Current methods for light delivery in in vivo optogenetic applications are typically accomplished via a single multimode fiber that diffuses light over a large area of the brain, and relies on the spatial distribution of transfected light-sensitive neurons for targeted control.
In our investigations, an imaging fiber bundle (Schott) containing 4,500 individual fibers, each with a diameter of 7.5 µm, and an overall outer bundle diameter of 530 µm, served as a conduit for light delivery and optical recording/imaging. The use of this fiber bundle, in contrast to a single multimode fiber, allows for individually-addressable fibers, spatial selectivity at the stimulus site, more precise control of light delivery, and full field-of-view imaging and/or optical recordings of individual neurons in local neural circuits. An objective coupled the two continuous wave diode laser sources (561nm/488nm) (Coherent) for stimulation and imaging into the fiber bundle while a set of galvanometer-scanning mirrors was used to couple the light stimulus to distinct fibers within the proximal end of the imaging fiber bundle. In our study, C1V1(E122T/E162T)-TS-p2A-mCherry (Karl Deisseroth, Stanford) and GCaMP6s transgenic mice (Jackson Labs) were utilized for this all-optical approach.
The results of our investigation demonstrate that imaging fiber bundles provide a new level of spatial selectivity and control of light delivery to specific neurons, as well as function as a conduit for optical imaging and recording at the in vivo site of stimulation, in contrast to the use of single multimode fibers that diffusely illuminate neural tissue and lack in vivo imaging capabilities.
Javier I. Suárez, Parijat Sengupta, Jonathan Mun, Rajashekar Iyer, Justin Rhodes, Martha U. Gillette, and Stephen A. Boppart, "Spatially controlled optogenetic light stimulation and recording platform via imaging fiber bundles
(Conference Presentation)," Proc. SPIE 9690, Clinical and Translational Neurophotonics; Neural Imaging and Sensing; and Optogenetics and Optical Manipulation, 969029 (Presented at SPIE BiOS: February 13, 2016; Published: 26 April 2016); https://doi.org/10.1117/12.2213320.4848636583001.
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