Analyse der schlagauslösenden Bewegungsparameter einer punktförmigen Beuteattrappe bei der Aeschnalarve

Zusammenfassung Bei der Libellenlarve Aeschna cyanea M. werden die einzelnen, für die Auslösung des Fangschlags relevanten Bewegungsparameter einer punktförmigen Beuteattrappe und die wirksamste Kombination dieser Parameter bestimmt.Als Beiz dient der beliebig bewegbare Leuchtpunkt eines Oszillographen, der auf die ebene Mattscheibe eines Versuchsaquariums projiziert wird. Die Schläge der frei beweglichen Larve werden vom Beobachter gezählt oder elektrisch registriert.Die Bahngeschwindigkeit von kontinuierlich gebotenen Bewegungsreizen wirkt sich stark auf die Schlagzahl aus: Die Schläge nehmen von 0,005–2,5 cm/sec zu, nehmen von 5,1 cm/sec an wieder ab und hören bei 41,0 cm/sec ganz auf. Die Veränderung der mittleren Geschwindigkeit von Sinusschwingungen und Zufallsbewegungen bewirkt ähnliche Reaktionskurven wie die Veränderung der gleichmäigen Geschwindigkeit von Dreiecksschwingungen und kreisförmigen Bewegungen; eine gleichförmige Optimalgesohwindigkeit wird jedoch stärker beantwortet als eine periodisch schwankende.Bietet man eine Folge von diskontinuierlichen Bewegungsreizen, die nach einer einmaligen Durchquerung eines begrenzten Feldes der Projektionsfläche verschwinden, so spielt die Dauer einer Einzelbewegung eine Rolle. Um die Schläge voll in Gang zu bringen, müssen eindimensionale Schwingungen 3–6 sec dauern, ein viel intensiver wirkender zweidimensionaler Reiz (Zickzackbewegung) jedoch nur 0,8 sec.Im optimalen, relativ hohen Geschwindigkeitsbereich läßt die Erhöhung der Bewegungsamplitude von 0,25 auf 2,0 cm die Schlagzahl progressiv absinken. Der Vergleich zwischen diesen Amplituden und dem Öffnungswinkel des frontalen, die Beute fixierenden Ommatidienfeldes zeigt, daß der Leuchtpunkt nur bei sehr kleinen Ablenkungen die frontalen Rezeptoren kontinuierlich reizt. — Die Bevorzugung von raschen Bewegungsreizen mit kleiner Amplitude besteht nicht bei Larven, die durch prompte Fixier- und Folgereaktionen den Leuchtpunkt in ihrer frontalen Fixierebene bewahren.Der Vergleich zwischen den 4 in dieser Untersuchung erzeugten Bewegungsmustern (ein- und zweidimensionale Schwingungen, Kreis- und Zufallsbewegungen) zeigt, daß eine Bewegung um so mehr Schläge auslöst, je vollständiger sie auf dicht aneinanderliegenden, zweidimensionalen Bahnen das frontale Ommatidienfeld abtastet.Die optimale Reizkombination (Zickzackbewegung) besteht aus einer kleinen (0,2–0,4 cm) Vertikalschwingung mit optimaler Geschwindigkeit, die sich langsam (0,32 cm/sec) seitlich verschiebt. Dieser Reiz stellt die Verbindung der optimalen Werte aller Bewegungsparameter dar und bewirkt, daß pro Zeiteinheit eine möglichst große Zahl frontaler Rezeptoren mit der optimalen Bahngeschwindigkeit gereizt wird.

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Analysis of the parameters of a moving lightspot which release the predatory strike in dragonfly larvae

Summary This study analyses the predatory strike response of the dragonfly larva Aeschna cyanea M. towards a moving spot of light. Its aim is to determine the single parameters of movement of the spot which release the strike and the most effective combination of these parameters.As the velocity of a continuously moving lightspot is increased the number of strikes rises to a maximum (at 2.5 cm/sec) and then declines to 0 (at 41.0 cm/sec). Both uniform and non uniform velocities give curves of similar shape but different magnitudes.In the presentation of a sequence of discontinuous movements (where the spot moves across a part of the screen and then disappears) the duration of a single movement is important: Unidimensional oscillations must last 3 to 6 sec in order to release predatory strikes; twodimensional zigzag movements, much more effective, need last only 0.8 sec.In the optimal velocity range, increasing the amplitude of a movement from 0.25 to 2.00 cm produces a progressive decrease of the response rate. The comparison between these amplitudes and the size of the field of the frontal ommatidia, which fixate the prey, suggests that the spot stimulates these receptors continuously only when it moves with small amplitudes. — However, this preference for small amplitudes does not exist in those individuals which have rapid fixation- and following-reactions and which thus can track the stimulus.Comparison between the four patterns of movement which have been presented (one- and two-dimensional oscillations, circular and random movements) suggests that the spot releases more strikes the more exactly its movement covers the frontal fixation plane.The most effective stimulus for eliciting strikes was found to be a twodimensional zigzag oscillation. This movement consists of a small (0.2–0.4 cm), rapid (2.5 cm/ sec), vertical oscillation, which progresses slowly (0.3 cm/sec) sideways. This movement combines the optimal values of all parameters and stimulates with the optimal velocity the greatest possible number of frontal receptors in a given time.

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Diese Arbeit wurde in Seewiesen mit Dr. H. C. Howland begonnen und dank der fortwährenden, großzügigen Unterstützung von Herrn Dr. H. Mittelstaedt beendet. Frau L. Dinnendahl fertigte die Zeichnungen an und durchsah das Manuskript, Dr. E. Kramer und Herr P. Heinecke standen mir ständig in technischen Fragen bei, Herr E. Butenandt leistete wertvolle Kritik am Manuskript. — In Genf gewährte mir Prof. J. Piaget vollkommene Freiheit in der Gestaltung meiner Arbeit. — Ihnen allen sei an dieser Stelle herzlichst gedankt.     

Development of sensory innervation in chick skin: comparison of nerve fibre and chondroitin sulphate distributions in vivo and in vitro

In bird skin, nerve fibres develop in the dermis but do not enter the epidermis. In co-cultures of 7-day-old chick embryo dorsal root ganglia and epidermis, the neurites also avoid the epidermis. Previous studies have shown that chondroitin sulphate proteoglycans may be involved. Chondroitin sulphate has therefore been visualized by immunocytochemistry, using themonoclonal antibody CS-56, both in vivo and in vitro using light and electron microscopy. Its distribution was compared to those of 2 other chondroitin sulphate epitopes and to that of the growing nerve fibres. In cultures of epidermis from 7-day-old embryonic chicks, immunoreactivity is found uniformly around the epidermal cells while at 7.5 days the distribution in dermis is heterogeneous, and particularly marked in feather buds. In vivo, chondroitin sulphate immunoreactivity is detected in the epidermis, on the basal lamina, on the surfaces of fibroblasts and along collagen fibrils. This localization is complementary to the distribution of cutaneous nerves. Chondroitin sulphate in the basal lamina could prevent innervation of the epidermis and the dermal heterogeneities could partly explain the nerve fibres surrounding the base of the feathers. Chondroitin sulphate could therefore be important for neural guidance in developing chick skin.     

Computer controlled fed-batch fermentation of the methylotroph Pseudomonas AM1

Summary A simple on-line computer control strategy based on dissolved oxygen level readings has been developed to control methanol addition during a fermentation of the methylotroph Pseudomonas AM1. This strategy has led to significant and reproducible improvements in the performance of the fermentation.     

ADP-ribosylation of brain synaptosomal proteins correlates with adenylate cyclase activation

ADP-ribosylation of the adenylate cyclase $\text{G}\text{F}$ regulatory subunit by cholera toxin is a major tool for the study of this enzyme. Investigation of the brain enzyme has been hampered up to now by the failure to demonstrate cholera toxin-dependent ADP-ribosylation of membrane-bound proteins. Synaptosomes prepared by flotation from fresh brains homogenized in the presence of protease inhibitors yielded membranes of which several proteins could be ADP-ribosylated by the toxin. The same membranes subjected to mild proteolysis could not be ADP-ribosylated. Adenylate cyclase activation and ADP-ribosylation were simultaneous processes. The major labeled species was of 47,000 M_r. It was solubilized by Lubrol-PX, together with other labeled polypeptides. As analyzed on sucrose gradients, the 47,000 M_r protein was found both in the 3S region, and in the adenylate cyclase containing fraction (9.1S).     

Formation of F''TRP Plasmids in ESCHERICHIA COLI K12

From strains carrying two different F-prime factors, we recovered F' derivatives that acquired the trp chromosomal region. These F'trp plasmids can be isolated at a frequency of 10^-5 to 10^-6. They were characterized genetically by looking at the size of the trp segment they acquired and at the location of that segment in the parental F' plasmid. Results are discussed in relationship to possible transposition mechanisms.     

Reversible bacteriophage resistance by shedding the bacterial cell wall

Phages are highly abundant in the environment and pose a major threat for bacteria. Therefore, bacteria have evolved sophisticated defence systems to withstand phage attacks. Here, we describe a previously unknown mechanism by which mono- and diderm bacteria survive infection with diverse lytic phages. Phage exposure leads to a rapid and near-complete conversion of walled cells to a cell-wall-deficient state, which remains viable in osmoprotective conditions and can revert to the walled state. While shedding the cell wall dramatically reduces the number of progeny phages produced by the host, it does not always preclude phage infection. Altogether, these results show that the formation of cell-wall-deficient cells prevents complete eradication of the bacterial population and suggest that cell wall deficiency may potentially limit the efficacy of phage therapy, especially in highly osmotic environments or when used together with antibiotics that target the cell wall.     

α/β-Hydrolase Domain Containing Protein 15 (ABHD15) – an Adipogenic Protein Protecting from Apoptosis

Our knowledge about adipocyte metabolism and development is steadily growing, yet many players are still undefined. Here, we show that α/β-hydrolase domain containing protein 15 (Abhd15) is a direct and functional target gene of peroxisome proliferator-activated receptor gamma (PPARγ), the master regulator of adipogenesis. In line, Abhd15 is mainly expressed in brown and white adipose tissue and strongly upregulated during adipogenesis in various murine and human cell lines. Stable knockdown of Abhd15 in 3T3-L1 cells evokes a striking differentiation defect, as evidenced by low lipid accumulation and decreased expression of adipocyte marker genes. In preconfluent cells, knockdown of Abhd15 leads to impaired proliferation, which is caused by apoptosis, as we see an increased SubG1 peak, caspase 3/7 activity, and BAX protein expression as well as a reduction in anti-apoptotic BCL-2 protein. Furthermore, apoptosis-inducing amounts of palmitic acid evoke a massive increase of Abhd15 expression, proposing an apoptosis-protecting role for ABHD15. On the other hand, in mature adipocytes physiological (i.e. non-apoptotic) concentrations of palmitic acid down-regulate Abhd15 expression. Accordingly, we found that the expression of Abhd15 in adipose tissue is reduced in physiological situations with high free fatty acid levels, like high-fat diet, fasting, and aging as well as in genetically obese mice. Collectively, our results position ABHD15 as an essential component in the development of adipocytes as well as in apoptosis, thereby connecting two substantial factors in the regulation of adipocyte number and size. Together with its intricate regulation by free fatty acids, ABHD15 might be an intriguing new target in obesity and diabetes research.