Functional Integration of Newborn Neurons in the Zebrafish Optic Tectum

Neurogenesis persists during adulthood in restricted parts of the vertebrate brain. In the optic tectum (OT) of the zebrafish larva, newborn neurons are continuously added and contribute to visual information processing. Recent studies have started to describe the functional development and fate of newborn neurons in the OT. Like the mammalian brain, newborn neurons in the OT require sensory inputs for their integration into local networks and survival. Recent findings suggest that the functional development of newborn neurons requires both activity-dependent and hard-wired mechanisms for proper circuit integration. Here, we review these findings and argue that the study of neurogenesis in non-mammalian species will help elucidate the general mechanisms of circuit assembly following neurogenesis

Sensorimotor Transformations in the Zebrafish Auditory System

Organisms use their sensory systems to acquire information from their environment and integrate this information to produce relevant behaviors. Nevertheless, how sensory information is converted into adequate motor patterns in the brain remains an open question. Here, we addressed this question using two-photon and light-sheet calcium imaging in intact, behaving zebrafish larvae. We monitored neural activity elicited by auditory stimuli while simultaneously recording tail movements. We observed a spatial organization of neural activity according to four different response profiles (frequency tuning curves), suggesting a low-dimensional representation of frequency information, maintained throughout the development of the larvae. Low frequencies (150–450 Hz) were locally processed in the hindbrain and elicited motor behaviors. In contrast, higher frequencies (900–1,000 Hz) rarely induced motor behaviors and were also represented in the midbrain. Finally, we found that the sensorimotor transformations in the zebrafish auditory system are a continuous and gradual process that involves the temporal integration of the sensory response in order to generate a motor behavior.Fil: Privat, Martin. Inserm; Francia. Centre National de la Recherche Scientifique; FranciaFil: Romano, Sebastián Alejo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigación en Biomedicina de Buenos Aires - Instituto Partner de la Sociedad Max Planck; ArgentinaFil: Pietri, Thomas. Centre National de la Recherche Scientifique; Francia. Inserm; FranciaFil: Jouary, Adrien. Champalimaud Centre For The Unknown; Portugal. Inserm; Francia. Centre National de la Recherche Scientifique; FranciaFil: Boulanger Weill, Jonathan. Centre National de la Recherche Scientifique; Francia. Inserm; FranciaFil: Elbaz, Nicolas. Inserm; Francia. Centre National de la Recherche Scientifique; FranciaFil: Duchemin, Auriane. Centre National de la Recherche Scientifique; Francia. Inserm; FranciaFil: Soares, Daphne. New Jersey Institute of Technology; Estados UnidosFil: Sumbre, Germán. Centre National de la Recherche Scientifique; Francia. Inserm; Franci

The world according to zebrafish: how neural circuits generate behavior

Peer reviewedPeer Reviewe

Octopuses Use a Human-like Strategy to Control Precise Point-to-Point Arm Movements

SummaryOne of the key problems in motor control is mastering or reducing the number of degrees of freedom (DOFs) through coordination [1]. This problem is especially prominent with hyper-redundant limbs such as the extremely flexible arm of the octopus [2]. Several strategies for simplifying these control problems have been suggested for human point-to-point arm movements [3–6]. Despite the evolutionary gap and morphological differences, humans and octopuses evolved similar strategies when fetching food to the mouth. To achieve this precise point-to-point-task, octopus arms generate a quasi-articulated structure based on three dynamic joints. A rotational movement around these joints brings the object to the mouth [7]. Here, we describe a peripheral neural mechanism—two waves of muscle activation propagate toward each other, and their collision point sets the medial-joint location. This is a remarkably simple mechanism for adjusting the length of the segments according to where the object is grasped. Furthermore, similar to certain human arm movements, kinematic invariants were observed at the joint level rather than at the end-effector level, suggesting intrinsic control coordination. The evolutionary convergence to similar geometrical and kinematic features suggests that a kinematically constrained articulated limb controlled at the level of joint space is the optimal solution for precise point-to-point movements

Whole-brain neuronal activity displays crackling noise dynamics

Previous studies suggest that the brain operates at a critical point in which phases of order and disorder coexist, producing emergent patterned dynamics at all scales and optimizing several brain functions. Here, we combined light-sheet microscopy with GCaMP zebrafish larvae to study whole-brain dynamics in vivo at near single-cell resolution. We show that spontaneous activity propagates in the brain’s three-dimensional space, generating scaleinvariant neuronal avalanches with time courses and recurrence times that exhibit statistical self-similarity at different magnitude, temporal, and frequency scales. This suggests that the nervous system operates close to a non-equilibrium phase transition, where a large repertoire of spatial, temporal, and interactive modes can be supported. Finally, we show that gap junctions contribute to the maintenance of criticality and that, during interactions with the environment (sensory inputs and self-generated behaviors), the system is transiently displaced to a more ordered regime, conceivably to limit the potential sensory representations and motor outcomes.A.P.-A. was supported by a Juan de la Cierva fellowship (IJCI-2014-21066) from the Spanish Ministry of Economy and Competitiveness. A.J. was supported by the Fondation pour la Recherche Medicale (FRM:FDT20140930915) and the ENS Cachan. M.P. was supported by the ENS Lyon. G.D. was funded by the European Research Council (ERC) Advanced Grant DYSTRUCTURE (No. 295129), by the Spanish Research Project PSI2016-75688-P (AEI/FEDER), and by the European Union’s Horizon 2020 research and innovation program under grant agreement No. 720270 (HBP SGA1). G.S. was supported by ERC StG 243106, ERC CoG 726280, ANR-10-LABX-54 MEMO LIFE, and ANR-11-IDEX-0001-02 PSL Research University. We thank J. Boulanger-Weill for technical assistance and discussions, Patricia Gongal for editorial assistance, and David Hildebrand for providing GCaMP6f line

Principles of functional circuit connectivity: insights from spontaneous activity in the zebrafish optic tectum

The brain is continuously active, even in the absence of external stimulation. In the optic tectum of the zebrafish larva, this spontaneous activity is spatially organized and reflects the circuit's functional connectivity. The structure of the spontaneous activity displayed patterns associated with aspects of the larva's preferences when engaging in complex visuo-motor behaviors, suggesting that the tectal circuit is adapted for the circuit's functional role in detecting visual cues and generating adequate motor behaviors. Further studies in sensory deprived larvae suggest that the basic structure of the functional connectivity patterns emerges even in the absence of retinal inputs, but that its fine structure is affected by visual experience

Whole-brain neuronal activity displays crackling noise dynamics

Previous studies suggest that the brain operates at a critical point in which phases of order and disorder coexist, producing emergent patterned dynamics at all scales and optimizing several brain functions. Here, we combined light-sheet microscopy with GCaMP zebrafish larvae to study whole-brain dynamics in vivo at near single-cell resolution. We show that spontaneous activity propagates in the brain’s three-dimensional space, generating scaleinvariant neuronal avalanches with time courses and recurrence times that exhibit statistical self-similarity at different magnitude, temporal, and frequency scales. This suggests that the nervous system operates close to a non-equilibrium phase transition, where a large repertoire of spatial, temporal, and interactive modes can be supported. Finally, we show that gap junctions contribute to the maintenance of criticality and that, during interactions with the environment (sensory inputs and self-generated behaviors), the system is transiently displaced to a more ordered regime, conceivably to limit the potential sensory representations and motor outcomes.A.P.-A. was supported by a Juan de la Cierva fellowship (IJCI-2014-21066) from the Spanish Ministry of Economy and Competitiveness. A.J. was supported by the Fondation pour la Recherche Medicale (FRM:FDT20140930915) and the ENS Cachan. M.P. was supported by the ENS Lyon. G.D. was funded by the European Research Council (ERC) Advanced Grant DYSTRUCTURE (No. 295129), by the Spanish Research Project PSI2016-75688-P (AEI/FEDER), and by the European Union’s Horizon 2020 research and innovation program under grant agreement No. 720270 (HBP SGA1). G.S. was supported by ERC StG 243106, ERC CoG 726280, ANR-10-LABX-54 MEMO LIFE, and ANR-11-IDEX-0001-02 PSL Research University. We thank J. Boulanger-Weill for technical assistance and discussions, Patricia Gongal for editorial assistance, and David Hildebrand for providing GCaMP6f line

The first mecp2-null zebrafish model shows altered motor behaviors

Rett syndrome (RTT) is an X-linked neurodevelopmental disorder and one of the most common causes of mental retardation in affected girls. Other symptoms include a rapid regression of motor and cognitive skills after an apparently early normal development. Sporadic mutations in the transcription factor MECP2 has been shown to be present in more than 90% of the patients and several models of MeCP2-deficient mice have been created to understand the role of this gene. These models have pointed toward alterations in the maintenance of the central nervous system rather than its development, in line with the late onset of the disease in humans. However, the exact functions of MeCP2 remain difficult to delineate and the animal models have yielded contradictory results. Here, we present the first mecp2-null allele mutation zebrafish model. Surprisingly and in contrast to MeCP2-null mouse models, mecp2-null zebrafish are viable and fertile. They present nonetheless clear behavioral alterations during their early development, including spontaneous and sensory-evoked motor anomalies, as well as defective thigmotaxis.This research was supported by fellowships from Autism Speak and the Fondation pour la Recherche Medicale to Thomas Pietri, and Juan de la Cierva (Spain) to Angel-Carlos Roman, grants from NINDS R01 NS065795 to Philip Washbourne, NIH R01 HD076585 to Cecilia B. Moens, Ministerio de Economia as Plan Nacional (Spain), EraSysBio+ ZeBrain to Gonzalo G. de Polavieja and Germán Sumbre and ERC stg 243106 to Germán Sumbre.Peer reviewedPeer Reviewe