Allosteric modulation of retinal GABA receptors by ascorbic acid

Ionotropic GABA receptors (GABAA and GABAC) belong to the Cys-loop receptor family of ligand-gated ion channels. GABAC receptors are highly expressed in the retina, mainly localized at the axon terminals of bipolar cells. Ascorbic acid, an endogenous redox agent, modulates the function of diverse proteins, and basal levels of ascorbic acid in the retina are very high. However, the effect of ascorbic acid on retinal GABA receptors has not been studied. Here we show that the function of GABAC and GABAA receptors is regulated by ascorbic acid. Patch-clamp recordings from bipolar cell terminals in goldfish retinal slices revealed that GABAC receptor-mediated currents activated by tonic background levels of extracellular GABA, and GABAC currents elicited by local GABA puffs, are both significantly enhanced by ascorbic acid. In addition, a significant rundown of GABA puff-evoked currents was observed in the absence of ascorbic acid. GABA-evoked Cl- currents mediated by homomeric ρ1 GABAC receptors expressed in Xenopus laevis oocytes were also potentiated by ascorbic acid in a concentration-dependent, stereo-specific, reversible, and voltage-independent manner. Studies involving the chemical modification of sulfhydryl groups showed that the two Cys-loop cysteines and histidine 141, all located in the ρ1 subunit extracellular domain, each play a key role in the modulation of GABAC receptors by ascorbic acid. Additionally, we show that retinal GABAA IPSCs and heterologously expressed GABAA receptor currents are similarly augmented by ascorbic acid. Our results suggest that ascorbic acid may act as an endogenous agent capable of potentiating GABAergic neurotransmission in the CNS.Fil: Calero, Cecilia Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres"; ArgentinaFil: Vickers, Evan. Oregon Health and Science University; Estados UnidosFil: Cid, Gustavo Moraga. Universidad de Concepción; ChileFil: Aguayo, Luis G.. Universidad de Concepción; ChileFil: von Gersdorff, Henrique. Oregon Health and Science University; Estados UnidosFil: Calvo, Daniel Juan. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres"; Argentin

Hemichannel-Mediated and pH-Based Feedback from Horizontal Cells to Cones in the Vertebrate Retina

Background: Recent studies designed to identify the mechanism by which retinal horizontal cells communicate with cones have implicated two processes. According to one account, horizontal cell hyperpolarization induces an increase in pH withinthe synaptic cleft that activates the calcium current (Ca2+-current) in cones, enhancing transmitter release. An alternative account suggests that horizontal cell hyperpolarization increases the Ca2+-current to promote transmitter release through ahemichannel-mediated ephaptic mechanism.Methodology/Principal Findings: To distinguish between these mechanisms, we interfered with the pH regulating systems in the retina and studied the effects on the feedback responses of cones and horizontal cells. We found that the pH buffers HEPES and Tris partially inhibit feedback responses in cones and horizontal cells and lead to intracellular acidification ofneurons. Application of 25 mM acetate, which does not change the extracellular pH buffer capacity, does lead to both intracellular acidification and inhibition of feedback. Because intracellular acidification is known to inhibit hemichannels, the key experiment used to test the pH hypothesis, i.e. increasing the extracellular pH buffer capacity, does not discriminatebetween a pH-based feedback system and a hemichannel-mediated feedback system. To test the pH hypothesis in a manner independent of artificial pH-buffer systems, we studied the effect of interfering with the endogenous pH buffer, the bicarbonate/carbonic anhydrase system. Inhibition of carbonic anhydrase allowed for large changes in pH in the synapticcleft of bipolar cell terminals and cone terminals, but the predicted enhancement of the cone feedback responses, according to the pH-hypothesis, was not observed. These experiments thus failed to support a proton mediated feedback mechanism. The alternative hypothesis, the hemichannel-mediated ephaptic feedback mechanism, was therefore studied experimentally, and its feasibility was buttressed by means of a quantitative computer model of the cone/horizontal cellsynapse.Conclusion: We conclude that the data presented in this paper offers further support for physiologically relevant ephaptic interactions in the retina

The Impossibility of a Perfectly Competitive Labor Market

Using the institutional theory of transaction cost, I demonstrate that the assumptions of the competitive labor market model are internally contradictory and lead to the conclusion that on purely theoretical grounds a perfectly competitive labor market is a logical impossibility. By extension, the familiar diagram of wage determination by supply and demand is also a logical impossibility and the neoclassical labor demand curve is not a well-defined construct. The reason is that the perfectly competitive market model presumes zero transaction cost and with zero transaction cost all labor is hired as independent contractors, implying multi-person firms, the employment relationship, and labor market disappear. With positive transaction cost, on the other hand, employment contracts are incomplete and the labor supply curve to the firm is upward sloping, again causing the labor demand curve to be ill-defined. As a result, theory suggests that wage rates are always and everywhere an amalgam of an administered and bargained price. Working Paper 06-0

Large expert-curated database for benchmarking document similarity detection in biomedical literature search

Document recommendation systems for locating relevant literature have mostly relied on methods developed a decade ago. This is largely due to the lack of a large offline gold-standard benchmark of relevant documents that cover a variety of research fields such that newly developed literature search techniques can be compared, improved and translated into practice. To overcome this bottleneck, we have established the RElevant LIterature SearcH consortium consisting of more than 1500 scientists from 84 countries, who have collectively annotated the relevance of over 180 000 PubMed-listed articles with regard to their respective seed (input) article/s. The majority of annotations were contributed by highly experienced, original authors of the seed articles. The collected data cover 76% of all unique PubMed Medical Subject Headings descriptors. No systematic biases were observed across different experience levels, research fields or time spent on annotations. More importantly, annotations of the same document pairs contributed by different scientists were highly concordant. We further show that the three representative baseline methods used to generate recommended articles for evaluation (Okapi Best Matching 25, Term Frequency-Inverse Document Frequency and PubMed Related Articles) had similar overall performances. Additionally, we found that these methods each tend to produce distinct collections of recommended articles, suggesting that a hybrid method may be required to completely capture all relevant articles. The established database server located at https://relishdb.ict.griffith.edu.au is freely available for the downloading of annotation data and the blind testing of new methods. We expect that this benchmark will be useful for stimulating the development of new powerful techniques for title and title/abstract-based search engines for relevant articles in biomedical research.Peer reviewe

Effects of Anacetrapib in Patients with Atherosclerotic Vascular Disease

BACKGROUND: Patients with atherosclerotic vascular disease remain at high risk for cardiovascular events despite effective statin-based treatment of low-density lipoprotein (LDL) cholesterol levels. The inhibition of cholesteryl ester transfer protein (CETP) by anacetrapib reduces LDL cholesterol levels and increases high-density lipoprotein (HDL) cholesterol levels. However, trials of other CETP inhibitors have shown neutral or adverse effects on cardiovascular outcomes. METHODS: We conducted a randomized, double-blind, placebo-controlled trial involving 30,449 adults with atherosclerotic vascular disease who were receiving intensive atorvastatin therapy and who had a mean LDL cholesterol level of 61 mg per deciliter (1.58 mmol per liter), a mean non-HDL cholesterol level of 92 mg per deciliter (2.38 mmol per liter), and a mean HDL cholesterol level of 40 mg per deciliter (1.03 mmol per liter). The patients were assigned to receive either 100 mg of anacetrapib once daily (15,225 patients) or matching placebo (15,224 patients). The primary outcome was the first major coronary event, a composite of coronary death, myocardial infarction, or coronary revascularization. RESULTS: During the median follow-up period of 4.1 years, the primary outcome occurred in significantly fewer patients in the anacetrapib group than in the placebo group (1640 of 15,225 patients [10.8%] vs. 1803 of 15,224 patients [11.8%]; rate ratio, 0.91; 95% confidence interval, 0.85 to 0.97; P=0.004). The relative difference in risk was similar across multiple prespecified subgroups. At the trial midpoint, the mean level of HDL cholesterol was higher by 43 mg per deciliter (1.12 mmol per liter) in the anacetrapib group than in the placebo group (a relative difference of 104%), and the mean level of non-HDL cholesterol was lower by 17 mg per deciliter (0.44 mmol per liter), a relative difference of -18%. There were no significant between-group differences in the risk of death, cancer, or other serious adverse events. CONCLUSIONS: Among patients with atherosclerotic vascular disease who were receiving intensive statin therapy, the use of anacetrapib resulted in a lower incidence of major coronary events than the use of placebo. (Funded by Merck and others; Current Controlled Trials number, ISRCTN48678192 ; ClinicalTrials.gov number, NCT01252953 ; and EudraCT number, 2010-023467-18 .)

Synthesis, Characterization, Surface Tailoring, and Applications of Hollow Gold Nanospheres and Perovskite Nanomaterial

Two-photon photoluminescence (2PPL) together with hollow gold nanosphere’s (HGN's) photothermal properties are utilized as a single theranostic agent for cancer. HGNs bioconjugated with folic acid-PEG-thiol (HGN-FA) selectively bind to the overexpressed folate receptor of cervical cancer HeLa cells and the 2PPL from HGN-FA captures high-resolution cancer cells images using multiphoton microscopy. Subsequent power increase and laser scanning dwell time results in highly efficient photothermal destruction of cancer cells. Using femtosecond laser pulses, microseconds of laser exposure generates well-localized superheating of HGNs, yielding subcellular thermal damage and cell death.The following chapters transition to the synthesis and characterization of colloidal and solid film perovskite quantum dots (PQDs). Important hindrances for commercialization of PQD solid film in optoelectronic devices are insufficient charge transport and long-term stability. This is mostly contributed to their lack of charge transfer in PQD solid films and degradation in the presence of moisture, oxygen, heat, and light. These hindrances can be overcome by exploring different surface ligand passivation strategies and understanding their functionality associated with PQD solid film's optical, electronic, and electrical properties. Enhancing the charge transport properties of PQDs is dependent on mitigating the tunneling barrier which is imposed by the distance charges must travel between PQDs. Using long alkyl chain passivating ligands instills greater stability, however, a diminishment in charge transport. Moreover, short alkyl chain or counter ion passivation leads to instability but improved charge transport. To overcome these inversely related properties, an effective strategy to mitigate the charge tunneling barrier and simultaneously provide stability is passivating with exciton-delocalization ligands (EDLs). EDLs consist of π delocalizing orbitals that hybridize with the electronic wave function of PQDs. This enables charges to delocalize to the PQD’s surface and eliminates the tunneling barrier imposed by surface ligands. The following chapters discuss the dependence of charge transport and stability of PQD solid film on the capping ligand chain length, and then, the investigations of using EDLs for enhancing the optical and charge transport properties of PQD solid film. The final chapter discusses the synthesis of perovskite magic sized clusters (PMSCs). Specifically, the ligand dependence of their growth and optical properties. Here, PMSCs are synthesized using an excess amount of capping ligands. The two different ligand combinations used to synthesized PMSCs are butylamine-valeric acid (BTYA-VA) and 3,3-diphenylpropylamine-valeric acid (DPPA-VA). These PMSCs were observed to have the bluest shifted absorption and PL peaks that correspond to their smallest stable size. For BTYA-VA PMSCs, the excitonic absorption peak is at 424 nm and PL peak at 434 nm, while the DPPA-VA PMSCs exhibited an absorption peak at 428 nm and PL peak at 451 nm. Due to the shift in absorption, the size of PMSCs is determined to be ligand dependent. In addition, it was discovered that different size PQDs can be synthesized from DPPA-VA PMSCs that correspond to a specific dilution. This method to precisely tune size, and hence, optical properties simply by dilution may provide a more exact and facile synthesis of PQDs

Synthesis, Characterization, Surface Tailoring, and Applications of Hollow Gold Nanospheres and Perovskite Nanomaterial

Two-photon photoluminescence (2PPL) together with hollow gold nanosphere’s (HGN's) photothermal properties are utilized as a single theranostic agent for cancer. HGNs bioconjugated with folic acid-PEG-thiol (HGN-FA) selectively bind to the overexpressed folate receptor of cervical cancer HeLa cells and the 2PPL from HGN-FA captures high-resolution cancer cells images using multiphoton microscopy. Subsequent power increase and laser scanning dwell time results in highly efficient photothermal destruction of cancer cells. Using femtosecond laser pulses, microseconds of laser exposure generates well-localized superheating of HGNs, yielding subcellular thermal damage and cell death.The following chapters transition to the synthesis and characterization of colloidal and solid film perovskite quantum dots (PQDs). Important hindrances for commercialization of PQD solid film in optoelectronic devices are insufficient charge transport and long-term stability. This is mostly contributed to their lack of charge transfer in PQD solid films and degradation in the presence of moisture, oxygen, heat, and light. These hindrances can be overcome by exploring different surface ligand passivation strategies and understanding their functionality associated with PQD solid film's optical, electronic, and electrical properties. Enhancing the charge transport properties of PQDs is dependent on mitigating the tunneling barrier which is imposed by the distance charges must travel between PQDs. Using long alkyl chain passivating ligands instills greater stability, however, a diminishment in charge transport. Moreover, short alkyl chain or counter ion passivation leads to instability but improved charge transport. To overcome these inversely related properties, an effective strategy to mitigate the charge tunneling barrier and simultaneously provide stability is passivating with exciton-delocalization ligands (EDLs). EDLs consist of π delocalizing orbitals that hybridize with the electronic wave function of PQDs. This enables charges to delocalize to the PQD’s surface and eliminates the tunneling barrier imposed by surface ligands. The following chapters discuss the dependence of charge transport and stability of PQD solid film on the capping ligand chain length, and then, the investigations of using EDLs for enhancing the optical and charge transport properties of PQD solid film. The final chapter discusses the synthesis of perovskite magic sized clusters (PMSCs). Specifically, the ligand dependence of their growth and optical properties. Here, PMSCs are synthesized using an excess amount of capping ligands. The two different ligand combinations used to synthesized PMSCs are butylamine-valeric acid (BTYA-VA) and 3,3-diphenylpropylamine-valeric acid (DPPA-VA). These PMSCs were observed to have the bluest shifted absorption and PL peaks that correspond to their smallest stable size. For BTYA-VA PMSCs, the excitonic absorption peak is at 424 nm and PL peak at 434 nm, while the DPPA-VA PMSCs exhibited an absorption peak at 428 nm and PL peak at 451 nm. Due to the shift in absorption, the size of PMSCs is determined to be ligand dependent. In addition, it was discovered that different size PQDs can be synthesized from DPPA-VA PMSCs that correspond to a specific dilution. This method to precisely tune size, and hence, optical properties simply by dilution may provide a more exact and facile synthesis of PQDs

LTP of inhibition at PV interneuron output synapses requires developmental BMP signaling

Parvalbumin (PV)-expressing interneurons (PV-INs) mediate well-timed inhibition of cortical principal neurons, and plasticity of these interneurons is involved in map remodeling of primary sensory cortices during critical periods of development. To assess whether bone morphogenetic protein (BMP) signaling contributes to the developmental acquisition of the synapse- and plasticity properties of PV-INs, we investigated conditional/conventional double KO mice of BMP-receptor 1a (BMPR1a; targeted to PV-INs) and 1b (BMPR1a/1b (c)DKO mice). We report that spike-timing dependent LTP at the synapse between PV-INs and principal neurons of layer 4 in the auditory cortex was absent, concomitant with a decreased paired-pulse ratio (PPR). On the other hand, baseline synaptic transmission at this connection, and action potential (AP) firing rates of PV-INs were unchanged. To explore possible gene expression targets of BMP signaling, we measured the mRNA levels of the BDNF receptor TrkB and of P/Q-type Ca; 2+; channel α-subunits, but did not detect expression changes of the corresponding genes in PV-INs of BMPR1a/1b (c)DKO mice. Our study suggests that BMP-signaling in PV-INs during and shortly after the critical period is necessary for the expression of LTP at PV-IN output synapses, involving gene expression programs that need to be addressed in future work