Development of a technique to manipulate local intracerebral blood flow by illumination

A joint research team at Keio University has developed a manipulation technique that can increase or decrease cerebral local blood flow by illumination and successfully implemented it in freely moving mice. The team consists of Project Assistant Professor Yoshifumi Abe and Associate Professor Kenji F. Tanaka, both of the Department of Neuropsychiatry at the Keio University School of Medicine and researchers from Tohoku University, the Central Institute for Experimental Animals, The University of Tokyo, Niigata University, and The University of Electro-communications. "Cerebral blood flow is frequently measured in humans. However, it is unclear whether changes in cerebral blood flow alter neural activity and behavior or vice versa," says Associate Professor Tanaka. "Therefore, we aimed to develop a technique to isolate the manipulation of cerebral blood flow."

The research team developed a technique to increase or decrease blood flow in any region of the brain by applying optogenetics to vascular cells and implemented this technique in mice. In this technique, the researchers first generated two genetically modified mice in which vascular cells express the proteins channelrhodopsin 2 (ChR2) or photoactive adenylyl cyclase (PACs). By inserting optical fibers into and photo stimulating the desired brain area, blood flow can be reduced (using ChR2) and increased (using PAC) as one wishes.

Using this mouse model, the researchers clarified the time course of changes and the spatial spread of changes in cerebral blood flow induced by light stimulation. They showed that this blood flow fluctuation was reversible, that it can be induced repeatedly, and that this blood flow manipulation technique can be applied to freely moving mice (without anesthesia). Next, this technology was used to examine how artificially manipulated cerebral blood flow fluctuation affects neural activity and the behavior of the mouse. The researchers demonstrated that reducing blood flow in the ventral striatum of mice by 34 ± 3.3% suppressed firing of neurons in the ventral globus pallidus by 87 ± 3.4% and reduced locomotor activity in mice by 89 ± 4.7%.

Here, they found that the process was continuously induced in the following order: Decrease in blood flow (decrease in blood flow 0.5±0.1 s after light stimulation) > decrease in firing of nerve cells (decrease in firing 11.4±1.4 s after light stimulation) > decrease in mouse activity (decrease in activity 22.2±1.4 after light stimulation). Through this research, the team not only developed a new technology to increase or decrease blood flow in any region of the brain but also confirmed the expansion of its application under freely moving situation and the spatial spread of blood flow changes depending on light intensity. As a result, they proposed that this technology be used as a methodology to clarify the interrelationship between local cerebral blood flow, neural activity under the control of the blood flow, and behavior.

"We do not know how neuronal activity or brain volume change in relation to short-term (minutes) and long-term (days/weeks) manipulation of cerebral blood flow," explains Associate Professor Tanaka. I would like to clarify this completely unknown causal relationship at the animal level. It may even be possible to clarify, for example, the relationship between dementia and blood flow, which remains a bit of a chicken and egg scenario--does dementia occur because blood flow decreases, or does blood flow decrease because dementia occurs. This could then be applied to many other pathological conditions, not limited to dementia."

■ Optogenetics: A technique in which opsin protein is expressed in nerve cells and nerve activity is excited or suppressed by light irradiation.