Octopamine increases the excitability of neurons in the snail feeding system by modulation of inward sodium current but not outward potassium currents

Background  

Although octopamine has long been known to have major roles as both transmitter and modulator in arthropods, it has only recently been shown to be functionally important in molluscs, playing a role as a neurotransmitter in the feeding network of the snail Lymnaea stagnalis. The synaptic potentials cannot explain all the effects of octopamine-containing neurons on the feeding network, and here we test the hypothesis that octopamine is also a neuromodulator.     

Update on design simulations for NIF ignition targets, and the rollup of all specifications into an error budget

Targets intended to produce ignition on NIF are being simulated and the simulations are used to set specifications for target fabrication and other program elements. Recent design work has focused on designs that assume only 1.0 MJ of laser energy instead of the previous 1.6 MJ. To perform with less laser energy, the hohlraum has been redesigned to be more efficient than previously, and the capsules are slightly smaller. Three hohlraum designs are being examined: gas fill, SiO₂ foam fill, and SiO₂ lined. All have a cocktail wall, and shields mounted between the capsule and the laser entrance holes. Two capsule designs are being considered. One has a graded doped Be(Cu) ablator, and the other graded doped CH(Ge). Both can perform acceptably with recently demonstrated ice layer quality, and with recently demonstrated outer surface roughness. Complete tables of specifications are being prepared for both targets, to be completed this fiscal year. All the specifications are being rolled together into an error budget indicating adequate margin for ignition with the new designs. The dominant source of error is hohlraum asymmetry at intermediate modes 4–8, indicating the importance of experimental techniques to measure and control this asymmetry.     

Migration of methyl groups between aliphatic amines in water

Glycine undergoes spontaneous decarboxylation in dilute aqueous solution at elevated temperatures to form methylamine. During that process, we noticed the appearance of dimethylamine and trimethylamine in smaller amounts that increased gradually with time. These observations suggested the existence of disproportionation reactions of methylamines in water, for which there appears to be no direct precedent in the literature. Every member of the methylamine series is found to yield other members of the methylamine series. When the total concentration of amine was held constant and the rate of reaction was examined as a function of changing pH using the amine itself as the buffer, the initial rate of appearance of the products was found to reach a maximum when the conjugate acid and the conjugate base were present at equivalent concentrations. Near this equivalence point, the rate of reaction varied with pH as expected for a second-order reaction between the protonated and the unprotonated species. Under similar conditions, methyl groups were also found to migrate between the nitrogen atoms of N,N-dimethyl-1,3-propanediamine in a first-order process. With dimethylamine as a common acceptor, trimethylsulfonium ion was found to be approximately 104-fold more reactive than the tetramethylammonium ion at ambient temperature.     

Charge development in the transition state for decarboxylations in water: spontaneous and acetone-catalyzed decarboxylation of aminomalonate

A covalent imminium adduct, formed by condensation of aminomalonate with acetone, undergoes decarboxylation (k = 0.03 s-1 at 25 degrees C) in water 30 000 times more rapidly than does aminomalonate in the absence of acetone. A Br?nsted plot of the observed rates of decarboxylation of these and other ionized carboxylic acids, as a function of the pKC-H values of the carbon acids generated by their decarboxylation, exhibits a betalg value of 0.7, indicating that the structures of the transition states for decarboxylation of the carboxylate forms of these acids approaches the structures of the carbanions generated by their decarboxylation. On the basis of an estimated pKC-H value for benzene in water ( approximately 43), extrapolation of that Br?nsted plot leads to the prediction that benzoate decarboxylation should proceed at detectable rates in water at temperatures below the critical point. That prediction was confirmed experimentally. Using this same relationship, and extrapolating to the observed rate constant for enzymatic decarboxylation of orotidine 5'-monophosphate, we estimate that the "effective" pKa value of the 6-CH group of uridine 5'-monophosphate, the product of decarboxylation, is 9.5 at the active site of yeast OMP decarboxylase.     

The effects of an electric field on an autocatalytic ionic reaction in a system with high ionic strength

The effects of an applied electric field on an ionic autocatalyticreaction with a quadratic rate law are considered, where thereacting species, A⁺ and B⁺, are present in a system which alsoincludes non-reacting species C^- and D⁺. The conditions areestablished under which the general terms which describe theelectric field effects in the reaction-diffusion equations canbe simplified to those used in previous studies, where theseeffects are modelled by linear advection terms. The resultingequations are then studied in detail by first obtaining conditionsfor the existence of travelling waves of permanent form. Thisdiscussion shows that _B, the ratio of the diffusion coefficientsof B⁺ and A⁺, is a critical parameter, with different formsof behaviour arising for _B < 1 and _B > 1. This analysisis augmented by obtaining solutions valid for large times andlarge values of (the dirnensionless applied field). Numericalsolutions of initial-value problems are obtained for a rangeof values of and _B, guided by and interpreted through the analysispreviously obtained. These numerical integrations show the formationof reaction fronts, with the possibility of greatly increasedreaction rates caused by the applied electric field, as wellas propagating electrophoretic fronts in B⁺ being formed incases where a reaction front is also initiated. There is alsothe possibility of separate electrophoretic fronts in A⁺ andB⁺ being formed, which become increasingly separated as timeincreases with the reaction being completely inhibited.