Effects of electrical coupling on the cone-horizontal cell circuit in the catfish retina

Based on experimental data, a model of the cone-horizontal cell (L-HC) circuit has been developed for the luminosity channel of the catfish retina and impulse responses of cones and L-HC's were replicated for various experimental conditions. Negative feedback from L-HC to the cone pedicle and increases in the dc levels of L-HC (H ⁰), that produce increases in the feedback gain, convert monophasic impulse responses to those that are biphasic, smaller and faster. Electrical coupling of cones and L-HC's lead to decremental spread of 2 radially outgoing waves with time courses of the coupled cones and L-HC's dependent on the spatial organization of the negative feedback circuit: however, the L-HC's impulse response on spreading outward shows an initial increase before decreasing. Interactions of the cone and L-HC waves were studied using Laplace transforms and the convolution theorem. The presence of a negative feedback circuit leads to deviations of the electrotonic decay from an exponential function. As a result of the dependency of the feedback gain on H ⁰, electrical coupling introduces non-linearities in the cone-L-HC circuit that are dependent on the mean illuminance level.     

Dynamics of the cone-horizontal cell circuit in the turtle retina

The model of the catfish retina (Siminoff, in press) has been extended to the turtle retina with incorporation of color-coding. The turtle retina contains 6 types of cones of which 4 are red-sensitive and the other 2 are green-and blue-sensitive, respectively. The cone-horizontal circuit incorporates negative feedback from the L-HC to all the cones having input to the L-HC. By use of systems analysis, Laplace transforms and the convolution theorem, impulse responses, that give information as to gain and phase, for the cone-types and L-HC were simulated. As with the catfish retina, negative feedback gain was proportional to the dc level of the L-HC and therefore, the mean illuminance level. It was shown that this mechanism can be an important factor in chromatic adaptation, since the gains of the various cone-types are preferentially altered dependent on mean illuminance level and wavelength of the background light.     

Dopaminergic interplexiform cells contact photoreceptor terminals in catfish retina

Summary Dopaminergic interplexiform cells in retinae of glass catfish were investigated using an antiserum against tyrosine hydroxylase and peroxidase-anti-peroxidase (PAP) visualization. In whole-mount preparations, we observed a homogeneous distribution of cell bodies throughout the retina without any indication of regional specializations. At the ultrastructural level, we studied the morphology of labelled telodendria within the outer plexiform layer. Apart from contacts with horizontal cells and bipolar cell dendrites, we report for the first time direct contacts with cone pepdicles and rod spherules. Quantitative evaluation of short series of sections showed that all cone pedicles, and a major part of the rod terminals, were approached in this way. The dopaminergic pathway terminating on photoreceptors is discussed in the context of pharmacological effects of this transmitter in the distal retina during light adaptation, i.e., cone contraction, spinule formation and horizontal cell coupling.     

Cones in the retina of the catfish, Clarias batrachus (L.)

The retina of the catfish Clarias butrachus (L.), supposed to possess an all-rod retina, is found on re-investigation to contain both rods and cones. The retina is characterized by a prominent tapetum and multiple optic papillae.     

Modelling the effects of a negative feedback circuit from horizontal cells to cones on the impulse responses of cones and horizontal cells in the catfish retina

A model of the cone-L-HC circuit for the catfish retina is presented with the following features: the outer segment consists of a compression factor and 7 low-pass filters in tandem; the cone pedicle consists of an internal negative feedback circuit in series with a low-pass filter; and the L-HC consists of a low-pass filter and forms a negative feedback circuit with the cone pedicle. By proper adjustment of the various time constants of the low-pass filters and the gain factors, the impulse responses for cones and L-HCs of the catfish retina (and turtle) can be duplicated. The negative feedback gain increases with increasing levels of mean illuminance which causes the monophasic impulse responses to become faster, biphasic and decrease in amplitude, i.e. in gain. This is an expression of the Weber-Fechner law.     

Landolt's club in the retina of catfish, Heteropneustes fossilis: a new finding in Teleostei

The visual cells in the retina of the freshwater catfish, Heteropneustes fossilis comprise rods, long single cones, short single cones and Landolt's clubs.     

Morphogenesis of blood cell lineages in channel catfish

The morphogenesis of blood cell lineages in channel catfish Ictalurus punctatus , from head and trunk kidney and spleen imprints as well as from blood smears of bled and control fish, showed that early maturation stages resembled those in higher vertebrates. The erythroid lineage consisted of the proerythroblast, erythroblasts (basophilic, polychromatic, orthochromic), young erythrocyte and erythrocyte. The rare bilobed erythrocyte seemed to be a cell in apoptosis while old erythrocytes and erythroplastids represented remnants of this process. Maturation stages of neutrophils and basophils encompassed the granuloblast, young progranulocyte, progranulocyte and metagranulocyte. The basophilic lineage was regularly present in kidneys, rare in spleen and absent from blood. It contained large Sudan Black and PAS-negative, water soluble granules and small PAS-positive ones. Lymphocytes with azurophilic granulation occured regularly in kidneys and spleen. Monoblasts and promonocytes in kidneys preceded monocytes. A phagocytic lineage devouring apoptotic blood cell remnants was present in kidneys and spleen. Its youngest identified stage (promacrophage) resembled more a granuloid cell without granules than a monocytoid one. The larger, young macrophages contained a few to several ingestions and the very large mature macrophages were loaded with them. The latter two stages corresponded to cells in melano-macrophage centres (macrophage aggregates). Precursor stages of the thrombocyte were not identified.     

klumpfuss regulates cell death in the Drosophila retina

Programmed cell death (PCD) plays a central role in the sculpting and maturation of developing epithelia. In adult tissue, PCD plays a further role in the prevention of malignancy though removal of damaged cells. Here, we report that mutations in klumpfuss result in an excess of support cells during maturation of the developing Drosophila pupal retina. These ectopic cells are the result of a partial and specific failure of apoptotic death during normal cell fate selection. klumpfuss is required and differentially expressed in the cells that choose the life or death cell fate. We also provide genetic and biochemical evidence that klumpfuss regulates this process through down-regulation of the Epidermal Growth Factor Receptor/dRas1 signaling pathway. Based on its sequence Klumpfuss is an EGR-class nuclear factor, and our results suggest a mechanism by which mutations in EGR-class factors such as Wilms' Tumor Suppressor-1 may result in oncogenic events such as pediatric kidney tumors.     

视网膜双极细胞的突触传递

双极细胞是视网膜中处于信号传递的直接通路中的中间神经元,以带型突触传递由分级电位编码的视觉信号。近年来,应用膜电容测定、钙光成像等技术,对双极细胞递质释放的特点及动力学特性进行了细致的研究,不仅有助于阐明这些细胞独特的生理功能,也对了解以带型突触传递信号的感觉神经元的功能特性提供了启示。     

Dynamics of the ganglion cell response in the catfish and frog retinas

Responses were evoked from ganglion cells in catfish and frog retinas by a Gaussian modulation of the mean luminance. An algorithm was devised to decompose intracellularly recorded responses into the slow and spike components and to extract the time of occurrence of a spike discharge. The dynamics of both signals were analyzed in terms of a series of first-through third-order kernels obtained by cross-correlating the slow (analog) or spike (discrete or point process) signals against the white-noise input. We found that, in the catfish, (a) the slow signals were composed mostly of postsynaptic potentials, (b) their linear components reflected the dynamics found in bipolar cells or in the linear response component of type-N (sustained) amacrine cells, and (c) their nonlinear components were similar to those found in either type-N or type-C (transient) amacrine cells. A comparison of the dynamics of slow and spike signals showed that the characteristic linear and nonlinear dynamics of slow signals were encoded into a spike train, which could be recovered through the cross-correlation between the white-noise input and the spike (point process signals. In addition, well-defined spike correlates could predict the observed slow potentials. In the spike discharges from frog ganglion cells, the linear (or first-order) kernels were all inhibitory, whereas the second-order kernels had characteristics of on-off transient excitation. The transient and sustained amacrine cells similar to those found in catfish retina were the sources of the nonlinear excitation. We conclude that bipolar cells and possibly the linear part of the type-N cell response are the source of linear, either excitatory or inhibitory, components of the ganglion cell responses, whereas amacrine cells are the source of the cells' static nonlinearity.     

Local nonuniformities in the horizontal cell syncytium of the turtle retina

Electrical coupling between horizontal cells of the turtle retina was investigated by means of two microelectrodes, stimulating and recording, inserted into neighboring cells at a fixed horizontal distance apart. Morphological coupling was estimated by studying the flow of the luminescent dye Lucifer yellow. The presence of electrical coupling was confirmed between structures of the same type (L₁ with axon terminals, L₂ withcell bodies, R/G with cells of color type) and absence of coupling between cells of different types was confirmed, although L₁ and L₂ are connected with each other directly by thin axons. The degree of electrical coupling in the syncytium of axon terminals (L₁), with a short (50 µ or less) but fixed distance between the electrodes, may vary by several times depending on the position of the microelectrodes. This local nonuniformity of coupling can be explained by the structural nonuniformity of the network of interconnected axon terminals. Local structural nonuniformities can hardly affect the functional properties of the horizontal cell syncytium under the conditions of photic stimulation of the retina.Institute of Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 17, No. 2, pp. 239–245, March–April, 1985.     

Bacterial cell cycle: completing the circuit

Recent advances in understanding bacterial cell-cycle regulation suggest circuit control mechanisms that operate analogously to those in the eukaryotic cell cycle.     

Ganglion cell axon pathfinding in the retina and optic nerve

The eye is a highly specialized structure that gathers and converts light information into neuronal signals. These signals are relayed along axons of retinal ganglion cells (RGCs) to visual centers in the brain for processing. In this review, we discuss the pathfinding tasks RGC axons face during development and the molecular mechanisms known to be involved. The data at hand support the presence of multiple axon guidance mechanisms concentrically organized around the optic nerve head, each of which appears to involve both growth-promoting and growth-inhibitory guidance molecules. Together, these strategies ensure proper optic nerve formation and establish the anatomical pathway for faithful transmission of information between the retina and the brain.