INHIBITION OF CONTRACTION RESPONSES OF HYDRA

The contraction reponse ot hydra to intermittent light stimulationmay be inhibited by exposing the animal to reduced glutathione(GSH). Such inhibitory acthity is dependent on: (1) the concentrationof GSH; (2) the pH of the medium; (3) previous exposure to GSH;and (4) the nutritional state of the animal. Hydra adapt tolO^–5 M GSH so that after approximately an hour the frequenciesof lightinduced contractions are restored to control levels.Such adaptation to GSH is due to changes occurring within theanimal rather than to the degradation of the glutathione molecule.S-methyl glutathione blocks contractions in response to light,showing that the sulfhydryl group is not essential for inhibition.Analogs with sterically large groups substituted for the sulfhydrylgroup, such as oxidized glutathione and S-acetyl glutathione,have no inhibitory activity. These compounds, however, reducethe inhibitory effect of GSH, indicating competition for theGSH receptor. Contractions of hydra in response to intermittent mechanicalagitation are also inhibited by GSH. The duration of inhibitionis dependent on the GSH concentration. Both oxidized glutathioneand S-acetyl glutathione reduce the inhibitory effect of GSH. Hydra adapted to the dark for 24 hours show a marked suppressionof contractions in response to mechanical agitation when exposedto light. On exposure to light, such animals elongate to approximatelyone and a half times their dark adapted length, and are relativelyinsensitive to agitation. The mechanisms by which such stimuliinhibit the contraction responses of hydra remain to be determined.     

GENETIC ANALYSIS OF DEVELOPMENTAL MECHANISMS IN HYDRA I. SEXUAL REPRODUCTION OF HYDRA MAGNIPAPILLATA AND ISOLATION OF MUTANTS

Hydra magnipapillata strains collected from various localities in Japan were induced to reproduce sexually.
From the survival data of the progeny, it was calculated that H. magnipapillata contained an average of between 3.5 and 4.0 lethal equivalent units of recessive deleterious genes per gamate (between 7.0 and 8.0 per animal).
Various types of developmental mutants were found among the offspring of crosses made between strains isolated from the same ponds. The mutant types isolated included mini strains, maxi strains, multi-headed strains, nematocyst-deficient strains, regeneration-deficient strains and male sterile strains. The characters of these strains were stably transmissible to the successive progeny produced by budding. These strains therefore were propagated by budding and maintained as clonal lines to be used later for developmental studies.     

FINE STRUCTURE OF THE NERVOUS SYSTEM OF HYDRA

Fine structural details of the cells and processes of the hydranenous system are reported in this paper. Ganglion cells aresmall bipolar or multipolar cells situated above the muscularprocesses of epitheliomusiular cells. An elaborate Colgi apparatusconsisting of parallel lamellae and small and large vesiclesis present in these cells. Some cells are poor in ribosomeswhile others contain numerous free ribosomes. In the ribosome-richcells, small membranous microtubules originating from the nuclearenvelope extend into the cytoplasm and neurites. The neuritesalso contain vesicles and mitochondria and terminate at thebases of cnidoblasts and on the muscular processes of epitheliomuscularcells. Specialized synapses were not observed. A second cell type contains many membrane-bounded dense granules,1000 A in diameter, and these are considered to be neurosecretorycells. Neurosecretory granules on cnidoblasts and epitheliomuscularcells. Sensory cells are small elongated cells originate inthe Golgi apparatus and are abundant in neurites which alsoterminate situated between the apical surfaces of epithelialand digestive cells. These cells are characterized by an apicalspecialization which appears to be a modified cilium. Neurosensorycells were also observed. The intimate connection of the nervoussystem with cnidoblasts suggests a role in nematocyst discharge.The finding of neurosecretory material supports the hypothesisthat the neural control of regeneration in hydra is regulatedby material released at nerve endings.     

大乳头水螅基盘再生进程中过氧化物酶的表达

目的观察大乳头水螅(Hydra magnipapillata)基盘再生进程中基盘过氧化物酶的表达情况,探讨水螅基盘过氧化物酶的生理作用。方法通过ABTS细胞化学染色法显示水螅基盘过氧化物酶的表达。结果水螅基盘再生20h后其基盘过氧化物酶开始出现少量表达,其后过氧化物酶表达量逐渐增加;基盘再生52h后该酶表达量趋于稳定。过氧化物酶仅在基盘周边区域外胚层中表达,而在基盘中央区域(反口孔)外胚层中无表达。结论水螅基盘再生进程中过氧化物酶的表达量逐渐增加直接反映了基盘再生时细胞分化过程,基盘表达的过氧化物酶可能在维持基盘结构的稳定上起一定的作用。     

EFFECTS OF COLCEMID ON HYDRA VIRIDIS WITH MULTIPLE-PEDUNCLE GRAFTS

The effect of Colcemid on multiple-graft Hydra viridis containing three peduncles (3p) grafted in tandem is reported. At grafting, the apical member of a 3p animal is a foot-less host, the middle member, an isolated peduncle, and the proximal member, a foot-bearing peduncle. In different experimental situations all three members are treated with Colcemid, the host member alone is treated, or the host member is not treated but the others are. Control animals have only non-treated members. Head and foot regeneration on graft pieces and the formation of waists and separations at the borders between these pieces are monitored and the significance of differences between frequencies tested by Chi square. Head formation on the middle and proximal peduncles is promoted by Colcemid when all pieces are treated, but animals with treated host pieces have significantly higher frequencies of heads on their non-treated proximal pieces than other experimental and control animals. Animals with Colcemid-treated proximal peduncles do not have significantly more heads on the most proximal peduncle compared to controls. Colcemid does not alter the frequency of foot formation significantly on the host peduncles of animals in the different categories, but foot formation is increased on the middle pieces of animals with three treated pieces and on animals with middle and proximal treated pieces. The rate of waist formation and graft separation is retarded when all three or just the host piece is treated, but not when only the middle and proximal pieces are treated. The direct action of Colcemid on nerves and on dividing cells may be responsible for these effects.     

THE STRUCTURAL ORGANIZATION OF THE SEPTATE AND GAP JUNCTIONS OF HYDRA

The septate junctions and gap junctions of Hydra were studied utilizing the extracellular tracers lanthanum hydroxide and ruthenium red. Analysis of the septate junction from four perspectives has shown that each septum consists of a single row of hexagons sharing common sides of 50–60 A. Each hexagon is folded into chair configuration. Two sets of projections emanate from the corners of the hexagons. One set (A projections) attaches the hexagons to the cell membranes at 80–100-A intervals, while the other set (V projections) joins some adjacent septa to each other. The septate junctions generally contain a few large interseptal spaces and a few septa which do not extend the full length of the junction. Basal to the septate junctions the cells in each layer are joined by numerous gap junctions. Gap junctions also join the muscular processes in each layer as well as those which connect the layers across the mesoglea. The gap junctions of Hydra are composed of rounded plaques 0.15–0.5 µ in diameter which contain 85-A hexagonally packed subunits. Each plaque is delimited from the surrounding intercellular space by a single 40-A band. Large numbers of these plaques are tightly packed, often lying about 20 A apart. This en plaque configuration of the gap junctions of Hydra contrasts with their sparser, more widely separated distribution in many vertebrate tissues. These studies conclude that the septate junction may possess some barrier properties and that both junctions are important in intercellular adhesion. On a morphological basis, the gap junction appears to be more suitable for intercellular coupling than the septate junction.     

STRUCTURE AND REPRODUCTION OF THE ALGAL SYMBIONTS OF HYDRA VIRIDIS1

The algal symbionts of Hydra viridis are found within vacuoles of the gastrodermal digestive cells of the host. Electron microscopy reveals that the symbionts possess cell walls, and that their reproductive cycle follows the general pattern of free-living Chlorella. Nuclear and chloroplast divisions arc followed by formation of new cell walls, the Golgi apparatus being quite active during cell wall synthesis. Autospores are released when the parent wall ruptures. The autospores are then usually segregated into separate animal vacuoles. Remnants of the ruptured parent wall persist in the vacuoles for an indefinite period. The ruptured parent walls curl at the breakage clefts, forming double-layered scroll-like structures. The fate of these wall remnants has not been firmly established. Long-term starvation of the animals does not result in a detectable change in the structure of the symbionts, and they continue to divide and to store carbohydrate as starch grains.     

水螅觸手數目之觀察

水螅(Hydra oligactus Pallus)之觸手數目,在天然環境中,可以有自十個至五個之差異。早期之研究皆以為觸手數目之决定皆由于水螅之大小及年齡。但實際觀察中有二點,顯示觸手數目似與水螅之大小無關:(1)此二者之間之相關係數極低,(2)水螅在生長條件最優時,可以增加其體積之大小,而觸手之數目不增多。但在某種環境下,水螅之觸手確能增加。此種環境之一即為華氏五十五度左右之温度。在該情形下,出芽生殖率降低,而觸手可以長出。此一情形,在自然間,即為晚晚春及早秋之温度。故水螅經年後,可以增加觸手之數目,亦可謂,觸手數目舆水螅之年齡有關。觸手增多無一定之規則。平常皆增加一至二觸手。但有時亦可增加一圈觸手(四個至五個)。水螅觸手數目正常或係六個,最少為三個,最多為十二個。但此二情形之水螅曾不能存在長久。三個觸手之水螅不久即長出第四個觸手,十二個觸手之水螅則不久即縱裂為二個水螅。     

SELECTIVE INHIBITION OF REGENERATION IN HYDRA VULGARIS BY ACTINOMYCIN D

Twelve-hour continuous pretreatment of regenerating Hydra with 60 μg/ml actinomycin D inhibited the synthesis of RNA by 98%. In such Hydra, hypostome regeneration was found more affected than basal disc regeneration since a complete blockage of development of oral structures occurred. It is assumed that the hypostome regeneration requires new DNA-dependent RNA synthesis. Better differentiation of the basal disc is explained on the basis of a stable variety of messenger RNA (mRNA), which would become activated at the time of determination. The formation of mesoglea and the development of fibrous materials in the basal disc are attributed to new DNA-dependent RNA synthesis.     

PACEMAKER INTERACTION IN HYDRA

Previous reports have described in detail the characteristicsof two pacemaker systems in hydras. Each of these, the rhythmicpotential (RP) system located near the base of the polyp, andthe contraction burst (CB) system at the sub-hypostome, hasits own conducting system running the length of the animal,so that the impulses originated at either end spread throughoutthe organism. It has been postulated that these conducted impulsesof each system can reach and influence both the pacemakers ofits own, and those of the other, system. The over-all behaviorof the hydra would thus be the integrated responses of the effectorsresponding to these interdependent coordinating systems. Certain evidence favoring this hypothesis is presented. It isevident that there are interactions between the two systems,especially in the control of contraction burst initiation. Duringperiods in which RP impulses are appearing at short, regularintervals, contraction bursts are characteristically absent.Paradoxically when RP frequency is low, CB firing is also minimal.Normal CB activity levels are associated with intermediate RPfrequencies. There is also a frequency correlation between RP rate and theonset of individual contraction bursts. The interval betweenRP impulses is longer just before the first CB pulse than itis midway between bursts. It is shortest just following theburst. The longest RP intervals occur during contraction bursts.It appears that the initiation of endogenous CB activity isinfluenced by RP frequency in a manner comparable to the triggeringof the distinctive locomotor CB after RP pacemaker stimulation. Comparable work with other coelenterates has stressed the importanceboth of endogenous rhythmicity and ordered interaction betweenseparate pacemaker-driven coordinating systems. Hydras are notexceptional to this pattern, but they do show distinctive featurescompared to strictly sessile polyps. Further investigation maydisclose how the so-far unique RP pattern of repeated individualpulses and the absence of pulse bursts or trains is responsiblefor hydras' distinctive behavior.     

ELECTRON MICROSCOPE OBSERVATIONS ON THE STRUCTURE AND DISCHARGE OF THE STENOTELE OF HYDRA

Sections of the stenotele type of nematocyst of Chlorohydra hadleyi have revealed that the stenotele, upon firing, completely everts its stylets and spines and the long, thin tubule, much as the eversion of the tubule of the nematocyst of the jewel anemone (Picken, 1953; Robson, 1953). Alternative mechanisms for supplying the energy necessary to forcefully discharge the stenotele contents are discussed as well as the possible significance of several regions containing highly ordered periodic structure. The origin of nematocysts as kinetosomal derivatives is discussed as a possibility suggested by the symmetry of the stenotele contents and the structure, location, and function of the cnidocil.     

强壮水螅的特征及其与寡水螅的种间差别问题

一种广泛分布于黑龙江省的大型具柄水螅被暂定为强壮水螅Hydra robusta(IT(?) 1947)。这一中国品系与IT(?)(1947)在日本报告的新种主要特征相同,包括具有精巢乳头。只是精巢乳头不稳定。在实验室条件下第一次有性生殖时每个雄体都发生精巢乳头,但第二次有性生殖时,同一群的后代可全部失去精巢乳头。这是介于强壮水螅与寡水螅Hydra oligactis Pallas(1766)之间的中间性状。从而导致作者做出结论,认为过去其他学者所主张的,以精巢乳头的有无做为鉴别特征来区分强壮水螅和寡水螅是不可靠的。因此,本文又检验了此种水螅的体细胞染色体,证明2n=30,其中第二对染色体上有明显近中位置的次缢痕,最小染色体的长度为最大染色体长度的二分之一以上。这些可做为此种水蝗的鉴别特征。对Niiyama(1944)和Datta(1970)在寡水螅上所做的染色体研究也做了比较及讨论。     

SOME PHYSIGOCHEMICAL ASPECTS OF THE MACROAND MICROENVIRONMENTS SURROUNDING HYDRA DURING ACTIVATION OF THEIR FEEDING BEHAVIOR

Three environmental zones which can influence the activationof the feeding response of Hydra littoralis are termed the macro-,micro-, and ultramicroenvironment. The first consists primarilyof the ions in the bulk medium, and of dissolved gases. Themicroenvironment is the area immediately surrounding the hydra;its composition is influenced by substances emitted from andtaken up by the animal. The third zone, the ultramicroenvironment,is presumed to be made up of a thin shell of ions in the mediumthat are attracted to the charged surfaces of the animal. Through a physicochemical study of these environments, we havedetermined: (1) the presence of ionizable groups at the receptorsite which may be involved in the binding of glutathione; (2)the role of potassium and other ions in influencing the feedingresponse; and, (3) the possible existence of charged surfaceson hydra surrounded by a pH shell. Further, these experimentshelp to resolve many seemingly inconsistent reports dealingwith the feeding behavior of hydras.     

LIGHT AND SCANNING ELECTRON MICROSCOPIC INVESTIGATIONS OF SEXUAL REPRODUCTION IN HYDRA CARNEA

In the freshwater hydrozoan Hydra carnea, the egg, matured and grown between the mesoglea and the epitheliomuscular cells of the ectoderm, is extruded after the emission of the second polar body. Surrounded by a clear jelly layer the egg remains attached to the polyp. Sperm which are released from the testicular sacs of male polyps are attracted by the egg. The jelly layer is penetrated only at the site of emission of the polar bodies by sperm which lack a structurally distinct acrosome. One sperm fuses with the egg at that site where the female pronucleus is found to lie close to the egg membrane. After fertilization and cleavage an acellular embryotheca is secreted by the blastomeres. These events were investigated by light and scanning electron microscopy.