![]() ![]() 3) are recognizable as profiles lacking synaptic vesicles but containing ribosomes, neurotubules and filaments. Ganglion cell dendrites (yellow profiles, Figs. 3, yellow dots in amacrine profile, Fig 4a) (Dowling and Boycott, 1966). Typically amacrine cells synapse upon other profiles (bipolar axons, amacrine cells or ganglion cell dendrites) in the enlarged varicosities at, what is known as a conventional synapse: the synapse consists of synaptic vesicles clustered at a pre- and post membrane density (blue arrows in Fig. Electron micrograph of the neuropil of the IPL Amacrine profiles vary between being very small cross sections through thin straight tubes, and larger varicosities budding off the dendrites. Amacrine cell dendrites are also vesicle-filled and have round mitochondria and sometimes neurofilaments as well as neurotubules (Fig. 3 and red dots in bipolar cell profiles, Fig. ![]() Their synapses are typified by a small synaptic ribbon pointing into a wedge with two post synaptic profiles (known as a dyad) at the apex (arrows in Fig. Bipolar cell axon terminals (red profiles) are vesicle-filled profiles, containing irregular, long mitochondria and neurotubules. Ultrastructure of the neuropil of the inner plexiform layer.Ī view of a small part of the neuropil of the inner plexiform layer is shown in Figure 3. Light micrograph of a vertical section through the IPLĢ. 3-D block of retina with IPL highlightedįig. The neuropil is a confusing network of interconnecting profiles that, to be understood, has to be investigated at the higher magnification afforded by the electron microscope over, the light microscope, and with knowledge gained from Golgi-staining for morphology, and intracellular electrophysiology for function of individual cells in the network.įig. Here bipolar cells talk to different varieties of functionally specialized amacrine cells and to dendrites of the various ganglion cells (Figs 1 and 2). ![]() The axonal endings of bipolar cells bring information from the outer plexiform layer (OPL) to the neuropil of the inner plexiform layer (IPL). Bipolar, amacrine and ganglion cells interact in the inner plexiform layer. The onset, the topography, and the developmental course of synaptogenesis correlate with the chronotopic course of maturation of retinal neurons and the age when spontaneous electrical activity occurs in the retina.1. The first synapses are formed close to the apex of the optic fissure and their frequency increases rapidly with age. Conventional chemical synapses appear in both plexiform layers on E8, in the inner plexiform layer (stage 34) only a few hours earlier than in the outer plexiform layer (stage 35). The first synapses are electrical synapses, which appear on E7, one day after the future inner plexiform layer emerged, and towards the end of E8 in the nascent outer plexiform layer. The study provides evidence that synaptogenesis in the chick retina begins shortly after the plexiform layers have started to emerge. Therefore, we investigated the chick retina from E6 to E12 at which age first synapses appear by transmission electron microscopy (TEM). The presently acknowledged onset of synaptogenesis in the chick retina from embryonic day 12 (E12) onward stands in contrast with the appearance of spontaneous electrical activity, of presynaptic proteins, or of neurotransmitters during early formation of the inner (E6-E8) and outer (E9) plexiform layers. ![]()
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