Leg movements of stick insects walking with five legs on a treadwheel and with one leg on a motor-driven belt

Stick insects walking with five legs on a self-propelled treadwheel and with the left hindleg (L3) on a motor-driven belt may move the "belt" leg L3 and the "wheel" legs with different frequencies. When L3 made less steps than L2, that step of L2, which was performed during the swing phase of L3, is prolonged. The time interval between the end of swing phase of L3 and the onset of the following swing phase of L2 was remarkably constant. When L3 made more steps than L2, that step of L3, which was performed during the swing phase of L2, is prolonged. Again, the time interval between the end of swing phase of L3 preceding a L2 swing phase and the onset of the L2 swing phase was relatively constant. For both kinds of walking situations phase response curves were drawn. They show that two types of coordinating channels exist: An anteriorly directed type is more dependent on absolute time than on phase. A posteriorly directed type is phase-dependent. Both inhibit the transition from stance to swing for some time. The results are compared with the existing coordination models.     

Influence of macroclimate and local conservation measures on taxonomic,functional, and phylogenetic diversities of saproxylic beetles and wood-inhabiting fungi

Wood-inhabiting fungi and saproxylic beetles are threatened by habitat degradation. Our understanding of the importance of macroclimate and local factors determining their taxonomic diversity has increased, but determinants of functional and phylogenetic diversity are poorly understood. We investigated assemblages of wood-inhabiting fungi and saproxylic beetles along a 1000 m elevational gradient of a temperate low mountain range. We (i) tested the relative importance of macroclimate (i.e. elevation) and local variables (microclimate, i.e. canopy closure, amount and diversity of dead wood) in determining observed and rarefied diversities and (ii) explored whether determinants of observed functional and phylogenetic diversities match those of taxonomic diversity. For both taxa, the determinants of observed phylogenetic and functional diversities largely matched those of taxonomic diversity. The diversity of wood-inhabiting fungi was predominantly determined by local variables, whereas that of saproxylic beetles was determined by both local variables and elevation. Taxonomic and phylogenetic diversities of saproxylic beetles decreased with increasing elevation, but standardized functional richness and entropy of both groups increased with increasing elevation. Diversities of wood-inhabiting fungi increased with canopy closure, while diversities of saproxylic beetles decreased with increasing canopy closure. Microclimate and dead-wood amount and diversity affected the observed and rarefied diversity of both saproxylic taxa, which justifies conservation actions that focus on attributes of dead wood and canopy cover. The contrasting responses of fungi and beetles highlight the need for amounts of diverse dead wood in the various microclimates to preserve functional and phylogenetic diversities of saproxylic organisms.     

Meta-stability of the hemifusion intermediate induced by glycosylphosphatidylinositol-anchored influenza hemagglutinin.

Fusion between influenza virus and target membranes is mediated by the viral glycoprotein hemagglutinin (HA). Replacement of the transmembrane domain of HA with a glycosylphosphatidylinositol (GPI) membrane anchor allows lipid mixing but not the establishment of cytoplasmic continuity. This observation led to the proposal that the fusion mechanism passes through an intermediate stage corresponding to hemifusion between outer monolayers. We have used confocal fluorescence microscopy to study the movement of probes for specific bilayer leaflets of erythrocytes fusing with HA-expressing cells. N-Rh-PE and NBD-PC were used for specific labeling of the outer and inner membrane leaflet, respectively. In the case of GPI-HA-induced fusion, different behaviors of lipid transfer were observed, which include 1) exclusive movement of N-Rh-PE (hemifusion), 2) preferential movement of N-Rh-PE relative to NBD-PC, and 3) equal movement of both lipid analogs. The relative population of these intermediate states was dependent on the time after application of a low pH trigger for fusion. At early time points, hemifusion was more common and full redistribution of both bilayers was rare, whereas later full redistribution of both probes was frequently observed. In contrast to wild-type HA, the latter was not accompanied by mixing of the cytoplasmic marker Lucifer Yellow. We conclude that 1) the GPI-HA-mediated hemifusion intermediate is meta-stable and 2) expansion of an aqueous fusion pore requires the transmembrane and/or cytoplasmic domain of HA.     

Experience‐related reorganization of giant synapses in the lateral complex: Potential role in plasticity of the sky‐compass pathway in the desert ant Cataglyphis fortis

Cataglyphis desert ants undergo an age‐related polyethism from interior workers to relatively short‐lived foragers with remarkable visual navigation capabilities, predominantly achieved by path integration using a polarized skylight‐based sun compass and a stride‐integrating odometer. Behavioral and physiological experiments revealed that the polarization (POL) pattern is processed via specialized UV‐photoreceptors in the dorsal rim area of the compound eye and POL sensitive optic lobe neurons. Further information about the neuronal substrate for processing of POL information in the ant brain has remained elusive. This work focuses on the lateral complex (LX), known as an important relay station in the insect sky‐compass pathway. Neuroanatomical results in Cataglyphis fortis show that LX giant synapses (GS) connect large presynaptic terminals from anterior optic tubercle neurons with postsynaptic GABAergic profiles of tangential neurons innervating the ellipsoid body of the central complex. At the ultrastructural level, the cup‐shaped presynaptic structures comprise many active zones contacting numerous small postsynaptic profiles. Three‐dimensional quantification demonstrated a significantly higher number of GS (～13%) in foragers compared with interior workers. Light exposure, as opposed to age, was necessary and sufficient to trigger a similar increase in GS numbers. Furthermore, the increase in GS numbers was sensitive to the exclusion of UV light. As previous experiments have demonstrated the importance of the UV spectrum for sky‐compass navigation in Cataglyphis, we conclude that plasticity in LX GS may reflect processes involved in the initial calibration of sky‐compass neuronal circuits during orientation walks preceding active foraging. © 2015 Wiley Periodicals, Inc. Develop Neurobiol 76: 390–404, 2016     

Der Regelkreis des Kniesehnenreflexes bei der Stabheuschrecke Carausius morosus

In Part B the tendon of the femoral chordotonal organ (receptor tendon) of a fixed leg is sinusoidally moved with different amplitudes and frequencies. This causes movements of the tibia. Figures 1–3 show the amplitudes of the tibia movements and the phase-shifts between tibia-movement and stimulus. As it is known, that a tibia-movement of about 13° corresponds to a movement of the receptor-tendon of 100 m, a bode-plot can be constructed. Figure 4 is the first part of a three-dimensional bode-plot (amplitude ratio) which additionally shows the values of amplitudes and frequencies, at which a phase shift of 180° can be observed. The system is stable, if the gain of the system is smaller than 1 at these values. A gain equal or larger than 1 causes instability. As it can be seen in Fig. 4, the system is stable, but it is not very far from instability. In Part C an inert mass is coupled to the tibia in order to enlarge the phase-shift. After a disturbance, which causes a higher gain of the system, intact legs often show long lasting oscillations of small amplitude (Fig. 6a, b). During these oscillations the other legs are not moved. Sometimes active movements of all legs occur. Active movements of the tested legs have larger amplitudes and are always followed by small-amplitude-oscillations. Legs with cut receptor tendons and intact legs of decerebrated animals never show small-amplitude-oscillations but only active movements. Therefore it is probable that the small-amplitude-oscillations are oscillations of the feedback-system. In Part C 4 another possible explanation for these oscillations is discussed: The forces, produced by the muscles, might be represented by a noise of broad bandwidth from which the mechanical system selects only a small band given by its resonance frequency. In order to test this hypothesis, electrophysiological experiments are done (C5): During slow-amplitude-oscillations of legs with an inert mass added a spike-burst can be observed in the flexor tibiae during extension and in the extensor tibiae during flexion of the femur-tibia-joint. Sometimes no activity in the extensor can be observed. This means, that the activity in the muscles has a phase-shift of about 180° relative to the movement of the tibia: These supports the hypothesis, that the small-amplitude-oscillations are oscillations of the control system of the Kniesehnenreflex. In Part D it is discussed, whether the rocking-movements of the whole animal could be explained by oscillations of control systems. It is, deduced, that if this hypothesis is true, the control system in the coxa-trochanter-joint must be as near to instability as the control system of the Kniesehnenreflex.     

Disturbed immune-endocrine communication in autoimmune disease. Lack of corticosterone response to immune signals in obese strain chickens with spontaneous autoimmune thyroiditis

Antigenic challenge as well as injection of lymphokine-containing media lead to a transient increase of serum glucocorticoids, a phenomenon that has been implicated in the regulation of the specificity of immune responses. In the present study we examined the dialogue between the immune and the neuroendocrine systems in Obese strain (OS) chickens, an animal model for human Hashimoto thyroiditis. The following results were obtained: A) OS and normal White Leghorn (NWL) chickens, 5-mo-old, were immunized with sheep red blood cells followed by daily monitoring of corticosterone (CN) serum levels. Whereas in NWL animals CN serum levels markedly increase 3 to 4 days after immunization, OS animals did not respond with CN elevation. B) A single i.v. injection of conditioned medium (CM) from concanavalin A-stimulated spleen cells also led to a transient, dose-dependent peak in plasma CN (maximum after 30 min). This CN response to a given CM preparation was significantly lower in OS than in NWL animals. C) CM, whether obtained from OS or NWL splenocytes, were equally effective to stimulate CN production. D) A single i.v. injection of CM leads--concomitantly to the CN peak--to a decrease of the concanavalin A-mediated proliferative response of peripheral blood lymphocytes in both OS and NWL chickens. This suppression, however, was significantly more pronounced in NWL chickens. In summary, these data suggest a disturbance of the immune-neuroendocrine communication in OS chickens with spontaneous thyroid autoimmunity. The possible implications for the generation of "forbidden" autoimmune responses are discussed.     

Elevation of corticosteroid-binding globulin in obese strain (OS) chickens: possible implications for the disturbed immunoregulation and the development of spontaneous autoimmune thyroiditis

Basal plasma levels of corticosterone and corticosteroid-binding globulin (CBG) have been investigated in Obese strain (OS) chickens afflicted with spontaneous autoimmune thyroiditis (SAT). Corticosterone was determined radioimmunologically, and CBG by using a highly sensitive radioligand saturation assay. OS chickens displayed total corticosterone levels not different from healthy normal White Leghorn (NWL) chickens. CBG, however, was found to be twice as high in OS chickens as compared with their healthy counterparts, irrespective of sex or age. This quantitative difference in the CBG level is not compensated for by either altered affinity or specificity of the molecule. Furthermore, no differences were found in the response of OS and NWL lymphocytes to the suppressive effect of glucocorticoids in vitro. We therefore assume that OS animals are deficient in free, hormonally active corticosterone. An additional indication for such a diminished glucocorticoid tonus was that in vivo treatment of OS chickens with glucocorticoid hormones, thus increasing the free and active hormone fraction, normalizes the T cell hyperreactivity and significantly reduces thyroid infiltration. Possible pathophysiological implications of a diminished glucocorticoid tonus for spontaneous autoimmunity, as well as possible explanations for the beneficial effects of glucocorticoid treatment on the development of SAT, are discussed.     

Degradation of the nitrogenase proteins during encystment of Azotobacter vinelandii

Nitrogenase activity in cell-free extracts of Azotobacter vinelandii declines during encystment. Upon germination a rapid increase in activity is observed, which is suppressed by rifampicin, suggesting that de novo biosynthesis of the nitrogenase proteins is required. The decline of activity during encystment is accompanied by disappearance of both nitrogenase proteins from cell extracts, indicating irreversible proteolysis. Total proteinase activity does not change significantly during encystment.