Phantom controllers: Misspecified models create the false appearance of adaptive control during value-based choice.

Decision scientists have grown increasingly interested in how people adaptively control their decision making. Researchers have demonstrated that parameters governing the accumulation of evidence towards a choice, such as the decision threshold, are shaped by information available prior to or in parallel with one's evaluation of an option set (e.g., recent outcomes or choice conflict). A recent account has taken a bold leap forward in this approach, suggesting that adjustments in decision parameters can be motivated by the value of the options under consideration. This motivated control account predicts that when faced with difficult choices (similarly valued options) under time pressure, people will adaptively lower their decision threshold to ensure that they make a choice in time. This account was supported by drift diffusion modeling of a deadlined choice task, demonstrating that decision thresholds decrease for difficult relative to easy choices. Here, we reanalyze the data from this experiment, and show that evidence for this novel account does not hold up to further scrutiny. Using a more systematic and comprehensive modeling approach, we show that this previously observed threshold adjustment disappears (or even reverses) under a more complete model of the data. Importantly, we further show how this and other apparent evidence for motivated control arises as an artifact of model (mis)specification, where one model's putatively controlled decision process (e.g., value-driven threshold adjustments) can mimic another model's stimulus-driven decision processes (e.g., accumulator competition or collapsing bounds). Collectively, this work reveals crucial insights and constraints in the pursuit of understanding how control guides decision-making, and when it doesn't.

Biosynthesis of riboflavin: studies on the mechanism of GTP cyclohydrolase II.

GTP cyclohydrolase II catalyzes the first committed reaction in the biosynthesis of the vitamin riboflavin. The recombinant enzyme from Escherichia coli is shown to produce 2,5-diamino-6-beta-ribosylamino-4(3H)-pyrimidinone 5'-phosphate and GMP at an approximate molar ratio of 10:1. The main product is subject to spontaneous isomerization affording the alpha-anomer. (18)O from solvent water is incorporated by the enzyme into the phosphate group of the 5-aminopyrimidine derivative as well as GMP. These data are consistent with the transient formation of a covalent phosphoguanosyl derivative of the enzyme. Subsequent ring opening of the covalently bound nucleotide followed by hydrolysis of the phosphodiester bond could then afford the pyrimidine type product. The hydrolysis of the phosphodiester bond without prior ring opening could afford GMP. The enzyme reaction is cooperative with a Hill coefficient of 1.3. Inhibition by pyrophosphate is competitive. Inhibition by orthophosphate is partially uncompetitive at low concentration and competitive at concentrations above 6 mm.

Generation of cytotoxic T lymphocytes and cytostatic acting cells in T. annulata-immune cattle.

Cattle immunized against Theileria annulata with schizont containing autologous cell lines are immune to challenge with a homologous parasite strain. Two cell types have been detected in the peripheral blood of the immunized animals: cytotoxic T lymphocytes (CTL) and cytostatic acting cells (CAC). Killing the target cells by CTL is infection associated and is MHC class I restricted. Hence, no cytotoxicity was observed against target cells that were treated with the theilericidal drug buparvaquone or autologous Con A-blasts. The growth inhibition of CAC is MHC unrestricted, and not mediated by cytokine interferon gamma (IFN-gamma).

Histidine 179 mutants of GTP cyclohydrolase I catalyze the formation of 2-amino-5-formylamino-6-ribofuranosylamino-4(3H)-pyrimidinone triphosphate.

GTP cyclohydrolase I catalyzes the conversion of GTP to dihydroneopterin triphosphate. The replacement of histidine 179 by other amino acids affords mutant enzymes that do not catalyze the formation of dihydroneopterin triphosphate. However, some of these mutant proteins catalyze the conversion of GTP to 2-amino-5-formylamino-6-ribofuranosylamino-4(3H)-pyrimidinone 5'-triphosphate as shown by multinuclear NMR analysis. The equilibrium constant for the reversible conversion of GTP to the ring-opened derivative is approximately 0.1. The wild-type enzyme converts the formylamino pyrimidine derivative to dihydroneopterin triphosphate; the rate is similar to that observed with GTP as substrate. The data support the conclusion that the formylamino pyrimidine derivative is an intermediate in the overall reaction catalyzed by GTP cyclohydrolase I.

Voltage-gated sodium and potassium channels in radial glial cells of trout optic tectum studied by patch clamp analysis and single cell RT-PCR.

Radial glial cells in the visual center of trout were analyzed immunocytochemically and with the whole cell mode of the patch-clamp technique in combination with RT-PCR. By immunostaining with anti-GFAP antibodies radially oriented cell processes spanning the entire width of the tectum were brightly labeled, while with anti-S-100 antiserum the cell bodies residing in a discrete layer close to the ventricular border became most clearly visible. Virtually all radial glial cells examined in brain slices exhibited voltage-gated sodium inward currents that were activated above -40 mV, blocked by micromolar concentrations of TTX and totally eliminated if sodium was substituted for Tris in the bath solution. In contrast with adjacent nerve cells of the same slices radial glial cells did not exhibit spontaneous electrical activity and could not be stimulated to generate action potentials by depolarizing current injections. Two types of voltage-gated potassium outward currents were elicited by depolarizing voltage steps: a sustained current with delayed rectifier properties and a superimposed transient "A"-type current, both being activated at a threshold potential of -40 mV. In cultured radial glial cells subtle differences were noticed regarding current density, inactivation kinetics, and TEA-sensitivity of the potassium currents. Inwardly rectifying potassium currents activating at hyperpolarized voltages were not observed. By single cell RT-PCR the transcripts of two shaker-related potassium channel genes (termed tsha1-a fish homologue to Kv1.2- and tsha3) were amplified, while transcripts for tsha 2 and tsha 4 were not detected.

Biosynthesis of pteridines. NMR studies on the reaction mechanisms of GTP cyclohydrolase I, pyruvoyltetrahydropterin synthase, and sepiapterin reductase.

GTP cyclohydrolase I catalyzes a ring expansion affording dihydroneopterin triphosphate from GTP. [1',2',3',4',5'-13C5, 2'-2H1]GTP was prepared enzymatically from [U-13C6]glucose for use as enzyme substrate. Multinuclear NMR experiments showed that the reaction catalyzed by GTP cyclohydrolase I involves the release of a proton from C-2' of GTP that is exchanged with the bulk solvent. Subsequently, a proton is reintroduced stereospecifically from the bulk solvent. This is in line with an Amadori rearrangement mechanism. The proton introduced from solvent occupies the pro-7R position in the enzyme product. The data also confirm that the reaction catalyzed by pyruvoyltetrahydropterin synthase results in the incorporation of solvent protons into positions C-6 and C-3' of the enzyme product. On the other hand, the reaction catalyzed by sepiapterin reductase does not involve any detectable incorporation of solvent protons into tetrahydrobiopterin.

Voltage-gated potassium channels of Schwann cells from trout lateral line nerve: a combined electrophysiological and molecular characterization.

Voltage-gated ionic currents were recorded from explant cultured and freshly dissociated SC from trout lateral line nerve using the whole-cell configuration of the patch clamp technique. In the majority of cases a delayed rectifier potassium outward current (KD) was found exclusively, which activated at potentials > or = -40 mV and reached maximal amplitudes of 240+/-25.2 nA at 60 mV testpulse potential. This current showed no voltage-dependent kinetics of inactivation and was insensitive to TEA but was effectively blocked by 4-AP. By single cell RT-PCR the transcript of a shaker-related potassium channel gene, termed tshal (a fish homologue of Kv1.2), was selectively amplified. In its biophysical and pharmacological properties the native whole cell potassium outward current of trout Schwann cells closely matched those of the cloned tshal subunit previously expressed in xenopus oocytes. A small subpopulation of freshly dissociated SC (less than 10%) at hyperpolarizing potentials elicited a potassium inward current instead, which in its kinetics closely resembled the inward rectifier (KIR) of mammalian SC. Neither voltage-gated sodium currents nor membrane currents activated by excitatory amino acids (glutamate, kainate, and quisqualate) were observed.

Respiratory allergenicity of detergent enzymes in the guinea pig intratracheal test: association with sensitization of occupationally exposed individuals.

A guinea pig intratracheal test was used to set occupational operating guidelines for new enzyme proteins used in the detergent industry. In these studies, animals were intratracheally dosed with different levels of enzyme protein and sera from the animals were titered for allergic antibody to the enzyme. The amount of antibody produced to an enzyme was compared to the amount of antibody produced to the same protein doses of Alcalase, for which effective operating guidelines exist. These comparisons were used to determine if a new enzyme was more potent, less potent, or equivalent to Alcalase; operating guidelines were then established for the new enzyme. Termamyl was about 10-fold more potent than Alcalase and the protease subtilisin B was shown to be less potent. Another protease, Savinase, was shown to be equivalent in potency to Alcalase. The operating guidelines for Termamyl were adjusted lower, whereas the operating guidelines for the proteases were set the same as that of Alcalase. Under these conditions, we would predict that sensitizations to new enzymes would be comparable to or lower than the sensitizations to Alcalase. Prospective evaluation of skin prick test data of factory workers showed that sensitizations to Termamyl and Savinase were similar to sensitizations to Alcalase. The sensitizations to subtilisin B were lower than those to Alcalase. During this time period (7 years), only three respiratory incidents (rhinitis) were reported, demonstrating that employees with positive skin prick tests can continue to work. These comparisons indicate that the guinea pig intratracheal test is a good animal model for evaluating enzymes as respiratory allergens and that the data generated can be used to set operating guidelines for occupational allergens.

Proteolytic detergent enzymes enhance the allergic antibody responses of guinea pigs to nonproteolytic detergent enzymes in a mixture: implications for occupational exposure.

A guinea pig intratracheal test was developed to assess the respiratory allergenicity of enzymes used in the detergent industry. Information gained from this test was used in a process for setting operational exposure guidelines to protect worker health. Mixtures of enzyme proteins were given to guinea pigs once per week for 10 weeks to determine whether there were interactions among enzymes that affected the induction of antibody responses to each enzyme in the mixture. Passive cutaneous anaphylaxis antibody titers against each enzyme were measured in sera. Mixtures of two or three enzymes always consisted of a protease (Alcalase, Savinase; Novo Industri A/S) with an alpha-amylase (Termamyl; Novo Industri A/S), a lipase (Lipolase; Novo Industri A/S), or both. Control animals were exposed to single enzymes. The antibody titers to Termamyl and Lipolase were significantly greater in animals dosed with the protease-containing mixtures as compared with control animals dosed with a single enzyme. Antibody titers to the protease were unchanged in the presence of additional enzymes in the mixture. Complete inactivation of protease activity abrogated the enhanced antibody response to Lipolase. Inhalation exposure of guinea pigs to a mixture of Alcalase and Lipolase also resulted in higher antibody titers to Lipolase as compared with animals exposed by inhalation to Lipolase alone, showing that the enhanced response was not due to intratracheal delivery of antigen to the respiratory tract. These results show that proteolytic enzymes in a mixture enhance antibody responses to other enzymes. This should be considered when defining exposure guidelines for protease-containing enzyme mixtures.

Active site topology and reaction mechanism of GTP cyclohydrolase I.

GTP cyclohydrolase I of Escherichia coli is a torus-shaped homodecamer with D5 symmetry and catalyzes a complex ring expansion reaction conducive to the formation of dihydroneopterin triphosphate from GTP. The x-ray structure of a complex of the enzyme with the substrate analog, dGTP, bound at the active site was determined at a resolution of 3 A. In the decamer, 10 equivalent active sites are present, each of which contains a 10-A deep pocket formed by surface areas of 3 adjacent subunits. The substrate forms a complex hydrogen bond network with the protein. Active site residues were modified by site-directed mutagenesis, and enzyme activities of the mutant proteins were measured. On this basis, a mechanism of the enzyme-catalyzed reaction is proposed. Cleavage of the imidazole ring is initiated by protonation of N7 by His-179 followed by the attack of water at C8 of the purine system. Cystine Cys-110 Cys-181 may be involved in this reaction step. Opening of the imidazole ring may be in concert with cleavage of the furanose ring to generate a Schiff's base from the glycoside. The gamma-phosphate of GTP may be involved in the subsequent Amadori rearrangement of the carbohydrate side chain by activating the hydroxyl group of Ser-135.

Biosynthesis of riboflavin: cloning, sequencing, mapping, and expression of the gene coding for GTP cyclohydrolase II in Escherichia coli.

GTP cyclohydrolase II catalyzes the first committed step in the biosynthesis of riboflavin. The gene coding for this enzyme in Escherichia coli has been cloned by marker rescue. Sequencing indicated an open reading frame of 588 bp coding for a 21.8-kDa peptide of 196 amino acids. The gene was mapped to a position at 28.2 min on the E. coli chromosome and is identical with ribA. GTP cyclohydrolase II was overexpressed in a recombinant strain carrying a plasmid with the cloned gene. The enzyme was purified to homogeneity from the recombinant strain. The N-terminal sequence determined by Edman degradation was identical to the predicted sequence. The sequence is homologous to the 3' part of the central open reading frame in the riboflavin operon of Bacillus subtilis.

Respiratory and immunological responses of guinea pigs to enzyme-containing detergents: a comparison of intratracheal and inhalation modes of exposure.

Guinea pigs were exposed once a week for 10 weeks by intratracheal exposure to solutions of 3, 1, 0.3, or 0.1 micrograms of the enzyme protein, Subtilisn Carlsberg (Alcalase), in 250 micrograms of a detergent base. Other groups of guinea pigs were exposed by inhalation (6 hr per day, 4 days a week) to 1 mg/m3 of the aerosolized detergent base containing either 3.5, 1.1, 0.3, or 0.1% Alcalase protein. Evaluations of gross respiratory responses immediately following each intratracheal exposure revealed a significant dose response in respiratory symptoms measurable after the fourth exposure and continuing throughout the study. In the inhalation experiment, during Weeks 4 through 10, animals were observed to have respiratory symptoms which were dependent upon both the dose of enzyme and on total exposure to the enzyme/detergent atmosphere. For both intratracheal and inhalation routes of exposure, the initial appearance of respiratory symptoms coincided with the first appearance of measurable serum allergic antibodies specific to Alcalase. The allergic antibody levels increased with time and dosage by both routes of exposure, and the antibody titers generated by the intratracheal administration of antigen were comparable to those generated by the inhalation route of exposure. These results indicate that the intratracheal technique is appropriate for the evaluation of the respiratory allergic response to a protein.

Antigenic and allergenic analysis of psyllium seed components.

The outer portions (husk) of psyllium seeds are a concentrated source of natural fiber used in some bulk-fiber laxatives and cereals. They are known to elicit respiratory allergic reactions after inhalation or ingestion among sensitized individuals. Antigenic and allergenic characterization of three psyllium-seed fractions (husk, endosperm, and embryo) was conducted with crossed immunoelectrophoresis (CIE), crossed radioimmunoelectrophoresis, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis to determine the source of psyllium allergenicity. Homologous CIE demonstrated psyllium endosperm and embryo extracts contained seven and four antigens, respectively. Husk extracts were too gelatinous to react by CIE. However, heterologous CIE profiles of endosperm or embryo extracts, reacted with antihusk antibodies, resulted in antigen-antibody precipitin peaks that matched the heavy staining precipitin lines of homologous reactions for endosperm and embryo, respectively. These results indicated that commercial-grade husk, endosperm, and embryo contained similar antigens. Extracts of all three seed components contained antigens that bound IgE antibodies in the sera of 11 psyllium RAST-positive individuals, as determined by crossed radioimmunoelectrophoresis. The few prominent husk protein/peptide bands resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis were common in either embryo or endosperm. Immunoblots revealed common IgE reactive bands in all three seed fractions. Microscopic examination of the powdered commercial-grade psyllium (95% pure) revealed it contained endosperm and embryo particles. These immunologic, biochemical, and microscopic findings suggest that other contaminating seed components are primarily responsible for the allergenicity of commercial-grade psyllium-husk powder rather than the husk itself.

A review of the Buehler guinea pig skin sensitization test and its use in a risk assessment process for human skin sensitization.

The Buehler test is a valuable procedure for screening the sensitization potential of chemicals prior to human exposure. Our experience of over 20 years has shown it to be effective in detecting strong, moderate, and most weak sensitizers. The topical exposure inherent in the Buehler test allows it to be utilized to investigate dose responses, cross reactivity between structurally related chemicals, and the sensitization potential of contaminants in raw material mixtures. For safety assessment purposes, Buehler test results provide an initial indication of the sensitization potential of the material in question under relevant, but exaggerated, exposure conditions. These results can be compared to results on benchmark chemicals to assess sensitization risk for subsequent human exposure. Optimizing the sensitivity of the Buehler test requires adherence to the published methodology and proper interpretation of the challenge and rechallenge data obtained. Adjuvant-type test methods are generally considered to be more sensitive than topical methods. However, when done properly, topical test procedures such as the Buehler test or the open epicutaneous test can accurately detect most chemicals with any realistic potential for sensitizing humans by the topical route. Moreover, from a risk assessment perspective, these topical tests avoid the problems of overestimating the weak sensitization potential of many topically applied materials or underestimating the sensitization potential of very strong sensitizers; both are potential concerns with invasive adjuvant-type test methods. The Buehler test or other topical test methods are particularly valuable for comparative sensitization risk assessment since human sensitization data on benchmark materials are all derived from topical exposure. The risk assessment is developed by comparing the guinea pig data on the new material versus relevant benchmark chemicals or formulations and also by evaluating the existing human sensitization data on the benchmark material. These data are then utilized to predict human sensitization risk from topical exposure to the new material. Confirmation of human safety can be derived from human repeat insult patch testing (HRIPT) and other clinical tests such as the product use test and the diagnostic patch test. Utilized in this manner, the Buehler test is an integral component of an overall skin sensitization safety assessment program for a new chemical or product formulation.

Antigenic and allergenic characterization of the enzymes alcalase and savinase by crossed immunoelectrophoresis and crossed radioimmunoelectrophoresis.

Alcalase and savinase, produced by Bacillus species, are proteolytic enzymes that are used in laundry products and are known to cause respiratory allergy. Antigenic and allergenic characteristics of alcalase and savinase and their potential cross-reactivity were evaluated using crossed immunoelectrophoresis and crossed radioimmunoelectrophoresis. Alcalase exhibited two distinct antigens; one electropositive and one electronegative. The electropositive antigen exhibited some retrograde anodic mobility when coupled with antiserum components. Savinase exhibited one electropositive and two electronegative antigens. The antigens of the two enzymes were clearly different from each other, the three savinase antigens exhibiting greater electrophoretic mobility than the two alcalase antigens. In crossed radioimmunoelectrophoresis studies, only the electropositive antigen of alcalase, its retrograde complex, and the electropositive antigen of savinase bound IgE from the sera of individuals who were skin test positive to one or both enzymes. No evidence of cross-reactivity was observed in heterologous and tandem crossed immunoelectrophoresis studies and heterologous microimmunodiffusion reactions.