Methoxyindoles of the retina

Melatonin and other 5-methoxyindoles are compounds usually associated with the pineal gland. Research is expanding from studies of pineal melatonin to studies of extrapineal organs and of other 5-methoxyindoles besides melatonin. Research in recent years has shown that the retina also contains and synthetises 5-methoxyindoles. The biochemical modes of action are still unclear. Nevertheless, they seem to have physiological roles in the pineal gland and the retina. These compounds are thought to participate in the regulation of the cyclic metabolism of the retina. Melatonin and other 5-methoxyindoles are often classified as neuromodulators.     

Hemopexin in the human retina: Protection of the retina against heme-mediated toxicity

The existence of the blood-retinal barrier means that proteins that protect the retina from damage by reactive oxygen species must either be made locally or specifically transported across the barrier cells; however, such transepithelial transport does not seem to occur. Among the circulatory proteins that protect against iron-catalyzed production of free radicals are apo-transferrin, which binds ferric iron and has previously been shown to be made by cells of the neural retina (Davis and Hunt, 1993, J. Cell Physiol., 156:280–285), and the extracellular antioxidant, apo-hemopexin, which binds free heme (iron-protoporphyrin IX). Since hemorrhage and heme release can be important contributing factors in retinal disease, evidence of a hemopexin-based retinal protection system was sought. The human retina has been shown to contain apo-hemopexin which is probably synthesized locally since its mRNA can be detected in retinal tissue dissected from human donor eyes. It is likely that the retina contains a mechanism for the degradation of hemopexin-bound heme since the blood-retinal barrier also precludes the exit of heme-hemopexin from the retina. Retinal pigment epithelial cells have been found to bind and internalize heme-hemopexin in a temperature-dependent, saturable, and specific manner, analogous to the receptor-mediated endocytic system of hepatoma cells. Moreover, the binding of heme-hemopexin to the cells stimulates the expression of heme oxygenase-1, metallothionein-1, and ferritin. © 1996 Wiley-Liss, Inc.     

A factor derived from chick embryo retina which inhibits DNA synthesis of retina itself

Chick embryo retinas contain a peptide factor that inhibits DNA synthesis in explants of chick embryo retina. The inhibitory factor, obtained by acid/ethanol extraction from 15-day-old chick embryo retinas, was partially purified by affinity chromatography on heparin-sepharose CL-6B and gel filtration on Sephadex G-100. The inhibitor reduced DNA synthesis with maximal effects observed in retinal explants from 7 to 8-day-old chick embryos. The inhibitory effect became apparent after 10 h of incubation and reached the maximum levels after 16 h. DNA-inhibiting activity was heat and acid-stable and was destroyed by trypsin and alkaline treatments. The inhibitory effect was observed in retinal explants incubated in a medium free froml-glutamine, and the addition of this compound to the medium reduced the inhibitory effect in a concentration-dependent manner.     

Response analysis of vertebrate retina

In a recent work (Ouztöreli, 1980) a mathematical model for studying the neural activities in a vertebrate retina has been investigated, where the basic network contains five interconnected neurons: a receptor cell, a bipolar cell, a horizontal cell, an amacrine cell, and a retinal ganglion cell. More recently, in (Ouztöreli and O'Mara, 1980) the basic network has been extended to a larger network containing twelve neurons. In both of these works, the performances of the basic and extended models were discussed under different structural and processing conditions with constant inputs by using the results of one of our earlier work (Ouztöreli, 1979). In the present paper we investigate by simulations the responses of the basic retinal network to piecewise constant and periodic inputs. The step and frequency responses of the extended retinal network will be discussed in a forthcoming paper.This work was partially supported by the Natural Sciences and Engineering Research Council of Canada under Grant A-4345 through the University of alberta     

Synchronized firing in the retina

Synchronized firing in neural populations has been proposed to constitute an elementary aspect of the neural code, but a complete understanding of its origins and significance has been elusive. Synchronized firing has been extensively documented in retinal ganglion cells, the output neurons of the retina. However, differences in synchronized firing across species and cell types have led to varied conclusions about its mechanisms and role in visual signaling. Recent work on two identified cell populations in the primate retina, the ON-parasol and OFF-parasol cells, permits a more unified understanding. Intracellular recordings reveal that synchronized firing in these cell types arises primarily from common synaptic input to adjacent pairs of cells. Statistical analysis indicates that local pairwise interactions can explain the pattern of synchronized firing in the entire parasol cell population. Computational analysis reveals that the aggregate impact of synchronized firing on the visual signal is substantial. Thus, in the parasol cells, the origin and impact of synchronized firing on the neural code may be understood as locally shared input which influences the visual signals transmitted from eye to brain.     

Adrenergic neurons in teleost retina

Summary The adrenergic retinal neurons of perch and trout were studied with the fluorescence microscopical method of Falck and Hillarp. Pilot studies were also performed on pike, plaice, cod, eel, goldfish, cunner, black moor, cichlid and carp. Only minor differences were noted between the species.Adrenergic varicose terminals occur in three sublayers of the inner plexiform layer. The layer adjacent to the ganglion cells is the most elaborate. Adrenergic perikarya occur in the innermost cell rows of the inner nuclear layer, sending branches to all sublayers of the inner plexiform layer. Adrenergic perikarya also occur among the ganglion cells, sending their branches to the innermost sublayer of adrenergic fibres in the inner plexiform layer. Weakly fluorescent adrenergic fibres can be seen running through the entire depth of the inner nuclear layer. They originate from the adrenergic perikarya of the inner nuclear layer, and they end in an elaborate plexus of adrenergic terminals among the horizontal cells. Either of the horizontal cell types can be in contact with adrenergic terminals, but the middle horizontal cells have the greatest density about them, being surrounded by baskets of adrenergic terminals of presumably synaptic character. It cannot be excluded that some horizontal cells contain a catecholamine.Microspectrofluometry revealed dopamine in the perch and trout retinal neurons.The research reported in this document has been sponsored by USPHS Grant No. 06092 and by a Research Professorship from Research to Prevent Blindness, Inc. to A.M.L. and by the Swedish Medical Research Council (B69-14X-712-04C and B68-14X-2321-01).