While whole-organism calcium imaging in small and semi-transparent animals has been demonstrated, capturing the functional dynamics of large-scale neuronal circuits in awake, behaving mammals at high speed and resolution has remained one of the main frontiers in systems neuroscience. Here we present a novel method based on light sculpting that enables unbiased single and dual-plane high-speed (up to 160 Hz) calcium imaging, as well as in vivo volumetric calcium imaging of a mouse cortical column (0.5 × 0.5 × 0.5 mm) at single-cell resolution and fast volume rates (3 – 6 Hz). This is achieved by tailoring the point-spread function of our microscope to the structures of interest, and by maximizing the signal-to-noise ratio by using a home-built fiber laser amplifier and synchronizing its pulses to the imaging voxel speed. This has enabled in-vivo recording of calcium dynamics of several thousand neurons across cortical layers and in the hippocampus of awake behaving mice.

Calcium imaging using two-photon scanning microscopy has become an essential tool in neuroscience. However, in its typical implementation, the tradeoffs between fields of view, acquisition speeds, and depth restrictions in scattering brain tissue pose severe limitations. Here, using an integrated systems-wide optimization approach combined with multiple technical innovations, we introduce a new design paradigm for optical microscopy based on maximizing biological information while maintaining the fidelity of obtained neuron signals. Our modular design utilizes hybrid multi-photon acquisition and allows volumetric recording of neuroactivity at single-cell resolution within up to 1 3 1 3 1.22 mm volumes at up to 17 Hz in awake behaving mice. We establish the capabilities and potential of the different configurations of our imaging system at depth and across brain regions by applying it to in vivo recording of up to 12,000 neurons in mouse auditory cortex, posterior parietal cortex, and hippocampus.

G protein–coupled receptors (GPCRs), including dopamine receptors, represent a group of important pharmacological targets. An increased formation of dopamine receptor D2 homodimers has been suggested to be associated with the pathophysiology of schizophrenia. Selective labeling and ligand-induced modulation of dimerization may therefore allow the investigation of the pathophysiological role of these dimers. Using TIRF microscopy at the single molecule level, transient formation of homodimers of dopamine receptors in the membrane of stably transfected CHO cells has been observed. The equilibrium between dimers and monomers was modulated by the binding of ligands; whereas antagonists showed a ratio that was identical to that of unliganded receptors, agonist-bound D2 receptor-ligand complexes resulted in an increase in dimerization. Addition of bivalent D2 receptor ligands also resulted in a large increase in D2 receptor dimers. A physical interaction between the protomers was confirmed using high resolution cryogenic localization microscopy, with ca. 9 nm between the centers of mass.

We investigate the role of electron-hole correlations in the absorption of freestanding monolayer and bilayer graphene using optical transmission spectroscopy from 1.5 to 5.5 eV. Line shape analysis demonstrates that the ultraviolet region is dominated by an asymmetric Fano resonance. We attribute this to an excitonic resonance that forms near the van-Hove singularity at the saddle point of the band structure and couples to the Dirac continuum. The Fano model quantitatively describes the experimental data all the way down to the infrared. In contrast, the common non-interacting particle picture cannot describe our data. These results suggest a profound connection between the absorption properties and the topology of the graphene band structure.The material properties and the atomic structure of graphene are intimately connected. Most electronic effects can be understood by the unique band structure deduced from a tight-binding model of uncorrelated electrons [1]. A prominent example is the constant optical absorption for photon energies in the infrared wavelength range. It is a consequence of the linear dispersion relation near the K points in the Brillouin zone, the so-called Dirac cones. The absorption is given by fundamental constants alone as the product of the fine structure constant in vacuum α ≈ 1/137 and π [2,3,4], and it is independent of the velocity of the Dirac fermions. Here, we demonstrate experimentally by line shape analysis that a single-particle model cannot describe the absorption spectrum of freestanding graphene in the visible and ultraviolet spectral region. The saddle point (M) in the band structure (see Fig. 1) causes a van-Hove singularity with a divergent density of states, allowing for a strong optical transition [5]. In this case, electron-hole correlations can lead to effects beyond the single-particle picture. An excitonic resonance at an energy slightly below the van-Hove singularity becomes possible. At a saddle point, the excitonic resonance takes a Fano shape as the discrete exciton state couples to the continuum formed by the band descending from the saddle point [5,6]. In the following we show that the Fano model of the excitonic resonance describes the complete optical spectrum of graphene from the ultraviolet all the way down to the infrared part of the electromagnetic spectrum.A Fano resonance occurs when a discrete state couples to a continuum of states [6]. The resulting spectrum has * These authors contributed equally.