Review: Abandoned mines as a resource or liability for wildlife

Abandoned Mine Lands (AMLs) are areas where previous mineral extraction or processing has occurred. Hundreds of thousands of AMLs exist within the United States. Contaminated runoff from AMLs can negatively affect the physiology and ecology of surrounding terrestrial and aquatic habitats and species and can be detrimental to human health. As a response, several U.S. federal and state agencies have launched programs to assess health risks associated with AMLs. In some cases, however, AMLs may be beneficial to specific wildlife taxa. There is a relative paucity of studies investigating the physiological and ecological impacts of AMLs on wildlife. We conducted a systematic review examining published scientific articles that assessed the negative and positive impacts of AMLs across invertebrate and vertebrate taxa. We also offer suggestions on evaluating AMLs to develop effective mitigation strategies that reduce their negative tole on human and wildlife communities. Peer-reviewed publications were screened across WebofScience, PubMed and Google Scholar databases. Abandoned mine lands were generally detrimental to wildlife, with adverse effects ranging from bioaccumulation of heavy metals to decreased ecological fitness. Conversely, AMLs were an overall benefit to imperiled bat populations and could serve as tools for conservation. Studies were unevenly distributed across different wildlife taxa groups, echoing the necessity for additional taxonomically diverse research. We suggest that standardized wildlife survey methods be used to assess how different species utilize AMLs. Federal and state agencies can use these surveys to establish effective remediation plans for individual AML sites and minimize the risks to both wildlife and humans.

Arsenic Impairs Wound Healing Processes in Dermal Fibroblasts and Mice

Inorganic arsenic (NaAsO2) is a naturally occurring metalloid found in water resources globally and in the United States at concentrations exceeding the U.S. Environmental Protection Agency Maximum Contamination Level of 10 ppb. While exposure to arsenic has been linked to cancer, cardiovascular disease, and skin lesions, the impact of arsenic exposure on wound healing is not fully understood. Cultured dermal fibroblasts exposed to NaAsO2 displayed reduced migration (scratch closure), proliferation, and viability with a lowest observable effect level (LOEL) of 10 µM NaAsO2 following 24 h exposure. An enrichment of Matrix Metalloproteinase 1 (MMP1) transcripts was observed at a LOEL of 1 µM NaAsO2 and 24 h exposure. In vivo, C57BL/6 mice were exposed to 10 µM NaAsO2 in their drinking water for eight weeks, then subjected to two full thickness dorsal wounds. Wounds were evaluated for closure after 6 days. Female mice displayed a significant reduction in wound closure and higher erythema levels, while males showed no effects. Gene expression analysis from skin excised from the wound site revealed significant enrichment in Arsenic 3-Methyltransferase (As3mt) and Estrogen Receptor 2 (Esr2) mRNA in the skin of female mice. These results indicate that arsenic at environmentally relevant concentrations may negatively impact wound healing processes in a sex-specific manner.

The USGS plans to severely curtail the National Pesticide Synthesis Project

The plan of the USGS, to consolidate data across a five-year time scale and to limit the number of pesticides included in the database will severely limit its utility as a tool to understand health risks associated with pesticide exposure.

Building Research Infrastructure: The Development of a Technical Assistance Group-Service Center at an RCMI

As one of the Research Centers for Minority Institutions (RCMI), the Southwest Health Equity Research Collaborative (SHERC) worked over the first five-year period of funding to foster the advancement of Early Stage Investigators, enhance the quality of health disparities research, and increase institution research capacity in basic Biomedical, Behavioral, and/or Clinical research; all priorities of RCMIs. In year 4, the Technical Assistance Group-Service Center (TAG-SC) was created to help achieve these goals. The TAG-SC provides one-on-one investigator project development support, including research design, data capture, and analysis. Successful implementation of the TAG-SC was tracked using Research Electronic Data Capture (REDCap), a secure, web-based software platform allowing for immediate tracking and evaluation processes. In the first two years, 86 tickets were submitted through the REDCap system for methodological support by TAG-SC experts (faculty and staff) for assistance with health-equity related research, primarily SHERC and externally funded Social/Behavioral research projects. The TAG-SC increased the research capacity for investigators, especially within the SHERC. In this manuscript, we describe the methods used to create the TAG-SC and the REDCap tracking system and lessons learned, which can help other RCMIs interested in creating a similar service center offering an innovative way to build methodological infrastructure.

Chemical Toxicants in Water: A GeoHealth Perspective in the Context of Climate Change

The editorial focuses on four major themes contextualized in a virtual GeoHealth workshop that occurred from June 14 to 16, 2021. Topics in that workshop included drinking water and chronic chemical exposure, environmental injustice, public health and drinking water policy, and the fate, transport, and human impact of aqueous contaminants in the context of climate change. The intent of the workshop was to further define the field of GeoHealth. This workshop emphasized on chemical toxicants that drive human health. The major calls for action emerged from the workshop include enhancing community engagement, advocating for equity and justice, and training the next generation.

Environmentally relevant arsenic exposure affects morphological and molecular endpoints associated with reproduction in the Western mosquitofish, Gambusia affinis

Arsenic (As) exposure, even at low environmentally relevant levels, may cause detrimental health outcomes through developmental toxicity and by acting as an endocrine disrupting compound (EDC). Although several studies indicate that wildlife bioaccumulate As, few evaluate the health impact on fish species in their natural environment. In the U.S., As has a drinking water regulatory limit of 10 μg/L. In many parts of Arizona, surface water and groundwater have naturally elevated levels of As from geologic deposits and contamination is exacerbated by anthropogenic activity. In aquatic environments, the Western mosquitofish, Gambusia affinis, is a good bioindicator for EDC exposure because of the distinct androgen-related development of an intromittent organ, the gonapodium, in males. We evaluated morphological and reproductive outcomes in mosquitofish exposed to As. In a laboratory experiment, juvenile male mosquitofish were exposed to sodium arsenite (0 μg/L, 0.75 μg/L, 7.50 μg/L, and 75 μg/L) for 30 days, and in a field study, populations of adult male mosquitofish were collected in Arizona waterways with As levels above and below the World Health Organization's regulatory limit. In both studies, higher As exposure was significantly associated with altered hepatosomatic indices, altered fish morphology, shortened gonopodia, and lower gonopodia-somatic indices. In the field experiment, populations from surface water with higher As concentrations exhibited lower condition factors, lower gonadal-somatic indices, distinct gonopodia shapes, and altered estrogen receptor alpha and vitellogenin gene expression; androgen receptor expression was unchanged. Together, laboratory and field results suggest that As exposure at environmentally-relevant levels affects general growth and reproductive development in mosquitofish. Observed effects may further influence individual health, mobility, or reproductive function, and because G. affinis is a species known to tolerate and adapt to a wide range of environments, it serves as a local bioindicator species as well as a model organism for parallel field and laboratory studies.

Investigation of Relationships Between the Geospatial Distribution of Cancer Incidence and Estimated Pesticide Use in the U.S. West

The objective of the study was to evaluate the potential geospatial relationship between agricultural pesticide use and two cancer metrics (pediatric cancer incidence and total cancer incidence) across each of the 11 contiguous states in the Western United States at state and county resolution. The pesticide usage data were collected from the U.S. Geological Survey Pesticide National Synthesis Project database, while cancer data for each state were compiled from the National Cancer Institute State Cancer Profiles. At the state spatial scale, this study identified a significant positive association between the total mass of fumigants and pediatric cancer incidence, and also between the mass of one fumigant in particular, metam, and total cancer incidence (P-value < 0.05). At the county scale, the relationship of all cancer incidence to pesticide usage was evaluated using a multilevel model including pesticide mass and pesticide mass tertiles. Low pediatric cancer rates in many counties precluded this type of evaluation in association with pesticide usage. At the county scale, the multilevel model using fumigant mass, fumigant mass tertiles, county, and state predicted the total cancer incidence (R-squared = 0.95, NSE = 0.91, and Sum of square of residuals [SSR] = 8.22). Moreover, this study identified significant associations between total fumigant mass, high and medium tertiles of fumigant mass, total pesticide mass, and high tertiles of pesticide mass relative to total cancer incidence across counties. Fumigant application rate was shown to be important relative to the incidence of total cancer and pediatric cancer, at both state and county scales.

Assessing Potential Environmental Impacts of Pesticide Usage in Paddy Ecosystems: A Case Study in the Deduru Oya River Basin, Sri Lanka

Rice paddies are unique ecosystems that provide rich wetland habitat. Their enduring existence across vast stretches of land has led them to evolve into unique systems serving a diverse assemblage of organisms and sustaining a staple grain for many people. With food demand rising, agricultural intensification through agrochemical application is a common practice used to boost food production in developing countries, including Sri Lanka. The aim of the present study was to assess the concentration of pesticide residues in water in rice ecosystems and discover their potential impacts on both environmental health and the most common fauna groups across a cropping year in Sri Lanka. A total of 270 water samples from waters associated with paddy fields within a watershed were analyzed for 20 commonly used pesticides; in addition, local farm holders were surveyed to assess pesticide usage details in three selected paddy tracts. We then used the Cornell University environmental impact quotient (EIQ) calculator and the ECOTOX Knowledgebase to determine the exposure risk associated with individual pesticides relative to their application rates and aquatic concentrations. Survey results demonstrate that several pesticides were overapplied at rates 1.2-11 times the recommended application, and the EIQ demonstrated high environmental risk of two of the agrochemicals detected, 2-methyl-4-chlorophenoxyacetic and diazinon. Fish, amphibians, insects, and beetles were found to have a wide range of potential adverse outcomes from exposure to diazinon, captan, thiamethoxam, and chlorantraniliprole. To balance the trade-offs between food security and ecosystem sustainability, the present study recommends that adoption of quantifiable environmental health indicators be considered as part of the national policy regulating pesticide use. Environ Toxicol Chem 2022;41:343-355. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Synonymous single nucleotide polymorphism in arsenic (+3) methyltransferase of the Western mosquitofish (Gambusia affinis) and its gene expression among field populations

Naturally occurring arsenic is toxic at extremely low concentrations, yet some species persist even in high arsenic environments. We wanted to test if these species show evidence of evolution associated with arsenic exposure. To do this, we compared allelic variation across 872 coding nucleotides of arsenic (+3) methyltransferase (as3mt) and whole fish as3mt gene expression from three field populations of Gambusia affinis, from water sources containing low (1.9 ppb), medium-low (3.3 ppb), and high (15.7 ppb) levels of arsenic. The high arsenic site exceeds the US EPA's Maximum Contamination Level for drinking water. Medium-low and high populations exhibited homozygosity, and no sequence variation across all animals sampled. Eleven of 24 fish examined (45.8%) in the low arsenic population harbored synonymous single nucleotide polymorphisms (SNPs) in exons 4 and/or 10. SNP presence in the low arsenic population was not associated with differences in as3mt transcript levels compared to fish from the medium-low site, where SNPs were noted; however, as3mt expression in fish from the high arsenic concentration site was significantly lower than the other two sites. Low sequence variation in fish populations from sites with medium-low and high arsenic concentrations suggests greater selective pressure on this allele, while higher variation in the low population suggests a relaxed selection. Our results suggest gene regulation associated with arsenic detoxification may play a more crucial role in influencing responses to arsenic than polymorphic gene sequence. Understanding microevolutionary processes to various contaminants require the evaluation of multiple populations across a wide range of pollution exposures.

Developmental assays using invasive cane toads, Rhinella marina, reveal safety concerns of a common formulation of the rice herbicide, butachlor

Identifying the adverse impacts of pesticide exposure is essential to guide regulations that are protective of wildlife and human health. Within rice ecosystems, amphibians are valuable indicators because pesticide applications coincide with sensitive reproductive and developmental life stages. We conducted two experiments using wild cane toads (Rhinella marina) to test 1) whether environmentally relevant exposure to a commercial formulation of butachlor, an acetanilide herbicide used extensively in rice, affects amphibian development and 2) whether cane toad tadpoles are capable of acclimatizing to sub-lethal exposure. First, we exposed wild cane toads to 0.002, 0.02, or 0.2 mg/L of butachlor (Machete EC), during distinct development stages (as eggs and hatchlings, as tadpoles, or continuously) for 12 days. Next, we exposed a subset of animals from the first experiment to a second, lethal concentration and examined survivorship. We found that cane toads exposed to butachlor developed slower and weighed less than controls, and that development of the thyroid gland was affected: exposed individuals had smaller thyroid glands and thyrocyte cells, and more individual follicles. Analyses of the transcriptome revealed that butachlor exposure resulted in downregulation of transcripts related to metabolic processes, anatomic structure development, immune system function, and response to stress. Last, we observed evidence of acclimatization, where animals exposed to butachlor early in life performed better than naïve animals during a second exposure. Our findings indicate that the commercial formulation of butachlor, Machete EC, causes thyroid endocrine disruption in vertebrates, and suggest that exposure in lowland irrigated rice fields presents a concern for wildlife and human health. Furthermore, we establish that developmental assays with cane toads can be used to screen for adverse effects of pesticides in rice fields.

In Vitro Scratch Assay to Demonstrate Effects of Arsenic on Skin Cell Migration

Understanding the physiologic mechanisms of wound healing has been the focus of ongoing research for many years. This research directly translates into changes in clinical standards used for treating wounds and decreasing morbidity and mortality for patients. Wound healing is a complex process that requires strategic cell and tissue interaction and function. One of the many critically important functions of wound healing is individual and collective cellular migration. Upon injury, various cells from the blood, surrounding connective, and epithelial tissues rapidly migrate to the wound site by way of chemical and/or physical stimuli. This migration response can largely dictate the outcomes and success of a healing wound. Understanding this specific cellular function is important for translational medicine that can lead to improved wound healing outcomes. Here, we describe a protocol used to better understand cellular migration as it pertains to wound healing, and how changes to the cellular environment can significantly alter this process. In this example study, dermal fibroblasts were grown in media supplemented with fetal bovine serum (FBS) as monolayer cultures in tissue culture flasks. Cells were aseptically transferred into tissue culture treated 12-well plates and grown to 100% confluence. Upon reaching confluence, the cells in the monolayer were vertically scratched using a p200 pipet tip. Arsenic diluted in culture media supplemented with FBS was added to individual wells at environmentally relevant doses ranging 0.1-10 M. Images were captured every 4 hours (h) over a 24 h period using an inverted light microscope to observe cellular migration (wound closure). Images were individually analyzed using image analysis software, and percent wound closure was calculated. Results demonstrate that arsenic slows down wound healing. This technique provides a rapid and inexpensive first screen for evaluation of the effects of contaminants on wound healing.

Estrogen Mitigates the Negative Effects of Arsenic Contamination in an In Vitro Wound Model

Arsenic, a naturally occurring environmental contaminant, is harmful to humans at elevated concentrations. Increased levels of arsenic in the environment occur as a result of human activities and from natural geologically sourced leaching into ground and surface water. These sources pose an exposure risk above the USEPA standard to individuals whose food and water sources become contaminated. Arsenic exposure negatively impacts organ function and increases the risk for developing pathologies, including cancer. Some of the effects of arsenic on cancer translate to normal cell function in wound healing. To evaluate whether arsenic influences wound healing, an in vitro scratch assay was employed to study the effects of arsenic on cellular migration, which is a key component in the normal wound-healing process. In this study, skin cells were exposed to environmentally relevant concentrations of arsenic, and wound closure was evaluated. Results indicated that arsenic significantly decreased the rate of cellular migration in the scratch assay when compared with controls. In addition, estradiol, which has been shown to positively influence cellular and tissue processes involved in wound healing, reversed the slowing effects of arsenic on wound closure. These results suggest that arsenic contamination may inhibit, and estrogen may provide a therapeutic benefit for individuals with arsenic-contaminated wounds.

Epigenetics of breast cancer: Modifying role of environmental and bioactive food compounds

SCOPE

Reduced expression of tumor suppressor genes (TSG) increases the susceptibility to breast cancer. However, only a small percentage of breast tumors is related to family history and mutational inactivation of TSG. Epigenetics refers to non-mutational events that alter gene expression. Endocrine disruptors found in foods and drinking water may disrupt epigenetically hormonal regulation and increase breast cancer risk. This review centers on the working hypothesis that agonists of the aromatic hydrocarbon receptor (AHR), bisphenol A (BPA), and arsenic compounds, induce in TSG epigenetic signatures that mirror those often seen in sporadic breast tumors. Conversely, it is hypothesized that bioactive food components that target epigenetic mechanisms protect against sporadic breast cancer induced by these disruptors.

METHODS AND RESULTS

This review highlights (i) overlaps between epigenetic signatures placed in TSG by AHR-ligands, BPA, and arsenic with epigenetic alterations associated with sporadic breast tumorigenesis; and (ii) potential opportunities for the prevention of sporadic breast cancer with food components that target the epigenetic machinery.

CONCLUSIONS

Characterizing the overlap between epigenetic signatures elicited in TSG by endocrine disruptors with those observed in sporadic breast tumors may afford new strategies for breast cancer prevention with specific bioactive food components or diet.

Competition and pesticide exposure affect development of invasive (Rhinella marina) and native (Fejervarya vittigera) rice paddy amphibian larvae

Increased pesticide use in rice agricultural ecosystems may alter competitive interactions between invasive and native amphibian species. We conducted an experiment with two rice paddy amphibians found in Luzon, Philippines, the invasive cane toad (Rhinella marina) and the endemic Luzon wart frog (Fejervarya vittigera), to determine whether exposure to a common herbicide, butachlor, drives competitive interactions in favor of the invasive amphibian. Our results revealed that competition had a strong effect on the development of both species, but in opposing directions; Luzon wart frog tadpoles were smaller and developed slower than when raised alone, whereas cane toad tadpoles were larger and developed faster. Contrary to our predictions, development and survival of endemic wart frog tadpoles was not affected by butachlor, whereas invasive cane toad tadpoles were affected across several endpoints including gene expression, body size, and survival. We also observed an interaction between pesticide exposure and competition for the cane toad, where survival declined but body size and expression of thyroid sensitive genes increased. Taken together, our findings indicate that the success of the cane toad larvae in rice fields may be best explained by increased rates of development and larger body sizes of tadpoles in response to competition with native Luzon wart frog tadpoles rather than lower sensitivity to a common pesticide. Our results for the cane toad also provide evidence that butachlor can disrupt thyroid hormone mediated development in amphibians, and further demonstrate that important species interactions such as competition can be affected by pesticide exposure in aquatic ecosystems.

Interactions between a small chronic increase in diel water temperature and exposure to a common environmental contaminant on development of Arizona tiger salamander larvae

Global climate change leading to increased temperatures may affect shifts in physiological processes especially in ectothermic organisms. Temperature-dependent shifts in developmental rate in particular, may lead to life-long changes in adult morphology and physiology. Combined with anthropogenic changes in the chemical environment, changes in developmental outcomes may affect adult functionality. The purpose of this study is to determine 1) if small increases in diel water temperature affect the development of Arizona tiger salamander (Ambystoma tigrinum nebulosum) larvae, and 2) if this change interacts with exposure to the common environmental thyroid disrupting compound, perchlorate. Larvae between Watson and Russell developmental stages 8-13 were exposed to ammonium perchlorate (AP) at doses of 0, 20 or 200ppb and then raised at either ambient or a 0.9°C elevated above ambient temperature for 81days in outdoor enclosures. During the first 5 treatment weeks, AP treatment induced slower development and smaller snout-vent length (SVL) of exposed larvae, but only in the elevated temperature group. During the later stages of development, the small increase in temperature, regardless of AP treatment, tended to decrease the time to metamorphosis and resulted in a significantly smaller body mass and worse body condition. Our results suggest that even small diel water temperature increases can affect the developmental process of salamanders and this shift in the water temperature may interact with a common environmental contaminant.

A meta-analysis synthesizing the effects of pesticides on swim speed and activity of aquatic vertebrates

Pesticide contaminants are ubiquitous in aquatic environments and pose a threat to biodiversity. Pesticides also have diverse mechanisms of action that make it difficult to identify impacts on exposed wildlife. Behavioral measures represent an important link between physiological and ecological processes, and are often used to generalize sub-lethal effects of pesticide exposure. In order to bridge the toxicological and behavioral literature, and identify chemical classes that denote the largest threat, we conducted a meta-analysis summarizing the effects of pesticides on swim speed and activity of aquatic vertebrates. We found that exposure to environmentally relevant concentrations of pesticides reduced the swim speed of exposed amphibians and fish by 35%, and reduced overall activity by 72%. There were also differences in the magnitude of this effect across chemical classes, which likely reflect underlying physiological processes. Pyrethroids, carbamates, and organophosphates all produced a large decrease in swim speed, where as phosphonoglycines and triazines showed no overall effect. Pyrethroids, carbamates, organophosphates, organochlorines, and organotins also produced a large decrease in activity, while phosphonoglycines had no overall effect, and triazines had the opposite effect of increasing activity. Our results indicate that even sub-lethal concentrations of pesticides have a strong effect on critical behaviors of aquatic vertebrates, which can affect fitness and alter species interactions. We expect our synthesis can be used to identify chemical classes producing the largest sub-lethal effects for further research and management.

Estrogenic environmental contaminants alter the mRNA abundance profiles of genes involved in gonadal differentiation of the American bullfrog

Wildlife and human populations are exposed to anthropogenic mixtures of chemicals in the environment that may adversely influence normal reproductive function and development. We determined the effects of exposure to estrogenic chemicals and wastewater effluent (WWE) on developing gonads of the American bullfrog, Rana (Lithobates) catesbeiana, a species whose widespread distribution make it an ideal model for environmental monitoring of endocrine effects of chemical contaminants. Premetamorphic bullfrog tadpoles were exposed to treatment vehicle, 17β-estradiol (E2; 10(-9)M) or 4-tert-octylphenol (OP; 10(-9)M, 10(-8)M, and 10(-7)M). Additionally, gonadal differentiation was evaluated in bullfrog tadpoles from a WWE-containing site versus those from a reference location receiving no WWE. In both studies, phenotypic sex, steroidogenic factor-1 (nr5a1), and aromatase (cyp19a1) mRNA levels using quantitative real-time PCR were determined. Exposure to E2 or OP did not alter sex ratios. In controls, both nr5a1 and cyp19a1 transcript levels exhibited sexual dimorphism, with males demonstrating higher levels of nr5a1 and females greater abundance of cyp19a1. However, E2 exposure increased cyp19a1 mRNA abundance in testes and decreased levels in ovaries, eliminating the sexual dimorphism observed in controls. E2-exposed males exhibited increased nr5a1 transcript levels in the testes compared to controls, while females demonstrated no E2 effect. OP treatment had no effect on female cyp19a1 mRNA abundance, but exposure to 10(-7)M OP increased testicular transcript levels. Treatment with 10(-9) and 10(-8)M OP, but not 10(-7)M, resulted in decreased abundance of nr5a1 transcript in both ovaries and testes. Animals from the field had sexually dimorphic gonadal levels of cyp19a1, but both sexes from the WWE site exhibited elevated cyp19a1 transcript abundance compared to the reference location. Individual chemical compounds and anthropogenic wastewater effluent dispersed within the environment influence the levels of gonadal mRNA encoding key proteins involved in gonadal differentiation.

Enabling comparative gene expression studies of thyroid hormone action through the development of a flexible real-time quantitative PCR assay for use across multiple anuran indicator and sentinel species

Studies performed across diverse frog species have made substantial contributions to our understanding of basic vertebrate development and the natural or anthropogenic environmental factors impacting sensitive life stages. Because, anurans are developmental models, provide ecosystems services, and act as sentinels for the identification of environmental chemical contaminants that interfere with thyroid hormone (TH) action during postembryonic development, there is demand for flexible assessment techniques that can be applied to multiple species. As part of the "thyroid assays across indicator and sentinel species" (TAXISS) initiative, we have designed and validated a series of cross-species real time quantitative PCR (qPCR) primer sets that provide information on transcriptome components in evolutionarily distant anurans. Validation for fifteen gene transcripts involved a rigorous three-tiered quality control within tissue/development-specific contexts. Assay performance was confirmed on multiple tissues (tail fin, liver, brain, and intestine) of Rana catesbeiana and Xenopus laevis tadpoles enabling comparisons between tissues and generation of response profiles to exogenous TH. This revealed notable differences in TH-responsive gene transcripts including thra, thrb, thibz, klf9, col1a2, fn1, plp1, mmp2, timm50, otc, and dio2, suggesting differential regulation and susceptibility to contaminant effects. Evidence for the applicability of the TAXISS anuran qPCR assay across seven other species is also provided with five frog families represented and its utility in defining genome structure was demonstrated. This novel validated approach will enable meaningful comparative studies between frog species and aid in extending knowledge of developmental regulatory pathways and the impact of environmental factors on TH signaling in frog species for which little or no genetic information is currently available.

Thyroid hormone-dependent development in Xenopus laevis: a sensitive screen of thyroid hormone signaling disruption by municipal wastewater treatment plant effluent

Because thyroid hormones (THs) are conserved modulators of development and physiology, identification of compounds adversely affecting TH signaling is critical to human and wildlife health. Anurans are an established model for studying disruption of TH signaling because metamorphosis is dependent upon the thyroid system. In order to strengthen this model and identify new gene transcript biomarkers for TH disruption, we performed DNA microarray analysis of Xenopus laevis tadpole tail transcriptomes following treatment with triiodothyronine (T(3)). Comparison of these results with previous studies in frogs and mammals identified 36 gene transcripts that were TH-sensitive across clades. We then tested molecular biomarkers for sensitivity to disruption by exposure to wastewater effluent (WWE). X. laevis tadpoles, exposed to WWE from embryo through metamorphosis, exhibited an increased developmental rate compared to controls. Cultured tadpole tails showed dramatic increases in levels of four TH-sensitive gene transcripts (thyroid hormone receptor β (TRβ), deiodinase type II (DIO2), and corticotropin releasing hormone binding protein (CRHBP), fibroblast activation protein α (FAPα)) when exposed to T(3) and WWE extracts. TRβ, DIO2, and CRHBP were identified as TH sensitive in other studies, while FAPα mRNA transcripts were highly TH sensitive in our array. The results validate the array and demonstrate TH-disrupting activity by WWE. Our findings demonstrate the usefulness of cross-clade analysis for identification of gene transcripts that provide sensitivity to endocrine disruption. Further, the results suggest that development is disrupted by exposure to complex mixes of compounds found in WWE possibly through interference with TH signaling.

Genes to ecosystems: exploring the frontiers of ecology with one of the smallest biological units

Genes and their expression levels in individual species can structure whole communities and affect ecosystem processes. Although much has been written about community and ecosystem phenotypes with a few model systems, such as poplar and goldenrod, here we explore the potential application of a community genetics approach with systems involving invasive species, climate change and pollution. We argue that community genetics can reveal patterns and processes that otherwise might remain undetected. To further facilitate the community genetics or genes-to-ecosystem concept, we propose four community genetics postulates that allow for the conclusion of a causal relationship between the gene and its effect on the ecosystem. Although most current studies do not satisfy these criteria completely, several come close and, in so doing, begin to provide a genetic-based understanding of communities and ecosystems, as well as a sound basis for conservation and management practices.

Comparative endocrinology in the 21st century

Hormones coordinate developmental, physiological, and behavioral processes within and between all living organisms. They orchestrate and shape organogenesis from early in development, regulate the acquisition, assimilation, and utilization of nutrients to support growth and metabolism, control gamete production and sexual behavior, mediate organismal responses to environmental change, and allow for communication of information between organisms. Genes that code for hormones; the enzymes that synthesize, metabolize, and transport hormones; and hormone receptors are important targets for natural selection, and variation in their expression and function is a major driving force for the evolution of morphology and life history. Hormones coordinate physiology and behavior of populations of organisms, and thus play key roles in determining the structure of populations, communities, and ecosystems. The field of endocrinology is concerned with the study of hormones and their actions. This field is rooted in the comparative study of hormones in diverse species, which has provided the foundation for the modern fields of evolutionary, environmental, and biomedical endocrinology. Comparative endocrinologists work at the cutting edge of the life sciences. They identify new hormones, hormone receptors and mechanisms of hormone action applicable to diverse species, including humans; study the impact of habitat destruction, pollution, and climatic change on populations of organisms; establish novel model systems for studying hormones and their functions; and develop new genetic strains and husbandry practices for efficient production of animal protein. While the model system approach has dominated biomedical research in recent years, and has provided extraordinary insight into many basic cellular and molecular processes, this approach is limited to investigating a small minority of organisms. Animals exhibit tremendous diversity in form and function, life-history strategies, and responses to the environment. A major challenge for life scientists in the 21st century is to understand how a changing environment impacts all life on earth. A full understanding of the capabilities of organisms to respond to environmental variation, and the resilience of organisms challenged by environmental changes and extremes, is necessary for understanding the impact of pollution and climatic change on the viability of populations. Comparative endocrinologists have a key role to play in these efforts.

Drinking water with uranium below the U.S. EPA water standard causes estrogen receptor-dependent responses in female mice

BACKGROUND

The deleterious impact of uranium on human health has been linked to its radioactive and heavy metal-chemical properties. Decades of research has defined the causal relationship between uranium mining/milling and onset of kidney and respiratory diseases 25 years later.

OBJECTIVE

We investigated the hypothesis that uranium, similar to other heavy metals such as cadmium, acts like estrogen.

METHODS

In several experiments, we exposed intact, ovariectomized, or pregnant mice to depleted uranium in drinking water [ranging from 0.5 microg/L (0.001 microM) to 28 mg/L (120 microM).

RESULTS

Mice that drank uranium-containing water exhibited estrogenic responses including selective reduction of primary follicles, increased uterine weight, greater uterine luminal epithelial cell height, accelerated vaginal opening, and persistent presence of cornified vaginal cells. Coincident treatment with the antiestrogen ICI 182,780 blocked these responses to uranium or the synthetic estrogen diethylstilbestrol. In addition, mouse dams that drank uranium-containing water delivered grossly normal pups, but they had significantly fewer primordial follicles than pups whose dams drank control tap water.

CONCLUSIONS

Because of the decades of uranium mining/milling in the Colorado plateau in the Four Corners region of the American Southwest, the uranium concentration and the route of exposure used in these studies are environmentally relevant. Our data support the conclusion that uranium is an endocrine-disrupting chemical and populations exposed to environmental uranium should be followed for increased risk of fertility problems and reproductive cancers.

Toxic response of endosulfan to breeding and non-breeding female mosquitofish

To investigate if toxic effects by endosulfan, a commonly used insecticide, are dependent on the breeding condition of an organism, both breeding and non-breeding female western mosquitofish, Gambusia affinis, were exposed to 0.1, 0.5, 1 ppb of endosulfan. After a 5-week exposure period, we examined physical factors such as ovary weight and anal fin length in fish of both reproductive conditions and the size of thyroid follicles in non-breeders. Breeding female fish exposed to endosulfan did not show any significant changes in physical factors, but non-breeding females exposed to endosulfan had a significantly greater ratio of anal fin/ body length and larger thyroid follicles than did control females. These results demonstrate that the response to exposure to environmental contaminants may be dependent upon seasonal reproductive condition.

Exposure to 4-tert-octylphenol accelerates sexual differentiation and disrupts expression of steroidogenic factor 1 in developing bullfrogs

Sex-specific gonadal steroidogenesis during development is critical to differentiation of the sexually dimorphic phenotype and reproductive function of adult organisms. Environmental contaminants may affect the process of sexual differentiation through disruption of steroid production and/or action. Control of the steroidogenic metabolic pathway is regulated partly by P450 cytochrome hydroxylases, and the expression of many of these enzymes is controlled by the orphan nuclear receptor, steroidogenic factor-1 (SF-1). In mammals, SF-1 expression is critical for development of the reproductive axis and adult reproductive function. In the bullfrog Rana catesbeiana, during sequential stages of development encompassing sexual differentiation, SF-1 protein expression becomes elevated in ovaries of sexually differentiating females, whereas expression in testes decreases. We exposed tadpoles to the industrial pollutant octylphenol (OP) for 24 hr before and during the critical stages of sexual differentiation to determine whether this known endocrine disruptor affects sex differentiation and SF-1 expression. We found that both females and males treated with an environmentally relevant low dose (10(-9)M) of OP underwent early gonadal differentiation. Furthermore, OP exposure disrupted the sexually dimorphic expression of SF-1 that occurs during sexual differentiation. Our results suggest that OP exposure may affect developmental processes that could ultimately influence adult reproductive function and that these disruptive effects may be mediated in partly through disturbances in gene regulation by SF-1.

Sexually dimorphic expression of steroidogenic factor 1 (SF-1) in developing gonads of the American bullfrog, Rana catesbeiana

Genetic sex determination leads to gonadal differentiation and ultimately the differences between the sexes in steroid hormone secretion. Gonadal steroidogenesis is critical for the development of a sexually dimorphic phenotype and adult reproductive function. Control of gonadal development and steroidogenesis is under the regulation, at least in part, of steroidogenic factor-1 (SF-1). We have begun to characterize SF-1 expression in an amphibian to determine the role of this protein in development and reproduction. We have detected a putative SF-1 protein from several tissues in the American bullfrog, Rana catesbeiana, that co-migrates with mouse SF-1 on a Western blot. Our results show that bullfrog SF-1 protein is expressed in steroidogenic and other reproductive tissues in a manner similar to that reported for other species, with high expression in the brain, pituitary, gonad, liver, and interrenal, but little or no expression in non-reproductive tissues such as skin and intestine. Using a quantitative Western blot analysis system, we documented changes in SF-1 protein in the gonads of developing tadpoles. Our results indicate that there is sexually dimorphic expression of SF-1 protein that becomes evident at the time of sexual differentiation of the gonads. In males, the expression of SF-1 decreases following testicular formation and in females the expression increases with the formation of ovaries. This is the first study to investigate changes in SF-1 during development at the protein level. The expression is similar to that reported for changes in SF-1 mRNA expression in chickens and alligators, however, opposite to that seen in mammals and turtles. These results indicate that SF-1 may play a pivotal role in development of the reproductive system in amphibians as it does in other vertebrate groups.

Endosulfan exposure disrupts pheromonal systems in the red-spotted newt: a mechanism for subtle effects of environmental chemicals

Because chemicals introduced into the environment by humans can affect both long-term survivorship and reproduction of amphibians, discovering the specific mechanisms through which these chemicals act may facilitate the development of plans for amphibian conservation. We investigated the amphibian pheromonal system as a potential target of common environmental chemicals. By treating female red-spotted newts, Notophthalmus viridescens, to a commonly used insecticide, endosulfan, we found that the pheromonal system is highly susceptible to low-concentration exposure. The impairment of the pheromonal system directly led to disrupted mate choice and lowered mating success. There were no other notable physiologic or behavioral changes demonstrated by the animals at the insecticide concentrations administered. Our findings suggest that the amphibian pheromonal system is one of the systems subject to subtle negative effects of environmental chemicals.

Repellent function of male pheromones in the red-spotted newt

Pheromones act as attractants and sexual stimulants in most vertebrates. For example, in red-spotted newts, Notophthalmus viridescens, female pheromones attract males, and male pheromones increase female receptivity. However, no studies have determined whether male vertebrates produce a pheromone that repels competing males. Through a series of olfactory mate selection tests, we found that sexually motivated male red-spotted newts produce a pheromone that functions to repel other approaching males. Our finding is the first report of a repelling function for pheromones in male vertebrates. The pheromones may act to increase both the sender's and receiver's mating success when the operational sex ratio (OSR) is male biased.

Effects of dehydration on plasma osmolality, thirst-related behavior, and plasma and brain angiotensin concentrations in Couch's spadefoot toad, Scaphiopus couchii

Under dehydrating conditions, many terrestrial vertebrates species exhibit increases in plasma osmolality and their drinking behavior. Under some circumstances, this behavioral change is accompanied by changes in plasma and central angiotensin concentrations, and it has been proposed that these changes in angiotensin levels induce the thirst-related behaviors. In response to dehydration, the spadefoot toad, Scaphiopus couchii, exhibits thirst-related behavior in the form of cutaneous drinking. This behavior has been termed water absorption response (WR) behavior. Spadefoot toads live in harsh desert environments and are subject annually to dehydrating conditions that may induce thirst-related behavior. We tested the hypothesis that an increase in WR behavior is associated with both an increase in plasma osmolality and an increase in plasma and brain angiotensin concentrations. First, we determined the degree of dehydration that was necessary to initiate WR behavior. Animals dehydrated to 85% of their standard bladder-empty weight via deprivation of water exhibited WR behavior more frequently than control toads left in home containers with water available. Next, using the same dehydration methods, we determined the plasma osmolality and sodium concentrations of dehydrated toads. Toads dehydrated to 85% standard weight also had a significant increase in plasma osmolality, but exhibited no overall change in plasma sodium concentrations, indicating that while an overall increase in plasma osmolality appears to be associated with WR behavior in S. couchii, changes in sodium concentrations alone are not sufficient to induce the behavior. Finally, plasma and brain angiotensin concentrations were measured in control toads and toads dehydrated to 85% standard weight. Plasma and brain angiotensin concentrations did not increase in dehydrated toads, indicating that dehydration-induced WR behavior that is associated with changes in plasma osmolality may not be induced by changes in endogenous angiotensin concentrations in S. couchii.

Intra- and extracellular dehydration has no effect on plasma levels of angiotensin II in an amphibian

Previous studies have demonstrated that both dehydration (intra and extracellular) and treatment with angiotensin II (A-II) induce changes in thirst-related behavior in the spadefoot toad, Scaphiopus couchii. One of the steps in determining a causal relationship between a hormone and a behavior is to determine that there is association between an animal's performance of the behavior and changes in endogenous hormonal concentrations. The hypothesis tested that plasma levels of the peptide hormone A-II would change as a result of dehydration known to induce water absorption response (WR) behavior in the spadefoot toad. Plasma samples were taken from toads dehydrated intracellularly by injection of hypertonic solutions of NaCl or sucrose at levels known to induce WR behavior. As an osmotic control, a group of animals was injected with urea, which has been demonstrated to not induce WR behavior. In order to determine the effects of extracellular dehydration on plasma, A-II levels in toads dehydrated by plasma volume depletion via cardiac puncture were compared to sham-punctured controls. None of the treatments in any experiment resulted in significant differences in plasma levels of angiotensin II among groups sampled at the time when WR behavior occurs. These results do not support the hypothesis that dehydration-induced thirst is stimulated by changes in plasma A-II concentrations at the onset of WR behavior. J. Exp. Zool. 286:343-349, 2000.

Cloning of proopiomelanocortin from the brain of the african lungfish, Protopterus annectens, and the brain of the western spadefoot toad, Spea multiplicatus

A degenerate primer, specific for the opioid core sequence YGGFM, was used to clone and sequence proopiomelanocortin (POMC) cDNAs from the brain of the African lungfish, Protopterus annectens, and from the brain of the western spadefoot toad, Spea multiplicatus. In addition, the opioid-specific primer was used to clone and sequence a 3'RACE product corresponding to a portion of the open reading frame of S. multiplicatus proenkephalin. For both species, cDNA was made from a single brain and a degenerate opioid-specific primer provided a reliable probe for detecting opioid-related cDNAs. The African lungfish POMC cDNA was 1,168 nucleotides in length, and contained regions that are similar to tetrapod POMCs and fish POMCs. The African lungfish POMC encodes a tetrapod-like gamma-MSH sequence that is flanked by sets of paired basic amino acid proteolytic cleavage sites. The gamma-MSH region in ray-finned fish POMCs either has degenerate cleavage sites or is totally absent in some species. However, the African lungfish gamma-MSH sequence does contain a deletion which has not been observed in tetrapod gamma-MSH sequences. The beta-endorphin region of lungfish POMC has the di-amino acid sequence tryptophan-aspartic acid in the N-terminal region and an additional glutamic acid residue in the C-terminal region of beta-endorphin - features found in fish beta-endorphin, but not tetrapod beta-endorphins. The western spadefoot toad POMC was 1,186 nucleotides in length, and exhibited an organizational scheme typical for tetrapod POMCs. However, the toad POMC did lack a paired basic amino acid proteolytic cleavage site N-terminal to the beta-MSH sequence. Thus, like rat POMC, it is doubtful that beta-MSH is an end product in either the toad brain or intermediate pituitary. At the amino acid level, the toad POMC had 76% sequence identity with Xenopus laevis POMC and 68% sequence identity with Rana ribidunda POMC. The use of these POMC sequences to assess phylogenetic relationships within anuran amphibians will be discussed. With respect to the fragment of S. multiplicatus proenkephalin cDNA, two metenkephalin sequences and the metenkephalin-RF sequence were found encoded in this fragment. As seen for X. laevis and R. ridibunda proenkephalin, a leuenkephalin sequence was not detected in the C-terminal region of the S. multiplicatus proenkephalin. The absence of a leuenkephalin sequence may be a common feature of anuran amphibian proenkephalins.

Intra- and extracellular dehydration-induced thirst-related behavior in an amphibian

The behavioral response to dehydration is critical to an animal's survival. Because of their permeable skin, amphibians are particularly sensitive to dehydrating conditions. We tested the hypothesis that different forms of dehydration induce water absorption response (WR) behavior in the desert spadefoot toad, Scaphiopus couchii. First, we determined the behavioral response to intracellular dehydration by treating fully hydrated toads with increasing concentrations of hypertonic solutions of NaCl or sucrose via intraperitoneal injection (i.p.). Animals that were treated to induce intracellular dehydration with either solute exhibited a significant increase in WR behavior compared to vehicle-treated controls. To distinguish that the response was a result of an increased osmotic gradient between the intra- and extracellular compartments, we treated fully hydrated animals i.p. with urea, which freely passes into the intracellular compartment and increases overall animal osmolarity. Urea treatment did not induce WR behavior. To determine the response to extracellular dehydration, the blood volume of fully hydrated toads was reduced via cardiac puncture, and the WR behavior was measured. Animals who had a reduction in blood volume exhibited a significant increase in WR behavior compared to sham-punctured controls. Our results are the first to demonstrate that multiple forms of dehydration can induce thirst-related behavior in amphibians.

Unilateral ovariectomy influences hypothalamic monoamine asymmetries in a lizard (Anolis) that exhibits alternation of ovulation

The lizard Anolis carolinensis alternates ovulation, and the resultant ovarian asymmetry correlates with alternating asymmetry of hypothalamic catecholamines. Unilateral and bilateral ovariectomies of cycling females were performed to determine if ovarian manipulations influence hypothalamic catecholamine asymmetries. During the middle of the ovarian cycle, we removed the larger ovary, i.e., the next one to ovulate an egg (N = 9), the smaller ovary with its corpus luteum (N = 8), or both ovaries (N = 5). A sham-operated control group was included (N = 9). The diameter of the largest ovarian follicle in each ovary was measured at the beginning and end of the experiment. After 12 days, the hemihypothalami from the sides of the initial smaller ovary (SO) and larger ovary (LO) were dissected and frozen for determination of monoamines and their metabolites using HPLC and electrochemical detection. Monoamine and metabolite concentrations at the end of the experiment in the original SO and LO sides of each hypothalamus were compared with an asymmetry ratio, or AR, of (SO side - LO side)/(SO side + LO side). No female ovulated during the experiment. Unilateral ovariectomy caused compensatory growth of the largest follicle in the remaining ovary. Removal of the SO or LO caused the AR of DOPAC to favor the brain side ipsilateral to that of the ovarian removal. Removal of the LO switched the NE AR from the SO to the LO side. Removal of the LO or SO caused the MHPG AR to favor the LO side. Ovariectomy of any kind caused 5-HT, which in the sham-operated animals favored the SO side, to become symmetric, and removal of the LO caused the 5-HIAA AR to favor the LO side. We conclude that the ovaries influence hypothalamic catecholamine asymmetries in Anolis via direct neural (as well as hormonal) pathways and that sensory input from the ovaries to the hypothalamus could be involved in control of ovarian alternation via both neural and hormonal efferent mechanisms.

Differential effects of arginine vasotocin and gonadotropin-releasing hormone on sexual behaviors in an anuran amphibian

Both arginine vasotocin (AVT) and gonadotropin-releasing hormone (GnRH) are known to influence sexual behavior in many vertebrate taxa. We investigated the effects of both of these peptides on two different sexual behaviors, calling and amplexus, in the Great Plains toad (Bufo cognatus). AVT, at a dosage of 100 microg/100 g toad, significantly increased both the amount of calling behavior per individual and the probability that an individual would call. GnRH, however, had no effect on calling behavior. There was a reciprocal effect of these peptides on amplexus: AVT did not induce amplexus, while GnRH significantly induced this behavior. Furthermore, AVT-induced calling could be inhibited by Manning compound (an arginine vasopressin receptor antagonist). This is the first report of GnRH influencing sexual behavior in an anuran amphibian. These results suggest that specific sexual behaviors in B. cognatus may be under the regulation of independent peptide control.

Effects of androgens on male sexual behavior and secondary sex characters in the explosively breeding spadefoot toad, Scaphiopus couchii

In male Scaphiopus couchii, plasma elevations in androgens are associated with the seasonal expression of sexual behavior. To test the hypothesis that androgens are necessary for the expression of one aspect of sexual behavior, amplexus, and for the development of secondary sex characteristics in male S. couchii, the effects of testosterone (T) and dihydrotestosterone (DHT) on clasping behavior and thumb pad growth were investigated. Forty toads were divided into five treatment groups as follows: (1) intact, with no hormonal or surgical treatment; (2) sham-castrated, with silastic implants of cholesterol; (3) sham-castrated, with implants of T and DHT; (4) castrated, with implants of cholesterol; and (5) castrated, with implants of T and DHT. Displays of sexual behavior (amplexus) for each individual were counted during a 3-hr observation period at 2, 4, and 7 weeks after the surgical procedure. For each observation trial, there was no significant difference in the amount of clasping among treatment groups: virtually all individuals from each group displayed vigorous clasping. No calling was noted at any time. Thumb pad darkness of each individual was assessed at the 4- and 7-week time intervals. At both time periods, the thumb pads of androgen-treated males were significantly darker than those of cholesterol-treated males, while intact males remained intermediate. Measurement of plasma steroid levels from the treatment groups indicated that androgens were basal in the castrate group and higher in the implant treatment. These results suggest that in S. couchii, although androgens are associated temporally with the onset of reproductive behavior, they are not necessary for its expression. The elevation in androgens during the reproductive period may be instead important in the development and maintanence of secondary sex characteristics and possibly other reproductive functions.

Reproductive endocrinology of the explosively breeding desert spadefoot toad, Scaphiopus couchii

The spadefoot toad, Scaphiopus couchii, is an explosively breeding, desert dwelling amphibian that shows two characteristics hypothesized to select for a dissociated breeding pattern: it lives in a harsh environment and it has a very short, but predictable breeding period. We tested the hypothesis that these factors select for a dissociated breeding cycle by measuring plasma steroid hormones and the gametogenic cycles in a free-living population of S. couchii. Blood and tissue samples were obtained from prebreeding, calling (males only), amplexed, and postbreeding toads. In males, plasma testosterone (T), dihydrotestosterone (DHT), and corticosterone (B) differed significantly among reproductive groups, with calling and amplexing toads having the highest levels of each of these steroids. In females, plasma T, DHT, B, progesterone (P), and estradiol (E2) were measured; all steroids except B changed significantly among mating groups. Plasma T and E2 were greatest in prebreeding and amplexed females, while P and DHT were highest only in amplexed females. Primary spermatogonia (SPG I), secondary spermatogonia (SPG II), spermatocytes, spermatids (SPT), and spermatozoa embedded in Sertoli cells (SPS) all changed significantly among male breeding groups. Although all stages were present in all breeding groups, early stages of spermatozoa (SPG I and SPG II) were greatest in postbreeding males, while late stages (SPT and SPS) were highest in prebreeding, calling, and amplexing males. In females, oocyte stages I, II, III, V, and VI and atretic follicles also differed significantly among mating groups. Prebreeding female ovaries were dominated by late-stage (V and VI) oocytes which were subsequently ovulated during amplexus. In postbreeding females, oogenesis was well under way as indicated by the rising numbers of stage II and III oocytes. These results indicate that aspects of gametogenesis occur during and after breeding in both sexes. Although the results demonstrate that gonadal activity was high during the period of sexual activity, suggesting that S. couchii most closely fits an associated pattern of reproduction as defined by Crews (1984, Horm. Behav. 18, 22-28), we also found that gonadal activity continued past the breeding season. For this reason, S. couchii does not completely conform to an associated pattern.

Central angiotensin II induces thirst-related responses in an amphibian

Angiotensin II (A-II), a potent inducer of thirst-related behavior in many vertebrate species, was injected into the third ventricle of the brain of the spadefoot toad, Scaphiopus couchii. Following injection of 10 ng A-II the animals demonstrated a significant increase in water absorption response (WR) behavior, in which toads press their ventral skin to a moist surface and absorb water by osmosis. This increase in the frequency of WR behavior was positively correlated with an increase in water gain during a 2-hr period indicating that centrally injected A-II stimulates water intake by this amphibian species. We have previously demonstrated that WR behavior is also induced by intraperitoneal (i.p.) injections of A-II in several anuran species, including S. couchii. Thus, amphibians, like other vertebrates, demonstrate an increase in water intake in response to either centrally administered or circulating A-II. A second series of experiments was conducted to determine whether the above response to A-II might be secondary to increases in the circulating levels of aldosterone (ALDO) or antidiuretic hormone because the release of both of these hormones has been shown by others to be stimulated by A-II. Scaphiopus couchii injected i.p. with either ALDO or arginine vasotocin in dosages of 1, 10, and 100 micrograms/100 g body weight showed no increase in WR behavior relative to toads injected with saline alone. These results suggest that A-II acts directly on the brain of S. couchii to induce WR behavior.