Barbara Müller

Fine structure of the antennal receptors of the bed bug, Cimex lectularius L.

Sensilla on the antenna of the bed bug, Cimex lectularius, were studied with the scanning and transmission electron microscope. Those which display a tubular body in the dendrite ending are presumed to have a mechanoreceptor function (bristles of type A, flat plate of type B). Bristles of type A1 contain additional dendrites which terminate at the tip of the bristle and may be gustatory receptors. Sensilla with pores in the hair wall are supposed to have an offactory, humidity and/or temperature receptor function (pegs and hairs of types C, D, E). Hairs of type E contain receptors for the alarm pheromones of the bed bug. Special attention has been paid to the pore structures and epicuticular layers of these sensilla. Possible differences in stimulus conduction are discussed between (i) sensilla with a simple wall and pores with pore tubules (types D and E) and (ii) the ribbed pegs (type C), which have a complex wall structure and spoke channels. The immersed cones of type F have a peculiar innervation, which has not been described previously. Two dendrites are held closely together by a third flat dendrite which wraps around them in the region of the outer segment. Coupling structures were found between the central dendrites, and between these and the third enveloping dendrite. Possible functions of this unique innervation are discussed. The dendrites innervating type D are grouped in three to eight bundles by multiple sheaths. The term thecogen cell is introduced to denote the innermost of the three sheath cells of a sensillum (the outer being the tormogen and the trichogen cell) which builds the dendrite sheath during ontogeny. Comparative morphometry revealed type-specific differences in the length and diameter of the dendrites. Some axons were found to lack any glial or perineurial sheath. Microorganisms were observed in the antennal tissue of several animals.

On the stimulus conducting structures in insect olfactory receptors

SummaryIn the olfactory sensilla trichodea of the silk moth, the cuticle of the sense hair is perforated by numerous pores. These pores are shown to be connected with the dendrites of the receptor cell by extracellular pore tubules. It is suggested, therefore, that odour molecules reach the stimulus transduction sites on the receptor membrane by surface diffusion alone, and need not diffuse three-dimensionally through the sensillum liquor.ZusammenfassungBei den olfaktorischen Sensilla trichodea des Seidenspinners wird die Cuticula des Sinneshaares von zahlreichen Poren durchbrochen. Es wird gezeigt, daß diese Poren mit den Dendriten der Sinneszellen durch extrazelluläre Porentubuli verbunden sind. Daraus folgt, daß die Duftmoleküle den Ort der Erregungsbildung an der Rezeptormembran wahrscheinlich allein durch Oberflächendiffusion erreichen, ohne eine dreidimensionale Diffusion durch den Sensillenliquor.

Structure of sensilla, olfactory perception, and behaviour of the bedbug, Cimex lectularius, in response to its alarm pheromone

Abstract When deprived of the terminal antennal segments, male and female bedbugs failed to respond to their alarm pheromone and to their assembling scent. Trans-oct-2-en-1-al or trans-hex-2-en-1-al, being the major constituents of the former, induce in adults and larvae of Cimex lectularius a typical alarm behaviour resulting in dispersal of assembled bedbugs; the rapidity of escape depends on the aldehyde concentration in the air. The behavioural threshold for adults is about 9×1014 molecules of trans-oct-2-en-1-al or 6×1015 molecules of trans-hex-2-en-1-al per ml air. The distal part of the terminal antennal segment of C. lectularius reveals the following sensilla: bristles (type A1), immersed cones (type B1), plates (type B2), grooved pegs (type C), smooth pegs (type D), hairs with even (type E1), and uneven wall thickness (type E2). The number and distribution of these sensilla is relatively constant and similar in both sexes, but differs slightly in neonate larvae. The pegs and hairs of types C, D, E1 and E2 were shown to have porous walls, a prerequisite for olfactory function. Receptor potentials were recorded from olfactory sensilla of types E1 and E2 after stimulation with trans-hex-2-en-1-al and trans-oct-2-en-1-al. The minimal concentration of trans-hex-2-en-1-al evoking a receptor potential is about 2×1010 molecules per ml air. The above olfactory sensilla were found to respond also to hexan-1-al, but almost no responses to pentan-1-al, butan-1-al, trans-hex-2-ene, and trans-oct-2-ene were observed. A minimum chain length of six carbons atoms and a terminal carbonyl group are molecular prerequisites for optimal odorant activity, while the presence of a Δ2-double bond is not essential for stimulation of the alarm pheromone receptors of the bedbug.

Factors contributing to the inhibition of HIV reverse transcriptase by chain‐terminating nucleotides in vitro and in vivo

Arguments are presented leading to the conclusion that two major factors contribute to the potency of inhibition of DNA‐polymerase activity by chain‐terminating nucleotides. The relative significance of these factors varies with the reaction conditions, particularly with the length of the template and the concentration ratio of enzyme (reverse transcriptase or other DNA polymerase) to primer. It is concluded that potent inhibition of HIV‐reverse transcriptase activity under typical in vitro and in vivo conditions arises from different features of the interaction of chain terminators with the enzyme. A new method of testing for the parameter important under in vivo conditions is suggested.

RNase H activity of HIV reverse transcriptases is confined exclusively to the dimeric forms

A method for the rapid preparation of a defined substrate to monitor RNase H activity has been developed. Using this substrate, we have investigated the RNase H activities of the different forms of recombinant HIV‐1 and HIV‐2 reverse, transcriptase (RT) in detail. As we report here, RNase H activity is associated only with the dimeric forms (p51/p66 or p66/p66) of the enzymes

The thermo-/hygrosensitive sensilla of the silkmoth, Bombyx mori : morphological changes after dry- and moist-adaptation

SummaryThe thermo-/hygrosensitive sensilla styloconica of the silk moth Bombyx mori were studied using cryofixation and freez-substitution. These sensilla are characterized by a short poreless cuticular peg, which is double-walled in its distal part. The central lumen is innervated by the unbranched outer dendritic segments of the two presumed hygroreceptor cells. The presumed thermoreceptor cell displays lamellae below the peg base. Within the peg lumen, the dendrites are surrounded by the peridendritic dense coat and the lowdensity matrix. Below the peg base, these structures continue as the dendrite sheath, which is separated from the outer sensillum-lymph space by a layer of the trichogen cell. The central lumen, therefore, is only connected with the inner sensillum-lymph space, but the appearance of the low-density matrix, within the peg, differs from that of the sensillum lymph below the peg. In moist-adapted (24 h) sensilla, the two hygroreceptor dendrites invade the peg for three quarters and one half of its length, respectively, and fill the cross-sectional area of the lumen by 50–80%. In dry-adapted (24 h) sensilla, the dendrites terminate more proximally and fill the cross-section by ∼35%. The volume of the low-density matrix increases under dry conditions and decreases under humid conditions. At intermediate ambient humidity, the morphology of these sensilla is halfway between the dry-adapted and the moist-adapted state. The effect of dry-adaptation is reversible, so that sensilla that were first dry-adapted and then moist-adapted (24 h each) before cryofixation cannot be distinguished from moist-adapted sensilla. The reduction of the exposed length of the dendrites is interpreted as a shift of the working range of the receptors and/or protection against desiccation. The current theories of sensory transduction in hygroreceptors, in particular the hygrometer and evaporimeter hypotheses, are discussed with respect to the present findings.

Template. Phosphorothioate oligonucleotides duplexes as inhibitors of HIV-1 reverse transcriptase

We have investigated the interaction between a number of 14 mers phosphorothioate oligonucleotides and HIV-1 reverse transcriptase. Two methods were used to measure the affinity of the analogs for the enzyme. In the first, the oligonucleotide or its duplex with Poly(rl) were used as inhibitors of the enzyme using Poly(rA).(dT)14 as template primer. In the second, the oligonucleotides or their duplexes were used to displace a fluorescent template primer complex of known affinity from its binding site on reverse transcriptase. The two methods gave the same relative order of affinity. Phosphorothioate oligodeoxyribonucleotides had a much higher affinity than oligo(dC)14 and it was increased on hybridization. Quantitatively similar results were obtained for S(dC)14 or its analog with bases in the alpha-configuration. Of the analogs tested, only S(dC)14 showed priming activity.

Studying reaction kinetics by simultaneous FRET and cross-correlation analysis in a miniaturized continuous flow reactor

In this study we present a refined optical detection technique for investigation of fast reactions based on confocal fluorescence spectroscopy in a miniaturized continuous flow (μCF) reactor. The special setup allows for simultaneous observation of the reaction on the basis of fluorescent resonance energy transfer (FRET) as an indicator of the reaction progress. Determination of the flow velocity via spatial fluorescence cross-correlation enables the conversion of spatial information, i.e. the position of the detection point, into the respective temporal information. To overcome the disadvantage of conventional continuous flow reactors of high sample consumption, we used a microfluidic chip allowing an economical expenditure of sample solution at low concentration, while the silicon/glass chip is perfectly adaptable to the confocal setup. Inside these channels, rapid, diffusion-based mixing under laminar flow conditions is performed at the crossing of three channels by squeezing the solutions into thin layers. Using this μCF device, we investigated the irreversible cleavage reaction of a double stranded DNA oligomer by the enzyme exonuclease III. The complementary DNA strands are stained with TAMRA and Cy 5 dye molecules, respectively, undergoing an energy transfer if both strands are annealed. The reduction of the Cy 5 fluorescence directly corresponds to the progress of the cleavage reaction.

FUNCTIONAL MORPHOLOGY OF PALP SENSILLA RELATED TO FOOD RECOGNITION IN GRYLLUS BIMACULATUS (SALTATORIA, GRYLLIDAE)

Peculiarities of the fine structure of three types of contact chemoreceptor on the tips of the maxillary palps of the cricket Gryllus bimaculatus De Geer, as observed by electron microscopy of serial sections, are described. At the tip of one of these is a complex system of slits and channels partially filled with electron‐dense material which is the stimulus conducting system between the external medium and the chemosensory dendrites. In other receptors there is an accessory dendrite with a tubular body, that ends proximal to the lower edge of the hair shaft. Various structures are discussed in relation to transduction of the mechanical stimulus, and to possible protection against excessive strain.