Search PubMed⌕ Search

Biomedical subjects

X L Yang

Publications and source records attributed to X L Yang.

At least 145 records · Page 8Linked to original sources
PubMed1988

Modulation of cone horizontal cell activity in the teleost fish retina. III. Effects of prolonged darkness and dopamine on electrical coupling between horizontal cells.

The effects of prolonged darkness and dopamine on the coupling between horizontal cells in the isolated, superfused white perch retina were studied. Two assays of coupling were employed; area versus amplitude relationships (area-response curves) and the diffusion of the fluorescent dye Lucifer yellow from intracellularly injected cells to neighboring cells. In prolonged dark-adapted retinas, area-response curves were difficult to determine because of the small light responses; however, light-evoked responses did not increase in size when light spots were larger than 0.8 mm in diameter. Following the presentation of dim background illumination that partially sensitized the retina, responses to light spots of various sizes were enhanced and an area-response curve could be constructed. Subsequent presentation of moderate background illumination that more fully sensitized the retina resulted in reduced responses to small spots (less than 1.6 mm in diameter) and enhanced responses to large spot or full-field stimuli. In retinas exposed to moderate background illumination, Lucifer yellow injected intracellularly into cone horizontal cells diffused into many neighboring horizontal cells. The coupled cells were very similar in morphology, suggesting they were of the same type. In prolonged dark-adapted retinas, on the other hand, the dye was usually restricted to the injected cell and a few adjacent cells. These results indicate that coupling between cone horizontal cells is modulated by prolonged darkness and background illumination. Following dopamine (50 microM) application, in both 6-OHDA-treated and untreated retinas, changes in area-response curves of cone horizontal cells were observed just opposite to those that occurred when prolonged dark-adapted retinas were exposed to background illumination. That is, following 5 min application of dopamine to the retina, responses to small spots (less than 2 mm in diameter) increased in size while responses to larger spots decreased in amplitude compared with control responses. Following 20 min of superfusion with dopamine, the recorded responses were very small, and an accurate area-response curve could not be determined. Following dopamine application to light-sensitized retinas, Lucifer yellow was restricted to the injected cells or to the injected cell and a few neighboring cells. The results suggest that the modulation of coupling between cone horizontal cells by prolonged darkness and background illumination may be mediated by dopamine. Spatial properties of rod horizontal cells were also examined.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1987

Photoreceptor inputs converging onto C-type horizontal cells of the retina of crucian carp.

Responses of R/G-type horizontal cells recorded intracellularly in eye cup preparations with normal circulation of crucian carp under dark-adapted conditions were studied and photoreceptor inputs converging onto them were identified. Spectral sensitivities of the hyperpolarizing component of responses, determined at different phases, suggested that it was produced by input from green-sensitive cones. This input and input from long wavelength sensitive cones, causing depolarization of cells, were almost linearly summated. Based on the linear summation assumption, an algebraic procedure was developed to isolate the depolarizing component from responses of R/G-type cells to flashes at wavelengths longer than 540 nm. Spectral sensitivities of the isolated depolarizing component were determined and agreed reasonably well with those of red-sensitive cones. Therefore, it is unlikely that depolarization of R/G-type cells may be due to input from some presumptive deep-red sensitive cones.

Animals↗
PubMed1987

Identification of new biphasic C-type horizontal cells in cyprinid fish.

New biphasic C-type horizontal cells were identified physiologically and morphologically in the retina of live immobilized crucian carp. These cells, like commonly studied R/G type cells, hyperpolarized to short wavelength lights and depolarized to long wavelength lights, but inverted response polarity at about 560 nm. Spectral sensitivities of hyperpolarizing and depolarizing components showed that they were produced by inputs from blue-sensitive cones and green-sensitive cones respectively. These cells are thus referred to as G/B type horizontal cells. Inputs from blue- and green-sensitive cones were not linearly summated, but interacted strongly at G/B type cells. G/B type cells stained intracellularly with HRP had smaller cell body and dendritic field, distinctly differing from R/G type cells.

Animals↗
PubMed1987

A computer-assisted study of quantitative morphological features of C type horizontal cells in retina.

Biphasic C type horizontal cells of the retina of crucian carp were intracellularly stained with horseradish peroxidase (HRP) and quantitatively studied with computer-aided three-dimensional reconstruction techniques. Several parameters characterizing their morphology were determined and compared among different subtypes of horizontal cells. The results show that both cell body area and horizontal extension are proper parameters by which different subtypes of biphasic horizontal cells can be clearly classified.

Animals↗
PubMed1985

An epidemiological investigation of minimal brain dysfunction in six elementary schools in Beijing.

Six elementary schools from urban, suburban and mountain areas of Beijing (containing 2770 school children) were screened with a standardized questionnaire and each suspected case was interviewed to determine whether diagnostic criteria were met for attention deficit disorder with hyperactivity (DSM-III), with some cultural modification. The MBD prevalence rate was 3.1% in the urban, 7.8% in the suburban and 7.0% in the mountain area. Lower rates were found in the families of scientific and technical professionals or in those with higher education than others. The mean score or the severity of some clinical manifestations of MBD children showed differences in families with different occupations or educational levels. Social environmental factors were considered to play an important role in the development of MBD, which is possibly based on biological factors.

Adolescent↗
PubMed1983

Convergence of signals from red-sensitive and green-sensitive cones onto L-type external horizontal cells of the goldfish retina.

The types of photoreceptors converging onto L-type external horizontal cells (LEHCs) were studied intracellularly in live, immobilized goldfish under dark-adapted conditions, and interactions between inputs from these photoreceptors were demonstrated. Our analysis of the color-dependence of response waveform, and the spectral sensitivity of LEHCs during various phases of their responses, suggests that LEHCs receive inputs not only from red-sensitive cones, but also from green-sensitive cones. Furthermore, inputs from red- and green-sensitive cones were found to interact so as to enhance LEHC responses. By presenting two successive flashes of different colors, the response enhancement was demonstrated only when green flashes preceded red flashes, indicating that responses to the input from green-sensitive cones affected the input from red-sensitive cones. A hypothetical model which incorporates reciprocal connections between green-sensitive cones and LEHCs is proposed, and shown to be consistent with most of the phenomena described in this paper, including the response enhancement.

Animals↗
PubMed1982

Quantitative analysis of photoreceptor inputs to external horizontal cells in the goldfish retina.

The types of photoreceptors converging onto L-type external horizontal cells (LEHCs) were identified, and their interactions studied, by analyzing responses recorded intracellularly in live, immobilized goldfish under dark-adapted conditions. Our observations indicate that LEHCs receive inputs from red-sensitive and green-sensitive cones, in that: (1) the response waveform differed markedly when elicited by shorter (less than 550 n m)-, as opposed to longer (greater than 600 nm)-, wavelength stimuli; (2) on plotting response amplitude vs. log stimulus intensity, the slope of the curves increased as the stimulus wavelengths were decreased, when the amplitude was measured at times greater than 100 msec after the onset of the flash; (3) the spectral sensitivity of LEHC responses, measured at times greater than 100 msec after stimulus onset, was intermediate between those of red-sensitive cones and green-sensitive cones; and (4) the amplitude of responses to flashes of mixed wavelengths differed from those predicted by the principle of univariance. When brief, red (706 nm) flashes were presented simultaneously with, or within 600 msec after brief, green (502 nm) flashes, the amplitudes of LEHC responses were significantly larger than predicted from linear summation of red and green inputs. Our observations thus indicate not only that red-sensitive and green-sensitive cones converge on the LEHC, but in addition, that their inputs interact to enhance LEHC responses. The enhancement might occur, at least in part, presynaptically.

Animals↗