On the organization of memory in the optomotor system of the crab pachygrapsus crassipes

Memory responses of the optomotor system to rotations of various stripe patterns were studied. The separate elements of the visual background are individually remembered in terms of the parts of the eye on which their images fell. A visual illusion resulting from this property is described. All parts of the retina have an equal capacity to contribute to memory. The memory response results from the summation of contributions from individual elements rather than the maintenance of a fixation upon any particular feature of the situation. Both the separation between background elements for angles from 6° up to 60° and the number of elements present affect the size of the memory evoked response.     

Neuromuscular relationships in the abdomen of the Californian shore crab Pachygrapsus crassipes

There are two pairs of muscles in each abdominal segment of the crab; one pair of flexors and one pair of extensors. In the early larval stages the muscles have short sarcomeres--a property of fast fibers--and high thin to thick filament ratios--a property of slow fibers. In the adult the abdominal muscles are intermediate and slow, since they have fibers with intermediate and long sarcomeres, high thin to thick filament ratios, low myofibrillar ATPase activity, and high NADH diaphorase activity. The different fiber types are regionally distributed within the flexor muscle. Microelectrode recordings from single flexor muscle fibers in the adult showed that most fibers are supplied by three excitatory motor axons, although some are supplied by as many as five efferents. One axon supplies all of the flexor muscle fibers in its own hemisegment, and the evoked junctional potentials exhibit depression. This feature together with the innervation patterns of the fibers are similar to those reported for the deep flexor muscles of crayfish and lobsters. Therefore, in the adult crab, the abdominal flexor muscles have some features in common with the slow superficial flexors of crayfish and other features in common with the fast deep flexor muscles.     

Lipid metabolism of the female crab Pachygrapsus marmoratus during the moulting cycle

The moult induces important variations in the concentration and fatty acids composition of lipid classes during the moulting cycle of the female crab Pachygrapsus marmoratus regardless of the maturational degree of ovaries. Sexual maturity is characterized by a rise in lipids. Juveniles contain high levels of polyunsaturated fatty acids except in the ovary, whereas adults are composed mainly of monoethylenic acids. The moulting decrease of saturated fatty acids shows their importance during this crucial period, owing to their utilization as energy sources at the time of ecdysis. The late premoult fall of hepatopancreatic lipids results at once from inanition during the period before the exuviation and transfer of lipids through the hemolymph to the periphery in order to realize numerous changes occurring during the moulting process. The relative stability of lipid composition of ovaries in sexual pause during the moulting cycle agrees with a reduced metabolism of ovarian cells.     

Effect of limb regeneration on size increase at molt of the shore crabs Hemigrapsus oregonensis and Pachygrapsus crassipes.

Size increase at molt is reduced following multiple limb regeneration in the shore crabs, Hemigrapsus oregonensis and Pachygrapsus crassipes. Limb loss per se does not influence postmolt size. Effect of increasing number of regenerating limbs is additive. Postmolt size is programmed early in the premolt period of the preceding instar and is probably not readily influenced by water uptake mechanics at ecdysis. A simple model for growth, molting, and regeneration in heavily calcified Crustacea is developed from the viewpoint of adaptive strategies and energetic considerations.     

Arousal changes in the locust optomotor system

The activity of the optomotor interneurons in the locust optic lobe varies with arousal states. Two behaviourally different arousal situations can be readily reproduced in the locust, a spontaneous and an evoked arousal change. These produce different neuronal correlates in the optomotor interneurons, suggesting the presence of different arousal pathways possibly acting at different sites in the motion detection chain. Furthermore, an additional arousal effect can be demonstrated at the motoneurons showing that a reflex system is sensitive to arousal modulation at several levels.     

Direction-sensitive partitioning of the honeybee optomotor system

ABSTRACT. The horizontal motion-detecting system controlling optomotor head-turning behaviour in honeybees, Apis mellifera , was found to be partitioned into two separate subsystems. Each subsystem is direction-specific such that visual stimulation in the preferred direction elicited a high level of responses that correcly followed the movement, whereas stimulation in the non-preferred direction resulted in response levels comparable to or lower than those for blinded controls. The results indicate that medial eye regions are specialized for the detection of posterior-to-anterior movements and lateral regions are specialized for detecting anterior-to-posterior motion. A model suggesting possible neural correlates for this functional subdivision of the optomotor response is proposed.     

Motion sensitive interneurons in the optomotor system of the fly

The functional properties of the three horizontal cells (north horizontal cell, HSN; equatorial horizontal cell, HSE; south horizontal cell, HSS) in the lobula plate of the blowflyCalliphora erythrocephala were investigated electrophysiologically. 1. The receptive fields of the HSN, HSE, and HSS cover the dorsal, equatorial and ventral part of the ipsilateral visual field, respectively. In all three cells, the sensitivity to visual stimulation is highest in the frontal visual field and decreases laterally. The receptive fields and spatial sensitivity distributions of the horizontal cells are directly determined by the position and extension of their dendritic fields in the lobula plate and the dendritic density distributions within these fields. 2. The horizontal cells respond mainly to progressive (front to back) motion and are inhibited by motion in the reverse direction, the preferred and null direction being antiparallel. The amplitudes of motion induced excitatory and inhibitory responses decline like a cosine function with increasing deviation of the direction of motion from the preferred direction. Stimulation with motion in directions perpendicular to the preferred direction is ineffective. 3. The preferred directions of the horizontal cells show characteristic gradual orientation changes in different parts of the receptive fields: they are horizontally oriented only in the equatorial region and increasingly tilted vertically towards the dorsofrontal and ventrofrontal margins of the visual field. These orientation changes can be correlated with equivalent changes in the local orientation of the lattice of ommatidial axes in the pertinent compound eye. 4. The response amplitudes of the horizontal cells under stimulation with a moving periodic grating depend strongly on the contrast frequency of the stimulus. Maximal responses were found at contrast frequencies of 2–5 Hz. 5. The spatial integration properties of the horizontal cells (studied in the HSE) are highly nonlinear. Under stimulation with extended moving patterns, their response amplitudes are nearly independent of the size of the stimuli. It is demonstrated that this response behaviour does not result from postsynaptic saturation in the dendrites of the cells. The results indicate that the horizontal system is essentially involved in the neural control of optomotor torque responses performed by the fly in order to minimize unvoluntary deviations from a straight flight course.     

Motion sensitive interneurons in the optomotor system of the fly

The three horizontal cells of the lobula plate of the blowflyCalliphora erythrocephala were studied anatomically and physiologically by means of cobalt impregnations and intracellular recordings combined with Procion and Lucifer Yellow injections. The cells are termed north, equatorial and south horizontal cell (HSN, HSE, HSS) and are major output neurons of the optic lobe. 1. The dendritic arborizations of the HSN, HSE, HSS reside in a thin anterior layer of the lobula plate and extend over the dorsal, equatorial and ventral parts of this neuropil, respectively. Due to the retinotopic organization of the optic lobe, these parts correspond anatomically to respective regions of the ipsilateral visual field. Homologue horizontal cells in both lobula plates of the same animal and in different animals are highly variable with respect to their individual dendritic branching patterns. They are extraordinarily constant, on the other hand, with regard to the position and size of their dendritic fields as well as their dendritic branching density distributions. Each cell covers about 40% of the total area of the lobula plate and shows the highest dendritic density near the lateral margin of the neuropil which subserves the frontal eye region. The axons of the horizontal cells are relatively short and large in diameter; they terminate in the posterior ventrolateral protocerebrum. 2. The horizontal cells are directionally selective motion sensitive visual interneurons responding preferentially to progressive (front to back) motion in the ipsilateral visual field with graded depolarization of their axons and superimposed action potentials. Stimulation with motion in the reverse direction leads to hyperpolarizing graded responses. The HSE and HSN are additionally activated by regressive motion in the contralateral visual field.     

Molecular characterization and phylogenetic position of a new mariner-like element in the coastal crab, Pachygrapsus marmoratus

Mariner-like elements (MLEs) are class-II transposable elements that move within the genome of their hosts by means of a DNA-mediated "cut and paste" mechanism. MLEs have been identified in several organisms, from most of the phyla. Nevertheless, only a few of the sequences characterized contain an intact open reading frame. Investigation of the genome of a coastal crab, Pachygrapsus marmoratus, has identified nine Pacmmar elements, two of which have an open reading frame encoding a putatively functional transposase. Nucleic acid analyses and comparison with the previous data showed that the GC contents of MLEs derived from coastal organisms such as P. marmoratus are significantly higher than those of terrestrial MLEs and significantly lower than those of hydrothermal ones. Furthermore, molecular phylogeny analyses have shown that Pacmmar elements constitute a new lineage of the irritans subfamily within the mariner family.     

An optomotor control system with automatic compensation for contrast and texture.

When an animal's surroundings move, the animal normally follows that movement by turning its eyes (that is, by an optomotor reaction). As a result, the retinal image is partly stabilized. The efficacy of this stabilization necessarily depends on the gain of the optomotor control circuit. So far no biological detectors of retinal image movements have been discovered in either vertebrates or invertebrates that is, elements capable of generating a signal proportional to the movement velocity, which could serve as sensors in this control system (Borst & Egelhaaf 1989). The reason is that many other parameters, such as the light intensity and the 'texture' of the pattern, also affect the neuronal output. If movement detection is texture dependent, for instance, the gain and hence the quality of stabilization must also be texture dependent. But in humans, at least, with large-field stimulation the quality of retinal image stabilization has been found to be largely independent of texture (de Graaf et al. 1990). Here I describe a control system with gain control that permits automatic compensation, under closed-loop conditions, of the dependence of movement detection on parameters such as texture, brightness and so on. Comparison with data from experiments on arthropods shows that, in these animals at least, a control circuit with nonlinear properties like those suggested here has in fact been realized.     

Properties of a motor output system involved in the optomotor response in flies

1. The optomotor response of tethered flying houseflies (Musca domestica) has been studied at the level of the neural output which controls the activities of some non-fibrillar flight muscles (N-muscles).-a) During visually induced turning responses in a given direction some N-muscles on the right side of the thorax are synergistically active together with other N-muscles on the left side of the thorax. The same muscles are inactive during turning reactions in the opposite direction while the corresponding antagonists are now active (synopsis in Table 1).-b) The response activities of the N-mussles show a considerable variation during the course of time in spite of constant visual input.-c) There is a strong tendency for N-muscle spikes to be phase-locked with respect to the wingbeat period.-d) The findings obtained fromMusca are in accordance with the corresponding results obtained fromCalliphora (Heide, 1971b).
2. TheN-muscle activities have also been investigated in tethered flying blowflies (Calliphora erythrocephala) which tried to yaw spontaneously with both wings beating. In spontaneous left (right) turn reactions the features of the observed neural output are nearly identical with the features of the motor output showing up during visually induced left (right) turn reactions.-A different motor output pattern has been found in flies with only one wing beating.
3. The wingbeat synchronous rhythm observed in spike trains from activeN-muscles is produced in the thorax without the participation of higher stages of the fly's CNS. On the other hand no distinct rhythms can be found in spike trains fromN-muscles of non-flying flies when their motoneurons are artificially activated by non-rhythmic stimuli. Afferent information from thoracic sense organs seems to be essential for the production of the rhythm observed during flight.
4. The results about the production of the wingbeat synchronous rhythm in spike trains fromN-muscles suggest that the information derived from the motion detectors only acts to gate the output needed to achieve yaw-turn reactions. The strength of the influence of signals from the motion detectors on the output producing system can be modified by the animals “state of excitement”.
5. A model is presented which summarizes some features of information processing in the output systems supplying theN-muscles of flies. Available physiological data are discussed in relation to the model.