The axon guidance molecule Robo is a transmembrane protein which is conserved during evolution. Robo and its ligand, Slit, have been implicated in regulating many developmental processes, such as axon guidance, neuronal migration, tumor metastasis, angiogenesis, lung morphogenesis, kidney morphogenesis, heart morphogenesis, ovary development and gonad development. Robo function mainly depends on the binding of its Ig1 domain to the LRR-2 domain of Slit ligand. Meanwhile, Robo function is also mediated by binding to some signaling molecules, including the heparan sulfate proteoglycans (HSPGs), GTPase-activating proteins (GAPs) and tyrosine kinase Abelson. Several transcription factors, including Hox, Midline and Nkx2.9, were shown to regulate robo expression. In addition, alternative splicing and transport regulation also affect Robo function. In this review, we summarized the studies on the molecular structure, functions and molecular mechanism of Robo, which would propose a novel strategy for the research of neural development, as well as prevention and treatment of nervous system diseases and cancers.
Axons ; physiology ; Nerve Tissue Proteins ; physiology ; Receptors, Immunologic ; physiology

Differing from other subtypes of inhibitory interneuron, chandelier or axo-axonic cells form depolarizing GABAergic synapses exclusively onto the axon initial segment (AIS) of targeted pyramidal cells (PCs). However, the debate whether these AIS-GABAergic inputs produce excitation or inhibition in neuronal processing is not resolved. Using realistic NEURON modeling and electrophysiological recording of cortical layer-5 PCs, we quantitatively demonstrate that the onset-timing of AIS-GABAergic input, relative to dendritic excitatory glutamatergic inputs, determines its bi-directional regulation of the efficacy of synaptic integration and spike generation in a PC. More specifically, AIS-GABAergic inputs promote the boosting effect of voltage-activated Na⁺ channels on summed synaptic excitation when they precede glutamatergic inputs by >15 ms, while for nearly concurrent excitatory inputs, they primarily produce a shunting inhibition at the AIS. Thus, our findings offer an integrative mechanism by which AIS-targeting interneurons exert sophisticated regulation of the input-output function in targeted PCs.
Axon Initial Segment ; Axons/physiology* ; Neurons ; Synapses/physiology* ; Pyramidal Cells/physiology* ; Interneurons/physiology* ; Action Potentials/physiology*

It has been well established that the recovery ability of central nervous system (CNS) is very poor in adult mammals. As a result, CNS trauma generally leads to severe and persistent functional deficits. Thus, the investigation in this field becomes a "hot spot". Up to date, accumulating evidence supports the hypothesis that the failure of CNS neurons to regenerate is not due to their intrinsic inability to grow new axons, but due to their growth state and due to lack of a permissive growth environment. Therefore, any successful approaches to facilitate the regeneration of injured CNS axons will likely include multiple steps: keeping neurons alive in a certain growth-state, preventing the formation of a glial scar, overcoming inhibitory molecules present in the myelin debris, and giving direction to the growing axons. This brief review focused on the recent progress in the neuron regeneration of CNS in adult mammals.
Animals ; Axons ; physiology ; Central Nervous System Diseases ; complications ; metabolism ; pathology ; Humans ; Mammals ; physiology ; Nerve Regeneration ; physiology

Deep brain stimulation (DBS), which usually utilizes high frequency stimulation (HFS) of electrical pulses, is effective for treating many brain disorders in clinic. Studying the dynamic response of downstream neurons to HFS and its time relationship with stimulus pulses can reveal important mechanisms of DBS and advance the development of new stimulation modes (e.g., closed-loop DBS). To exhibit the dynamic neuronal firing and its relationship with stimuli, we designed a two-dimensional raster plot to visualize neuronal activity during HFS (especially in the initial stage of HFS). Additionally, the influence of plot resolution on the visualization effect was investigated. The method was then validated by investigating the neuronal responses to the axonal HFS in the hippocampal CA1 region of rats. Results show that the new design of raster plot is able to illustrate the dynamics of indexes (such as phase-locked relationship and latency) of single unit activity (i.e., spikes) during periodic pulse stimulations. Furthermore, the plots can intuitively show changes of neuronal firing from the baseline before stimulation to the onset dynamics during stimulation, as well as other information including the silent period of spikes immediately following the end of HFS. In addition, by adjusting resolution, the raster plot can be adapted to a large range of firing rates for clear illustration of neuronal activity. The new raster plot can illustrate more information with a clearer image than a regular raster plot, and thereby provides a useful tool for studying neuronal behaviors during high-frequency stimulations in brain.
Action Potentials ; Animals ; Axons ; physiology ; CA1 Region, Hippocampal ; physiology ; Deep Brain Stimulation ; Neurons ; physiology ; Rats

The axon initial segment (AIS) is a highly specialized axonal compartment where the action potential is initiated. The heterogeneity of AISs has been suggested to occur between interneurons and pyramidal neurons (PyNs), which likely contributes to their unique spiking properties. However, whether the various characteristics of AISs can be linked to specific PyN subtypes remains unknown. Here, we report that in the prelimbic cortex (PL) of the mouse, two types of PyNs with axon projections either to the contralateral PL or to the ipsilateral basal lateral amygdala, possess distinct AIS properties reflected by morphology, ion channel expression, action potential initiation, and axo-axonic synaptic inputs from chandelier cells. Furthermore, projection-specific AIS diversity is more prominent in the superficial layer than in the deep layer. Thus, our study reveals the cortical layer- and axon projection-specific heterogeneity of PyN AISs, which may endow the spiking of various PyN types with exquisite modulation.
Mice ; Animals ; Axon Initial Segment ; Synapses/physiology* ; Pyramidal Cells/physiology* ; Cerebral Cortex ; Axons/physiology*

Neurotransmission begins with neurotransmitter being released from synaptic vesicles. To achieve this function, synaptic vesicles endure the dynamic "release-recycle" process to maintain the function and structure of presynaptic terminal. Synaptic transmission starts with a single action potential that depolarizes axonal bouton, followed by an increase in the cytosolic calcium concentration that triggers the synaptic vesicle membrane fusion with presynaptic membrane to release neurotransmitter; then the vesicle membrane can be endocytosed for reusing afterwards. This process requires delicate regulation, intermediate steps and dynamic balances. Accumulating evidence showed that the release ability and mobility of synapses varies under different stimulations. Synaptic vesicle heterogeneity has been studied at molecular and cellular levels, hopefully leading to the identification of the relationships between structure and function and understanding how vesicle regulation affects synaptic transmission and plasticity. People are beginning to realize that different types of synapses show diverse presynaptic activities. The steady advances of technology studying synaptic vesicle recycling promote people's understanding of this field. In this review, we discuss the following three aspects of the research progresses on synaptic vesicle recycling: 1) presynaptic vesicle pools and recycling; 2) research progresses on the differences of glutamatergic and GABAergic presynaptic vesicle recycling mechanism and 3) comparison of the technologies used in studying presyanptic vesicle recycling and the latest progress in the technology development in this field.
Action Potentials ; Axons ; physiology ; Calcium ; physiology ; Endocytosis ; Humans ; Presynaptic Terminals ; physiology ; Synapses ; physiology ; Synaptic Transmission ; Synaptic Vesicles ; physiology

OBJECTIVETo study the effect of nerve growth factor (NGF) and Schwann cells on axon regeneration of the inferior alveolar nerve following mandibular lengthening with distraction osteogenesis.

METHODSUnilateral mandibular osteodistraction was performed in 9 healthy adult male goats with a distraction rate of 1 mm/d. Every 3 goats were killed on days 7, 14 and 28 after mandibular lengthening, respectively. The inferior alveolar nerves in the distraction callus were harvested and processed for ultrastructural and NGF immunohistochemical study. The inferior alveolar nerves from the contralateral side were used as controls.

RESULTSOn day 7 after distraction, axon degeneration and Schwann cell proliferation were observed, and very strong staining of NGF in the distracted nerve was detected. On day 14 after distraction, axon regeneration and remyelination were easily observed, and NGF expression started to decline. On day 28 after distraction, the gray scale of NGF immunoreactivity recovered to the normal value and the Schwann cells almost recovered to their normal state.

CONCLUSIONSGradual mandibular osteodistraction can result in mild or moderate axon degeneration of the inferior alveolar nerve. Nerve trauma may stimulate the proliferation of Schwann cells and promote the synthesis and secretion of NGF in the Schwann cells. Schwann cells and NGF might play important roles in axon regeneration of the injured inferior alveolar nerve following mandibular lengthening.

Animals ; Axons ; pathology ; physiology ; Goats ; Immunohistochemistry ; Male ; Mandible ; surgery ; Mandibular Nerve ; physiology ; Nerve Growth Factor ; physiology ; Nerve Regeneration ; physiology ; Osteogenesis, Distraction ; Schwann Cells ; physiology

With the application of the photoconversion technology of genetically expressed fluorescent proteins in biologic field, more powerful confocal imaging ability was demanded. The aim of the present study was to establish an experimental model employing confocal simultaneous scanner unit for simultaneous laser stimulation and imaging, taking study of forebrain neurodevelopment in zebrafish as an example. In the present study, 36-48-hour-old Tg(lhx5:kaede) zebrafish embryos were mounted with 1.2% low melting temperature agarose. The forebrain neurons marked with kaede were observed using the simultaneous scanner unit of confocal microscopy. The 405 nm laser was used to stimulate the region of interest (ROI), while 488 and 559 nm lasers were used to acquire images at the same time. The photoconversion state of kaede protein was then reviewed, and the projecting pattern of neurons stimulated by the ultraviolet laser was examined. The results showed that, the fluorescence of stimulated kaede turned from green to red, and the photoconversion of kaede demonstrated anterior dorsal telencephalon (ADt) neurons projected axons ventrally into the anterior commissure (AC) and supraoptic tract (SOT). These results suggest the confocal simultaneous scanner unit meets the demand of the photoconversion experiment. The application of confocal simultaneous scanning technology in examining Tg(lhx5:kaede) zebrafish embryos affords an ideal experimental model in neurodevelopment study.
Animals ; Axons ; physiology ; Microscopy, Confocal ; Neurons ; cytology ; Prosencephalon ; embryology ; Ultraviolet Rays ; Zebrafish ; embryology

The intrinsic regrowth ability of injured neurons is essential for axon regeneration and functional recovery. Recently, numerous intrinsic pathways that regulate axon regeneration have been discovered, among which the mitogen-activated protein kinase (MAPK) pathway and the phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) pathway are arguably the best characterized examples. MAPK signaling pathway is involved in multiple processes including sensing injury signals, initiating and promoting axonal regrowth through regulating cytoskeleton dynamics and protein synthesis. The PI3K/Akt signaling pathway regulates axon regeneration mainly through gene transcription and translation. Combinatory manipulation of multiple regeneration-promoting signals can further improve the extend of axonal regrowth. This paper summarizes current progresses on axon regeneration studies in various organisms and discuss their potentials in promoting functional recovery .
Axons ; physiology ; Nerve Regeneration ; Neurons ; Phosphatidylinositol 3-Kinases ; Regeneration ; Signal Transduction

Spinal cord injury (SCI) disrupts the structural and functional connectivity between the higher center and the spinal cord, resulting in severe motor, sensory, and autonomic dysfunction with a variety of complications. The pathophysiology of SCI is complicated and multifaceted, and thus individual treatments acting on a specific aspect or process are inadequate to elicit neuronal regeneration and functional recovery after SCI. Combinatory strategies targeting multiple aspects of SCI pathology have achieved greater beneficial effects than individual therapy alone. Although many problems and challenges remain, the encouraging outcomes that have been achieved in preclinical models offer a promising foothold for the development of novel clinical strategies to treat SCI. In this review, we characterize the mechanisms underlying axon regeneration of adult neurons and summarize recent advances in facilitating functional recovery following SCI at both the acute and chronic stages. In addition, we analyze the current status, remaining problems, and realistic challenges towards clinical translation. Finally, we consider the future of SCI treatment and provide insights into how to narrow the translational gap that currently exists between preclinical studies and clinical practice. Going forward, clinical trials should emphasize multidisciplinary conversation and cooperation to identify optimal combinatorial approaches to maximize therapeutic benefit in humans with SCI.
Humans ; Axons/pathology* ; Nerve Regeneration/physiology* ; Spinal Cord Injuries/therapy* ; Neurons/pathology* ; Recovery of Function