Nervöse Wechselwirkung in der pupillomotorischen Bahn des Menschen

Summary Comparison of the human pupillary responses to monocular and simultaneous binocular stimuli indicates that the signals evoked in both eyes by binocular stimulation first inhibit each other and then combine by addition. In this paper several possible inhibitory mechanisms are considered and a functional model is proposed which involves a shunting type non-recurrent lateral inhibition. Although the site of inhibitory interaction is not specified by the model, certain assumptions are made regarding the succession of neural events along the pupillomotor pathway. The postulated succession of transmitting stages is: nonlinear transformation, first order lowpass filter with time constant characteristic for the pupillary response, lateral inhibition, addition and second order lowpass filter with the same time constant as before. Besides predicting the experimental data this functional model resolves certain contradictions in the conclusions of different autors regarding the succession of nonlinear transformation and signal combination in the human pupillary system.     

Maturation depresses mouse cerebrovascular tone through endothelium-dependent mechanisms

In light of previous observations that the range of arterial pressures over which cerebral blood flow is autoregulated differs dramatically in neonates and adults, the present experiments explored the hypothesis that pressure-induced intrinsic arterial tone is regulated differently in neonatal and adult cerebral arteries. In cannulated and pressurized endothelium-intact mouse cerebral arteries <150 microm in diameter, active intrinsic tone was evident at intraluminal pressures as low as 10 mmHg in neonatal arteries, but only at pressures of 60 mmHg or greater in adult arteries. Administration of 10 microM indomethacin produced no significant effect on tone at any pressure in either neonatal or adult arteries, but subsequent addition of 100 microroarginine methyl ester (NAME) significantly vasoconstricted both neonatal and adult arteries at all pressures. Conversely, administration of 100 microE alone significantly vasoconstricted adult arteries only, and subsequent addition of 10 microomethacin produced a significant additional vasoconstriction in adult arteries only, indicating an important interaction between the nitric oxide synthase and cyclooxygenase pathways, at least in adult arteries. In the presence of both indomethacin and NAME, intrinsic tone was significantly greater in neonatal than adult arteries, but when the endothelium was removed, tone was similar in neonatal and adult arteries at all pressures. Together, these results suggest that pressure-induced myogenic tone is regulated similarly in neonatal and adult mouse cerebral arteries but that the contribution of endothelial vasoactive factors to intrinsic tone is highly age dependent.     

Evolving détente: the origin of warning signals via concurrent reciprocal selection

Casualties and impediments inflicted on consumers by defended prey, and vice versa, may be averted by vocalizations, postures, coloration, scents, and other warning, or so‐called aposematic, displays. The existence of aposematic signals has challenged biologists who have sought plausible mechanisms for their evolution. Here, we elaborate on the rationale for the hypothesis that aposematic signals arise via concurrent reciprocal selection (CRS) enacted between inimical signal receivers and signal emitters, where signal emitters, e.g., defended prey, select against non‐discriminating signal receivers, e.g., predators, and signal receivers select against unrecognized signal emitters. It is postulated that this mutual selective interaction culminates in the survival of discriminating signal receivers that avoid signal emitters, and recognized (distinctive) signal emitters that are avoided by signal receivers. A CRS hypothesis for the evolution of aposematism, therefore, maintains that distinctive features of prey arise in response to selection imposed by consumers, and that avoidances of those features by consumers arise in response to selection imposed by defended prey. We discuss the plausible inception of aposematism via CRS in light of related hypotheses, and describe points of concordance with previous observations and suggestions on the origin of aposematism. Aposematism arising via CRS is not contingent upon the relatedness of signallers, aversions acquired by learning, or other conditions postulated for some other evolutionary hypotheses. CRS is a credible alternative hypothesis for the evolution of warning signals in diverse consumer‐prey interactions.     

The ecological significance of rapid wound-induced changes in plants: insect grazing and plant competition

Summary This paper investigates the hypothesis that a rapidly induced phytochemical response to grazing damage, such as that seen in tomato, serves to deflect insect herbivores away from leaves soon after damaging them (the grazing dispersal hypothesis). As a result, grazing damage is more dispersed than it otherwise would be, and young leaves, which may be of particular importance to a plant in competition for light, are not damaged excessively. In the first experiment, artificial removal of c. 15% of leaf area led to a significant reduction in plant performance compared with undamaged controls, but only when the plants were grown together in competition for light. The second experiment demonstrated that the distribution of grazing damage within the plant was an important factor in the outcome of competition; in those plants in which grazing was applied to the lower leaves there was no effect of damage upon performance compared with undamaged controls, whereas grazing to the upper leaves significantly reduced plant performance. A third experiment provided some insight into how this interaction between damage and competition comes about. It was shown that damage to leaves led to a rapid drop in the rate of extension growth of the main shoot, especially when the upper leaves were damaged, and normal rates of growth were not resumed for at least 3 days. It is argued that in a rapidly growing canopy, such an effect may mean that a damaged plant loses its position in the height hierarchy. The final experiment showed that previous damage to plants can affect the distribution of subsequent grazing by larvae of Spodoptera littoralis, apparently through a wound-induced reduction in leaf palatability. Plants which had been artificially damaged 48 h previously were grazed significantly less than controls, and the avoidance effect was greatest in the young leaves. These results are consistent with the grazing dispersal hypothesis, and suggest that rapid wound-induced responses may be of greatest significance in species characteristic of fertile environments where competition for light is particularly intense.     

A General Framework for Formal Tests of Interaction after Exhaustive Search Methods with Applications to MDR and MDR-PDT

The initial presentation of multifactor dimensionality reduction (MDR) featured cross-validation to mitigate over-fitting, computationally efficient searches of the epistatic model space, and variable construction with constructive induction to alleviate the curse of dimensionality. However, the method was unable to differentiate association signals arising from true interactions from those due to independent main effects at individual loci. This issue leads to problems in inference and interpretability for the results from MDR and the family-based compliment the MDR-pedigree disequilibrium test (PDT). A suggestion from previous work was to fit regression models post hoc to specifically evaluate the null hypothesis of no interaction for MDR or MDR-PDT models. We demonstrate with simulation that fitting a regression model on the same data as that analyzed by MDR or MDR-PDT is not a valid test of interaction. This is likely to be true for any other procedure that searches for models, and then performs an uncorrected test for interaction. We also show with simulation that when strong main effects are present and the null hypothesis of no interaction is true, that MDR and MDR-PDT reject at far greater than the nominal rate. We also provide a valid regression-based permutation test procedure that specifically tests the null hypothesis of no interaction, and does not reject the null when only main effects are present. The regression-based permutation test implemented here conducts a valid test of interaction after a search for multilocus models, and can be applied to any method that conducts a search to find a multilocus model representing an interaction.     

Viable sorting of intact multicellular spheroids by flow cytometry

A flow cytometric method has been developed for sorting viable, intact multicellular spheroids in order to obtain uniformly-sized populations with diameters in the range of 50-100 microns. A FACS II instrument was modified for this purpose by installing a 200-microns-diameter exit orifice and by making adjustments in the sheath flow, oscillator frequency, and number of droplets sorted. Polystyrene microspheres (44 and 88 microns diameter) and 41-96-microns-diameter spheroids could be sorted and recovered with 70-100% efficiency, an improvement over previous reports. Unstained, viable spheroids were simultaneously analyzed for small-angle forward light scatter, 90 degree light scatter, and autofluorescence using a 488-nm laser operating at 100 mW. Analysis of the data demonstrated a considerable variation in both the 90 degrees light scatter and the autofluorescence signals for a given forward angle light scattering signal. By setting narrow sort windows on the forward angle light scattering signal and either the 90 degree light scatter or autofluorescence signals, uniformly spherical spheroid populations could be recovered. These sorted populations had coefficients of variation of the mean diameter in the range of 5-9%. This represents a variation of less than one cell diameter, and is a major improvement over any other technique. There was no significant difference in the subsequent growth rates of sorted spheroids compared to the unsorted spheroids. This technique will apply when uniform populations of small spheroids are required, such as investigations of the contact effect or in the initiation of growth curve studies.     

IL-2 is required for the activation of memory CD8+ T cells via antigen cross-presentation

Dendritic cells (DCs) are capable of capturing exogenous Ag for the generation of MHC class I/peptide complexes. For efficient activation of memory CD8(+) T cells to occur via a cross-presentation pathway, DCs must receive helper signals from CD4(+) T cells. Using an in vitro system that reflects physiologic recall memory responses, we have evaluated signals that influence helper-dependent cross-priming, while focusing on the source and cellular target of such effector molecules. Concerning the interaction between CD4(+) T cells and DCs, we tested the hypothesis that CD40 engagement on DCs is critical for IL-12p70 (IL-12) production and subsequent stimulation of IFN-gamma release by CD8(+) T cells. Although CD40 engagement on DCs, or addition of exogenous IL-12 are both sufficient to overcome the lack of help, neither is essential. We next evaluated cytokines and chemokines produced during CD4(+) T cell/DC cross talk and observed high levels of IL-2 produced within the first 18-24 h of Ag-specific T cell engagement. Functional studies using blocking Abs to CD25 completely abrogated IFN-gamma production by the CD8(+) T cells. Although required, addition of exogenous IL-2 did not itself confer signals sufficient to overcome the lack of CD4(+) T cell help. Thus, these data support a combined role for Ag-specific, cognate interactions at the CD4(+) T cell/DC as well as the DC/CD8(+) T cell interface, with the helper effect mediated by soluble noncognate signals.     

Attention-altering signal interactions in the multimodal courtship display of the wolf spider Schizocosa uetzi

Complex signals are common throughout the animal kingdom, consistingof one or more signals in one or more sensory modalities presentedwithin a single display. I tested an efficacy-based backup hypothesisof complex signal function using the bimodal courtship signalingwolf spider Schizocosa uetzi. This hypothesis predicts thatthe visual and vibratory courtship displays function as backupsto each other in the presence of environmental variability.I compared mating frequencies across four environmental treatmentsin which the visual and vibratory environments were manipulatedindependently in a 2 x 2 design with visual treatments of light/dark(i.e., visual signal present/absent) and vibratory treatmentsof filter paper substratum/granite substratum (i.e., vibratorysignal present/absent). Results did not match the predictionsof an efficacy-based backup hypothesis. The vibratory environmentaffected mating frequency, with more mating occurring in thevibration-present treatments compared to the vibration-absenttreatments, but the visual environment had no effect on matingfrequency. A second experiment was then conducted to test foran inter-signal interaction. Using the video-playback technique,I presented females with manipulated video sequences simultaneouswith a controlled vibratory signal to test the hypothesis thatthe presence of a vibratory signal alters a female's responseto the visual signal. In the presence of a vibratory courtshipsignal, females were more receptive to more visually ornamentedmales. This increased receptivity to increased visual ornamentationwas not seen in a previous study conducted on S. uetzi in theabsence of a vibratory signal, suggesting a potential inter-signalinteraction. In a third experiment, I tested whether a female'svisual attention was altered by the vibratory signal by examiningfemale response to a visual "predator" while exposed to allpossible combinations of male courtship signals. Females weremore likely to get caught, and thus less likely to notice apredatory visual stimulus when exposed to a courtship vibration,supporting the hypothesis that the vibratory signal alters afemale's visual attention.     

An aortic spontaneously active phosphatase dephosphorylates myosin and inhibits actin-myosin interaction

Actin-myosin interaction in aortic actomyosin reportedly requires phosphorylation of the 20,000 dalton myosin light chains. A spontaneously active phosphatase which dephosphorylates phosphorylase $\text{a}$ and isolated phosphorylated cardiac myosin light chains was extracted from bovine aortic smooth muscle. This enzyme, when added to aortic native actomyosin (a) significantly suppressed phosphorylation of the light chains of the native hexameric smooth muscle myosin, (b) accelerated the rate and increased the magnitude of myosin light chain dephosphorylation in actomyosin that had been prephosphorylated, and (c) markedly attenuated the rate of actin-myosin interaction. These results support the hypothesis that myosin phosphorylation and subsequent actin-myosin interactions (contractility) in vascular smooth muscle may be modulated by spontaneously active aortic phosphatase.     

光点位移运动激发的瞬态瞳孔反应

用等高度的光点位移运动作为刺激来测量瞳孔反应,实验记录表明,即使输入到视网膜的总光通量不变,仅仅是刺激点的位置改变就能激发起瞳孔反应,且其反应的位置分辨率可达１０’,这一实检结果揭示了瞳孔对光反射通路不仅传递了进入瞳孔的总光通量的信息,而且还检测了刺激光点位置变化的信息。     

Revisiting the Stimulus-Secretion Coupling in the Adrenal Medulla: Role of Gap Junction-Mediated Intercellular Communication

The current view of stimulation-secretion coupling in adrenal neuroendocrine chromaffin cells holds that catecholamines are released upon transsynaptic sympathetic stimulation mediated by acetylcholine released from the splanchnic nerve terminals. However, this traditional vertical scheme would merit to be revisited in the light of recent data. Although electrical discharges invading the splanchnic nerve endings are the major physiological stimulus to trigger catecholamine release in vivo, growing evidence indicates that intercellular chromaffin cell communication mediated by gap junctions represents an additional route by which biological signals (electrical activity, changes in intracellular Ca²⁺ concentration,…) propagate between adjacent cells and trigger subsequent catecholamine exocytosis. Accordingly, it has been proposed that gap junctional communication efficiently helps synapses to lead chromaffin cell function and, in particular, hormone secretion. The experimental clues supporting this hypothesis are presented and discussed with regards to both interaction with the excitatory cholinergic synaptic transmission and physiopathology of the adrenal medulla.     

Cytoplasmic utilization of human immunodeficiency virus type 1 genomic RNA is not dependent on a nuclear interaction with gag

In some retroviruses, such as Rous sarcoma virus and prototype foamy virus, Gag proteins are known to shuttle between the nucleus and the cytoplasm and are implicated in nuclear export of the viral genomic unspliced RNA (gRNA) for subsequent encapsidation. A similar function has been proposed for human immunodeficiency virus type 1 (HIV-1) Gag based on the identification of nuclear localization and export signals. However, the ability of HIV-1 Gag to transit through the nucleus has never been confirmed. In addition, the lentiviral Rev protein promotes efficient nuclear gRNA export, and previous reports indicate a cytoplasmic interaction between Gag and gRNA. Therefore, functional effects of HIV-1 Gag on gRNA and its usage were explored. Expression of gag in the absence of Rev was not able to increase cytoplasmic gRNA levels of subgenomic, proviral, or lentiviral vector constructs, and gene expression from genomic reporter plasmids could not be induced by Gag provided in trans. Furthermore, Gag lacking the reported nuclear localization and export signals was still able to mediate an efficient packaging process. Although small amounts of Gag were detectable in the nuclei of transfected cells, a Crm1-dependent nuclear export signal in Gag could not be confirmed. Thus, our study does not provide any evidence for a nuclear function of HIV-1 Gag. The encapsidation process of HIV-1 therefore clearly differs from that of Rous sarcoma virus and prototype foamy virus.     

Human Thy-1 (CD90) on activated endothelial cells is a counterreceptor for the leukocyte integrin Mac-1 (CD11b/CD18)

Leukocyte recruitment in response to inflammatory signals is in part governed by interactions between endothelial cell receptors belonging to the Ig superfamily and leukocyte integrins. In our previous work, the human Ig superfamily glycoprotein Thy-1 (CD90) was identified as an activation-associated cell adhesion molecule on human dermal microvascular endothelial cells. Furthermore, the interaction of Thy-1 with a corresponding ligand on monocytes and polymorphonuclear cells was shown to be involved in the adhesion of these leukocytes to activated Thy-1-expressing endothelial cells. In this study, we have identified the specific interaction between human Thy-1 and the leukocyte integrin Mac-1 (CD11b/CD18; alphaMbeta2) both in cellular systems and in purified form. Monocytes and polymorphonuclear cells were shown to adhere to transfectants expressing human Thy-1 as well as to primary Thy-1-expressing human dermal microvascular endothelial cells. Furthermore, leukocyte adhesion to activated endothelium as well as the subsequent transendothelial migration was mediated by the interaction between Thy-1 and Mac-1. This additional pathway in leukocyte-endothelium interaction may play an important role in the regulation of leukocyte recruitment to sites of inflammation.     

Modulation of tumor cell susceptibility to cytokine-induced cell death by hormones, growth factors, and cell density.

The mechanisms controlling "spontaneous" cellular death rates in normal and tumorigenic tissues are largely unknown. An important parameter in this respect is the susceptibility of the target cell to induction of the lytic pathway by appropriate signals. In the present article it is demonstrated in a serum-free in vitro system that the susceptibility of human tumor cells (TC) to induction of lysis by cytokine signals generated during interaction of TC with elutriated human monocytes (MO) is a highly dynamic parameter subject to modulation by hormones, growth factors, and tumor cell density. It was found that growth stimulatory signals such as insulin, and especially epidermal growth factor (EGF), increase lytic susceptibility, whereas hydrocortisone, which does not exert significant growth modulatory effects in these examples, protects TC against the induction of lysis. Increasing TC density above confluence dramatically enhances lytic susceptibility, suggesting interactions between TC to be involved in the induction of their death. In conjunction with previous data demonstrating the insusceptibility of TC, which are forced out of the cell cycle into the quiescent state (G0), the hypothesis is put forward that growth stimulatory factors increase a TC's lytic susceptibility by preventing its transit from G1 to G0 in response to growth inhibitory signals generated during MO/TC interaction. The data support the concept that TC susceptibility to the induction of cell death is a consequence of simultaneously activated growth stimulatory and growth inhibitory signalling pathways.     

Physiological and molecular mechanisms underlying the integration of light and temperature cues in Arabidopsis thaliana seeds

The relief of dormancy and the promotion of seed germination are of extreme importance for a successful seedling establishment. Although alternating temperatures and light are signals promoting the relief of seed dormancy, the underlying mechanisms of their interaction in seeds are scarcely known. By exposing imbibed Arabidopsis thaliana dormant seeds to two‐day temperature cycles previous of a red light pulse, we demonstrate that the germination mediated by phytochrome B requires the presence of functional PSEUDO‐RESPONSE REGULATOR 7 (PRR7) and TIMING OF CAB EXPRESSION 1 (TOC1) alleles. In addition, daily cycles of alternating temperatures in darkness reduce the protein levels of DELAY OF GERMINATION 1 (DOG1), allowing the expression of TOC1 to induce seed germination. Our results suggest a functional role for some components of the circadian clock related with the action of DOG1 for the integration of alternating temperatures and light signals in the relief of seed dormancy. The synchronization of germination by the synergic action of light and temperature through the activity of circadian clock might have ecological and adaptive consequences.     

Cellular analysis of ocular circadian pacemaker coupling in Bulla: role of efferent impulses in phase shifting

The eyes of Bulla gouldiana, a marine snail, contain circadian oscillators that are coupled to each other. Obvious candidates for the coupling signals are the optic nerve compound action potentials (CAPs) that express the circadian rhythm and lead to efferent impulses in the contralateral optic nerve. In the present experiments, the role of the CAPs as coupling signals was evaluated. We found that, following desynchronization of the two ocular oscillators by phase-delaying one eye with manganese, subsequent phase shifts in the initially unshifted ocular rhythm only occurred during the time that efferent optic nerve signals were present. In addition, in the absence of ocular desynchrony, phase shifts of the ocular rhythm could still be effected by activation of the efferent pathway. The influence of efferent impulses on identified retinal cells was also evaluated. No effect of efferent signals on receptor layer cells was detected, while it was found that efferent impulses generated depolarizations in basal retinal neurons (BRNs), the putative circadian oscillator cells. Depolarization of the BRNs has been shown previously to be involved in the light entrainment pathway. Depolarization appears to be similarly involved in the coupling pathway, since membrane depolarizations that mimicked the efferent-induced postsynaptic potentials likewise generated phase shifts of the ocular rhythm.     

The role of light in regulating seed dormancy and germination

Seed dormancy is an adaptive trait in plants. Breaking seed dormancy determines the timing of germination and is, thereby essential for ensuring plant survival and agricultural production. Seed dormancy and the subsequent germination are controlled by both internal cues (mainly hormones) and environmental signals. In the past few years, the roles of plant hormones in regulating seed dormancy and germination have been uncovered. However, we are only beginning to understand how light signaling pathways modulate seed dormancy and interaction with endogenous hormones. In this review, we summarize current views of the molecular mechanisms by which light controls the induction, maintenance and release of seed dormancy, as well as seed germination, by regulating hormone metabolism and signaling pathways.     

Melanopsin Bistability: A Fly's Eye Technology in the Human Retina

In addition to rods and cones, the human retina contains light-sensitive ganglion cells that express melanopsin, a photopigment with signal transduction mechanisms similar to that of invertebrate rhabdomeric photopigments (IRP). Like fly rhodopsins, melanopsin acts as a dual-state photosensitive flip-flop in which light drives both phototransduction responses and chromophore photoregeneration that bestows independence from the retinoid cycle required by rods and cones to regenerate photoresponsiveness following bleaching by light. To explore the hypothesis that melanopsin in humans expresses the properties of a bistable photopigment in vivo we used the pupillary light reflex (PLR) as a tool but with methods designed to study invertebrate photoreceptors. We show that the pupil only attains a fully stabilized state of constriction after several minutes of light exposure, a feature that is consistent with typical IRP photoequilibrium spectra. We further demonstrate that previous exposure to long wavelength light increases, while short wavelength light decreases the amplitude of pupil constriction, a fundamental property of IRP difference spectra. Modelling these responses to invertebrate photopigment templates yields two putative spectra for the underlying R and M photopigment states with peaks at 481 nm and 587 nm respectively. Furthermore, this bistable mechanism may confer a novel form of “photic memory” since information of prior light conditions is retained and shapes subsequent responses to light. These results suggest that the human retina exploits fly-like photoreceptive mechanisms that are potentially important for the modulation of non-visual responses to light and highlights the ubiquitous nature of photoswitchable photosensors across living organisms.