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Biomedical subjects

W A Dunson

Publications and source records attributed to W A Dunson.

At least 19 recordsLinked to original sources
PubMed2006

Early pathologic findings and long-term improvement in anti-Ma2-associated encephalitis.

A 67-year-old man sequentially developed anti-Ma2-associated paraneoplastic encephalitis (PNE) and contralateral herpes simplex encephalitis (HSE). Brain biopsy 1 month before HSE revealed extensive infiltrates of T cells, B cells, and plasma cells. Most T cells expressed the cytotoxic granule-associated protein TIA-1 and the membranolytic protein granzyme-B. Although recovery was thought to be unlikely, treatment of the PNE with corticosteroids and resection of the associated lung cancer resulted in dramatic improvement for 21 months.

Aged↗
PubMed2000

Effects of spray-irrigated wastewater effluent on temporary pond-breeding amphibians.

Comparison was made of abiotic conditions, amphibian reproductive outputs, and the survival of embryonic and larval amphibians in wastewater effluent-irrigated and natural temporary ponds in an area in Centre County, Pennsylvania that has been spray-irrigated with secondarily treated, chlorinated wastewater effluent from The Pennsylvania State University for approximately 14 years. Three species of temporary pond-breeding amphibians were studied: wood frogs (Rana sylvatica LeConte), Jefferson salamanders (Ambystoma jeffersonianum Green), and spotted salamanders (A. maculatum Gravenhorst). Comparisons of physico-chemical parameters in 10 wastewater-irrigated and 10 natural temporary ponds over 19 weeks in 1997 indicated that wastewater -irrigated ponds had significantly higher median conductance, pH, ¿Na, ¿K, ¿Ca, ¿Mg, and ¿N-NO(3) and lower ¿dissolved oxygen. Many of the wastewater-irrigated ponds supported large mats of duckweed (Lemna spp.) that completely blanketed the pond's surface by mid-May. There were significantly fewer egg masses of all three species in wastewater-irrigated ponds than in natural ponds in both 1997 and 1998. In situ egg hatching success and larval survival (over a 6-day period) of all species was lower in wastewater-irrigated ponds than in natural ponds. Cumulatively, these studies suggest that wastewater effluent irrigation may impact amphibian populations by reducing the survival of amphibian eggs and larvae.

Ambystoma↗
PubMed1998

Effects of boron and nitrate on hatching success of amphibian eggs.

As part of a land-application wastewater disposal system in central Pennsylvania, vernal ponds are commonly exposed to wastewater effluent containing high levels of boron and nitrate. We examined the individual effects of these compounds on the eggs of amphibians breeding in these ponds. Wood frog (Rana sylvatica), Jefferson salamander (Ambystoma jeffersonianum), spotted salamander (A. maculatum), and American toad (Bufo americanus) eggs were exposed to boron (0, 50, and 100 mg L-1) and nitrate (0, 10, 25, and 40 mg L-1) under laboratory conditions. There was no difference in the hatching success or proportion of deformed larvae among the four nitrate levels in any of the species. High boron concentrations reduced the hatching success of B. americanus and produced more deformed offspring in R. sylvatica, A. jeffersonianum, and A. maculatum. Deformed R. sylvatica and A. jeffersonianum hatchlings displayed a "curling defect" in which the larvae had a crescent body shape and expressed difficulty in swimming. A. maculatum larvae from high boron treatments displayed a different abnormality, possibly because of longer times to hatching, characterized by a swelling of the thoracic region and altered gill morphology. Although the concentrations of boron and nitrate tested were within the range measured in wastewater effluent, maximum levels of boron and nitrate in breeding ponds were only 1.5 mg L-1 and 26.7 mg L-1 respectively, likely due to rainwater dilution and biological and chemical processes reducing the levels of these compounds in vernal ponds. Nonetheless, these studies are the first to examine the effects of boron and nitrate on amphibian egg hatching success, and to demonstrate that elevated boron concentrations can detrimentally affect the development of amphibian embryos.

Amphibians↗
PubMed1998

Effects of sodium concentration on Aedes triseriatus (Diptera: Culicidae) and microorganisms in treeholes.

A 2-factor field microcosm experiment with 2 concentrations of sodium ([Na]) was performed with and without mosquitoes to test the hypothesis that Na is a limiting nutrient for the treehole mosquito, Aedes triseriatus (Say), at concentrations observed in the field. This experiment also tested the effects of both water [Na] and mosquito larvae on cohabiting treehole microorganisms. Female Ae. triseriatus emerging from microcosms with high-[Na] were significantly larger than females emerging from low-[Na] microcosms. There was no effect of [Na] on the size of males; however, males had higher body [Na] than females at both [Na]. Densities of protozoans were lower in the presence of mosquitoes, and densities of bacteria were lower at high than low [Na]. Water [Na] may affect mosquito populations by decreasing energy expenditures to obtain Na at higher [Na], allowing for more allocation to growth. Males were not affected by the [Na]s tested here. This experiment agrees with field observations and other laboratory studies indicating that [Na] may affect populations of Ae. triseriatus under certain conditions.

Aedes↗
PubMed1997

Effects of pH and sulfate on insects and protozoans inhabiting treeholes.

We used laboratory microcosms designed to simulate treeholes to study the effect of changing levels of chemicals found in precipitation in central Pennsylvania (H+ and SO4=) on the treehole insects Aedes triseriatus (a mosquito), Helodes pulchella (a helodid beetle), and Culicoides guttipennis (a ceratopogonid midge), and treehole protozoans. Protozoans were tested in both the presence and absence of insects. We hypothesized that the individual insect species would have differential tolerances to abiotic stresses, and that effects of low pH on protozoans would be especially strong. Survival of helodids was higher than mosquitoes and midges. Emergence and survival of mosquitoes and midges were lower at low pH. Densities of ciliates increased the most at high pH in the absence of insects. Densities of flagellates increased the most at low pH in the absence of insects. The presence of helodids, mosquitoes, and protozoans was associated with higher final [SO4=], as was low pH. Mosquitoes at low pH caused the largest increases in cation concentrations, and protozoans at high pH caused the largest decreases in cation concentrations. It appears that the biota of treeholes are affected by ionic changes in simulated tree stemflow that can be caused by anthropogenic atmospheric deposition. The species studied here were sometimes differentially affected by the common pollutants, [H+] and [SO4=]. The resulting changes in these discrete treehole communities may allow them to be useful bioindicators of the status of forest ecosystems altered by changing atmospheric chemistry.

Animals↗
PubMed1995

The interactive effects of low pH, toxic metals, and DOC on a simulated temporary pond community.

The effects of pH, potentially toxic metals, and dissolved organic carbon (DOC) on a freshwater, palustrine wetland assemblage (three amphibian species, one mosquito genus, and 18 genera of algae) were examined in 500 liter outdoor mesocosms. The design was fully factorial and exposure levels were set to represent concentrations that occur naturally in temporary ponds in central Pennsylvania, an acid-impacted region of the USA. Water chemistry was precisely regulated by use of an artificial pond water rather than using stream water or well water with partially unknown composition. Jefferson (Ambystoma jeffersonianum) and spotted salamanders (A. maculatum) were negatively impacted by low pH and high metal concentrations. Wood frogs (Rana sylvatica) were negatively impacted by high DOC and low pH. These negative effects included increased time to metamorphosis and decreased survival and wet body mass at metamorphosis. Mosquito emergence was unaffected by pH, metals, or DOC. All three abiotic factors (metals, pH, and DOC) interacted to determine algal taxonomic composition. Hence, abiotic conditions may determine amphibian reproductive success both directly and indirectly, via effects on algae, since a primary food source of salamanders, zooplankton, are affected by changes in algal composition. These complex interactions should be considered in evaluating the possible toxicity of pond waters to fauna and flora. Until now, pH alone has been considered the primary limiting factor for amphibians breeding in temporary ponds.

Journal Article↗
PubMed1994

Behavioral and physiological responses of the terrestrial life stages of the Jefferson salamander, Ambystoma jeffersonianum, to low soil pH.

Terrestrial metamorphs of the salamander, Ambystoma jeffersonianum, were exposed to four levels of pH on artificial substrates in the laboratory. Short-term exposure (7 d) to pH levels between 3.5 and 5.0 had no effect on total body mass, Na+, K+, Ca2+, and Mg2+ concentrations. However, at 14 d in both laboratory experiments and in field microcosms, whole body water and Na+ concentrations were significantly lower at the lower pH level. Terrestrial metamorphs and adults of the Jefferson salamander preferred artificial substrates that were higher in pH. Ponds not utilized for breeding all had adjacent soil pH below 3.7. Pond water and soil pH were directly and highly correlated. Soil pH may indirectly affect breeding success of Jefferson salamanders by influencing pond pH or directly by physiologically stressing the terrestrial life stages. Laboratory data implicate direct effects on the physiology of terrestrial young of the year salamanders by induction of loss of body water and Na+. Apparently, soil pH is a critical factor not only in the selection of vernal ponds by Jefferson salamander adults for breeding, but in determining the likelihood of reproductive success as judged by recruitment into the adult population.

Ambystoma↗
PubMed1993

The effect of salinity on the acute toxicity of cadmium to the tropical, estuarine, hermaphroditic fish, Rivulus marmoratus: a comparison of Cd, Cu, and Zn tolerance with Fundulus heteroclitus.

The mangrove-dwelling fish, Rivulus marmoratus, is the only vertebrate that is a synchronous, internally self-fertilizing hermaphrodite. This unique reproductive mode yields offspring with little genetic variation, which offers significant advantages for the use of this species in bioassays. We conducted acute (96 h) LC50 tests of Cd toxicity under four different water chemistry conditions, representing fresh water (low [Ca+Mg] and low [Na+K]), 14 ppt sea water simulated with Cl salts (high [Ca+Mg] and high [Na+K]) and two artificial conditions (high [Ca+Mg], low [Na+K] and low [Ca+Mg], high [Na+K]). Two replicates were conducted at different times for each of the four treatments and the results were very reproducible. The mean LC50's as mg total Cd/L were 2.96 (fresh water), 21.12 (high [Ca+Mg], high [Na+K]), 17.86 (high [Ca+Mg], low [Na+K]) and 12.67 (low [Ca+Mg], high [Na+K]). An additional test in 14 ppt sea water (made up from Instant Ocean salts) yielded a 96h LC50 of 24.48 mg Cd/L, and was thus similar to the high [Ca+Mg]-high [Na+K] treatment, despite some differences in anion and cation concentrations. The degree to which [Ca+Mg], [Na+K] and [Cl] interact to determine Cd toxicity is still unclear, although the role of [Cl] is likely to be equal to or greater than that of [Ca+Mg]. When all solutes are high, it is likely that the formation of a Cd complex with Cl (248 mM) leads to the observed reduction in Cd toxicity in comparison with hard fresh water, not the increased divalent [Ca+Mg] levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Effects of acute and chronic acidification on three larval amphibians that breed in temporary ponds.

This study explored the effects of acute (7 days) and chronic (4 months) exposure to pH 4.2 on three species of larval amphibians, Ambystoma jeffersonianum, Ambystoma maculatum, and Rana sylvatica. Acute tests were conducted in 24 impermeable enclosures in three temporary ponds. Total dissolved aluminum was higher in acidified enclosures in comparison with controls (pH 4.2, [Al] approximately 10-30 microM and pH greater than 4.7, [Al] approximately 5-15 microM, respectively). Greater mortality of A. jeffersonianum occurred at pH 4.2 than at pH greater than 4.7, whereas survival of A. maculatum and R. sylvatica were unaffected by pH. Mean wet masses of R. sylvatica were significantly lower at pH 4.2 than at pH greater than 4.7, but mean wet masses of surviving A. jeffersonianum and A. maculatum were not influenced by pH. There were no pH-related differences in body sodium concentration in larval R. sylvatica. Chronic acidification of mesocosms to pH 4.2 ([Al] approximately 16 microM) (controls = pH greater than 6, [Al] approximately 0.1 microM) resulted in total mortality of A. jeffersonianum. Survival of A. maculatum and R. sylvatica were not associated with pH, but survival of A. maculatum was low at both pH levels. Time to metamorphosis was longer for R. sylvatica maintained at pH 4.2, but not for A. maculatum. No differences in wet masses at metamorphosis were observed for R. sylvatica or A. maculatum. These results indicate that short and long term acidification of temporary wetlands could dramatically affect amphibians which rely upon them as breeding sites, either by causing mortality or by decreasing growth rates.

Acid Rain↗
PubMed1991

Use of whole body sodium loss from the fathead minnow (Pimephales promelas) as an indicator of acid and metal toxicity.

The use of an easily measured physiological change as a method of detecting the effect of toxic mine effluent (acidity, heavy metals) on a standard aquatic test organism was examined. Changes in whole body sodium concentration of Pimephales promelas after exposure for eight hours to mine water in the field were assessed as a physiological indicator of acid and metal pollution from coal mines. Static 96-h lethality tests were also performed in the laboratory in water collected from severely acidic (pH 3.49), moderately acidic (pH 4.65) and circumneutral (pH 6.25) mine effluent impacted streams as well as an artificially prepared (reconstituted) water (RMW) at three similar pH's (but lacking potentially toxic metals). This allowed comparison of the two assays in their sensitivity and ability to detect interactions between heavy metals and acidity. Exposure of P. promelas to severely acidic mine water caused the same mortality as exposure to RMW, although in the latter the fish died more rapidly (2 vs. 3 h); moderately acidic water was more toxic than RMW lacking metals. No mortality was observed in circumneutral mine water or corresponding RMW. Toxicity as estimated by changes in whole body sodium levels of P. promelas followed a pattern similar to toxicity as determined by the 96-h lethality tests. Exposures of P. promelas to moderately acidic mine water at two pHs and trace metals concentrations resulted in significantly different body sodium concentrations and net sodium efflux between groups of fish within six hours. The results suggest that the whole body sodium assay is a useful indicator of coal mine pollution.

Acids↗
PubMed1986

Effect of relative shell size in turtles on water and electrolyte composition.

Interspecific differences in water, sodium, and potassium concentrations of entire freshwater turtles are related to the relative size of the shell. Species with proportionately smaller shells have higher water and potassium concentrations but lower sodium concentrations (expressed as mumol/g wet mass). These effects are associated with variation in the amount of shell bone, which is lower in water and potassium concentrations than other tissues. Within a single species there are also differences in composition related to total wet mass and relative shell mass. Smaller turtles have a relatively larger overall water concentration, a lower overall sodium concentration (expressed as mumol/g wet mass), and a larger relative wet mass of shell (expressed as % total wet mass). The shell in small turtles is lower in relative dry mass, higher in water concentration, and lower in sodium concentration (expressed as mumol/g wet mass) than in large turtles. There is also a striking inverse size-related difference in the proportion of overall sodium that is exchangeable. This is due to a decrease in the proportion of exchangeable sodium in the shell of larger turtles, perhaps related to progressive calcification. The magnitude of the effects of size and/or age on water and electrolyte composition of turtles has not been previously recognized but must now be taken into account before any interspecific or intraspecific comparisons in body composition are made.

Animals↗
PubMed1985

Stimulation of sodium efflux in air-breathing fish exposed to low pH.

Sodium efflux and survival times at low pHs were measured in two species of facultative air-breathing fish. Mudminnows (Umbra pygmaea) and gar (Lepisosteus platyrhincus) were quite tolerant of exposure to acidic waters. This tolerance was associated with a striking capacity for resisting the acceleration in sodium efflux usually characteristic of low pH toxicity. Such a specialization for ionic regulation may have evolved within the context of life in naturally acidic swamps low in sodium concentration. The presence of a very strong degree of resistance to low pH-induced sodium loss in these species affirms the crucial importance of net sodium loss as a mechanism of acid toxicity. Both species showed similar relationships between sodium efflux and low pH. Survival times at low pHs were inversely related to sodium efflux. At death, body sodium concentrations in both species were severely depressed, reflecting large net losses of sodium. An acid resistant salmonid, Salvelinus fontinalis, shows a correlation between sodium efflux and survival time similar to those of the air-breathers studied here. Possession of the capacity for aerial respiration is obviously not the only or perhaps even the primary factor that confers increased resistance to acid toxicity in these two air-breathing fish.

Acid-Base Equilibrium↗
PubMed1982

Permeability and channel structure of reptilian skin.

A study of the permeability of shed epidermis from some terrestrial and freshwater snakes was conducted. Permeability to Br, Na, and K ions was very low and showed a higher influx than efflux in most cases. Permeability to the smaller water molecule was much greater, and in contrast efflux was higher than influx. Skins from aquatic snakes with larger water permeabilities also showed greater permeabilities to Na and K. The highly aquatic Regina septemvittata has the most permeable skin of any snake. Ethanol fluxes were higher than expected for a tracer of its size, perhaps due to its solubility in lipid. Na fluxes through whole live skins of Nerodia cyclopion floridana in vitro were not significantly different from those of the shed skin alone. Isolated hinge regions showed complete water impermeability, suggesting that channels through the skin are located only in the scale region. Dermal water efflux into dry air was considerably less than water-to-water efflux. Lipid extraction increased permeability markedly and eliminated the asymmetry of water and ion fluxes. Lipid replacement with linoleic acid restored half of the water impermeability lost during extraction. Protein extraction did not significantly increase membrane permeability but did eliminate the permeability difference between dry and hydrated skins. Two sizes of lipid-lined channels extending through a protein matrix are suggested as a possible model for snake skin. The diameter of the channels apparently varies in relation to the differing water, Na, and Cl concentrations on opposite sides of the skin, but the mechanism of this adjustment is unknown.

Animals↗
PubMed1976

Evidence for the presence of nasal salt glands in the roadrunner and the Coturnix quail.

The purpose of this investigation was to determine whether or not the nasal glands of the roadrunner and the Coturnix quail show cytological specializations for salt secretion. In addition, the Na-K ATPase content of the quail gland was determined before and after drinking of saline solutions, in an effort to evaluate the functional status of the gland. The ability to maintain weight while drinking salt water was also measured as a general index of tolerance to saline conditions. The ultrastructure of the nasal glands of the roadrunner injected with salt and of quail drinking 200 mM NaCl was similar to that of salt glands in reptiles and the fresh-water acclimated duck. Numerous lateral cell evaginations and abundant mitochondria were present in the principal cell types. There was a significant increase in quail nasal gland Na-K ATPase when young birds were offered only saline solutions to drink. The ability of Coturnix quail to maintain weight while drinking saline solutions improves with age and at adulthood is comparable to that of some North American desert quail. Roadrunners were previously known to possess functional salt glands whereas quail were not. However the characteristic fine structure and the high Na-KATPase content of the quail nasal gland suggest that it is a salt gland.

Adenosine Triphosphatases↗