Postsynaptic density zone

Fig. 2 Electron micrograph of synapses. The image shows synapses formed by cultured cortical neurons from mouse. Note abundant synaptic vesicles in nerve terminals adjacent to synaptic junctions that are composed of presynaptic active zones and postsynaptic densities (open arrows point to postsynaptic densities of synaptic junctions synapse on the right contains two junctions). In addition to synaptic vesicles, two of the nerve terminals contain LDCVs (closed arrows). Calibration bar = 500 nm. (Image courtesy of Dr. Xinran Liu, UT Southwestern).

Keywords Active zone Central nervous system Dendrites Dendritic spine Neuron Neurotransmitter Peripheral nervous system Postsynaptic density Synapse... 

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The postsynaptic response to a chemical messenger appears to occur at postsynaptic active zones, which can be recognized morphologically at sites where nerve terminals make contact with other neurons or effector cells such as striated muscle. They consist of a pronounced density of intra-membranous particles as viewed under electron microscopy. These particles are at least 100-fold more enriched in active zones when compared to the remainder of the membrane. At the cholinergic nerve-muscle junction, evidence exists to suggest that these intramembranous particles are in fact ion channel—receptor complexes. Portions of the particles, thought to be the receptors, turn over with a time course of days, but the overall integrity of the active zones remains intact. In the cerebral cortex of the central nervous system, dendritic spines of neurons have been shown to be concentrated with active zones. These active zones appear to be intimately associated with portions of the neuronal cytoskeleton, since the cytoplasmic portion of the active zone displays a prominent band of fuzzy material, which, in turn, makes contact with microfilaments. 

In addition to labeling NMJs, we have included procedures for transmission electron microscopy (TEM) preparation of NMJs in embryos and first-, second-, and third-instar larvae (see Protocol 11.5). These protocols are not described in detail elsewhere, and the ultrastructure of the NMJ can provide very valuable information about, for example, the number and morphology of active zones, size and number of synaptic vesicles, size of boutons, and alignment of pre- and postsynaptic densities. This information cannot be obtained in any other fashion than by TEM. 

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