Neurons synaptic vesicles

Synaptophysin - 38-kD membrane component of neuron synaptic vesicles Synthetic human synaptophysin peptide coupled to ovalbumin Cell Marque NA HIER... 

The recent development of these electrochemical techniques for the study of vesicular release from single cells provides a powerful tool for the study of chemical signaling in the nervous system. However, the application of these methods to mammalian neurons is difficult, mainly due to size constraints, the extremely small quantities of chemical transmitter released at a single synaptic vesicle, and the complex working enviromnent of nerve cell cultures [15]. Neuronal synaptic vesicles are only about 50 mn in diameter and have been estimated... 

While the basic features of SNARE assembly and disassembly provide a convenient framework for explaining how membrane fusion works, both the regulation of SNAREs and the molecular details of fusion are not well understood. Most is known about the neuronal SNAREs that mediate regulated membrane fusion of synaptic vesicles and of secretory granules in neuroendocrine cells. They include synaptobrevin2, localized to the synaptic vesicle, and SNAP25 ( SNAPs) and syntaxinlA, both of which are localized to the plasma... 

Membrane-bound GTP rabs recruit effectors to the membrane. In neurons and neuroendocrine cells, the vesicle-associated Rab3 binds to rabphilin and to RIM. RIM is a component of the presynaptic cytomatrix and may thus serve as a docking receptor for synaptic vesicles at the active zone. 

Synaptic vesicles are the organelles in axon terminals that store neurotransmitters and release them by exocytosis. There are two types, the large dense-core vesicles, diameter about 90 nm, that contain neuropeptides, and the small synaptic vesicles, diameter about 50nm, that contain non-peptide transmitters. About ten vesicles per synapse are docked to the plasma membrane and ready for release, the readily releasable pool . Many more vesicles per synapse are stored farther away from the plasma membrane, the resting pool . When needed, the latter vesicles may be recruited into the readily releasable pool. Neuronal depolarization and activation of voltage-sensitive Ca2+... 

Due to their physicochemical properties trace amines can pass the cell membrane to a limited extent by passive diffusion, with the more lipophilic PEA and TRP crossing membranes more readily than the more polar amines TYR. and OCT. In spite of these features, trace amines show a heterogeneous tissue distribution in the vertebrate brain, and for TYR. and OCT storage in synaptic vesicles as well as activity-dependent release have been demonstrated. So far, trace amines have always been found co-localized with monoamine neurotransmitters, and there is no evidence for neurons or synapses exclusively containing trace amines. 

Chromaffin granules, platelet dense core vesicles, and synaptic vesicles accumulate ATP. ATP uptake has been demonstrated using chromaffin granules and synaptic vesicles and the process appears to depend on A(.lh+. It has generally been assumed that ATP is costored only with monoamines and acetylcholine, as an anion to balance to cationic charge of those transmitters. However, the extent of ATP storage and release by different neuronal populations remains unknown, and the proteins responsible for ATP uptake by secretory vesicles have not been identified. 

Zenisek D, Steyer JA, Eeldman ME, Aimers W (2002) A membrane marker leaves synaptic vesicles in nulliseconds after exocytosis in retinal bipolar cells. Neuron 35 1085-1097 Zhang L, He T, Talal A, Wang G, Frankel SS, Ho DD (1998) In vivo distribution of the human immunodeficiency virus/simian immunodeficiency virus coreceptors CXCR4, CCR3, and CCR5. J Virol 72 5035-5045... 

Frederickson, C.J., Suh, S.W., Silva, D. and Thompson, R.B. (2000). Importance of zinc in the central nervous system the zinc-containing neuron. J. Nutr., 130, 1471S-1483S Holt, M. and Jahn, R. (2004). Synaptic vesicles in the fast lane. Science, 303, 1986-1987 Kandel, E.R. (2001). The molecular biology of memory storage a dialogue between genes and synapses. Science, 294, 1030-1038... 

FIGURE 1-8 A dendrite (D) emerging from a motor neuron in the anterior horn of a rat spinal cord is contacted by four axonal terminals terminal 1 contains clear, spherical synaptic vesicles terminals 2 and 3 contain both clear, spherical and dense-core vesicles (arrow) and terminal 4 contains many clear, flattened (inhibitory) synaptic vesicles. Note also the synaptic thickenings and, within the dendrite, the mitochondria, neurofilaments and neurotubules. x33,000. 

FIGURE 1-10 An axonal terminal at the surface of a neuron from the dorsal horn of a rabbit spinal cord contains both dense-core and clear, spherical synaptic vesicles lying above the membrane thickenings. A subsurface cisterna (arrow) is also seen. x68,000. 

The recovery of neurotransmitters from synaptic clefts and their storage in cytoplasmic vesicles is accomplished by the tandem actions of the secondary transporters in plasma and vesicular membranes. Sodium-dependent symporters mediate neurotransmitter reuptake from synaptic clefts into neurons and glia, whereas proton-dependent antiporters concentrate neurotransmitters from neuronal cytoplasm into synaptic vesicles (Fig. 5-13). 

Neurons constitute the most striking example of membrane polarization. A single neuron typically maintains thousands of discrete, functional microdomains, each with a distinctive protein complement, location and lifetime. Synaptic terminals are highly specialized for the vesicle cycling that underlies neurotransmitter release and neurotrophin uptake. The intracellular trafficking of a specialized type of transport vesicles in the presynaptic terminal, known as synaptic vesicles, underlies the ability of neurons to receive, process and transmit information. The axonal plasma membrane is specialized for transmission of the action potential, whereas the plasma... 

Most pathways in the endocytic system are shared with cells in general, but a special case exists in synaptic vesicle cycling, which is unique to neurons and a keystone in neuronal function. Three categories will be considered here endocytic processes important for degradation of macromolecules and uptake of nutrients constitutive and regulated neuroendocrine secretion and receptor-mediated endocytosis. Synaptic vesicle cycling will then be considered separately and in greater detail. 

The bulk of pinocytosis in the nervous system is mediated by clathrin-mediated endocytosis (CME) [55] and this is the best-characterized pathway. More detail about clathrin-mediated pathways will be given when receptor-mediated endocytosis and the synaptic vesicle cycle pathways are considered. Pinocytosis through CME is responsible for uptake of essential nutrients such as cholesterol bound to low density lipoprotein (LDL) and transferring, but also plays a role in regulating the levels of membrane pumps and channels in neurons. Finally, CME is critical for normal synaptic vesicle recycling. 

At least two classes of regulated secretion can be defined [54]. The standard regulated secretion pathway is common to all secretory cells (i.e. adrenal chromaffin cells, pancreatic beta cells, etc.) and works on a time scale of minutes or even longer in terms of both secretory response to a stimulus and reuptake of membranes after secretion. The second, much faster, neuron-specific form of regulated secretion is release of neurotransmitters at the synapse. Release of neurotransmitters may occur within fractions of a second after a stimulus and reuptake is on the order of seconds. Indeed, synaptic vesicles may be recycled and ready for another round of neurotransmitter release within 1-2 minutes [64]. These two classes of regulated secretion will be discussed separately after a consideration of secretory vesicle biogenesis. 

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