Synaptic zones

Our fixed tissue technique has been described in several papers (Rubio and Wenthold, 1997, 1999a Petralia et al., 1997, 1998, 1999a,b Wang et al., 1998 Zhao et al., 1998 for a detailed description, see Petralia and Wenthold, 1999) it was based originally on the methods of Matsubara et al. (1996) and Landsend et al. (1997). In the live tissue technique (unpublished data in Petralia et al., 1999b modified from a similar method described in Petralia and Wenthold, 1998), the live tissue is removed from the brain quickly, slam-frozen, and stored 

The first of the four zones includes the postsynaptic membrane and approximately the upper half of the PSD. In this zone, preferential labeling is seen for all ionotropic glutamate receptors and for the associated proteins known as membrane-associated guanylate kinases (MAGUKs) including PSD-95, SAP-102, PSD-93, and SAP-97 (Valtschanoff et al., 1999) (Figs. 7 and 8). The second zone includes approximately the bottom half (for the purpose 

In the adult cerebellum, as noted above, parallel fiber synapses have abundant delta receptors, while delta receptors are rare or absent from climbing fiber synapses. AMPA receptors are found at both excitatory synapse populations but are more abundant at climbing fiber synapses. In the first postnatal week, presumptive climbing fiber synapses have high 

1994 Rao et al., 1998). Also and as discussed below, formation of postsynaptic structures at glutamatergic synapses may require an initial cluster of glutamate receptor-associated proteins that can anchor the glutamate receptors to the postsynaptic membrane. 

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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. 

Yao I, Takagi H, Ageta H, et al. SCRAPPER-dependent ubiquitination of active zone protein RIM1 regulates synaptic vesicle release. Cell 2007 130 943-957. 

Uchida, N., Honjo, Y., Johnson, K. R., Wheelock, M. J. and Takeichi, M. The catenin/cadherin adhesion system is localized in synaptic junctions bordering transmitter release zones. /. Cell Biol. 135 767-779,1996. 

Those vesicles have been primed by docking at the active zone and are therefore ready for exocytosis upon arrival of an action potential. However, for the synapse to respond rapidly and repeatedly under heavy physiological demand, these exocytosed vesicles must be rapidly replaced. This is accomplished first from the recycled pool of vesicles and, as the demand increases, from the reserve pool. To be recycled, synaptic vesicles must be reloaded quickly after they release their contents. The sequence of events that is triggered by neurotransmitter exocytosis is known as the synaptic vesicle cycle [73,74] (Fig. 9-8). 

In the classic model of synaptic vesicle recycling in nerve terminals, synaptic vesicles fuse completely with the plasma membrane and the integrated vesicle proteins move away from the active zone to adjacent membrane regions (Fig. 9-9A). In these regions, clathrin-mediated synaptic vesicle endocytosis takes place rapidly after neurotransmitter release (within seconds) [64]. The process starts with the formation of a clathrin-coated pit that invaginates toward the interior of the cell and pinches off to form a clathrin-coated vesicle [83]. Coated vesicles are transient organelles that rapidly shed their coats in an ATP/chaperone dependent process. Once uncoated, the recycled vesicle fuses with a local EE for reconstitution as a synaptic vesicle. Subsequently, the recycled synaptic vesicle is filled with neurotransmitter and it returns to the release site ready for use. This may be the normal pathway when neurotransmitter release rates are modest. Clathrin/ EE-based pathways become essential when synaptic proteins have been incorporated into the presynaptic plasma membrane. 

FIGURE 43-2 Photomicrograph of the human neuromuscular junction. In normal muscle, Ach receptors are associated with the terminal expansions of the junctional folds and the architecture of the postjunctional membrane follows closely the distribution of active zones in the presynaptic membrane, b, basal lamina I, infoldings m, mitochondria M, myocyte N, nerve terminal r, ribosomes s, synaptic space S, Schwann cell. Courtesy of A. Engel. 

Smith SJ, Augustine GJ 1988 Calcium ions, active zones and synaptic transmitter release. Trends Neurosci 11 458-464... 

Vesicle You should demonstrate that there are two stores of acetylcholine (ACh), one deep in the nerve terminal and one clustered beneath the surface opposite the ACh receptors in the so-called active zones . The deep stores serve as a reserve of ACh while those in the active zones are required for immediate release of ACh into the synaptic cleft. 

Transplant experiments indicate that the receptors for the secreted SCN factors are located near the 3rd ventricle (LeSauter Silver 1998). The major projection of the SCN is to the subparaventricular zone (SPZ) (Watts Swanson 1987), a little understood hypothalamic region flanking the 3rd ventricle. Lesions of the SPZ disrupt circadian regulation of locomotor activity (Lu et al 2001), making the SPZ the likely location of receptors for secreted SCN locomotor factors, whether synaptic or paracrine. 

Acetylcholine release is inhibited by one of the most potent toxins, the botulims toxin produced by the anaerobic bacterium Clostridium botulinum. The toxin, lethal at 1 ng/kg in humans, enters the synapse by endocytosis at nonmyelinated synaptic membranes and produces muscle paralysis by blocking the active zone of the presynaptic membrane... 

A synaptic vesicle cycle. The number of synaptic vesicles in a single synapse in the brain varies from fewer than 100 to several hundred. In specialized synapses there may be thousands. However, at any moment only a fraction of the total are in the "active zone," often aligned along the presynaptic membrane (Fig. 30-20A) or in specialized ribbons such as those in Fig. 30-10B. The vesicles are normally reused repeatedly, undergoing a cycle of filling with neurotransmitter, translocation to the active zone, ATP-dependent priming, exocytosis with release of the neurotransmitter into the synaptic cleft, coating with clathrin, endocytosis, and acidification as outlined in Fig. 30-20B.554-557 The entire cycle may be completed within 40-60 s to avoid depletion of active vesicles.558 559 A key event in the cycle is the arrival of an action potential at the presynaptic neuron end. 

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