RESUMEN
Ribbon-type presynaptic active zones are a hallmark of excitatory retinal synapses, and the ribbon organelle is thought to serve as the organizing point of the presynaptic active zone. Imaging of exocytosis from isolated retinal neurons, however, has revealed ectopic release (i.e., release away from ribbons) in significant quantities. Here, we demonstrate in an in vitro mouse retinal slice preparation that ribbon-independent release from rod bipolar cells activates postsynaptic AMPARs on AII amacrine cells. This form of release appears to draw on a unique, ribbon-independent, vesicle pool. Experimental, anatomical, and computational analyses indicate that it is elicited by a significant, global elevation of intraterminal [Ca(2+)] arising following local buffer saturation. Our observations support the conclusion that ribbon-independent release provides a read-out of the average behavior of all of the active zones in a rod bipolar cell's terminal.
Asunto(s)
Señalización del Calcio/fisiología , Calcio/metabolismo , Células Bipolares de la Retina/fisiología , Sinapsis/fisiología , Transmisión Sináptica/fisiología , Animales , Señalización del Calcio/efectos de los fármacos , Quelantes/farmacología , Ácido Egtácico/análogos & derivados , Ácido Egtácico/farmacología , Inhibidores Enzimáticos/farmacología , Potenciales Postsinápticos Excitadores/efectos de los fármacos , Potenciales Postsinápticos Excitadores/fisiología , Femenino , Técnicas In Vitro , Masculino , Ratones , Ratones Endogámicos C57BL , Modelos Biológicos , Retina/citología , Células Bipolares de la Retina/efectos de los fármacos , Células Bipolares de la Retina/ultraestructura , Sinapsis/efectos de los fármacos , Sinapsis/ultraestructura , Transmisión Sináptica/efectos de los fármacos , Vesículas Sinápticas/ultraestructuraRESUMEN
Resurgent interest in synaptic circuitry and plasticity has emphasized the importance of 3D reconstruction from serial section electron microscopy (3DEM). Three volumes of hippocampal CA1 neuropil from adult rat were imaged at X-Y resolution of ~2 nm on serial sections of ~50-60 nm thickness. These are the first densely reconstructed hippocampal volumes. All axons, dendrites, glia, and synapses were reconstructed in a cube (~10 µm(3)) surrounding a large dendritic spine, a cylinder (~43 µm(3)) surrounding an oblique dendritic segment (3.4 µm long), and a parallelepiped (~178 µm(3)) surrounding an apical dendritic segment (4.9 µm long). The data provide standards for identifying ultrastructural objects in 3DEM, realistic reconstructions for modeling biophysical properties of synaptic transmission, and a test bed for enhancing reconstruction tools. Representative synapses are quantified from varying section planes, and microtubules, polyribosomes, smooth endoplasmic reticulum, and endosomes are identified and reconstructed in a subset of dendrites. The original images, traces, and Reconstruct software and files are freely available and visualized at the Open Connectome Project (Data Citation 1).