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 heavily on the spatial distribution of transfected light-sensitive neurons for targeted control.
In our investigations, an imaging fiber bundle (Schott, 1534702) containing 4,500 individual fibers, each with a diameter of 7.5 µm, and an overall outer bundle diameter of 530 µm, was used as the conduit for light delivery and optical recording/imaging in neuron cultures and in in vivo mouse brain. We demonstrated that the use of this fiber bundle, in contrast to a single multimode fiber, allowed for individually-addressable fibers, spatial selectivity at the stimulus site, precise control of light delivery, and full field-of-view imaging and/or optical recordings of neurons. An objective coupled the two continuous wave diode laser sources (561 nm/488 nm) for stimulation and imaging into the proximal end of the fiber bundle while a set of galvanometer-scanning mirrors was used to couple the light stimulus to distinct fibers. A micro lens aided in focusing the light at the neurons. In vivo studies utilized C1V1(E122T/E162T)-TS-p2A-mCherry (Karl Deisseroth, Stanford) and GCaMP6s transgenic mice (Jackson Labs) for this all-optical approach.
Our results demonstrate that imaging fiber bundles provide superior control of spatial selectivity of light delivery to specific neurons, and 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 tissue and lack in vivo imaging capabilities.
Javier I. Suárez, Parijat Sengupta, Jonathan Guo-Han Mun, Justin Rhodes, and Stephen A. Boppart, "Spatial control of in vivo optogenetic light stimulation and recording via an imaging fiber bundle (Conference Presentation)," Proc. SPIE 10052, Optogenetics and Optical Manipulation, 1005203 (Presented at SPIE BiOS: January 28, 2017; Published: 19 April 2017); https://doi.org/10.1117/12.2252582.5371339435001.
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