The eyes of deep-sea fish II. Functional morphology of the retina

Three different aspects of the morphological organisation of deep-sea fish retinae are reviewed: First, questions of general cell biological relevance are addressed with respect to the development and proliferation patterns of photoreceptors, and problems associated with the growth of multibank retinae, and with outer segment renewal are discussed in situations where there is no direct contact between the retinal pigment epithelium and the tips of rod outer segments. The second part deals with the neural portion of the deep-sea fish retina. Cell densities are greatly reduced, yet neurohistochemistry demonstrates that all major neurotransmitters and neuropeptides found in other vertebrate retinae are also present in deep-sea fish. Quantitatively, convergence rates in unspecialised parts of the retina are similar to those in nocturnal mammals. The differentiation of horizontal cells makes it unlikely that species with more than a single visual pigment are capable of colour vision. In the third part. the diversity of deep-sea fish retinae is highlighted. Based on the topography of ganglion cells, species are identified with areae or foveae located in various parts of the retina, giving them a greatly improved spatial resolving power in specific parts of their visual fields. The highest degree of specialisation is found in tubular eyes. This is demonstrated in a case study of the scopelarchid retina, where as many as seven regions with different degrees of differentiation can be distinguished, ranging from an area giganto cellularis, regions with grouped rods to retinal diverticulum. (C) 1998 Elsevier Science Ltd. All rights reserved.

Finite element analysis of flow patterns near geological lenses in hydrodynamic and hydrothermal systems

We use theoretical and numerical methods to investigate the general pore-fluid flow patterns near geological lenses in hydrodynamic and hydrothermal systems respectively. Analytical solutions have been rigorously derived for the pore-fluid velocity, stream function and excess pore-fluid pressure near a circular lens in a hydrodynamic system. These analytical solutions provide not only a better understanding of the physics behind the problem, but also a valuable benchmark solution for validating any numerical method. Since a geological lens is surrounded by a medium of large extent in nature and the finite element method is efficient at modelling only media of finite size, the determination of the size of the computational domain of a finite element model, which is often overlooked by numerical analysts, is very important in order to ensure both the efficiency of the method and the accuracy of the numerical solution obtained. To highlight this issue, we use the derived analytical solutions to deduce a rigorous mathematical formula for designing the computational domain size of a finite element model. The proposed mathematical formula has indicated that, no matter how fine the mesh or how high the order of elements, the desired accuracy of a finite element solution for pore-fluid flow near a geological lens cannot be achieved unless the size of the finite element model is determined appropriately. Once the finite element computational model has been appropriately designed and validated in a hydrodynamic system, it is used to examine general pore-fluid flow patterns near geological lenses in hydrothermal systems. Some interesting conclusions on the behaviour of geological lenses in hydrodynamic and hydrothermal systems have been reached through the analytical and numerical analyses carried out in this paper.

Implication of the visual system in the regulation of activity cycles in the absence of solar light: 2-[I-125]iodomelatonin binding sites and melatonin receptor gene expression in the brains of demersal deep-sea gadiform fish

Relative eye size, gross brain morphology and central localization of 2-[I-125]iodomelatonin binding sites and melatonin receptor gene expression were compared in six gadiform fish living at different depths in the north-east Atlantic Ocean: Phycis blennoides (capture depth range 265-1260 m), Nezumia aequalis (445-1512 m), Coryphaenoides rupestris (706-1932 m), Trachyrincus murrayi (1010-1884 m), Coryphaenoides guentheri (1030 m) and Coryphaenoides (Nematonurus) armatus (2172-4787 m). Amongst these, the eye size range was 0.15-0.35 of head length with a value of 0.19 for C.(N.) armatus, the deepest species. Brain morphology reflected behavioural differences with well-developed olfactory regions in P.blennoides, T.murrayi and C. (N.) armatus and evidence of olfactory deficit in N. aequalis, C. rupestris and C. guentheri. All species had a clearly defined optic tectum with 2-[I-125] iodomelatonin binding and melatonin receptor gene expression localized to specific brain regions in a similar pattern to that found in shallow-water fish. Melatonin receptors were found throughout the visual structures of the brains of all species. Despite living beyond the depth of penetration of solar light these fish have retained central features associated with the coupling of cycles of growth, behaviour and reproduction to the diel light-dark cycle. How this functions in the deep sea remains enigmatic.

The role of mobile belts for the longevity of deep cratonic lithosphere: The crumple zone model

Many Archean cratons are surrounded by Proterozoic mobile belts that have experienced episodes of tectonic re-activation over their lifetimes. This suggests that mobile belt lithosphere may be associated with long lived, inherited weakness. It is proposed that the proximity of this weakness can increase the longevity of deep Archean lithosphere by buffering Archean cratons from mantle derived stresses. The physical plausibility of this idea is explored through numerical simulations of mantle convection that include continents and allow for material rheologies that model the combined brittle and ductile behavior of the lithosphere. Within the simulations, the longevity of deep cratonic lithosphere does increase if it is buffered by mobile belts that can fail at relatively low stress levels.

Petrographic and isotope constraints on the origin of authigenic carbonate minerals and the associated fluid evolution in Late Permian coal measures, Bowen Basin (Queensland), Australia

Authigenic carbonate minerals are ubiquitous throughout the Late Permian coal measures of the Bowen Basin, Queensland, Australia. In the northern Bowen Basin, carbonates include the following assemblages: siderite I (delta O-18(SMOW) = +11.4 to + 17%, delta C-13(PDB) = - 5.3 to + 120), Fe-Mg calcite-ankerite-siderite II mineral association (delta O-18(SMOW) = +7.2 to + 10.20, delta C-13(PDB) = 10.9 to - 1.80 for ankerite) and a later calcite (delta O-18(SMOW) = +5.9 to + 14.60, delta C-13(PDB) = -11.4 to + 4.40). In the southern Bowen Basin, the carbonate phase consists only of calcite (delta O-18(SMOW) = +12.5 to + 14.80, delta C-13(PDB) = -19.4 to + 0.80), where it occurs extensively throughout all stratigraphic levels. Siderite I occurs in mudrocks and sandstones and predates all other carbonate minerals. This carbonate phase is interpreted to have formed as an early diagenetic mineral from meteoric waters under cold climate and reducing conditions. Fe-Mg calcite-ankerite-siderite Il occur in sandstones as replacement of volcanic rock fragments. Clay minerals (illite-smectite, chlorite and kaolinite) postdate Ca-Fe-Mg carbonates, and precipitation of the later calcite is associated with clay mineral formation. The Ca-Fe-Mg carbonates and later calcite of the northern Bowen Basin are regarded as having formed as a result of hydrothermal activity during the latest Triassic extensional tectonic event which affected this part of the basin, rather than deep burial diagenesis during the Middle to Late Triassic as previously reported. This hypothesis is based on the timing relationships of the authigenic mineral phases and the low delta O-18 values of ankerite and calcite, together with radiometric dating of illitic clays and recently published regional geological evidence. Following the precipitation of the Ca-Fe-Mg carbonates from strongly O-18-depleted meteoric-hydrothermal fluids, continuing fluid circulation and water-rock interaction resulted in dissolution of these carbonate phases as well as labile fragments of volcaniclastic rocks. Subsequently, the later calcite and day minerals precipitated from relatively evolved (O-18-enriched) fluids. The nearly uniform delta O-18 values of the southern Bowen Basin calcite have been attributed to very low water/rock ratio in the system, where the fluid isotropic composition was buffered by the delta O-18 values of rocks. (C) 2000 Elsevier Science B.V. All rights reserved.

Computer simulations of coupled problems in geological and geochemical systems

The finite element method is used to simulate coupled problems, which describe the related physical and chemical processes of ore body formation and mineralization, in geological and geochemical systems. The main purpose of this paper is to illustrate some simulation results for different types of modelling problems in pore-fluid saturated rock masses. The aims of the simulation results presented in this paper are: (1) getting a better understanding of the processes and mechanisms of ore body formation and mineralization in the upper crust of the Earth; (2) demonstrating the usefulness and applicability of the finite element method in dealing with a wide range of coupled problems in geological and geochemical systems; (3) qualitatively establishing a set of showcase problems, against which any numerical method and computer package can be reasonably validated. (C) 2002 Published by Elsevier Science B.V.

Coaxial flattening at deep levels of orogenic belts: evidence from blueschists and eclogites on Syros and Sifnos (Cyclades, Greece)

This work presents new Structural data from a high-pressure/low-temperature (HP/LT) metamorphic terrane exposed on the islands of Syros and Sifnos (Cyclades, Greece). The structure and the metamorphism of a relatively coherent HP/LT rock section were studied in order to elucidate how strain was accommodated at deep crustal levels during the formation and exhumation of HP/LT rocks. At least three deformation phases associated with eclogite- and blueschist-facies conditions (P = 8-15 kbar; T = 400-550 degreesC) were recognised. The earliest deformation fabric (S1), preserved as inclusion trails within garnet porphyroblasts, is aligned to define a sub-vertical schistosity (at present orientation), which is frequently orthogonal to the flat matrix schistosity (S2), and may indicate that deep crustal thickening involved upright folding. The currently dominant fabric in the HP rock section, S2, is Usually moderately dipping and locally contains NW-trending glaucophane lineations, symmetric pressure-shadows and eclogitic boudins. The symmetric structures associated with this fabric seem to indicate coaxial vertical thinning, although the existence of non-coaxial structures out of the study area cannot be excluded. Glaucophane-bearing shear bands (S3), with top-to-NW sense of shearing, locally crosscut the earlier structures. The latest recognised fabric (D4) is scarce and often absent within the HP rocks. It is associated with top-to-NE kinematic criteria that formed at greenschist-facies conditions (P = 4-7 kbar; T = 400-450 degreesC). Based on these observations, it is suggested that partitioning of strain occurred at different crustal levels and at different times. Deep crustal deformation was governed by thickening via upright folding followed by coaxial vertical thinning, whereas non-coaxial shearing occurred when the rocks were already exhumed to relatively shallow crustal levels. The earliest fabrics (D1 to D3) pertain to Alpine orogenesis and possibly to syn-orogenic extension, whereas the latest correspond to whole-crust back-are extension. (C) 2002 Elsevier Science Ltd. All rights reserved.

Convective instability of 3-D fluid-saturated geological fault zones heated from below

We conduct a theoretical analysis to investigate the convective instability of 3-D fluid-saturated geological fault zones when they are heated uniformly from below. In particular, we have derived exact analytical solutions for the critical Rayleigh numbers of different convective flow structures. Using these critical Rayleigh numbers, three interesting convective flow structures have been identified in a geological fault zone system. It has been recognized that the critical Rayleigh numbers of the system have a minimum value only for the fault zone of infinite length, in which the corresponding convective flow structure is a 2-D slender-circle flow. However, if the length of the fault zone is finite, the convective flow in the system must be 3-D. Even if the length of the fault zone is infinite, since the minimum critical Rayleigh number for the 2-D slender-circle flow structure is so close to that for the 3-D convective flow structure, the system may have almost the same chance to pick up the 3-D convective flow structures. Also, because the convection modes are so close for the 3-D convective flow structures, the convective flow may evolve into the 3-D finger-like structures, especially for the case of the fault thickness to height ratio approaching zero. This understanding demonstrates the beautiful aspects of the present analytical solution for the convective instability of 3-D geological fault zones, because the present analytical solution is valid for any value of the ratio of the fault height to thickness. Using the present analytical solution, the conditions, under which different convective flow structures may take place, can be easily determined.

Observations of anti-winds in a deep alpine valley, Lake Tekapo, New Zealand

This paper presents observations of summertime anti-winds monitored under ideal conditions in the Lake Tekapo hydro-catchment situated in the central Southern Alps, New Zealand. Onset and cessation of anti-winds was observed to coincide with the change in phase of the surface limbs of thermally generated valley and mountain winds under settled anti-cyclonic conditions. Anti-winds were best developed in the early morning before surface heating and associated convective mixing of the valley atmosphere began to mask the boundaries between the surface based limb of the mountain-valley wind and the corresponding anti-wind. By mid-day, the anti-valley wind exceeded the height of the surrounding ridgeline and became embedded in the topographically channeled gradient wind. Observations presented here have both theoretical and applied implications with regard to the development of thermally generated wind systems in deep alpine valleys, and their role in the dispersion of air pollution.

Antidepressant-Like Effects of Medial Prefrontal Cortex Deep Brain Stimulation in Rats

Background: Subcallosal cingulate gyrus (SCG) deep brain stimulation (DBS) is being investigated as a treatment for major depression. We report on the effects of ventromedial prefrontal cortex (vmPFC) DBS in rats, focusing on possible mechanisms involved in an antidepressant-like response in the forced swim test (FST). Methods: The outcome of vmPFC stimulation alone or combined with different types of lesions, including serotonin (5-HT) or nore-pineprhine (NE) depletion, was characterized in the FST. We also explored the effects of DBS on novelty-suppressed feeding, learned helplessness, and sucrose consumption in animals predisposed to helplessness. Results: Stimulation at parameters approximating those used in clinical practice induced a significant antidepressant-like response in the FST. Ventromedial PFC lesions or local muscimol injections did not lead to a similar outcome. However, animals treated with vmPFC ibotenic acid lesions still responded to DBS, suggesting that the modulation of fiber near the electrodes could play a role in the antidepressant-like effects of stimulation. Also important was the integrity of the serotonergic system, as the effects of DBS in the FST were completely abolished in animals bearing 5-HT, but not NE, depleting lesions. In addition, vmPFC stimulation induced a sustained increase in hippocampal 5-HT levels. Preliminary work with other models showed that DBS was also able to influence specific aspects of depressive-like states in rodents, including anxiety and anhedonia, but not helplessness. Conclusions: Our study suggests that vmPFC DES in rats maybe useful to investigate mechanisms involved in the antidepressant effects of SCG DBS.

Double diffusion-driven convective instability of three-dimensional fluid-saturated geological fault zones heated from below

We conduct a theoretical analysis to investigate the double diffusion-driven convective instability of three-dimensional fluid-saturated geological fault zones when they are heated uniformly from below. The fault zone is assumed to be more permeable than its surrounding rocks. In particular, we have derived exact analytical solutions to the total critical Rayleigh numbers of the double diffusion-driven convective flow. Using the corresponding total critical Rayleigh numbers, the double diffusion-driven convective instability of a fluid-saturated three-dimensional geological fault zone system has been investigated. The related theoretical analysis demonstrates that: (1) The relative higher concentration of the chemical species at the top of the three-dimensional geological fault zone system can destabilize the convective flow of the system, while the relative lower concentration of the chemical species at the top of the three-dimensional geological fault zone system can stabilize the convective flow of the system. (2) The double diffusion-driven convective flow modes of the three-dimensional geological fault zone system are very close each other and therefore, the system may have the similar chance to pick up different double diffusion-driven convective flow modes, especially in the case of the fault thickness to height ratio approaching 0. (3) The significant influence of the chemical species diffusion on the convective instability of the three-dimensional geological fault zone system implies that the seawater intrusion into the surface of the Earth is a potential mechanism to trigger the convective flow in the shallow three-dimensional geological fault zone system.

Numerical simulation of double-diffusion driven convective flow and rock alteration in three-dimensional fluid-saturated geological fault zones

Numerical methods are used to simulate the double-diffusion driven convective pore-fluid flow and rock alteration in three-dimensional fluid-saturated geological fault zones. The double diffusion is caused by a combination of both the positive upward temperature gradient and the positive downward salinity concentration gradient within a three-dimensional fluid-saturated geological fault zone, which is assumed to be more permeable than its surrounding rocks. In order to ensure the physical meaningfulness of the obtained numerical solutions, the numerical method used in this study is validated by a benchmark problem, for which the analytical solution to the critical Rayleigh number of the system is available. The theoretical value of the critical Rayleigh number of a three-dimensional fluid-saturated geological fault zone system can be used to judge whether or not the double-diffusion driven convective pore-fluid flow can take place within the system. After the possibility of triggering the double-diffusion driven convective pore-fluid flow is theoretically validated for the numerical model of a three-dimensional fluid-saturated geological fault zone system, the corresponding numerical solutions for the convective flow and temperature are directly coupled with a geochemical system. Through the numerical simulation of the coupled system between the convective fluid flow, heat transfer, mass transport and chemical reactions, we have investigated the effect of the double-diffusion driven convective pore-fluid flow on the rock alteration, which is the direct consequence of mineral redistribution due to its dissolution, transportation and precipitation, within the three-dimensional fluid-saturated geological fault zone system. (c) 2005 Elsevier B.V. All rights reserved.

Distribution of lymph nodes in the mesorectum: how deep is TME necessary?

Background Standardization of total mesorectal excision (TME) had a great impact on decreasing local recurrence rates for the treatment of rectal cancer. However, exact numbers and distribution of lymph nodes (LN) along the mesorectum remains controversial with some studies suggesting that few LNs are present in the distal third of the mesorectum. Methods Eighteen fresh cadavers without a history of rectal cancer were studied. The rectum was removed by TME and then was divided into right lateral, posterior and left lateral sides, which were further subdivided into 3 levels (upper, middle and lower). A pathologist determined the number and sizes of the LNs in each of the nine areas, b linded to their anatomical origin. Results Overall, the mesorectum had a mean of 5.7 LNs (SD=3.7) and on average each LN had a maximum diameter of 3.0 mm (SD=2.7). There was no association between the mean number or size of LNs with gender, BMI, or age. There was a significantly higher prevalence of LNs in the posterior location (2.8 per mesorectum) than in the two lateral locations (0.8 and 1.2 per mesorectum; p=0.02). The distribution of LNs in the three levels of the rectum was not significant. Conclusions The distribution of LNs reinforces the fact that TME should always include the distal third of the mesorectum. Care must be taken to not violate the posterior aspect of the mesorectum.

Tubular eyes of deep-sea fishes: A comparative study of retinal topography

The world's deep oceans are home to a number of teleosts with asymmetrical or tubular eyes. These immobile eyes possess large spherical lenses and subtend a large binocular visual field directed either dorsally or rostrally. Derived from a lateral non-tubular eye, the tubular eye is comprised of a thick main retina, subserving the rostrally or dorsally directed binocular visual field, and a thin accessory retina subserving, the lateral, monocular visual field. The main retina is thought to receive a focussed image, while the accessory retina is too close to the lens for a focussed image to be received. Several species also possess retinal diverticula, which are small evaginations of differentiated retina located in the rostrolateral wall of the eye and thought to increase the visual field. In order to investigate the spatial resolving power of these retinae (main, accessory and diverticulum), the distribution of cells within the ganglion cell layer was analysed from retinal wholemounts and sectioned material in ten species representing four genera. In all species, the main retina possesses a marked increase in cell density towards a specialised retinal region (area centralis), with a centro-peripheral gradient range between 7.1 and 60:1 and a peak density range of between 30 and 55 x 10(3) cells per mm(2). The accessory retinae and the transitional zone between the main and accessory retinae possess relatively low cell densities (between 1 and 10 x 10(3) cells per mm(2)) and lack an area centralis. Retinal diverticula examined in four species possess mean ganglion cell densities of between 7.2 and 109.4 x 10(3) cells per mm(2). Analyses of soma areas show that the ganglion cell layer of most species possesses cells with areas in a range of 8.0 to 15.4 mu m(2) in the main retina and between 15.1 and 17.4 mu m(2) in the accessory retina. The peak spatial resolving power of the main retina of the ten species varies from 4.1 to 9.1 cycles per degree. The positions of the retinal areae centrales relative to each species' binocular visual field are discussed in relation to what is known of feeding behaviour of these fishes in the deep-sea.