Proper axon guidance requires the presence of highly glycosylated heparan sulfate (HS) proteoglycans (HSPGs) on the surface of axons and growth cones. Multiple HSPGs, including Syndecans, Glypicans and Perlecans, carry similar carbohydrate polymers, rai...

More evidence suggests that Wnt proteins are conserved axon guidance cues that control the direction of growth cone navigation. However, the intracellular signaling mechanisms that lead to specific changes of cytoskeleton or membrane dynamics involved i...

ER Exit Sites (ERES) are the first sorting sites of the secretory pathway. We hypothesized that in neurons ERES are not uniform and their activity is spatially regulated to support local biosynthetic transport load. To test this hypothesis, we studied t...

Recent studies have convincingly shown that newly born cortical pyramidal neurons embark on a complex route and undergo dynamic morphogenesis during migration. Most, if not all, pyramidal neurons switch from multipolar to bipolar in morphology before en...

Despite intense investigation, the role of intracellular cAMP in the guidance of axons to netrin-1 remains unclear. Both gradients of netrin-1 and membrane-permeable cAMP analogs attract Xenopus laevis spinal axons in vitro, suggesting that cAMP might f...

There is increasing evidence that the vesicular glutamate transporter 2 (VGluT2) is expressed in mesencephalic dopamine (DA) neurons of rat in vitro and in vivo. Recently, we showed by double in situ hybridization that, within the first two weeks after ...

The developmental refinement of topographic projections in the brain is reflected in the dynamic sculpting of axonal arbors that takes place as connections between CNS structures form and mature. To examine the role of synaptogenesis and synaptic maturation in the structural development of axonal projections during the formation of the topographic retinotectal projection, we coexpressed cytosolic fluorescent protein (FP) and FP-tagged synaptophysin (SYP) in small numbers of retinal ganglion cells in living albino Xenopus laevis tadpoles to reveal the distribution and dynamics of presynaptic sites within labeled retinotectal axons. Two-photon time-lapse observations followed by quantitative analysis of tagged SYP levels at individual synapses demonstrated the time course of synaptogenesis: increases in presynaptic punctum intensity are detectable within minutes of punctum emergence and continue over many hours. Puncta lifetimes correlate with their intensities. Furthermore, we found that axon arbor dynamics...

Damaged neurons in the adult CNS do not regenerate, in part due to the barrier of the glial scar. The NG2 CSPG is a potent inhibitor of axon growth that is found at high levels in glial scars. To address the function of NG2, we infused anti-NG2 monoclonal antibodies into a bilateral dorsal spinal cord lesion in adult rats. Ascending mechanosensory axons of the sciatic nerve were labeled with the retrograde tracer cholera toxin-B (CTB). At 1-week post-injury, labeled axons in control animals terminated caudal to the lesion in an area of dense NG2 immunoreactivity. Many of these axons had dystrophic endings. In animals treated with neutralizing anti-NG2 antibodies, labeled axons penetrated the caudal border of the lesion and grew beyond the lesion center. Thus, neutralizing NG2 in vivo promotes axon regeneration into the normally growth-inhibitory glial scar. To increase the growth capacity of DRG neurons, we performed peripheral nerve conditioning-lesions 1 week prior to dorsal column injury. Sensory axon r...

Heteromeric KCNQ2/KCNQ3 (Q2/Q3) channels underlie M-type voltage-gated K+ currents in sympathetic and hippocampal neurons. In brain, spinal cord, and sciatic nerve, a subpopulation of Q2 and Q3 proteins are concentrated at neuronal axon initial segments (AIS) and nodes of Ranvier, where they colocalize with the fast Na+ channels that initiate and propagate action potentials (APs). Physiological evidence indicates that KCNQ subunits underlie the slow, low-voltage-activated nodal K+ current, Ks (Schwarz JR et al., this meeting). Although it is believed that AP initiation occurs in the proximal axon, the exact locations, mechanisms, and modes of regulation of initiation are all incompletely understood. We have explored the potential function of KCNQ channels in the proximal axon, using computational modeling. We assembled a morphologically realistic CA1 pyramidal cell model, including dendrites, soma, and a myelinated axon, using NEURON. Somatodendritic compartments contained Na+ and K+ conductances at densit...

Glycogen synthase kinase 3 (GSK-3) beta and alpha are serine/threonine kinases involved in growth factor signaling and embryonic development. Recently regulation of GSK-3 has been implicated in establishment of hippocampal neuronal polarity and neurotrophin-induced extension of DRG, SCG, and hippocampal axons. However, whether GSK-3 function is absolutely required for axonal development has not been decisively demonstrated. In fact, previous studies in which different concentrations and classes of pharmacological inhibitors were used showed differing results in relation to hippocampal axonal specification. Here using a highly specific pharmacological inhibitor and siRNA, we sought to determine whether GSK3 is required for axon growth. Both GSK-3 beta and alpha are expressed throughout the embryonic nervous system. Treatment of neurotrophin-responsive peripheral embryonic neurons (DRG and SCG) neurons with a highly specific pharmacological inhibitor (6-bromoindirubin-3¡ä-acetoxime) active against both isofo...