Postural control under clinorotation in upside-down catfish, Synodontis nigriventris.

The upside-down catfish Synodontis nigriventris has a unique habit of swimming and resting upside-down in free water. This behavior leads to the assumption that the catfish has a specific gravity information processing system. We examined the postural control behaviors in the catfish under clinorotation which is usually used for producing pseudo-microgravity. Synodontis nigriventris kept its body posture at a stable area of the rotated flask in which the catfish was kept, when it was clinorotated at the rate of 60 rpm. In contrast to Synodontis nigriventris, a related species, Corydoras paleatus, did not show such steady postural control. When the flask was rotated at a lower rate of 30 rpm or a higher rate of 100 rpm, Synodontis nigriventris as well as Corydoras paleatus showed a considerable disturbed control of body posture. In this condition, they were frequently rotated with the flask. These findings suggest that Synodontis nigriventris has a high ability to keep upside-down posture and the gravity sensation in this catfish is likely to contribute to its different postural control from that of many other fishes.     

The effect of clinorotation on vestibular compensation in upside-down swimming catfish.

Upside-down swimming catfish Synodontis nigriventris can keep upside-down swimming posture stably under pseudo-microgravity generated by clinostat. When the vestibular organ is unilaterally ablated, the operated S. nigriventris shows disturbed swimming postures under the clinorotation condition. However, about 1 month after the operation, unilateral vestibular organ-ablated S. nigriventris shows stable upside-down swimming posture under the condition (vestibular compensation). In contrast, a closely related upside-up swimming catfish Synodontis multipunctatus belonging to same Synodontis family can not keep stable swimming postures under the clinorotation conditions. In this study, we examined the effect of continuous clinorotation on vestibular compensation in intact and unilateral vestibular organ-ablated Synodontis nigriventris and Synodontis multipunctatus. After the exposure to continuous clinorotation, the postures of the catfish were observed under microgravity provided by parabolic flights of an aircraft. Unilateral vestibular organ-ablated S. nigriventris which had been exposed to continuous clinorotation showed stable swimming postures and did not show dorsal light reaction (DLR) under microgravity. This postural control pattern of the operated catfish was similar to that of intact catfish. Intact and unilateral vestibular organ-ablated S. multipunctatus showed DLR during microgravity. Our results confirmed that S. nigriventris has a novel balance sensation which is not affected by microgravity. DLR seems not to play an important role in postural control. It remains unclear that the continuous clinorotation effects on vestibular compensation because we could not keep used unilateral vestibular organ-ablated fish alive under continuous clinorotation for uninterrupted 25 days. This study suggests that space flight experiments are required to explore whether gravity information is essential for vestibular compensation.     

Comparative study of otolith organs between two species of upside-down swimming catfish Synodontis nigriventris showing converse swimming postures

To clarify whether the unique postural control of the upside‐down swimming catfish (Synodontis nigriventris, family Mochokidae) is related to the histological characteristics of the otolith organs, we performed light microscopic observation of the utricle, the saccule and the lagena. The histological aspects of the otolith organs were compared between S. nigriventris and Synodontis multipunctatus, which belong to the same genus. S. multipunctatus usually shows upside‐up swimming posture except for feeding behaviour near water surface. As controls, we additionally used a miniature catfish, Corydoras paleatus and goldfish, Carassius auratus, which shows upside‐up swimming posture. We concluded that the structural aspects of the otolith organs did not cause the unique postural control of S. nigriventris. Light microscopic observation clarified the following aspects: (1) The utricle of S. nigriventris was located at the anterior region of the otocyst and under the semicircular canals, and the saccule and the lagena were located at the posteroventral region of the otocyst like those of S. multipunctatus and the other two fishes. (2) The hair cells of the utricle were arranged on the horizontal plane of the fishes with a variation in cell size at the ventral and ventrolateral sites in S. nigriventris, S. multipunctatus and the other two fishes. (3) The hair cells of the saccule and lagena of S. nigriventris, S. multipunctatus and C. auratus presented perpendicular to the horizontal plane of the fish. (4) Region‐specific differences in the size and shape of the hair cells of S. nigriventris were observed along the three‐dimensional axes of the otolith organs like those of S. multipunctatus and the other two fishes. It is unlikely that the unique postural control of upside‐down catfish is related to the localization of the utricle, the saccule and the lagena and the distribution of the different types of hair cell of the otolith organs. Furthermore, the distribution of the hair cells suggests that the otolith organs in S. nigriventris can detect three‐dimensional postural changes like the organs of other fishes showing generally observed upside‐up swimming posture.     

Unique postural control of upside-down swimming catfish,Synodontis nigriventris,not affected by the change of gravity

In general, most fishes maintain a swimming posture with the dorsal side towards the water surface under normal gravity condition. In contrast to normal fishes, a catfish Synodontis nigriventris, shows a unique postural control. The catfish keeps its posture with the ventral side towards the water surface and the dorsal side towards water bottom under normal gravity. This evidence leads one to assume that the upside-down posture of the catfish is controlled by gravity sensation in a manner different from that of other fishes. However, it has remained unclear to date whether the gravity sensation contributes to the unique postural control of this catfish. We examined its postural control in intact and labyrinth-removed catfish using a clinostat which generates a specific gravity environment (pseudo-microgravity) on earth. In addition, we examined its postural control under microgravity during parabolic flights.     

Relationship between frequency of upside-down posture and space size around upside-down catfish, Synodontis nigriventris.

The catfish Synodontis nigriventris shows a unique habit taking a stable upside-down posture in free water regardless of an above, one-sided illumination. This upside-down posture can be observed when the catfish is apart from objects because the catfish usually orients its ventral side towards the water bottom or objects due to a so-called ventral substrate response. Thus, it is not easy to study the mechanism of the upside-down posture. To resolve this problem, the frequency of the upside-down posture was measured by using various sizes of vessel in which the catfish was kept. Video analysis showed that the frequency of the upside-down posture depended on the space size around the catfish. The smaller the size became, the higher the frequency of the upside-down posture became. Furthermore, the frequency of the upside-down posture depended on the shape of the vessel bottom. Curved-bottom vessels induced the upside-down posture more frequently than flat bottom. These findings suggest that a small, curved-bottom vessel is ideal for researching the upside-down postural control mechanism.     

Structure and Innervation of the Inner Ear Sensory Organs in an Otophysine Fish,the Upside–down Catfish (Synodontis nigriventrisDavid)

All the sensory epithelia of the inner ear in the upside–down catfish (Synodontis nigriventrisDavid) were examined by light microscopy. The morphology of the membranous labyrinth and the orientation of the hair cells is similar to what has been found in other otophysine fishes. The sensory cells are of variable size both inter– and intraepithelially; particularly the macula sacculi is equipped with heterogeneous receptors. Regional differences in the hair cell density are presented for all the otolith organs plus the papilla neglecta. Nerve stainings reveal regional differentiation. The central areas are innervated by stout and stubbly nerve endings intermingled with a few thin nerve fibres while the peripheral parts are reached exclusively by thin axons. In the anterior region of the macula sacculi are found unique cup–shaped axon terminations which surround the basal parts of a single or a few sensory cells. The number and diameter range of the myelinated nerve fibres as well as the hair cell/axon ratio are presented. Electron microscopy demonstrates the presence of unmyelinated axons in all inner ear nerve ramuli.     

Postural control mechanisms in the upside-down catfish (Synodontis nigriventris)

The catfishSynodontis nigriventris normally swims upside-down but can assume any posture in response to a substrate it swims close to. Postural reflexes of the body and the eyes, labyrinthine anatomy and passively maintained posture were investigated to obtain indications for possible mechanisms controlling the peculiar postural behavior of this fish. Saccade-like resetting movements of the eyes during counter-roll to body tilt about the longitudinal axis, and maintained tilted swimming positions in blinded fish suggest that these animals reset their vestibular CNS circuits to zero when in tilted positions.Synodontis nigriventris is thus able to maintain any posture without interference from tilt-counteracting vestibular reflexes. The normal upside-down swimming apparently results from a central bias for this position and a supporting ventral light response.We conclude that if the reafference principle applies to the phenomena investigated, the efference copy may be fed through an integrator before reaching vestibular reflex circuits.     

Electric Discharges in African Upside-Down Catfishes Synodontis (Mochokidae,Siluriformes): Peculiarities and Mechanisms of Electrogeneration

Journal of Ichthyology - The patterns of electric discharges were studied in two species of upside-down catfishes, Synodontis clarias and S. membranaceus. In S. clarias, constant generation of weak...     

Retinofugal and retinopetal connections in the upside-down catfish (Synodontis nigriventris)

Summary The retinofugal and retinopetal connections in the upside-down catfish Synodontis nigriventris were studied by use of the horseradish-peroxidase (HRP) techniques, autoradiography, and degeneration-silver methods. An unusual retinal projection to the torus semicircularis as well as projections to the retina from three different sources in the brain are described. After intra-ocular injections of HRP, labeled cells were found in the optic tectum, the dorsomedial optic nucleus and one of the pretectal nuclei. These new findings support the basic hypothesis (i) that neuronal connections are more extensive in primitive brains, and (ii) that the evolutionary development of more complex brains involves the loss of some selected connections.     

Haematology and habits in catfish of the genus Synodontis

African catfish of the genus Synodontis vary in their habits, from inverted plankton eaters to normally oriented benthos eaters. Haemoglobin concentrations and red cell counts vary between populations of one species, and between species of differing habits. Synodontis schall from the well-aerated White Nile had lower haemoglobin concentrations than members of the same species from Lake Kainji, Nigeria. Synodontis membranaceus , an inverted plankton eater, had lower haemoglobin concentrations than the bottom dwelling S. filamentosus and S. nigrita. Species with intermediate habits, such as S. batensoda and S. ocellifer had intermediate concentrations of haemoglobin.
It is suggested that these differences in haemoglobin concentration are a result of differing habits. Those species that enter poorly aerated water are stimulated to make more haemoglobin.     

Hair Cell Polarization in the Flatfish Inner Ear

The hair cell polarization of the various sensory epithelia in the inner ear was examined in two species of flatfish, the Plaice (Pleuronectes platessa) and the Dab (Limanda limanda). The hair cells in the macula utriculi are polarized in the pattern usually seen for this macula in vertebrates. In the macula sacculi and macula lagenae the hair cell polarization is different from that hitherto described from bony fishes and other vertebrates. The polarization seen in these maculae in the flatfish explains their ability to sense movements in all directions, which is necessary if these sensory areas are the most important inner ear organs in the regulation of postural orientation.     

Sensory surface of the saccule and lagena in the ears of ostariophysan fishes

The inner ears of a few fishes in the teleost superorder Ostariophysi are structurally unlike those of most other teleosts. Scanning electron microscopy was used to determine if other ostariophysans share these unusual features. Examined were the families Cyprinidae, Characidae, and Gymnotidae (all of the series Otophysi), and Chanidae (of the sister series Anotophysi), representing the four major ostariophysan lineages, the auditory organs of which have not yet been well described. Among the Otophysi, the saccular and lagenar otolith organs are similar to those reported for other ostariophysans. The lagena is generally the larger of the two organs. The saccular sensory epithelium (macula) contains long ciliary bundles on the sensory hair cells in the caudal region, and short bundles in the rostral region. The saccule and the lagena each have hair cells organized into two groups having opposing directional orientations. In contrast, Chanos, the anotophysan, has a saccular otolith larger than the lagenar otolith, and ciliary bundles that are more uniform in size over most of its saccular macula. Most strikingly, its saccular macula has hair cells organized into groups oriented in four directions instead of two, in a pattern very similar to that in many nonostariophysan teleosts. We suggest that the bi-directional pattern seen consistently in the Otophysi is a derived development related to particular auditory capabilities of these species.     

Correlation between body color and behavior in the upside-down catfish,Synodontis nigriventris

• 1.1. Unlike common fishes and as its Latin name implies, the upside-down catfish, Synodontis nigriventris, possesses dark ventral skin. Microscopic observation reveals that melanophores are present on both the ventral and the dorsal skin but differ in size and density of distribution.
• 2.2. The darkness of both sides of the fish changes in accordance with that of the background.
• 3.3. At night, the fish are very active and the body becomes pale. The change in color is more noticeable in the dorsal than the ventral skin.
• 4.4. When melatonin was added to the bathing water, the fish became pale and swam restlessly even when they were exposed to the black background.
• 5.5. It was found that the catfish preferred the black background to the white one.

     

Organization of the superficial neuromast system in goldfish, Carassius auratus

Distribution, morphology, and orientation of superficial neuromasts and polarization of the hair cells within superficial neuromasts of the goldfish (Carassius auratus) were examined using fluorescence labeling and scanning electron microscopy. On each body side, goldfish have 1,800-2,000 superficial neuromasts distributed across the head, trunk and tail fin. Each superficial neuromast had about 14-32 hair cells that were arranged in the sensory epithelium with the axis of best sensitivity aligned perpendicular to the long axis of the neuromast. Hair cell polarization was rostro-caudal in most superficial neuromasts on trunk scales (with the exception of those on the lateral line scales), or on the tail fin. On lateral line scales, the most frequent hair cell polarization was dorso-ventral in 45% and rostro-caudal in 20% of the superficial neuromasts. On individual trunk scales, superficial neuromasts were organized in rows which in most scales showed similar orientations with angle deviations smaller than 45 degrees . In about 16% of all trunk scales, groups of superficial neuromasts in the dorsal and ventral half of the scale were oriented orthogonal to each other. On the head, most superficial neuromasts were arranged in rows or groups of similar orientation with angle deviations smaller than 45 degrees . Neighboring groups of superficial neuromasts could differ with respect to their orientation. The most frequent hair cell polarization was dorso-ventral in front of the eyes and on the ventral mandible and rostro-caudal below the eye and on the operculum.     

Characteristic Features of Disorders of the Upright Posture in Patients with Poststroke Hemipareses

Characteristic features of upright posture maintenance and mechanisms of postural disorders in poststroke hemiparetic patients were studied using a bilateral force platform. The following features of postural disorders were revealed in the patients tested: an increase in the velocity and amplitude of the center-of-pressure (CP) sway as compared to in healthy subjects, an absolute decrease in the half-cycles of the CP sway, asymmetry of weight bearing by both feet, and a shift of the center of pressure of an affected foot towards the toe. The disturbance of stability of the vertical posture in such patients is to a greater extent associated with weight-bearing asymmetry. It was shown that the character of the CP sway is mainly determined by a disorder of the sensory motor control, whereas damage to the efferent pathways is responsible for the postural asymmetry. Increase in the muscle tone restricts the sway amplitude. Thus, several forms of postural instability are characteristic of hemiparetic patients. Predominantly sensory, motor, or tonic disorders are responsible for these disturbances of stability.     

A balance of form and function: Planar polarity and development of the vestibular maculae

The mechanosensory hair cells of the inner ear have emerged as one of the primary models for studying the development of planar polarity in vertebrates. Planar polarity is the polarized organization of cells or cellular structures in the plane of an epithelium. For hair cells, planar polarity is manifest at the subcellular level in the polarized organization of the stereociliary bundle and at the cellular level in the coordinated orientation of stereociliary bundles between adjacent cells. This latter organization is commonly called Planar Cell Polarity and has been described in the greatest detail for auditory hair cells of the cochlea. A third level of planar polarity, referred to as tissue polarity, occurs in the utricular and saccular maculae; two inner ear sensory organs that use hair cells to detect linear acceleration and gravity. In the utricle and saccule hair cells are divided between two groups that have opposite stereociliary bundle polarities and, as a result, are able to detect movements in opposite directions. Thus vestibular hair cells are a unique model system for studying planar polarity because polarization develops at three different anatomical scales in the same sensory organ. Moreover the system has the potential to be used to dissect functional interactions between molecules regulating planar polarity at each of the three levels. Here the significance of planar polarity on vestibular system function will be discussed, and the molecular mechanisms associated with development of planar polarity at each anatomical level will be reviewed. Additional aspects of planar polarity that are unique to the vestibular maculae will also be introduced.     

Brood parasitism of an open-water spawning cichlid by the cuckoo catfish

The cuckoo catfish Synodontis multipunctatus and S. grandiops are endemic to Lake Tanganyika and the only known nonavian vertebrates that exhibit obligate interspecific brood parasitism. Seven maternal mouth-brooding cichlid fish species are reported to be natural hosts of the parasitic catfish and share a common reproductive behaviour that the catfish exploits: cichlid females spawn eggs on the bottom, allowing the catfish female to place her eggs near the cichlid eggs, and the cichlid females collect the catfish eggs by mouth together with their own eggs. However, so far it has not been reported that the cuckoo catfish exploit different spawning behaviours. The genus Cyprichromis consists of five maternal mouth-brooding species endemic to Lake Tanganyika, most of which spawn and collect eggs in open water. This study reports that the cuckoo catfish also parasitizes the open-water spawning Cyprichromis coloratus, although it may not be a regular host.     

Modern view of cortical control of posture and brain asymmetry: a literature review

Review concerns cortical mechanisms of postural control. Data on different role of the right and the left cerebral hemispheres in postural control are analyzed. These data are compared with the data on lateralization of perception and action. Peculiarities of sensory perception and motor control in the right and the left hemispheres are supposed to be connected with the specialization of the left hemisphere on the dynamic tasks and of the right hemisphere on the static tasks which include orthograde posture control in human beings.