True physiological imaging of subcellular dynamics requires studying cells within their parent organisms, where all the environmental cues that drive gene expression, and hence the phenotypes that we actually observe, are present. A complete understanding also requires volumetric imaging of the cell and its surroundings at high spatiotemporal resolution, without inducing undue stress on either. We combined lattice light-sheet microscopy with adaptive optics to achieve, across large multicellular volumes, noninvasive aberration-free imaging of subcellular processes, including endocytosis, organelle remodeling during mitosis, and the migration of axons, immune cells, and metastatic cancer cells in vivo. The technology reveals the phenotypic diversity within cells across different organisms and developmental stages and may offer insights into how cells harness their intrinsic variability to adapt to different physiological environments.

Genetically encoded voltage indicators (GEVIs) enable monitoring of neuronal activity at high spatial and temporal resolution. However, the utility of existing GEVIs has been limited by the brightness and photostability of fluorescent proteins and rhodopsins. We engineered a GEVI, called Voltron, that uses bright and photostable synthetic dyes instead of protein-based fluorophores, thereby extending the number of neurons imaged simultaneously in vivo by a factor of 10 and enabling imaging for significantly longer durations relative to existing GEVIs. We used Voltron for in vivo voltage imaging in mice, zebrafish, and fruit flies. In the mouse cortex, Voltron allowed single-trial recording of spikes and subthreshold voltage signals from dozens of neurons simultaneously over a 15-minute period of continuous imaging. In larval zebrafish, Voltron enabled the precise correlation of spike timing with behavior.

The frontal and parietal eye fields serve as functional landmarks of the primate brain, although their correspondences between humans and macaque monkeys remain unclear. We conducted fMRI at 4.7 T in monkeys performing visually-guided saccade tasks and compared brain activations with those in humans using identical paradigms. Among multiple parietal activations, the dorsal lateral intraparietal area in monkeys and an area in the posterior superior parietal lobule in humans exhibited the highest selectivity to saccade directions. In the frontal cortex, the selectivity was highest at the junction of the precentral and superior frontal sulci in humans and in the frontal eye field (FEF) in monkeys. BOLD activation peaks were also found in premotor areas (BA6) in monkeys, which suggests that the apparent discrepancy in location between putative human FEF (BA6, suggested by imaging studies) and monkey FEF (BA8, identified by microstimulation studies) partly arose from methodological differences.

The vertebrate hindbrain contains various sensory-motor networks controlling movements of the eyes, jaw, head, and body. Here we show that stripes of neurons with shared neurotransmitter phenotype that extend throughout the hindbrain of young zebrafish reflect a broad underlying structural and functional patterning. The neurotransmitter stripes contain cell types with shared gross morphologies and transcription factor markers. Neurons within a stripe are stacked systematically by extent and location of axonal projections, input resistance, and age, and are recruited along the axis of the stripe during behavior. The implication of this pattern is that the many networks in hindbrain are constructed from a series of neuronal components organized into stripes that are ordered from top to bottom according to a neuron's age, structural and functional properties, and behavioral roles. This simple organization probably forms a foundation for the construction of the networks underlying the many behaviors produced by the hindbrain.interneuron | locomotion | recruitment | topography T he hindbrain contains a diverse set of sensory-motor networks that control movements required for vision, respiration, mastication, and locomotion in all vertebrates (1, 2). Most often these different networks are studied separately from one another, perhaps because the behaviors are distinct, and the regional differentiation of hindbrain suggests that its several networks might have little in common. Thus, we have strong data for the hindbrain control of eye movements, respiration, and locomotion (3-10), but fewer unifying principles of structural and functional organization that apply across the different networks.Structurally, the hindbrain is divided into segments, called rhombomeres, which differ in the expression of homeotic genes, in the morphological differentiation of neurons, and in their sensory inputs and motor outputs (2, 11). Though there are clear distinctions among rhombomeres, there are indications from previous developmental work using in situ staining for transcription factors and backfilling of hindbrain neurons that there may be structural patterns that cross rhombomere boundaries (12-16). Prior work has also revealed parallels in the development of hindbrain and spinal cord, with the hindbrain sharing features of the now-classic transcription factor code that directs development in spinal cord (17)(18)(19)(20)(21)(22). Though these studies did not explore function because they were performed during early development, they raised the possibility of a broader structuralfunctional patterning that spans rhomobomeres and may underlie the organization of circuits for different behaviors.Here we show that there is indeed a broad structural and functional patterning of neurons in the hindbrain of young zebrafish. The work was initially prompted by a striking patterning observed in earlier work in which we used in situ staining for markers of neurotransmitter phenotype to reveal putative glycinergic, GABAergic, and glutamatergic ...

Neurons and neural networks often extend hundreds to thousands of micrometers in three dimensions. To capture all the calcium transients associated with their activity, we need volume imaging methods with sub-second temporal resolution. Such speed is challenging for conventional two-photon laser scanning microscopy (2PLSM) to achieve, because of its dependence on serial focal scanning in 3D and the limited brightness of indicators. Here we present an optical module that can be easily integrated into standard 2PLSMs to generate an axially elongated Bessel focus. Scanning the Bessel focus in 2D turned frame rate into volume rate and enabled video-rate volumetric imaging. Using Bessel foci designed to maintain lateral resolution that resolves synapses in sparsely labeled brains in vivo, we demonstrated the power of this approach in enabling discoveries for neurobiology by imaging the calcium dynamics of volumes of neurons and synapses in fruit flies, zebrafish larvae, mice, and ferrets in vivo.

The hindbrain of larval zebrafish contains a relatively simple ground plan in which the neurons throughout it are arranged into stripes that represent broad neuronal classes that differ in transmitter identity, morphology, and transcription factor expression. Within the stripes, neurons are stacked continuously according to age as well as structural and functional properties, such as axonal extent, input resistance, and the speed at which they are recruited during movements. Here we address the question of how particular networks among the many different sensory-motor networks in hindbrain arise from such an orderly plan. We use a combination of transgenic lines and pairwise patch recording to identify excitatory and inhibitory interneurons in the hindbrain network for escape behaviors initiated by the Mauthner cell. We map this network onto the ground plan to show that an individual hindbrain network is built by drawing components in predictable ways from the underlying broad patterning of cell types stacked within stripes according to their age and structural and functional properties. Many different specialized hindbrain networks may arise similarly from a simple early patterning.T he vertebrate hindbrain contains many different sensorymotor networks that control movements of structures in the body and the head. Our recent work shows that despite the diverse networks it contains, there is a remarkably orderly patterning of neurons that extends throughout the hindbrain in young zebrafish, across the well-studied segments, or rhombomeres (1-4). This pattern consists of a series of neurotransmitter stripes that represent broad neuronal classes that differ in transmitter identity, morphology, and transcription factor expression. Within these stripes, neurons are stacked continuously according to age as well as structural and functional characteristics, such as axonal extent, input resistance, and the speed at which they are recruited during movements.The presence of such an orderly array of neurons suggests that networks are built by drawing components from particular stripes that contain cell types with the required structure and transmitter phenotype, and from the particular position within a stripe occupied by neurons with the appropriate functional properties, much like selecting parts from a catalog. Here we test this possibility through a study of the hindbrain network for the escape behavior initiated by the Mauthner cell (M-cell) (5-8). We conclusively identify neurons in the hindbrain escape network of the M-cell in zebrafish and map each cell type onto the arrangement into the stripes that we describe in the previous work. Our work reveals that this network is built from neurons in predictable locations that are consistent with the idea that the stripe patterning in hindbrain represents an orderly array of neurons from which network components are drawn. Many different hindbrain networks probably arise in a similar way by drawing neurons from a shared structurally and functionally ordered set of parts. ...

Imaging changes in membrane potential using genetically encoded fluorescent voltage indicators (GEVIs) has great potential for monitoring neuronal activity with high spatial and temporal resolution. Brightness and photostability of fluorescent proteins and rhodopsins have limited the utility of existing GEVIs. We engineered a novel GEVI, 'Voltron', that utilizes bright and photostable synthetic dyes instead of protein-based fluorophores, extending the combined duration of imaging and number of neurons imaged simultaneously by more than tenfold relative to existing GEVIs. We used Voltron for in vivo voltage imaging in mice, zebrafish, and fruit flies. In mouse cortex, Voltron allowed single-trial recording of spikes and subthreshold voltage signals from dozens of neurons simultaneously, over 15 minutes of continuous imaging. In larval zebrafish, Voltron enabled the precise correlation of spike timing with behavior.Animal behavior is produced by patterns of neuronal activity that span a wide range of spatial and temporal scales. To understand how neural circuits mediate behavior thus requires high-speed recording from ensembles of neurons for long periods of time.Although the activity of large numbers of neurons can now be routinely recorded using genetically encoded calcium indicators (GECIs) (1), the slow kinetics of calcium signals complicate the measurement of action potentials, and sub-threshold voltage signals are missed entirely (1-3). Voltage imaging using genetically encoded voltage indicators (GEVIs) can overcome these challenges, enabling imaging of fast spikes and subthreshold dynamics in genetically defined neurons (4, 5). The high imaging speed and excitation intensity required for voltage imaging, combined with the smaller volume of the cellular membrane, place increased demands on voltage indicators relative to GECIs.Extant GEVIs rely on fluorescence from either microbial rhodopsins (6-8) or fluorescent proteins (FPs) (9-13). These fluorophores lack the brightness and photostability to allow in vivo voltage imaging from large fields of view over timescales of many behavioral events, precluding the millisecond-timescale interrogation of neural circuits. Recent development of improved rhodamine dyes such as the Janelia Fluor ® (JF) dyes enable their use in complex biological experiments due to their high brightness and photostability (14), compatibility with self-labeling protein tags (15, 16), and the ability to traverse the blood-brain barrier for in vivo delivery (17). Here we describe a 'chemigenetic' GEVI scaffold-termed 'Voltron'-which incorporates these synthetic fluorophore dyes. Voltron provides an increased photon yield that enables in vivo imaging of neuronal spiking and sub-threshold voltage signals in model organisms with order-of-magnitude improvement in the number of neurons imaged simultaneously over substantially longer durations.Our design for a chemigenetic voltage indicator combines a voltage-sensitive microbial rhodopsin domain (6, 7, 11) with a self-labeling protein tag domain (F...

Here we design and optimize a genetically encoded fluorescent indicator, iAChSnFR, for the ubiquitous neurotransmitter acetylcholine, based on a bacterial periplasmic binding protein. iAChSnFR shows large fluorescence changes, rapid rise and decay kinetics, and insensitivity to most cholinergic drugs. iAChSnFR revealed large transients in a variety of slice and in vivo preparations in mouse, fish, fly and worm. iAChSnFR will be useful for the study of acetylcholine in all animals. IntroductionAcetylcholine (ACh) is a critical neurotransmitter in all animals. Among invertebrates, it is the most prevalent excitatory transmitter in the brain, sensory ganglia, and frequently the neuromuscular junction (NMJ). Among vertebrates, only a minority of neurons release ACh, but these signals play varying key roles. For instance, ACh signals at the NMJ, in the autonomic nervous system, and in subsets of the central nervous system, particularly projections arising from the brainstem and basal forebrain. Other cholinergic neuron populations in the brain include striatal interneurons, the stria vascularis-medial habenula-interpeduncular nucleus pathway, and sparse, incompletely characterized cell types such as intrinsic cholinergic interneurons in cortex 1 and hippocampus 2 . ACh helps to regulate attention 3 and wakefulness 4 , and participates in memory formation and consolidation 5 . ACh is also an important transmitter in glia, and between the nervous and immune systems 6 .Acetylcholine is synthesized pre-synaptically from choline and acetyl-CoA by choline acetyltransferase (ChAT), then packaged into synaptic vesicles by the vesicular acetylcholine transporter (VAChT). A key, partially understood aspect of cholinergic signaling is co-release with other neurotransmitters, including GABA, ATP, and glutamate 7,8 . To understand the role of co-release, one must measure ACh release alongside emerging measurements of other neurotransmitters.Acetylcholine receptors are among the most diverse neurotransmitter receptor families. Humans possess five muscarinic G protein-coupled receptors (GPCRs) for ACh (mAChRs) with diverse expression in the brain and smooth, cardiac, and skeletal muscle. Vertebrate nicotinic ACh receptors (nAChRs) are pentameric ligand-gated cation channels. Humans have a total of 17 nAChR subunit genes, in five classes: 10 a, 4 b, and one each of g, d, and e. nAChRs occur with many subunit combinations 9 , and others may be undiscovered. Invertebrates also have AChgated chloride channels. On neurons, receptors can be localized pre-, post-, and extrasynaptically, often with different isoforms in each place 10