James A Carr

James A Carr
Texas Tech University | TTU · Department of Biological Sciences

About

138
Publications
47,003
Reads
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3,787
Citations
Additional affiliations
August 1991 - present
Texas Tech University
Position
  • Professor (Full)
August 1988 - August 1991
University of New Mexico Hospitals
Position
  • NIH Postdoctoral Fellow
August 1982 - August 1988
University of Colorado Boulder
Position
  • PhD Student

Publications

Publications (138)
Article
Full-text available
Animals in the wild must balance food intake with vigilance for predators in order to survive. The optic tectum plays an important role in the integration of external (predators) and internal (energy status) cues related to predator defense and prey capture. However, the role of neuromodulators involved in tectal sensorimotor processing is poorly s...
Article
Full-text available
There are no behavioral models for testing anxiety in amphibians, a group of animals widely used for developmental, ecotoxicological, and genetic research. We aimed to validate two common rodent paradigms, the plus maze and the scototaxis test, for use in the aquatic African clawed frog (Xenopus laevis). We predicted: (a) that frogs would prefer th...
Article
The optic tectum and superior colliculus rapidly inhibit food intake when a visual threat is present. Previous work indicates that CRF, acting on CRFR1 receptors, may play a role in tectal inhibition of feeding behavior and food intake. Here we test the hypothesis that tectal CRFR1 receptors modulate food intake and feeding behavior in juvenile Xen...
Article
It is well established that hypothalamic neurons producing the peptide corticotropin-releasing factor (CRF) play a key role in stress adaptation, including reduction of food intake when a threat or stressor is present. We have previously reported on the presence of an intrinsic CRF signaling system within the optic tectum (OT), a brain area that pl...
Article
We examined gonads and thyroid glands of Gulf killifish (Fundulus grandis) 1yr after the Deepwater Horizon oil spill. F. grandis were trapped from two impacted sites in Barataria Bay (Bayou St. Denis, Bay Jimmy) and an un-impacted site in East Texas (Sabine Pass). The greatest number of F. grandis were collected at Sabine Pass. F. grandis collected...
Article
Full-text available
Predators impact prey in direct (lethal) and indirect (non-lethal) manners. Predator-avoidance models capitalize on the non-lethal effects of predators to study how predator-induced fear impacts prey behavior and physiology. Here, we aimed to develop a predator avoidance model to determine how predators alter feeding and anxiety-like behavior in th...
Article
Full-text available
Although there is general agreement that the central nucleus of the amygdala (CeA) is critical for triggering the neuroendocrine response to visual threats, there is uncertainty about the role of subcortical visual pathways in this process. Primates in general appear to depend less on subcortical visual pathways than other mammals. Yet, imaging stu...
Article
We investigated stage-dependent changes in sensitivity of the thyroid gland to perchlorate during development of African clawed frog tadpoles (Xenopus laevis) in relation to non-thyroidal iodide transporting tissues. Perchlorate-induced increases in thyroid follicle cell size and colloid depletion were blunted when exposures began at Nieuwkoop-Fabe...
Chapter
The thyroid axis of non-mammalian vertebrates shows many parallels to mammals with respect to thyroid structure and to the synthesis and metabolism of thyroid hormones as well as to their actions. T3 appears to be the more active form of thyroid hormones in all vertebrates. Thyroid hormones appear to interact with a variety of other endocrine-regul...
Chapter
Feeding is regulated by bioregulators secreted from adipose tissue and the GI tract as well as by local neuropeptides and endocannabinoids secreted by neurons in appetite-regulating areas of the NTS and hypothalamus. Peripheral factors affecting feeding are largely inhibitory (anorexic). Only one peptide produced in the periphery, ghrelin, stimulat...
Chapter
Regulation of feeding in non-mammals is similar to mammals although it has not been studied extensively in non-mammals other than teleost fishes. Orexigenic actions in fishes have been shown for ghrelin, NPY, galanin and orexins. CCK8 , CRH, urotensin-I, CART, and PrRP are anorexic. Orexins stimulate feeding in anurans and leptin is present in newt...
Chapter
Non-mammalian vertebrates do not exhibit the anatomical cortex-medullary relationship like mammals for the homologous adrenocortical cells and chromaffin cells. However, there is a general trend for a closer anatomical relationship between these tissues from being entirely separate in ancient fishes with direct associations with the kidneys to the...
Chapter
Neurotransmitters, neurohormones, and hormones occur as peptides, proteins, modified amino acids (indoleamines, catecholamines, thyroid hormones), or lipids (steroids, eicosanoids). Peptides and proteins neurohormones and hormones are synthesized as preprohormones and are modified posttranslationally to prohormones and then cleaved again to the fin...
Chapter
Endocrinologists use the scientific method to develop and test hypotheses involved in bioregulation. Experiments are designed using rigorous controls and appropriate sample sizes to ensure reproducibility. A scientific theory develops from a collection of facts that are constructed using the scientific theory and careful experimentation. There are...
Chapter
The mammalian adrenal gland consists of an outer region (cortex) of adrenocortical cells (steroidogenic) and an inner region (medulla) of chromaffin cells (adrenergic). The cortex consists of a zona glomerulosa that secretes aldosterone and two inner zones, zona fasciculata and zona reticularis. The zona fasciculata secretes primarily glucocorticoi...
Chapter
The adenohypophysis produces tropic hormones and consists of a pars distalis, a pars intermedia and a pars tuberalis. The embryonic origin of the secretory cells in the adenohypophysis appears to be neural in origin similar to the neurohypophysis and hypothalamus. The pars distalis produces GH, PRL, GTHs, (FSH, LH), ACTH, TSH and endorphins (EOPs)....
Chapter
The reproductive system includes the HPG axis and sex accessory structures. Primary control resides in pulsatile production of GnRH, which controls pituitary production of FSH and LH, which in turn cause gamete formation, gonadal steroid secretion, and regulation of sexual characters and reproductive behaviors. FSH is involved primarily with gamete...
Chapter
The progressive evolution of hypothalamic centers in vertebrates is evident from examination of different vertebrates. The pattern of regulation has branched within the fishes, with the most recent fishes (teleosts) exhibiting predominantly neuroglandular control of tropic hormone release. Primitive fishes, including the chondrichthyeans, and tetra...
Chapter
Bioregulation in vertebrate animals involves secretion of chemical messengers primarily by cells of the endocrine system, the immune system, and the nervous system. These bioregulators include hormones, neurocrines (neurotransmitters, neuromodulators, and neurohormones), cytocrines (autocrines, paracrines), and seminochemicals (pheromones, allelomo...
Chapter
The vertebrate thyroid gland is composed of the follicles that store T4 extracellularly in the colloid. Normal thyroid gland functioning depends upon iodide and stimuli from the hypothalamus (TRH) and the adenohypophysis (TSH). Iodide is incorporated into tyrosine residues Tgb. Iodide is added to tyrosine by TPO to form DIT. Two DITs within the Tgb...
Article
Vertebrate Endocrinology represents more than just a treatment of the endocrine system-it integrates hormones with other chemical bioregulatory agents not classically included with the endocrine system. It provides a complete overview of the endocrine system of vertebrates by first emphasizing the mammalian system as the basis of most terminology a...
Article
Previous work indicates that CRF administration inhibits visually guided feeding in amphibians. We used the African clawed frog Xenopus laevis to examine the hypothesis that CRF acts as a neurotransmitter in the in the optic tectum, the major brain area integrating the visual and premotor pathways regulating visually guided feeding in anurans. Reve...
Article
Full-text available
The use of dispersants in the Gulf of Mexico has created a number of environmental and human health concerns, chief among them are questions regarding the potential impact of Corexit 9500 on the health and fitness of Gulf wildlife. These studies were designed to use a biological toxicity test during post-fertilization and early development to evalu...
Article
Full-text available
The use of dispersants in the Gulf of Mexico has created a number of environmental and human health concerns, chief among them are questions regarding the potential impact of Corexit 9500 on the health and fitness of Gulf wildlife. These studies were designed to use a biological toxicity test during post-fertilization and early development to evalu...
Article
This study evaluated the interactions of flight, fasting, and 1,1,1-trichloro-bis(4-chlorophenyl)ethane (p,p'-DDT) loading on residue metabolism and distribution in recently exposed white-crowned sparrows (Zonotrichia leucophrys). Female sparrows were dosed with 5 mg p,p'-DDT per kg body weight over 3 d. Following 1 d of recovery, sparrows were flo...
Article
This chapter reviews the evidence that exposure to stressors alters the activity of the hypothalamus–pituitary–adrenal axis and influences reproduction in amphibians. The competing selective pressures of successfully reproducing and avoiding predation can have an impact on many aspects of an animal's behavior and physiology. At stake in this trade-...
Presentation
Leptin is a polypeptide secreted by adipose and other tissues that has a dramatic inhibitory effect on appetite in mammals. Recently, the structure of non-mammalian leptin peptides has been elucidated. Despite having very little similarity based upon primary amino acid sequences, vertebrate leptins are surprisingly conserved based upon tertiary str...
Article
Teleosts and pond-breeding amphibians may be exposed to a wide variety of anthropogenic, waterborne contaminants that affect the hypothalamus-pituitary-thyroid (HPT) axis. Because thyroid hormone is required for their normal development and reproduction, the potential impact of HPT-disrupting contaminants on natural teleost and amphibian population...
Article
Previous work has suggested that the peptide corticotropin-releasing factor (CRF) acts to inhibit visually guided feeding in anurans, but little is known about potential targets for CRF within the subcortical visuomotor circuitry. Here we investigated the relationship between CRF neuronal organization and visual pathways in toads. CRF-immunoreactiv...
Article
We examined the expression of steroidogenic acute regulatory (StAR) protein mRNA in the American bullfrog (Rana catesbeiana). Primers and probes were designed to obtain a partial sequence of bullfrog StAR cDNA consisting of 349 base pairs. Quantitative PCR analysis of StAR mRNA equivalents was performed in tissues of juvenile and adult bullfrogs. I...
Article
Nucleotide sequence comparisons have identified a gene product in the genome database of African clawed frogs (Xenopus laevis) as a probable member of the solute carrier family of membrane transporters. To confirm its identity as a putative iodide transporter, we examined the function of this sequence after heterologous expression in mammalian cell...
Article
Reproductive success and development of F2 offspring from F1 adult African clawed frogs (Xenopus laevis) exposed to atrazine throughout larval development and as sexually mature adults was examined. Larval X. laevis were exposed to one of four nominal concentrations of atrazine (0, 1, 10, 25 microg atrazine/l) beginning 96 hr after fertilization an...
Article
Full-text available
The herbicide atrazine is widely used in agriculture for the production of corn and other crops. Because of its physical and chemical properties, atrazine is found in small concentrations in surface waters--habitats for some species. A number of reports on the effects of atrazine on aquatic vertebrates, mostly amphibians, have been published, yet t...
Article
Estrogen or eco-estrogenic chemicals can disrupt normal gonadal sex differentiation, causing intersex formation and feminization in amphibians. The cellular basis for estrogen-induced sex reversal is not well understood. In the present study, we investigated the concentration- and stage-dependent effects of estradiol (E(2)) exposure during the larv...
Article
Full-text available
The purpose of this study was to determine if changes in colloidal thyroxine (T(4)) immunoreactivity can be used as a biomarker of perchlorate exposure in amphibian thyroid tissue. Larval African clawed frogs (Xenopus laevis) were exposed to 0, 1, 8, 93, and 1131 microg perchlorate/l for 38 and 69 days to cover the normal period of larval developme...
Article
Full-text available
In vitro studies have demonstrated atrazine-mediated induction of 7-ethoxyresorufin O-deethylase (EROD) activity. EROD is an enzyme active in the metabolism of many compounds, including many xenobiotics. These studies have suggested that atrazine may affect reproductive function by altering steroid metabolism. The goal of this study was to determin...
Article
The effect of ophthalmectomy (enucleation) on plasma melatonin in Rana tadpoles and froglets was studied under various experimental conditions to determine if ocular melatonin is released into the circulation from the eyes and to study the factors which might affect this process. Where operations occurred in early or mid-photophase on a 12 light:12...
Article
The triazine herbicide atrazine has been hypothesized to disrupt sexual development in frogs by up-regulating aromatase activity, resulting in greater estradiol (E2) concentrations and causing feminization in males. The goal of this study was to collect native ranid frogs from atrazine-exposed ponds and determine whether relationships exist between...
Article
Ammonium perchlorate (AP) is a widespread military waste product in the United States and is a potent thyroid function disruptor in all vertebrates tested thus far. To determine the relative contribution of ammonium ions to the toxicity of AP, we exposed embryonic and larval Xenopus laevis to various concentrations of sodium perchlorate (SP) or amm...
Article
Due to limitations of the currently used enzymatic assays, it is difficult to determine aromatase activity in testicular tissue of amphibians. Quantitative reverse transcription polymerase chain reaction (Q-RT PCR) is a sensitive and reliable technique to detect low amounts of mRNA for specific genes. This study was designed to develop and optimize...
Article
The triazine herbicide atrazine has been suggested to be a potential disruptor of normal sexual development in male frogs. The goals of this study were to collect native ranid frogs from sites in agricultural and non-agricultural areas and determine whether hypothesised atrazine effects on the gonads could be observed at the gross morphological and...
Article
Administration of corticotropin-releasing factor (CRF) or exposure to stressors inhibits feeding in anuran amphibians. Since most amphibians rely on visual cues for feeding, these findings have led to the hypothesis that CRF may modulate visuomotor pathways involved in prey detection and predator avoidance. The inhibitory effects of CRF on feeding...
Article
Full-text available
In October 2001 and March 2002, a field survey of central stonerollers (Campostoma anomalum) from perchlorate-contaminated streams in central Texas was conducted to assess thyroid endocrine disruption. A survey of adult male and female cricket frogs (Acris crepitans) was performed at the same site between 2001 and 2003. Perchlorate is an oxidizer p...
Article
Full-text available
During the past decade, the scientific community and the public have become increasingly aware that some chemicals have the potential to interfere with endocrine systems in both vertebrate and invertebrate wildlife species (WHO 2002; Ankley et al. 1998). One aspect of these effects has been the observation of gonadal abnormalities in fish, amphibia...
Article
Pollution from agrochemicals may be contributing to the global decline in amphibian populations. Environmentally relevant concentrations of nitrate and/or atrazine on anuran development and gonadal differentiation were tested. Four replicates of 20 tadpoles per tank (80/treatment) were exposed from Taylor-Kollros stage 2 to 3 to stage 23 to 34 to e...
Article
African clawed frogs (Xenopus laevis) were exposed to one of eight nominal waterborne concentrations including 0, 0.1, 1.0, 10, or 25 microg/L atrazine, 0.005% ethanol (EtOH), or 0.1mg/L estradiol (E2) or dihydrotestosterone (DHT) containing 0.005% EtOH. Frogs were exposed from 72 h posthatch until 2--3 months postmetamorphosis via a 3-day static r...
Article
The potential effects of atrazine on gonadal development in metamorphs and subadults of the African clawed frog (Xenopus laevis) were studied under conditions of natural photoperiod and temperatures in outdoor microcosms from August 2002 to June 2003 in South Africa. Triplicate 1100 L microcosms for each nominal concentration of 0.0, 1, 10, and 25...
Article
Full-text available
Some investigators have suggested that the triazine herbicide atrazine can cause demasculinization of male amphibians via upregulation of the enzyme aromatase. Male adult African clawed frogs (Xenopus laevis) were exposed to three nominal concentrations of atrazine (1, 25, or 250 microg atrazine/l) for 36 days, and testicular aromatase activity and...
Article
The purpose of this study was to determine the effects of perchlorate on thyroid function in mosquitofish. Adult mosquitofish were exposed to 0, 0.1, 1, 10, 100, and 1000 mg/L sodium perchlorate for 2, 10, and 30 d. Whole body thyroxin (T4) content and histological assessment of thyroid follicles (e.g., follicular epithelial height, hyperplasia, hy...
Article
Full-text available
The potential effects of atrazine on gonadal development in metamorphs and subadults of the African clawed frog (Xenopus laevis) were studied under conditions of natural photoperiod and temperatures in outdoor microcosms from August 2002 to June 2003 in South Africa. Triplicate 1100 L microcosms for each nominal concentration of 0.0, 1, 10, and 25...
Article
Full-text available
We tested the hypothesis that adult African clawed frogs (Xenopus laevis) inhabiting water bodies in maize-growing areas (MGA) of South Africa would exhibit differences in testicular structure compared to frogs from water bodies in non-maize-growing areas (NMGA) in the same locale. Adults of both sexes were collected during the autumn of 2002 in So...
Article
Perchlorate inhibits iodide uptake by thyroid follicles and lowers thyroid hormone production. Although several effects of perchlorate on the thyroid system have been reported, the utility of these pathologies as markers of environmental perchlorate exposures has not been adequately assessed. The present study examined time-course and concentration...
Article
The ultrastructure of testicular cells of adult male African clawed frogs (Xenopus laevis) exposed to either estradiol (0.1 microg/L) or 2-chloro-4-ethylamino-6-isopropyl-amino-s-triazine (atrazine; 10 or 100 microg/L) was examined by electron microscopy and compared to plasma concentrations of the steroid hormones, testosterone (T) and estradiol (...
Article
The objective of this study was to characterize concentrations of atrazine, terbuthylazine, and other pesticides in amphibian habitats in surface waters of a corn-production area of the western Highveld region (North-West Province) of South Africa. The study was conducted from November 2001 to June 2002, coinciding with the corn-production season....
Article
The objective of this study was to characterize concentrations of atrazine, terbuthylazine, and other pesticides in amphibian habitats in surface waters of a corn-production area of the western Highveld region (North-West Province) of South Africa. The study was conducted from November 2001 to June 2002, coinciding with the corn-production season....
Chapter
Full-text available
Although the ecological risks of atrazine in surface waters have been extensively reviewed with respect to its potential effects on a number of components of ecological systems, there is a lack of specific data on amphibians, especially for endpoints related to development and reproduction. To assess whether atrazine causes adverse effects in frogs...
Article
Adult African clawed frogs (Xenopus laevis) were collected from a corn-growing region (CGR) and a non-corn-growing region (NCGR) with different exposure profiles for atrazine and related triazines. Physical, chemical, and biological parameters from the catchment areas were also measured. Frogs were surveyed for possible effects of exposure to triaz...
Article
Full-text available
Embryos of the green frog (Rana clamitans) were collected from the field and exposed to 1 of 6 water-borne treatments for 273 d (mid July 2001 to mid April 2002). The treatments were 0, 10, or 25 microg/L atrazine, 0.005% ethanol (EtOH), or 0.1 mg/L estradiol or dihydrotestosterone carried in 0.005% EtOH. Treatments were applied in a static renewal...