The nitric oxide-cGMP pathway may mediate communication between sensory afferents and projection neurons in the antennal lobe of Manduca sexta

The nitric oxide (NO)-cGMP signaling system is thought to play important roles in the function of the olfactory system in both vertebrates and invertebrates. One way of studying the role of NO in the nervous system is to study the distribution and properties of NO synthase (NOS), as well as the soluble guanylyl cyclases (sGCs), which are the best characterized targets of NO. We study NOS and sGC in the relatively simple and well characterized insect olfactory system of the hawkmoth, Manduca sexta. We have cloned Manduca sexta nitric oxide synthase (MsNOS) and two sGCs (MsGCalpha1 and MsGCbeta1), characterized their basic biochemical properties, and studied their expression in the olfactory system. The sequences of the Manduca genes are highly similar to their mammalian homologs and show similar biochemical properties when expressed in COS-7 cells. In particular, we find that MsGC functions as an obligate heterodimer that is stimulated significantly by NO. We also find that MsNOS has a Ca2+-sensitive NO-producing activity similar to that of mammalian neuronal NOS. Northern and in situ hybridization analyses show that MsNOS and the MsGCs are expressed in a complementary pattern, with MsNOS expressed at high levels in the antennae and the MsGCs expressed at high levels in a subset of antennal lobe neurons. The expression patterns of these genes suggest that the NO-sGC signaling system may play a role in mediating communication between olfactory receptor neurons and projection neurons in the glomeruli of the antennal lobe.     

Characterization of arylamine N-acetyltransferase in Enterobacter aerogenes

N-acetyltransferase (NAT) activity was determined by incubation of purified Enterobacter aerogenes enzyme with 2-aminofluorene (2-AF) as the substrate, followed by high pressure liquid chromatography assays. The NAT activity from E. aerogenes was 0.58 +/- 0.08 nmol/min/mg protein for 2-AF. The values of apparent K(m) and Vmax were 0.72 +/- 0.14 mM and 2.45 +/- 0.29 nmol/min/mg protein, respectively, for 2-AF. The optimal pH value for the enzyme activity was 7.5 for the 2-AF tested. The optimal temperature for enzyme activity was 37 degrees C for the 2-AF substrate. The molecular weight of NAT from E. aerogenes was 44.9 kD. Among a series of divalent cations and salts, Zn2+, Ca2+, and Fe2+ were demonstrated to be the most potent protease inhibitors, and only ethylenediaminetetraacetic acid significantly protected the NAT. Iodoacetamide, in contrast to other agents, markedly inhibited NAT.     

Excretion of a radiolabelled anticancer biodegradable polymeric implant from the rabbit brain

The elimination of a clinically used anticancer biodegradable polymer implant (Gliadel) in the rabbit brain was studied. The implant is composed of N,N-bis(2-chloroethyl)-N-nitrosourea (BCNU) (1.6 wt%) dispersed in a copolyanhydride matrix of 1,3-bis(p-carboxyphenoxypropane) (CPP) and sebacic acid (SA) in a 20:80 molar ratio. Four groups of rabbits were implanted with wafers loaded with BCNU, one in a 14C-SA-labelled polymer, another in a 14C-CPP-labelled polymer and two groups with 14C-BCNU in a non-labelled polymer, one for BCNU disposition study and one for residual drug study. In the rabbits implanted with the 14C-SA-labelled polymer, approximately 10% of the radioactivity was found in the urine and 2% in the faeces, and about 10% remained in the device 7 d after implantation. In contrast, only 4% of the radioactivity of the 14C-CPP-labelled polymer was found in urine and faeces during this period. However, a drastic increase in the CPP excretion was found after 9 d, and at 21 d, 64% of the implanted 14C-CPP was found in the urine and faeces, and 29% was still in the recovered wafers. Approximately 50% of the BCNU in the wafers was released in 3 d, and over 95% was released after 6 d in the rabbit brain. This study demonstrates that BCNU-loaded polyanhydride is biodegradable and is excreted from the body primarily through the renal system. The water-soluble components SA and BCNU were rapidly excreted, while the insoluble CPP was gradually eliminated after a lag time of 9 d.     

The third order nonlinear optical properties of gold nanoparticles in glasses, part II

The optical properties of gold nanoparticles have been known for a number of years and recent advances in laser power have now allowed the non-linear optical properties to be studied. In this short review paper, the various theories that have been used to describe the optical properties of gold nanoparticles are presented. Methods of preparing gold nanoparticles in glasses are explained briefly, as well as characterization techniques. The optical properties of gold nanoparticles are reviewed, as well as the effects of particle size, shape, concentration and c.     

The wall-jet electrode and the study of electrode reaction mechanisms: the EC reaction

The theory of EC reactions at a wall-jet electrode is developed using a computational procedure based on the Backwards Implicit Method. In particular, for the case of a reversible electron transfer, it is shown that the variation of the halfwave potential with solution flow rate provides a means of characterizing the EC mechanism. A working curve is presented which permits the analysis of experimental data and the deduction of the rate constant for the following chemical reaction.Nomenclature a diameter of the jet - a _j matrix element (j = 2,3,..., ) - b _j matrix element (j = 1,2,..., ) - C _j matrix element (j = 1,2,..., ) - D diffusion coefficient - d _j vector element (j = 1,2,..., ) - E electrode potential - E ⁰ standard electrode potential of A/B couple - F Faraday constant - g(A) normalized concentration of A - g(B) normalized concentration of B - I current - I _LIM transport limited curren - J number of points inr-direction on finite difference grid - j conter,j=1, 2,...,J - K Number of points inz-direction on finite difference grid - K _j,k+1 normalized rate constant (Equation 23) - k counter,k=1, 2,...,K - k counter,k=1, 2,...,K - k _c experimental constant - first order rate constant - M constant defined byM =k _c ⁴ V _f ³ /2³a² - R electrode radius - r radial coordinate - u _j vector element (j = 1,2,..., ) - V volume flow rate (cm³ s^–1) - _r solution velocity inr-direction - _z solution velocity inz-direction - z coordinate normal to electrode surface - dimensionless distance parameter (see Equation 5) - dimensionless variable (Equation 25) - normalized electrode potential - _1/2 normalized halfwave potential - kinematic viscosity (cm² s^–1) - dimensionless variable (Equation 26) - {d} _k vector{d _1,k ,d _2,k ,...d _j–1,k} - {u} _k vector {u _1,k+1,u _2,k+1,...,u _j–1,k+1}     

Responses of fig wasps to host plant volatile cues

Fig wasps (Chalcidoidea; Agaonidae) are intimately associated with the 750 or so species of fig trees (Ficus, Moraceae). Each tree species is usually pollinated by a single species of wasp belonging to the subfamily Agaoninae, while other wasps of the family are parasitoids or seed predators. Previous experiments have shown that the wasps are attracted to the trees by volatiles emanating from the figs. Using fig-bearing trees and arrays of sticky traps baited with figs, we investigated the specificity of wasp attraction and its timing. The pollinators of two closely relatedFicus species were specifically attracted to figs of their host species and only at the time when figs were ready to be pollinated. Some nonpollinating fig wasps appear to respond to the same volatile cues.     

Cyclic voltammetry on electrode surfaces covered with porous layers: An analysis of electron transfer kinetics at single-walled carbon nanotube modified electrodes

Cyclic voltammetry is recorded of the oxidation of ferrocyanide on a glassy carbon electrode modified with multiple layers of single-walled carbon nanotubes. The current response is interpreted in terms of semi-infinite planar diffusion towards the macro-electrode surface and in terms of oxidation of the electroactive species trapped in pockets in between the nanotubes. A thin layer model is used to illustrate the effects of diffusion within a porous layer. It is found that a semi-infinite planar diffusion model alone is not appropriate for interpreting the kinetics of the electron transfer at this electrode surface. In particular, caution should be exercised in respect of comparing voltammetric peak-to-peak potential separations between naked electrodes and nanotube-modified electrodes for the inference of electrocatalysis via electron transfer via the nanotubes.