Neuronal light switches : Neurophilosophy. The September issue of Scientific American contains an excellent and lengthy article about a state-of-the-art technique called optogenetics, by molecular physiologist Gero Miesenböck, who has been instrumental in its development. As its name suggests, optogenetics is a combination of optics and genetic engineering. It is a powerful new method for investigating the function of neuronal circuits, based a number of light-sensitive proteins which have recently been isolated from various micro-organisms.
By fusing their genes to promoters which control where they will be activated, researchers can target the proteins to specified cells and thus render those cells sensitive to light. Importantly, each protein is sensitive to a specific wavelength of light and responds to it by changing its three-dimensional structure so that ions can flow into or out of the cell. The activity of cells expressing these proteins can therefore be controlled by laser pulses. Related: Light switches on the brain | Moheb Costandi | Science. Leading lights in optogenetics presented the latest developments in their field during a mini-symposium at the 40th annual meeting of the Society for Neuroscience in San Diego at the weekend. Optogenetics has emerged in the past decade as a high-precision tool for monitoring and controlling the activity of nerve cells.
It is based on light-sensitive proteins called rhodopsins, which are isolated from algae and bacteria and are related to the proteins found in the human retina. When rhodopsins in the human eye's photoreceptors are struck by light, they initiate a cascade of biochemical reactions, causing the cells to send signals to the brain via the optic nerve. But the microbial rhodopsins behave differently – they alter the electrical properties of neurons directly, and it is these properties that make them so useful.
When introduced into neurons, they insert themselves into the membrane, making the cells sensitive to light. Mo Costandi writes the Neurophilosophy blog. Versatility of optogenetics brain-research technique vastly expanded. Recently, brain researchers have gained a powerful new way to troubleshoot neural circuits associated with depression, Parkinson's disease and other conditions in small animals such as rats. They use an optogenetics technology, invented at Stanford University, that precisely turns select brain cells on or off with flashes of light. Although useful, the optogenetics tool set has been limited. In a paper to be published in the April 2 edition of Cell, the Stanford researchers describe major advances that will enable a much wider range of experiments in larger animals.
The new capabilities include ways to use any visible color of light (instead of just a few) to control cells, and ways to make cells susceptible to the optogenetics technique even if they cannot be genetically engineered directly. To date, optogenetics worked by using a specially engineered virus to insert genes into cells so that they would make light-sensitive proteins. Optogenetics: controlling brain cells with lasers - life - 07 January 2010. Brain cells can be switched on and off like light bulbs using newly identified microbial proteins that are sensitive to the colour of laser light. The discovery is the latest in the fast-moving field of optogenetics, which has already given researchers unparalleled control over brain circuits in laboratory animals.
The technology may lead to treatments for conditions such as epilepsy, Parkinson's disease and blindness. New Scientist explains the science and its promise. How do scientists control brain cells with lasers? Neurons fire when electrically charged atoms – ions – flood in and out of them, creating a tiny electric potential across their membranes. One algal protein, channelrhodopsin-2, turns neurons on when bathed in blue light, while its foil, halorhodopsin, silences neurons under yellow light. If these proteins are already around, what's new?
Channelrhodopsin-2 works swimmingly: it recently helped identify a brain circuit that, when activated, may ease symptoms of Parkinson's. Optogenetics: Controlling the Brain with Light [Extended Version] Despite the enormous efforts of clinicians and researchers, our limited insight into psychiatric disease (the worldwide-leading cause of years of life lost to death or disability) hinders the search for cures and contributes to stigmatization.
Clearly, we need new answers in psychiatry. But as philosopher of science Karl Popper might have said, before we can find the answers, we need the power to ask new questions. In other words, we need new technology. Developing appropriate techniques is difficult, however, because the mammalian brain is beyond compare in its complexity. In a 1979 Scientific American article Nobel laureate Francis Crick suggested that the major challenge facing neuroscience was the need to control one type of cell in the brain while leaving others unaltered. Meanwhile, in a realm of biology as distant from the study of the mammalian brain as might seem possible, researchers were working on microorganisms that would only much later turn out to be relevant.
Neuroscience: Illuminating the brain.