发表于 2015-11-24 20:19:36
本帖最后由 tempid123 于 2015-11-24 20:35 编辑 |
The "far-fetched" possibility of using light for selectively controlling precise neural activity (action potential) patterns within subtypes of cells in the brain was articulated by Francis Crick in his Kuffler Lectures at the University of California in San Diego in 1999. An early use of light to activate neurons was carried out by Richard Fork who demonstrated laser activation of neurons within intact tissue, although not in a genetically-targeted manner. The earliest genetically targeted method, which used light to control genetically-sensitised neurons, was reported in January 2002 by Boris Zemelman (now at UT Austin) and Gero Miesenböck, who employed Drosophila rhodopsin photoreceptors for controlling neural activity in cultured mammalian neurons. In 2003 Zemelman and Miesenböck developed a second method for light-dependent activation of neurons in which single ionotropic channels TRPV1, TRPM8 and P2X2 were gated by caged ligands in response to light. Beginning in 2004, the Kramer and Isacoff groups developed organic photoswitches or "reversibly caged" compounds in collaboration with the Trauner group that could interact with genetically introduced ion channels. However, these earlier approaches were not applied outside the original laboratories, likely because of technical challenges in delivering the multiple component parts required.
In April 2005, Susana Lima and Miesenböck reported the first use of genetically-targeted P2X2 photostimulation to control the behaviour of an animal. They showed that photostimulation of genetically circumscribed groups of neurons, such as those of the dopaminergic system, elicited characteristic behavioural changes in fruit flies. In August 2005, Karl Deisseroth's laboratory in the Bioengineering Department at Stanford including graduate students Ed Boyden and Feng Zhang (both now at MIT) published the first demonstration of a single-component optogenetic system, beginning in cultured mammalian neurons. using channelrhodopsin, a single-component light-activated cation channel from unicellular algae, whose molecular identity and principal properties rendering it useful for optogenetic studies had been first reported in November 2003 by Georg Nagel. The groups of Gottschalk and Nagel were the first to extend the usability of Channelrhodopsin-2 for controlling neuronal activity to the intact animal by showing that motor patterns in the roundworm Caenorhabditis elegans could be evoked by targeted expression and stimulation of Channelrhodopsin-2 in selected neural circuits (published in December 2005). Now optogenetics has been routinely combined with brain region-and cell type-specific Cre/loxP genetic methods developed for Neuroscience by Joe Z. Tsien back in 1990s  to activate or inhibit specific brain regions and cell-types in vivo.
Motility and photoorientation of microalgae have been studied over more than hundred years in many laboratories worldwide. In 1980, Ken Foster developed the first consistent theory about the functionality of algal eyes. He also analyzed published action spectra and complemented blind cells with retinal and retinal analogues, which led to the conclusion that the photoreceptor for motility responses in Chlorophyceae is rhodopsin. Photocurrents of the Chlorophyceae Heamatococcus pluvialis and Chlamydomonas reinhardtii were studied over many years in the groups of Oleg Sineshchekov and Peter Hegemann, resulting in two seminal publications in the years 1978 and 1991. Based on action spectroscopy and simultaneous recordings of photocurrents and flagellar beating, it was determined that the photoreceptor currents and subsequent flagellar movements are mediated by rhodopsin and control phototaxis and photophobic responses. The extremely fast rise of the photoreceptor current after a brief light flash led to the conclusion that that the rhodopsin and the channel are intimately linked in a protein complex, or even within one single protein. However, biochemical purification of the rhodopsin-photoreceptor(s) was unsuccessful over many years. The nucleotide sequences of the rhodopsins now called channelrhodopsins ChR1 and ChR2 were finally uncovered in a large-scale EST sequencing project in C. reinhardtii. Independent submission of the same sequences to GenBank by three research groups generated confusion about their naming: The names cop-3 and cop-4 were used for initial submission by Hegemann's group; csoA and csoB by Spudich's group; and acop-1 and acop-2 by Takahashi's group. Both sequences were found to function as single-component light-activated cation channels in a Xenopus oocytes and human kidney cells (HEK) by Georg Nagel, Ernst Bamberg, Peter Hegemann and others. The name "channelrhodopsin" was coined to highlight this unusual property, and the sequences were renamed accordingly. Meanwhile, their roles in generation of photoreceptor currents in algal cells were characterized by Oleg Sineshchekov, Kwang-Hwan Jung and John Spudich, and Peter Berthold and Peter Hegemann. In 2005, three groups sequentially established ChR2 as a tool for genetically targeted optical remote control (optogenetics) of neurons, neural circuits and behavior.