a mouse under anaesthetic, while a marker dye is injected into the brain to label blood plasma, but leave blood cells unaffected. The microscope uses light delivered by a mercury arc lamp through a bundle of optical fibres. Light from the lamp causes the dyed blood plasma to fluoresce, showing up individual blood cells as dark spots. The image is sent back up the fibre-optic bundle to a camera that records the image. Roughly 100 images are taken every second, allowing the researchers to watch high-speed video of individual blood cells flowing in the brain. Once the mouse wakes up from the anaesthetic, it is possible to watch the movement of cells as it behaves normally.
This research work has been published by Nature Methods under the title “High-speed, miniaturized fluorescence microscopy in freely moving mice” as an advanced online publication on October 5, 2008. Here is the the abstract of this paper. “A central goal in biomedicine is to explain organismic behavior in terms of causal cellular processes. However, concurrent observation of mammalian behavior and underlying cellular dynamics has been a longstanding challenge. We describe a miniaturized (1.1 g mass) epifluorescence microscope for cellular-level brain imaging in freely moving mice, and its application to imaging microcirculation and neuronal Ca2+ dynamics.”
The Schnitzer’s team has previously used this mini microscope to study muscles. As an example, you can read a recent article published by Nature named “Minimally invasive high-speed imaging of sarcomere contractile dynamics in mice and humans” (Volume 454, Number 7205, Pages 784-788, August 7, 2008). Here is the beginning of the abstract. “Sarcomeres are the basic contractile units of striated muscle. Our knowledge about sarcomere dynamics has primarily come from in vitro studies of muscle fibres and analysis of optical diffraction patterns obtained from living muscles. Both approaches involve highly invasive procedures and neither allows examination of individual sarcomeres in live subjects. Here we report direct visualization of individual sarcomeres and their dynamical length variations using minimally invasive optical microendoscopy to observe second-harmonic frequencies of light generated in the muscle fibres of live mice and humans.”
For more information, here is a link to the full paper (PDF format, 5 pages, 704 KB), from which the above illustration has been extracted.
Finally, if you’re curious, here is a link to a Wikipedia page about sarcomeres. “A sarcomere is the basic unit of a muscle’s cross-striated myofibril. Sarcomeres are multi-protein complexes composed of three different filament systems.”
Now, it’s up to you to decide if this kind of mini microscope will help to study human diseases.
Sources: Colin Barras, New Scientist, October 5, 2008; and various websites
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