Tunnel field-effect transistors for sensitive terahertz detection

The rectification of electromagnetic waves to direct currents is a crucial process for energy harvesting, beyond-5G wireless communications, ultra-fast science, and observational astronomy. As the radiation frequency is raised to the sub-terahertz (THz) domain, ac-to-dc conversion by conventional electronics becomes challenging and requires alternative rectification protocols. Here, we address this challenge by tunnel field-effect transistors made of bilayer graphene (BLG). Taking advantage of BLG's electrically tunable band structure, we create a lateral tunnel junction and couple it to an antenna exposed to THz radiation. The incoming radiation is then down-converted by the tunnel junction nonlinearity, resulting in high responsivity (>4 kV/W) and low-noise (0.2 pW/[Formula: see text]) detection. We demonstrate how switching from intraband Ohmic to interband tunneling regime can raise detectors' responsivity by few orders of magnitude, in agreement with the developed theory. Our work demonstrates a potential application of tunnel transistors for THz detection and reveals BLG as a promising platform therefor.

[Impact of "Elaphurus davidianus return home project" on the transmission of schistosomiasis in Poyang Lake areas]

OBJECTIVE

To investigate the prevalence of Schistosoma japonicum infections in Elaphurus davidianus released to Poyang Lake areas and evaluate the impact of the project of "E. davidianus released to wild environments for natural reproduction and growth" "(E. davidianus return home project") on the transmission of schistosomiasis in Poyang Lake areas.

METHODS

During the period from April 2018 to December 2019, the population distribution, inhabiting activity and natural reproduction of E. davidianus released to Poyang Lake areas were investigated by means of GPS and artificial observations. The S. japonicum infection was identified in animal feces in E. davidianus inhabitats using a hatching test, and snail distribution was surveyed in E. davidianus inhabiting grass islands using a systematic sampling method.

RESULTS

A total of 51 E. davidianus were released to the Poyang Lake areas in 2018, which subsequently produced 5 E. davidianus habitats in Yinlong Lake, Longkou, Nanchi Lake, Lianzi Lake and Zhu Lake. E. davidianus was found to predominantly inhibit in grass islands, farmlands and forest lands in hilly regions around the Poyang Lake areas. The natural reproduction rate of E. davidianus was 25% in the habitats in 2019, and the mean density of snails was 0.009 to 0.039 snails/0.1 m² in E. davidianus inhabitats; however, no S. japonicum infection was identified in snails. In addition, the mean densities of wild E. davidianus and bovine feces were 4.6 samples/hm² and 2.1 samples/hm², Conclusions The E. davidianus released to Poyang Lake areas may get infections with S. japonicum, and cause schistosomiasis transmission through fecal contamination in grass islands. The impact on and the prevalence of S. japonicum infection was 4.35% and 13.16% (P = 0.236), respectively; however, the intensities of S. japonicum infections were "+++" and "+", respectively.

CONCLUSIONS

The E. davidianus released to Poyang Lake areas may get infections with S. japonicum, and cause schistosomiasis transmission through fecal contamination in grass islands. The impact on local schistosomiasis transmission and the response strategy requires to be investigated following the release of E. davidianus to lake regions, to ensure the achievement of the goal of schistosomiasis elimination and the successful implementation of the "E. davidianus return home project" in Poyang Lake areas.

Giant oscillations in a triangular network of one-dimensional states in marginally twisted graphene

At very small twist angles of ∼0.1°, bilayer graphene exhibits a strain-accompanied lattice reconstruction that results in submicron-size triangular domains with the standard, Bernal stacking. If the interlayer bias is applied to open an energy gap inside the domain regions making them insulating, such marginally twisted bilayer graphene is expected to remain conductive due to a triangular network of chiral one-dimensional states hosted by domain boundaries. Here we study electron transport through this helical network and report giant Aharonov-Bohm oscillations that reach in amplitude up to 50% of resistivity and persist to temperatures above 100 K. At liquid helium temperatures, the network exhibits another kind of oscillations that appear as a function of carrier density and are accompanied by a sign-changing Hall effect. The latter are attributed to consecutive population of the narrow minibands formed by the network of one-dimensional states inside the gap.

The conductivity of marginally-twisted bilayer graphene is predicted to persist in presence of a bandgap-opening interlayer bias, owing to a network of 1D conductive states at domain boundaries. Here, the authors report Aharonov–Bohm oscillations up to 100 K, whereas at liquid helium temperatures another kind of oscillation appears, due to progressive population of the narrow minibands formed by the 2D network of 1D states inside the gap.

Curcumin suppresses intestinal microvascular endothelial cells invasion and angiogenesis induced by activated platelets

The present study investigated the effects and mechanism by which curcumin suppresses intestinal microvascular endothelial cells (INMECs) invasion and angiogenesis induced by activated platelets. INMECs were obtained from healthy rats, and divided into five groups: Control, platelets, platelets +2.5 µM curcumin, platelets +5.0 µM curcumin and platelets +10.0 µM curcumin. Curcumin toxicity was determined and vascular endothelial growth factor (VEGF) concentrations of the five groups were measured using ELISA. The branch point numbers were measured using a capillary tube formation experiment, invasion cell numbers were evaluated with the Transwell assay, relative protein expression levels were measured with western blot assay and immunofluorescence staining of the nucleus. The 2.5, 5 and 10 µM curcumin concentrations were found to be suitable for INMECs. Curcumin significantly downregulated VEGF concentration, suppressed vascular lumen formation and inhibited invasion cell numbers in a dose-dependent manner. The α-smooth muscle actin, collagen I, E-cadherin, phosphorylated (p-) phosphoinositide 3-kinase (PI3K), p-protein kinase B (AKT), p-mammalian target of rapamycin (m-TOR) and hypoxia inducible factor subunit alpha (HIF-1α) protein expression levels of the curcumin-treated groups were significantly downregulated in a dose-dependent manner compared with the platelet group. HIF-1α protein expression levels in the nucleus of the curcumin-treated groups were significantly suppressed in a dose-dependent manner compared with the platelet group. In conclusion, curcumin suppressed INMEC invasion and angiogenesis induced by activated platelets via inhibiting the activation of the PI3K/AKT/mTOR pathway.

Measuring Hall viscosity of graphene's electron fluid

An electrical conductor subjected to a magnetic field exhibits the Hall effect in the presence of current flow. Here, we report a qualitative deviation from the standard behavior in electron systems with high viscosity. We found that the viscous electron fluid in graphene responds to nonquantizing magnetic fields by producing an electric field opposite to that generated by the ordinary Hall effect. The viscous contribution is substantial and identified by studying local voltages that arise in the vicinity of current-injecting contacts. We analyzed the anomaly over a wide range of temperatures and carrier densities and extracted the Hall viscosity, a dissipationless transport coefficient that was long identified theoretically but remained elusive in experiments.

Removing a metal foreign object successfully from a patient's retroperitoneal space using laparoscopy and a novel navigation system

Trauma with foreign objects retained within the human body has become a common surgical emergency condition. Traditional surgical methods often involve creating large incisions in soft tissue and may lead to additional complications during wound healing. We have developed a new method of removing foreign bodies from patients' abdomens by using laparoscopy with the help of a novel navigation system that provides accurate positioning. This approach is minimally invasive and simple. This is the first combination of both technologies in this field.

First Report of Gray Mold on Amorphophallus muelleri Caused by Botrytis cinerea in China

Amorphophallus muelleri is a perennial tuberous plant in the family Araceae. The name konjac is commonly used for the species of genus Amorphophallus that produce a polysaccharide, glucomannan. The latter, called konjac glucomannan, is extracted from the tubers of these species. Glucomannan is an excellent gelling agent used in food, pharmaceutical and chemical industry, a specialty crop grown as a source of glucomannan for industrial use. It is an important cash crop and thus contributes to poverty alleviation in southwest China. Its planting area is about 150 million mu (10 million ha). In July 2012, symptoms of an unknown blight were observed on 5 to 10% of A. muelleri flowers and seeds being grown for commercial seed production. Greenhouses temperatures ranged from 20 to 34°C (avg. 26°C). A light grey mycelium was observed on symptomatic tissues, especially flowers. Severely infected flowers and stems eventually rotted, then dried out. Diseased tissue was excised from affected flowers and surfaces and disinfected with 1% sodium hypochlorite, followed by 70% alcohol. The tissue was then rinsed in sterile distilled water, plated on potato dextrose agar (PDA), and incubated at 26°C. Mycelial growth on PDA was initially whitish and turned gray with age. Dark appearing conidiophores bore botryose heads of hyaline, ellipsoid, unicellular conidia, grey in mass, measuring 7.2 (6.2 to 9.5) × 5.3 (4.5 to 6.0) μm. Black, irregular sclerotia formed at random in the culture. These morphological features were typical of those described for Botrytis cinerea (2). The internal transcribed spacer (ITS) region of rDNA was amplified using primers ITS4/ITS6 and sequenced (1). BLAST analysis of a 557-bp segment had a 99% similarity with the sequence of Botryotinia fuckeliana (anamorph = B. cinerea). The representative nucleotide sequence has been assigned the GenBank Accession No. KC999986. On the basis of morphological and molecular results, the fungus isolated from diseased konjac flowers and flower tissue was confirmed to be B. cinerea. Pathogenicity tests: Inoculum was prepared from 7-day-old cultures on PDA. Six flowering A. muelleri in 1-liter pots were spray inoculated with a 1.0 × 10⁶ conidia/ml suspension from 7-day-old PDA cultures. As a control, six healthy plants were sprayed with sterile distilled water. Each plant was covered with a transparent polyethylene bag for 3 days and maintained in a greenhouse at temperatures between 20 and 26°C. After 8 days, small, round to irregular brown spots developed on both flowers and stems, which finally blighted. Water-treated plants remained symptomless. Koch's postulates were fulfilled when the pathogen was re-isolated from the diseased organs. Blight on common calla lily (calla lily and Amorphophallus are in the same family, different genera) flower attributed to B. cinerea was previously reported in Argentina (3). To our knowledge, this is the first report of the presence of B. cinerea on A. muelleri in China. References: (1) D. E. L. Cooke and J. M. Duncan. Mycol. Res. 101:667, 1997. (2) M. B. Ellis. Dematiaceous Hyphomycetes. Commonwealth Mycological Institute, Kew, England, 1971. (3) M. C. Rivera and S. E. Lopez. Plant Dis. 90:970, 2006.

Molybdenum(VI) removal by using constructed wetlands with different filter media and plants

The efficacy and capacity of vertical-flow wetland filters on molybdenum (Mo) removal from wastewater was examined, employing reed (Phragmites australis) and cattail (Typha latifolia) as well as different adsorption granular media. Humus, cinder, modified cinder, as well as pyrite were used as filter media. A synthetic effluent with different concentrations of Mo(VI) at different hydraulic retention times was used for simulating Mo leached mine wastewater. Laboratory experiments showed that the equilibrium adsorption data were in agreement with the Langmuir isotherm model, and the maximum Mo(VI) adsorption capacities of modified cinder and pyrite were 10.01 and 6.25 mg/g, respectively. Mo(VI) removal in F5 (combination substrates of pyrite and cinder) was found to be more stable and effective than that of F1 (conventional gravel and soil filter media) during the 14-week experiment. Most of the Mo(VI) was retained in the 10-20 cm of the substrate, and adsorbed by the modified cinder and pyrite. The largest fraction of Mo(VI) retained was the water-soluble fraction on the surface of the pyrite. Cattail was more suitable for Mo(VI) absorption than reed, but the bioaccumulation accounted for a very small portion of the total removal.

First Report of Botryosphaeria dothidea Causing Canker and Dieback Disease of Helwingia chinensis in China

Helwingia chinensis Batal is distributed in the western and southern regions of China. The aerial part of this plant has long been used to treat dysentery, hematochezia, and swelling. An outbreak of cankers and dieback was observed for the first time on H. chinensis in China during June of 2010. Disease symptoms included dieback of shoots and branches, lesions, and canker formation on the stems. In order to identify the causal agent(s) of this canker disease, samples composed of inner bark and woody tissues were collected from the junction of healthy and diseased tissues of declining trees from Kunming and Wenshan districts of China during July to October of 2010. Pieces of surface-sterilized tissue samples were plated on potato dextrose agar (PDA) and incubated at 26°C. Fungal colonies developed copious, white, aerial mycelium that became dark green with age. Pycnidia started to develop after 20 days. Macroconidia, which were 20 to 29 × 4 to 6 μm, were hyaline, aseptate, and fusiform. No fungus was isolated from water-inoculated tissues of control plants and healthy trees. Identity was confirmed by analysis of the rDNA internal transcribed spacer region (ITS1-5.8S-ITS2) with primers ITS1 and ITS4. BLAST searches showed 99% identity with Botryosphaeria dothidea isolates from GenBank (Accession Nos. HQ660454 and FJ790846). Representative sequences of B. dothidea from H. chinensis from China have been deposited in GenBank (Accession No. JQ766122). On the basis of morphological and molecular results, the fungus isolated from diseased H. chinensis was confirmed to be B. dothidea. Pathogenicity tests were conducted by stem inoculation of 1-year-old H. chinensis seedlings. Mycelial plugs (3 to 4 mm in diameter) of B. dothidea from actively growing colonies were applied to same-sized bark wounds on the middle point of the stems. Control seedlings were inoculated with sterile PDA plugs. Inoculated and control seedlings (three each) were kept in a greenhouse and watered as needed. After 4 weeks, all H. chinensis seedlings developed vascular tissue discoloration and leaf wilting; no such symptoms were manifested by seedlings in the control treatment. B. dothidea was reisolated from all B. dothidea-inoculated, symptomatic tissues, fulfilling Koch's postulates. In China, B. dothidea has previously been reported to cause canker and dieback disease of Eucalyptus grandis (2) and gummosis of peach (1); however, to our knowledge, this is the first report of B. dothidea causing canker and dieback on H. chinensis. References: (1) Y. Ko et al. Plant Pathol. Bull. 1:70, 1992. (2) L. Yu et al. Plant Dis. 93:764, 2009.

First Report of Stem Blight of Blueberry Caused by Botryosphaeria dothidea in China

Blueberry (Vaccinium spp.) production in southwest and northeast China has grown to over 100,000 ha in the last 20 years thanks to the fruit's high nutritional and economic value. As blueberry acreage increases, the diversity of diseases and challenges for control are gaining more attention. In August 2010, stem and branch blight occurred on Highbush Blueberries (Vaccinium corymbosum L.) at commercial farms in Lijiang and Zongdian, Yunnan Province (southwestern China), with crop damage ranging from 10 to 15%. Typical symptoms of the disease were blight and dieback on the stems with lesions extending along entire branches. Diseased samples (phloem and xylem sectors in the wood) were washed with running tap water, disinfected with 2% sodium hypochlorite, then 70% alcohol, rinsed in sterile distilled water, plated on potato dextrose agar (PDA), and incubated at 28°C. Fungal isolates developed copious, white aerial mycelium that became dark gray after 4 to 5 days and formed black pycnidia after 18 days. Conidia were hyaline, aseptate, thin walled, fusiform, and measured 21 to 27 × 4 to 6 μm. Identity was confirmed by analysis of the ribosomal DNA internal transcribed spacer region ITSI-5.8S -ITS2 with primers ITS1 and ITS4. BLAST searches showed 99% identity with Botryosphaeria dothidea isolates from GenBank (Accession Nos. AB693904 and JF800139). Representative sequences of B. dothidea from Highbush Blueberries from China were deposited into GenBank (Accession No. JX096631). On the basis of morphological and molecular results, the fungus isolated from diseased Highbush Blueberries stem was confirmed to be B. dothidea. Pathogenicity tests were conducted on 2-year-old blueberry seedlings (Highbush Blueberries). Mycelial plugs (2 to 3 mm in diameter) of B. dothidea from actively growing colonies (PDA) were applied to same-size bark wounds in the center of the stems. Inoculation wounds were wrapped with Parafilm. Control seedlings received sterile PDA plugs. Inoculated and control seedlings (five each) were kept in a greenhouse and watered as needed. After 12 days, all of the inoculated but none of the control blueberry seedlings showed dark vascular stem tissue. B. dothidea was reisolated from symptomatic tissues, thus fulfilling Koch's postulates. No symptoms were visible in the control seedlings. B. dothidea has been reported as a pathogen of sycamore (3), olives (1), and peach (2). However, no research has been conducted on stem blight of blueberry caused by B. dothidea in southwest or mainland China. To our knowledge, this is the first report of B. dothidea on blueberry in southwest China. References: (1) M. Chattaoui, et al. Plant Dis. 95:770, 2011. (2) Y. Ko et al. Plant Pathol. Bull. 1:70, 1992. (3) E. Turco, et al. Plant Dis. 90:1106, 2006.

Prolonged retrograde amnesia following sedation with propofol in a 12-year-old boy

Propofol is commonly used for sedation in a variety of clinical settings, as well as for induction and maintenance of anesthesia. The ease with which propofol can be administered and titrated to clinical effect, in addition to its accepted safety profile, has made it the drug of choice for sedation in outpatient procedures, such as gastrointestinal endoscopy. While short-term amnesia is a well-known side-effect of propofol, we present the first documented case of prolonged retrograde amnesia following propofol administration in a pediatric patient. Possible mechanisms and clinical management strategies related to this unique event are discussed.

Gas-initiation under UV and liquid-grafting polymerization on the surface of polysulfone hollow fiber ultrafiltration membrane by dynamic method

Using the inner-surface of polysulfone hollow fiber ultrafiltration membranes as grafted layer, the method of gas-initiation and liquid-polymerization has been studied, which aimed to adjust the diameter of the pores in the membranes. The degree of polymerization varied with the changes of the parameters, such as irradiation time, monomer concentration, temperature and time of polymerization and soon. The results indicated that using benzophenone (BP) which is in a gaseous condition as photo-initiator, acrylamide as graft monomer, the polyacrylamide chain was grafted on the surface of membranes. After the surface membrane being modified, the water flux and retention altered, and thus it can be seen that the diameter of the pores in the membrane was altered. These experiments contribute to finding a new way to produce the hollow fiber membrane with the small pore size and are extraordinarily worth developing and studying.

Ultrastructural organization of GABA-like immunoreactive profiles in the weaver substantia nigra

GABA-like immunoreactivity (GABA-LI) in the substantia nigra pars compacta (SNc) of mutant weaver mice was investigated at the electron microscope level. Eight-week-old homozygous mutant weaver mice, paired with wildtype littermates as controls, were perfused with a buffered paraformadehyde/acrolein solution. Sections containing the SN were immunocytochemically reacted with an antiserum to GABA using the peroxidase-antiperoxidase (PAP) procedure. Ultrastructural examination revealed that profiles of GABA-LI dendrites were decreased in number while profiles of labeled axonal processes were increased. In addition, there were an increased number of GABA-LI terminals in contact with similarly labeled GABA-LI dendrites. Double-labeling experiments using the antibodies to GABA and dopamine D(2) receptors showed that a small number of GABA-LI profiles exhibited D(2)-like immunoreactivity in both controls and weavers. These results suggest that the GABA-LI synaptic connections are altered as a result of the loss of DA neurons in the SNc of the weaver mice.

Neurons exhibiting dopamine D2 receptor immunoreactivity in the substantia nigra of the mutant weaver mouse

Neurons exhibiting D2 receptor-like immunoreactivity were investigated in the substantia nigra pars compacta of weaver mice at the light and electron microscope levels using immunocytochemical techniques. At the light microscope level, there was significant loss of D2-like immunoreactive cells in weaver mice and the remaining labeled cells exhibited less intense immunoreactivity. At the ultrastructural level, there was a decrease in the number of immunoreactive profiles and fewer synapses were observed abutting labeled dendritic profiles. In addition, degenerative changes were noted in some of the D2 receptor-like immunoreactive profiles. Double labeling with D2 and tyrosine hydroxylase indicated that the majority of the labeled profiles were double labeled. Eight-week-old homozygous weavers were paired with wild-type littermates as controls and perfused with a buffered solution of acrolein/paraformadehyde. Midbrain sections were reacted immunocytochemically either with an antiserum to D2 or with antisera to D2 and tyrosine hydroxylase, using a double-labeling technique. Sections were processed for light and electron microscopy by standard methods. The results of this study confirm the autoreceptor-like activity of D2 receptors on nigral dopamine neurons. The cell degeneration, down-regulation of D2 receptors, and decreased dendritic and synaptic components in the neuropil suggest that the synaptic integrity of the substantia nigra has been compromised, which in turn would affect the functional efficacy of the basal ganglia circuitry. This altered circuity is expressed in the Parkinson-like symptoms displayed by this mutant mouse.

Age-related differences in the effects of GABAA agonists microinjected into rat substantia nigra: pro- and anticonvulsant actions

GABAergic transmission in the substantia nigra pars reticulata (SNR) has an important role in the control of experimental seizures. In the flurothyl seizure model, SNR microinjection of the selective GABAA receptor agonist muscimol results in a biphasic dose-response curve in adults: Intermediate doses are anticonvulsant, but high doses have proconvulsant effects. Another GABAA agonist, THIP (4,5,6,7-tetrahydroisoxazolo-[5,4-c]pyridin-3-ol), also produces anticonvulsant effects at lower doses, whereas higher doses tend to produce a proconvulsant effect. In 16-day-old rat pups, no anticonvulsant but only proconvulsant effects of muscimol occur, and at lower doses than in adults. These data suggest that the immature SNR is significantly more sensitive to the proconvulsant effects of GABAA receptor agonists than is the SNR of adults. We hypothesize that the age-related differences in nigral GABAergic response may be due to ontogenic changes in GABAA-sensitive neuronal circuits in the SNR.

Further evidence of involvement of substantia nigra GABAB receptors in seizure suppression in developing rats

To determine whether the substantia nigra GABAergic anticonvulsant effects depend on GABAB receptor activation, we tested the effects of intranigral CGP 35,348 (a GABAB receptor antagonist) alone or in combination with gamma-vinyl-GABA (GVG; a GABA-transaminase inhibitor) on flurothyl seizures in rat pups and adult rats. In pups, nigral infusions of CGP 35,348 decreased the thresholds for clonic and tonic seizures and attenuated the anticonvulsant effects of GVG. In adults, nigral infusions of CGP 35,348 did not alter seizure thresholds. The data suggest that, in rat pups, nigral GABAB receptors regulate, in part, flurothyl-induced seizures.

The influence of thalamic GABA transmission on the susceptibility of adult rats to flurothyl induced seizures

There is considerable evidence that thalamic nuclei are involved in the propagation and regulation of seizures. In the present study, we investigated the possible role in seizure mechanisms of GABAergic transmission in two thalamic nuclei, the posterior nucleus (PO) and the ventromedial nucleus (VM). Several GABAergic drugs were bilaterally microinfused into PO or VM of adult rats via chronically implanted cannulae, before testing the rats' susceptibility to seizures induced by flurothyl. In PO, infusions of the GABA elevating agent gamma-vinyl-GABA (20 micrograms) or of the GABAA receptor agonist muscimol (100 ng) suppressed both clonic and tonic seizures. Infusions into PO of the GABAA receptor antagonist bicuculline (100 ng) facilitated both these seizure types. Administration of the GABAB receptor agonist baclofen (200 ng) also suppressed clonic seizure susceptibility. Drug infusions into VM, however, did not significantly modify the susceptibility to seizures. These findings lead us to conclude that GABAergic transmission in the vicinity of the PO, but perhaps not in VM, affects flurothyl seizure susceptibility. We hypothesize that GABA synapses in PO may be part of a seizure propagation or control circuit including striatum, substantia nigra, and superior colliculus.

Reduced susceptibility to seizures in carbonic anhydrase II deficient mutant mice

The seizure susceptibility of carbonic anhydrase II (CA) deficient mice and their normal littermates was determined and compared. In flurothyl-induced seizures, CA deficient mice displayed longer latencies to the onset of both clonic and tonic-clonic seizures. In pentylenetetrazole-induced seizures mutant mice exhibited a lower incidence of clonic seizures than did their normal littermates. Acetazolamide (a CA blocker) was used for the pretreatment of normal mice to compare them to CA deficient littermates. The pretreated mice displayed a lower incidence of flurothyl-induced tonic-clonic seizures and of both types of pentylenetetrazole seizures. The attempts to elicit audiogenic seizure did not reveal any difference between normal and mutant littermates. However, when the mice were primed by a loud sound during the critical period and retested for audiogenic seizures again at age 1.5 months, the CA deficient mice displayed a significantly lower incidence of seizures. The similarity between the anticonvulsant action of CA deficiency and the anticonvulsant action of acetazolamide suggests an important role of CA in seizures. The exact mechanism of anticonvulsant action by CA inhibition, however, remains to be elucidated.

The proconvulsant effect of nigral infusions of THIP on flurothyl-induced seizures in rat pups

The substantia nigra gamma-aminobutyric acid (GABA) system is crucial for seizure control. Our previous work indicates that in 16-day-old rat pups, nigral administration of the GABAA receptor agonist muscimol facilitates flurothyl-induced seizures, whereas it suppresses seizures in adult rats. To determine whether the proconvulsant effect of muscimol in rat pups may be mediated by nigral GABAA receptors, in the present study we applied a selective GABAA receptor agonist 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP). Bilateral nigral infusions of THIP (500 or 700 ng) significantly decreased the thresholds for flurothyl seizures in a dose-dependent fashion. Doses of 350 ng or less did not significantly modify the susceptibility to seizures. An anticonvulsant action of THIP could not be detected at any dose. Administration of an effective THIP dose (500 ng) 2 mm dorsal to the SNR had no influence on seizures. These findings suggest that in rat pups the proconvulsant effect of nigral GABAA receptor agonists may be attributed to unique pharmacologic characteristics of GABAA receptors during development.

Effects of substantia nigra gamma-vinyl-GABA infusions on flurothyl seizures in adult rats

There is evidence implicating the nigral gamma-aminobutyric acid (GABA) system in the control of seizures. Our previous studies have demonstrated that, in rat pups, intranigrally infused gamma-vinyl-GABA (GVG, 5-20 micrograms) strongly suppresses flurothyl-induced tonic but not clonic seizures. Furthermore, nigral infusions of bicuculline or muscimol abolish the anticonvulsant effect of GVG. In this study, we report that in adult rats bilateral infusions of GVG (20 micrograms) into the substantia nigra pars reticulata (SNR) significantly elevated the thresholds for both clonic and tonic seizures induced by flurothyl. Lower doses (5 and 10 micrograms) did not significantly protect adult rats against seizures, but there was a significant effect of GVG dose. Unilateral infusion of GVG (20 micrograms) in the SNR did not alter the thresholds for flurothyl-induced seizures. Intranigral infusions of bicuculline following pretreatment with GVG abolished the protective effect of GVG on flurothyl-induced seizures, indicating that the anticonvulsant effect of GVG is most likely mediated by the nigral GABAA receptor. Intranigral administration of muscimol after GVG pretreatment significantly suppressed flurothyl-induced seizures, but the combined effect of the two drugs was not as strong as that of GVG alone. The data suggest that GVG protects adult rats against flurothyl-induced seizures. In adults, however, the dose of GVG required to protect against both clonic and tonic seizures is higher than that needed in rat pup SNR.

Is the anticonvulsant effect of substantia nigra infusion of gamma-vinyl-GABA (GVG) mediated by the GABAA receptor in rat pups?

The substantia nigra GABAergic system is considered important for the modification of seizures. Our previous studies have shown that, in rat pups, nigral infusions of baclofen suppressed flurothyl-induced seizures. In the present study, we determined, in rat pups, the effect of nigral infusions of gamma-vinyl-GABA (GVG) on clonic-tonic seizures induced by flurothyl, generated a dose-response curve of the GVG effect and investigated the possible role of the nigral GABAA receptor in mediating the GVG effect. Bilateral nigral infusions of GVG profoundly suppressed flurothyl-induced tonic seizures in a dose-dependent fashion. Flurothyl-induced clonic seizures were not modified. The lowest effective dose of nigral GVG administration was 5 micrograms/0.25 microliter per site. Nigral infusions of GVG at doses greater than 10 micrograms/0.25 microliter induced sedation as well. Infusions of GVG, 2 mm dorsal to the substantia nigra, did not alter seizure latencies. Bilateral nigral infusions of bicuculline, a specific GABAA receptor antagonist, reduced the protective potency of GVG against flurothyl-induced seizures. Nigrally administered muscimol, a GABAA receptor agonist, also attenuated the anticonvulsant effect of GVG. These findings suggest that the optimal dose of nigrally infused GVG against flurothyl-induced seizures is in the range of 5-10 micrograms/0.25 microliter and that GVG may be more efficient as an anticonvulsant for the treatment of tonic seizures in developing animals. The anticonvulsant effect of GVG may, in part, involve the nigral GABAA receptor. The data, together with the previous experiments, indicate that both nigral GABAA and GABAB receptors may play a role in the regulation of seizures in rat pups.(ABSTRACT TRUNCATED AT 250 WORDS)

X-ray diffraction studies of the structural state of crossbridges in skinned frog sartorius muscle at low ionic strength

Low-angle X-ray diffraction diagrams were obtained from chemically skinned frog sartorius muscles under low ionic strength relaxing conditions. Experiments on single muscle fibres from rabbit muscle and on muscle proteins in solution have suggested the presence of a 'low ionic strength attached state' of the myosin crossbridges to actin, in which the overall ATP splitting and force-generating cycle is still blocked. This opened up the possibility that structural information about one of the intermediate states in the crossbridge cycle might be obtained under these conditions. Using synchrotron radiation as a high intensity X-ray source we were able to record the appropriate diffraction diagrams with short exposure times and were able to compare the same muscles at normal and at low ionic strength. Changes in the intensities of the equatorial reflections an increase in the 143 A meridional intensity can be interpreted in a similar way. However, these attached bridges do not give rise to changes in the actin-based layer line reflections, nor is their presence associated with a weakening of the myosin layer line pattern. These results provide further evidence for the existence of bound states of crossbridges, in which their orientation relative to actin is not sharply defined.