Velarium control and visual steering in box jellyfish

Directional swimming in the box jellyfish Tripedalia cystophora (cubozoa, cnidaria) is controlled by the shape of the velarium, which is a thin muscular sheet that forms the opening of the bell. It was unclear how different patterns of visual stimulation control directional swimming and that is the focus of this study. Jellyfish were tethered inside a small experimental tank, where the four vertical walls formed light panels. All four panels were lit at the start of an experiment. The shape of the opening in the velarium was recorded in response to switching off different combinations of panels. We found that under the experimental conditions the opening in the velarium assumed three distinct shapes during a swim contraction. The opening was (1) centred or it was off-centred and pocketed out either towards (2) a rhopalium or (3) a pedalium. The shape of the opening in the velarium followed the direction of the stimulus as long as the stimulus contained directional information. When the stimulus contained no directional information, the percentage of centred pulses increased and the shape of the off-centred pulses had a random orientation. Removing one rhopalium did not change the directional response of the animals, however, the number of centred pulses increased. When three rhopalia were removed, the percentage of centred pulses increased even further and the animals lost their ability to respond to directional information.     

Scene perception and the visual control of travel direction in navigating wood ants

This review reflects a few of Mike Land''s many and varied contributions to visual science. In it, we show for wood ants, as Mike has done for a variety of animals, including readers of this piece, what can be learnt from a detailed analysis of an animal''s visually guided eye, head or body movements. In the case of wood ants, close examination of their body movements, as they follow visually guided routes, is starting to reveal how they perceive and respond to their visual world and negotiate a path within it. We describe first some of the mechanisms that underlie the visual control of their paths, emphasizing that vision is not the ant''s only sense. In the second part, we discuss how remembered local shape-dependent and global shape-independent features of a visual scene may interact in guiding the ant''s path.     

A contribution to the mathematical biophysics of visual aesthetics

In continuation of previous studies, inequalities between different parameters of the brain are derived which determine whether an individual prefers in general visual patterns consisting of a relatively small number of relatively strongly excited elements, or such patterns which consist of a very large number of relatively weakly excited elements. As has been discussed in a previous publication, the first type of pattern is usually represented by artificial human-made designs, whereas the second type of pattern is formed predominantly in natural landscapes and sceneries. Thus the inequalities established in this paper give us the biophysical conditions which determine an individual's preference for either artificial designs or for landscapes and other natural objects.     

Functional contribution of P2Y1 receptors to the control of coronary blood flow

Activation of ADP-sensitive P2Y(1) receptors has been proposed as an integral step in the putative "nucleotide axis" regulating coronary blood flow. However, the specific mechanism(s) and overall contribution of P2Y(1) receptors to the control of coronary blood flow have not been clearly defined. Using vertically integrative studies in isolated coronary arterioles and open-chest anesthetized dogs, we examined the hypothesis that P2Y(1) receptors induce coronary vasodilation via an endothelium-dependent mechanism and contribute to coronary pressure-flow autoregulation and/or ischemic coronary vasodilation. Immunohistochemistry revealed P2Y(1) receptor expression in coronary arteriolar endothelial and vascular smooth muscle cells. The ADP analog 2-methylthio-ADP induced arteriolar dilation in vitro and in vivo that was abolished by the selective P2Y(1) antagonist MRS-2179 and the nitric oxide synthase inhibitor N(G)-nitro-l-arginine methyl ester. MRS-2179 did not alter baseline coronary flow in vivo but significantly attenuated coronary vasodilation to ATP in vitro and in vivo and the nonhydrolyzable ATP analog ATPγS in vitro. Coronary blood flow responses to alterations in coronary perfusion pressure (40-100 mmHg) or to a brief 15-s coronary artery occlusion were unaffected by MRS-2179. Our data reveal that P2Y(1) receptors are functionally expressed in the coronary circulation and that activation produces coronary vasodilation via an endothelium/nitric oxide-dependent mechanism. Although these receptors represent a critical component of purinergic coronary vasodilation, our findings indicate that P2Y(1) receptor activation is not required for coronary pressure-flow autoregulation or reactive hyperemia.     

Testing visual sensitivity to the speed and direction of motion in lizards

Testing visual sensitivity in any species provides basic information regarding behaviour, evolution, and ecology. However, testing specific features of the visual system provide more empirical evidence for functional applications. Investigation into the sensory system provides information about the sensory capacity, learning and memory ability, and establishes known baseline behaviour in which to gauge deviations (Burghardt, 1977). However, unlike mammalian or avian systems, testing for learning and memory in a reptile species is difficult. Furthermore, using an operant paradigm as a psychophysical measure of sensory ability is likewise as difficult. Historically, reptilian species have responded poorly to conditioning trials because of issues related to motivation, physiology, metabolism, and basic biological characteristics. Here, I demonstrate an operant paradigm used a novel model lizard species, the Jacky dragon (Amphibolurus muricatus) and describe how to test peripheral sensitivity to salient speed and motion characteristics. This method uses an innovative approach to assessing learning and sensory capacity in lizards. I employ the use of random-dot kinematograms (RDKs) to measure sensitivity to speed, and manipulate the level of signal strength by changing the proportion of dots moving in a coherent direction. RDKs do not represent a biologically meaningful stimulus, engages the visual system, and is a classic psychophysical tool used to measure sensitivity in humans and other animals. Here, RDKs are displayed to lizards using three video playback systems. Lizards are to select the direction (left or right) in which they perceive dots to be moving. Selection of the appropriate direction is reinforced by biologically important prey stimuli, simulated by computer-animated invertebrates.     

A contribution to the mathematical biophycics of visual perception and aesthetics

In continuation of previous studies of the mathematical biophysics of visual perception in relation to the aesthetic evaluation of visual patterns, an expression for the total intensity of excitation in a discriminating center as a function of the intensity of the peripheral stimulus is derived. This expression is applied to the case of aesthetic judgments of similar polygons of different sizes. The theoretical conclusions are tested experimentally by use of standard psychological scaling methods. The theoretical predictions are found to be in agreement with the experimental results.     

Neuronal control of the kidney: contribution to hypertension.

The renal nerves contribute to hypertension in experimental models of the disease, and appear to play a role in human hypertension. Several lines of evidence indicate that both in spontaneously hypertensive rats and in deoxycorticosterone acetate--NaCl rats, the full development of hypertension is dependent on renal efferent nerves and their induction of excess sodium retention. Renal sensory (afferent nerve) feedback to the central nervous system does not contribute to either of these forms of hypertension. In contrast, renovascular hypertension in rats and aortic coarctation hypertension in dogs are mediated, at least in part, by overactivity of renal afferent nerves and a resultant increase in systemic sympathetic nervous system activity. These forms of hypertension are not associated with sodium retention, and selective sensory denervation of renal afferent nerves by dorsal rhizotomy and total renal denervation result in similar reductions in hypertension. Surprisingly, the renal nerves do not contribute to dietary NaCl exacerbated hypertension in the spontaneously hypertensive rat, dietary NaCl-induced hypertension in the Dahl NaCl-sensitive rat, or the chronic hypertensive and nephrotoxic effects of cyclosporine A therapy in the rat, despite the finding that in all three forms of hypertension, overactivity of the sympathetic nervous system is prominent. Clinical studies indicate that the renal afferent and efferent nerves contribute to hypertension of different etiologies. Together these data point to the complex role that the renal nerves likely play in human essential hypertension.     

Curvature in hand movements as a result of visual misjudgements of direction

The path that our hand takes when moving from one position to another is often slightly curved. Part of this curvature is caused by perceptual errors. We examine here whether this is so for the influence that a surface's orientation has on the approaching hand's path. When moving our hand towards a point on a surface we tend to follow a path that makes the final approach more orthogonal to the surface at that point. Doing so makes us less sensitive to imperfections in controlling our movements. Here we show that this tendency is also present when moving towards a point along an edge of a drawing of an oriented bar. The influence of the bar's orientation is no smaller when people are explicitly asked to move as straight as possible, than when they are instructed to move as fast as possible. The bar's orientation also influences perceptual judgements of a straight path, but this influence is only as large as it is on the curvature of the hand's path for judgements of the direction from the hand's initial position to the target. We conclude that the influence of the bar's orientation on the curvature of the hand's path is caused by a misperception of the initial direction in which the hand has to move to reach the target.     

Growth direction of nodal roots in rice: its variation and contribution to root system formation

The root system of a rice plant (Oryza sativa L.) consists of numerous nodal roots and their laterals. The growth direction of these nodal roots affects the spatial distribution of the root system in soil, which seems to relate to yield and lodging resistance. The growth angle of a nodal root varies with the type and timing of emergence of the nodal root. The body of a rice plant can be recognized as an integrated set of shoot units, each unit consisting of an internode with a leaf and several roots. Nodal roots formed at the apical part of a shoot unit often elongate horizontally, whereas those formed at the basal part of the shoot unit show various growth directions depending on both the growth stages of the plant and the environmental conditions. Moreover, nodal roots that emerge from the most basal shoot unit of a tiller are usually thick and grow downwards. External factors such as planting density and nitrogen application affect the growth direction of nodal roots, probably partly because of the changing tillering pattern of the shoot. In addition to the growth angle of nodal roots, size of nodal roots may be another important factor determining the spatial distribution of the root system in soil.     

Predicting persistence in a changing climate: flow direction and limitations to redistribution

Synthesis Impending climate changes beg the question: which populations and species will go extinct and which will persist under future environmental conditions? When tolerance in situ is not possible, then species must undergo range shifts to avoid extinction. This synthesis explores ways in which directional air and water flow could impede such redistribution and the characteristics that might allow species to disperse against the flow. Considering flow patterns in tandem with climate and range projections has the potential to improve predictions of persistence for the earth’s many non‐moving foundation and basal species as well as the communities and food webs that they support. Predicting which populations and species will persist (i.e. avoid extinction and continue to exist) in the face of climate change requires an understanding of mechanisms that allow species to cope with altered environmental conditions. When processes of tolerance, acclimation, and adaptation are insufficient to allow persistence in situ, redistribution is required for population or species persistence. Here, I review evidence that directional flows of water and air have the potential to restrict species’ range boundaries under ambient conditions, the spread of introduced species, and the redistribution of native species under changing climatic conditions. I develop the hypothesis that flow patterns, such as the speed and directionality (i.e. poleward vs equatorward) of asymmetric air and water currents, may need to be considered when assessing the vulnerability of populations and species to climate change. To the degree that directional flows are found to limit redistribution, there may be disproportionate losses of diversity where the dominant flow direction opposes that of shifting climate space. Within this context, I highlight flow conditions and life‐history traits that could help the most passively‐dispersed species redistribute to track changing climate. These predictions merit further examination in order to better anticipate which populations, species, and associated communities are likely to persist under climate change.     

The cGMP-phosphodiesterase and its contribution to sensitivity regulation in retinal rods

We have used the truncated outer segment preparation to measure rod cGMP-phosphodiesterase activity, as well as its modulation by Ca2+, in darkness and in light. The basal enzyme activity in darkness was approximately 0-3 s-1, and was largely independent of Ca2+ concentration from 10 nM to 10 microM. The steady state activity elicited by a step of light (lambda = 520 nm) was strongly enhanced by Ca2+, increasing from approximately 0.005 s-1/(h nu micron-2 s-1) at 10 nM Ca2+ to approximately 0.16 s-1/h nu micron-2 s-1) at 10 microM Ca2+. Based on these measurements, as well as previous measurements on the effects of Ca2+ on rod guanylate cyclase and the cGMP-gated channel, we have calculated the step response-intensity relation for the rod cell in steady state. This relation agrees reasonably well with the relation directly measured from intact rods. We have also evaluated the relative contributions from the three Ca2+ effects to rod sensitivity. At low background light intensities, the Ca2+ modulation of the guanylate cyclase appears to be the most important for sensitivity regulation. At higher light intensities, especially above half-saturation of the response, the Ca2+ modulation of the light-stimulated phosphodiesterase shows a progressively important influence on the light response; it also extends the Weber-Fechner behavior of the cell to higher intensities. The contribution of the Ca2+ modulation of the cGMP-gated channel is slight throughout.     

Invertebrate neurobiology: visual direction of arm movements in an octopus

An operant task in which octopuses learn to locate food by a visual cue in a three-choice maze shows that they are capable of integrating visual and mechanosensory information to direct their arm movements to a goal.     

Attention: control in the visual cortex

A recent study in which the human visual cortex was directly stimulated to create visual percepts has shown that visual spatial attention can act directly on neural activity in sensory cortex without involving attentional modulation of subcortical visual inputs.     

Visual control of steering in locust flight: the effects of head movement on responses to roll stimuli

The contribution of head movement to the control of roll responses in flying locusts (Locusta migratoria) has been examined (i) on a flight balance, recording the angles through which the locust turns when following an artificial horizon; (ii) by recording activity in a pair of flight muscles in restrained conditions; and (iii) by observations on free flying locusts. Responses were compared when the head was free to turn about the thorax, as normal, and when the head was waxed to the thorax, blocking any relative motion between the two (head-fixed). These experiments suggest that the major signal generating corrective roll manoeuvres is the visual error between the angle of the head and the horizon, rather than a signal that includes a measure of the head-thorax angle.

Mechanoreceptor system of the respiratory center and its contribution to respiratory control

The mechanoreceptor system of the respiratory center (RC) includes airway mechanoreceptors together with their conducting pathways and bulbar neuronal structures conveying impulses from mechanoreceptors to the RCV.A. A. Bogomolets Institute of Physiology, Ukrainian Academy of Sciences, Kiev. Translated from Neirofiziologiya, Vol. 24, No. 4, pp. 351–368, May–June, 1992.