Nonsteaming method improves the nutritional value and utilization efficiency of silkworm artificial diets

Artificial diets for silkworms overcome the seasonal limitations of traditional rearing methods with fresh mulberry leaves. However, the current wet artificial diets, steamed at high temperatures, are not favored by silkworms, and they are cumbersome and challenging to preserve. These conditions adversely affected the development of artificial diet-based sericulture production. In this study, we disinfected dry powder diets with radiation and added distilled water without steaming before use. Then, the nutritional value of finished diets and their impact on silkworm development was assessed. Compared with steamed diets, nonsteamed diets were more attractive to silkworms. Chemical assays showed significantly more essential nutrients for silkworms, including l-ascorbic acid, vitamin B1, vitamin B2, and urease in nonsteamed diets than in steamed diets. Feeding fifth-instar silkworm larvae with nonsteamed diets significantly improved the ammonia utilization efficiency of the diet and increased the cocoon shell rate and diet/silk protein conversion efficiency by 5.9% and 13.3%, respectively. When fed with nonsteamed diets, the abundance of aerobic microorganisms in silkworm intestines increased and the abundance of pathogenic bacteria decreased. Furthermore, the vitality of the silkworm, measured by the dead worm cocoon rate, significantly improved by 16.90%. In summary, preparing sterile wet diets without high-temperature steaming effectively improved the nutritional value of the diet and enhanced silkworm growth.

Tuning Electrocatalytic Water Oxidation Activity: Insights from the Active-Site Distance in LnCu6 Clusters

Atomically precise metal clusters serve as a unique model for unraveling the intricate mechanism of the catalytic reaction and exploring the complex relationship between structure and activity. Herein, three series of water-soluble heterometallic clusters LnCu6, abbreviated as LnCu6-AC (Ln = La, Nd, Gd, Er, Yb; HAC = acetic acid), LnCu6-IM (Ln = La and Nd; IM = Imidazole), and LnCu6-IDA (Ln = Nd; H2IDA = Iminodiacetic acid) are presented, each featuring a uniform metallic core stabilized by distinct protected ligands. Crystal structure analysis reveals a triangular prism topology formed by six Cu2+ ions around one Ln3+ ion in LnCu6, with variations in Cu···Cu distances attributed to different ligands. Electrocatalytic oxygen evolution reaction (OER) shows that these different LnCu6 clusters exhibit different OER activities with remarkable turnover frequency of 135 s-1 for NdCu6-AC, 79 s-1 for NdCu6-IM and 32 s-1 for NdCu6-IDA. Structural analysis and Density Functional Theory (DFT) calculations underscore the correlation between shorter Cu···Cu distances and improves OER catalytic activity, emphasizing the pivotal role of active-site distance in regulating electrocatalytic OER activities. These results provide valuable insights into the OER mechanism and contribute to the design of efficient homogeneous OER electrocatalysts.

Soluble Gd6Cu24 clusters: effective molecular electrocatalysts for water oxidation

The water oxidation half reaction in water splitting for hydrogen production is extremely rate-limiting. This study reports the synthesis of two heterometallic clusters (Gd6Cu24-IM and Gd6Cu24-AC) for application as efficient water oxidation catalysts. Interestingly, the maximum turnover frequency of Gd6Cu24-IM in an NaAc solution of a weak acid (pH 6) was 319 s-1. The trimetallic catalytic site, H2O-GdIIICuII2-H2O, underwent two consecutive two-electron two-proton coupled transfer processes to form high-valent GdIII-O-O-CuIII2 intermediates. Furthermore, the O-O bond was formed via intramolecular interactions between the CuIII and GdIII centers. The results of this study revealed that synergistic catalytic water oxidation between polymetallic sites can be an effective strategy for regulating O-O bond formation.

The clock gene Cryptochrome 1 is involved in the photoresponse of embryonic hatching behavior in Bombyx mori

The hatching of insect eggs is a classic circadian behavior rhythm controlled by the biological clock. Its function is considered to impose a daily rhythm on the embryo, allowing it to hatch within a permissible time window. However, the molecular pathways through which the clock affects embryonic hatching behavior remain unclear. Here, we utilized a clock gene Cryptochrome1 (Cry1) knockout mutant to dissect the pathways by which the circadian clock affects embryonic hatching rhythm in the silkworm. In the Cry1 mutant, the embryo hatching rhythm was disrupted. Under the constant light or constant dark incubation conditions, mutant embryos lost their hatching rhythm, while wild-type embryos hatch exhibiting free-running rhythm. In the light-dark cycle (LD), the hatching rhythm of CRY1-deficient silkworms could not be entrained by the LD photoperiod during the incubation period. The messenger RNA levels and enzymatic activities of Cht and Hel in the mutant embryos were significantly reduced at circadian time 24 (CT24). Transcriptome analysis revealed significant differences in gene expression at CT24 between the Cry1 knockout mutant and the wild-type, with 2616 differentially expressed genes identified. The enriched Gene Ontology pathway includes enzyme activity, energy availability, and protein translation. Short neuropeptide F signaling was reduced in the CT24 embryonic brain of the mutant, the expression of the neuropeptide PTTH was also reduced and the rhythm was lost, which further affects ecdysteroid signaling. Our results suggested that the silkworm circadian clock affects neuropeptide-hormone signaling as well as physiological functions related to hatching, which may regulate the hatching rhythm.

Total Structure, Electronic Structure and Catalytic Hydrogenation Activity of Metal-Deficient Chiral Polyhydride Cu57 Nanoclusters

Accurate identifying and in-depth understanding of the defect sites in a working nanomaterial could hinge on establishing specific defect-activity relationships. Yet, atomically precise coinage-metal nanoclusters (NCs) possessing surface vacancy defects are scarce primarily owing to challenges in the synthesis and isolation of such defective NCs. Herein we report a mixed-ligand strategy to synthesizing an intrinsically chiral and metal-deficient copper hydride-rich NC [Cu57 H20 (PET)36 (TPP)4 ]+ (Cu57 H20 ). Its total structure (including hydrides) and electronic structure are well established by combined experimental and computational results. Crystal structure reveals Cu57 H20 features a cube-like Cu8 kernel embedded in a corner-missing metal-ligand shell of Cu49 (PET)36 (TPP)4 . Single Cu vacancy defect site occurs at one corner of the shell, evocative of mono-lacunary polyoxometalates. Theoretical calculations demonstrate that the above-mentioned point vacancy causes one surface hydride exposed as an interfacial capping μ3 -H- , which is accessible in chemical reaction, as proved by deuterated experiment. Moreover, Cu57 H20 shows catalytic activity in the hydrogenation of nitroarene. The success of this work opens the way for the research on well-defined chiral metal-deficient Cu and other metal NCs, including exploring their application in asymmetrical catalysis.

Functional analysis of a miRNA-like small RNA derived from Bombyx mori cytoplasmic polyhedrosis virus

Bombyx mori cytoplasmic polyhedrosis virus (BmCPV) is a major pathogen of the economic insect silkworm, Bombyx mori. Virus-encoded microRNAs (miRNAs) have been proven to play important roles in host-pathogen interactions. In this study we identified a BmCPV-derived miRNA-like 21 nt small RNA, BmCPV-miR-1, from the small RNA deep sequencing of BmCPV-infected silkworm larvae by stem-loop quantitative real-time PCR (qPCR) and investigated its functions with qPCR and lentiviral expression systems. Bombyx mori inhibitor of apoptosis protein (BmIAP) gene was predicted by both target prediction software miRanda and Targetscan to be one of its target genes with a binding site for BmCPV-miR-1 at the 5' untranslated region. It was found that the expression of BmCPV-miR-1 and its target gene BmIAP were both up-regulated in BmCPV-infected larvae. At the same time, it was confirmed that BmCPV-miR-1 could up-regulate the expression of BmIAP gene in HEK293T cells with lentiviral expression systems and in BmN cells by transfecting mimics. Furthermore, BmCPV-miR-1 mimics could up-regulate the expression level of BmIAP gene in midgut and fat body in the silkworm. In the midgut of BmCPV-infected larvae, BmCPV-miR-1 mimics could be further up-regulated and inhibitors could lower the virus-mediated expression of BmIAP gene. With the viral genomic RNA segments S1 and S10 as indicators, BmCPV-miR-1 mimics could up-regulate and inhibitors down-regulate their replication in the infected silkworm. These results implied that BmCPV-miR-1 could inhibit cell apoptosis in the infected silkworm through up-regulating BmIAP expression, providing the virus with a better cell circumstance for its replication.

Silver clusters templated by homo- and hetero-anions

This article highlights the use of homo- and hetero-anion templates for the ordered assembly of high-nuclearity silver clusters.

[Anatomical relationship between fascia propria of the rectum and visceral pelvic fascia in the view of continuity of fasciae]

Objective: To perform an anatomical observation on the extension of the mesocolon to the mesorectum and the continuity of the fasciae lining the abdomen and pelvis, in order to clarify the appropriate surgical plane of total mesorectal excision. Methods: This is an descriptive study. The operation videos of 61 cases (28 males, 33 females, median age of 61) were collected. All the patients underwent laparoscopic colorectal surgery from January 2018 to December 2018 in Yangpu Hospital, including low anterior resection for rectal cancer in 25 cases, left hemicolectomy for descending colon cancer in 15 cases, and subtotal resection of the colon for intractable constipation in 21 cases. Among these 21 constipation patients, 8 received additional modified Duhamel surgeries. Gross anatomy was performed on 24 adult cadavers provided by Department of Anatomy, Shanghai Jiaotong University School of Medicine, including 23 formalin-fixed and 1 fresh cadaver (12 males, 12 females). Sixty-one patients and 24 cadavers had no previous abdominal or pelvic surgical history. The anatomy and extension of fasciae related to descending colon, sigmoid colon and rectum, especially the morphology of Toldt fascia, and the continuities of mesocolon and mesorectum were observed carefully. The distribution characteristics of the fasciae and anatomical landmarks during laparoscopic surgery were recorded and described. Results: The anatomical study on 24 cadavers showed that visceral fascia was the densest connective tissue in the pelvic, posterolateral to the rectum, and stretched as a hammock to lift all pelvic organs. Among 61 patients undergoing laparoscopic surgery, 36 (59.0%) needed to free the left colon during operation, and Toldt fascia in the descending colon segment presented as potential, avascular and extensible loose connective tissue plane between the mesocolon and posterior Gerota fascia; 33 (54.1%) needed to free the rectum during operation, and Toldt fascia extended downward to pelvis as loose connective tissue between the fascia propria of the rectum and visceral fascia; the fascia propria of the rectum exposed completely in 32 (32/33, 97.0%) cases, which ran downward and fused with visceral fascia at the level of the fourth sacral vertebra. The anatomy of 24 cadavers also showed that fascia propria of the rectum fused with visceral fascia at the level of Waldeyer fascia. The fusion line of these two fasciae was supposed to be the extension of Waldeyer fascia. There were two avascular planes behind the rectum: one between the fascia propria of the rectum and visceral fascia, and the other between the visceral fascia and parietal fascia. In 8 constipation cases undergoing laparoscopic subtotal colon resection plus modified Duhamel operation, both mesocolon and mesorectum needed to be mobilized. It was obvious that the mesocolon of descending colon extended and became the mesocolon of sigmoid colon, and ran further into the pelvic and became the mesorectum. The colon fascia of descending colon served as the natural boundary of mesocolon extended downward as the fascia of sigmoid colon and the fascia propria of the rectum, respectively. Toldt fascia locating between mesocolon of descending colon and Gerota fascia extended to pelvis as the 'presacral space' between the fascia propria of the rectum and visceral fascia. Gerota fascia in descending colon segment extended as urogenital fascia in sigmoid colon segment and visceral fascia in the pelvis, respectively. In the cadaver anatomy study, the visceral fascia served as a corridor carrying the hypogastric nerve, and ureter was observed in 23 (23/24, 95.8%) cases. The visceral fascia passed from posterior to anterior lateral of rectum, fusing with Denonvilliers fascia in a fan shape. The pelvic plexus located exactly external to the junction of visceral fascia and Denonvilliers fascia. Pelvic splanchnic nerves went through the parietal fascia toward to the inferolateral of the pelvic plexus. Conclusion: Fascia propria of the rectum and the visceral pelvic fascia are two independent layers of fascia, and the TME surgical plane is between the fascia propria of the rectum and visceral pelvic fascia instead of between the visceral and the parietal pelvic fascia.

Tethered sensitizer-catalyst noble-metal-free molecular devices for solar-driven hydrogen generation

Inspired by natural photosynthesis in an organized assembly, compact H2-evolving molecular devices, which tether sensitizer and catalyst modules in one single molecule, present an opportunity to overcome the diffusion limit required for multi-component molecular systems, and increase intramolecular electron transfer rates from the photoactivated unit to the catalytic center to improve H2-evolving efficiency. Thereinto absolutely noble-metal free H2-evolving molecular devices are of particular interest because they don't contain precious and scarce noble-metal based components. This Frontier article focuses specifically on the recent advances in the design, synthesis, and photocatalytic properties of all-abundant-element molecular devices for photoinduced H2 generation via intramolecular processes. Some challenges and suggestions for future directions in this field are also illustrated.

A review of the genus Atrovirensis Kononenko, 2001 with description of four new species from China (Lepidoptera, Noctuidae: Xyleninae, Apameini)

The genus Atrovirensis Kononenko, 2001 is reviewed. Four new species (Atrovirensis parannamita sp. n., Atrovirensis furcatus sp. n., Atrovirensis sacculatus sp. n. and Atrovirensis miraculosus sp. n.) are described from China. A new combination Atrovirensis euplexina (Draudt, 1950), comb. n. [Valeria] is proposed. Two taxa of uncertain status (Atrovirensis sp. cf. parannamita and Atrovirensis sp. cf. furcatus) are included to the review. The updated checklist of the genus is presented. All taxa of the genus Atrovirensis are illustrated in colour with black and white photographs of their genitalia in 48 figures.

dsRNA interference on expression of a RNA-dependent RNA polymerase gene of Bombyx mori cytoplasmic polyhedrosis virus

Bombyx mori cytoplasmic polyhedrosis virus (BmCPV) is one of the major viral pathogens in silkworm. Its infection often results in significant losses to sericulture. Studies have demonstrated that RNAi is one of the important anti-viral mechanisms in organisms. In this study, three dsRNAs targeting the RNA-dependent RNA polymerase (RDRP) gene of BmCPV were designed and synthesized with 2'-F modification to explore their interference effects on BmCPV replication in silkworm larvae. The results showed that injecting dsRNA in the dosage of 4-6 ng per mg body weight into the 5th instar larvae can interfere with the BmCPV-RDRP expression by 93% after virus infection and by 99.9% before virus infection. In addition, the expression of two viral structural protein genes (genome RNA segments 1 and 5) was also decreased with the decrease of RDRP expression, suggesting that RNAi interference of BmCPV-RDRP expression could affect viral replication. The study provides an effective method for investigating virus replication as well as the virus-host interactions in the silkworm larvae using dsRNA.

A simple BODIPY-aniline-based fluorescent chemosensor as multiple logic operations for the detection of pH and CO2gas

4-Aniline BODIPY dye was developed as a highly sensitive fluorescent chemosensor for the detection of pH and CO₂gas.

Experimental and theoretical study of enol–keto prototropic tautomerism and photophysics of azomethine–BODIPY dyads

Enol ↔ keto prototropic tautomerism can be exploited to modulate the photophysics of BODIPY chromophores based on proton-coupled photoinduced electron transfer processes.

T-type Ca(2+) channels mediate neurotransmitter release in retinal bipolar cells

Transmitter release in neurons is thought to be mediated exclusively by high-voltage-activated (HVA) Ca(2+) channels. However, we now report that, in retinal bipolar cells, low-voltage-activated (LVA) Ca(2+) channels also mediate neurotransmitter release. Bipolar cells are specialized neurons that release neurotransmitter in response to graded depolarizations. Here we show that these cells express T-type Ca(2+) channel subunits and functional LVA Ca(2+) currents sensitive to mibefradil. Activation of these currents results in Ca(2+) influx into presynaptic terminals and exocytosis, which we detected as a capacitance increase in isolated terminals and the appearance of reciprocal currents in retinal slices. The involvement of T-type Ca(2+) channels in bipolar cell transmitter release may contribute to retinal information processing.

[The development and mechanism of the argon ion high-frequency combined electrotome]

This article gives you a brief introduction about the main functions and general structure of Argon Ion high-frequency combined electrotome which can reduce hemorrhage in operation, prevent uncontrollable bloold-oozing, shorten the time of operation and decrease the risk of cross-infection. It also recommends some key technologies in the system, especially the use of a computer to monitor and control the system for the security and reliability of the system.

Structure and function of GABA(C) receptors: a comparison of native versus recombinant receptors

In less than a decade our knowledge of the GABA(C) receptor, a new type of Cl(-)-permeable ionotropic GABA receptor, has greatly increased based on studies of both native and recombinant receptors. Careful comparison of properties of native and recombinant receptors has provided compelling evidence that GABA receptor rho-subunits are the major molecular components of GABA(C) receptors. Three distinct rho-subunits from various species have been cloned and the pattern of their expression in the retina, as well as in various brain regions, has been established. The pharmacological profile of GABA(C) receptors has been refined and more specific drugs have been developed. Molecular determinants that underlie functional properties of the receptors have been assigned to specific amino acid residues in rho-subunits. This information has helped determine the subunit composition of native receptors, as well as the molecular basis underlying subtle variations among GABA(C) receptors in different species. Finally, GABA(C) receptors play a unique functional role in retinal signal processing via three mechanisms: (1) slow activation; (2) segregation from other inhibitory receptors; and (3) contribution to multi-neuronal pathways.

Voltage-activated Ca2+ channels and ionotropic GABA receptors localized at axon terminals of mammalian retinal bipolar cells

A preparation of isolated presynaptic terminals of rat retinal rod bipolar cells was developed. Patch-clamp recordings were performed on the isolated terminal to determine the type(s) of voltage-activated Ca2+ channels and the contribution of GABA(A) and GABA(C) receptor-mediated currents localized in the terminal region. Both low-voltage-activated (LVA) and high-voltage-activated (HVA) Ca2+ currents, with properties similar to those found in intact cell recordings, were observed in the isolated terminal recordings. Consistent with previous studies, the HVA Ca2+ currents are L-type since the currents were blocked by low micromolar concentrations of nimodipine and potentiated by BayK 8644. Also, both GABA(A) and GABA(C) receptor-mediated currents were observed in the isolated terminal. The current density of GABA(C) receptors in the terminal was more than three times higher than that in the soma. In contrast, the current density of GABA(A) currents between the terminal and the soma was not significantly different. Assessed by 100 microM GABA, the contributions of GABA(A) and GABA(C) receptors to the total GABA-mediated currents at the terminal were comparable. This study directly demonstrates the localization of LVA Ca2+ channels at the axon terminal of mammalian rod bipolar cells, suggesting that LVA Ca2+ channels may play a role in bipolar cell transmitter release. Results of this study also support the notion that both types of ionotropic GABA receptors regulate synaptic transmission in mammalian rod bipolar cells. In addition, this study reports for the first time the feasibility of direct patch-clamp recordings of isolated axon terminals of mammalian retinal bipolar cells. The isolated presynaptic terminal preparation of mammalian retinal bipolar cells could be a valuable system for the study of transmitter release in the central nervous system (CNS).

Voltage-dependent Na(+) currents in mammalian retinal cone bipolar cells

Voltage-dependent Na(+) channels are usually expressed in neurons that use spikes as a means of signal coding. Retinal bipolar cells are commonly thought to be nonspiking neurons, a category of neurons in the CNS that uses graded potential for signal transmission. Here we report for the first time voltage-dependent Na(+) currents in acutely isolated mammalian retinal bipolar cells with whole cell patch-clamp recordings. Na(+) currents were observed in approximately 45% of recorded cone bipolar cells but not in rod bipolar cells. Both ON and OFF cone bipolar cells were found to express Na(+) channels. The Na(+) currents were activated at membrane potentials around -50 to -40 mV and reached their peak around -20 to 0 mV. The half-maximal activation and steady-state inactivation potentials were -24.7 and -68.0 mV, respectively. The time course of recovery from inactivation could be fitted by two time constants of 6.2 and 81 ms. The amplitude of the Na(+) currents ranged from a few to >300 pA with the current density in some cells close or comparable to that of retinal third neurons. In current-clamp recordings, Na(+)-dependent action potentials were evoked in Na(+)-current-bearing bipolar cells by current injections. These findings raise the possibility that voltage-dependent Na(+) currents may play a role in bipolar cell function.

Evidence for coassembly of mutant GABAC rho1 with GABAA gamma2S, glycine alpha1 and glycine alpha2 receptor subunits in vitro

Functional coassembly of gamma-aminobutyric acid (GABA)C rho1 subunits with GABAA (alpha1, beta2, and gamma2S) or glycine (alpha1, alpha2, and beta) subunits was examined using two-electrode voltage-clamp recordings in the Xenopus laevis oocyte expression system. To facilitate this study, we took advantage of the unique gating and pharmacological properties of two mutant rho1 subunits, rho1(T314A) and rho1(T314A/L317A). When the rho1(T314A) subunit was coexpressed with GABA gamma2S, glycine alpha1 or glycine alpha2 subunits, GABA response properties were different from those of homomeric rho1(T314A) receptors. Additionally, the sensitivity of heteromeric rho1(T314A) and gamma2S receptors to picrotoxinin (PTX) blockade of GABA-evoked responses was altered compared to that of homomeric rho1(T314A) receptors. Changes in GABA response properties and picrotoxinin sensitivity were also observed when rho1(T314A) subunits were coexpressed with wild-type rho1 subunits. When rho1(T314A/L317A) subunits were coexpressed with GABA gamma2S, glycine alpha1 or glycine alpha2 subunits, suppression by GABA of spontaneously active current was reduced compared to that of homomeric rho1(T314A/L317A) receptors. Recovery of the spontaneous current from inhibition by GABA for GABA rho1(T314A/L317A)/gamma2S heteromeric receptors displayed an additional component. Coinjection of wild-type rho1 with gamma2S cRNAs at a ratio of 1 : 1 resulted in a > 10-fold reduction in GABA-evoked current. Furthermore, coexpression of wild-type rho1 and gamma2S subunits was found to shift the GABA dose-response curve. Our results provide functional evidence that the GABAC rho1 subunit can coassemble with the GABAA gamma2S subunit, and, at least in its mutated form, rho1 can also form heteromeric receptors with glycine alpha1 or alpha2 subunits in vitro.

Redox modulation of recombinant human GABA(A) receptors

We previously reported that GABA-evoked currents of rat retinal ganglion cells were modulated by redox agents. In this study, we further characterized the effects of redox modulation on GABA receptors using recombinant human subunits in the Xenopus oocyte expression system with two-electrode voltage-clamp recording. GABA receptors composed of subunits alpha(1-3), beta(1-3), gamma(1), gamma(2S,) and rho(1) were expressed. The sulfhydryl reducing agent dithiothreitol reversibly potentiated the responses of various combinations of functional recombinant GABA(A) subunits, whether expressed as triplets (alpha(1)beta(1-3)gamma(1,2S)), pairs (alpha(1-3)beta(1-3); beta(1-3)gamma(1,2S)), or singly (beta(2)). These effects of dithiothreitol were rapidly reversible, and the oxidizing agent 5-5'-dithiobis-2-nitrobenzoic acid exerted the opposite effect. In contrast to these effects on GABA(A) receptors, dithiothreitol had no effect on the responses of homomeric GABA rho(1) (GABA(C)) receptors. The degree of dithiothreitol potentiation of GABA(A) receptor responses depended on subunit composition. Co-expression of gamma(2S) with alpha(1)beta(1-3) subunits resulted in markedly less dithiothreitol potentiation of GABA-evoked currents than that observed for alpha(1-3)beta(1-3) subunits in the absence of gamma(2S). None the less, the magnitude of dithiothreitol potentiation could be restored by using a combination of lower GABA concentrations (5-10 microM) and higher dithiothreitol concentrations (5-20mM). N,N,N', N'-tetrakis(2-pyridyl-methyl)ethylenediamine, a high-affinity Zn(2+) chelator, also potentiated GABA(A) receptor currents. However, the potentiation produced by 10mM dithiothreitol was larger than that produced by saturating concentrations of N,N,N', N'-tetrakis(2-pyridyl-methyl)ethylenediamine (100 microM), implying that at least part of the effect of dithiothreitol was due to redox modulation rather than Zn(2+) chelation. Dithiothreitol also potentiated the spontaneous current of homomeric GABA(A) receptors composed of beta subunits. Mutation of a single cysteine residue in the M3 domain, yielding homomeric beta(3)(C313A) receptors, abrogated dithiothreitol potentiation of the spontaneous current. In summary, this study further characterizes the modulatory effects of redox agents on recombinant GABA(A) receptors. The degree of redox modulation of GABA(A) receptors depended on subunit composition. In contrast to their effect on GABA(A) receptors, redox agents were not found to modulate GABA(C) receptors composed of homomeric rho(1) subunits. Using site-directed mutagenesis, a cysteine residue was located in the beta(3) subunit which may comprise one of the redox-active sites that underlies the modulation of heteromeric GABA(A) receptors by reducing and oxidizing agents.

Differential expression of high- and two types of low-voltage-activated calcium currents in rod and cone bipolar cells of the rat retina

Whole cell voltage-clamp recordings were performed to investigate voltage-activated Ca(2+) currents in acutely isolated retinal bipolar cells of rats. Two groups of morphologically different bipolar cells were observed. Bipolar cells of the first group, which represent the majority of isolated bipolar cells, were immunoreactive to protein kinase C (PKC) and, therefore likely to be rod bipolar cells. Bipolar cells of the second group, which represent only a small population of isolated bipolar cells, did not show PKC immunoreactivity and were likely to be cone bipolar cells. The validity of morphological identification of bipolar cells was further confirmed by the presence of GABA(C) responses in these cells. Bipolar cells of both groups displayed low-voltage-activated (LVA) Ca(2+) currents with similar voltage dependence of activation and steady-state inactivation. However, the activation, inactivation, and deactivation kinetics of the LVA Ca(2+) currents between rod and cone bipolar cells differed. Particularly, the LVA Ca(2+) currents of rod bipolar cells displayed both transient and sustained components. In contrast, the LVA Ca(2+) currents of cone bipolar cells were mainly transient. In addition, the LVA Ca(2+) channels of rod bipolar cells were more permeable to Ba(2+) than to Ca(2+), whereas those of cone bipolar cells were equally or less permeable to Ba(2+) than to Ca(2+). The LVA Ca(2+) currents of both rod and cone bipolar cells were antagonized by high concentrations of nimodipine with IC(50) of 17 and 23 microM, respectively, but largely resistant to Cd(2+) and Ni(2+). Bipolar cells of both groups also displayed high-voltage-activated (HVA) Ca(2+) currents. The HVA Ca(2+) currents were, at least in part, to be L-type that were potentiated by BayK-8644 (1 microM) and largely antagonized by low concentrations of nimodipine (5 microM). The L-type Ca(2+) channels were almost exclusively located at the axon terminals of rod bipolar cells but expressed at least in the cell soma of cone bipolar cells. Results of this study indicate that rod and cone bipolar cells of the mammalian retina differentially express at least two types of LVA Ca(2+) channels. Rod and cone bipolar cells also show different spatial distribution of L-type Ca(2+) channels.

Agonist-induced closure of constitutively open gamma-aminobutyric acid channels with mutated M2 domains

Ligand-gated ion channels display a fundamental property-channels remain virtually closed at rest and open upon agonist binding. Here we show that substituting alanines for either of two amino acid residues (T314 or L317) in the M2 region of the gamma-aminobutyric acid (GABA) rho1 subunit results in spontaneous channel opening in the absence of ligand. Surprisingly, for two single point mutants (T314A or L317A), application of very low concentrations of agonist partially suppressed this spontaneous current, while higher concentrations re-activated the receptors. When both of these sites were mutated (T314A/L317A), GABA nearly completely suppressed the constitutive current and did not re-activate the current even at very high concentrations. This study provides important new insights into the structure-function relationship of ligand-gated ion channels, where modification of the structure of the channel pore region not only alters the allosteric transition of the receptor protein but also reverses the polarity of agonist regulation of channel gating. Our results suggest that the sites where these two residues are located are structurally critical for channel gating.

Nitric oxide-related species inhibit evoked neurotransmission but enhance spontaneous miniature synaptic currents in central neuronal cultures

Nitric oxide (NO.) does not react significantly with thiol groups under physiological conditions, whereas a variety of endogenous NO donor molecules facilitate rapid transfer to thiol of nitrosonium ion (NO+, with one less electron than NO.). Here, nitrosonium donors are shown to decrease the efficacy of evoked neurotransmission while increasing the frequency of spontaneous miniature excitatory postsynaptic currents (mEPSCs). In contrast, pure NO donors have little effect (displaying at most only a slight increase) on the amplitude of evoked EPSCs and frequency of spontaneous mEPSCs in our preparations. These findings may help explain heretofore paradoxical observations that the NO moiety can either increase, decrease, or have no net effect on synaptic activity in various preparations.

Cloning of a gamma-aminobutyric acid type C receptor subunit in rat retina with a methionine residue critical for picrotoxinin channel block

Ionotropic receptors for gamma-aminobutyric acid (GABA) are important to inhibitory neurotransmission in the mammalian retina, mediating GABAA and GABAC responses. In many species, these responses are blocked by the convulsant picrotoxinin (PTX), although the mechanism of block is not fully understood. In contrast, GABAC responses in the rat retina are extremely resistant to PTX. We hypothesized that this difference could be explained by molecular characterization of the receptors underlying the GABAC response. Here we report the cloning of two rat GABA receptor subunits, designated r rho 1 and r rho 2 after their previously identified human homologues. When coexpressed in Xenopus oocytes, r rho 1/r rho 2 heteromeric receptors mimicked PTX-resistant GABAC responses of the rat retina. PTX resistance is apparently conferred in native heteromeric receptors by r rho 2 subunits since homomeric r rho 1 receptors were sensitive to PTX; r rho 2 subunits alone were unable to form functional homomeric receptors. Site-directed mutagenesis confirmed that a single amino acid residue in the second membrane-spanning region (a methionine in r rho 2 in place of a threonine in r rho 1) is the predominant determinant of PTX resistance in the rat receptor. This study reveals not only the molecular mechanism underlying PTX blockade of GABA receptors but also the heteromeric nature of native receptors in the rat retina that underlie the PTX-resistant GABAC response.

Multiple GABA receptor subtypes mediate inhibition of calcium influx at rat retinal bipolar cell terminals

Inhibitory effects of GABA on K(+)-evoked Ca2+ influx into rat retinal bipolar cell terminals were studied using calcium imaging methods. Application of high K+ evokes a sustained, reversible increase in [Ca2+]i at bipolar cell terminals, which occurs mainly via dihydropyridine-sensitive (L-type) Ca2+ channels. There are at least two GABA receptor subtypes coexisting at bipolar cell terminals: a conventional GABAA receptor and a bicuculline/baclofen-insensitive GABA receptor. Activation of either GABA receptor inhibited the K(+)-evoked Ca2+ response. However, these two GABA receptor subtypes have distinct properties. GABAA receptors suppress the Ca2+ response only at relatively high concentrations of agonist, and with fas kinetics and a narrow dynamic range. In contrast, the bicuculline/baclofen-insensitive GABA receptors produce inhibition on the Ca2+ response at a much lower concentration of agonist, and with slow onset and a wider dynamic range. The pharmacologic profile of the bicuculline/baclofen-insensitive GABA receptor at bipolar cell terminals is most similar to the GABAC receptor reported by Feigenspan et al. (1993). Unlike the GABAC receptors described in other species, it is extremely insensitive to picrotoxin. Therefore, it may be appropriate to refer to this receptor as a picrotoxin-insensitive GABAc receptor. 3-Aminopropyl(methyl)phosphinic acid (3-APMPA) and 3-aminopropylphosphonic (3-APA), two phosphate analogs of GABA, selectively antagonize the picrotoxin-insensitive GABAc receptors but not the GABAA receptors in this system. These results imply a functional role for multiple GABA receptors in regulating synaptic transmission at bipolar cell terminals.

Differential modulation by sulfhydryl redox agents and glutathione of GABA- and glycine-evoked currents in rat retinal ganglion cells

Some areas of the mammalian CNS, such as the retina, contain not one but two fast inhibitory neurotransmitter systems whose actions are mediated by GABA and glycine. Each inhibitory receptor system is encoded by a separate gene family and has a unique set of agonists and antagonists. Therefore, in rat retinal ganglion cells we were surprised to find that a single agent, extracellular glutathione, was capable of modulating currents activated by either GABAA or glycine receptor stimulation. Both oxidized and reduced glutathione influence inhibitory neurotransmission in a manner similar to that of the sulfhydryl redox agents dithiothreitol (DTT) and 5,5'-dithio-bis-(2-nitrobenzoic acid) (DTNB). Remarkably, the actions of glutathione are diametrically opposed on the GABAA and glycine systems. In whole-cell recordings of single retinal ganglion cells with patch pipettes, reduced glutathione enhances GABA-evoked currents but decreases glycine-evoked currents. These findings suggest that endogenous redox agents, such as glutathione, may constitute a novel modulatory system for the differential regulation of inhibitory neurotransmission in the mammalian retina.

Comparison of the actions of glycine and related amino acids on isolated third order neurons from the tiger salamander retina

Whole cell voltage and current clamp recordings were obtained from third order neurons isolated from the salamander retina. Using cross desensitization, the structure-function relationship of short chain amino acids on the glycine receptor were examined. L-Serine, L-alanine, beta-alanine and taurine all cross desensitized with glycine, but did not show significant cross desensitization with GABA. This indicates that these amino acids act at the glycine receptor. The order of potency was glycine >> beta-alanine > taurine >> L-alanine > L-serine. TAG, a reputed selective taurine antagonist, was equally effective in blocking taurine and glycine currents. There is no evidence for distinct receptors for taurine. Amino acids with larger moieties at the alpha carbon, such as threonine and valine, produced inactive ligands. Placing a methyl group on the amine of glycine or esterification of the carboxyl group also greatly reduced activity. Based on these modifications of the glycine molecule, it appears that selectivity at the glycine receptor results in part from steric restrictions at all three sites in the glycine chain. The steric interference is most critical at the carboxyl and amino ends, and less limiting at the alpha carbon. Doses of L-serine that had only slight effects in voltage clamp experiments, nevertheless produced large effects in current clamp experiments. This indicates that several endogenous amino acids can have significant effects on membrane voltage, even when their shunting activity may be small. High concentrations of agonists produced desensitization in the voltage clamp records, but there was little evidence of desensitization in the current clamp experiments. These results indicate that several endogenous amino acids can activate the glycine receptor, but there is no evidence for a discrete receptor for taurine, beta-alanine, L-alanine or L-serine. Since all these endogenous amino acids have similar amino and acid terminals, reduction in potency results from steric interference around the alpha carbon. This graded potency may have functional significance in mediating inhibition.

Greater sensitivity of larger retinal ganglion cells to NMDA-mediated cell death

Glutamate toxicity in retinal ganglion cells has well documented both in vitro and in vivo, and has been suggested to play a role in the neuronal loss in glaucoma. Of note, glaucoma selectively damages larger retinal ganglion cells first, and we therefore sought to explore whether glutamate-mediated cell death was likewise more pronounced in larger retinal ganglion cells. We now report that glutamate--which exerts its toxic effect on neurons predominantly through the N-methyl-D-aspartate (NMDA) subtype of glutamate receptor--is more toxic to larger retinal ganglion cells both in tissue culture and in the intact rat eye. Cells smaller than 10 microns were relatively unaffected by glutamate or NMDA. These agents are, however, markedly toxic to retinal ganglion cells larger than 10 microns. These observations indicate that glutamate-mediated loss is seen first in larger retinal ganglion cells, in a similar fashion to the pattern of loss seen in glaucoma.

A redox-based mechanism for the neuroprotective and neurodestructive effects of nitric oxide and related nitroso-compounds

Congeners of nitrogen monoxide (NO) are neuroprotective and neurodestructive. To address this apparent paradox, we considered the effects on neurons of compounds characterized by alternative redox states of NO: nitric oxide (NO.) and nitrosonium ion (NO+). Nitric oxide, generated from NO. donors or synthesized endogenously after NMDA (N-methyl-D-aspartate) receptor activation, can lead to neurotoxicity. Here, we report that NO.- mediated neurotoxicity is engendered, at least in part, by reaction with superoxide anion (O2.-), apparently leading to formation of peroxynitrite (ONOO-), and not by NO. alone. In contrast, the neuroprotective effects of NO result from downregulation of NMDA-receptor activity by reaction with thiol group(s) of the receptor's redox modulatory site. This reaction is not mediated by NO. itself, but occurs under conditions supporting S-nitrosylation of NMDA receptor thiol (reaction or transfer of NO+). Moreover, the redox versatility of NO allows for its interconversion from neuroprotective to neurotoxic species by a change in the ambient redox milieu. The details of this complex redox chemistry of NO may provide a mechanism for harnessing neuroprotective effects and avoiding neurotoxicity in the central nervous system.

Effect of nitric oxide production on the redox modulatory site of the NMDA receptor-channel complex

Nitric oxide (NO) is an important messenger both systemically and in the CNS. In digital Ca2+ imaging and patch-clamp experiments, clinically available nitroso compounds that generate NO are shown to inhibit responses mediated by the NMDA subtype of the glutamate receptor on rat cortical neurons in vitro. A mechanism of action for this effect was investigated by using the specific NO-generating agent S-nitrosocysteine. We propose that free sulfhydryl groups on the NMDA receptor-channel complex react to form one or more S-nitrosothiols in the presence of NO. If vicinal thiol groups react in this manner, they can form a disulfide bond(s), which is thought to constitute the redox modulatory site of the receptor, resulting in a relatively persistent blockade of NMDA responses. These reactions with NO can afford protection from NMDA receptor-mediated neurotoxicity. Our results demonstrate a new pathway for NO regulation of physiological function that is not via cGMP, but instead involves reactions with membrane-bound thiol groups on the NMDA receptor-channel complex.

The physiology of GABAB receptors in the vertebrate retina

Writing a chapter on retinal GABAB receptors is premature, as evidenced by the paucity of citations more than two years old. Despite that, this area of retinal pharmacology has made significant strides and, although it is a story without an ending, it has had an exciting beginning. To date, the experiments indicate that horizontal cell feedback to cones is mediated, at least in part, by the GABAB receptor system which probably regulates a potassium conductance. In the inner retina, GABAB receptors are found on bipolar cells, amacrines, and ganglion cells. Here, the actions are a subtle regulation of channel conductance, but the effects are a dramatic reorganization of a fundamental coding property of the retina, namely the distinction between tonic and phasic responses to light. In both the distal and proximal retina, the GABAB receptor does not appear to work alone, but instead works in concert with the GABAA receptor. The full significance of these interactions has yet to be determined. Although the discovery of the GABAB receptor has led to the resolution of several retinal mysteries, the case is far from closed. At this juncture, what can be said is that the GABAB receptor represents a unique and ubiquitous system that reveals the power of regulating calcium and potassium conductances, as opposed to the more familiar properties of the glutamate/acetylcholine regulated cationic conductances or the GABAA/glycine controlled chloride channels.

Control of retinal information coding by GABAB receptors

The directional selectivity of amacrine and ganglion cells was studied using conventional intracellular recording techniques and drug application in the superfused retina-eyecup preparation of the tiger salamander. Baclofen, a GABAB receptor agonist, enhanced normal directional responses in some directionally selective third-order neurons. In about 30% of the cells that were not normally directional, baclofen induced direction-selective responses. This effect was particularly marked when 2-amino-4-phosphonobutyrate (APB) was used to isolate the OFF pathway. Comparisons of the effects of APB and baclofen on induced directional cells indicate that directional information in the ON and OFF channels is often handled separately and frequently is not aligned. This tends to obscure the observation of directionality as seen from the soma. Application of picrotoxin blocked both normal directional selectivity and baclofen-induced directional selectivity in some cells. Superfusion of picrotoxin and strychnine together blocked directionality in almost all cells. In both normal and induced directionality, the null direction response varied from cell to cell between a small depolarization, no voltage response, or a hyperpolarization. Injection of positive current often revealed "silent" inhibition. Some induced direction-selective cells did not show any evidence of inhibition in the null direction. The similarities in the response to baclofen, the influence of GABA and glycine antagonists, and the characteristics of the null-direction responses suggest that both normal and induced directionality originate from the same sources or mechanisms. Baclofen also induced orientation selectivity, but this was rarely observed.