Channelrhodopsins are a group of molecules used to optogenetically depolarize neurons. Here, Tsien and colleagues report their development of a red-activatable channelrhodopsin (ReaChR), that is optimally excited with orange to red light (λ ∼590-630 nm) and offers improved membrane trafficking, higher photocurrents and faster kinetics compared to existing red-shifted channelrhodopsins. Red light is less scattered by tissue and is absorbed less by blood than the blue to green wavelengths that are required by other channelrhodopsin variants. They used ReaChR expressed in the vibrissa motor cortex to drive spiking and vibrissa motion in awake mice when excited with red light through the intact skull. ReaChR has strong potential for future medical treatment technologies since it enables transcranial optical activation of neurons in deep brain structures without the need to surgically thin the skull, form a transcranial window or implant optical fibers.

Lin JY, Knutsen PM, Muller A, Kleinfeld D, Tsien RY: ReaChR: a red-shifted variant of channelrhodopsin enables deep transcranial optogenetic excitation. Nature Neuroscience [Epub ahead of print, Sept. 1, 2013;  doi: 10.1038/nn.3502 ].

http://www.ncbi.nlm.nih.gov/pubmed/23995068