C. Di Cristo

Effects of estradiol and progesterone on the reproduction of the freshwater crayfish Cherax albidus.

In this study we have investigated the role of 17β-estradiol and progesterone in the reproduction of the crayfish Cherax albidus by using vitellogenin (VTG) as a biomarker. Early-vitellogenic (EV), full-vitellogenic (FV), and non-vitellogenic (NV) females of Cherax albidus were treated with 17β-estradiol, progesterone, or both for 4 weeks. Levels of VTG mRNA in the hepatopancreas were detected by RT-PCR. The PCR product was sequenced and showed 97% homology with Cherax quadricarinatus VTG. 17β-estradiol was more effective than progesterone and 17β-estradiol plus progesterone in increasing the vitellogenin transcript in the hepatopancreas of EV and FV females. On the contrary, progesterone was more effective than 17β-estradiol and 17β-estradiol plus progesterone in increasing the vitellogenin concentration in the hemolymph of EV and FV females. Hepatopancreas histology and fatty acid composition of females injected with hormones showed major modifications. No effects were registered in NV females. In conclusion, 17β-estradiol and progesterone influence VTG synthesis, although our data indicate that they act through different pathways and are not effective until the proper hormonal environment is established, as demonstrated by their inefficacy in NV females.

On the convective nature of roll waves instability

A theoretical analysis of the Saint-Venant one-dimensional flow model is performed in order to define the nature of its instability. Following the Brigg criterion, the investigation is carried out by examining the branch points singularities of dispersion relation in the complex ω and k planes, where ω and k are the complex pulsation and wave number of the disturbance, respectively. The nature of the linearly unstable conditions of flow is shown to be of convective type, independently of the Froude number value. Starting from this result a linear spatial stability analysis of the one-dimensional flow model is performed, in terms of time asymptotic response to a pointwise time periodic disturbance. The study reveals an influence of the disturbance frequency on the perturbation spatial growth rate, which constitutes the theoretical foundation of semiempirical criteria commonly employed for predicting roll waves occurrence.

L-Glutamate and its Ionotropic Receptors in the Nervous System of Cephalopods

In several species of cephalopod molluscs there is good evidence for the presence of L-glutamate in the central and peripheral nervous system and evidence for both classes of ionotropic receptor, AMPA/kainate and NMDA.The best evidence for glutamate being a transmitter in cephalopods comes from pharmacological, immunohistochemical and molecular investigations on the giant fibre system in the squid stellate ganglion. These studies confirm there are AMPA/kainate-like receptors on the third-order giant axon. In the (glial) Schwann cells associated with the giant axons both classes of glutamate receptor occur.Glutamate is an excitatory transmitter in the chromatophores and in certain somatic muscles and its action is mediated primarily via AMPA/kainate-like receptors, but at some chromatophores there are NMDA-like receptors.In the statocysts the afferent crista fibres are also glutamatergic, acting at non-NMDA receptors.In the brain (of Sepia) a neuronal NOS is activated by glutamate with subsequent production of nitric oxide and elevation of cGMP levels. This signal transduction pathway is blocked by D-AP-5, a specific antagonist of the NMDA receptor.Recently immunohistochemical analysis has demonstrated (in Sepia and Octopus) the presence of NMDAR2A /B - like receptors in motor centres, in the visual and olfactory systems and in the learning system. Physiological experiments have shown that glutamatergic transmission is involved in long term potentation (LTP) in the vertical lobe of Octopus, a brain area involved in learning. This effect seems to be mediated by non-NMDA receptors. Finally in the CNS of Sepia NMDA-mediated nitration of tyrosine residues of cytoskeletal protein such as alpha-tubulin, has been demonstrated.

Minimum channel length for roll-wave generation

The initial phase of roll-wave development is investigated by means of spatial linear stability analysis using the St. Venant equations, subject to a pointwise time-varying oscillating disturbance. The predicted spatial growth is compared with both Vedernikovs results and those computed with a fully non-linear model. It is shown that for large values of the channel slope Vedernikovs theory systematically overpredicts the roll waves spatial growth rate, whereas the present analysis yields significant improvements. A modification of Montuoris criterion for the minimum channel length prediction is finally proposed, which agrees with available experimental data independently of the channel slope.

Quantitative dynamic imaging of biological processes with solid state radiation detectors

We have developed a technique and a prototype for /spl beta/-rays and /spl gamma/-rays quantitative imaging of biological samples which have been radioactively labeled. The prototype is based on a solid state pixel detector, bump-bonded to a low threshold, single particle counting chip: the detector we used is 200-/spl mu/m thick GaAs, with pixel size 170 /spl mu/m. In this paper we describe an experiment that shows the capability of monitoring a dynamic process. Specifically, [/sup 14/C]L-Leucine uptake by eggs of mollusk cephalopod Octopus vulgaris and the consequent migration of marker into the ooplasm was followed.

EXPERIMENTAL STUDY ON LIQUID AND SUSPENDED SEDIMENT TURBULENCE CHARACTERISTICS IN OPEN-CHANNEL FLOWS

ABSTRACT Many studies show that suspended sediment may substantially affect the turbulence characteristics of the carrier fluid in sediment-laden flows. This effect should be taken into account when modeling such flows, which is not usually done due to the incomplete knowledge of this interdependence. Another conventional modeling simplification is based on the assumption that fluid and particles have the same hydrodynamic characteristics. Recent experimental evidence shows that this assumption is not accurate. However, the available results describing separately the two-phases in the flow are scarce and often inconsistent to appropriately substantiate this statement. This paper presents some preliminary results of investigations on water and suspended sediment turbulence characteristics in an open-channel flow addressing these important modeling issue. Two kinds of sediment were used in the investigations. Results obtained with crushed walnut shell with relative density of 1.3 and particle diameter ranging from 0.590 mm to 0.710 mm are only presented here. The fluid phase in the mixture was traced with spherical glass particles with a diameter of 0.040 mm. Velocities for particles and water were measured, simultaneously, using Particle Tracking Velocimetry (PTV). Phase separation was made using the size of the particles as phase-discrimination criterion. A self-adaptive, iterative, procedure for discarding the erroneous measurements introduced by the PTV technique was developed. For the experimental conditions investigated, the stream wise and vertical turbulence intensities of the water were enhanced by the addition of the sediment. The comparison between water and sediment turbulence intensities shows that the particle turbulence intensities are lower than those for water, both in the streamwise and vertical directions.