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  • Peering deeper into the brain

Mar 2011
BioPhotonics staff

STANFORD, Calif. – A new technique to monitor the tiny branches of neurons deep inside a live brain for months at a time has been devised by scientists at Stanford University. Neuroscientists will now be able to monitor the microscopic changes that occur over time in progressive brain disease.

Monitoring neurons for two months. Column (a) shows the delicate branches of the same neurons in a living mouse over 20 days. Column (b) is an enlarged view of one region of column (a). The ability to revisit the same neurons over a long-term experiment will be a benefit to researchers of brain disease. Courtesy of Mark Schnitzer and Nature Medicine.

Looking deep into the interior of a living brain, where memories are formed and diseases such as dementia and cancer take their toll, is not possible with standard light microscopes. Because light microscopy can penetrate only the outermost layer of tissues, any region of the brain deeper than 700 μm cannot be reached by traditional microscopy techniques. While recent advances in micro-optics allowed scientists to briefly peer deeper into living tissue, it was almost impossible to return to the same location of the brain without damaging or infecting the tissue.

The new method makes imaging possible over a long period of time without damaging the region of interest. The scientists carefully inserted tiny glass tubes, about half the width of a grain of rice, deep into the brain of an anesthetized mouse. Once in place, the tubes allow researchers to examine the cells and their interactions at that site using a microendoscope inserted inside the glass guide tube. Like portholes in a submarine, the guide tubes have glass windows at the end through which the researchers can examine the interior of the brain.

A diagram of the experimental setup. At left, tiny optical instruments called microendoscopes are inserted into glass imaging guide tubes, which maintain a precise position in the brain. This allows researchers to view the exact same neuron with a microscope, at right, again and again. Scientists can also compare diseased tissue, such as a tumor, to healthy tissue in the same animal. Modified image courtesy of Mark Schnitzer and Nature Medicine.

Because the tubes provide no exposure to the outside environment, infection of the brain is prevented. The guide tubes also allow the researchers to return repeatedly to exactly the same location of the deep brain over weeks or months. Although traditional MRI scans examine deep within the brain, they cannot look at individual cells on the microscopic level.

The scientists tested the technique for investigating brain disease by looking at a mouse model of glioma, a deadly form of brain cancer. Their research was published online Jan. 16, 2011, in Nature Medicine (Vol. 17, pp. 223-228).

Tiny (less than 2 mm in diameter) lenses, beamsplitters and other optical components used, for example, in endoscopes or microscopes or to focus light from semiconductor lasers and optical fibers.
An instrument consisting essentially of a tube 160 mm long, with an objective lens at the distant end and an eyepiece at the near end. The objective forms a real aerial image of the object in the focal plane of the eyepiece where it is observed by the eye. The overall magnifying power is equal to the linear magnification of the objective multiplied by the magnifying power of the eyepiece. The eyepiece can be replaced by a film to photograph the primary image, or a positive or negative relay...
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