If you're curious about the background image (which most inquisitive neuroscientists would be!), it is a cultured glutamatergic pyramidal neuron from the hippocampus transfected with a gene encoding a protein known as channelrhodopsin-2 with an EYFP (enhanced yellow fluorescent protein that fluoresces green) tag (Deisseroth et al.). As you can see, the protein is expressed ubiquitously throughout the cell. Channelrhodopsin-2 is an excitatory opsin protein that forms a functional ion channel permeable to Na+ ions. This protein is sensitive to photons of a blue frequency, and when these photons are absorbed, the proteins undergo a conformational change that opens the channel, allowing Na+ ions to pass through, thereby invoking action potentials. This is a powerful tool to selectively activate (or inactivate) specific populations of neurons within living organisms, and is known as optogenetics.

The New York Times published an article in May 2011 discussing the exciting and impressive possibilities of new optogenetic technology. It seems as if this novel method is catching on!

Control Desk for the Neural Switchboard

This is the ribbon diagram of the x-ray crystalline structure of native rhodopsin from bovine rod cells. It makes sense that these are the proteins that exist in many animals' retinas, absorbing light and transducing energy. By isolating the gene and transplanting it using fancy molecular tricks, we can get any cell we want to express the protein and respond to light!

This is an artist's depiction of the channelrhodopsin protein in action. Notice how the blue light wave/particle (photon) is being absorbed by the protein complex that is embedded in the cell membrane, and how the subunit to the right is forming an permeable channel, allowing the flow of ions through. In this case, they are Sodium ions, and they are depolarizing the cell.

This is a video produced by Nature about their selected method of the year for 2010, that being optogenetics. It is a really informative synopsis of optogenetics, so it is definitely worth watching!

Here is the excerpt from the Nature video of a transgenic mouse containing the gene for a protein known as channelrhodopsin-2 within its right secondary motor cortex. Notice what happens as the blue laser light is initiated, and then when it is terminated. This is a prime example of the power that this molecular tool possesses.

Gradinaru V, Thompson KR, Zhang F, Mogri M, Kay K, Schneider MB, Deisseroth K. Targeting and readout strategies for fast optical neural control in vitro and in vivo. J Neurosci. 2007 Dec 26;27(52):14231-8.

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