Prolonged Periods Of Exposure Research Articles

Topical Thymidine Dinucleotide Treatment Reduces Development of Ultraviolet-Induced Basal Cell Carcinoma in Ptch-1+/− Mice

Treatment with thymidine dinucleotide (pTT) has well documented DNA-protective effects and reduces development of squamous cell carcinoma in UV-irradiated mice. The preventive effect of pTT on basal cell carcinoma (BCC) was evaluated in UV-irradiated Ptch-1(+/-) mice, a model of the human disease Gorlin syndrome. Topical pTT treatment significantly reduced the number and size (P < 0.001) of BCCs in murine skin after 7 months of chronic irradiation. Skin biopsies collected 24 hours after the final UV exposure showed that pTT reduced the number of nuclei positive for cyclobutane pyrimidine dimers by 40% (P < 0.0002) and for 8-hydroxy-2'-deoxyguanosine by 61% (P < 0.01 compared with vehicle control). Immunostaining with an antibody specific for mutated p53 revealed 63% fewer positive patches in BCCs of pTT-treated mice compared with controls (P < 0.01), and the number of Ki-67-positive cells was decreased by 56% (P < 0.01) in pTT-treated tumor-free epidermis and by 76% (P < 0.001) in BCC tumor nests (P < 0.001). Terminal dUTP nick-end labeling staining revealed a 213% increase (P < 0.04) in the number of apoptotic cells in BCCs of pTT-treated mice. Cox-2 immunostaining was decreased by 80% in tumor-free epidermis of pTT-treated mice compared with controls (P < 0.01). We conclude that topical pTT treatment during a prolonged period of intermittent UV exposure decreases the number and size of UV-induced BCCs through several anti-cancer mechanisms.

Group interpersonal therapy reduces depression in adolescent survivors of war

<h3>Abstract</h3> Macrophages are highly dynamic innate immune cells that adopt temporary phenotypes, known as polarization states, in response to changing environmental signals to combat microbial infection and contribute to the...

DoesLitomosoides sigmodontissynthesize dimethylethanolamine from choline?

Juvenile female Litomosoides sigmodontis secrete a protein (Juv-p120) highly modified with dimethylethanolamine (DMAE). In an attempt to establish the source of this decoration worms were pulsed with [3H]-choline and [3H]-ethanolamine and the radio-isotope labelled products analysed. Both isotope labels were successfully taken up by the worms, as demonstrated by labelling of phospholipids with [3H]-choline, being predominantly incorporated into phosphatidylcholine and [3H]-ethanolamine into phosphatidylethanolamine. Isotope labelling of phosphatidylethanolamine was particularly striking with the worms taking up approximately 30 times as much labelled ethanolamine as choline. It was possible to detect faint labelling of Juv-p120 with [3H]-ethanolamine after prolonged exposure periods but, unlike the situation with the phospholipids, it was much more readily labelled with [3H]-choline. When pulsing with [3H]-ethanolamine it was also possible to detect isotope-labelled phosphatidylcholine, which may ultimately account for the low levels of labelling of Juv-p120. Overall our results raise the previously unconsidered but intriguing possibility that in L. sigmodontis, choline may be the precursor of DMAE.

Rapid increase in the partial pressure of NH3 on the cutaneous surface of air-exposed mangrove killifish,Rivulus marmoratus

Mangrove killifish, Rivulus marmoratus, are tolerant of prolonged periods of air exposure (>30 days). Air-exposed R. marmoratus eliminate more than 40% of their total ammonia through NH(3) volatilization; however, the sites and mechanisms are unclear. We hypothesized that the cutaneous surface is an important site of NH(3) volatilization in air-exposed R. marmoratus. Ion-selective microelectrodes were used to measure the NH(4)(+) concentration and pH in the boundary layer on the cutaneous surface of fish in water or air (acute: 1 h, chronic: 11 days). Following acute and chronic air exposure, there was a approximately 18-fold increase in the NH(4)(+) concentration and a 0.3-0.6 pH unit increase on the cutaneous surface of R. marmoratus. In air-exposed fish, the calculated cutaneous partial pressure (P(NH(3))) was 608-1,251 microTorr, representing a 33- to 75-fold increase over control (immersed) fish. The P(NH(3)) on the cutaneous surface water film was more than sufficient to account for the rate of NH(3) volatilization under terrestrial conditions. Together, these data indicate that during air exposure, R. marmoratus utilize the cutaneous surface as a key site of NH(3) volatilization.

Regulation of the Cardiorespiratory System of Common Carp (Cyprinus carpio) during Severe Hypoxia at Three Seasonal Acclimation Temperatures

Little is known of the cardiorespiratory control mechanisms utilized by hypoxia-tolerant teleost fish to tolerate prolonged periods (h) of near anoxic exposure. Here, we report on the cardiorespiratory control mechanisms of the common carp Cyprinus carpio L. during normoxia and prolonged, severe hypoxic (<0.3 mg O(2) L(-1)) exposure at acclimation temperatures of 5 degrees C, 10 degrees C, and 15 degrees C. Through serial intra-arterial injections of alpha - and beta -adrenergic, cholinergic, and purinergic antagonists while measuring cardiac output (Q), heart rate (f(H)), ventral aortic blood pressure, and respiration rate, we established that autonomic cardiovascular and respiratory control was preserved during severe hypoxia at all three acclimation temperatures and contributed to downregulation of cardiorespiratory activity. Specifically, inhibitory cholinergic tone mediated up to 76% reductions in f(H) and Q during hypoxia, whereas the accompanying arterial hypotension was attenuated by an upregulation of an alpha -adrenergically mediated peripheral vasoconstriction. Despite the overall cardiac downregulation, a large, stimulatory cardiac beta -adrenergic tone was present during prolonged, severe hypoxia, possibly to protect the heart from attendant acidotic conditions. Purinergic blockade, following alpha -adrenergic and cholinergic antagonists, showed that the hypoxic ventilatory depression, which reversed the 2.3- to 7.7-fold increases in respiration rate that occurred with the onset of hypoxia, was a result of purinergic inhibition at all three acclimation temperatures. In contrast, purinergic inhibition of cardiac activity during hypoxia might be important only at 5 degrees C. Finally, given that cardiac power output was reduced 72%-87% during prolonged, severe hypoxia and that glycolysis yields approximately 94% less ATP per mole glucose than oxidative phosphorylation, it seems unlikely that the common carp sufficiently reduces its cardiac energy demand to a level to preclude activation of a partial Pasteur effect. This means that glycogen stores will be used and waste products will accumulate at faster rates, a finding that may help explain why the common carp cannot tolerate such extended periods of severe hypoxia (weeks to months) at cold acclimation temperatures as the freshwater turtle, which is able to reduce its cardiac energy demand to a level that does not require a Pasteur effect and also blunts autonomic cardiovascular control.

What's in a beach? Soil micromorphology of sediments from the Lower Paleolithic site of ‘Ubeidiya, Israel

A micromorphological study of archaeological sediments from the early Pleistocene site of ‘Ubeidiya (Jordan Valley, Israel) was conducted to provide microenvironmental detail for the hominin occupation contexts and investigate site formation issues. Previous research shows that the hominin groups occupied the marshes and pebbly beaches at the shores of a lake during a regressive period, but given that some portions of the lithic and faunal assemblages are abraded and others fresh, there remains a question of whether the archaeological assemblages are in situ or reworked, and if reworked, by what mechanisms and from where. The rates of sedimentation within the regressive cycle, by which we can learn about the frequency and duration of exposed surfaces amenable for hominin occupation is also unknown. Finally, the artificial nature of some of the pebbly layers has been questioned. The micromorphological analysis yielded the identification of twelve microfacies; the majority of these represent fluvially derived floodplain soils or distal mudflow deposits, and a minor number are sediments of lacustrine origin: mudflats and shallow subaqueous sediments. These represent the natural habitats of the ‘Ubeidiya hominins and might serve as a reference to similar contexts of other early hominin sites. The sedimentary model proposed here entails the rapid deposition of fluvially derived low-energy sediments at and around the shoreline, followed by prolonged periods of exposure, during which surfaces stabilized within a relatively wet, marshy environment. This interpretation suggests that the abraded portions of the archaeological assemblages are a result of prolonged surface exposure rather than high-energy transport from a distant source or to wave reworking at the shoreline, and supports the consideration of these assemblages as archaeological palimpsests, with locally reworked fresh and abraded elements. No micromorphological evidence supporting anthropogenic agency in the formation of the pebbly layers was found. The entire regressive cycle entailed unvarying climatic conditions with seasonal fluctuations and episodic lacustrine incursions, and with a trend towards arid conditions in the end.

Study of ageing of adhesive bonds with various surface treatments: Part VI. Dicyandiamide-cured epoxy joints aged at 70°C in a water bath

Adhesive-bonded aluminium/dicyandiamide-cured epoxy joints prepared using two different surface treatments, a silica/siloxane and an etched only process, were exposed at 70°C to moisture and their ageing behaviour was studied using broadband dielectric spectroscopy and destructive mechanical tests. The dielectric measurements allow the uptake of moisture and changes in the nature of the surface oxide and pre-treatment to be monitored. Both sets of joints exhibited almost similar changes in their dielectric spectra as a function of exposure time to moisture; small differences being attributed to the influence of the pre-treatment on the moisture absorption behaviour. Changes in the mechanical properties as a result of exposure to moisture were monitored via lap-shear tests. Detailed electron microscopic examination of the surfaces indicated that after prolonged exposure to moisture changes in the physical state of the pre-treatment and oxide layer were observed. Small differences were observed in the dielectric data between the two pre-treatments and are a consequence of the differences in the extent and nature of the oxide to hydroxide conversion and hydration of the surface treatment which occurs on exposure to moisture. Further evidence for the nature of the change that occurred was obtained using X-ray photoelectron spectroscopy of the fracture surfaces. One side of the fractured joint was predominantly resin irrespective of the exposure conditions. The other fracture surface had a more metallic appearance but was covered by a nitrogen-containing organic material with high oxygen content. Predominantly, the initial changes observed in the mechanical strength of the joints are consistent with the plasticization of the adhesive in the joint. The effects observed after prolonged period of exposure to moisture are consistent with an increased contribution from inter-facial failure to the loss of the mechanical properties. The losses in mechanical properties are less dramatic than would be anticipated considering the mild nature of the surface treatments used and the severity of the exposure conditions.

Morbidity and mortality in Norway lobsters, Nephrops norvegicus: physiological, immunological and pathological effects of aerial exposure

A multivariate approach has been used to study progression in the post-capture condition of trawl-caught Nephrops norvegicus destined for the live transport market. A range of biochemical (L-lactate, glucose, glycogen), endocrinological (crustacean hyperglycaemic hormone), immunological (total haemocyte counts, phenoloxidase), microbiological and pathological measures of condition were utilised. During prolonged periods of aerial exposure N. norvegicus experience large disruptions to the carbohydrate profile, with increases in haemolymph L-lactate and crustacean hyperglycaemic hormone concentrations, and corresponding fluctuations in haemolymph pH; the severity of this disruption increases with the temperature of aerial exposure. This in turn impacts on the immune competence of the lobsters, with significant reductions in the number of circulating haemocytes and phenoloxidase levels observed as well as increases in the degree of bacteraemia of the haemolymph. Utilising evidence obtained during histological and other studies, possible causes of the immuno-suppression and subsequent meat spoilage are discussed. The information obtained should help to identify critical periods in the post-capture period that promote poor stock condition and mortality. Such data may be used to generate an internationally accepted Code of Practice for the capture, handling and transport of commercially exploited decapod crustaceans.

Altered expression of connexin43 in the inhibition of gap junctional intercellular communication by chlorohydroxyfuranones in WB-F344 rat liver epithelial cells

3-Chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX), 3,4-dichloro-5-hydroxy-2(5H)-furanone (MCA), and 3-chloro-4-methyl-5-hydroxy-2(5H)-furanone (MCF) promote foci formation in the two-stage cell transformation assay in vitro. These chlorohydroxyfuranones (CHFs) and their structural congener 3-chloro-4-(chloromethyl)-5-hydroxy-2(5H)-furanone (CMCF) inhibit gap junctional intercellular communication (GJIC) in Balb/c 3T3 mouse fibroblast cells. In the present study, the effects of MX, MCA, CMCF, and MCF on GJIC were evaluated in liver cells (WB-F344 rat liver epithelial cells), the target cells of MX-induced carcinogenicity, using the scrape-loading dye transfer technique. The CHFs inhibited GJIC after 1 h exposure in a concentration-dependent fashion. The order of potency was MX>CMCF approximately MCA>MCF. In terms of the lowest observed effective concentrations, the difference in the potency was about 27-fold (MX 1.875 microM, MCF 50 microM). After a prolonged exposure period (12 h), the inhibition of GJIC by MX and CMCF remained stable, but MCA and MCF exhibited increasing inhibitory effects. After removal of the CHFs, the GJIC slowly recovered. At the transcriptional level, CHFs caused essentially no change in the level of connexin43 (Cx43) mRNA. Preincubation of cells with the protein kinase C (PKC) inhibitor did not modify the response, but the specific MEK 1 inhibitor PD98059 decreased substantially the inhibition of GJIC by all four CHFs. Activation of the mitogen-activated protein kinases (MAPKs) signaling pathway was necessary for inhibition of GJIC. CHFs did not increase the basal phosphorylation state of the Cx43 protein, but all CHFs caused a concentration-dependent degradation of the Cx43 protein. The results indicate that all the studied CHFs inhibit GJIC in WB-F344 cells by altering Cx43 expression.

Mechanism of action of ethanol in the down-regulation of Gal β1, 4GlcNAc α2,6-sialyltransferase messenger RNA in human liver cell lines

Gal βl, 4GlcNAc α2,6-sialyltransferase (2,6-ST) mediates the addition of α2,6-linked sialic acid to glycoproteins in the Golgi compartment. Down-regulation of its gene and consequent impaired activity of 2,6-ST seems to be the major cause for the appearance of asialoconjugates in the blood of long-term alcoholics. Therefore, mechanism(s) involved in the regulation of 2,6-ST gene is important and clinically relevant. Our previous work showed that long-term ethanol feeding in rats caused a marked 59% decrease of 2,6-ST activity as well as 2,6-ST messenger RNA (mRNA) level in liver that were due to the decreased stability of its mRNA. We now mimic these actions of ethanol using ( a) human liver HepG2 cells stably transfected with ethanol-inducible human cytochrome P4502E1 (CYP2E1 cells), or ( b) with high alcohol dehydrogenase (HAD cells) but not in wild-type HepG2 cells lacking either of the above 2 enzymes as models. Incubation of these cells for 72 hours with 100 mmol/L ethanol caused decreases (up to 76%, P < .05) of 2,6-ST mRNA levels in CYP2E1 and HAD cells but not in the wild type. However, incubation of wild-type cells with acetaldehyde at concentrations of 50 and 100 μmol/L showed a dramatic decrease (up to 69%, P < .02) in the 2,6-ST mRNA levels. Furthermore, exposure of CYP2E1 cells to 4-hydroxy-2-nonenal, an endogenous lipid peroxidation product of reactive oxygen species, strongly decreased 2,6-ST mRNA level by 61% ( P < .02). These results demonstrate that 2,6-ST gene is highly sensitive to ethanol action in human liver cells either via its oxidation product, acetaldehyde, or via reactive oxygen species leading to the generation of a more reactive aldehyde such as 4-hydroxy-2-nonenal. Thus, this study assumes major importance and clinical relevance because 2,6-ST gene regulation in a human liver cell model is demonstrated within a few days of ethanol exposure, whereas its in vivo regulation in liver generally takes prolonged period of ethanol exposure.

Anesthetic agents and the immature brain: are these toxic or therapeutic?

Anesthetic agents and the immature brain: are these toxic or therapeutic?

Potent inhibition of gap junctional intercellular communication by 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5 H)-furanone (MX) in BALB/c 3T3 cells

The chlorohydroxyfuranones (CHFs) MX [3-chloro-4-(dichloromethyl)-5-hydroxy-2(5 H)-furanone], MCA [3,4-dichloro-5-hydroxy-2(5 H)-furanone], CMCF [3-chloro-4-(chloromethyl)-5-hydroxy-2(5 H)-furanone], and MCF [3-chloro-4-methyl-5-hydroxy-2(5 H)-furanone] are genotoxic disinfection by-products of drinking water chlorination. MX, MCA, and MCF also promote foci formation in the two-stage cell transformation assay. The cellular mechanisms underlying this apparent promotional effect are not known. In the present study, the effects of MX, MCA, CMCF, and MCF on gap junctional intercellular communication (GJIC) were measured in BALB/c 3T3 cells using the scrape loading dye technique. The effect of MX on apoptosis in the same cell line was explored by assaying caspase-3-like protease activity. All the four CHFs inhibited GJIC after 30 min exposure in a dose-dependent fashion but there was a marked difference in the ranges of their active concentrations. MX was almost as potent an inhibitor of GJIC (inhibition at nanomolar concentrations) as 12- O-tetradecanoylphorbol-13-acetate (TPA) (positive control), while MCA was 10 times weaker, CMCF 10,000 times weaker, and MCF 20,000 times weaker than MX. After prolonged exposure periods (up to 6 h), GJIC recovered somewhat upon MX and MCA exposures, the inhibition of GJIC by MCF remained constant but CMCF showed an irreversible increasing inhibitory effect. MX caused apoptosis as a “window” effect at concentrations 2000–4000-fold higher than those needed to inhibit GJIC. The results indicate that MX is a potent inhibitor of GJIC in BALB/c 3T3 cells and this inhibition might be one mechanism by which MX can promote malignant foci formation. MCA also has a specific potential to inhibit GJIC whereas MCF and CMCF affected GJIC at concentrations, similar to those evoking genotoxicity in vitro.

Palmar-plantar erythrodysesthesia

Objective. To provide a comprehensive review of the chemotherapy induced dermatological toxi-city, palmar-plantar erythrodysesthesia (PPE), including clinical presentation, drugs implication in causing the reaction, and approaches for management. Data sources. A search of MEDLINE (1966-2002), IDIS (1985- 2002) and CANCERLIT (1993-2002) databases was conducted using the terms (and variations of the terms) palmar-plantar erythrodysesthesia, hand-foot syndrome, and acral erythema. Bibliographies from selected articles were also reviewed for appropriate references. Data extraction. The retrieved literature was reviewed to include all articles pertaining to the incidence, clinical presentation, mechanism, pathology, diagnosis, treatment and prevention of PPE. Data synthesis. PPE is a distinctive, localized cutaneous reaction to certain antineoplastic agents. A number of drugs have been implicated, including most commonly cytarabine, fluorouracil, doxorubicin, and capecitabine. There appears to be an association with administration schedules that lead to elevated peak plasma concentrations, such as in high-dose therapy, or after prolonged periods of constant exposure, as with continuous infusions, regular oral dosing, or liposomal formulations. The extent and severity of the reaction, time of onset, and duration are variable. Symptoms can occur to both hands and feet, and include dysesthesia, paresthesia, erythema, swelling, pain, blistering, ulceration, and desquamination. Cessation of the offending agent appears to be the most important step in the management of PPE. Dose modification may be necessary for subsequent cycles. As the course of PPE is self-limiting, treatment is commonly supportive and based on the type and severity of symptoms encountered. This can include analgesia, emollient or soothing creams, wound care, and cold compresses. Administration of corticosteroids has produced mixed results. Pyridoxine shows promise as both a treatment and preventative strategy, although confirmation in prospective clinical trials is needed. Advice should be provided to patients to ensure prompt recognition of toxicity and plans for prevention and amelioration of symptoms provided.

Cardiovascular deconditioning in microgravity: some possible countermeasures.

Microgravity is an extreme environment inducing relevant adaptive changes in the human body, especially after prolonged periods of exposure. Since the early sixties, numerous studies on the effects of microgravity, during manned Space flights, have produced an increasing amount of information concerning its physiological effects, globally defined "deconditioning". Microgravity deconditioning of the cardiovascular system (CVD) is briefly reviewed. It consists of: (1) a decrease of circulating blood and interstitial fluid volumes, (2) a decrease of arterial blood diastolic pressure, (3) a decrease of ventricular stroke volume, (4) a decrease of the estimated left ventricular mass and (5) resetting of the carotid baroreceptors. The negative effects of microgravity deconditioning manifest themselves mostly upon the reentry to Earth. They consist mainly of: (1) dizziness, (2) increased heart rate and heart palpitations, (3) an inability to assume the standing position (orthostatic intolerance), (4) pre-syncopal feelings due to postural stress and (5) reduced exercise capacity. To avoid these drawbacks several countermeasures have been proposed; they will be briefly mentioned with emphasis on the "Twin Bikes System" (TBS). This consists of two coupled bicycles operated by astronauts and counter-rotating along the inner wall of a cylindrical Space module, thus generating a centrifugal force vector, mimicking gravity.

Arrestin migrates in photoreceptors in response to light: a study of arrestin localization using an arrestin-GFP fusion protein in transgenic frogs

Subcellular translocation of phototransduction proteins in response to light has previously been detected by immunocytochemistry. This movement is consistent with the hypothesis that migration is part of a basic cellular mechanism regulating photoreceptor sensitivity. In order to monitor the putative migration of arrestin in response to light, we expressed a functional fusion between the signal transduction protein arrestin and green fluorescent protein (GFP) in rod photoreceptors of transgenic Xenopus laevis. In addition to confirming reports that arrestin is translocated, this alternative approach generated unique observations, raising new questions regarding the nature and time scale of migration. Confocal fluorescence microscopy was performed on fixed frozen retinal sections from tadpoles exposed to three different lighting conditions. A consistent pattern of localization emerged in each case. During early light exposure, arrestin-GFP levels diminished in the inner segments (ISs) and simultaneously increased in the outer segments (OSs), initially at the base and eventually at the distal tips as time progressed. Arrestin-GFP reached the distal tips of the photoreceptors by 45–75 min at which time the ratio of arrestin-GFP fluorescence in the OSs compared to the ISs was maximal. When dark-adaptation was initiated after 45 min of light exposure, arrestin-GFP rapidly re-localized to the ISs and axoneme within 30 min. Curiously, prolonged periods of light exposure also resulted in re-localization of arrestin-GFP. Between 150 and 240 min of light adaptation the arrestin-GFP in the ROS gradually declined until the pattern of arrestin-GFP localization was indistinguishable from that of dark-adapted photoreceptors. This distribution pattern was observed over a wide range of lighting intensity (25–2700 lux). Immunocytochemical analysis of arrestin in wild-type Xenopus retinas gave similar results.

Sperm motion characteristics of Garole rams raised for a prolonged period in a semi-arid tropical environment.

The Garole is a prolific but less well known and rare breed of small sheep found in the hot and humid Sunderban region of West Bengal. An ability to breed throughout the year and to graze in knee-deep water, resistance to foot rot and a strong mothering instinct are some of the special features of this breed. Garole rams could provide germplasm to incorporate prolificacy traits by artificial insemination of the nonprolific sheep breeds found in abundance in the semi-arid and arid tropical climates of India. The aim of the present study was to evaluate the semen production by Garole rams maintained in a semi-arid climate for three years and to objectively assess their semen quality by a computer-assisted sperm analysis technique. The donor rams were randomly selected each year from the original flock procured from their natural habitat or from the offspring born at the Institute farm. Semen was collected weekly for three weeks each autumn for three consecutive years from 8 rams each year. The overall means (SD) of the traits that did not differ significantly with age or year were volume, concentration, curvilinear velocity, average path velocity, amplitude of lateral head displacement, beat frequency, motility and the percentages of rapid motile sperms and of slow motile sperms. The age of the rams had a significant effect (p<0.05) on the straight-line velocity but this was not significantly affected by the length of exposure to the semi-arid climate. However, the age and year had significant effects (p<0.05) on linearity, straightness and the percentage of medium motile sperms. It was concluded that Garole rams are capable of producing good-quality semen even after a prolonged period of exposure to a semi-arid tropical climate.

High resolution sequence stratigraphic architecture of a transgressive coastal succession: Albian Bow Island Formation, southwestern Alberta

ABSTRACT We here present the first detailed published sequence stratigraphic study of the Lower Cretaceous Bow Island Formation. Two orders of sequences are identified, based on the integration of sedimentology, micropaleontology, ichnology and petrophysical characteristics. The studied interval encompasses two lower-order sequences. Shelf, shoreface, and coastal plain deposits of the lower and middle members of the Bow Island Formation form the transgressive and highstand systems tracts of the basal sequence. A major relative sea level fall caused a prolonged period of sub-aerial exposure and weathering of the deposits of the middle member of the Bow Island Formation, and farther to the east and northeast, incision of deep valleys into shoreface deposits of the Viking Formation. An overlying complex succession of tidal flat, estuarine, shoreface, and shelf deposits of the upper member of the Bow Island Formation and marine shales of the Westgate Formation represent the transgressive systems tract of the younger low-order sequence. Within the transgressive succession of the upper member of the Bow Island Formation and Westgate Formation, five higher-order sequences are identified. The high-order sequence boundaries are marked by basinward shifts of facies, incision of up to 15 m deep valleys and soil development on intervalley areas. This demonstrates that this period of overall sea level rise was punctuated by relative sea level falls, justifying subdivision into sequences rather than parasequences. Transgressive surfaces, often developed as prominent, pebble-mantled ravinement surfaces, subdivide the individual highorder sequences into lower and upper units. The lower units are comprised of tidal influenced incised valley fill, forming the main reservoirs, and tidal and storm influenced back-barrier lagoons deposited during lowstand and early transgressive periods. Foraminiferal assemblages were critical in distinguishing between these lagoonal deposits and open marine shoreface deposits. Deposits of the basal part of the upper units are characterized by a stepwise change towards more open marine conditions following each transgression, from marginal marine tidal flat and lagoonal deposits to shoreface and finally to shelf deposits of the Westgate Formation. This demonstrates the stacking in a retrogradational sequence set of the high-order sequences of the upper member of the Bow Island Formation and Westgate Formation. Erosion associated with the transgressions increases upward in intensity with each successive transgression with the greatest depth of erosion associated with the Westgate transgression. This reflects an upward increase in energy regime of the sedimentary environments that bypassed the area during the transgression. Within the overall transgressive upper member of the Bow Island Formation, an upward increase in the depth of incised valleys with each successive incision event likely reflects an upward increase in depositional relief due to the development of more open marine conditions and to the retrogradational and aggradational character of the upper member of the Bow Island Formation. The Westgate transgressive surface is a complex ravinement surface characterized by a westward, stepwise rise, indicating that it was formed during a period of gradual relative sea level rise, interrupted by phases of more rapid sea level rise. Establishment of this high-resolution sequence stratigraphic framework allows differentiation between these various generations of incision and thereby the mapping of the individual valleys and reservoirs associated with them. * Current address: Petroleum Geology, Saskatchewan Industry and Resources, 201 Dewdney Ave East, Regina, SK, Canada, S4N 4G3; E-mail: ppedersen@ir.gov.sk.ca End_Page 441------------------------

Short-term assay for the identification of neurotoxic compounds and their liver derived stable metabolites

The release of stable neurotoxic metabolites from liver after metabolic activation of xenobiotics can be investigated in cultures of primary rat hepatocytes as metabolic activation system and embryonic chicken brain cell cultures as target. It was shown that adult rat hepatocyte cell cultures are a reliable bioactivating system for xenobiotics such as cyclophosphamide and isophenphos resulting in the release of stable metabolites into the supernatant. The cultured embryonic chicken brain cells were able to discriminate between the toxicity of parent drugs and its metabolite(s) and between metabolites with an unspecific cytotoxic activity (cyclophosphamide) and metabolites with a high potential to damage specific nerve cell population(s) (isophenphos). The observed neurotoxicity of the isophenphos metabolites is not an acute effect but induced only after a prolonged exposure period. The present study provides evidence that the subsequent use of hepatocytes and brain cell cultures has the potential to be used as an in vitro screening system for the identification of specific and non-specific neurotoxic compounds. Solely stable metabolites are taken into account, since in the in vivo situation only stable metabolites have a change to reach the nervous system. Our data suggest that the present approach is able to discriminate (a) between cell-type and organ specific toxicity, (b) between neurotoxicity derived after long-term or acute exposure, and (c) between the neurotoxicity induced by the native test compound or stable metabolites.

Indirect Measurement of Biologically Important Compounds by Means of X-Ray Microanalysis

The main objective of our work was to investigate the possibility and usefulness of indirect methods in X-ray microanalysis for the quantification of biologically important compounds. Metallothionein-like proteins (MT-like proteins) from kidney and liver, rich in sulfur were chosen as an indicator of heavy metal presence in cells and their environment. Tissues from goldfish (Carassius auratus gibelio) were sampled after short and prolonged periods of exposure to Co+2, CrO4−2, Pb+2, Cu+2 and control treatment and prepared for histochemical staining for peroxidated thiolate groups. Commonly used –S–S– bonds dye (Nitro Red) was replaced with iodine atoms and they were quantified at L line by means of X-ray microanalysis combined with SEM. After fish treatments with heavy metal solutions changes in MT-like proteins and in I atom contents were expected. There was statistically significant decrease in MT-like proteins level in kidney after lead treatment (Pb/C = 0.62). In liver a statistically significant increase in MT-like proteins concentration was observed after chromium, cobalt and lead ions treatment in comparison to control animals. The following ratios were noted: 3.04 for Cr/C, 2.18 for Co/C and 2.10 for Pb/C. Our finding indicates that the method of indirect measurement of MT-like proteins in fish and other animal tissues is possible. The concentration of iodine atoms is above their detection level by EDS and their changes are possible to identify. During histochemical procedures it is worth taking into account sample preparation methods which might disturb the quality and quantity of the analysed material.

Seasonal variations in the rates of aquatic and aerial respiration and ammonium excretion of the ribbed mussel, Geukensia demissa (Dillwyn)

Aquatic and aerial rates of oxygen consumption and ammonium excretion of ribbed mussels, Geukensia demissa (Dillwyn), collected from the mid-intertidal zone of a mid-Atlantic salt marsh, were measured under ambient conditions of food, temperature, and salinity over five seasons. Rates of aquatic respiration covaried with body size and season, as the rates were high and strongly related to mussel tissue weight in spring and summer but low and weight independent in winter. There was a significant interannual difference between summer of 1995 and 1996. Rates of aerial respiration also varied seasonally, with high rates of oxygen consumption in summer and low rates in winter. The magnitude of these seasonal variations were greater than those for aquatic respiration, and as a result, the ratio of aerial to aquatic respiration was higher in summer (0.61 and 0.52) than in winter (0.11). This indicates that G. demissa was able to actively regulate aerial respiration, thereby permitting high aerobic metabolism during prolonged periods of air exposure in summer. We hypothesize that such high rates of aerial respiration, during the seasons of high metabolic activity, are required to provide sufficient energy for mussels to facilitate food digestion during air exposure at low tide. Rates of ammonium excretion varied seasonally and increased with mussel weight in all seasons. The atomic ratio of oxygen to nitrogen (O:N), calculated from aquatic respiration vs. ammonium excretion, was significantly lower in autumn (26) than in other seasons (46–60) among which the O:N did not vary significantly.