The neural basis of orienting behavior: a computational approach to the escape turn of the cockroach

Using computer simulation, we demonstrate that the information encoded by the ventral giant interneurons is particularly suited to orienting the escape turn of the adult cockroach with a degree of variation seen experimentally. The type of model we present for sensorimotor integration incorporates a simple comparator of sensory evoked GI activity and is extremely robust with respect to underlying assumptions.     

Reactivity and fate of benzene and formaldehyde in culture medium with and without fetal calf serum; relevance to in vitro mutagenicity testing

Gas chromatographic-mass spectrometric analyses were performed to determine the reactivity and fate of benzene (BEN) and formaldehyde (FA) in culture medium. BEN (solubility in water: 500 ppm) does not react with culture medium, either with or without fetal calf serum, but its volatility, even in closed vials, is so great that 90% of a 250-ppm solution is lost to the head space after 1 h at 24°C. FA, as a 37% aqueous solution, is a complex mixture that changes composition after 15-min incubation at 38°C. FA is extremely reactive in culture medium containing fetal calf serum, and is much less reactive with medium components in the absence of serum. There is a dramatic increase in the number of daughter products in FA-treated medium over time, such that those seen immediately after FA is added to medium have been replaced after 60-min incubation (38°C in closed vials) by many other interaction products. Methods ensuring maximum solubilization and minimal volatilization of BEN during exposure are essential for obtaining reproducible data on the mutagenic potential of BEN. The volatilization of FA from stock formalin solutions, and, more importantly, the interaction product(s) formed by this highly reactive compound with medium components, especially those in serum, are probably the critical aspects of an effective testing protocol for FA.     

Transmission of Megatrypanum Trypanosomes to Cervus dama by Tabanidae1

Four fallow deer, Cervus dama, became infected with Trypanosoma (Megatrypanum) sp. by oral application of triturated guts from tabanids collected in an area with deer but without any cattle; four control calves remained negative. Upon challenge with triturated guts from tabanids from an area with pastured cattle, the four calves became infected with Trypanosoma (M.) theileri. The prepatent period in deer was five days or less. Haematopota spp. and Tabanus spp. were identified as vectors of the deer trypanosomes. It is concluded that the trypanosomes of C. dama belong to a Megatrypanum species that is not identical with T. theileri.     

Biological consequences of a reduction in the non-target DNA scanning capacity of a DNA repair enzyme

Numerous DNA-interactive proteins have been shown to locate specific sequences within large domains of non-target DNA in vitro and in vivo by a one-dimensional diffusion mechanism; however, the biological significance of this process has not been evaluated. We have examined the biological consequences of sliding for the pyrimidine dimer-specific DNA repair enzyme T4 endonuclease V, an enzyme which scans non-target DNA both in vitro and in vivo. An endonuclease V mutant was constructed whose only altered biochemical characteristic, measured in vitro, was a loss in its ability to slide on non-target DNA. In contrast to the native enzyme, when the mutated endonuclease V was expressed in DNA repair-deficient Escherichia coli, no enhanced ultraviolet survival was conferred. These results suggest that the mechanisms which DNA-interactive proteins employ to enhance the probability of locating their target sequences are of significant biological importance.     

Rapid Stimulation of EAAC1-Mediated Na+-Dependent l-Glutamate Transport Activity in C6 Glioma Cells by Phorbol Ester

Abstract: C6 glioma cells were used as a model system to study the regulation of EAAC1-mediated Na⁺-dependent l -[³H]glutamate transport. Although a 30-min preincubation with forskolin had no effect on transport activity, preincubation with phorbol 12-myristate 13-acetate (PMA) increased transport activity two- to threefold. PMA caused a time-dependent and concentration-dependent increase in EAAC1-mediated l -[³H]glutamate transport activity. A 2-min preincubation with PMA was sufficient to cause more than a twofold increase in transport activity and the protein synthesis inhibitor cycloheximide had no effect on the increase. These data suggest that this increase is independent of protein synthesis. The EC₅₀ value of PMA for stimulation of transport activity was 80 nM. Kinetic analyses demonstrated that the increase in transport activity was due to a 2.5-fold increase in V_max with no change in K_m. PMA also increased the transport of the nonmetabolizable analogue, d -[³H]aspartate to the same extent. In parallel assays, PMA did not, however, increase Na⁺-dependent glycine transport activity in C6 glioma. The inactive phorbol ester 4α-phorbol 12,13-didecanoate, did not stimulate l -[³H]glutamate transport activity, and the protein kinase C inhibitor chelerythrine blocked the stimulation caused by PMA. Okadaic acid and cyclosporin A, which are phosphatase inhibitors, had no effect on the stimulation of transport activity caused by PMA. The Ca²⁺ ionophore A23187 did not act synergistically to increase PMA stimulation. In previous studies, PMA caused a rapid increase in amiloride-sensitive Na⁺/H⁺ transport activity in C6 glioma. In the present study, pre- and coincubation with amiloride had no effect on the stimulation of transport activity caused by PMA. These studies suggest that activation of protein kinase C causes a rapid increase in EAAC1-mediated transport activity. This rapid increase in Na⁺-dependent l -[³H]-glutamate transport activity may provide a novel mechanism for protection against acute insults to the CNS.     

Fine structure of cells specialized for secretion of aggregation pheromone in a nitidulid beetle Carpophilus freemani (coleoptera: Nitidulidae)

The cells that secrete the aggregation pheromone of the male nitidulid beetle Carpophilus freemani are exceptionally large and lie within the body cavity. These secretory cells share many ultrastructural features with cells of other pheromone and defense glands, but they also have several unique features. A deep invagination of the surface of each of these cells acts as the secretory surface for the pheromone. The invaginated surface is highly convoluted and surrounds a narrow cuticular ductule that is connected to the tracheal system. This surface is not covered with microvilli as the comparable surfaces are in other insect secretory cells. Each secretory cell is filled with an abundance of lipid spheres that presumably contain precursors for the pheromone. Examining cells from beetles producing different levels of pheromone showed that sizes of secretory cells are positively correlated with rates of pheromone production. Whereas secretory and ductule cells of other insect glands are usually epidermal cells, these cells of nitidulid beetles represent the first pheromone glands in which oenocytes are believed to have been recruited for pheromone production and tracheal cells have been recruited as ductules for these cells.     

Occurrence of airborne bacteria and pathogen indicators during land application of sewage sludge.

Glass impingers (AGI-30) were used at a commercial sludge application site to determine the levels of airborne bacteria and pathogen indicators. Even though heterotrophic bacteria averaged 10(5) CFU/m3, none of the sites showed the presence of Salmonella spp. or indicators such as fecal coliforms or coliphages. Indicators such as H2S producers and pathogenic clostridia were present in locations having significant physical agitation of the sludge material. PCR-based ribotyping using the 16S-23S interspacer region is a promising method to identify the genetic relatedness and origins of airborne clostridia.     

Physical mapping of three fruit ripening genes：Endopolygalacturonase,ACC oxidase and ACC synthase from apple（Malus x domestica） in an apple rootstock A106（Malus sieboldii

The apple rootstock,A106(Malus sieboldii),had 17 bivalents in pollen mother cells at meiotic metaphase 1,and 17 chromosomes in a haploid pollen cell.Karyotypes were prepared from root-tip cells with 2n=34 chromosomes,Seven out of 82 karyotypes(8.5%) showed one pari of satellites at the end of the short arm of chromosome 3.C-bands were shown on 6 pairs of chromosomes 2,4,6,8,14,and 16 near the telomeric regions of short arms.Probes for three ripening-related genes from Malus x domestica:endopolygalacturonase(EPG,0.6kb),ACC oxidase(1.2kb),and ACC synthase(2kb)were hybridized in situ to metaphase chromosomes of A106.Hybridization sites for the EPG gene were observed on the long arm of chromosome 14 in 15 out of 16 replicate spreads and proximal to the centromere of chromosomes 6 and 11.For the ACC oxidase gene,hylridization sites were observed in the telomeric region of the short arm of chromosomes 5 and 11 in 87% and 81% of 16 spreads respectively,proxiaml to the centromere of chromosome 1 in 81% of the spreads,and on the long arm of chromosome 13 in 50% of the spreads. Physical mapping of three fruit ripening genes in an apple rootstock A106.Twenty five spreads were studied for the ACC synthase gene and hybridization sites were observed in the telomeric region of the short arm of chromosome 12 in 96% of the spreads.chromosomes 9 and 10 in 76% of the spreads,and chromosome 17 in 56% of the spreads.