Medical Technology

Optpgentics Controlling Brain Circuits with Light



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Optogenetics is the science of controlling brain circuits with light. It is a field that shows great potential for brain study, and treatment of its disorders. This exciting study "...combines optical and genetic techniques".

Its promise lies in being able to turn neurons on and off. By activating or blocking specific neurons as result of controlled gene expression, a therapist will be able to better understand and control neurological diseases such as Parkinson's. One advantage is that the approach is not a drug, and can therefore target specific kinds of cells in particular without damaging the surrounding cells and tissue. Thus, the effects are limited to only those cells that are problematic and or of interest.

Optogenetics "combines optical and genetic techniques to probe neural circuits." Through it, the researcher attempting to navigate the murky and uncharted neurological waters at last has a better version of the brain ship's dashboard, has a clearer map to lead to new discoveries. The reseacher gains a much better picture of brain operation. "Imagine how much easier mapping the circuits in the brain would be if every type of neuron came equipped with its own on-off switch you could control at will."

Dr.Karl Diesseroth, MD, PhD. is a prof of bioengineering and psychiatry, who pioneered this technique. The technique "...employs light-activated membrane proteins- channelrhodospins and halorhodopsins- found in microorganisms. Each protein is sensitive to a different frequency of light," The channelrhodospins may be thought of as "on" switches. Conversely, the halorhodospins may be thought of as "off" switches. "The channelrhodospins are cation channels while the halorhodospins are chloride pumps. In neurons, activating a channelrhodospin allows sodium or calcium ions in, lowering membrane potential ions and causing the neuron to fire. By pumping in chloride ions and raising the potential, the halorhodospins do the opposite."

To deliver light to the cell membrane, a scientist simply uses a very thin glass fiber within a millimeter of the target cells. These fibers are much thinner than current brain electrodes, and "...can be used to record neuronal activity" as it happens in virtual time. Dr. Deisseroth talks about his work with Parkinson's disease lab rodents. First, he used yellow light to inhibit thalamic neurons, with no behavior affect resulting. He then tried blue light; again, no behavior affect. In each case, the neurons were successfully manipulated with the light therapy.As expected, one light frequency raised the membrane potential, and the other lowered it. However, this was not successful in terms of behavior affect and therefore not useful as a Parkinson's treatment. Finally, they decided to target "...transferted axons arriving from the cerebral cortex." This technique met with success. The subjects behaved as their normal peers

Doctor Lorenzo, a professor and surgeon, lauds optogentics: "It is a wonderful new window into neural and circuit function, much more specific than electrical stimulation, because you can dissect out the relative attributes of having one element active or inhibited. This gives us the option to hone down on the mechanism." Optogenetics promises to literally shed light on the complex world of brains and neurons and their response to genetic material.


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