System Of Hydra Research Articles

The influence of oceanic swell on flows over an estuarine intertidal mudflat in San Francisco Bay

In this study, we examine the role that remotely forced ocean waves play in the hydrodynamics of an intertidal, estuarine mudflat. The observations indicate that long-period (10–20 s) ocean waves are a potentially important source of near-bed energy and shear stress in this environment. Over a two-week period in February 2001, we deployed an autonomous SonTek Hydra system on a mudflat in Central San Francisco Bay, and measured velocity and sediment concentration approximately 10 cm from the bed using an acoustic Doppler velocimeter (ADV) and an optical backscatter sensor (OBS). The experiment continued through wet (high tide) and dry (low tide) periods over an entire spring–neap cycle, and thus included the variation of near-bed velocity over a range of timescales. Results show that during large ebb tides, tidally forced flows dominate the near-bed dynamics during calm conditions. Wind waves dominate whenever the wind direction exposes the mudflat to wind coming off the bay (from the south and southwest), as occurs during winter storms. During periods when tidal forcing is limited and wind waves are small, remotely forced ocean swells become an important energy source. These motions appear in the burst samples at frequencies between 0.1 and 0.04 Hz and their energy correlates well ( ρ>0.8) with ocean swell measured from a buoy offshore of San Francisco. Spectral analysis of data shows that the average energy of ocean waves per tide varied between 2 and 15% of total energy load. Moreover, extreme values in the distribution of ocean waves bring episodic bursts of greater energy onto the estuarine mudflat, which may influence local suspension of sediments.

Large grains in the disk of CQ Tau

We present 7 mm observations of the dusty disk surrounding the 10 Myr old pre-main-sequence star CQ Tauri obtained at the Very Large Array with 0.8 arcsec resolution and 0.1 mJy rms sensitivity. These observations resolve the 7 mm emission in approximately the north-south direction, confirming previous results obtained with lower resolution. We use a two-layer flared disk model to interpret the observed fluxes from 7 mm to 1.3 mm together with the resolved 7 mm structure. We find that the disk radius is constrained to the range 100 to 300 AU, depending on the steepness of the disk surface density distribution. The power law index of the dust opacity coefficient, β, is constrained to be 0.5 to 0.7. Since the models indicate that the disk is optically thin at millimeter wavelengths for radii greater than 8 AU, the contribution of an optically thick region to the emission is less than 10%. This implies that high optical depth or complex disk geometry cannot be the cause of the observed shallow millimeter spectral index. Instead, the new analysis supports the earlier suggestion that dust particles in the disk have grown to sizes as large as a few centimeters. The dust in the CQ Tauri system appears to be evolved much like that in the TW Hydra system, a well-studied pre-main-sequence star of similar age and lower mass. The survival of gas-rich disks with incomplete grain evolution at such old ages deserves further investigations.

Feeding and wounding responses in Hydra suggest functional and structural polarization of the tentacle nervous system

The nervous system of Hydra, a freshwater cnidaria, occurs as dispersed, or diffuse, nerve net throughout the animal. It is widely accepted that in a diffuse nervous system an external stimulus is conducted in all directions over the net. Here I report observations that hydra tentacles respond to feeding and wounding stimuli in a unidirectional manner. Upon contact of a tentacle with a brine shrimp larva during feeding, tissue on the proximal side of the point of contact contracted strongly, whereas tissue on the distal side contracted only very weakly. Feeding a tentacle to which a second tentacle was grafted to the proximal end in the reversed orientation showed that unidirectional conduction, once initiated, was blocked by the reversal of polarity, demonstrating that the distal to proximal polarity of tissue is crucial for unidirectional conduction. Unidirectional conduction was obtained also by mechanically pinching the tissue. The response of tentacles devoid of neurons examined was bidirectional, demonstrating that the nervous system is responsible for the unidirectional responses. These observations suggest that polarized property of the nerve net in hydra tentacles is responsible for the unidirectional tentacle contraction.

Molecular and functional evidence for early divergence of an endothelin-like system during metazoan evolution: analysis of the Cnidarian, hydra.

A novel putative endothelin-converting enzyme (ECE) has been cloned from hydra, a freshwater invertebrate that belongs to the second oldest phylum of the animal kingdom. As an integral component of the endothelin system, vertebrate ECE functions in the activation of endothelin (ET) peptides. Vertebrate ETs are (1) the most potent vasoconstrictors known in mammals; and (2) function as essential signaling ligands during development of tissues derived from neural crest cells. To date, only a limited number of immunocytochemical studies have suggested the presence of endothelin-like peptides in invertebrates. Based on structural and functional analyses, we present evidence for a functional endothelin-like system in hydra that is involved in both muscle contraction and developmental processes. These findings indicate the broad use of endothelin systems in metazoans and also indicate that this type of signaling system arose early in evolution even before divergence of protostomes and deuterostomes.

VLA Imaging of the Disk Surrounding the Nearby Young Star TW Hydrae.

The TW Hydrae system is perhaps the closest analog to the early solar nebula. We have used the Very Large Array to image TW Hya at wavelengths of 7 mm and 3.6 cm with resolutions of 0&farcs;1 ( approximately 5 AU) and 1&farcs;0 ( approximately 50 AU), respectively. The 7 mm emission is extended and appears dominated by a dusty disk of radius greater than 50 AU surrounding the star. The 3.6 cm emission is unresolved and likely arises from an ionized wind or gyrosynchrotron activity. The dust spectrum and spatially resolved 7 mm images of the TW Hya disk are fitted by a simple model with temperature and surface density described by radial power laws, T&parl0;r&parr0;~r-0.5 and Sigma&parl0;r&parr0;~r-1. These properties are consistent with an irradiated gaseous accretion disk of mass approximately 0.03 M middle dot in circle with an accretion rate approximately 10-8 M middle dot in circle yr-1 and viscosity parameter alpha=0.01. The estimates of mass and mass accretion rates are uncertain since the gas-to-dust ratio in the TW Hya disk may have evolved from the standard interstellar value.

Finding of the endocannabinoid signalling system in Hydra, a very primitive organism: possible role in the feeding response

Hydra (Cnidaria) is the first animal organism to have developed a neural network, which has been proposed to control, inter alia, the “feeding response”, i.e. a mechanism through which the coelenterate opens and then closes its mouth in the presence of prey and/or glutathione. Here, we report that Hydra contains: (i) selective cannabinoid binding sites; (ii) the endogenous cannabinoid receptor ligand, anandamide (arachidonoylethanolamide); (iii) a fatty acid amide hydrolase-like activity catalysing anandamide hydrolysis; and (iv) the putative biosynthetic precursor of anandamide, N-arachidonoylphosphatidylethanolamine. We suggest that this “endogenous cannabinoid system” is involved in the modulation of the “feeding response”. Anandamide (1 nM–1 μM) potently inhibited (up to 45%) the glutathione-induced “feeding response” by accelerating Hydra vulgaris mouth closure. The effect was maximal at 100 nM anandamide and was reversed by the selective antagonist of the CB 1 subtype of mammalian cannabinoid receptors, SR 141716A (50–100 nM). Specific cannabinoid binding sites were detected in membranes from Hydra polyps by using [ 3H]SR 141716A ( K d =1.87 nM, B max=26.7 fmol/mg protein), and increasing anandamide concentrations were found to displace the binding of [ 3H]SR 141716A to these membranes ( K i =505 nM). Hydra polyps were also found to contain amounts of anandamide (15.6 pmol/g) and N-arachidonoylphosphatidylethanolamine (32.4 pmol/g), as well as the other “endocannabinoid” 2-arachidonoylglycerol (11.2 nmol/g), comparable to those described previously for mammalian brain. Finally, a fatty acid amide hydrolase activity ( V max=3.4 nmol/min/mg protein), with subcellular distribution, pH dependency and sensitivity to inhibitors similar to those reported for the mammalian enzyme, but with a lower affinity for anandamide ( K m =400 μM), was also detected in Hydra polyps. These data suggest that the endocannabinoid signalling system plays a physiological role in Hydra that is to control the feeding response. Hydra is the simplest living organism described so far to use this recently discovered regulatory system.

ヒドラの散在神経系の神経生物学

ヒドラの散在神経系の神経生物学

Stimulation of Tentacle and Bud Formation by the Neuropeptide Head Activator inHydra magnipapillata

Stimulation of epithelial cell cycling by the neuropeptide head activator was analyzed inHydra magnipapillataand compared with the action of head activator on bud formation and tentacle formation during head regeneration. The results obtained indicate that head activator treatment stimulates epithelial cell division and induces the formation of more tentacle-specific epithelial cells. The number of additional epithelial cells which undergo mitosis during head activator treatment accounts for the increased number of epithelial cells present in the regenerated tentacles. Therefore, the head activator stimulation of tentacle formation can be explained by the mitogenic action of head activator on tentacle cell precursors. To analyze stimulation of bud formation by head activator, polyps of different developmental age were tested under conditions of long-term treatment, and effects on bud formation were compared with effects on epithelial cell proliferation. Head activator treatment strongly stimulated bud formation, but had no detectable effect on epithelial cell numbers. Bud formation occurs at smaller polyp size as a result of head activator treatment, indicating that head activator significantly interferes with the patterning system in hydra.

Pattern Formation in Hydra vulgaris Is Controlled by Lithium-Sensitive Processes

Application of lithium ions leads to dramatic alterations in the positional value and subsequently to the formation of ectopic foot or head structures in Hydra vulgaris . Prolonged LiCl treatment decreases and pulse treatment increases the positional value. The decrease in the positional value is manifested in the formation of multiple ectopic feet along the body axis of intact animals or regenerates. Regeneration experiments reveal that long term application of the ion leads to transformation of prospective head into foot tissue. This transformation requires lithium pretreatment and exposure of the excised pieces to lithium for a further 5-8 hr. Pulse treatment of hydra with lithium elevates the positional value. Regenerating distal thirds differentiate ectopic head structures instead of a foot. Changes in the lithium concentration during the experiment lead to the differentiation of ectopic heads in the upper as well as ectopic feet in the lower body region. The characteristics of pattern respecification presented in this paper suggest that lithium interferes with the main pattern forming system(s) in hydra.

Maintenance of nerve net in the diffuse nervous system of hydra: Morphogenetic gradients and neuronal distribution

Maintenance of nerve net in the diffuse nervous system of hydra: Morphogenetic gradients and neuronal distribution

Plasticity in the nervous system of adult hydra. III. Conversion of neurons to expression of a vasopressin-like immunoreactivity depends on axial location

The nervous system of hydra consists of a nerve net that extends throughout the animal. Because of the tissue dynamics of hydra, the nerve net is in a steady state of production and loss of neurons. Neurons are continuously produced in the body column and are constantly lost by sloughing at the extremities and into developing buds. Consequently, every neuron is continuously displaced towards an extremity. A subset of the neurons of the nerve net, termed vasopressin-like-immunoreactive (VLI+) neurons, has been identified with an antiserum against vasopressin. This subset has a specific regional distribution in that it is found in the head, peduncle, and foot of an adult hydra. The VLI+ neurons in the head and peduncle are ganglion cells, while those in the foot include a newly described sensory cell. How is the regional distribution of the subset maintained when every neuron is continually changing location? Removal of the neuron precursors indicates the VLI+ neurons can arise by conversion from VLI- neurons of the body column. In the normal animal they probably arise by conversion as well as by differentiation. Conversion of VLI- to VLI+ neurons is due to a change in axial position, or region, instead of a maturation process.

Nerve net fomation in the diffused nervous system of hydra I. Regeneration of hypostomal nerve net

Nerve net fomation in the diffused nervous system of hydra I. Regeneration of hypostomal nerve net

Nerve net formation in the primitive nervous system of Hydra — an overview

Nerve net formation was examined during head-regeneration and budding of Hydra using indirect immunofluorescence on whole mounts. The nerve net was visualized with an antiserum to a neuropeptide, RFamide. The nerve net forms in two steps: the first is the appearance of ganglion cells at the regenerating tip, and the second is the appearance of sensory cells at the apex and the simultaneous disappearance of ganglion cells from the apex. The behavior of epithelial cells during head-regeneration, as defined by monoclonal antibody TS19, corresponded with nerve net formation. We examined nerve net formation in 3 morphogenetic mutants: a head-regeneration deficient mutant (reg-16), a budding deficient mutant (L4) and a multi-headed mutant (mh-1). In addition, we also examined chimeric strains which consist of the epithelial cells from the wild type and nerve cells from a mutant, and vice versa. We obtained clear evidence that nerve net formation is controlled by the environment provided by the epithelial cells.

Nerve net fomation in the diffused nervous system of hydra I. Regeneration of hypostomal nerve net

Nerve net fomation in the diffused nervous system of hydra I. Regeneration of hypostomal nerve net

Plasticity in the nervous system of adult hydra: II. Conversion of ganglion cells of the body column into epidermal sensory cells of the hypostome

Plasticity in the nervous system of adult hydra: II. Conversion of ganglion cells of the body column into epidermal sensory cells of the hypostome

Plasticity in the nervous system of adult hydra: II. Conversion of ganglion cells of the body column into epidermal sensory cells of the hypostome

Due to the tissue dynamics of hydra, every neuron is constantly changing its location within the animal. At the same time specific subsets of neurons defined by morphological or immunological criteria maintain their particular spatial distributions, suggesting that neurons switch their phenotype as they change their location. A position-dependent switch in neuropeptide expression has been demonstrated. The possibility that ganglion cells of the body column are converted into epidermal sensory cells of the head was examined using a monoclonal antibody, TS33, whose binding is restricted to a subset of epidermal sensory cells of the hypostome, the apical end of the head. When animals devoid of interstitial cells, which are the nerve cell precursors, were decapitated and allowed to regenerate, they formed TS33 + epidermal sensory cells. As this latter cell type is not found in the body column, and the interstitial cell-free animals contained only epithelial cells and ganglion cells in the part of the ectoderm that formed the head during regeneration, the TS33 + epidermal sensory cells most likely arose from the TS33 − ganglion cells. The observation of epidermal sensory cells labeled with both TS33 and TS26, a monoclonal antibody that binds to ganglion cells, in regenerating and normal heads provides further support. The double-labeled cells are probably in transition from a ganglion cell to an epidermal sensory cell. These results provide a second example of position-dependent changes in neuron phenotype, and suggest that the differentiated state of a neuron in hydra is only metastable with regard to phenotype.

Plasticity in the nervous system of adult hydra: I. The position-dependent expression of FMRFamide-like immunoreactivity

Abstract The plasticity of nerve cells expressing the neuropeptide FMRFamide was examined in adult hydra. Using a whole-mount technique with indirect immunofluorescence, the spatial pattern of neurons showing FMRFamide-like immunoreactivity (FLI) was visualized. These neurons were located in the tentacles, hypostome, and peduncle, but not in the body column or basal disc. Since every neuron in the nerve net is continuously displaced toward an extremity and eventually sloughed, the constant pattern of FLI + neurons could arise in one of two ways. When displaced into the appropriate region, FLI − neurons are converted to FLI + neurons, or FLI + neurons arise by differentiation from interstitial cells. To distinguish between these two possibilities, interstitial cells, the multipotent precursors of the nerve cells, were eliminated by treatment with hydroxyurea or nitrogen mustard. Following head, or foot and peduncle, removal from these animals, the missing structures regenerated. The spatial pattern of FLI + neurons reappeared in the newly regenerated head or peduncle. This shows FLI − neurons in the body column were converted to FLI + when their position was changed to the head or the peduncle. When the peduncle was grafted into the body column, it was converted to basal disc or body column tissue, and FLI disappeared. The appearance and loss of FLI was always position dependent. These results indicate that the neurons in the mature nerve net can change their neuropeptide phenotype in response to changes in their position.

Plasticity in the nervous system of adult hydra: I. The position-dependent expression of FMRFamide-like immunoreactivity

The plasticity of nerve cells expressing the neuropeptide FMRFamide was examined in adult hydra. Using a whole-mount technique with indirect immunofluorescence, the spatial pattern of neurons showing FMRFamide-like immunoreactivity (FLI) was visualized. These neurons were located in the tentacles, hypostome, and peduncle, but not in the body column or basal disc. Since every neuron in the nerve net is continuously displaced toward an extremity and eventually sloughed, the constant pattern of FLI + neurons could arise in one of two ways. When displaced into the appropriate region, FLI − neurons are converted to FLI + neurons, or FLI + neurons arise by differentiation from interstitial cells. To distinguish between these two possibilities, interstitial cells, the multipotent precursors of the nerve cells, were eliminated by treatment with hydroxyurea or nitrogen mustard. Following head, or foot and peduncle, removal from these animals, the missing structures regenerated. The spatial pattern of FLI + neurons reappeared in the newly regenerated head or peduncle. This shows FLI − neurons in the body column were converted to FLI + when their position was changed to the head or the peduncle. When the peduncle was grafted into the body column, it was converted to basal disc or body column tissue, and FLI disappeared. The appearance and loss of FLI was always position dependent. These results indicate that the neurons in the mature nerve net can change their neuropeptide phenotype in response to changes in their position.

Plasticity of FMRFamide-like immunoreactivity in the nervous system of hydra: [formula omitted] and [formula omitted]. Developmental Biology Ctr., UCI, Irvine CA 92717

Plasticity of FMRFamide-like immunoreactivity in the nervous system of hydra: [formula omitted] and [formula omitted]. Developmental Biology Ctr., UCI, Irvine CA 92717

Cell migration in the patterning of the nervous system of Hydra

Different regional nerve densities in Hydra have often been thought to arise by position-dependent determination of cells. Now two recent articles by Shelley Heimford and Hans Bode 1,2 suggest that extensive cell migration also contributes to patterning in the nervous system. These findings are particularly interesting since the cells which migrate may represent a developmentally distinct population of committed nerve cell precursors.