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Single-cell intracellular recordings have been used as the primary tool for estimating driving forces across inhibitory receptors within the nervous system. Here, the authors present ORCHID as an all-optical method to measure inhibitory receptor driving forces in targeted brain cell types.

Genetically-encoded indicators with more red-shifted excitation and emission wavelengths are advantageous for in vivo imaging. Here, Dalangin et al. report the engineering of far-red fluorescent Ca2+ indicators and demonstrate their utility for monitoring of all-optical cardiac pacing in embryonic zebrafish.

Combining the self-labeling HaloTag protein with synthetic environmentally sensitive fluorophores provides a platform for the construction of bright, far-red fluorescent calcium and voltage sensors with tunable photophysical and chemical properties.

WHaloCaMP is a chemigenetic calcium indicator that can be combined with different rhodamine dyes for multiplexed or FLIM imaging in vivo, as demonstrated for calcium imaging in neuronal cultures, brain slices, Drosophila, zebrafish larvae and the mouse brain.

Using large-scale screening and structure-guided mutagenesis, fast and sensitive GCaMP sensors are developed and optimized with improved kinetics without compromising sensitivity or brightness.

The authors defined a roadmap for investigating the genetic covariance between structural or functional brain phenotypes and risk for psychiatric disorders. Their proof-of-concept study using the largest available common variant data sets for schizophrenia and volumes of several (mainly subcortical) brain structures did not find evidence of genetic overlap.

Calcium imaging has been used to visualize the activity of individual synapses, but cannot be scaled up to monitor thousands of synapses in tissue. Here, the authors present genetic tools that can be photoconverted from green to red to create a map of active synapses.

iGluSnFR variants with improved signal-to-noise ratios and targeting to postsynaptic sites have been developed, enabling the analysis of glutamatergic neurotransmission in vivo as illustrated in the mouse visual and somatosensory cortex.

Despite sharing common features with the helix–turn–helix family of transcription factors, ribbon–helix–helix proteins recognize different operator sequences, bind to both symmetric and asymmetric DNA sites, bend DNA by varying amounts and make unique protein–protein interactions to stabilize their complexes with DNA.

Methods to directly label active neurons are still lacking. Here the authors develop CaMPARI2, a photoconvertible fluorescent protein sensor for neuronal activity with improved brightness and calcium binding kinetics, as well as an antibody to amplify the activated sensor signal in fixed samples.

The ‘jGCaMP7’ sensors are four genetically encoded calcium indicators with better sensitivity than state-of-the-art GCaMP6 and specifically improved for applications such as neuropil or wide-field imaging. The sensors are validated in vivo in both flies and mice.

Sensitive protein sensors of calcium have been created; these new tools are shown to report neural activity in cultured neurons, flies and zebrafish and can detect single action potentials and synaptic activation in the mouse visual cortex in vivo.

A two-photon computed tomography approach, called scanned line angular projection microscopy, enables high-speed imaging at over 1 kHz frame rates, as demonstrated for glutamate imaging in the in vivo mouse brain.

Genetically encoded voltage indicators (GEVIs) allow visualisation of fast action potentials in neurons but most are bright at rest and dimmer during an action potential. Here, the authors engineer electrochromic FRET GEVIs with fast, bright and positive-going fluorescence signals for in vivo imaging.

An improved version of the GCaMP genetically encoded calcium indicator, called GCaMP3, has higher calcium affinity and increased baseline fluorescence, dynamic range and stability. GCaMP3 performs better than existing genetically encoded calcium indicators in several assays and organisms, including in vivo imaging of neuronal signaling in worms, flies and mice.

Using two-color two-photon calcium imaging, the authors identified transformations of representations across synaptically connected pairs of neurons along a visual pathway to the Drosophila central complex. Neural responses to stimuli in the ipsilateral field are modulated by stimuli in the contralateral field, an effect that depends on past stimulus history.

In a GWAS study of 32,438 adults, the authors discovered five novel loci for intracranial volume and confirmed two known signals. Variants for intracranial volume were also related to childhood and adult cognitive function and to Parkinson's disease, and enriched near genes involved in growth pathways, including PI3K-AKT signaling.

A single-wavelength genetically encoded sensor of extracellular glutamate is reported. The sensor—iGluSnFR—is bright and photostable under both one- and two-photon illumination and is shown to work for in vivo imaging in worms, zebrafish and mice.

NIR-GECO1, the first near-infrared genetically encoded calcium ion (Ca²⁺) indicator, enables improved Ca²⁺ imaging in conjunction with blue-light-activated optogenetic tools and multiplexed imaging in cell cultures and tissue slices.

jYCaMP1, a yellow variant of the calcium indicator jGCaMP7, enables fast multicolor two-photon imaging at excitation wavelengths above 1,000 nm for use with popular ytterbium-doped fiber and modelocked semiconductor lasers.

Epigenetic clocks are widely used aging biomarkers, but their utility is limited by technical noise. The authors report a method for producing high-reliability clocks for applications such as longitudinal studies and intervention trials.

Paul Thompson and colleagues report a genome-wide association study for hippocampal, intracranial and total brain volume. They identify a locus at 12q24 associated with hippocampal volume and a locus at 12q14 associated with intracranial volume.