Structure and function of the locomotory system ofPolyorchis montereyensis (Cnidaria,Hydrozoa)

Summary 1. The structure and function of the locomotory system of the anthomedusanPolyorchis montereyensis Skogsberg were studied in detail. Anatomical investigations were carried out primarily on fresh or formalin fixed specimens; histology was done on specimens fixed in Bouin's fluid. Functional analyses were based largely on photography and cinematography.2. Swimming inP. montereyensis involves the alternating antagonistic action of the subumbrellar swimming muscles and the elastic mesoglea.3. The swimming muscle consists of striated contractile elements arranged circularly in four discontinuous subumbrellar sheets and a sheet on the subumbrellar side of the velum. There is also a sheet of radially arranged fibers on the exumbrellar side of the velum. The four subumbrellar sheets are anchored to the bell along the perand interradii.4. The mesogleal skeleton consists of five components: (a) the matrix of the bell mesoglea, (b) optically visible fibers that traverse the bell from gastrodermal lamella to exumbrella, (c) the basement membrane or supporting lamella, (d) a system of joints, and (e) the velar mesoglea.5. The morphology, orientation, and distribution of the mesogleal fibers suggest that their major role is maintaining the radial integrity of the bell during deformation. The amount of stretch in a region of the bell wall during contraction is inversely proportional to the number of fibers per unit area there. In regions of the bell which are not deformed during contraction fibers are sparse or absent.6. Mesogleal volume remains constant during swimming. Locally the mesoglea is subjected to forces of stretch and compression, but the critical element in narrowing the bell involves bending or folding the mesoglea around a series of structural joints. The fulcrum of these joints is anchored to the exumbrella by concentrations of mesogleal fibers. The joints consist of eight adradial regions of highly deformable mesoglea lacking visible fibers. The regions are triangular in cross section and are separated from the remainder of the mesoglea (98–99 % of the total) by the gastrodermal lamella. A circular apical joint is also present.7. Sequential changes in shape and position of the bell relative to a fixed grid during contraction and recovery were measured in order to determine such parameters of swimming as rate of contraction, rate of expulsion of water, change in bell velocity during contraction and recovery, momentum, etc.8. The function of the velum was determined by cinematographic analysis of swimming animals both before and after removal of the velum. In normal swimming the velum serves mainly to constrict the aperture of the bell, thus increasing the velocity of expelled water, and hence increasing the force driving the medusa foward. Medusae swam with a greatly decreased velocity after velum removal.9. Turning is accomplished primarily by asymmetrical contraction of the exumbrellar velar radial muscles, whereby the velar aperture is displaced to one side, water is expelled obliquely, and the bell turns toward that same side. The ability to turn was lost after velum removal.10. Studies of the relationship between individual size and the various parameters of swimming inP. montereyensis show that: (a) the duration of the contraction phase of the swimming beat is roughly proportional to the square root of the subumbrellar circumference (or bell height); (b) smaller individuals swim faster relative to their bell height than do larger ones; (c) the velum is relatively better developed in small animals and plays a proportionately more important role during swimming.

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Struktur und Funktion des lokomotorischen Systems vonPolyorchis montereyensis (Cnidaria, Hydrozoa)

Kurzfassung Mit Hilfe histologischer und kinematographischer Methoden wurden Bau und Funktion des lokomotorischen Systems der AnthomedusePolyorchis montereyensis Skogsberg analysiert. Die Schwimmbewegungen resultieren aus der antagonistischen Wirkung der Muskulatur der Subumbrella und der elastischen Mesogloea. Struktur, Anordnung, Verteilung und Verankerung der Muskelzellen werden beschrieben. Die Körperschicht der Mesogloea besteht aus 5 Komponenten mit Skelettfunktion: der Matrix der Schirmmesogloea, einem System von Muskelfasern, der Stützlamelle, acht adradialen Verbindungssträngen von stark deformierbarer, fibrillenloser Mesogloea und der Mesogloea des Velums. Die Fribrillen und Verbindungsstränge der Mesogloea bewirken, daß die Schirmglocke während der Kontraktion deformiert werden kann. Die Funktion des Velums sowie die kontinuierlichen Veränderungen der Glocke in bezug auf Form und Lage während des Schwimmvorgangs, insbesondere die Geschwindigkeit der Kontraktion, des Wasserausstoßes und der Fortbewegung bei Individuen verschiedener Größe, wurden eingehend untersucht. Kleinere Medusen schwimmen relativ schneller als größere, was hauptsächlich auf stärkere Kontraktionen des Velums zurückzuführen ist.

     

Swimming medusoid gonophores in two species of Sertularella (Cnidaria,Hydrozoa, Sertulariidae) from Réunion Island,Indian Ocean

Summary

Two life cycle patterns predominate in thecate hydroids, those with alternating polyp and medusa stages, and those with fixed gonophores. Relatively few species release short-lived medusoids, also called swimming gonophores, that carry the gametes. In the family Sertulariidae, with its large number of taxa, this mode of metagenesis has been documented previously for only two species. It is described here for two others, Sertularella diaphana (Allman, 1885) and Sertularella n. sp., from the coastal waters of Reunion Island. Freshly collected fertile male and female colonies released medusoids near dawn, one per gonotheca. Strong contractions of the bell in the swimming movements induced the shedding of gametes. Once gametes were shed, medusoids quickly degenerated and died. The medusoids were similar morphologically in these two related species, and no obvious sexual dimorphism was noted. They were ovoid in shape, the spadix was eccentric, and a velum was present; but they lacked a mouth, tentacles, sense organs, and radial and circular canals as described earlier in Amphisbetia operculata (Linneus, 1758) and Sertularia marginata Kirchenpauer, 1864. However, the medusoids described here lacked exumbrellar nematocysts. Moreover, the spadix with its dense mass of gametes was different from all other described in being stuck from base to top on one side of the subumbrella in spite of hanging freely in the subumbrellar cavity. The hypothesis that this unusual reproductive mode in sertulariids has been underestimated is confirmed by these findings.     

The fibrous system in the extracellular matrix of hydromedusae

The ultrastructure and the histochemistry of the fibrous system in the mesogloeal extracellular matrix (ECM) of two hydromedusae (Polyorchis penicillatus and Aglanlha digitale) has been examined. There is a fundamental difference in the architecture of the fibrous system between the two species. In Polyorchis, 60-150 A thick, striated fibrils with periodicities of 60-65 A form a three-dimensional network which fills in the entire ECM of outer and inner mesogloea. In the outer mesogloea vertical fibres (up to 1.8 mum in diameter) penetrate the threedimensional network and branch near the exumbrellar and subumbrellar side. These branches impinge on a dense matrix covering the exumbrellar and subumbrellar surface. In Aglantha the branches of thick vertical fibres anchor at the subumbrellar side in a dense plexus (0.2-0.3 mum in thickness) which consists of two types of fibrils (35-40 and 80-100 nm in diameter). Towards the exumbrellar side the vertical fibres branch and intermingle with a meshwork of non-striated fibrils with uniform diameter (35-40 nm). These fibrils form a laminated structure (about 1 mum in thickness) so that fibrils of each layer course in the same direction but fibrils of adjacent layers run perpendicularly to each other. The banded pattern with periodicities of 600-640 A observed in the electron microscope and by histochemical methods confirm the thick vertical fibres and their branches to be a collagen. There is also strong evidence that the laminated structure in Aglantha represents layers of collagen fibrils.     

Cyanea capillata Bell Kinematics Analysis through Corrected In Situ Imaging and Modeling Using Strategic Discretization Techniques

Obtaining accurate kinematic data of animals is essential for many biological studies and bio-inspired engineering. Many animals, however, are either too large or too delicate to transport to controlled environments where accurate kinematic data can be easily obtained. Often, in situ recordings are the only means available but are often subject to multi-axis motion and relative magnification changes with time leading to large discrepancies in the animal kinematics. Techniques to compensate for these artifacts were applied to a large jellyfish, Cyanea capillata, freely swimming in ocean waters. The bell kinematics were captured by digitizing exumbrella profiles for two full swimming cycles. Magnification was accounted for by tracking a reference point on the ocean floor and by observing the C. capillata exumbrella arclength in order to have a constant scale through the swimming cycles. A linear fit of the top bell section was used to find the body angle with respect to the camera coordinate system. Bell margin trajectories over two swimming cycles confirmed the accuracy of the correction techniques. The corrected profiles were filtered and interpolated to provide a set of time-dependent points along the bell. Discrete models of the exumbrella were used to analyze the bell kinematics. Exumbrella discretization was conducted using three different methods. Fourier series were fitted to the discretized models and subsequently used to analyze the bell kinematics of the C. capillata. The analysis showed that the bell did not deform uniformly over time with different segments lagging behind each other. Looping of the bell trajectory between contraction and relaxation was also present through most of the exumbrella. The bell margin had the largest looping with an outer path during contraction and inner path during relaxation. The subumbrella volume was approximated based on the exumbrella kinematics and was found to increase during contraction.     

The fibrous system of the extracellular matrix of Podocoryne carnea and its degradation by the subumbrellar plate endoderm demonstrated by a monoclonal antibody

Homogenized fragments of crude umbrellar material of the hydromedusa Podocoryne carnea was injected into BALB/c mice. The immunization resulted in the isolation of a monoclonal antibody designated 3A1 which specifically binds to fibrils in the mesogloeal extracellular matrix (ECM) of hydromedusae. In vivo, the architecture and the ultrastructure of the fibrous system in the outer mesogloea (outer ECM) of Podocoryne carnea, and its degradation under in vitro conditions have been described by morphological and immunological criteria. In vivo, 120-150 A thick, striated fibrils (with periodicities up to 50 nm) form a threedimensional network which fills in the entire outer ECM. Vertical fibers (up to 150 nm in diameter) penetrate the three-dimensional network and branch at the subumbrellar and the exumbrellar side. The vertical fibers show uniform distribution over the entire outer ECM. The branches impinge on a dense matrix (about 30 nm in thickness) covering the exumbrellar and subumbrellar surface. In vitro, the fibrillar system does not alter in its basic pattern, neither in isolated outer ECM, nor in portions of outer ECM which is either covered by the exumbrella, or which is attached to both: the exumbrella at the outside, and the subumbrellar plate endoderm at the inner side. After removal of the exumbrellar cells in the latter portions, a characteristic pattern of selective degradation of the outer ECM by the endodermal cells is observed. This process involves three distinct steps: an initial extracellular condensation within the ECM fibrillar network, followed by intercellular internalization of the fibrillar elements and subsequent endocytosis of ECM material. The first step immediately follows the removeal procedure of the exumbrellar cells and is completed within minutes. This process cannot be interrupted by dihydrocytochalasin B (H(2)CB). The second step lasts 24-48 hr, is mediated by cell mechanisms, and can be stopped by H(2)CB. The third step is a slow process (of up to 14 days). It involves intercellular degradation of fibrillar material, endocytosis, and completion of digestion within lysosomes.     

Organization of the subumbrellar musculature in the ephyra,juvenile, and adult stages of Aurelia aurita Medusae

We used fluorescently labeled phalloidin to examine the subumbrellar musculature of the scyphozoan jellyfish Aurelia aurita in a developmental series from ephyra to adult medusa. In the ephyra, the swim musculature includes a disc‐like sheet of circular muscle, in addition to two radial bands of muscle in each of the eight ephyral arms. The radial muscle bands join with the circular muscle, and both circular and radial muscle act together during each swim contraction. As the ephyra grows into a juvenile medusa, arms tissue is resorbed as the bell tissue grows outward, so eventually, the ephyral arms disappear. During this process, the circular muscle disc also grows outward and the radial muscle bands of the arms also disappear. At this time, a marginal gap appears at the bell margin, which is devoid of circular muscle cells, but has a loose arrangement of radial muscle fibers. This marginal gap is preserved as the medusa grows, and contributes to the floppy nature of the bell margin. Radial distortions in the circular muscle layer involve muscle fibers that run in random directions, with a primarily radial orientation. These are believed to be remnants of the radial muscle of the ephyral arms, and the distortions decrease in number and extent as the medusa grows. Since the mechanics of swimming changes from drag‐based paddling in the ephyra to marginal rowing in the adult medusa, the development of the marginal gap and the presence of radial distortions should be considered in terms of this mechanical transition.     

Acoustic survey of a jellyfish-dominated ecosystem (Mljet Island,Croatia)

Acoustic techniques have been proposed as a new tool to assess jellyfish populations. However, the presence of mixed echoes from jellyfish and other organisms that share their distribution often prevent accurate estimates of their abundance and distribution being obtained. The isolated population of Aurelia inhabiting the Veliko Jezero (Big Lake-BL) of Mljet Island, in the South Adriatic Sea, offered a good opportunity to employ acoustic techniques to assess an entire jellyfish population. During October 2–5, 2006, combined video and acoustic methods were used in BL to determine the vertical distribution of medusae. Two synoptic acoustic surveys were performed during the day and night. In the daylight echograms, medusae were clearly discernible from the acoustic data, and their presence verified by video camera images, as forming a layer of varying density at and below the thermocline (15–30 m). The depth of the jellyfish layer also coincided with the depth of maximum dissolved oxygen concentration. The echointegration of these daylight data enabled quantification the Aurelia population, at a frequency of 120 kHz. In the night echograms, the acoustic signals of Aurelia were at least partially masked by pelagic and demersal fish, which disaggregated from schools and formed a layer associated with a strong thermocline at 15 m. An average target strength (TS) of −76.4 dB was obtained in situ corresponding to a mean length of 10.8 cm and a mean wet weight of 134 g measured from sampled medusae. These results were combined with echo-integration values to provide an estimate of 4,238,602 individuals and a biomass of 568 tons of Aurelia in BL. This study provided a synoptic view of Mljet Lake and illustrated the potential of acoustic surveys of jellyfish populations to contribute to ecosystems studies. Guest editors: K. A. Pitt & J. E. Purcell Jellyfish Blooms: Causes, Consequences, and Recent Advances     

Three dimensional registration of mechanical bladder activity using polystyrene fluorescent spheres: A technical note

Optical marker tracing methods have been applied successfully in recent years to quantify local material deformation of heart tissue, skin and striated muscles. In this study, polystyrene fluorescent spheres (d = 0.6 mm) are glued to the ventral serosal bladder wall in the rabbit. Three dimensional video registration of the polystyrene spheres is used to calculate two directions of principal strain (epsilon (1), epsilon (2) ) on the bladder surface in vivo. The aim is to investigate the feasibility of the technique for this new application in two experimental circumstances: during spontaneous bladder wall activity and after electrical stimulation of bladder innervating nerve fibers. During spontaneous activity, random contraction and relaxation occurred simultaneously and separately across the bladder wall for the two principal strains epsilon (1) and epsilon (2). After extradural electrical stimulation of sacral nerve root S2, the principal strains epsilon ( 1) and epsilon (2) synchronized in time in such a way that epsilon ( 1) and epsilon (2) both represented contraction or both represented relaxation. One and the same bladder wall area passed through phases of contraction followed by relaxation and vice versa. After multiple stimulation periods, the coordination between the two principal strains during stimulation was reduced. This technique allows to identify local areas of contraction and relaxation in the intact bladder wall in vivo. Three dimensional video registration of polystyrene fluorescent spheres to study bladder wall contraction and its relaxation proved to be a feasible technique, with which electrical stimulation effects and spontaneous activity could be measured.     

腔肠动物平衡感觉器官结构的研究进展

本文概述了腔肠动物的平衡感觉器官结构：刺胞动物掌状伞形螅（Corymorpha palma）固着器末端的无纤毛平衡囊、软水母（Leptomedusae）钟形伞缘的开放型和封闭型平衡囊、筐水母（Narcomedusae）外伞表面外伞神经环上方边缘有感觉棍的间囊水母（Aegina）和有感觉乳突及感觉棍的嗜阳水母（Solmissus）的平衡囊、硬水母（Trachymedusae）外伞神经环上方边缘的平衡囊、钵水母（Scyphozoa）伞缘的感觉棍和立方水母（Cubozoa）伞缘稍上方的感觉棍,栉水母（Ctenophore）反口面中央的平衡囊或顶器官。本文内容对理解其他水生无脊椎动物的平衡感觉器官的结构及功能有重要意义,同时也可能作为对现行动物学相关教材内容的有益补充。     

Contrast and rate of light intensity decrease control directional swimming in the box jellyfish Tripedalia cystophora (Cnidaria, Cubomedusae)

Box jellyfish respond to visual stimuli by changing the dynamics and frequency of bell contractions. In this study, we determined how the contrast and the dimming time of a simple visual stimulus affected bell contraction dynamics in the box jellyfish Tripedalia cystophora. Animals were tethered in an experimental chamber where the vertical walls formed the light stimuli. Two neighbouring walls were darkened and the contraction of the bell was monitored by high-speed video. We found that (1) bell contraction frequency increased with increasing contrast and decreasing dimming time. Furthermore, (2) when increasing the contrast and decreasing the dimming time pulses with an off-centred opening had a better defined direction and (3) the number of centred pulses decreased. Only weak effects were found on the relative diameter of the contracted bell and no correlation was found for the duration of bell contraction. Our observations show that visual stimuli modulate swim speed in T. cystophora by changing the swim pulse frequency. Furthermore, the direction of swimming is better defined when the animal perceives a high-contrast, or fast dimming, stimulus.     

The behavior of the plasma membrane following osmotic contraction of isolated protoplasts: Implications in freezing injury

Summary Following osmotic contraction of isolated rye protoplast (Secale cereale L. cv. Puma) that results in nearly a 50% reduction in volume, the plasma membrane was smooth, with no folding or pleating. Instead, deletion of plasma membrane occurred and numerous cytoplasmic vesicles were observed. As a result, the area of the plasma membrane was reduced by approximately 40%. Thin sections revealed that the cytoplasmic vesicles were membrane bound and not merely voids in the cytoplasm. High resolution video microscopy revealed the extent of vesiculation showing large clusters of cytoplasmic vesicles following osmotic contraction. Labeling the plasma membrane with fluorescein-Con-A prior to hypertonic contraction suggested that the cytoplasmic vesicles were derived from the plasma membrane. Freeze-fracture particle density on both the protoplasmic (PFp) and exoplasmic face (EFp) of the plasma membrane remained unchanged following contraction, which is consistent with a unit-membrane deletion into cytoplasmic vesicles. Upon partial re-expansion of the protoplasts, thin sections showed that the vesicles remained in the cytoplasm. These results using osmotic manipulation confirm earlier observations of isolated protoplasts at the light microscope level. Upon contraction plasma membrane is deleted into cytoplasmic vesicles, which are not readily reincorporated into the plasma membrane upon expansion. Lysis occurs before the original volume and surface area are regained.Department of Agronomy Series Paper no. 1456.     

Biomass and size structure of the scyphomedusa Aurelia aurita in the northwestern Black Sea during spring and summer

The abundance, biomass and size structure of the scyphomedusa,Aurelia aurita, was measured during two research cruises tothe northwestern Black Sea (July–August 1995 and April–May1997). Average biomass of Aurelia was relatively constant (132–179g wwt m^–2) throughout the investigation period and similarto previous years. Abundance and biomass at individual stationsappeared to be unrelated to temperature and salinity when thelatter exceeded ~13. Biomass was low at coastal stations inthe plume of the Danube where depth was <20 m and salinitydropped to <11. The spring cruise (April–May) coincidedwith, or just followed the peak of strobilation. The summercruise (July–August) took place near the beginning ofplanulae larvae release. The population size structure was dominatedby small individuals in spring, while large medusae prevailedmainly in late summer. Aurelia was, on average, larger at deepwater stations during summer, suggesting that per capita foodsupply was higher further offshore. The individual body massincreased from spring through summer. Accordingly, the volume(wet wt) to length (bell diameter) relation changed significantly.If all medusae measured throughout the seasons were pooled,volume (V, in cm³) was related to length (L, in cm) accordingto V = 0.08 L^2.71, which is similar to measurements conductedin other coastal areas. In contrast to the common conjecture,we did not find inverse relations between biomasses of Aureliaand the combjelly Mnemiopsis leidyi. Preliminary feeding experimentsindicate that Aurelia may feed upon small Mnemiopsis. The significanceof indirect trophic relations and direct feeding interactionsamong the gelatinous zooplankton in the Black Sea has importantconsequences for the energy flow along the food web and, therefore,needs further study.     

Functional anatomy of pulmonary ventilation in the garter snake, Thamnophis elegans

The functional anatomy of pulmonary ventilation in Thamnophis elegans was studied by electromyography. Flow of air into and out of the lungs follows a triphasic pattern and occurs while the glottis is held open by a dilator muscle. Non-ventilatory rest periods characterized by a closed glottis and lack of ventilatory movements occur between breaths. Exhalation is caused by contraction of a pair of dorsolateral sheets of muscle that extends from the ventral surface of the vertebral column to the medial surfaces of the ribs and a pair of ventro-lateral sheets that extends from the medial surfaces of the ribs to the mid-ventral skin. Inspiration is powered by contraction of a series of rib levators and retractors. The last phase of the ventilatory cycle is a passive expiration that may be caused by elastic recoil of the walls of the filled lungs and relaxation of muscles used during inspiration. The site of respiratory pumping is shifted craniad after large prey items have been completely ingested. The significance of this shift and its anatomical basis are considered.     

Dynamics of the ectoplasmic walls during pulsation of plasmodial veins ofPhysarum polycephalum

Summary The thickness of ectoplasmic walls decreases at the contraction phase and increases at the expansion phase of each pulsation cycle. In average, 29% of material forming the walls of expanded veins is evacuated during contraction with the endoplasm streaming.     

Volume quantification of chest wall motion in dogs

We employed high-speed multisliced X-ray-computed tomography to determine the relative volume contributions of rib cage (delta Vrc) and diaphragmatic motion (delta Vdi) to tidal volume (VT) during spontaneous breathing in 6 anesthetized dogs lying supine. Mean values were 40 +/- 6% (SE) for delta Vrc and 62 +/- 8% of VT for delta Vdi. The difference between VT and changes in thoracic cavity volume was taken to represent a change in thoracic blood volume (2 +/- 3% of VT). To estimate how much of delta Vrc was caused by diaphragmatic contraction and how much of delta Vdi was caused by rib cage motion, delta Vrc and delta Vdi were determined during bilateral stimulation of the C5-C6 phrenic nerve roots in the apneic dog and again during spontaneous breathing after phrenicotomy. Thoracic cavity volume (Vth) measured during hypocapnic apnea was consistently larger than Vth at end expiration, suggesting that relaxation of expiratory muscles contributed significantly to both delta Vrc and delta Vdi during spontaneous inspiration. Phrenic nerve stimulation did not contribute to delta Vrc, suggesting that diaphragmatic contraction had no net expanding action on the rib cage above the zone of apposition. Spontaneous breathing after phrenicotomy resulted in small and inconsistent diaphragmatic displacement (8 +/- 4% of VT). We conclude that the diaphragm does not drive the rib cage to inflate the lungs and that rib cage motion does not significantly affect diaphragmatic position during spontaneous breathing in anesthetized dogs lying supine.     

Thermodynamic phase plane analysis of ventricular contraction and relaxation

Background  

Ventricular function has conventionally been characterized using indexes of systolic (contractile) or diastolic (relaxation/stiffness) function. Systolic indexes include maximum elastance or equivalently the end-systolic pressure volume relation and left ventricular ejection fraction. Diastolic indexes include the time constant of isovolumic relaxation - and the end-diastolic pressure-volume relation. Conceptualization of ventricular contraction/relaxation coupling presents a challenge when mechanical events of the cardiac cycle are depicted in conventional pressure, P, or volume, V, terms. Additional conceptual difficulty arises when ventricular/vascular coupling is considered using P, V variables.     

Propulsion in Cubomedusae: Mechanisms and Utility

Evolutionary constraints which limit the forces produced during bell contractions of medusae affect the overall medusan morphospace such that jet propulsion is limited to only small medusae. Cubomedusae, which often possess large prolate bells and are thought to swim via jet propulsion, appear to violate the theoretical constraints which determine the medusan morphospace. To examine propulsion by cubomedusae, we quantified size related changes in wake dynamics, bell shape, swimming and turning kinematics of two species of cubomedusae, Chironex fleckeri and Chiropsella bronzie. During growth, these cubomedusae transitioned from using jet propulsion at smaller sizes to a rowing-jetting hybrid mode of propulsion at larger sizes. Simple modifications in the flexibility and kinematics of their velarium appeared to be sufficient to alter their propulsive mode. Turning occurs during both bell contraction and expansion and is achieved by generating asymmetric vortex structures during both stages of the swimming cycle. Swimming characteristics were considered in conjunction with the unique foraging strategy used by cubomedusae.     

Contractile adaptations in the human triceps surae after isometric exercise

Ultrastructural and twitch contractile characteristics of the human triceps surae were determined in seven healthy but very sedentary subjects before and after 16 wk of unilateral isometric training at 100% maximal voluntary contraction. After training, twitch contraction time decreased by approximately 20%. One-half relaxation time, peak twitch torque, and percent fiber type in any of the muscles of the triceps surae complex were not changed by training. Type I and type II fiber areas increased in the soleus by approximately 30%, but only type II fibers showed an increased in area in the lateral gastrocnemius (40%). Despite such changes in fiber area, the volume density of the sarcoplasmic reticulum-transverse tubular (SR) network averaged 3.2 +/- 0.6 and 5.9 +/- 0.9% in type I and type II fibers, respectively, before and after training in the two heads of the gastrocnemius. Type I SR fraction increased to 3.5 +/- 1.2% after training in the soleus; however, correlations were not significant between the change in the volume density of SR and the change in twitch contraction time (R = 0.46, P = 0.45) or the change in one-half relaxation time (R = -0.68, P = 0.08). The results demonstrate that isometric training at 100% maximal voluntary contraction induced changes in twitch contraction time that were not directly related to changes in the volume density of SR in fibers of the triceps surae.     

Cytologische Veränderungen während der Metamorphose des CubopolypenTripedalia cystophora (Cubozoa,Carybdeidae) in die Meduse

The life cycle ofTripedalia cystophora includes a sessile saclike polyp — the asexual reproducing form — and a pelagic tetraradial medusa — the sexually reproducing generation. Medusan development can be induced by temperature increase. It reveals neither budding nor strobilation, but a real metamorphosis of a polyp to only one medusa. According to morphological and anatomical criteria the metamorphosis can be subdivided into four different stages: (1) four longitudinal furrows segment the polyp, the tentacles of which are apportionated on the four quadrants of the body. (2) The subumbrellar cavity develops by invagination of the peristom; the relicts of the fused tentacles change to four rhopalia buds. (3) Medusan architecture including four new interradial tentacles, four rhopalia and the subumbrellar swimming musculature is completed. (4) A young tetraradial medusa starts swimming. Ultrastructural analysis of those metamorphic stages show the different processes of morphogenesis: (a) Gastrodermal cells — absorptive and spumous cells — undergo transdifferentiation and proliferation to medusan cells of the same structure and function. (b) Epidermal cells, excluding the epithel muscle cells, dissociate and are autolytically withdrawn. Dedifferentiated epithel muscle cells — interstitial cells — regain the ability to develop a complete new set of somatic cells, not originally present in the polyp. They include amongst others cross-striated muscle cells, medusan typic nematocyts and particularly sensory and nervous cells. Those cells establish a nervous system with lens-eyes, simple ocelli, statocysts, diffuse nerve net and an additional nerve ring.