Spatial organization of detector neurons in the caudo-medial part of the frog tectum opticum

Investigation of the spatial organization of detector neurons of the frog tectum opticum showed that these neurons are mainly in the nuclear layers. When responding to a photic stimulus they form a mosaic of groups of synergically excited cells separated by inhibited or nonresponding neurons. Inhibited neurons are much more numerous than excited. Different photic stimuli (shaped or diffuse) evoke the appearance of mosaics of different structure; mosaics connected with different forms of detection are to a considerable degree stratified.Rostov State University. Research Institute of Neurocybernetics, Rostov-on-Don. Translated from Neirofiziologiya, Vol. 5, No. 5, pp. 468–475, September–October, 1973.     

Localization of Crystallins in Muller Cells of Common Frog Retina

Cell localization of 23 kDa- and 35 kDa-crystallins in the retina of adult common frogs Rana temporaria L. was studied using indirect immunofluorescence. Intense specific fluorescence of both crystallins was observed all over the retina, in both periphery and central area. It was localized in elongated radially oriented cells, whose bodies were located in the inner nuclear layer. These cells gave many fluorescing processes in the same layer and main processes in the outer nuclear and ganglion layers, one in each. The processes formed a strong network of fibers around the photoreceptor and ganglion cells. Intense fluorescence was also observed in the layer of nerve fibers and adjoining inner limiting membrane. The distribution and morphology of crystalline-containing cells mostly coincides with what is known for the Muller cells of vertebrate eye. The identity of the cells we described and Muller cells was also confirmed using the antiserum to glial fibrillary acidic protein.     

The retinal pigment epithelial cells of the adult newt and rat under conditions of in vitro organotypic culture

To understand why the retinal pigment epithelium (RPE) has different potentials for neural differentiation in lower and higher vertebrates, the RPEs of adult newts and rats were compared under similar in vitro cultivation conditions. The RPEs of both animal species were organotypically cultivated within the posterior eye wall under constant rotation in the serum medium free of growth factors. Comparison of the cell morphology, proliferation, and expression of pan-neural markers demonstrated that the RPE cells of adult newts and rats under similar in vitro conditions displayed both similarities and differemces. They were able to synthesize DNA but rarely divided mitotically. In addition, part of the RPE cells of both the newt and the rat were dislodged from the layer, migrated, and acquired a macrophage phenotype. However, the majority of the cells retained the initial morphology and remained within the layer. In several cases, these cells displayed the initial characteristics of neural differentiation, namely, expression of pan-neural proteins. The difference between the newt and rat RPE cells was in the ability of the former to generate in vitro an additional row of dedifferentiated NF-200-positive cells, characteristic of in vivo newt retinal regeneration. These data demonstrate that the RPE cells of the adult newt and rat retain the potential of manifesting neural cell traits; however, more advanced changes towards differentiation are characteristic of only the newt RPE.     

Spatiotemporal organization of unit activity in the frog tectum and its modification by visual stimuli

Unit activity was recorded in the tectum of curarized frogs during presentation of various visual stimuli (on- and off-responses to diffuse illumination and movement of an object of recognizable shape). It was shown that different types of stimulation lead to the organization of a different distribution of unit activity in the tectum, in the form of excitatory-inhibitory neuronal mosaics; inhibitory responses, limiting and exacerbating the excitatory responses of other neurons, predominate. The differences observed in the spatiotemporal characteristics of the neuronal mosaics under the influence of different stimuli may be evidence of specificity of coding of visual impulses carrying different information from the retina in the tectum.     

Role of the C-terminal fragment of human transthyretin in abnormal fibrillogenesis

Polypeptide chain fragments of recombinant transthyretin (TTR) with leucine-55 substituted by proline (L55P), which are involved in abnormal fibrillogenesis of this protein, were studied. No fibrils were produced in purified preparations of TTR(L55P) under the optimum conditions for fibrillogenesis but in absence of protease inhibitors. The ability of TTR for fibrillogenesis was lost because of a limited proteolysis resulting in detachment of the TTR polypeptide chain C-terminal fragment of approximately 18 amino acid residues in length. This proteolysis seemed to occur with involvement of a bacterial serine endopeptidase sohB (EC 3.4.21), which was identified in TTR preparations by the MALDI-TOF method. The presence of the C-terminal fragment of the TTR polypeptide chain seems to be crucial for production of abnormal fibrils.     

Visual information coding in the frog optic tectum

The possible mechanisms of visual information coding in the frog optic tectum were studied by extracellular recording of unit activity. It was postulated that information is coded spatially and that its precision is increased by the use of various types of time codes, making wide use in particular of differences in response latencies. These differences are also important on their own account, and they act as a component of the time codes (latency-frequency, latency-structural, and so on). The uniform distribution of neurons processing visual information and, in particular, analyzing the different parameters of visual signals (direction-velocity, lightness-darkness, and so on), among the structures of the tectum is evidence that the mechanism of analysis of the parameters of visual stimulus movement is distributive in type.Research Institute of Neurocybernetics, State University, Rostov-on-Don. Translated from Neirofiziologiya, Vol. 14, No. 1, pp. 26–34, January–February, 1982.