Mammalian rod terminal: architecture of a binary synapse.
The mammalian rod synapse transmits a binary signal (one photon or none) using tonic, rapid exocytosis. We constructed a quantitative, physical model of the synapse. Presynaptically, a single, linear active zone provides docking sites for approximately 130 vesicles, and a "ribbon" anchored to the active zone provides a depot for approximately 640 vesicles. Postsynaptically, 4 processes invaginate the terminal: 2 (known to have low affinity glutamate receptors) lie near the active zone (16 nm), and 2 (known to have high affinity glutamate receptors) lie at a distance (130-640 nm). The presynaptic structure seems designed to minimize fluctuations in tonic rate owing to empty docking sites, whereas the postsynaptic geometry may permit 1 vesicle to evoke an all-or-none response at all 4 postsynaptic processes.
Rao-Mirotznik
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R
Department of Neuroscience, University of Pennsylvania, Philadelphia 19104.
Harkins
A B
AB
Buchsbaum
G
G
Sterling
P
P
D000818:Animals; D002415:Cats; D003624:Darkness; D008027:Light; D008854:Microscopy, Electron; D008959:Models, Neurological; D008961:Models, Structural; D017948:Retinal Rod Photoreceptor Cells / Q000502:physiology / Q000648:ultrastructure*; D013569:Synapses / Q000502:physiology / Q000648:ultrastructure*