A theory of steady-state activity in nerve-fiber networks: IV.N circuits with a common synapse

Conditions under which either of two distinct activity patterns may arise from the same stimulus pattern are deduced for the case of a net-work which consists ofN simple circuits all jointed at a common synapse. If the product of the activity parameters of all the fibers in any circuit is called the activity parameter of the circuit, or, more briefly, the circuit parameter, then the condition for the existence of such mutually consistent activity patterns is that there be a sum of circuit paramaters which is not less than unity.     

A theory of steady-state activity in nerve-fiber networks II: The simple circuit

It is found that for a simple circuit of neurons, if this contains an odd number of inhibitory fibers, or none at all, or if the product of the activity parameters is less than unity, then the stimulus pattern always determines uniquely the steady-state activity. For circuits not of one of these types, it is possible to classify exclusively and exhaustively all possible activity patterns into three types, here called “odd”, “even”, and “mixed”. For any pattern of odd type and any pattern of even type there always exists a stimulus pattern consistent with both, but in no other way can such an association of activity patterns be made.     

Teratogenic and goitrogenic activity of propineb and propylenethiourea in the rat

The teratogenic and goitrogenic effects of Propineb, dithiocarbamate pesticide and Propylenthiourea (PLTU), its metabolite and degradation product have been studied. The aim of this study was to show the possible correlation between the two activities. Female Sprague-Dawley rats were treated with Propineb and PLTU starting from 6th to 16th day of pregnancy. The functional state of maternal and foetal thyroid, the toxicity of products versus dams and embryotoxic and teratogenic effects were examined. The observed goitrogenic effect may be compared to that reported in the previous studies of the authors, if considering time of sacrifice. In fact, the lesion quickly rises and as rapidly regresses when treatment is stopped. The foetal thyroid has not been affected by the product administered to the dams. PLTU showed a clear teratogenic activity at doses that did not show any maternal toxicity (45 and 90 mg/k).     

Decline in microbial activity does not necessarily indicate an end to biodegradation in MSW-biowaste: a case study

The aim of this study was to examine whether a decline in microbial activity (i.e., CO(2) output) during the biodegradation of municipal solid waste (MSW) indicated an end to biodegradation and the appearance of a stable, final product. As the organic fraction of MSW was biodegraded in an 8 clamp Cambridge Batch System composter, CO(2) output declined by 50% and moisture content at the end of the process was <20%. Levels of biodegradable material remaining in the product were determined by the dynamic respiration index (DRI) method but despite 151 days in the composting system biodegradable material was still present at levels (24130mgO(2)/kgdry matter (DM)) which exceeded draft EU biowaste directive (2001) guidelines (10,000mgO(2)/kgDM). Further laboratory based incubations demonstrated that microbial activity and hence biodegradation of organic material could be restarted if moisture levels were adjusted suggesting that dehydration limited microbial activity. Low levels of microbial activity alone did not therefore indicate and end to biodegradation, biodegradable material was not exhausted and the final product was not stable which has serious implications for its end-use.     

Regulation of the biomass and activity of soil microorganisms by microfauna

Microcosm experiments showed that the microbial biomass and the respiration activity in soil were regulated by nematodes. Depending on nematode number and plant residue composition, the trophic activity of nematodes can either stimulate or inhibit microbial growth and respiration as compared to soil containing no nematodes. The stimulating effect was observed when nitrogen-free (starch) or low-nitrogen (wheat straw, C:N = 87) organic substrates were applied. Inhibition occurred when a substrate rich in nitrogen (alfalfa meal, C:N = 28) was decomposed and the nematode population exceeded the naturally occurring level. A conceptual model was developed to describe trophic regulation by microfauna (nematodes) of the microbial productivity and respiration activity and decomposition of not readily decomposable organic matter in soil. The stimulating and inhibiting influence of microfauna on soil microorganisms was not a linear function of the rate of microbial consumption by nematodes. These effects are largely associated with the induced change in the physiological state of microorganisms rather than with the mobilization of biogenic elements from the decomposed microbial biomass.     

Regulation of the biomass and activity of soil microorganisms by microfauna

Microcosm experiments showed that the microbial biomass and the respiration activity in soil were regulated by nematodes. Depending on nematode number and plant residue composition, the trophic activity of nematodes can either stimulate or inhibit microbial growth and respiration as compared to soil containing no nematodes. The stimulating effect was observed when nitrogen-free (starch) or low-nitrogen (wheat straw, C : N = 87) organic substrates were applied. Inhibition occurred when a substrate rich in nitrogen (alfalfa meal, C : N = 28) was decomposed and the nematode population exceeded the naturally occurring level. A conceptual model was developed to describe trophic regulation by microfauna (nematodes) of the microbial productivity and respiration ctivity and decomposition of not readily decomposable organic matter in soil. The stimulating and inhibiting influence of microfauna on soil microorganisms was not a linear function of the rate of microbial consumption by nematodes. These effects are largely associated with the induced change in the physiological state of microorganisms rather than with the mobilization of biogenic elements from the decomposed microbial biomass.     

Rational behavioral response and the transmission of STDs

The susceptible-infected (SI) model is extended by allowing for individual optimal choices of self-protective actions against infection, where agents differ with respect to preferences and costs of self-protection. It is shown that a unique endemic equilibrium prevalence exists when the basic reproductive number of a STD is strictly greater than unity, and that the disease-free equilibrium is the unique steady state equilibrium when the basic reproductive number is less than or equal to one. Unlike in models that take individual behavior as given and fixed, the endemic equilibrium prevalence need not vary monotonically with respect to the basic reproductive number. Specifically, with endogenously determined self-protective behavior, a reduction in the basic reproductive number may in fact increase the endemic equilibrium prevalence. The global stability of the endemic steady state is established for the case of a homogeneous population by showing that, for any non-zero initial disease prevalence, there exists an equilibrium path which converges to the endemic steady state.     

DNA-dependent protein methylase activity in bull seminal plasma.

The existence of a DNA-dependent protein methylase activity without any concomitant DNA methylase activity was demonstrated in bull seminal plasma. The enzyme utilized S-adenosyl-L-methionine as a methyl donor, and endogenous seminal plasma protein as the substrate. There was no demonstrable enzyme activity when the seminal plasma was preheated at 100 degrees for 10 min, or when the enzyme reaction mixture was incubated at 4 degrees. The protein methylase required a heterologous DNA source, had optimal activity at pH 8.1, and was enhanced in the presence of Mg2+, NH4+, and reduced glutathione. After the methylated protein product was separated from DNA by extraction with 0.2 M HCl, the incorporated radioactivity was shown to be totally solubilized by incubating the protein either with Pronase or 1 M NaOH, while RNase and DNase had no effect. Approximately 70% of the enzymatically synthesized amino acids in the protein product were tentatively identified as O-methylated amino acid ethers by virtue of their elution from a Dowex 50 H+ column with 0.2 M pyridine, and their stability to acid and base hydrolysis. The partially purified methylated product was shown by Sephadex G-50 chromatography to consist of three distinct radioactive proteins with molecular weights of approximately 21,000, 15,000, and 10,000.     

The pro-oxidative activity of SOD and nitroxide SOD mimics.

Native Cu,Zn-SOD and synthetic SOD mimics sometimes demonstrate an apparently anomalous bell-shaped dose-response relationship when protecting various biological systems from oxidative stress. Several mechanisms have been proposed to account for such an effect, including: overproduction of H(2)O(2), peroxidative activity of SOD, and opposing roles played by O(2)(*-) in both initiation and termination of radical chain reactions. In the present study, ferrocyanide and thiols, which are susceptible to one-electron and two-electron oxidation, respectively, were subjected to a flux of superoxide in the presence and absence of SOD or SOD mimics. The results show that 1) either O(2)(*-)/HO(2)(*) or H(2)O(2) alone partially inactivates papain, whereas when combined they act synergistically; 2) nitroxide SOD mimics, but not SOD, exhibit a bell-shaped dose-response relationship in protecting papain from inactivation; 3) SOD, which at low dose inhibits superoxide-induced oxidation of ferrocyanide, loses its antioxidative effect as its concentration increases. These findings offer an additional explanation for the pro-oxidative activity of SOD and SOD mimics without invoking any dual activity of O(2)(*-) or a combined effect of SOD and H(2)O(2). The most significant outcome of an increase in SOD level is a decrease of [O(2)(*-)](steady state), rather than any notable elevation of [H(2)O(2)](steady state). As a result, the reaction kinetics of the high oxidation state of each catalyst is altered. In the presence of ultra-low [O(2)(*-)](steady state), the oxidized form of SOD [Cu(II),Zn-SOD] or SOD mimic (oxo-ammonium cation) does not react with O(2)(*-) but rather oxidizes the target molecule that it was supposed to have protected. Consequently, these catalysts exert an anti- or pro-oxidative effect depending on their concentration.     

Continuous production of ethanol by yeast "immobilized" in a membrane-contained fermentor

A dialysate-feed, immobilized-cell dialysis continuous fermentation system was investigated as a method of relieving product inhibition in the conversion of glucose to ethanol by cells of Saccharomyces cerevisiae ATCC 4126. The substrate was fed into a continuous dialysate circuit and then into a batch fermentor circuit via diffusion through the microporous membranes of an intermediate dialyzer. Simultaneously, product was withdrawn from the fermentor circuit through the dialyzer membranes into the dialysate circuit and out in the effluent. Since the fermentor was operated without an effluent, the cells essentially were immobilized and converted substrate to product by maintenance metabolism. Contrary to prior results with this novel system for the continuous fermentation of lactose to lactate by lactobacillus cells, a steady state of yeast cells in the fermentor did not occur initially but was obtained by the depletion of medium nitrogen and the prevention of cell breakage, although the substrate and product concentrations then became unsteady. The inherent advantages of the system was offset in the ethanol fermentation by relatively low productivity, which appeared to be limited by membrane permeability.     

Catalytic activity of rabbit skeletal muscle aldolase in the crystalline state

The monoclinic crystalline form of aldolase from rabbit skeletal muscle grown at 29 degrees C is catalytically active in the direction of aldol cleavage. Activity was assayed for in a crystallization buffer containing 45% saturated ammonium sulfate using chemically unmodified single crystals cut to precise dimensions. Diffusion effects on velocities from assays employing aldolase crystals do not appear to be limiting when cut single crystals are crushed. Assays of crushed crystals are linear with respect to both time and enzyme concentration. Kinetic constants are reported for both substrates fructose 1-phosphate and fructose 1,6-phosphate. Maximal velocities and binding constants determined differ by no more than a factor of 2 between the crystalline and the soluble state of the enzyme. Analysis of the kinetic constants for fructose 1-phosphate as substrate shows that binding of substrate does not change in going to the crystalline state. Release of product is reduced roughly 2-fold in the crystalline state. A similar conclusion can be reached in the case of fructose 1,6-phosphate as substrate provided the "on" steps of substrate and product are only diffusion limited but independent of the physical state of the enzyme. It is not possible to distinguish between a more sluggish conformational change during catalysis or simply tighter product binding in the crystalline state as compared to the soluble enzyme state.     

The human c-fps/fes gene product expressed ectopically in rat fibroblasts is nontransforming and has restrained protein-tyrosine kinase activity.

A 13-kilobase EcoRI genomic restriction fragment containing the human c-fps/fes proto-oncogene locus was expressed transiently in Cos-1 monkey cells and stably in Rat-2 fibroblasts. In both cases, human c-fps/fes directed synthesis of a 92-kilodalton protein-tyrosine kinase (p92c-fes) indistinguishable from a tyrosine kinase previously identified with anti-fps antiserum which is specifically expressed in human myeloid cells. Transfected Rat-2 cells containing approximately 50-fold more human p92c-fes than is found in human leukemic cells remained morphologically normal and failed to grow in soft agar. Synthesis of p92c-fes in this phenotypically normal line exceeded that of the P130gag-fps oncoprotein in a v-fps-transformed Rat-2 line. Despite this elevated expression, human p92c-fes induced no substantial increase in cellular phosphotyrosine and was not itself phosphorylated on tyrosine. In contrast, p92c-fes immunoprecipitated from these Rat-2 cells or expressed as an enzymatically active fragment in Escherichia coli from a c-fps/fes cDNA catalyzed tyrosine phosphorylation with an activity similar to that of v-fps/fes polypeptides. Thus, p92c-fes is not transforming when ectopically overexpressed in Rat-2 fibroblasts. This lack of transforming activity correlates with a restriction imposed on the kinase activity of the normal c-fps/fes product in vivo which is apparently lifted for v-fps/fes oncoproteins, suggesting that regulatory interactions within the host cell modify fps/fes protein function and normally restrain its oncogenic potential.     

Hyperdopaminergia and altered locomotor activity in GABAB1-deficient mice

GABAB1-/- mice, which are devoid of functional GABAB receptors, consistently exhibit marked hyperlocomotion when exposed to a novel environment. Telemetry recordings now revealed that, in a familiar environment, GABAB1-/- mice display an altered pattern of circadian activity but no hyperlocomotion. This indicates that hyperlocomotion is only triggered when GABAB1-/- mice are aroused by novelty. In microdialysis experiments, GABAB1-/- mice exhibited a 2-fold increased extracellular level of dopamine in the striatum. Following D-amphetamine administration, GABAB1-/- mice released less dopamine than wild-type mice, indicative of a reduced cytoplasmic dopamine pool. The hyperdopaminergic state of GABAB1-/- mice is accompanied by molecular changes, including reduced levels of tyrosine hydroxylase mRNA, D1 receptor binding-sites and Ser40 phosphorylation of tyrosine hydroxylase. Tyrosine hydroxylase activity, tissue dopamine content and dopamine metabolism do not appear to be measurably altered. Pharmacological and electrophysiological experiments support that the hyperdopaminergic state of GABAB1-/- mice is not severe enough to inactivate dopamine D2 receptors and to disrupt D2-mediated feedback inhibition of tyrosine hydroxylase activity. The data support that loss of GABAB activity results in a sustained moderate hyperdopaminergic state, which is phenotypically revealed by contextual hyperlocomotor activity. Importantly, the presence of an inhibitory GABA tone on the dopaminergic system mediated by GABAB receptors provides an opportunity for therapeutic intervention.     

Inhibition of denitrification activity but not of mRNA induction in Paracoccus denitrificans by nitrite at a suboptimal pH

The influence of pH on the denitrification activity of a continuous culture of Paracoccus denitrificans was studied in relation to the presence of nitrite. After a transition from aerobic to anaerobic conditions at the suboptimal pH of 6.8, P. denitrificans was not able to build up a functional denitrification pathway. Nitrite accumulated in the medium as the predominant denitrification product. Although the nitrite reductase gene was induced properly, the enzyme could not be detected at sufficient amounts in the culture. These observations indicate that either translation was somehow inhibited, or once synthesized nitrite reductase was inactivated, possibly by the high concentrations of nitrous acid (HNO₂. Interestingly, when a P. denitrificans culture which was grown to steady-state under anaerobic conditions was then exposed to suboptimal pHs, cells exhibited a reduced overall denitrification activity, but neither nitrite nor any other denitrification intermediate accumulated.     

cAMP- and RAS-independent nutritional regulation of plasma-membrane H+-ATPase activity in Saccharomyces cerevisiae

The plasma-membrane ATPase of Saccharomyces cerevisiae is a proton pump whose activity, essential fro proliferation, is subject to regulation by nutritional signals. The previous finding that the CDC25 gene product is required for the glucose-induced H+-ATPase activation suggested that H+-ATPase activity is regulated by cAMP. Analysis of starvation-induced inactivation and glucose-induced activation of the H+-ATPase in mutants affected in activity of the RAS proteins, adenylyl cyclase or cAMP-dependent protein kinase showed that nutritional regulation of H+-ATPase activity does not depend directly on any of these factors. We conclude that adenlyl cyclase does not mediate all nutritional responses. This also indicates that the specific CDC25 requirement for the glucose-induced activation of the H+-ATPase identifies a new function for the CDC25 gene product, a function that appears to be independent of CDC25-mediated modulation of the RAS/adenylyl cyclase/cAMP pathway.     

Stimulus-induced changes in methylesterase activity during chemotaxis in Escherichia coli

Responses of Escherichia coli to chemical stimuli are mediated by a family of sensory transducer proteins. These transmembrane proteins detect stimuli and convey sensory information to the flagella. Behavioral adaptation to environmental changes is correlated with the reversible methylation of the transducer proteins on several (4 to 6) specific glutamic acid residues to form methyl esters. We have assayed the activity of the chemotaxis-specific methylesterase, the product of the cheB gene, by measuring the product of the demethylation reaction, methanol, using a modification of a previous method (Toews, M.L., Goy, M.F., Springer, M.S., and Adler, J. (1979) Proc. Natl. Acad. Sci. U.S.A. 76, 5544-5548; Terwilliger, T.C., Bogonez, E., Wang, E.A., and Koshland, D. E., Jr. (1983) J. Biol. Chem. 258, 9608-9611). In this study, we establish the use of a sensitive flow apparatus for measuring stimulus-induced changes in methylesterase activity of intact E. coli cells. Responses to positive and negative stimuli consist of transient decrease and increases in methylesterase activity, respectively. In addition, chase experiments demonstrated that all assayable methyl groups are nearly equivalent. The results are not consistent with the view that the methyl groups put on the transducer proteins as a result of a positive stimulus are the first to be removed when that stimulus is withdrawn. It seems more likely that recently added methyl groups become part of a pool of kinetically equivalent members, any of which can be removed when the stimulus is withdrawn. The flow measurements provide a powerful and simple biochemical assay that complements behavioral studies of chemotaxis.     

A novel calcineurin-independent activity of cyclosporin A in Saccharomyces cerevisiae

Fungi rely on regulatory networks to coordinate sensing of environmental stress with initiation of responses crucial for survival. Antifungal drugs are a specific type of environmental stress with broad clinical relevance. Small molecules with antifungal activity are ubiquitous in the environment, and are produced by a myriad of microbes in competitive natural communities. The echinocandins are fungal fermentation products and the most recently developed class of antifungals, with those in clinical use being semisynthetic derivatives that target the fungal cell wall by inhibiting 1,3-β-D-glucan synthase. Recent studies implicate the protein phosphatase calcineurin as a key regulator of cellular stress responses required for fungal survival of echinocandin-induced cell wall stress. Pharmacological inhibition of calcineurin can be achieved using the natural product and immunosuppressive drug cyclosporin A, which inhibits calcineurin by binding to the immunophilin Cpr1. This drug-protein complex inhibits the interaction between the regulatory and catalytic subunits of calcineurin, an interaction necessary for calcineurin function. Here, we report on potent activity of cyclosporin A when combined with the echinocandin micafungin against the model yeast Saccharomyces cerevisiae that is independent of its known mechanism of action of calcineurin inhibition. This calcineurin-independent synergy does not involve any of the 12 immunophilins known in yeast, individually or in combination, and is not mediated by any of the multidrug transporters encoded or controlled by YOR1, SNQ2, PDR5, PDR10, PDR11, YCF1, PDR15, ADP1, VMR1, NFT1, BPT1, YBT1, YNR070w, YOL075c, AUS1, PDR12, PDR1 and/or PDR3. Genome-wide haploinsufficiency profiling (HIP) and homozygous deletion profiling (HOP) strongly implicate the cell wall biosynthesis and integrity pathways as being central to the calcineurin-independent activity of cyclosporin A. Thus, systems level chemical genomic approaches implicate key cellular pathways in a novel mechanism of antifungal drug synergy.     

Some factors affecting flight in field populations of the Australian plague locust, Chortoicetes terminifera (walker), in New South Wales

An attempt was made to determine some of the factors regulating flight activity in the Australian plague locust, Chortoicetes terminifera (Walk.) by comparing the physiological characteristics of flying and non-flying locusts at different times of the day. Flight during the day did not appear to involve extensive displacements of the insects and was dependent largely on the, environmental conditions. The physiological state and age did not seem important and the milling flight of swarms involved insects of all ages and states of sexual maturity and the insects were commonly fully fed. There was probably at this time a continual interchange of insects between the air and the ground provided wind speeds are not too high and the air temperature was not below 19°C. Night flight, however, was observed only in locusts after the teneral period, when cuticle deposition was nearing completion around 10 days after the imaginal ecdysis and, in the case of the females, the oocytes were relatively undeveloped. Night flight was also associated with a failure to feed prior to sunset; only those with empty foreguts being stimulated to fly with the drop in light intensity, when the temperature was not too low and certainly not below 17·5°C. It is probably the older insects which take-off in these circumstances for by the time of sunset 30 to 40 per cent of the older, ones apparently fail to feed on any one evening and empty locusts tend to be more active than fully fed ones. The females appeared to show a flight periodicity related to the oviposition cycle, which under suitable conditions, leads to the displacement of about one-third of the population which is sexually immature or which has already recently oviposited. The flight activity of females is probably greater than that of the males for the sexes were in equal ratio in insects caught in flight while males exceeded females in ground populations. At sunset, fewer females than males still had full foreguts and were perhaps more likely to take-off while a higher proportion of younger females than males may soon re-alight if their physiological state is unfavourable for prolonged flight at night.     

Sudden unexpected death in epileptics following sudden,intense, increases in geomagnetic activity: Prevalence of effect and potential mechanisms

Abrupt, intense increases in global geomagnetic activity during the local night may precipitate a significant proportion of sudden unexpected (or unexplained) deaths (SUD) in epileptics. Over a 2-year period SUD in healthy chronic epileptic rats occurred when the average daily geomagnetic activity exceeded 50 nT (nanoTesla) and suddenly began during local night. Other experiments demonstrated that epileptic rats displayed more spontaneous seizures per night if there had been sudden increases in geomagnetic activity. Analyses of previously published data indicated that the number of SUDs/month in a population of human epileptics was positively associated with the number of days/month when the average geomagnetic activity exceeded 50 nT. The results support the hypothesis that suppression of the nocturnal concentrations of the endogenous anticonvulsant melatonin by sudden increases in geomagnetic activity may encourage fatal cardiac arrhythmias by uncoupling the insular/amygdaloid-paraventricular hypothalamic-solitary nucleus pathways.