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Axon Hillock

The Experts below are selected from a list of 198 Experts worldwide ranked by ideXlab platform

Efrain C Azmitia – 1st expert on this subject based on the ideXlab platform

  • 5 ht1a receptor localization on the Axon Hillock of cervical spinal motoneurons in primates
    The Journal of Comparative Neurology, 1995
    Co-Authors: Nancy M Kheck, Patrick J Gannon, Efrain C Azmitia

    Abstract:

    Serotonin (5-HT) has direct and specific effects on the activity of spinal cord motoneurons. The 5-HTlA receptor has been shown to mediate motoneuron responses in spinal reflex pathways using the highly selective 5-HTIA receptor agonist 8-OH-DPAT. We have developed an antipeptide antibody that recognizes a specific region (the second external loop) of the ~-HT~A receptor. This 5-HT1~ receptor antibody labels populations of neurons and glia in the primate cervical spinal cord. The highest receptor density is present in the superficial lamina of the dorsal horn, around the central canal, and on the Axon Hillock of large ventral horn motoneurons. The cellular labeling pattern on motoneurons shows a single, densely stained, tapering process emanating from the perikaryon. A more diffuse label is also present throughout the soma. Dendritic labeling was not apparent. These results suggest that post-synaptic 5-HT1~ receptors may be involved in modulating spinal motoneuron activity at the key site of action potential initiation, the Axon Hillock, o 1995 WiIey-Liss, Inc. Indexing terms: serotonin, receptor antibody, autoreceptor, Macaca, immunocytochemistry

Samuel Schacher – 2nd expert on this subject based on the ideXlab platform

  • Two mRNA-Binding Proteins Regulate the Distribution of Syntaxin mRNA in Aplysia Sensory Neurons
    The Journal of Neuroscience, 2006
    Co-Authors: Jiang-yuan Hu, Fang Wu, James H. Schwartz, Samuel Schacher

    Abstract:

    Targeting mRNAs to different functional domains within neurons is crucial to memory storage. In Aplysia sensory neurons, syntaxin mRNA accumulates at the Axon Hillock during long-term facilitation of sensory-motor neuron synapses produced by serotonin (5-HT). We find that the 3′ untranslated region of Aplysia syntaxin mRNA has two targeting elements, the cytosolic polyadenylation element (CPE) and stem-loop double-stranded structures that appear to interact with mRNA-binding proteins CPEB and Staufen. Blocking the interaction between these targeting elements and their RNA-binding proteins abolished both accumulation at the Axon Hillock and long-term facilitation. CPEB, which we previously have shown to be upregulated after stimulation with 5-HT, is required for the relocalization of syntaxin mRNA to the Axon Hillock from the opposite pole in the cell body of the sensory neuron during long-term facilitation, whereas Staufen is required for maintaining the accumulation of the mRNA both at the Axon Hillock after the treatment with 5-HT and at the opposite pole in stable, unstimulated sensory neurons. Thus, the cooperative actions of the two mRNA-binding proteins serve to direct the distribution of an mRNA encoding a key synaptic protein.

  • Redistribution of Syntaxin mRNA in Neuronal Cell Bodies Regulates Protein Expression and Transport during Synapse Formation and Long-Term Synaptic Plasticity
    The Journal of Neuroscience, 2003
    Co-Authors: Jiang-yuan Hu, Xu Meng, Samuel Schacher

    Abstract:

    Syntaxin has an important role in regulating vesicle docking and fusion essential for neurotransmitter release. Here, we demonstrate that the distribution of syntaxin mRNA in cell bodies of sensory neurons (SNs) of Aplysia maintained in cell culture is affected by synapse formation, synapse stabilization, and long-term facilitation (LTF) produced by 5-HT. The distribution of the mRNA in turn regulates expression and Axonal transport of the protein. Syntaxin mRNA and protein accumulated at the Axon Hillock of SNs during the initial phase of synapse formation. Significant numbers of granules containing syntaxin were detected in the SN Axon. When synaptic strength was stable, both mRNA and protein were targeted away from the Axon Hillock, and the number of syntaxin granules in the SN Axon was reduced. Dramatic increases in mRNA and protein accumulation at the Axon Hillock and number of syntaxin granules in the SN Axon were produced when cultures with stable connections were treated with 5-HT that evoked LTF. Anisomycin (protein synthesis inhibitor) or KT5720 (protein kinase A inhibitor) blocked LTF, accumulation of syntaxin mRNA and protein at the Axon Hillock, and the increase in syntaxin granules in SN Axons. The results indicate that without significant effects on overall mRNA expression, both target interaction and 5-HT via activation of protein kinase A pathway regulate expression of syntaxin and its packaging for transport into Axons by influencing the distribution of its mRNA in the SN cell body.

  • Target Interaction Regulates Distribution and Stability of Specific mRNAs
    The Journal of Neuroscience, 2002
    Co-Authors: Jiang-yuan Hu, Xu Meng, Samuel Schacher

    Abstract:

    Several factors regulate export of mRNAs from neuronal cell bodies. Using in situ hybridization and RT-PCR, we examined how target interaction influences the distribution of mRNAs expressed in sensory neurons (SNs) of Aplysia maintained in cell culture. Interaction with a synaptic target has two effects on the distribution of mRNA encoding an SN-specific peptide, sensorin: the target affects the accumulation of sensorin mRNA at the Axon Hillock and the stability of sensorin mRNA exported to distal sites. Synapse formation with motor neuron L7 results in the accumulation of high levels of sensorin mRNA in the Axon Hillock of the SN and in SN neurites contacting L7. SNs cultured alone or in contact with motor neuron L11, with which no synapses form, show a more uniform distribution of sensorin mRNA in the cytoplasm of the SN cell body, with little expression in neurites. Contact with L7 or L11 had little or no effect on the distribution of two other mRNAs in the cytoplasm of SN cell bodies. Sensorin mRNA exported to SN neurites after 1 d in culture is more stable when the SN contacts L7 compared with SN neurites that contact L11. After removal of the SN cell body, the amounts of sensorin mRNA already exported to the neurites are greater when neurites contact L7 compared with neurites in contact with L11. The results indicate that target interaction and synapse formation regulate both the accumulations of specific mRNAs destined for export and their stability at distant sites.

Horstmar Hollander – 3rd expert on this subject based on the ideXlab platform

  • the glial ensheathment of the soma and Axon Hillock of retinal ganglion cells
    Visual Neuroscience, 1995
    Co-Authors: Jonathan Stone, Felix Makarov, Horstmar Hollander

    Abstract:

    : We have studied the glial investment of ganglion cells of the cat’s retina, orienting the sections taken for electron microscopy so that the investment could be traced from the soma along the Axon. The soma of each ganglion cell is covered by a close-fitting, continuous sheath formed by Muller cells. The Axon Hillock and the first part of the initial segment are invested by an extension of the somal sheath, and are thus enclosed in the same glial compartment as the soma. The initial segment extends a few microns past the Muller cell sheath; this last length of the initial segment is contacted by numerous processes of astrocytes, which converge on it in a pattern found also on nodes of the same Axons, in the optic nerve. Beyond the initial segment, the intraretinal lengths of the Axons are invested by both Muller cells and astrocytes, but the investment is strikingly incomplete. Large areas of Axonal membrane have no glial cover, and lie close to other Axonal membranes. The sequential arrangement of these distinct forms of glial wrapping of the soma, initial segment, and Axon is described here for the first time. It is suggested that this pattern of glial investment controls the flow of current between dendrite and initial segment of the ganglion cell, defines the site of initiation of action spikes, and controls the formation of synapses on the soma and initial segment.