Primary neurons that express the L2/HNK-1 carbohydrate during early development in the zebrafish

In zebrafish, many nerve pathways in both the CNS and periphery are pioneered by a small and relatively simple set of ‘primary’ neurons that arise in the early embryo. We now have used monoclonal antibodies to show that, as they develop, primary neurons of several functional classes express on their surfaces the L2/HNK-1 tetrasaccharide that is associated with a variety of cell surface adhesion molecules. We have studied the early labeling patterns of these neurons, as well as some non-neural cells, and found that the time of onset and intensity of immunolabeling vary specifically according to cell type. The first neuronal expression is by Rohon-Beard and trigeminal ganglion neurons, both of which are primary sensory neurons that mediate touch sensitivity. These cells express the epitope very strongly on their growth cones and axons, permitting study of their development unobscured by labeling in other cells. Both types initiate axogenesis at the same early time, and appear to be the first neurons in the embryo to do so. Their peripheral neurites display similar branching patterns and have similar distinctive growth cone morphologies. Their central axons grow at the same rate along the same longitudinal fiber pathway, but in opposite directions, and where they meet they appear to fasciculate with one another. The similarities suggest that Rohon-Beard and trigeminal ganglion neurons, despite their different positions, share a common program of early development. Immunolabeling is also specifically present on a region of the brain surface where the newly arriving trigeminal sensory axons will enter the brain. Further, the trigeminal expression of the antigen persists in growth cones during the time that they contact an individually identified central target neuron, the Mauthner cell, which also expresses the epitope. These findings provide descriptive evidence for possible roles of L2/HNK-1 immunoreactive molecules in axonal growth and synaptogenesis

Examining Wildlife Interactions with Large Wood In Streams

It is well known that in-stream large wood affects river channel shape, sediment deposits, stream flow, and available habitat for aquatic species. However, less is known about how wildlife interact with this large wood. Previous research has shown that small mammals and birds utilize woody debris in river channels for foraging and refuge, but this still leaves much to be answered. This study aims to capture both wildlife and their behaviors as they interact with in-stream large wood in order to gain a better understanding of the role of large wood in riparian ecology. Thirteen camera traps were placed at artificial and naturally occurring in-stream large wood structures for 9 months capturing videos of wildlife interacting with the structures. Over 30 species have been detected including small mammals, birds, meso-carnivores, large carnivores, and semi-aquatic mammals. Common behaviors observed include movement, food handling/eating, and rest. Videos have provided information on the diel activity of common species as well as seasonality of structure use. This study will provide foundational information for future studies focusing on restoration ecology and the use of large wood in streams.Key Words: Large Wood, Diel, Riparian, Behavior, Wildlif

Power Training Improves the Sensorimotor Cortical Oscillations in Youth with Cerebral Palsy

Background: Our magnetoencephalographic (MEG) brain imaging studies have shown that youth with cerebral palsy (CP) demonstrate altered sensorimotor beta (18-24Hz) cortical oscillations when controlling their leg motor actions and these anomalous cortical oscillations are linked with the extent of their mobility impairments. Current therapeutic trends for improving mobility have shifted from strength training to high-velocity power training, which has shown improvements in isokinetic strength, power production and mobility of youth with CP. However, no studies have assessed whether these clinically relevant improvements are linked with changes in the sensorimotor cortical oscillations. The objective of this study was to utilize MEG brain imaging to examine the potential changes in sensorimotor cortical oscillations following power training. Methods: Youth with CP (N=11; Age=15.9 ±1.1yrs; GMFCS I-III) and neurotypical controls (NT) (N=16; Age=14.6 ±0.8yrs) were recruited to participate in this study. The youth with CP underwent 24 high-velocity leg press power training sessions that were performed on a Total Gym® sled. Pre-Post bilateral leg press 1-repetition maximum (1RM) and peak power production were used to assess the muscular performance changes. The 1-minute walk was used to assess mobility changes. During MEG recordings, participants used their right leg to complete a goal-directed isometric target-matching task. Advanced beamforming methods were subsequently used to image the strength of the sensorimotor beta oscillatory power. The NTs only underwent the baseline MEG assessment. Results: Youth with CP increased their 1RM (Pre=158.3 ±24.7kg, Post=247.5 ±41.5kg, p\u3c0.01), and peak power production (Pre=509.9 ±64.7W, Post=677.1 ±113.3W, p=0.04). Participants with CP also improved their 1-minute walk (Pre=77.4 ±9.2m, Post=80.8 ±8.4m, p = 0.02). The beta sensorimotor cortical oscillations in the leg region were stronger in the youth with CP prior to training compared with the NTs (CP=-25.9±1.8%; NT=-17.2±3.6%, p=0.04). However, the youth with CP had a reduction in the strength of the beta oscillations after undergoing the power training (pre=-25.9 ±1.8%, post=-14.8 ±3.6%, p=0.02), and the strength of the oscillations was not significantly different from the NTs after training (p=0.68). Lastly, the peak power production after training was tightly linked with the strength of the post-therapy sensorimotor cortical oscillations (r=0.79, p=0.03). Conclusion: Power training appears to improve the neural generators that control the leg motor actions, and these neuroplastic changes partly contribute to improvements in the peak power production of youth with CP. Potentially, power training might provide the key therapeutic ingredients for complementary muscular and neurological plastic change.https://digitalcommons.unmc.edu/chri_forum/1001/thumbnail.jp

Expression of glial fibrillary acidic protein and its relation to tract formation in embryonic zebrafish ( Danio rerio )

To address possible roles of glial cells during axon outgrowth in the vertebrate central nervous system, we investigated the appearance and distribution of the glial-specific intermediate filament, glial fibrillary acidic protein (GFAP), during early embryogenesis of the zebrafish ( Danio rerio ). Immunopositive cells first appear at 15 hours, which is at the time of, or slightly before, the first axon outgrowth in the brain. Immunopositive processes are not initially present in a pattern that prefigures the location of the first tracts but rather are distributed widely as endfeet adjacent to the pia, overlying most of the surface of the brain with the exception of the dorsal and ventral midline. The first evidence for a specific association of immunopositive cells with the developing tracts is observed at 24 hours in the hindbrain, where immunopositive processes border axons in the medial longitudinal fasciculus. By 48 hours, immunopositive processes have disappeared from most of the subpial lamina and are found exclusively in association with tracts and commissures in three forms: endfeet, radially oriented processes, and tangentially oriented processes parallel to axons. This last form is particularly prominent in the transverse plane of the hindbrain, where they define the boundaries between rhombomeres. These results suggest that glial cells contribute to the development and organization of the central nervous system by supporting early axon outgrowth in the subpial lamina and by forming boundaries around tracts and between neuromeres. The results are discussed in relation to previous results A neuron-glia interactions and possible roles of glial cells in axonal guidance. © 1995 Wiley-Liss, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/50065/1/903590302_ftp.pd

An Integrin-Dependent Role of Pouch Endoderm in Hyoid Cartilage Development

Pharyngeal endoderm is essential for and can reprogram development of the head skeleton. Here we investigate the roles of specific endodermal structures in regulating craniofacial development. We have isolated an integrinα5 mutant in zebrafish that has region-specific losses of facial cartilages derived from hyoid neural crest cells. In addition, the cranial muscles that normally attach to the affected cartilage region and their associated nerve are secondarily reduced in integrinα5(−) animals. Earlier in development, integrinα5 mutants also have specific defects in the formation of the first pouch, an outpocketing of the pharyngeal endoderm. By fate mapping, we show that the cartilage regions that are lost in integrinα5 mutants develop from neural crest cells directly adjacent to the first pouch in wild-type animals. Furthermore, we demonstrate that Integrinα5 functions in the endoderm to control pouch formation and cartilage development. Time-lapse recordings suggest that the first pouch promotes region-specific cartilage development by regulating the local compaction and survival of skeletogenic neural crest cells. Thus, our results reveal a hierarchy of tissue interactions, at the top of which is the first endodermal pouch, which locally coordinates the development of multiple tissues in a specific region of the vertebrate face. Lastly, we discuss the implications of a mosaic assembly of the facial skeleton for the evolution of ray-finned fish

Genetic dissection of dopaminergic and noradrenergic contributions to catecholaminergic tracts in early larval zebrafish

The catecholamines dopamine and noradrenaline provide some of the major neuromodulatory systems with far-ranging projections in the brain and spinal cord of vertebrates. However, development of these complex systems is only partially understood. Zebrafish provide an excellent model for genetic analysis of neuronal specification and axonal projections in vertebrates. Here, we analyze the ontogeny of the catecholaminergic projections in zebrafish embryos and larvae up to the fifth day of development and establish the basic scaffold of catecholaminergic connectivity. The earliest dopaminergic diencephalospinal projections do not navigate along the zebrafish primary neuron axonal scaffold but establish their own tracts at defined ventrolateral positions. By using genetic tools, we study quantitative and qualitative contributions of noradrenergic and defined dopaminergic groups to the catecholaminergic scaffold. Suppression of Tfap2a activity allows us to eliminate noradrenergic contributions, and depletion of Otp activity deletes mammalian A11-like Otp-dependent ventral diencephalic dopaminergic groups. This analysis reveals a predominant contribution of Otp-dependent dopaminergic neurons to diencephalospinal as well as hypothalamic catecholaminergic tracts. In contrast, noradrenergic projections make only a minor contribution to hindbrain and spinal catecholaminergic tracts. Furthermore, we can demonstrate that, in zebrafish larvae, ascending catecholaminergic projections to the telencephalon are generated exclusively by Otp-dependent diencephalic dopaminergic neurons as well as by hindbrain noradrenergic groups. Our data reveal the Otp-dependent A11-type dopaminergic neurons as the by far most prominent dopaminergic system in larval zebrafish. These findings are consistent with a hypothesis that Otp-dependent dopaminergic neurons establish the major modulatory system for somatomotor and somatosensory circuits in larval fish. J. Comp. Neurol. 518:439–458, 2010. © 2009 Wiley-Liss, Inc

Development and Notch Signaling Requirements of the Zebrafish Choroid Plexus

The choroid plexus (CP) is an epithelial and vascular structure in the ventricular system of the brain that is a critical part of the blood-brain barrier. The CP has two primary functions, 1) to produce and regulate components of the cerebral spinal fluid, and 2) to inhibit entry into the brain of exogenous substances. Despite its importance in neurobiology, little is known about how this structure forms.Here we show that the transposon-mediated enhancer trap zebrafish line Et(Mn16) expresses green fluorescent protein within a population of cells that migrate toward the midline and coalesce to form the definitive CP. We further demonstrate the development of the integral vascular network of the definitive CP. Utilizing pharmacologic pan-notch inhibition and specific morpholino-mediated knockdown, we demonstrate a requirement for Notch signaling in choroid plexus development. We identify three Notch signaling pathway members as mediating this effect, notch1b, deltaA, and deltaD.This work is the first to identify the zebrafish choroid plexus and to characterize its epithelial and vasculature integration. This study, in the context of other comparative anatomical studies, strongly indicates a conserved mechanism for development of the CP. Finally, we characterize a requirement for Notch signaling in the developing CP. This establishes the zebrafish CP as an important new system for the determination of key signaling pathways in the formation of this essential component of the vertebrate brain

Embryonic motor activity and implications for regulating motoneuron axonal pathfinding in zebrafish

Zebrafish embryos exhibit spontaneous contractions of the musculature as early as 18–19 h post fertilization (hpf) when removed from their protective chorion. These movements are likely initiated by early embryonic central nervous system activity. We have made the observation that narrowminded mutant embryos (hereafter, nrd−/−) lack normal embryonic motor output upon dechorionation. However, these mutants can swim and respond to tactile stimulation by larval stages of development. nrd−/− embryos exhibit defects in neural crest development, slow muscle development and also lack spinal mechanosensory neurons known as Rohon–Beard (RB) neurons. At early developmental stages (i.e. 21–22 hpf) and while still in their chorions, nrd siblings (nrd+/?) exhibited contractions of the musculature at a rate similar to wild-type embryos. Anatomical analysis indicated that RB neurons were present in the motile embryos, but absent in the non-motile embryos, indicating that the non-motile embryos were nrd−/− embryos. Further anatomical analysis of nrd−/− embryos revealed errors in motoneuron axonal pathfinding that persisted into the larval stage of development. These errors were reversed when nrd−/− embryos were raised in high [K+] beginning at 21 hpf, indicating that the abnormal axonal phenotypes may be related to a lack of depolarizing activity early in development. When activity was blocked with tricaine in wild-type embryos, motoneuron phenotypes were similar to the motoneuron phenotypes in nrd−/− embryos. These results implicate early embryonic activity in conjunction with other factors as necessary for normal motoneuron development

Differential Developmental Deficits in Retinal Function in the Absence of either Protein Tyrosine Sulfotransferase-1 or -2

To investigate the role(s) of protein-tyrosine sulfation in the retina and to determine the differential role(s) of tyrosylprotein sulfotransferases (TPST) 1 and 2 in vision, retinal function and structure were examined in mice lacking TPST-1 or TPST-2. Despite the normal histologic retinal appearance in both Tpst1−/− and Tpst2−/− mice, retinal function was compromised during early development. However, Tpst1−/− retinas became electrophysiologically normal by postnatal day 90 while Tpst2−/− mice did not functionally normalize with age. Ultrastructurally, the absence of TPST-1 or TPST-2 caused minor reductions in neuronal plexus. These results demonstrate the functional importance of protein-tyrosine sulfation for proper development of the retina and suggest that the different phenotypes resulting from elimination of either TPST-1 or -2 may reflect differential expression patterns or levels of the enzymes. Furthermore, single knock-out mice of either TPST-1 or -2 did not phenocopy mice with double-knockout of both TPSTs, suggesting that the functions of the TPSTs are at least partially redundant, which points to the functional importance of these enzymes in the retina