Multimodal nonlinear-optical imaging of nucleoli.

Multimodal nonlinear microscopy combining third-harmonic generation (THG) with two- and three-photon-excited fluorescence (2PEF and 3PEF) is shown to provide a powerful resource for high-fidelity imaging of nucleoli and nucleolar proteins. We demonstrate that, with a suitably tailored genetically encoded fluorescent stain, the 2PEF/3PEF readout from specific nucleolar proteins can be reliably detected against the extranucleolar 2PEF/3PEF signal, enabling high-contrast imaging of the key nucleolar ribosome biogenesis components, such as fibrillarin. THG is shown to provide a versatile readout for unstained nucleolus imaging in a vast class of biological systems as different as neurons in brain slices and cultured HeLa cells.

Cell-specific three-photon-fluorescence brain imaging: neurons, astrocytes, and gliovascular interfaces.

We present brain imaging experiments on rat cortical areas, demonstrating that, when combined with a suitable high-brightness, cell-specific genetically encoded fluorescent marker, three-photon-excited fluorescence (3PEF), enables subcellular-resolution, cell-specific 3D brain imaging that is fully compatible and readily integrable with other nonlinear-optical imaging modalities, including two-photon-fluorescence and harmonic-generation microscopy. With laser excitation provided by sub-100-fs, 1.25-µm laser pulses, cell-specific 3PEF from astrocytes and their processes detected in parallel with a three-photon-resonance-enhanced third harmonic from blood vessels is shown to enable a high-contrast 3D imaging of gliovascular interfaces.

Stain-free subcellular-resolution astrocyte imaging using third-harmonic generation.

We demonstrate stain-free, high-contrast, subcellular-resolution imaging of astroglial cells using epi-detected third-harmonic generation (THG). The astrocyte-imaging capability of THG is verified by colocalizing THG images with fluorescence images of astrocytes expressing a genetically encodable fluorescent reporter. We show that THG imaging with an optimized point-spread function can reliably detect significant subcellular features of astrocytes, including cell nuclei, as well as the soma shape and boundaries.

Reconnectable fiberscopes for chronic in vivo deep-brain imaging.

Reconnectable bundles consisting of thousands of optical fibers are shown to enable high-quality image transmission, offering a platform for the creation of implantable fiberscopes for minimally invasive in vivo brain imaging. Experiments on various lines of transgenic mice verify the performance of this fiberscope as a powerful tool for chronic in vivo neuroimaging using genetically encoded calcium indicators, neuronal activity markers as well as axon growth regulators and brain-specific protein drivers in deep regions of live brain.

Two-photon imaging of fiber-coupled neurons.

Optical coupling between a single, individually addressable neuron and a properly designed optical fiber is demonstrated. Two-photon imaging is shown to enable a quantitative in situ analysis of such fiber-single-neuron coupling in the live brain of transgenic mice. Fiber-optic interrogation of single pyramidal neurons in mouse brain cortex is performed with the positioning of the fiber probe relative to the neuron accurately mapped by means of two-photon imaging. These results pave the way for fiber-optic interfaces to single neurons for a stimulation and interrogation of individually addressable brain cells in chronic in vivo studies on freely behaving transgenic animal models, as well as the integration of fiber-optic single-neuron stimulation into the optical imaging framework.

Quantitative cognitive-test characterization of reconnectable implantable fiber-optic neurointerfaces for optogenetic neurostimulation.

Cognitive tests on representative groups of freely behaving transgenic mice are shown to enable a quantitative characterization of reconnectable implantable fiber-optic neurointerfaces for optogenetic neurostimulation. A systematic analysis of such tests provides a robust quantitative measure for the cognitive effects induced by fiber-optic neurostimulation, validating the performance of fiber-optic neurointerfaces for long-term optogenetic brain stimulations and showing no statistically significant artifacts in the behavior of transgenic mice due to interface implantation.

Three-dimensional fiber-optic readout of single-neuron-resolved fluorescence in living brain of transgenic mice.

A bundle of individually addressable optical fibers is shown to enable three-dimensional optical readout from single neurons in live brain, as well as in intact brain extracted from transgenic mice. With individual fibers in the bundle being only a few microns in diameter, single neurons are readily resolved in brain images transmitted by the fiber bundle. The third dimension is added by scanning the fiber in the longitudinal direction, with the fluorescence return read out from only one of the fibers in the bundle.