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The optogenetics iPhone app

A recently developed smartphone application allows estimating the required optical power for a given in vivo optogenetic stimulation experiment or any other experimental approach that includes light delivery to deep brain areas via optical fibers. Different brain areas have different optical properties, which determine how light scatters and distributes (and how deeply it penetrates the tissue), once it exits the fiber. The application has a complete mouse brain atlas included that can be used to determine the optical properties of any brain area in the mouse brain (the data on which the calculations are based on was recently published in PlosONE: Aj-Juboori et al, 2013). The user can find the brain areas of his choice, mark it on the atlas, then tell the application what type of optogenetic protein he/she wants to use, as well as the type of optical fiber, desired optical power, and desired protein activation ratio. The application then estimates how far the light will spread in this particular experimental situation (and thus, up to which distance from the fiber tip optogenetic protein activation can be expected). The APP comes in two versions, a free version and a Pro Version that costs $1.99. The two versions are … Continue reading

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Stop lights for temporal lobe seizures

Unlike electrical stimulation, optogenetics allows neuronal manipulation with great cell-type specificity, with light directly affecting only those cells expressing opsins. In a recent report in Nature Communications, Krook-Magnuson et al harnessed this specificity to stop seizures in vivo in a mouse model of temporal lobe epilepsy. Mice were implanted with electrodes to record brain activity and 200µm thick optical fibers to deliver light to the brain. A closed-loop, on-demand responsive system detected seizures in real time, allowing temporal specificity, in addition to the cell-type specificity achieved through selective opsin expression. Specifically, the authors either selectively inhibited excitatory principal cells or, alternatively, excited a subpopulation of GABAergic inhibitory neurons in the hippocampus by delivering light at the time of a seizure. Both approaches proved successful, despite the less than 5% of illuminated neurons expressing opsins in the latter approach. Light arrested ongoing electrical seizure activity and reduced the incidence of events progressing to overt behavioral seizures.

Epilepsy, a condition of recurrent, spontaneous seizures, is a prevalent disorder, with 1 out of 26 people developing epilepsy during their lifetime. Unfortunately, for over 40% of patients, seizures cannot be controlled with current treatment options. Temporal lobe epilepsy, the most common form of epilepsy … Continue reading

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A photoconvertible genetically-encoded calcium indicator

One of the primary goal of neuroscience research is to dissect the role of different cell-types in neuronal circuits. Thanks to the development of optogenetic reporters and control tools in recent years, researchers can now optically control and monitor the activity of genetically defined neuronal populations. Going deeper into the understanding of neuronal circuit requires to follow and control the activity of individual cells within these genetically-defined populations. Imaging the activity of individual neurons in vitro and in vivo can be achieved with classical microscopy techniques but labelling and following the activity of arbitrarily defined subsets of cells in a given population remains hard to implement. Optical highlighters which can be photoactivated or photoconverted are routinely used to label cell subpopulations but have only been used so far for anatomical tracing or cell migration studies. In a recent study published in JACS, Campbell and coworkers introduce a photoconvertible genetically-encoded calcium indicator, providing the possibility to easily monitor the activity of subsets of cells of a given cell type.

This dual-function Ca2+ indicator was made by combining two of the most powerful implementations of fluorescent protein (FP) technology: the “highlighters” that can be converted from non-fluorescent to fluorescent or from one … Continue reading

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KENGE-tet System for Expanding the Repertoire of Optogenetically Targeted Cells

Optogenetics has proven to be a powerful tool capable of manipulating the activity of a specific population of cells in a complex multicellular organism. This approach is enthusiastically pursued in recent neuroscience field and the causal relationship between neural activity and behavior is finally starting to become unveiled. However, most studies utilize virus mediated gene transfer for the induction of light-sensitive proteins, such as channelrhodopsin-2 (ChR2), and such method inevitably introduces surgical injuries and variability of expression between trials. Therefore, transgenic approach has long been sought, however, satisfying the demands of the specificity as well as the abundance of expression were difficult.

In a recent paper published in the Cell Reports, Tanaka and Matsui and their colleagues at the National Institute for Physiological Sciences (Okazaki, Japan) established Knockin-mediated ENhanced Gene Expression by improved tetracycline-controlled gene induction system (KENGE-tet). The authors found that high levels of tTA-mediated transcription can be achieved by knocking in tetO-ChR2 cassette into a locus at a housekeeping gene, beta-actin. The authors crossed this tetO-ChR2 knockin mouse with 7 different tTA lines and achieved ChR2 expression in specific cell-types including sub-populations of neurons, astrocytes, oligodendrocytes, and microglial cells. In all cases, the level of ChR2 expression was … Continue reading

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Progress in Brain Research Vol.196

The latest volume from the book series Progress in Brain Research is entitled “Optogenetics: Tools for Controlling and Monitoring Neuronal Activity”, gathering 12 chapters of about 20 pages each. The volume is edited by Thomas Knöpfel and Edward S. Boyden and chooses to embed monitoring and controlling strategies into a unique, comprehensive concept of optogenetics, as explicited in the introductory chapter.

Table of Contents:

Chapter 1: A comprehensive concept of optogenetics. Chapter 2: Optogenetic excitation of neurons with channelrhodopsins: Light instrumentation, expression systems, and channelrhodopsin variants. Chapter 3: Genetically encoded molecular tools for light-driven silencing of targeted neurons. Chapter 4: Genetically encoded probes for optical imaging of brain electrical activity. Chapter 5: Neural activity imaging with genetically encoded calcium indicators. Chapter 6: Manipulating cellular processes using optical control of protein–protein interactions. Chapter 7: Two-photon optogenetics. Chapter 8: Zebrafish as an appealing model for optogenetic studies. Chapter 9: Genetic targeting of specific neuronal cell types in the cerebral cortex. Chapter 10: Mouse transgenic approaches in optogenetics. Chapter 11: Optogenetics in the nonhuman primate. Chapter 12: Optogenetic reporters: Fluorescent protein-based genetically encoded indicators of signaling and metabolism in the brain.

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