Matching stimulation paradigms resolve apparent differences between optogenetic and electrical VTA stimulation.

BACKGROUND: Optogenetic stimulation has grown into a popular brain stimulation method in basic neuroscience while electrical stimulation predominates in clinical applications. In order to explain the effects of electrical stimulation on a cellular level and evaluate potential advantages of optogenetic therapies, comparisons between the two stimulation modalities are necessary. This comparison is hindered, however, by the difficulty of effectively matching the two fundamentally different modalities. OBJECTIVE: Comparison of brain-wide activation patterns in response to intensity-matched electrical and optogenetic VTA stimulation. METHODS: We mapped optogenetic and electrical self-stimulation rates in the same mice over stimulation intensity and determined iso-behavioral intensities. Using functional 99mTc-HMPAO SPECT imaging of cerebral blood flow in awake animals, we obtained brain-wide activation patterns for both modalities at these iso-behavioral intensities. We performed these experiments in two mouse lines commonly used for optogenetic VTA stimulation, DAT::Cre and TH::Cre mice. RESULTS: We find iso-behavioral intensity matching of stimulation gives rise to similar brain activation patterns. Differences between mouse lines were more pronounced than differences between modalities. CONCLUSIONS: Previously found large differences of electrical and optogenetic stimulation might be due to unmatched stimulation intensity, particularly relative electrical overstimulation. These findings imply that therapeutic electrical VTA stimulation might be relatively specific if employed with optimized parameters.

A Guide to Creating and Testing New INTRSECT Constructs.

As the power of genetically encoded interventional and observational tools for neuroscience expands, the boundaries of experimental design are increasingly defined by limits in selectively expressing these tools in relevant cell types. Single-recombinase-dependent expression systems have been widely used as a means to restrict gene expression based on single features by combining recombinase-dependent viruses with recombinase-expressing transgenic animals. This protocol details how to create INTRSECT constructs and use multiple recombinases to achieve targeting of a desired gene to subsets of neurons that are defined by multiple genetic and/or topological features. This method includes the design and utilization of both viruses and transgenic animals: these tools are inherently flexible and modular and may be used in different combinations to achieve the desired gene expression pattern. © 2017 by John Wiley & Sons, Inc.

Comparison of fMRI analysis methods for heterogeneous BOLD responses in block design studies.

A large number of fMRI studies have shown that the temporal dynamics of evoked BOLD responses can be highly heterogeneous. Failing to model heterogeneous responses in statistical analysis can lead to significant errors in signal detection and characterization and alter the neurobiological interpretation. However, to date it is not clear that, out of a large number of options, which methods are robust against variability in the temporal dynamics of BOLD responses in block-design studies. Here, we used rodent optogenetic fMRI data with heterogeneous BOLD responses and simulations guided by experimental data as a means to investigate different analysis methods' performance against heterogeneous BOLD responses. Evaluations are carried out within the general linear model (GLM) framework and consist of standard basis sets as well as independent component analysis (ICA). Analyses show that, in the presence of heterogeneous BOLD responses, conventionally used GLM with a canonical basis set leads to considerable errors in the detection and characterization of BOLD responses. Our results suggest that the 3rd and 4th order gamma basis sets, the 7th to 9th order finite impulse response (FIR) basis sets, the 5th to 9th order B-spline basis sets, and the 2nd to 5th order Fourier basis sets are optimal for good balance between detection and characterization, while the 1st order Fourier basis set (coherence analysis) used in our earlier studies show good detection capability. ICA has mostly good detection and characterization capabilities, but detects a large volume of spurious activation with the control fMRI data.

TAEL: a zebrafish-optimized optogenetic gene expression system with fine spatial and temporal control.

Here, we describe an optogenetic gene expression system optimized for use in zebrafish. This system overcomes the limitations of current inducible expression systems by enabling robust spatial and temporal regulation of gene expression in living organisms. Because existing optogenetic systems show toxicity in zebrafish, we re-engineered the blue-light-activated EL222 system for minimal toxicity while exhibiting a large range of induction, fine spatial precision and rapid kinetics. We validate several strategies to spatially restrict illumination and thus gene induction with our new TAEL (TA4-EL222) system. As a functional example, we show that TAEL is able to induce ectopic endodermal cells in the presumptive ectoderm via targeted sox32 induction. We also demonstrate that TAEL can be used to resolve multiple roles of Nodal signaling at different stages of embryonic development. Finally, we show how inducible gene editing can be achieved by combining the TAEL and CRISPR/Cas9 systems. This toolkit should be a broadly useful resource for the fish community.

Precise detection of direct glomerular input duration by the olfactory bulb.

Sensory neuron input to the olfactory bulb (OB) was activated precisely for different durations with blue light in mice expressing channelrhodopsin-2 in olfactory sensory neurons. Behaviorally the mice discriminated differences of 10 ms in duration of direct glomerular activation. In addition, a subset of mitral/tufted cells in the OB of awake mice responded tonically therefore conveying information on stimulus duration. Our study provides evidence that duration of the input to glomeruli not synchronized to sniffing is detected. This potent cue may be used to obtain information on puffs in odor plumes.