bluuebunny/crossref_metadata_2025 huggingface dataset:
The Human Dorsal Premotor Cortex Generates On-Line Error Corrections during Sensorimotor Adaptation
Authors: Lee Ji-Hang , van Donkelaar Paul
Published: March 2006

A number of different sites in the human brain have been shown to play a role in sensorimotor adaptation. However, the specific role played by each of these structures in the learning process is poorly understood. In the present study, the contribution of the dorsal aspect of the premotor cortex was examined by disrupting activity at this site using transcranial magnetic stimulation (TMS) while subjects wearing prism goggles pointed at visual targets. This manipulation slowed down the rate of adaptation when vision of the hand was available throughout the movement and reduced the presence of on-line trajectory corrections. This was accompanied by a reduced shift in the felt position of the arm. In contrast, TMS did not cause any alteration in the performance of this task when vision of the hand was available only at the end of the movement. Thus, we infer from this pattern of results that the human dorsal premotor cortex contributes to the generation of the visually based on-line error corrections that are responsible for the remapping of arm position sense underlying sensorimotor adaptation.
Oligodendroglial Progenitor Cell Therapy Limits Central Neurological Deficits in Mice with Metachromatic Leukodystrophy
Authors: Givogri Maria I. , Galbiati Francesca , Fasano Stefania , Amadio Stefano , Perani Laura , Superchi Daniela , Morana Pablo , Del Carro Ubaldo , Marchesini Sergio , Brambilla Riccardo , Wrabetz Lawrence , Bongarzone Ernesto
Published: March 2006

This work describes the first successful oligodendrocyte-based cell therapy for presymptomatic arylsulfatase A (ARSA) null neonate mice, a murine model for human metachromatic leukodystrophy (MLD). We found that oligodendrocyte progenitors (OLPs) engrafted and survived into adulthood when transplanted in the neonatal MLD brain. Transplanted cells integrated nondisruptively, did not produce tumors, and survived as proteolipid protein- and MBP-positive postmitotic myelinating oligodendrocytes (OLs) intermingled with endogenous MLD OLs within the adult MLD white matter. TransplantedMLDmice had reduced sulfatide accumulation in the CNS, increased brain ARSA activity, and full prevention of the electrophysiological and motor deficits that characterize untreatedMLDmice. Our results provide direct evidence that healthy OLPs can tolerate the neurotoxic accumulation of sulfatides that evolves during the postnatal development of the MLD brain and contribute to OL cell replacement to limit the accumulation of sulfatides and the evolution of CNS defects in this lysosomal storage disease mouse model.
Contributions of the GABAAReceptor α6 Subunit to Phasic and Tonic Inhibition Revealed by a Naturally Occurring Polymorphism in the α6 Gene
Authors: Santhakumar Vijayalakshmi , Hanchar H. Jacob , Wallner Martin , Olsen Richard W. , Otis Thomas S.
Published: March 2006

GABAAreceptors (GABARs) are heteromultimeric proteins composed of five subunits. The specific subunit composition determines critical properties of a GABAR such as pharmacological sensitivities and whether the receptor contributes to synaptic or extrasynaptic forms of inhibition. Classically, synaptic but not extrasynaptic GABARs are thought to respond to benzodiazepines, whereas the reverse has been suggested for ethanol. To examine the effects of subunit composition on GABAR functionin situ, we took advantage of two naturally occurring alleles of the rat gene for GABAR subunit α6 (Gabra6100RandGabra6100Q). Depending on their subunit partners, these two variants of α6 can lead to differential sensitivities to benzodiazepines and ethanol. An examination of synaptic and extrasynaptic GABA-mediated currents in cerebellar granule cells fromGabra6100R/100RandGabra6100Q/100Qrats uncovered marked allele-dependent differences in benzodiazepine sensitivity. Unexpectedly, we found that the benzodiazepines flunitrazepam and diazepam enhanced extrasynaptic inhibition mediated by δ subunit-containing GABARs inGabra6100Q/100Qrats. Complementary experiments on recombinant GABARs confirmed that, at subsaturating [GABA], flunitrazepam potentiates α6/δ subunit-containing GABARs. Based on data and a simple theoretical analysis, we estimate that the average extrasynaptic [GABA] is ∼160 nmin perfused slices. These results (1) demonstrate contributions of α6 subunits to both synaptic and extrasynaptic GABA responses, (2) establish that δ subunit-containing GABARs are benzodiazepine sensitive at subsaturating [GABA] and, (3) provide an empirical estimate of extrasynaptic [GABA] in slices.
Disruption of Glycine Transporter 1 Restricted to Forebrain Neurons Is Associated with a Procognitive and Antipsychotic Phenotypic Profile
Authors: Yee Benjamin K. , Balic Ela , Singer Philipp , Schwerdel Cornelia , Grampp Thomas , Gabernet Laetitia , Knuesel Irene , Benke Dietmar , Feldon Joram , Mohler Hanns , Boison Detlev
Published: March 2006

The NMDA receptor is thought to play a central role in some forms of neuronal plasticity, including the induction of long-term potentiation. NMDA receptor hypofunction can result in mnemonic impairment and has been implicated in the cognitive symptoms of schizophrenia. The activity of NMDA receptors is controlled by its endogenous coagonist glycine, and a local elevation of glycine levels is expected to enhance NMDA receptor function. Here, we achieved this by the generation of a novel mouse line (CamKIIαCre;Glyt1tm1.2fl/fl) with a neuron and forebrain selective disruption of glycine transporter 1 (GlyT1). The mutation led to a significant reduction of GlyT1 and a corresponding reduction of glycine reuptake in forebrain samples, without affecting NMDA receptor expression. NMDA (but not AMPA) receptor-evoked EPSCs recorded in hippocampal slices of mutant mice were 2.5 times of those recorded in littermate controls, suggesting that neuronal GlyT1 normally assumes a specific role in the regulation of NMDA receptor responses. Concomitantly, the mutants were less responsive to phencyclidine than controls. The mutation enhanced aversive Pavlovian conditioning without affecting spontaneous anxiety-like behavior in the elevated plus maze and augmented a form of attentional learning called latent inhibition in three different experimental paradigms: conditioned freezing, conditioned active avoidance, conditioned taste aversion. The CamKIIαCre;Glyt1tm1.2fl/fl mouse model thus suggests that augmentation of forebrain neuronal glycine transmission is promnesic and may also offer an effective therapeutic intervention against the cognitive and attentional impairments characteristic of schizophrenia.
System Xc−and Apolipoprotein E Expressed by Microglia Have Opposite Effects on the Neurotoxicity of Amyloid-β Peptide 1–40
Authors: Qin Si , Colin Catherine , Hinners Ina , Gervais Annie , Cheret Cyril , Mallat Michel
Published: March 2006

Because senile plaques in Alzheimer's disease (AD) contain reactive microglia in addition to potentially neurotoxic aggregates of amyloid-β (Aβ), we examined the influence of microglia on the viability of rodent neurons in culture exposed to aggregated Aβ 1–40. Microglia enhanced the toxicity of Aβ by releasing glutamate through the cystine-glutamate antiporter system Xc−. This may be relevant to Aβ toxicity in AD, because the system Xc−-specific xCT gene is expressed not only in cultured microglia but also in reactive microglia within or surrounding amyloid plaques in transgenic mice expressing mutant human amyloid precursor protein or in wild-type mice injected with Aβ. Inhibition of NMDA receptors or system Xc−prevented the microglia-enhanced neurotoxicity of Aβ but also unmasked a neuroprotective effect of microglia mediated by microglial secretion of apolipoprotein E (apoE) in the culture medium. Immunodepletion of apoE or targeted inactivation of the apoE gene in microglia abrogated neuroprotection by microglial conditioned medium, whereas supplementation by human apoE isoforms restored protection, which was potentiated by the presence of microglia-derived cofactors. These results suggest that inhibition of microglial system Xc−might be of therapeutic value in the treatment of AD. Its inhibition not only prevents glutamate excitotoxicity but also facilitates neuroprotection by apoE.
Axonal Ensheathment and Septate Junction Formation in the Peripheral Nervous System ofDrosophila
Authors: Banerjee Swati , Pillai Anilkumar M. , Paik Raehum , Li Jingjun , Bhat Manzoor A.
Published: March 2006

Axonal insulation is critical for efficient action potential propagation and normal functioning of the nervous system. InDrosophila, the underlying basis of nerve ensheathment is the axonal insulation by glial cells and the establishment of septate junctions (SJs) between glial cell membranes. However, the details of the cellular and molecular mechanisms underlying axonal insulation and SJ formation are still obscure. Here, we report the characterization of axonal insulation in theDrosophilaperipheral nervous system (PNS). Targeted expression oftau-green fluorescent proteinin the glial cells and ultrastructural analysis of the peripheral nerves allowed us to visualize the glial ensheathment of axons. We show that individual or a group of axons are ensheathed by inner glial processes, which in turn are ensheathed by the outer perineurial glial cells. SJs are formed between the inner and outer glial membranes. We also show that Neurexin IV, Contactin, and Neuroglian are coexpressed in the peripheral glial membranes and that these proteins exist as a complex in theDrosophilanervous system. Mutations inneurexin IV,contactin, andneuroglianresult in the disruption of blood–nerve barrier function in the PNS, and ultrastructural analyses of the mutant embryonic peripheral nerves show loss of glial SJs. Interestingly, the murine homologs of Neurexin IV, Contactin, and Neuroglian are expressed at the paranodal SJs and play a key role in axon-glial interactions of myelinated axons. Together, our data suggest that the molecular machinery underlying axonal insulation and axon-glial interactions may be conserved across species.
Associations between Plasma Growth Hormone, Insulin-Like Growth Factor-I, and Cortisol with Stress Responsiveness and Growth Performance in a Selective Breeding Program for Rainbow Trout
Authors: Lankford Scott E , Weber Gregory M
Published: March 2006

The National Center for Cool and Cold Water Aquaculture is conducting a selective breeding program to improve the germplasm of rainbow trout Oncorhynchus mykiss for aquaculture. Two lines are being selected for improved growth. We previously found a positive correlation between stress responsiveness, indicated by plasma cortisol concentration after a 3-h confinement stressor, and growth performance, indicated by body weight at selection (approximately 300 d posthatching [dph]), in families from the first line. This correlation is confirmed for the second line in the present study. In addition to stressor-induced cortisol levels, resting plasma growth hormone (GH), insulin-like growth factor-I (IGF-I), and cortisol concentrations were measured in the second line as a first step in determining the physiological and genetic bases for growth performance variation and the association between stress responsiveness and growth performance in our germplasm. Hormone levels were compared against two measures of growth: body weight and thermal growth coefficient (TGC). Plasma concentrations of IGF-I and GH in resting fish were not correlated with stress responsiveness and thus provided no link between stress responsiveness and the growth regulatory axis. The TGC was negatively correlated with resting plasma GH and cortisol and positively correlated with IGF-I, whereas only GH was correlated with body weight at 297 dph. Our results suggest that the variation in growth performance among our broodstock families is explained, in part, by variations in resting levels of the growth regulatory and stress axes. In addition, TGC more accurately predicted future growth—body weight at 459 dph—than did body weight at 297 dph.
Using On-Site Bioassays to Determine Selenium Risk to Propagated Endangered Fishes
Authors: Allert Ann L. , Fairchild James F. , May Tom W. , Sappington Linda C. , Darnall Nathan , Wilson Maureen
Published: March 2006

The Utah Reclamation, Mitigation and Conservation Commission is determining the feasibility of establishing a hatchery and grow-out facility for endangered June suckers Chasmistes liorus at Goshen Warm Springs, Utah. A survey of water quality indicated that selenium and other contaminants may be of concern at Goshen Warm Springs. We conducted an ecotoxicological study with three objectives: (1) to determine the growth rates of juvenile June suckers in two ponds (Lily Pond and North Pond) at Goshen Warm Springs and in Utah Lake, (2) to determine the uptake and depuration rates of selenium in juvenile June suckers, and (3) to evaluate limnological factors that may influence growth and selenium accumulation in June suckers. Fish growth was significantly greater at Utah Lake and North Pond than at Lily Pond or under current hatchery conditions. At the end of the uptake phase of the study (day 87), selenium concentrations in June suckers from Lily Pond, North Pond, and Utah Lake were 1.62, 1.90, and 1.32 μg/g of dry weight, respectively. Selenium uptake in June suckers was statistically significant at Lily Pond (0.005 μg·g−1  ·d−1), North Pond (0.010 μg·g−1  ·d−1), and Utah Lake (0.003 μg·g−1  ·d−1). At day 87, the fish were transferred to well water for selenium depuration. Significant selenium depuration occurred after the transfer of June suckers to clean water. Results indicated that selenium bioaccumulated to statistically significant levels at both Lily and North ponds. However, these concentrations are not likely to be of concern because they are not known to cause chronic toxicity. Depuration experiments indicated that June suckers stocked into Utah Lake would eliminate accumulated selenium residues within 3 months. Results indicated that Goshen Warm Springs could be used for fish propagation. In addition, further evaluation of Utah Lake as an interim hatchery site for June suckers should be considered.
Fish and Blue Crab Passage through Water Control Structures of a Coastal Bay Lake
Authors: Rulifson Roger A. , Wall Brian L.
Published: March 2006

Coastal bay lakes in the southeastern United States may be connected to coastal waters by natural openings or artificial channels, but often access to them by aquatic organisms is restricted by water control structures (WCSs) designed to minimize saltwater intrusion into freshwater habitats. Our study examined movements of alewife Alosa pseudoharengus, white perch Morone americana, American eel Anguilla rostrata, and blue crab Callinectes sapidus through two WCSs separating Lake Mattamuskeet, North Carolina, and canals leading to Pamlico Sound. All WCSs were located on Mattamuskeet National Wildlife Refuge property. Three WCS designs were tested for fish passage efficiency. The original wooden flapgate configuration was hinged at the top, which opened the full width of the embayment and was pressure activated from lake levels. A replacement design, installed in each WCS embayment in 1987, was a wooden stopblock containing a small, hinged stainless steel flapgate mounted near the bottom. This design minimized saltwater intrusion but required a considerable lakeside head to open. High water velocities produced conditions unfavorable for alewife and blue crab passage, but some species, especially white perch, were capable of moving through the restrictive opening. Small, experimental slotted weirs installed in the stopblocks near the surface passed organisms more effectively than the stainless steel flapgates. After 10 years of steel flapgate operation, the alewife spawning run into Lake Mattamuskeet decreased from an estimated high of 199,600 fish in 1970 to only 178 fish in 1997 and 454 fish in 1998. In 1999, wooden flapgates of the original design were installed experimentally, which resulted in favorable conditions (wider aperture and reduced velocities) for fish and blue crab passage. Reverting to the original flapgate design should maintain the mixed community of freshwater and marine–estuarine species in the lake.
Role of sediment organic matter quality and feeding history in dietary absorption and accumulation of pyrene in the mud snail (Hydrobia ulvae)
Authors: Granberg Maria E. , Forbes Thomas L.
Published: March 2006

Oganic matter (OM) input to marine sediments varies seasonally both in quantity and quality. Because sedimentary OM (SOM) constitutes food for many benthic organisms, its properties should affect the dietary uptake of sediment-associated contaminants. We explored the effect of SOM quality/food value on short- and long-term pyrene accumulation in the mud snail (Hydrobia ulvae) and performed dual-tracer pulse-chase experiments to investigate the feeding mechanisms driving dietary pyrene uptake. The quality of the SOM was manipulated by enriching sediments either with high-quality microalgae or low-quality lignin, adding equal amounts of total organic carbon. Long- and short-term bioaccumulation increased with increasing SOM quality, as did pyrene ingestion rate (IRpyr), which also was affected by feeding history. By feeding selectively, snails concentrated pyrene 10-fold in ingested compared to ambient sediment, independent of SOM quality. Average pyrene absorption efficiency (AEpyr: ∼ 65%) varied inversely with SOM quality and IRpyr. Both AEpyr and gut passage time (α 1/IRpyr) agreed with theoretical models incorporating the time-dependence of absorption efficiency. Thus, SOM quality moderates dietary contaminant uptake in deposit feeders, and in H. ulvae, this occurs via OM-induced alterations of ingestion rate. Consequently, enhanced sediment-associated contaminant uptake is predicted for deposit feeders following phytoplankton blooms, principally because of OM quality-driven increases in the ingestion rate.
A perspective on the environmental risk of halogenated by-products from uses of hypochlorite using a whole effluent toxicity based approach
Authors: Johnson Ian , Pickup John A. , van Wijk Dolf
Published: March 2006

An assessment has been made of the potential for toxic effects to aquatic life that may arise from halogenated organic by-products formed by reaction of hypochlorite with organic matter in various use scenarios as a contribution to the risk assessment of sodium hypochlorite under the European Union Existing Chemicals legislation. In the study, samples that would represent worst-case models for effluents containing halogenated by-products from a range of uses of hypochlorite were prepared by chlorinating and then dechlorinating (removing residual chlorine) raw settled sewage (C/D-RSS). This sample was then compared to raw settled sewage that had not been treated (RSS) to assess whether halogenated by-products formed in the chlorination process were toxic or bioaccumulable and persistent. The relative toxicity of the samples was assessed using a series of tests with representatives of different taxonomic groups (bacteria, algae, and invertebrates). The persistence and potential for bioaccumulation of chlorinated by-products was assessed by exposing solid-phase microextraction fibers to samples of RSS and C/D-RSS before and after degradation in a Zahn-Wellens test. For all the taxa tested in the study, the mixture of by-products formed in the C/D-RSS sample did not increase toxicity relative to that measured in the RSS sample. Chlorination of the raw settled sewage did produce additional potentially bioaccumulable halogenated substances compared to the raw settled sewage. However, after degradation, the amount of potentially bioaccumulable halogenated substances in the RSS and C/D-RSS samples was comparable, indicating that these substances were degradable. The results are discussed in the context of the overall risk assessment for sodium hypochlorite.
Metal trophic transfer from algae to cladocerans and the relative importance of dietary metal exposure
Authors: Sofyan Agus , Shaw Joseph R. , Birge Wesley J.
Published: March 2006

We initially investigated effects and uptake of cadmium and copperon Pseudokirchneriella subcapitata (primary producer; formerly known as Selenastrum capricornutum). Our major efforts focused on the effects of metal-laden (i.e., Cd, Cu) P. subcapitata when used to provide dietary metal exposure to Ceriodaphnia dubia (primary consumer). Major test endpoints included feeding rate, survival, and reproduction. Metal body burden in C. dubia increased dose dependently at dietary exposure concentrations of 0.6 μg/g algal dry weight or less for cadmium and 74.7 μg/g algal dry weight or less for copper. However, it decreased sharply when dietary concentrations exceeded 0.6 μg/g algal dry weight for cadmium and 74.7 μg/g algal dry weight copper. Both dietary cadmium and copper affected all the major test endpoints. Whereas reproduction was observed to be the most sensitive endpoint, survival was observed to be the least sensitive endpoint. These results demonstrated the potential importance of dietary exposure for consideration in metal regulations or risk assessment.
Evidence of pesticide impacts in the Santa Maria River watershed, California, USA
Authors: Anderson Brian S. , Phillips Bryn M. , Hunt John W. , Worcester Karen , Adams Mary , Kapellas Nancy , Tjeerdema Ron S.
Published: March 2006

The Santa Maria River provides significant freshwater and coastal habitat in a semiarid region of central California, USA. We conducted a water and sediment quality assessment consisting of chemical analyses, toxicity tests, toxicity identification evaluations, and macroinvertebrate bioassessments of samples from six stations collected during four surveys conducted between July 2002 and May 2003. Santa Maria River water samples collected downstream of Orcutt Creek (Santa Maria, Santa Barbara County, CA, USA), which conveys agriculture drain water, were acutely toxic to cladocera (Ceriodaphnia dubia), as were samples from Orcutt Creek. Toxicity identification evaluations (TIEs) suggested that toxicity to C. dubia in Orcutt Creek and the Santa Maria River was due to chlorpyrifos. Sediments from these two stations also were acutely toxic to the amphipod Hyalella azteca, a resident invertebrate. The TIEs conducted on sediment suggested that toxicity to amphipods, in part, was due to organophosphate pesticides. Concentrations of chlorpyrifos in pore water sometimes exceeded the 10-d median lethal concentration for H. azteca. Additional TIE and chemical evidence suggested sediment toxicity also partly could be due to pyrethroid pesticides. Relative to an upstream reference station, macroinvertebrate community structure was impacted in Orcutt Creek and in the Santa Maria River downstream of the Creek input. This study suggests that pesticide pollution likely is the cause of ecological damage in the Santa Maria River.
Photoinduced toxicity of polycyclic aromatic hydrocarbons toDaphnia magna: Ultraviolet-mediated effects and the toxicity of polycyclic aromatic hydrocarbon photoproducts
Authors: Lampi Mark A. , Gurska Jolanta , McDonald Kristina I. C. , Xie Fangli , Huang Xiao-Dong , Dixon D. George , Greenberg Bruce M.
Published: March 2006

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental contaminants known for their photoinduced toxicity. This toxicity may occur through two mechanisms: Photosensitization, and photomodification. Photosensitization generally leads to the production of singlet oxygen, a reactive oxygen species that is highly damaging to biological molecules. Photomodi-fication of PAHs, usually via oxidation, results in the formation of new compounds and can occur under environmentally relevant levels of actinic radiation. The toxicities of 16 intact PAHs to Daphnia magna were assessed under two ultraviolet radiation conditions. The toxicity of intact PAHs generally increased in the presence of full-spectrum simulated solar radiation relative to that in the presence of visible light plus ultraviolet A only. Despite the knowledge of a bipartite mechanism of phototoxicity that includes photosensitization and photomodification, few studies have examined the effects of PAH photoproducts on animals. To expand the existing data, 14 PAH photoproducts (oxy-PAHs) also were assayed, most of which were highly toxic without further photomodification. Two photoproducts of benzo[a]pyrene, 1,6- and 3,6-benzo[a]pyrenequinone, were the most toxic compounds tested, followed closely by benz[a]anthraquinone. Each of these three compounds had a median effective concentration in the low nanomolar range. The data presented highlight the effects of ultraviolet radiation on mediating PAH toxicity and the need to analyze absorption spectra of contaminants in the prediction of photoinduced toxicity. The importance of the role of photomodification also is stressed, because several oxy-PAHs, an unregulated group of contaminants, were highly toxic to D. magna, a key bioindicator species in aquatic ecosystems.
Body residues as dose for sublethal responses in alevins of landlocked salmon (Salmo salarm.sebago): A direct calorimetry study
Authors: Penttinen Olli-Pekka , Kukkonen Jussi V. K.
Published: March 2006

Qestions of organism-specific factors, toxicity endpoints, and their relation to mode-of-action all are related to consistency and applicability of body residue-based approaches. To address this issue, direct calorimetry was used to evaluate metabolic responses of alevins of landlocked salmon (Salmo salar m. sebago) to pentachlorophenol (PCP) exposure ranging from 0 to 1.04 μM for 24 h or 24, 48, and 72 h (0, 0.26, and 0.55 μM, respectively). The body residues were used as a dose metric for sublethal responses. The body size, rapid ontogenetic development, and exposure to a specific pollutant all were heat output-modifying factors. The acute exposure (24–72 h) to PCP led to a heat output-enhancing effect, which directly was related to an internal concentration of PCP in the range of 0.01 to 0.15 μmol/g. Within the treatments, body size per level of metabolic rate and magnitude of physiological response were not correlated, thus the alevins with higher mass-specific metabolic rate were not more sensitive to PCP. Primarily, increasing metabolic rate during posthatch development controls PCP toxicity only by affecting bioaccumulation kinetics, not the toxic potency of the chemical. New information of a relationship between observed natural variation in measured physiological trait offish and PCP-induced response and its body residue-based level is of ecotoxicological importance.
Predicted effects of toxicant mixtures are confirmed by changes in fish species assemblages in Ohio, USA, rivers
Authors: Posthuma Leo , de Zwart Dick
Published: March 2006

The purposes of this study were to investigate whether exposure to toxicant mixtures is associated with fish assemblage characteristics in the field and to describe the relationships between predicted chronic and acute mixture risks and observed impacts. Fish abundance and abiotic monitoring data from Ohio, USA, surface waters were compiled and analyzed. Variability of biotic and abiotic parameters was large. Exposure assessment, risk assessment with species-sensitivity distributions, and mixture toxicity rules were used to calculate a relative risk predictor: The multisubstance potentially affected fraction of species (msPAF). Predicted acute and chronic risks ranged from low values to more than 10 and 50% of species potentially affected, respectively. Pearson correlations between predicted risk and observed assemblage characteristics were nonsignificant for total abundance, number of species, Shannon-Weaver index, and evenness. Moderately significant correlations were found between predicted risk and abundance for 23% of individual species. Both abundance increases and decreases were observed. Generalized linear model (GLM) regressions revealed significant nonlinear associations between predicted risk and the abundance for 50% (metals and ammonia) and 55% (household product ingredients) of the species. Local ecological impact was expressed as the fraction of species expected but not observed, both with and without attribution of impact to mixture exposure. The association between predicted impacted fraction and the fraction of species expected but not observed was not significant. Predicted acute and chronic impacted fractions were associated significantly with the observed fraction of species likely lost by the action of toxicant mixtures under field conditions, with wide confidence bounds. These findings confirm the view that higher mixture impacts are expected in the field at higher msPAF.
A meta-analysis comparing the toxicity of sediments in the laboratory and in situ
Authors: Hose Grant C. , Murray Brad R. , Park Margaux L. , Kelaher Brendan P. , Figueira Will F.
Published: March 2006

Sediment toxicity tests in the laboratory are an important part of ecological risk assessments, yet how they relate to sediment toxicity in situ has rarely been explored. Using meta-analysis, we examined differences in the toxicity of sediment tested in the laboratory and in situ. Data from four published studies were subjected to rigorous statistical analyses. Overall, the toxicity of sediments in laboratory tests was substantially less than their toxicity in situ. Differences between laboratory and in situ toxicity, expressed using the log odds ratio effect size, varied significantly among published studies. Effect size increased significantly with increasing sediment toxicity, showing that the more toxic the sediment, the greater the disparity between laboratory and field toxicities. Our findings may not apply to all laboratory/field comparisons; however, we consider that the overlying water in field situations is a significant contributor to this relationship through additional contamination and toxicity. Our findings also have important implications for the use of laboratory tests to assess improvements in sediment quality and remediation, because changes in laboratory toxicity may not reflect the true improvements to sediment quality in situ.
Use of carboxylesterase activity to remove pyrethroid-associated toxicity to Ceriodaphnia dubia and Hyalella azteca in toxicity identification evaluations
Authors: Wheelock Craig E. , Miller Jeff L. , Miller Mike J. , Phillips Bryn M. , Huntley Sarah A. , Gee Shirley J. , Tjeerdema Ronald S. , Hammock Bruce D.
Published: March 2006

Increases in the use and application of pyrethroid insecticides have resulted in concern regarding potential effects on aquatic ecosystems. Methods for the detection of pyrethroids in receiving waters are required to monitor environmental levels of these insecticides. One method employed for the identification of causes of toxicity in aquatic samples is the toxicity identification evaluation (TIE); however, current TIE protocols do not include specific methods for pyrethroid detection. Recent work identified carboxylesterase treatment as a useful method for removing/detecting pyrethroid-associated toxicity. The present study has extended this earlier work and examined the ability of carboxylesterase activity to remove permethrin- and bifenthrin-associated toxicity to Ceriodaphnia dubia and Hyalella azteca in a variety of matrices, including laboratory water, Sacramento River (CA, USA) water, and Salinas River (CA, USA) interstitial water. Esterase activity successfully removed 1,000 ng/L of permethrin-associated toxicity and 600 ng/L of bifenthrin-associated toxicity to C. dubia in Sacramento River water. In interstitial water, 200 ng/L of permethrin-associated toxicity and 60 ng/L of bifenthrin-associated toxicity to H. azteca were removed. The selectivity of the method was validated using heat-inactivated enzyme and bovine serum albumin, demonstrating that catalytically active esterase is required. Further studies showed that the enzyme is not significantly inhibited by metals. Matrix effects on esterase activity were examined with municipal effluent and seawater in addition to the matrices discussed above. Results confirmed that the esterase retains catalytic function in a diverse array of matrices, suggesting that this technique can be adapted to a variety of aquatic samples. These data demonstrate the utility of carboxylesterase treatment as a viable step to detect the presence of pyrethroids in receiving waters.
Bioavailability of polycyclic aromatic hydrocarbons from buried shoreline oil residues thirteen years after theExxon Valdezoil spill: A multispecies assessment
Authors: Neff Jerry M. , Bence A. Edward , Parker Keith R. , Page David S. , Brown John S. , Boehm Paul D.
Published: March 2006

Seven taxa of intertidal plants and animals were sampled at 17 shoreline sites in Prince William Sound ([PWS]; AK, USA), that were heavily oiled in 1989 by the Exxon Valdez oil spill (EVOS) to determine if polycyclic aromatic hydrocarbons (PAH) from buried oil in intertidal sediments are sufficiently bioavailable to intertidal prey organisms that they might pose a health risk to populations of birds and wildlife that forage on the shore. Buried residues of EVOS oil are present in upper and middle intertidal sediments at 16 sites. Lower intertidal (0 m) sediments contain little oil. Much of the PAH in lower intertidal sediments are from combustion sources. Mean tissue total PAH (TPAH) concentrations in intertidal clams, mussels, and worms from oiled sites range from 24 to 36 ng/g (parts per billion) dry weight; sea lettuce, whelks, hermit crabs, and intertidal fish contain lower concentrations. Concentrations of TPAH are similar or slightly lower in biota from unoiled reference sites. The low EVOS PAH concentrations detected in intertidal biota at oiled shoreline sites indicate that the PAH from EVOS oil buried in intertidal sediments at these sites have a low bioavailability to intertidal plants and animals. Individual sea otters or shorebirds that consumed a diet of intertidal clams and mussels exclusively from the 17 oiled shores in 2002 were at low risk of significant health problems. The low concentrations of EVOS PAH found in some intertidal organisms at some oiled shoreline sites in PWS do not represent a health risk to populations of marine birds and mammals that forage in the intertidal zone.
Kinetics of adsorption and desorption of some organochlorine compounds on black carbon in a sediment
Authors: Vrind Bea A. , ten Hulscher Theodora E. M. , van Noort Paul C. M.
Published: March 2006

Rate constants for adsorption and desorption of four organochlorine compounds on black carbon in a sediment were determined from measurements of the rate of removal, by gas purge, of the organochlorine compounds as single solutes from a water-sediment mixture immediately after addition of the solute to the system. The rates of removal fitted to a kinetic scheme based on Langmuir adsorption onto two types of sites in black carbon. The first-order rate constants for desorption from these sites were comparable to those for slow and very slow desorption from sediment. The time needed to reach apparent equilibrium in the experimental setup, with 10 g sediment/L water, ranged from 13 to 166 h, depending on the sorbate and the adsorption process. These short times to equilibrium suggest no need to assume rate-limiting diffusion from and to adsorption sites in this sediment. Average Gibbs free energies for adsorption of the four organochlorine compounds from the pure solid state were —10 ± 3 and —20 ± 3 kJ/mol for low-energy and high-energy sites, respectively, pointing to two different adsorption mechanisms.
STIMULUS FUNCTIONS IN CHAINED FIXED‐INTERVAL SCHEDULES
Authors: Kelleher Roger T. , Fry William T.
Published: March 2006

Pigeons were required to complete three successive fixed‐interval components to obtain food. When the same exteroceptive stimulus was correlated with the three components, responding was positively accelerated between food deliveries. When different exteroceptive stimuli were correlated with each component in a fixed sequence, prolonged pauses developed in the first component; low response rates developed in the second component; and responding was positively accelerated in the second and third components. When different exteroceptive stimuli were correlated with each component in a variable sequence, responding was positively accelerated in each component. Because the response and reinforcement contingencies were the same in all three procedures, the differences in performances must be due to the changes in the sequence of stimuli.
INDEPENDENCE OF CONCURRENT RESPONDING MAINTAINED BY INTERVAL SCHEDULES OF REINFORCEMENT1
Authors: Catania A. Charles
Published: March 2006

A pigeon's responses were reinforced on a variable‐interval schedule on one key; and, concurrently, either a multiple or a fixed‐interval schedule of reinforcement was in effect on a second key. These concurrent schedules, conc VI 3 (mult VI 3 EXT) or conc VI 3 FI 6, were programmed with or without a changeover delay (COD). Because the COD provided that responses on one key could not be followed by reinforced responses on the other key, responding on one key was not likely to accidentally come under the control of the reinforcement schedule on the other. When the COD was used, the performances on each key were comparable to the performances maintained when these interval schedules are programmed separately. The VI schedule maintained a relatively constant rate of responding, even though the rate of responding on the second key varied in a manner appropriate to the schedule on the second key. The mult VI 3 EXT schedule maintained two separate rates of responding: a relatively high rate during the VI 3 component, and almost no responding during the EXT component. The FI schedule maintained the gradually increasing rate of responding within each interval that is characteristic of the performance maintained by this schedule. The concurrent performances, however, did include certain interactions involving the local characteristics of responding and the over‐all rates of responding maintained by the various schedules. The relevance of the present findings to an inter‐response time analysis of VI responding, a chaining account of FI responding, and the concept of the reflex reserve was discussed.
A FACILITATIVE EFFECT OF PUNISHMENT ON UNPUNISHED BEHAVIOR1
Authors: Brethower Dale M. , Reynolds G. S.
Published: March 2006

The key pecking of two pigeons was reinforced on a variable‐interval schedule of reinforcement during the presentation of each of two stimuli. In various phases of the experiment, punishment followed every response emitted in the presence of one of the stimuli. In general, when the rate of punished responding changed during the presentation of one stimulus, the rate of unpunished responding during the other stimulus changed in the opposite direction. This sort of change in rate is an example of behavioral contrast. When punishment was introduced, the rate of punished responding decreased and the rate of unpunished responding increased as functions of shock intensity. When the rate of previously punished responding increased after the termination of the shock, the rate of the always unpunished responding decreased. When the procedure correlated with a red key was changed from variable‐interval reinforcement and punishment for each response to extinction and no punishment, the rate of reinforced responding during presentations of a green key decreased and then increased while the rate of the previously punished responding during red first increased and then decreased during extinction.
SOME EFFECTS OF RESPONSE COST UPON HUMAN OPERANT BEHAVIOR
Authors: Weiner Harold
Published: March 2006

Three experiments are reported which investigated the effects of cost (point loss per response) upon human‐observer responses maintained by VI and FI schedules of reinforcement (acquisition of points via critical‐signal detections). (I) Cost attenuated VI response rates without substantially disturbing the constancy of responding, regardless of the presentation sequence of the no‐cost and cost conditions. (II) FI scalloping appeared only under cost conditions. Under no cost, a constant rate of responding (similar to VI performance) characterized inter‐reinforcement intervals. Exposure to cost did not prevent the recovery of previously established no‐cost baselines. (III) FI irregularities, analogous to those commonly observed under FI reinforcement schedules, may be produced by different temporal presentations of the no‐cost and cost conditions.

The results of all three experiments emphasize the importance of cost as a factor in the maintenance of human behavior on schedules of positive reinforcement.
FOOD SATIATION IN THE PIGEON
Authors: Reese T. W. , Hogenson Marilyn J.
Published: March 2006

The experiment was designed to find the shape of food satiation curves of the pigeon as a function of hours of deprivation or percentage of free‐feeding weight, and to study the fluctuation in free‐feeding weight as a function of deprivation and satiation. At a systematically and progressively increased number of hours' deprivation, eight birds were allowed to satiate on grain presented contingent upon the emission of a pecking response. In the second part of the experiment, in which two birds were used, a similar procedure was followed except that the independent variable was percentage of free‐feeding weight. These were the conclusions.

. Approximately 64% of the satiation curves were classified as straight with an abrupt stop. The next highest percentage of curves was 18% for curves classified as straight with a curvilinear stop. No “classic” satiation curves, curvilinear with curvilinear stop, were found.

. The pigeons responded at fairly constant rate during the early part of each satiation session, or they did not respond at all. The critical weight, above which they did not respond, was 85% of free feeding.
REDUCTION OF SHOCK FREQUENCY AS REINFORCEMENT FOR AVOIDANCE BEHAVIOR
Authors: Sidman Murray
Published: March 2006

An avoidance technique was used in which rats had two levers available, with independent shock schedules associated with each. Behavioral patterns in initial conditioning and in the maintenance of the responses with various response‐shock intervals led to the suggestion that reduction of shock density be considered an important variable in avoidance behavior.
THE OPERANT CONDITIONING OF CONVERSATION1
Authors: Levin Gilbert , Shapiro David
Published: March 2006

Human conversation is a natural place to begin the study of social responses. In a conversation, a number of individuals use one another's responses as cues for their own behavior. So long as a conversation is being held, the speakers must talk in some order. Four experiments were conducted to test whether differentially reinforcing a group of speakers can bring the order of speakers under experimental control. The results are all consistent with the hypothesis. The paper also devises and evaluates different procedures for studying conversational sequences and examines associated statistical problems.
EFFECTS OF OPERANT REINFORCEMENT ON THE GSR1
Authors: Mandler George , Toronto University of , Preven David W. , Kuhlman Clementina K.
Published: March 2006

Each of nine Ss was run for 11 daily sessions. Except for the first (operant level) and last two (extinction) sessions, 500‐ohm drops in skin resistance were followed by reinforcement (light). These reinforcement periods lasted 20 min and were preceded by 10‐min control periods during which no reinforcement was administered. Although the results showed no evidence for operant conditioning of the GSR, they did indicate that increased emission of GSR's occurred during the reinforcement period. This effect was shown to hold for Ss with low operant levels of GSR's but not for Ss with high operant levels.
FI LENGTH AND PERFORMANCE ON AN FI FR CHAIN SCHEDULE OF REINFORCEMENT
Authors: Hanson H. M. , Campbell E. H. , Witoslawski J. J.
Published: March 2006

In a chained FI FR schedule, manipulating the length of the FI component produced changes confined almost entirely to the FI performance; increasing the interval length increased the total number of responses emitted per reinforcement. The configuration of the fixed‐interval scallop was clearly modified as the interval length was increased, with the larger intervals becoming flatter (i.e., a larger proportion of the total responses earlier in an interval). Measurement of the postreinforcement pause is suggested as a possible indicator of fixed‐interval scalloping.
PRODUCING EITHER POSITIVE OR NEGATIVE TENDENCIES TO A STIMULUS ASSOCIATED WITH SHOCK1
Authors: Evans Wayne O.
Published: March 2006

A technique is described in which rats are pretrained with reinforcement to bar press. Each bar press was associated with a tone. This tone was later paired with one of two aspects of an electric shock, either at the onset or at the end of the shock, in a situation in which the shock is inescapable. These animals were retested in the operant situation under conditions of extinction, but with tone present as a conditioned reinforcer. The finding was that animals for which the tone was associated with shock onset extinguished quickly, whereas animals for which the tone was paired with shock termination extinguished more slowly.
MACHINE DEFINITION OF ONGOING SILENT AND ORAL READING RATE1
Authors: Goldiamond Israel
Published: March 2006

A procedure is described by which a machine defines the ongoing silent and oral reading rates, and thus subjects them to environmental control and experimental analysis. Reading is considered as a form of monitoring in which response sequences are linear and successive. Applications for other types of monitoring are considered.

A page is projected on a screen, and the subject is required to read, aloud or silently. Through the same optical system, an opaque loop is presented that masks the projection, and a transparent slit on the opaque loop exposes part of a line of type. With each frame, the slit moves linearly and sequentially, exposing successive reading material. Recycling the loop triggers the presentation of another page. The subject controls the loop by pressing a microswitch to advance the frame, thereby explicitly defining a monitoring response. The procedure is sensitive to variables such as signal‐noise ratio, item difficulty, transient and long‐term effects, reinforcement schedules (pay‐offs), and age. Monitoring rates are extremely steady, suggesting their use as a base line.

Procedures are suggested for training subjects to be differentially attentive to different parts of a complex display.
THE OPERANT CONTROL OF VOCALIZATION IN THE DOG1
Authors: Salzinger Kurt , Waller Marcus B.
Published: March 2006

Control over the vocal responses of three dogs was established using operant‐conditioning procedures. Several points of interest were observed in the data. First, fixed‐ratio schedules of reinforcement generated a vocal response topography which was similar in detail to that of a “motor” bar‐nosing response. Second, vocal responding was brought under the control of external visual stimuli as a result of differential reinforcement. Third, good stimulus control was maintained on a multiple schedule containing a vocal‐response component and a bar‐response component. Fourth, the stimulus control on the multiple schedule transferred with minimal disruption to a chain schedule requiring a sequence of 10 bar responses followed by 10 vocal responses. Fifth, because vocal and bar responses are not mutually exclusive, concurrent responding tended to develop on the chain schedule.

These results were discussed with reference to the advisability of applying the terms operant and respondent to unconditioned behavior, and, particularly, to unconditioned verbal behavior.
TIME OUT FROM AVOIDANCE AS A REINFORCER: A STUDY OF RESPONSE INTERACTION1
Authors: Sidman Murray
Published: March 2006

Monkeys could either postpone shock by pressing a lever or pull a chain to produce a period of time out from the avoidance procedure. The period of time out proved to be an effective positive reinforcer. Certain features of the animals' behavior were attributed to interactions between the two responses.