Numbers on the left represent percent depth level in the IPL. Solid horizontal lines represent the inner and outer borders of the IPL, whereas dashed lines separate the 5 IPL strata. The question is how this lamination arises.įigure 4: Dendritic ramification depth of the 22 mouse RGC subtypes (From Volgi et al., 20009). In most mammals, these lamina-restricted distributions of RGC dendrites and synaptic connections are formed during pre- and post-natal development. Most of these RGCs have specific dendritic distribution in the IPL in adult retina as exemplified by the schematic (Figure 4) showing the branching patterns of mouse RGCs. Camera lucida drawings show the RGCs of mouse retina (Adapted from Volgi et al., 2009). See also RGCs of human, cat and rabbit retinas in the ganglion cell chapter in Webvision).įigure 3: About 22 subtypes of RGCs are present in the mammalian retina (See chapter on ganglion cells, Webvision). 3) illustrate the diversity of morphologies present in mammalian RGCs (Volgi et al., 2009. The wholemount drawings of mouse RGCs (Fig. In most mammals, RGCs can be divided into about 20 morphological subtypes based on their distinctive dendritic structure and synaptic connections (Kolb et al., 1981 1992 Badea and Nathans, 2004 Berson, 2008 Coombs et al., 2006 Dacey and Packer, 2003 Kong et al., 2005 Rockhill et al., 2002 Sun et al., 2002 Volgyi et al., 2009). Thus, the synaptic circuitries processing distinct visual features, the so called “parallel pathways” (Coombs and Chalupa, 2008 Famiglietti and Kolb, 1976 Ghosh et al. (Adapted from MacNeil and Masland, 1998). 2) (MacNeil and Masland, 1998) have their axonal/dendritic terminals in the specific sublaminae of the IPL, it is crucial that dendrites of individual RGCs are also confined to specific strata in order to synapses with them.įigure 2: Schematic drawings of some of the amacrine cells of rabbit retina to show each type has a characteristic morphology and stratification of the dendrites to specific strata (1-5) of the inner plexiform layer. Because different subtypes of bipolar cells (Fig 1) (Euler and Wässle, 1995) and amacrine cells (Fig. The axons of RGCs travel through the optic nerve to retinorecipient structures in the brain, where they transfer their specific aspects of visual information to the higher centers (Schiller, 2010). In the retina, RGCs synapse with bipolar and amacrine cells in the inner plexiform layer (IPL) to receive excitatory and inhibitory synaptic inputs respectively. Retinal ganglion cells (RGCs) are the output neurons of the retina. Similar ones have been observed in the rats (Euler and Wässle, 1995), rabbit, cat (Kolb et al., 1981 Cohen and Sterling, 1990), monkey (Boycott and Wässle, 1991) and human (Kolb et al., 1992). The morphological basis for the formation of these parallel synaptic pathways is the laminar-specific structure of the retina, in which specific subtypes of retinal neurons form synapses only with highly selective presynaptic and postsynaptic cells (Famiglietti and Kolb, 1976 Nelson et al., 1978 Schiller, 2010).įigure 1: The major subtypes of bipolar cells of primate retina (Adapted from Wässle, 2004). The neuronal information of the visual scene that is processed by the retina is conducted to the brain by a set of separate spatio-temporal synaptic pathways.
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