Dendritic organelles. (A) Hippocampal neuron stained for MAP2 (red), DAPI (blue), and the Golgi marker GM130 (green). Adapted from ; reproduced with permission from Elsevier, copyright 2005. (B) Three-dimensional reconstruction of serial electron micrographs showing the distribution of SER (dark gray) in dendrites and spines. Large flat compartments (arrowheads) are linked by thin extensions (thin arrows). Several spines are invaginated by SER (asterisks). Adapted from ; reprinted with permission from the Society for Neuroscience, copyright 2002 and deg; (C) Cultured hippocampal neurons expressing the mitochondrial targeting sequence of cytochrome oxidase fused to DsRed2. Dendritic mitochondria (red) are present in the dendritic shaft where they occasionally associate with dendritic spines (arrows). Adapted from ; reproduced with permission from Elsevier, copyright 2004. (D) Three-dimensional reconstruction of serial electron micrographs showing the distribution of dendritic endosomes in hippocampal neurons from adult rats (bottom) and rats at postnatal day 15 (top), postnatal day 21 (middle). Endocytic vesicles (yellow), endosomes (red), small vesicles (blue), and amorphous vesicles (black) are distributed throughout dendrites. Adapted from ; reprinted with permission from the Society for Neuroscience, copyright 2002; (E) Electron micrograph of the spine apparatus showing lamination of smooth ER (straight arrows) between regions of high electron density (wavy arrows). Adapted from ; reproduced with permission from the Society for Neuroscience, copyright 1997.

Dendritic Golgi outposts. (A) Labeling with GM130 (green) demonstrates the presence of local Golgi outposts (arrowheads) in dendritic shafts from three different cultured hippocampal neurons. (B) Immunogold labeling for GM130 in adult rat hippocampus demonstrates the presence of Golgi in the apical dendrite of a CA1 pyramidal neuron in vivo. Scale bar, 1 μm. (C) Golgi outposts at dendritic branch points. VSVGtsO45 (green) accumulates at primary (1°), secondary (2°), and tertiary (3°) dendritic branch points following release from the ER at 20°C. Scale bar, 5 μm. Adapted from ;reprinted with permission from Elsevier, copyright 2005.

The spine endocytic zone. (A) Clathrin-YFP (yellow) localizes to dendritic spines. Scale bar, 2 μm. (B) Clathrin-DsRed (red) lies adjacent to, but not overlapping, PSD95-GFP (green) in the spine head. Four different spines are shown. Scale bar, 1 μm. Adapted from ; reprinted with permission from Elsevier, copyright 2002; (C) Electron micrographs showing the different stages of endocytosis in different dendritic spines: clathrin-coated invagination prior to scission (left panel), a coated invagination (middle panel), coated vesicle postscission (right panel). Adapted from ; reprinted with permission from Macmillan Publishers Ltd., copyright 2004.

Model for local postsynaptic trafficking. Components of the synapse either diffuse from the synapse or are actively transported to endocytic zones surrounding the PSD, where they are internalized and trafficked to early endosomes (EE) and sorted either to late endosomes (LE) for degradation or to recycling endosomes (RE) for return to the spine surface. Cargo destined for the synapse is exocytosed to the cell surface at an unknown location, perhaps at the plasma membrane of the spine head. Alternatively, synaptic components could be exocytosed to the surface of the dendritic shaft and diffused through the spine neck to the synapse. See for a partial list of molecules known to be involved in dendritic trafficking.

Recycling endosomes act as AMPA receptor reservoirs. (A) HA-tagged GluR1 is trafficked to the cell surface of cultured hippocampal neurons in response to glycine stimulation (left and middle panels). Glycine-stimulated surface expression of GluR1 is impaired in neurons expressing a dominant-negative mutant of Rab11a (S25N) (right panels). Cells were transfected with GFP for visualization (upper panels). (B) Blocking transport through recycling endosomes with dominant-negative forms of Rme1 (G429R) and Rab11a (S25N) abolishes LTP. EPSCs were measured by whole-cell patch clamp from CA1 pyramidal neurons transfected with Rme1 (G429R), Rab11a (S25N), or GFP before and after high-frequency stimulus (100 Hz, four 1-s trains).