Notes: Zusammenfassung Bei gewässerten Versuchspersonen bewirkt die intravenöse Gabe von 1 · 10−4 IE/kg Vasopressin (Tonephin „Hoechst“) eine konstante Hemmung der Diurese mit Verminderung der absoluten Na.-, K.- und Cl'-Ausscheidungen trotz Konzentrationsanstieg dieser Ionen. Dabei kommt es zu einer zeitlichen Verschiebung zwischen Antidiurese und Konzentrationsanstieg der Ionen im Harn. Während der Wasserdiurese hat Oxytocin (Oxytocin „Hormonchemie“ oder Syntocinon „Sandoz“) in Dosen von 2–6 · 10−4 IE/kg, intravenös gegeben, keinen deutlichen Effekt auf die Wasser-, Na.-, K0.-und Cl'-Ausscheidungen. Wenn Oxytocin (2–6 · 10−4 IE/kg intravenös) 15 min vor Vasopressin (1 · 10−4 IE/kg intravenös) gegeben wird, vermag es die Vasopressinwirkungen wie Diuresehemmung, Konzentrationsanstieg der Ionen im Harn bei Minderung der absoluten Ionenausscheidungen, ganz aufzuheben. Bei gleichzeitiger Gabe von Oxytocin und Vasopressin im Verhältnis 2:1 tritt die zu erwartende Anti-diurese vermindert und zeitlich verkürzt ein, bei Konzentrationsanstieg der untersuchten Ionen und nahezu gleichbleibender absoluter Ionenausscheidung. Eine kompetitive Hemmung der Vasopressinwirkung durch Oxytocin wird angenommen. Hochgereinigtes Oxytocin und synthetisches Oxytocin verhalten sich wirkungsgleich.

Notes: Abstract  O2 and pH microsensors were used to analyse the microdistribution of O2 and pH inside and outside roots of lowland rice (Oryza sativa L.). The roots of 3-week-old transplants had O2 concentrations of about 20% air saturation at the surface, but due to a high rate of O2 consumption in the rhizosphere, the oxic region only extended about 0.4 mm into the surrounding soil. Also the fine lateral roots created an oxic zone extending about 0.15 mm into the soil. The O2 concentration within the roots approached air saturation close to the base, but only about 40–60% of air saturation in a region about 8 cm below the base where lateral rootlets were present. A shift from air to N2 around the leaves led to a drop of 50% in the O2 concentration after 12 min at a distance of 8.5 cm from the base. Flowering plants did not export O2 to the soil from the majority of their roots, but high microbial activity was present in a very thin biofilm covering the root surface. A brown colour around the thin lateral roots indicated some O2 export from these also during flowering. No oxidized zone was present around the roots at later stages of crop growth. The roots caused only minor minima in pH (〈0.2 pH units) in the rhizosphere as compared to the bulk soil. Illumination of the plants had no effect on rhizosphere pH.

Notes: Abstract The visual system of the fly is able to extract different types of global retinal motion patterns as may be induced on the eyes during different flight maneuvers and to use this information to control visual orientation. The mechanisms underlying these tasks were analyzed by a combination of quantitative behavioral experiments on tethered flying flies (Musca domestica) and model simulations using different conditions of oscillatory large-field motion and relative motion of different segments of the stimulus pattern. Only torque responses about the vertical axis of the animal were determined. The stimulus patterns consisted of random dot textures (“Julesz patterns”) which could be moved either horizontally or vertically. Horizontal rotatory large-field motion leads to compensatory optomotor turning responses, which under natural conditions would tend to stabilize the retinal image. The response amplitude depends on the oscillation frequency: It is much larger at low oscillation frequencies than at high ones. When an object and its background move relative to each other, the object may, in principle, be discriminated and then induce turning responses of the fly towards the object. However, whether the object is distinguished by the fly depends not only on the phase relationship between object and background motion but also on the oscillation frequency. At all phase relations tested, the object is detected only at high oscillation frequencies. For the patterns used here, the turning responses are only affected by motion along the horizontal axis of the eye. No influences caused by vertical motion could be detected. The experimental data can be explained best by assuming two parallel control systems with different temporal and spatial integration properties: TheLF-system which is most sensitive to coherent rotatory large-field motion and mediates compensatory optomotor responses mainly at low oscillation frequencies. In contrast, theSF-system is tuned to small-field and relative motion and thus specialized to discriminate a moving object from its background; it mediates turning responses towards objects mainly at high oscillation frequencies. The principal organization of the neural networks underlying these control systems could be derived from the characteristic features of the responses to the different stimulus conditions. The input to the model circuits responsible for the characteristic sensitivity of the SF-system to small-field and relative motion is provided by retinotopic arrays of local movement detectors. The movement detectors are integrated by a large-field element, the output cell of the network. The synapses between the detectors and the output cells have nonlinear transmission characteristics. Another type of large-field elements (“pool cells”) which respond to motion in front of both eyes and have characteristic direction selectivities are assumed to interact with the local movement detector channels by inhibitory synapses of the shunting type, before the movement detectors are integrated by the output cells. The properties of the LF-system can be accounted for by similar model circuits which, however, differ with respect to the transmission characteristic of the synapses between the movement detectors and the output cell; moreover, their pool cells are only monocular. This type of network, however, is not necessary to account for the functional properties of the LF-system. Instead, intrinsic properties of single neurons may be sufficient. Computer simulations of the postulated mechanisms of the SF-and LF-system reveal that these can account for the specific features of the behavioral responses under quite different conditions of coherent large-field motion and relative motion of different pattern segments.

Notes: Abstract The performance of the fly's movement detection system is analysed using the visually induced yaw torque generated during tethered flight as a behavioural indicator. In earlier studies usually large parts of the visual field were exposed to the movement stimuli; the fly's response, therefore, represented the spatially pooled output signals of a large number of local movement detectors. Here we examined the responses of individual movement detectors. The stimulus pattern was presented to the fly via small vertical slits, thus, nearly avoiding spatial integration of local movement information along the horizontal axis of the eye. The stimulus consisted of a vertically oriented sine-wave grating which was moved with a constant velocity either clockwise or counterclockwise. In agreement with the theory of movement detectors of the correlation type, the time-course of the detector signal is modulated with the spatial phase of the stimulus pattern. It can even assume negative values for some time during the response cycle and thus signal the wrong direction of motion. By spatially integrating the response over sufficiently large arrays of movement detectors these response modulations disappear. Finally, one obtains a signal of the movement detection system which is constant while the pattern moves in one direction and only changes its sign when the pattern reverses its direction of motion. Spatial integration thus represents a simple means to obtain a meaningful representations of motion information.