Outer plexiform layer

About: Outer plexiform layer is a research topic. Over the lifetime, 1465 publications have been published within this topic receiving 58015 citations.

Organization of the primate retina: electron microscopy.

Abstract: The retinae of monkey and man have been studied by electron microscopy to identify cell types, their processes and synaptic contacts. In the inner plexiform layer, the morphological characteristics of the three types of cells (bipolar, ganglion and amacrine) are described and seven synaptic relationships are identified. The bipolar terminals contain ribbons at points of synaptic contact, and, at these points, there are typically two postsynaptic processes, one a ganglion cell dendrite, the other an amacrine cell process. This synaptic arrangement is here termed a dyad. The amacrine cell processes themselves make synaptic contacts with ganglion cell dendrites and somata, other amacrine cell processes, and, most frequently, with the bipolar cell terminals. Often, the amacrine-bipolar contact is adjacent to a bipolar-amacrine junction, forming a reciprocal synaptic arrangement between the bipolar and the amacrine. In the more peripheral retina, large bipolar cell terminals (probably of rod bipolars) are occasionally observed adjacent to the perikarya of the ganglion cells. At these junctions, areas of fusion between the plasma membranes are seen, suggesting that such axosomatic junctions could be electrical. In the outer plexiform layer, synapses have been identified only in the receptor cell bases where receptor cells contact bipolar and horizontal cell processes. Synaptic contacts of the horizontal cells have not been clearly identified, but their strategic terminations in the receptor cell ending are described and interpreted as possibly synaptic. A model of the retina, based on the described anatomy, is presented and correlated with ganglion cell physiology.

Organization of the Primate Retina: Light Microscopy

Abstract: The structure of the human, but mainly of the rhesus monkey, retina as examined by Golgi-staining techniques is described and interpreted on evidence from both light and electron microscopy. One type of rod bipolar cell and two types of cone bipolar cell are recognized. The rod bipolar is exclusively connected to rods. The midget bipolar is postsynaptic to only one cone but each cone is also presynaptic to a diffuse cone (flat) bipolar. Such flat bipolar cells are in synaptic relationship with about seven cones. No other bipolar cell types have been found. The brush bipolar of Polyak is interpreted as probably a distorted rod bipolar, while Polyak's centrifugal bipolar is a misinterpretation of the morphology of diffuse amacrine cells. When presumptive centrifugal bipolars were observed they appeared to be a developmental stage of amacrine cells. In the outer plexiform layer two types of horizontal cell have been defined. Each type of horizontal cell has a single axon and two kinds of horizontal cell axon terminals are recognized. In the inner plexiform layer there are two main classes of amacrine cells: the stratified amacrines and the diffuse amacrines. Each class of amacrine has a wide variety of shapes. Polyak's midget ganglion cell is confirmed and his five other kinds of ganglion cell are classified into diffuse and stratified ganglion cells according to the level at which their dendrites branch within the inner plexiform layer. A fuller summary is given by the diagram and in the legend of figure 98, p. 174. A new type of midget bipolar is described in the Appendix (p. 177).

Cell death during differentiation of the retina in the mouse

Abstract: A reproducible pattern of cell death associated with differentiation of the retina in mice was analyzed quantitatively by microscopy. Cell death occurs primarily during the first 2 weeks after birth and is essentially complete by the end of the third week. Death of individual cells involves nuclear condensation and pyknosis (apoptosis), followed by phagocytosis of the cellular remains by adjacent cells or motile phagocytes. From birth through 4 days, an increasing incidence of cell death is observed among ventricular cells. Ganglion cell degeneration is prominent during the first 11 days, peaking on days 2-5. Many presumptive amacrine cells die within the inner plexiform and inner nuclear layers, particularly between 3 and 8 days. Among adjoining bipolar and Muller cells, degeneration reaches a peak at 8-11 days. On day 5, formation of the outer plexiform layer separates the rods into two groups. Rod nuclei situated on the inner side of that layer immediately move across it to enter the outer nuclear layer, but numerous cells die during nuclear migration. Sporadic death of rods continues during the following 2 weeks. Cell death associated with cell differentiation (histogenetic death) is considered to represent a normal developmental process. Possible mechanisms resulting in cell degeneration are discussed. It is suggested that genetically regulated cell death serves to fine-tune neuronal networks during the terminal stages of development.