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Shirai F, Hayashi-Takagi A. Optogenetics: Applications in psychiatric research. Psychiatry Clin Neurosci. 2017 Jun;71(6):363-372. doi: 10.1111/pcn.12516. Epub 2017 Mar 30. PMID: 28233379.
Optogenetics, which is essentially a combination of the words “optical” and “genetic,” involves the use of light in order to control changes in cells within living tissue. This technique is done by taking advantage of opsins, proteins that have developed sensitivity to light and are able to convert the light energy into electrical signals that the brain can process and turn into visual images. The opsins that scientists are most interested in are microbial opsins that have the ability to change cellular behavior in response to light as these opsins can be used to modulate neural activity.
The very first study on optogenetics involved the manipulation of neurons that produce orexin, a protein associated with waking up from sleep. This study utilized a machine that pulsed blue light into orexin-producing neurons, allowing the sleeping test mice to wake up. As a result of this monumental study, more researchers began to use optogenetics in their studies. In fact, the same researchers that performed the first study began to work on expanding optogenetic applications on Schizophrenia, proving that the activation of a specific neuron called parvalbumin using light will result in reduced Schizophrenic symptoms.
Multiple other studies have shown the potential for the use of optogenetics in an array of drug addictions and psychiatric diseases by using light to manipulate neurotransmitters, chemicals that are transmitted between neurons and are in charge of both behavioral and physiological processes. For example, when neurons responsible for acetylcholine (a neurotransmitter that controls memory and learning) are activated, the brain undergoes cocaine conditioning, where cocaine becomes associated with negative stimuli so that the patient will no longer feel the urge to take cocaine. Another example is how light can be used to activate dopamine neurons, which play a key role in motivation and pleasure, preventing stress caused by depression. Optogenetics has also shown its ability to alter the imbalance between excitatory neurons and inhibitory neurons. These neurons affect other neurons by either exciting them or inhibiting them. This imbalance has commonly been linked to autistic spectrum disorders, and research has demonstrated that optogenetics can increase the number of inhibitory neurons to match the number of excitatory neurons in order to prevent behavioral impairments.
Despite the success optogenetics has shown in trials with organisms such as mice, researchers are hesitant about applying optogenetics to human trials. Many ethical research boards have stated that the drastic interference with the brain brought upon by optogenetics is too drastic to apply to the human body.
Summarised by Brenton Lee
Works Cited
Lewis DA, Curley AA, Glausier JR, Volk DW. Cortical parvalbumin interneurons and cognitive dysfunction in schizophrenia. Trends Neurosci. 2012; 35: 57–67.
Sohal, V. S., & Rubenstein, J. L. R. (2019). Excitation-inhibition balance as a framework for investigating mechanisms in neuropsychiatric disorders. Molecular psychiatry, 24(9), 1248–1257. https://doi.org/10.1038/s41380-019-0426-0
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