Genetic and optical targeting of neural circuits and behavior—zebrafish in the spotlight

University of California, San Francisco, Department of Physiology, San Francisco, CA 94158-2324, USA.
Current opinion in neurobiology (Impact Factor: 6.77). 09/2009; 19(5):553-60. DOI: 10.1016/j.conb.2009.08.001
Source: PubMed

ABSTRACT Methods to label neurons and to monitor their activity with genetically encoded fluorescent reporters have been a staple of neuroscience research for several years. The recent introduction of photoswitchable ion channels and pumps, such as channelrhodopsin (ChR2), halorhodopsin (NpHR), and light-gated glutamate receptor (LiGluR), is enabling remote optical manipulation of neuronal activity. The translucent brains of zebrafish offer superior experimental conditions for optogenetic approaches in vivo. Enhancer and gene trapping approaches have generated hundreds of Gal4 driver lines in which the expression of UAS-linked effectors can be targeted to subpopulations of neurons. Local photoactivation of genetically targeted LiGluR, ChR2, or NpHR has uncovered novel functions for specific areas and cell types in zebrafish behavior. Because the manipulation is restricted to times and places where genetics (cell types) and optics (beams of light) intersect, this method affords excellent resolving power for the functional analysis of neural circuitry.

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    • "As the experimental applications of ChR2 move to include biophysically diverse interneurons (Markram et al., 2004; Katzel et al., 2011; Schultheis et al., 2011; English et al., 2012; Chiu et al., 2013; Owen et al., 2013), a fuller understanding of its possibilities and limitations becomes essential. Although ChR2 expression, trafficking, and activation has been achieved in most types of nervous tissue (Li et al., 2005; Nagel et al., 2005; Bi et al., 2006; Schroll et al., 2006; Adamantidis et al., 2007; Zhang et al., 2007; Douglass et al., 2008; Mahoney et al., 2008; Baier and Scott, 2009; Guo et al., 2009; Han et al., 2009; Liu et al., 2009; Zhu et al., 2009; Gourine et al., 2010; Hagglund et al., 2010; Diester and et al, 2011; Figueiredo et al., 2011; Sasaki et al., 2012; Ljaschenko et al., 2013), little consideration has been given to the kinetics that constrain light-induced firing properties in different neuronal subtypes. Factors that affect the degree of neuronal photostimulation, including intrinsic differences in firing dynamics, membrane properties, and channel composition differ among neuronal cell types. "
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    ABSTRACT: eLife digest The brain is a highly complex structure composed of trillions of interconnecting nerve cells. The pattern of connections between these cells gives rise to the various brain circuits that govern how the brain functions. Understanding how the brain is wired together is important for determining how ‘faulty circuits’ contribute to various neurological disorders. New optogenetic technique tools allow neuroscientists to turn on specific neurons simply by shining light on them. These techniques involve genetically manipulating the organisms so that their neurons express proteins that are activated when they are exposed to light of a particular wavelength. However, it is important to understand the limitations of this approach—including the possibility that the light might actually turn off some neurons—when using it to study animal behavior. Now, Herman, Huang et al. show that shining light pulses for long durations onto neurons expressing a light-activated protein called channelrhodopsin-2 causes the neurons to become silenced rather than activated. Moreover, certain types of neurons, called interneurons, are more susceptible to this effect—termed ‘depolarization block’—than the other types of neurons. Researchers need to be mindful of this effect when channelrhodopsin-2 is used in optogenetic experiments to study the behavior of living animals. However, this silencing property could be useful in experiments that investigate situations in which depolarization block is thought to contribute to brain function and health: such as in the treatments of schizophrenia and Parkinson’s disease. DOI:
    eLife Sciences 01/2014; 3:e01481. DOI:10.7554/eLife.01481 · 8.52 Impact Factor
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    • "The functional study of neural circuits in zebrafish has benefited from the development of optogenetic and transgenic techniques that together allow the close monitoring of activity in neural networks and experimental gain and loss of function manipulations to assess causal relationships between specific neural patterns and specific behaviors (Baier and Scott, 2009; Portugues et al., 2013). Imaging of neural activity in the brain of both larvae and adults (explants in the later case) has been achieved using genetically encoded calcium indicators, of which successive versions of GCaMP have been the more widely used (Baier and Scott, 2009; Portugues et al., 2013). The use of these fluorescent reporters requires the restrain of the animal during image acquisition which limits the behavioral tasks that can be investigated. "
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    ABSTRACT: Understanding how the brain implements social behavior on one hand, and how social processes feedback on the brain to promote fine-tuning of behavioral output according to changes in the social environment is a major challenge in contemporary neuroscience. A critical step to take this challenge successfully is finding the appropriate level of analysis when relating social to biological phenomena. Given the enormous complexity of both the neural networks of the brain and social systems, the use of a cognitive level of analysis (in an information processing perspective) is proposed here as an explanatory interface between brain and behavior. A conceptual framework for a cognitive approach to comparative social neuroscience is proposed, consisting of the following steps to be taken across different species with varying social systems: (1) identification of the functional building blocks of social skills; (2) identification of the cognitive mechanisms underlying the previously identified social skills; and (3) mapping these information processing mechanisms onto the brain. Teleost fish are presented here as a group of choice to develop this approach, given the diversity of social systems present in closely related species that allows for planned phylogenetic comparisons, and the availability of neurogenetic tools that allows the visualization and manipulation of selected neural circuits in model species such as the zebrafish. Finally, the state-of-the art of zebrafish social cognition and of the tools available to map social cognitive abilities to neural circuits in zebrafish are reviewed.
    Frontiers in Neural Circuits 08/2013; 7:131. DOI:10.3389/fncir.2013.00131 · 2.95 Impact Factor
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    • "Some advantages of zebrafish for neuroscience are " convenient " rather than " essential. " For example, the transparency of zebrafish larvae is often considered an advantage because it allows for calcium imaging of neuronal activity patterns and for optogenetic manipulations of neurons without the need for surgical procedures (O'Malley et al., 1996; Baier and Scott, 2009; Wyart et al., 2009; Blumhagen et al., 2011; Ahrens et al., 2012; del Bene and Wyart, 2012; Ahrens and Keller, 2013; Portugues et al., 2013). In some cases, however, surgical procedures are no principal barrier to reach the scientific goal. "
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    ABSTRACT: The clever choice of animal models has been instrumental for many breakthrough discoveries in life sciences. One of the outstanding challenges in neuroscience is the in-depth analysis of neuronal circuits to understand how interactions between large numbers of neurons give rise to the computational power of the brain. A promising model organism to address this challenge is the zebrafish, not only because it is cheap, transparent and accessible to sophisticated genetic manipulations but also because it offers unique advantages for quantitative analyses of circuit structure and function. One of the most important advantages of zebrafish is its small brain size, both at larval and adult stages. Small brains enable exhaustive measurements of neuronal activity patterns by optical imaging and facilitate large-scale reconstructions of wiring diagrams by electron microscopic approaches. Such information is important, and probably essential, to obtain mechanistic insights into neuronal computations underlying higher brain functions and dysfunctions. This review provides a brief overview over current methods and motivations for dense reconstructions of neuronal activity and connectivity patterns. It then discusses selective advantages of zebrafish and provides examples how these advantages are exploited to study neuronal computations in the olfactory bulb.
    Frontiers in Neural Circuits 04/2013; 7:71. DOI:10.3389/fncir.2013.00071 · 2.95 Impact Factor
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