Research Highlight: Light controls cerebral blood flow in naive animals

Photoactivation of specific populations of cells via a combination of Optogenetics and fMRI is currently used to generate brain maps of connectivity and function. Group leader Serge Charpak and coll. now thoroughly examined in vivo the potential side effects of light on cerebral blood flow (CBF) in anesthetized naive mice using 2-photon laser scanning microscopy and ultrafast functional ultrasound. The authors reveal that light per se causes a pronounced increased of CBF of similar magnitude to a sensory (odour-evoked) stimulation.

Using transgenic mice, they show that photodilation is not mediated by activation of neuronal and/or astrocyte Ca2+-dependent neurovascular coupling pathways but is directly related to a calcium efflux from vascular smooth muscle cells leading to their dilation thus to CBF increase. The molecular mechanim that trigger photodilation remains unknown but according to their study the authors suggest that photoactivation could be related to a specific protein involved in vascular regulation independently of heat. Finally, since arterioles dilate to blue light under ketamine-xylazine but not under isofluorane anaesthesia, it is important to stress that control and investigation experiments should be performed under the same anesthesia protocole.

Check out the article: 

Rungta RL, Osmanski BF, Boido D, Tanter M, Charpak S. Light controls cerebral blood flow in naive animals. Nat Commun. 2017 Jan 31;8:14191. doi: 10.1038/ncomms14191. PMID: 28139643 

Figure: Light triggers dilation via a decrease in SMC calcium.

Left, an arteriole in which the smooth muscle cell (SMC) wall shows typical stripe patterns of GCaMP6f expression. Middle, the arteriole the lumen is labelled with Texas red. Right, a transversal linescan acquisition allows simultaneous recording of SMC calcium and vessel diameter. Light lowers calcium in the SMC wall and dilates the vessel. Scale bar, 30 mm.