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Fig. 1. GFP-synaptobrevin specifically localizes to presynaptic sites in RGC axon
terminals. (A-D) The localization of GFP-synaptobrevin was determined by
examining the distribution of GFP immunoreactivity by electron microscopy.
Morphologically mature synapses (black arrows), containing presynaptic
terminals with numerous synaptic vesicles (v) and clearly defined pre- and
postsynaptic specializations, are present in the tectal neuropil of stage 45
tadpoles. (B-D) Electron photomicrographs of tadpole brains immunostained with
an antibody to GFP show the localization of gold particles (open arrows) to
presynaptic terminals in the tectal neuropil. Silver enhancement of the
secondary antibody coupled to 1 nm gold particles shows that the GFP
immunolabel is preferentially associated to synaptic vesicles in
morphologically mature retinotectal synapses (B,D), as well as in presynaptic
terminals near contact sites (C). Scale bar: 0.2 µm. (E) Regions of an
individual RGC axon arbor imaged at 5 minute intervals illustrate the
distribution of GFP-synaptobrevin puncta. The majority of the
GFP-synaptobrevin puncta remain constant throughout time. This is in contrast
to motile GFP-synaptobrevin puncta present in small transport packets,
prevalent in axon terminals of neurons grown in culture
(Ahmari et al., 2000). Scale
bar: 20 µm.
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