Lamination Speeds the Functional Development of Visual Circuits

SummaryA common feature of the brain is the arrangement of synapses in layers. To examine the significance of this organizational feature, we studied the functional development of direction-selective (DS) circuits in the tectum of astray mutant zebrafish in which lamination of retinal ganglion cell (RGC) axons is lost. We show that although never laminar, the tuning of DS-RGC axons targeting the mutant tectum is normal. Analysis of mutant tectal neurons at late developmental stages reveals that directional tuning is indistinguishable from wild-type larvae. Furthermore, we show that structural plasticity of tectal dendrites and RGC axons compensates for the loss of lamination, establishing connectivity between DS-RGCs and their normal tectal targets. However, tectal direction selectivity is severely perturbed at earlier developmental stages. Thus, the formation of synaptic laminae is ultimately dispensable for the correct wiring of direction-selective tectal circuits, but it is crucial for the rapid assembly of these networks.Video Abstrac

A Systems-Based Dissection of Retinal Inputs to the Zebrafish Tectum Reveals Different Rules for Different Functional Classes during Development

We have examined the form, diversity, and organization of three functional classes of retinal inputs to the zebrafish optic tectum during development. Our systems-based approach was to analyze data from populations of retinal ganglion cells labeled with a presynaptic targeted calcium indicator, synaptophysin GCaMP3 (SyGCaMP3). Collectively, our findings provide an insight as to the degree of visual encoding during retino-tectal development and how it dynamically evolves from a nascent and noisy presynaptic neural-scape to an increasingly complex and refined representation. We report five key features: (1) direction-selective inputs are developmentally invariant; (2) orientation-selective inputs exhibit highly dynamic properties over the same period, with changes in their functional characteristics and spatial organization; (3) inputs defined as anisotropic are an early dominant functional class, with heterogeneous response profiles, which progressively diminish in incidence and spatial extent; (4) dark rearing selectively affects the orientation-selective responses: both functional characteristics and relative spatial distributions; and (5) orientation-selective inputs exhibit four subtypes, two more than previously identified in any species. Our approach was to label RGC axon terminals with an indicator of activity and quantitatively characterize coherent response properties to different visual stimuli. Its application in the zebrafish, given its small size and the accessibility of the tectum, has enabled a quick yet robust assessment of multiple functional populations of responses

Advanced software for MRgFUS treatment planning

Herein, a user-friendly software platform for 3-dimensional Focused Ultrasound treatment planning based on Magnetic Resonance Imaging (MRI) images is presented

Lunatic fringe promotes the lateral inhibition of neurogenesis

Previous studies have identified roles of the modulation of Notch activation by Fringe homologues in boundary formation and in regulating the differentiation of vertebrate thymocytes and Drosophila glial cells. We have investigated the role of Lunatic fringe (Lfng) expression during neurogenesis in the vertebrate neural tube. We find that in the zebrafish hindbrain, Lfng is expressed by progenitors in neurogenic regions and downregulated in cells that have initiated neuronal differentiation. Lfng is required cell autonomously in neural epithelial cells to limit the amount of neurogenesis and to maintain progenitors. By contrast, Lfng is not required for the role of Notch in interneuronal fate choice, which we show is mediated by Notch1a. The expression of Lfng does not require Notch activity, but rather is regulated downstream of proneural genes that are widely expressed by neural progenitors. These findings suggest that Lfng acts in a feedback loop downstream of proneural genes, which, by promoting Notch activation, maintains the sensitivity of progenitors to lateral inhibition and thus limits further proneural upregulation

Phantom-based assessment of motion and needle targeting accuracy of robotic devices for magnetic resonance imaging-guided needle biopsy

Background:The current study proposessimple methodsfor assessingthe per-formance of robotic devices intended for Magnetic ResonanceImaging (MRI)‐guided needle biopsy. Methods:In‐housemade agar‐based breast phantoms containingbiopsy targetsservedasthemaintoolintheevaluationprocessofanMRIcompatiblepositioningdevice comprising a needle navigator. The motion accuracy of mechanical stages was assessed by calliper measurements. Laboratoryevaluationof needle targeting included a repeatability phantomtest and a laser‐based method. The accuracy andrepeatability of needle targeting was also assessed by MRI. Results: The maximum error of linear motion for steps up to 10 mm was 0.1 mm. Needle navigation relative to the phantomand alignment with the various biopsy targets were performed successfully in both the laboratory and MRI settings. The proposed biopsy phantoms offered tissue‐like signal in MRI and good haptic feed-back during needle insertion. Conclusions: The proposed methods could be valuable in the process of validating the accuracy of MRI‐guided biopsy robotic devices in both laboratory and real environments