Orientation and ingestion rates of larval Anopheles albimanus in response to floating particles

Response of fourth-instar larvae of Anopheles albimanus Wiedemann (Diptera: Culicidae) to food and inert particles floating at the water surface was studied. In a choice test, larvae aggregated at powdered organic materials (blood meal, liver powder alfalfa flour and wheat flour) but not at inert materials (kaolin, chalk or charcoal). Larvae responded positively to proteins as well as some carbohydrates, but not to cellulose. Retention of larvae at food sources found by random locomotion was found to be responsible for larval aggregation. Larvae ingested food particles 6–9 times faster than insert particles. The significance of Anopheline feeding behavior in the development of formulations of stomach toxins (bacterial agents) used in larval control is discussed.

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Zusammenfassung Die vorliegende Studie befasst sich mit Verhaltensreaktionen von Anopheles albimanus Viertlarven auf an der Wasseroberfläche schwimmende Partikel. Verteilung und Orientierung der Larven wurde in einer Wahlapparatur quantifiziert. Nach Auftrag von Alfalfamehl, Weizenmehl, Stärke, Blutmehl, Leberpulver und Fischmehl wurde Aggregation der Larven in den beköderten Fächern der Apparatur beobachtet. Sowohl Proteine (Casein) als auch einige Kohlehydrate (Amylose, Amylopectin) lösten Aggregationen der Larven aus. Im Unterschied dazu führte Auftrag von Kreide, Kaolin, Polyaethylenpulver, Talcum oder Cellulose nicht zu Aggregationen. Zur Beschreibung der Entstehung larvaler Aggregationen bei Futterstoffen wurden die Schwimmbewegungen der Larven in Anwesenheit von Weizenmehl als Ködersubstanz quantifiziert. Da keine Attraktion der Larven im Sinne einer gerichteten Schwimmbewegung beobachtet werden konnte, wird geschlussfolgert, dass sofortige Beendung der Suchaktivität der Larven bei zufällig gefundenen Futterquellen für die beobachteten Aggregationen bei organischen Substanzen verantwortlich ist.Die Fressraten der Larven bei Angebot verschiedener Substanzen im Überschuss wurde bestimmt. Larven fülten drei von insgesamt sechs Darmabschnitten innerhalb von 15–30 min bei Angebot von Futtersubstanzen, während die Füllung von nur zwei Darmabschnitten mit inerten Materialien erst nach 90–120 min zu beobachten war. Die Resultate werden in Bezug auf wasseroberflächengebundene Formulierungen von Frassgiften diskutiert. Inerte Trägersubstanzen werden wahrscheinlich wesentlich langsamer aufgenommen als Futtersubstanzen. Da An. albimanus Larven nicht von Futterquellen angezogen werden, ist eine rasche und wirksame Giftaufnahme besonders dann zu erwarten, wenn die gesamte Oberfläche der Brutgewässer mit toxinhaltigen Trägerpartikeln bedeckt werden kann.

     

The Thatcher illusion in humans and monkeys

Primates possess the remarkable ability to differentiate faces of group members and to extract relevant information about the individual directly from the face. Recognition of conspecific faces is achieved by means of holistic processing, i.e. the processing of the face as an unparsed, perceptual whole, rather than as the collection of independent features (part-based processing). The most striking example of holistic processing is the Thatcher illusion. Local changes in facial features are hardly noticeable when the whole face is inverted (rotated 180°), but strikingly grotesque when the face is upright. This effect can be explained by a lack of processing capabilities for locally rotated facial features when the face is turned upside down. Recently, a Thatcher illusion was described in the macaque monkey analogous to that known from human investigations. Using a habituation paradigm combined with eye tracking, we address the critical follow-up questions raised in the aforementioned study to show the Thatcher illusion as a function of the observer''s species (humans and macaques), the stimulus'' species (humans and macaques) and the level of perceptual expertise (novice, expert).     

The cytomegalovirus enhancer: a pan-active control element in transgenic mice.

In an effort to identify widely active positive regulatory elements, we have examined the action of the cytomegalovirus enhancer-promoter in transgenic mice. These elements activated expression in 24 of 28 tissues tested. The greatest expression was observed in the heart, kidney, brain, and testis. Maximum expression further localized to specific cells within the heart and kidney.     

Functional asymmetry of the F0 motor in bacterial ATP synthases

F₁F₀ ATP synthases use the electrochemical potential of H⁺ or Na⁺ across biological membranes to synthesize ATP by a rotary mechanism. In bacteria, the enzymes can act in reverse as ATP-driven ion pumps creating the indispensable membrane potential. Here, we demonstrate that the F₀ parts of a Na⁺- and H⁺-dependent enzyme display major asymmetries with respect to their mode of operation, reflected by the requirement of ∼100 times higher Na⁺ or H⁺ concentrations for the synthesis compared with the hydrolysis of ATP. A similar asymmetry is observed during ion transport through isolated F₀ parts, indicating different affinities for the binding sites in the a/c interface. Together with further data, we propose a model that provides a rationale for a differential usage of membrane potential and ion gradient during ATP synthesis as observed experimentally. The functional asymmetry might also reflect an important property of the ATP synthesis mechanism in vivo . In Escherichia coli , we observed respiratory chain-driven ATP production at pH 7–8, while P -site pH values < 6.5 were required for ATP synthesis in vitro . This discrepancy is discussed with respect to the hypothesis that during respiration lateral proton diffusion could lead to significant acidification at the membrane surface.     

Utility of [16 alpha-125I] iodoestradiol for autoradiography for the study of cellular and regional distribution of receptors

We demonstrate the utility of [16 alpha-125I]iodoestradiol for thaw-mount autoradiography with 2 micron and 4 micron thick sections of rat and mouse uterus, pituitary, and brain after in vivo administration. Under the conditions of the experiments, short-term autoradiography with exposure times between 3 and 14 days provides optimal cellular resolution, whereas long-term autoradiography with 1-2 months of exposure may be used to obtain topographic-regional surveys of distribution.     

Odorant stimulation of secretory and neural processes in the salamander olfactory mucosa

Topical application of the odorants guaiacol (10(-3) mol/l, 1-30 min) and 2-isobutyl-3-methoxypyrazine (IBMP, 10(-5)-10(-3) mol/l, 15 min) caused time- and concentration-dependent reductions in the secretory granule content of acinar cells of the superficial Bowman's glands (sBG) and moderate to extensive vacuolation in acinar cells of sBG and deep olfactory glands (dG). Topical application of 9.8 mg/ml scopolamine 10 min before 10(-4) mol/l IBMP significantly reduced the amount of secretory granule depletion from sBG compared to that seen with IBMP alone and resulted in less extensive vacuolation in sBG and dG acinar cells. The i.p. injection of 42 mg/kg propranolol 10 min before topical application of 10(-4) mol/l IBMP had no effect on the action of IBMP. Guaiacol and IBMP also had time- and concentration-dependent effects on the secretory activity of sustentacular cells in the olfactory epithelium. The protrusion of secretory material into the mucociliary matrix that covers the epithelial surface and vacuolation within the secretory material resulted from odorant application. Scopolamine and propranolol had no effects on the action of IBMP on sustentacular cell secretory activity. When applied in the vapor phase, guaiacol elicited action potentials recorded from individual olfactory receptor neurons; the impulse frequency was concentration-dependent and showed tonic and phasic components when the duration of stimulation was varied. Low to moderate concentrations of IBMP delivered in the vapor phase evoked monophasic negative slow voltage transients recorded from the surface of the olfactory mucosa. The amplitudes of these transients increased with increasing stimulus concentrations. Higher concentrations or longer stimulus durations evoked longer-latency positive-voltage generating processes and negative afterpotentials. The properties of the electrophysiological responses to both odorants were characteristic of responses evoked by a wide variety of 'typical' odorants.     

Coordinate Expression of Rubisco Activase and Rubisco during Barley Leaf Cell Development

We have utilized the cellular differentiation gradient and photomorphogenic responses of the first leaf of 7-day-old barley (Hordeum vulgare L.) to examine the accumulation of mRNA and protein encoded by the ribulose-1,5-biphosphate carboxylase holoenzyme (rubisco) activase gene (rca). Previous studies have revealed a pattern of coordinate expression of rubisco subunit polypeptides during development. We compared the expression of rubisco polypeptides and mRNAs with those encoded by rca. The mRNAs encoding both rubisco activase and rubisco are expressed exclusively in leaf tissue of 7-day-old barley seedlings; mRNAs and polypeptides of rca accumulate progressively from the leaf base in a pattern that is qualitatively similar to that of rubisco subunit mRNAs and polypeptides. The parallel pattern of rca protein and mRNA accumulation indicate that a primary control of rca gene expression in this system lies at the level of mRNA production. Light-induced expression of rca in etiolated barley follows a different pattern from that of the acropetal barley leaf gradient, however. Etiolated, 7-day-old barley seedlings contain levels of rca mRNA near the limit of detection in Northern blot hybridization assays. White light induces a 50- to 100-fold accumulation of rca mRNA, which is detectable within 30 min after the onset of illumination. In contrast, steady state levels of mRNAs encoding the small rubisco subunit are affected little by light, and mRNAs encoding the large subunit accumulate about 5-fold in response to illumination. While rca mRNA levels are low in etiolated barley leaves, levels of the protein are approximately 50 to 75% of those found in fully green leaves.