PET scan of blood flowing through a brain. Some areas have better access to blood than others.
Credit: LBNL
BRISBANE: Oxygen use in living animal brain tissue can be seen with new technology, a major breakthrough for helping stroke patients, scientists said.
Oxygen consumption is critical for normal brain function, and the ability to map oxygen concentration in real-time in the brain tissue of living animals will have benefits for many areas of science, both in health and disease.
“This new tool will give us new insights into the metabolic responses to normal physiological events such as stimulus induced brain activation, as well as the metabolic responses to brain injury and stroke and degenerative diseases, and how they might exacerbate the injury,” said biophysicist David Boas from Harvard Medical School in Boston, an author of the study published in the journal Nature Methods.
Measuring brain oxygen levels
The research team used an existing imaging technique known as two-photon microscopy, where a phosphorescent probe is injected into the brain (in this case of mice), and when excited by high-frequency laser pulses, the probe releases photons that are detected by the two-photon microscope.
The generation of high-energy photons can damage cells, but two-photon excitation keeps it to a minimum because the probe is excited only in a very tiny volume near the laser and not excited anywhere else. In fact, the research team reported no evidence of cell damage (phototoxicity) in their study.
However technical limitations have prevented the measurement of oxygen consumption deeper within the brain of living animals – until now.
Oxygen levels in deep brain tissue
“Ordinary phosphorescent probes cannot be efficiently excited via the two-photon process,” said co-author and biophysicist Sergei Vinogradov from the University of Pennsylvania.
“In the specially designed probe used in our study, two-photon radiation is harvested by one part of the probe, called the two-photon antenna, and passed to another part, which emits phosphorescence and senses oxygen.”
The research team were able to measure the levels of oxygen use in deep brain tissue with a high spatial resolution of 30-50 micrometers.
By temporarily stopping the mice from breathing, the research team were also able to precisely measure how brain oxygen was used by the tissues, and how different locations were more susceptible to lack of oxygen.
