Injuries to nervous system are devastating that patients often suffer from irreversible and permanent loss of sensory and motor functions after injuries. Mature neurons in central nervous system (CNS) failed to regrow the damaged axons after injury. In ...

The sprouting of axon collateral branches is important in the establishment and refinement of neuronal connections during both development and regeneration. Collateral branches are initiated by the appearance of localized filopodial activity along quiescent axonal shafts. We report here that sensory neuron axonal shafts rapidly sprout filopodia at sites of contact with nerve growth factor-coated polystyrene beads. Some sprouts can extend up to at least 60 μm through multiple bead contacts. Axonal filopodial sprouts often contained microtubules and exhibited a debundling of axonal microtubules at the site of bead–axon contact. Cytochalasin treatment abolished the filopodial sprouting, but not the accumulation of actin filaments at sites of bead–axon contact. The axonal sprouting response is mediated by the trkA receptor and likely acts through a phosphoinositide-3 kinase-dependent pathway, in a manner independent of intracellular Ca2+ fluctuations. These findings implicate neurotrophins as local cues that d...

In the chick embryo, the segmental pattern of motor outgrowth depends on guidance cues provided by sclerotome cells. Motor axons preferentially invade the anterior sclerotome but avoid the posterior sclerotome. To determine how motor growth cone motility is influenced by these cells, we used videomicroscopy to analyze the behavior of motor growth cones as they confronted identified sclerotome cells in vitro. After contact, motor growth cones invariably avoided posterior sclerotome cells by either branching or turning. Both types of avoidance behavior were initiated by a local inhibition of veil protrusion: veils failed to progress along the contacting filopodia. This inhibition was specific to veils since contact failed to alter the number of filopodia protruded. Moreover, motor growth cones turned away from posterior cells despite more persistent filopodial contacts with these cells than with the laminin substratum. In no case did contact with posterior cells cause a complete loss of growth cone motility ...

We have sought to determine the principal site(s) in the neuron where axonal microtubules (MTs) are stabilized. To accomplish this, we compared the proximal and distal regions of the axon and the axon shaft with regard to their content of newly stabilized MT polymer, using the following criteria. Stable polymer was identified by its resistance to nocodazole, and newly stabilized polymer was distinguished from older stable polymer by the staining of the former but not the latter for tyrosinated alpha-tubulin. Our results indicate that roughly 36.4%, 5.4%, and 2.4% of the total MT mass in the proximal and distal regions of the axon and the axon shaft is newly stabilized, respectively. Thus, while MT stabilization occurs throughout the axon, the proximal region is by far the most active with regard to this process.

Nogo-66 receptors (NgR1-3) are glycosylphosphatidyl inositol-linked proteins that belong to the leucine-rich repeat superfamily. Through binding to myelin-associated inhibitors, NgRs contribute to the inhibition of axonal regeneration after spinal cord injury. Their role in limiting synaptic plasticity and axonal outgrowth in the adult CNS has been described previously, but not much is known about their role during the development of the nervous system. Here, we show that NgR1 and NgR3 mRNAs are expressed during spinal cord development of the chicken embryo. In particular, they are expressed in the dI1 subpopulation of commissural neurons during the time when their axons navigate toward and across the floorplate, the ventral midline of the spinal cord. To assess a potential role of NgR1 and NgR3 in axon guidance, we downregulated them using in ovo RNAi and analyzed the trajectory of commissural axons by tracing them in open-book preparations of spinal cords. Our results show that loss of either NgR1 or NgR...

The mouse retina encodes diverse visual features in the spike trains of >40 retinal ganglion cell (RGC) types. Each RGC type innervates a specific subset of the >50 retinorecipient brain areas. Our catalog of RGC types and feature representations is nearing completion. Yet, we know little about where specific RGC types send their information. Furthermore, the developmental strategies by which RGC axons choose their targets and pattern their terminal arbors remain obscure. Here, we identify a genetic intersection ( Cck-Cre and Brn3cCKOAP ) that selectively labels transient Suppressed-by-Contrast (tSbC) RGCs, a member of an evolutionarily conserved functionally mysterious RGC subclass. We find that tSbC RGCs selectively innervate the dorsolateral geniculate nucleus (dLGN) and ventrolateral geniculate nucleus (vLGN) of the thalamus, the superior colliculus (SC), and the nucleus of the optic tract (NOT) in mice of either sex. They binocularly innervate dLGN and vLGN but project only contralaterally to SC and N...

Understanding the bioenergetics of axon extension and maintenance has wide ranging implications for neurodevelopment and disease states. Glycolysis is a pathway consisting of 10 enzymes and separated into preparatory and payoff phases, the latter producing ATP. Using embryonic chicken sensory neurons, we report that glycolytic enzymes are found through the axon and the growth cone. Pharmacological inhibition of glycolysis in the presence of NGF impairs axon extension and growth cone dynamics within minutes without affecting axon maintenance. Experiments using microfluidic chambers show that the effect of inhibiting glycolysis on axon extension is local along distal axons and can be reversed by promoting mitochondrial respiration. Knockdown of GAPDH simplifies growth cone morphology and is rescued by shRNA-resistant GAPDH expression. Rescue of GAPDH using KillerRed fused to GAPDH followed by localized chromophore-assisted light inactivation of KillerRed-GAPDH in distal axons halts growth cone dynamics. Cons...

Spectrins are a family of cytoskeletal proteins that provide structural support of the cell membrane, link membrane-associated proteins to actin and serve as platforms for cell signaling. Spectrins consist of α and β subunits, forming heterotetramers to...

Precise connection of thalamic barreloids with their corresponding cortical barrels is critical for processing of vibrissal sensory information. Here, we show that the phospholipid interacting molecule PRG-2 plays an important role in thalamocortical ax...

Signals from sensory half-fields are processed separately in the two hemispheres of our brain but give rise to a coherent percept due to interhemispheric integration. Previous research indicates that functional communication between the two hemispheres ...