Next-Generation Optical Technologies for Illuminating Genetically Targeted Brain Circuits

Abstract

Emerging technologies from optics, genetics, and bioengineering are being combined for studies of intact neural circuits. The rapid progression of such interdisciplinary "optogenetic" approaches has expanded capabilities for optical imaging and genetic targeting of specific cell types. Here we explore key recent advances that unite optical and genetic approaches, focusing on promising techniques that either allow novel studies of neural dynamics and behavior or provide fresh perspectives on classic model systems.Optogenetic technology combines genetic targeting of specific neurons or proteins with optical technology for imaging or control of the targets within intact, living neural circuits. The roots of this approach extend back decades. The utility of labeling individual neurons was clear to Ramon y Cajal who conducted detailed histological analyses of single neurons embedded in dense neural circuitry using Golgi stains. The advent of combined optical/genetic methods now allows researchers to visualize genetically targeted neurons in living animals and to track and control electrical and biochemical events within targeted cell types.The growth of optogenetic methodologies has included the advancement of several approaches: (1) one-and two-photon fluorescence microendoscopy for imaging fluorescently labeled cells deep within the mammalian brain; (2) simultaneous imaging of mammalian functional brain maps and the dynamics of neuronal morphology in genetically targeted neocortical cells; (3) genetically targeted reporters for imaging subcellular biochemical function in living neurons; (4) mouse transgenic techniques for genetic control of biochemical function in fluorescently labeled neurons embedded within intact mammalian circuitry; (5) genetically targeted optical control of neural activity in behaving Drosophila; and (6) high-speed, genetically targeted optical control of electrical activity in mammalian circuits. In this minireview, we highlight advances in these six areas and explore potential future applications of such technologies.

Single-neuron labeling with inducible Cre-mediated knockout in transgenic mice

“…Many genetically encoded tools to both monitor and manipulate various physiological properties of neurons have been developed in recent years [2][3][4][5][6][7][8][29][30][31][32] . These include fluorescent reporters of synaptic transmission and ion concentrations, as well as reagents to modulate neuronal excitability and neurotransmitter release.…”

“…Thus, the development of tools for conditional genetic manipulation of individual neurons in mice would greatly facilitate functional genomics in the nervous system. Furthermore, a wealth of genetically encoded tools is now available to both monitor and manipulate various properties of neurons [2][3][4][5][6][7][8] . Genetic approaches that allow the application of these tools in single identifiable neurons would greatly expand their utility in probing neuronal structure and function 9 .…”

Image Informatics Strategies for Deciphering Neuronal Network Connectivity

“…This enables the study of cell-cell interactions on calcium bursting behaviour, which might be of interest to investigate the effect of trans-synaptically transmitted toxic proteins 112 . In addition, calcium imaging can be combined with optogenetics 113 or photostimulation 114 , so as to perturb specific cells (or even subcellular compartments) and monitor response within a multicellular context. Closing the loop between optical readouts and the generation of these stimuli (i.e.…”

Selective Manipulation of Neural Circuits

“…Optogenetics is a technique that uses optical stimulation of genetically encoded light-sensitive channels and pumps to achieve neuromodulation [105,107,108]. Optogenetics was born with the discovery of light-sensitive microbial membrane proteins [107,[109][110][111].…”

“…Optogenetics was born with the discovery of light-sensitive microbial membrane proteins [107,[109][110][111]. Channelrhodopsins, light-sensitive cation channels, rapidly open and depolarize neurons in response to blue light (460 nm) [110,111].…”