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Biomedical subjects

X L Yang

Publications and source records attributed to X L Yang.

At least 19 recordsLinked to original sources
PubMed1992

Modulation of synaptic gain by light.

Although synaptic transmission in the retina has been assumed to be static, it appears that the voltage gains of the synapses between photoreceptors and second-order cells can be enhanced by light. Voltage gains of the synapses between rods and bipolar (or horizontal) cells are about 10 times higher in the presence of dim background light than in darkness. This increase in synaptic gain may compensate for the loss of rod light responsiveness caused by weak background light so that the animal can maintain good rod sensitivity under moonlight or starlight, the natural lighting condition for mating and food catching.

Ambystoma↗
PubMed1992

Nonoperative treatment of membranous obstruction of the inferior vena cava by percutaneous balloon transluminal angioplasty.

Percutaneous transluminal angioplasty (PTA) was performed with the Inoue balloon catheter in nine patients with membranous obstruction of the inferior vena cava (MOVC) between November 1988 and April 1991. There were five men and four women, aged 30.8 +/- 8.5 years. Two patients had had previous surgical treatment. Three patients had complete and six had incomplete MOVC. The caval pressure below the MOVC was 24.0 +/- 5.6 and 11.8 +/- 5.3 mm Hg (p less than 0.0001) before and after PTA, respectively. The caval diameter at the site of MOVC increased from 1.5 +/- 1.7 to 20.3 +/- 2.6 mm (p less than 0.0001), and the maximal caval diameter below the MOVC decreased from 28.7 +/- 12.9 to 19.8 +/- 9.9 mm (p = 0.006), before and after PTA, respectively. One patient died of massive pulmonary embolism following successful PTA. All the other eight patients remained asymptomatic during an 18.5 +/- 11.5 months (range 3.5 to 32) follow-up period. Two-dimensional ultrasonograms showed no recurrence of MOVC. We conclude that PTA with the Inoue balloon catheter is an effective and safe alternative to surgical treatment of MOVC.

Adult↗
PubMed1992

Relationship of the cAMP-dependent protein kinase pathway to the SNF1 protein kinase and invertase expression in Saccharomyces cerevisiae.

The SNF1 protein kinase and the associated SNF4 protein are required for release of glucose repression in Saccharomyces cerevisiae. To identify functionally related proteins, we selected genes that in multicopy suppress the raffinose growth defect of snf4 mutants. Among the nine genes recovered were two genes from the cAMP-dependent protein kinase (cAPK) pathway, MSI1 and PDE2. Increased dosage of these genes partially compensates for defects in nutrient utilization and sporulation in snf1 and snf4 null mutants, but does not restore invertase expression. These results suggest that SNF1 and cAPK affect some of the same cellular responses to nutrients. To examine the role of the cAPK pathway in regulation of invertase, we assayed mutants in which the cAPK is not modulated by cAMP. Expression of invertase was regulated in response to glucose and was dependent on SNF1 function. Thus, a cAMP-responsive cAPK is dispensable for regulation of invertase.

Blotting, Northern↗
PubMed1992

Effects of neuropeptide Y injected into A1 noradrenergic nucleus on blood pressure and catecholamines in plasma of cats.

The microinjection of neuropeptide Y (NPY) 0.75 and 1.5 micrograms into A1 noradrenergic nucleus of cats produced dose-dependent falls in mean arterial blood pressure of 2.0 +/- 0.6 and 4.9 +/- 2.4 kPa, respectively. NPY microinjection (1.5 micrograms) also produced marked decreases in noradrenaline (5 +/- 4 pmol.ml-1) and adrenaline (23 +/- 8 pmol.ml-1), but no significant change in dopamine in blood plasma. The results suggest that the depressor effect of NPY in A1 noradrenergic nucleus may be realized by not only reducing the release of noradrenaline in sympathetic terminals around the peripheral vascular beds but also inhibiting the sympathetico-adrenal system.

Animals↗
PubMed1992

[Effects of prolonged darkness and background illumination on cone horizontal cells in carp retina: a correlative study of morphology and physiology].

Using intact, immobilized carp preparations, changes in light responsiveness of cone horizontal cells and ultrastructures of their terminals in cone pedicles (HCTs) were correlatively examined in prolonged (greater than 2 h) darkness and after the presentation of a dim background light. Following background illumination cone horizontal cells exhibit high light responsiveness and HCTs give rise to a lot of long, fingerlike or ball-like extensions, called slender or round spinules. When the retina is left in the dark for more than 2 h, the light responsiveness of these cells is depressed, which is accompanied by a dramatic decrease of spinules. Thus light responsiveness of the cone horizontal cells seems to be well correlated with the number of spinules. The results suggest that spinules may play an important role in regulating light responsiveness of cone horizontal cells following background illumination by altering the efficacy of signal transfer across the synapses between cone photoreceptors and cone horizontal cells.

Animals↗
PubMed1992

[The expression of kainate and GABA receptors in oocytes of Bufo bufo gargarizans].

Oocytes of Bufo bufo gargarizans were used as an expression system for analyzing structure of exogenous membrane protein and their functions. Poly (A)+ mRNA isolated from rat brain was injected into Toad (Bufo bufo gargarizans) oocytes (50 ng/oocyte). Rat brain kainic acid and gamma-aminobutyric acid(GABA) receptors expressed by the injected mRNA were integrated in the oocyte membrane 48 h after the injection at 19 degrees C. Membrane currents induced by kainic acid (5 x 10(-5) mol/L) and GABA (10(-4) mol/L) were 294.0 +/- 6.4 nA (n = 5) and 309.5 +/- 4.9 nA (n = 4) respectively. The kainic acid induced current reached its maximum value at about 10(-3) mol/L. Moreover, it was observed that the 36Cl- influx of the oocytes microinjected with mRNA was one-fold more rapid than the control oocytes. These results indicate that the oocytes of Bufo bufo gargarizans as those of Xenopus laevis can be used to express membrane proteins (receptors & transports) to acquire their proper functions from exogenous mRNA.

Animals↗
PubMed1992

[Central analgesic action of calcitonin and its relationship with central monoamine transmitters].

The analgesic action of calcitonin (0.25 MRC units.kg-1) injected into lateral cerebral ventricle was investigated in rats. The pain threshold was evaluated by the tail-flick test. The influences of icv naloxone 5 micrograms/rat, a blocker of opiate receptor, on the analgesic action of calcitonin were observed. The results showed that icv calcitonin produced a significant analgesic action, which was reversed by naloxone. While the pain threshold was raised by calcitonin, the contents of central monoamines (5-HT, NE, DA) in brain (diencephalon, brain stem) were examined by fluorophotometry, which were increased remarkably. It is suggested that calcitonin-induced analgesia is related to the opiate receptors and the contents of 5-HT, NE, and DA in CNS.

Analgesics↗
PubMed1992

Rod-cone interaction in carp retina: an analysis of electroretinographic B-waves.

Changes in electroretinographic b-wave in the presence of background lights of increasing intensity were examined in isolated, superfused carp retinas. Within a certain range of ambient illumination b-waves elicited by red (695 nm) test flashes against dimmer background lights were smaller in size than against brighter ones. Accordingly, incremental thresholds for red flashes decreased as the intensity of background lights increased within this intensity range. The results suggest that cone pathways may be suppressed by rods in darkness and dim illumination. The phenomenon was absent for photoreceptor potentials (PIII components), indicating that the rod-cone interaction occurs in second-order retinal neurons.

Animals↗
PubMed1991

Feedforward lateral inhibition in retinal bipolar cells: input-output relation of the horizontal cell-depolarizing bipolar cell synapse.

Lateral inhibition is the ubiquitous strategy used by visual neurons for spatial resolution throughout the animal kingdom. It has been a puzzle whether lateral inputs in retinal bipolar cells are mediated by the horizontal cell (HC)-cone feedback synapse, by the HC-bipolar cell feedforward synapse, or by both. By blocking the central inputs of the depolarizing bipolar cells (DBCs) with L-2-amino-4-phosphonobutyrate, we were able to eliminate the contribution of the feedback synapse and to demonstrate the postsynaptic light response in DBCs mediated by the HC-DBC feedforward synapse. The HC-DBC feedforward synapse contributes roughly one-third of the surround response whereas the HC-cone-DBC feedback synapse probably contributes the rest.

Ambystoma↗
PubMed1991

Modulation of synaptic transmission in the retina.

Synaptic transmission between photoreceptors and horizontal cells can be modulated in at least two domains: amplitude and time. In teleost fish, synaptic transmission is modulated mainly in the amplitude domain. Cone-driven horizontal cells in this species require background illumination to maintain high light responsiveness, and they are strongly suppressed in prolonged darkness. Moreover, in light, cone horizontal cells are extensively coupled via gap junctions, and the coupling is reduced in strength after prolonged darkness. The dopaminergic interplexiform cells play a major role in the regulation of cone horizontal cell activity. They may release dopamine tonically in darkness, which suppresses the light responsiveness of horizontal cells and uncouples them. In amphibians, whose horizontal cells receive input from both rods and cones, the modulation appears to be in the time domain, i.e., the rise time of horizontal cell responses is slow in prolonged darkness and accelerated after background illumination. gamma-aminobutyric acid and glycine may mediate the changes in response rise time. Despite the differences of the neuromodulators involved, these species provide two complementary modes of modulation of synaptic transmission in the retina.

Animals↗
PubMed1991

Coexistence and function of glutamate receptor subtypes in the horizontal cells of the tiger salamander retina.

Effects of the major glutamate receptor agonists, kainate (KA), alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA), quisqualate (QA), N-methyl-D-aspartate (NMDA), L-alpha-amino-4-phosphonobutyrate (L-AP4), and trans-1-aminocyclopentane-1,3-dicarboxylic acid (ACPD) on horizontal cells (HCs) were studied in superfused larval tiger salamander retina. 20 microM of KA, AMPA, and QA mimicked the action of 3 mM glutamate in the absence and presence of 1 mM Co2+. 20 microM 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) blocked the actions of KA and AMPA, but not those of QA and glutamate, indicative of the existence of CNQX-resistant QA receptors in the tiger salamander HCs. Prolonged application of ACPD hyperpolarized the HCs and enhanced the light responses, probably by shifting the resting HC voltage (Er) to a more hyperpolarized position. It is possible that the KA, AMPA, and CNQX-resistant QA receptors are involved in mediating the postsynaptic light responses in HCs, and ACPD receptors are involved in sensitivity adjustment of the HC responses.

Animals↗
PubMed1991

[Light adaptation properties of receptor potentials of cyprinid retina].

It was previously reported that changes in sensitivities of electroretinographic b-wave in the course of light adaptation depended on the intensity of background lights. B-wave sensitivity decreased with time by dimmer background lights, while it recovered during illumination with background lights of higher intensities. In this work we examined light adaptation properties of glutamate-isolated receptor potentials (P III components), using isolated and superfused cyprinid retinas. During dimmer background illumination, P III components were unchanged. When background lights were increased above certain levels, P III components showed partial recovery with time in the light. A detailed analysis of spectral sensitivities of P III components and their increment thresholds for several wavelengths indicated that the recovery of P III sensitivity appeared with background lights at which rod function was taken over by cone function. The results suggest that the recovery of b-wave sensitivity during brighter background illumination is partially a reflection of the adaptation property of cone photoreceptors.

Adaptation, Ocular↗
PubMed1991

Dark adaptation of horizontal cells in the teleost fish retina.

The dark adaptation behaviors of rod-driven and cone-driven horizontal cells were examined by analyzing their light responses recorded intracellularly in the intact, immobilized carp, and compared with that of the electroretinographic b-wave recorded simultaneously. Like the b-wave, the light responsiveness of rod horizontal cells increased gradually with time in the dark and attained a steady level at 60 min. On the other hand, cone horizontal cells initially increased in light responsiveness in the first 10 min, but thereafter decreased steadily so that the response amplitudes of these cells to bright light flashes were only 3-5 mV. The results suggest that cone horizontal cells are strongly suppressed in prolonged darkness.

Animals↗
PubMed1990

Developmental expression of plasminogen activator inhibitor type 1 by human alveolar macrophages. Possible role in lung injury.

Urokinase activity is regulated by the specific endogenous plasminogen activator inhibitors type 1 (PAI-1) and type 2 (PAI-2). One of these inhibitors, PAI-1, has been directly implicated in connective tissue metabolism by virtue of its ability to bind extracellular matrix proteins. Because the normal lung is relatively rich in urokinase and abnormalities in urokinase activity have been associated with fibrotic lung diseases, we have explored the possibility of local production of PAI-1 and PAI-2 in human lung. Reverse transcription and subsequent amplification by the polymerase chain reaction of total lung RNA revealed PAI-1 mRNA in each of three normal samples and in two specimens from patients with the adult respiratory distress syndrome (ARDS). In situ hybridizations of lung biopsy specimens from a patient with ARDS with cRNA probes to PAI-1 and PAI-2 indicated that alveolar macrophages express PAI-1 mRNA during the acute injury phase. Subsequent reverse transcription and PCR amplification of normal human monocyte and alveolar macrophage mRNA revealed that neither cell type expressed mRNA for urokinase inhibitors. However, after 24 h stimulation with endotoxin in vitro, monocytes were strongly positive for PAI-2 but negative for PAI-1 mRNA whereas, under the same conditions, alveolar macrophages exhibited mRNA for both PAI-1 and PAI-2. Metabolic labeling of endotoxin-stimulated alveolar macrophages with 35S-methionine followed by immunoprecipitation with PAI-1 and PAI-2 antibodies revealed that macrophages synthesized both PAI-1 and PAI-2. As judged by immunoprecipitation and functional studies, PAI-2 was found to be the major intracellular PA inhibitor whereas PAI-1 was found to predominate outside the cell. Thus, mononuclear phagocytes exhibit a developmental potential for PAI-1 expression. The release of PAI-1 by stimulated macrophages, as observed in the setting of ARDS, may be one mechanism by which these cells promote connective tissue accumulation.

Endotoxins↗
PubMed1990

Electroretinographic b-wave merely reflects the activity of the rod system in the dark-adapted carp retina.

The electroretinogram and responses of intermediate horizontal cells (IHCs) were recorded simultaneously and studied under dark-adapted conditions in intact crucian carp, with the hope of providing an answer to the controversy whether the scotopic b-wave contains contribution from both rods and cones. Our observations indicate that the dark-adapted b-wave follows the univariance principle perfectly in that: (1) b-wave forms and shapes of response amplitude vs light intensity relationships did not depend on the stimulus wavelength; (2) response amplitudes to flashes of mixed wavelengths agreed exactly with the values predicted in accordance with the univariance principle. Furthermore, the spectral sensitivity of the b-wave matched well that of the IHC, receiving input exclusively from rods. In consequence, we conclude that the dark-adapted b-wave merely reflects the activity of the rod system, and the discrepancy between the spectral sensitivities of the b-wave and IHC response compared with the absorption spectrum of the rod photopigment may be due to the self-screening effect caused by the high optical density of porphyropsin in situ.

Animals↗