page_title: Optogenetics
section_title: Technique
hierarchical_section_title: Optogenetics / Technique
caption_attribution_description: English: Three primary components in the application of Optogenetics are as follows (A) Identification or synthesis of a light-sensitive protein (Opsin) such as Channelrhodopsin-2 (ChR2),Halorhodopsin (NpHR), etc... (B) The design of a system to introduce the genetic material containing the opsin into cells for protein expression such as application of Cre-Recombinase or an Adeno-Associated-Virus (C) Application of light emitting instruments
context_page_description: Optogenetics most commonly refers to a biological technique that involves the use of light to control neurons that have been genetically modified to express light-sensitive ion channels. As such, optogenetics is a neuromodulation method that uses a combination of techniques from optics and genetics to control the activities of individual neurons in living tissue—even within freely-moving animals. In some usages, optogenetics also refers to optical monitoring of neuronal activity and control of biochemical pathways in non-neuronal cells, although these research activities preceded the use of light-sensitive ion channels in neurons. As optogenetics is used by some authors to refer to only optical control of the activity of genetically defined neurons and not these additional research approaches, the term optogenetics is an example of polysemy.
  Neuronal control is achieved using optogenetic actuators like channelrhodopsin, halorhodopsin, and archaerhodopsin, while optical recording of neuronal activities can be made with the help of optogenetic sensors for calcium, vesicular release, neurotransmitters, or membrane voltage.
context_section_description: The technique of using optogenetics is flexible and adaptable to the experimenter's needs. For starters, experimenters genetically engineer a microbial opsin based on the gating properties (rate of excitability, refractory period, etc..) required for the experiment.
  There is a challenge in introducing the microbial opsin, an optogenetic actuator, into a specific region of the organism in question. A rudimentary approach is to introduce an engineered viral vector that contains the optogenetic actuator gene attached to a recognizable promoter such as CAMKIIα. This allows for some level of specificity as cells that already contain and can translate the given promoter will be infected with the viral vector and hopefully express the optogenetic actuator gene.
  Another approach is the creation of transgenic mice where the optogenetic actuator gene is introduced into mice zygotes with a given promoter, most commonly Thy1. Introduction of the optogenetic actuator at an early stage allows for a larger genetic code to be incorporated and as a result, increases the specificity of cells to be infected.
  A third and rather novel approach that has been developed is creating transgenic mice with Cre recombinase, an enzyme that catalyzes recombination between two lox-P sites. Then by introducing an engineered viral vector containing the optogenetic actuator gene in between two lox-P sites, only the cells containing the Cre recombinase will express the microbial opsin. This last technique has allowed for multiple modified optogenetic actuators to be used without the need to create a whole line of transgenic animals every time a new microbial opsin is needed.
  After the introduction and expression of the microbial opsin, depending on the type of analysis being performed, application of light can be placed at the terminal ends or the main region where the infected cells are situated. Light stimulation can be performed with a vast array of instruments from light emitting diodes (LEDs) or diode-pumped solid state (DPSS). These light sources are most commonly connected to a computer through a fiber optic cable. Recent advances include the advent of wireless head-mounted devices that also apply LED to targeted areas and as a result give the animal more freedom of mobility to reproduce in vivo results.
caption: Three primary components in the application of optogenetics are as follows (A) Identification or synthesis of a light-sensitive protein (opsin) such as channelrhodopsin-2 (ChR2), halorhodopsin (NpHR), etc... (B) The design of a system to introduce the genetic material containing the opsin into cells for protein expression such as application of Cre recombinase or an adeno-associated-virus (C) application of light emitting instruments.[78]
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