Publications
| Title | Abstract | Year Filter | PMID(sorted ascending) Filter |
|---|
| the relative effectiveness of androstenedione, testosterone, and estrone, precursors to estradiol, in sex reversal in the red-eared slider (trachemys scripta), a turtle with temperature-dependent sex determination. | in many turtles the temperature during the middle of incubation determines the gonadal sex of the hatchling. sex steroid hormones have been implicated in temperature-dependent sex determination in the red-eared slider turtle, trachemys scripta; androgen is involved in male sex determination and estradiol in female sex determination. administration of exogenous estradiol and its agonists to eggs incubating at a male-producing temperature can overcome the effect of temperature and result in all-fe ... | 1995 | 8575652 |
| steroid-induced sex determination at incubation temperatures producing mixed sex ratios in a turtle with tsd. | previous studies have shown that exogenous steroid hormones can affect sex determination in reptiles with temperature-dependent sex determination (tsd). these studies have also suggested that the sensitivity of tsd to exogenous steroids may vary with incubation temperature. the majority of these studies, however, have utilized incubation temperatures producing all males or all females in the control groups, rather than temperatures which produced mixed sex ratios in control groups. the goals of ... | 1995 | 8575659 |
| role of nitric oxide in the elevation of cerebral blood flow induced by acetylcholine and anoxia in the turtle. | nitric oxide (no)-dependent regulation of brain blood flow has hitherto not been studied in reptiles. by observing the brain surface (telencephalon) of the freshwater turtle (trachemys scripta) with epiillumination microscopy, we show that topical application of acetylcholine (ach) induces an increase in cbf velocity that can be completely blocked by the no synthase inhibitor n(g)-nitro-l-arginine methyl ester (l-name). the effect of l-name was reversed by l-arginine. also, sodium nitroprusside ... | 1996 | 8594061 |
| microvascularization of the pineal gland in the freshwater turtle, pseudemys scripta elegans (reptilia): a scanning electron microscopic study of vascular corrosion casts. | gross supply, microvascular patterns, and drainage routes of the pineal gland and its vascular relations with associated structures (dorsal sac, paraphysis, choroid plexus of the third ventricle) were studied by scanning electron microscopy of microvascular corrosion casts in 10 specimens of the freshwater turtle, pseudemys scripta elegans. light microscopy of tissue sections (one transverse and one longitudinal series) served to attribute cast vascular territories to anatomical structures. the ... | 1995 | 8609602 |
| the generation of antibody diversity in the turtle. | the ab response in reptiles has been studied at the protein level, and in turtles some aspects resemble those of cold-blooded vertebrates from other classes. the genetic bases for these features are not clear. the present study is the first on the igh organization and complexity of a reptilian ig gene system. the approach to cloning turtle (pseudemys scripta) sequences is entirely pcr based, and its efficacy is demonstrated by obtaining extensive information on a heretofore unexplored ig gene sy ... | 1996 | 8621916 |
| adrenergic and cholinergic response of ventricular muscle from the turtle, trachemys (pseudemys) scripta. | muscle strips were dissected from the ventricle of the turtle, trachemys (pseudemys) scripta. individual strips were placed in a muscle bath, set at a resting tension of three grams and electrically paced at 24 min(-1) for a control period of 1 hr. cumulative dose-response curves were constructed using the adrenergic agonist, epinephrine (epi) and the cholinergic agonist, metacholine (mch). the administration of epi to the muscle bath resulted in a dose-dependent increase in active tension devel ... | 1996 | 8624904 |
| protein sequences indicate that turtles branched off from the amniote tree after mammals. | the phylogenetic relationships among the major groups of amniote vertebrates remain a matter of controversy. various alternatives for the position of the turtles have been proposed, branching off either before or after the mammals. to discover the phylogenetic position of turtles in relation to mammals and birds, we have determined cdna sequences for the eye lens proteins alpha a- and alpha b-crystallin of the red-eared slider turtle (trachemys scripta elegans). in addition, databases were searc ... | 1996 | 8662010 |
| temperature and non-aromatizable androgens: a common pathway in male sex determination in a turtle with temperature-dependent sex determination? | this study addressed the hypothesis that, in the red-eared slider turtle, trachemys scripta, non-aromatizable androgens are the physiological equivalent of temperature in determining male development. in the first experiment, eggs were treated in the middle of the temperature-sensitive period with 1.0 or 10.0 micrograms androsterone, 5 alpha-dihydrotestosterone, 3 alpha-androstanediol, or 3 beta-androstanediol, while at an all-male, male-biased, or one of two female-biased incubation temperature ... | 1996 | 8691104 |
| the mechanism of cardiac shunting in reptiles: a new synthesis. | the mechanism of cardiac shunting in reptiles is controversial. recent evidence suggests that a right-to-left shunt in turtles results primarily from a washout mechanism. the mechanism that accounts for left-to-right (l-r) shunting is unresolved. this study used haemodynamic analysis and digital subtraction angiography to determine the mechanism of l-r cardiac shunting in the turtle trachemys (pseudemys) scripta. animals were instrumented with ultrasonic blood flow probes (transonic systems, inc ... | 1996 | 8691116 |
| cardiorespiratory synchrony in turtles. | many reptiles, particularly diving species, display characteristic cardiovascular changes associated with lung ventilation (cardiorespiratory synchrony). previous studies on freshwater turtles show that heart rate and pulmonary blood flow rate (qpul) increase two- to fourfold during ventilation compared with breath-holding, and some studies report concomitant decreases in systemic blood flow rate (qsys). the primary aim of this study was to provide a detailed description of cardiorespiratory syn ... | 1996 | 8708580 |
| prevalence and histopathology of shell disease in turtles from lake blackshear, georgia. | turtles in lake blackshear, crisp county, georgia (usa) were evaluated for shell disease during intensive trapping efforts on 8 and 9 may 1990. the disease was most prevalent in pseudemys concinna (74%) and trachemys scripta (35%). the degree of necrosis on the carapace was significantly positively correlated with the degree of necrosis on the plastron in t. scripta (rs = 0.50), but not in p. concinna (rs = 0.06). female t. scripta with lesions were significantly larger than females without lesi ... | 1996 | 8722263 |
| water compartmentalization and extracellular tortuosity after osmotic changes in cerebellum of trachemys scripta. | 1. water compartmentalization in the turtle cerebellum subject to media of different osmolalities was quantified by combining extracellular diffusion analysis with wet weight and dry weight measurements. the diffusion analysis also determined the tortuosity of the extracellular space. 2. isolated cerebella were immersed in normal, oxygenated physiological saline (302 mosmol kg-1), hypotonic saline (238 mosmol kg-1) and a series of hypertonic salines (up to 668 mosmol kg-1). the osmolality was va ... | 1996 | 8734998 |
| the relative effectiveness of estrone, estradiol-17 beta, and estriol in sex reversal in the red-eared slider (trachemys scripta), a turtle with temperature-dependent sex determination. | in many turtles the temperature during the middle of incubation determines the gonadal sex of the hatchling. sex steroid hormones have been implicated in temperature-dependent sex determination in the red-eared slider turtle, trachemys scripta; nonaromatizable androgens are involved in male sex determination and estrogens and aromatizable androgens in female sex determination. administration of exogenous estradiol-17 beta to eggs incubating at a temperature that normally produces only males can ... | 1996 | 8804562 |
| effects of prolactin and cortisol on the harderian gland of the terrapin, pseudemys scripta, adapted to different salinities. | the harderian gland (hg) of the terrapin, pseudemys scripta, plays a prominent role in osmoregulation owing to the presence of "salt secreting cells" among the acinar cells of its glandular epithelium. osmotic stress provokes different responses according to salinity. seawater adaptation activates a major structural reorganization. the most striking change is shown by the type i glandular cells and "salt secreting cells." the latter increase in number and change from a unicellular form to multic ... | 1996 | 8808397 |
| identification of surface glycoconjugates in the olfactory system of turtle. | lectin binding histochemistry was performed on the olfactory system of pseudemys scripta to investigate the distribution and density of defined carbohydrate terminals on the cell surface glycoproteins of the olfactory receptors and their terminals in the olfactory bulbs. the lectin staining patterns indicate that the receptor cells of the olfactory mucosa are characterized by glycoconjugates containing alpha-d-galactose and n-acetyl-d-glucosamine terminal residues. the vomeronasal receptor cells ... | 1996 | 8828589 |
| multicatalytic proteinase activity in turtle liver: responses to anoxia stress and recovery. | activities of the multicatalytic proteinase complex (mpc) were detected in turtle (trachemys scripta elegans) liver. the ratio of peptidylglutamyl-peptide bond hydrolyzing, trypsin-like, and chymotrypsin-like activities was 6:2.7:1 for the mpc partially purified by sepharose cl-6b gel filtration. molecular mass of the turtle liver enzyme was 940 +/- 46 kd. nondenaturing page revealed a single band containing mpc activity reacting with peptide substrate. in vivo anoxia exposure (20 h submergence ... | 1996 | 8829603 |
| the effect of altering pulmonary blood flow on pulmonary gas exchange in the turtle trachemys (pseudemys) scripta. | in resting reptiles, the po2 of pulmonary venous return (plao2; left atrial blood) may be 20 mmhg (1 mmhg = 0.1333 kpa) lower than the po2 of gas in the lung. this level of po2 is considerably higher than that observed in resting mammals and birds and results from ventilation-perfusion (v/q) heterogeneity, pulmonary diffusion limitation and intrapulmonary shunting. however, the relative contribution of each of these factors is unknown. many reptiles, particularly chelonians, exhibit an intermitt ... | 1996 | 8896364 |
| anoxia-induced gene expression in turtle heart. upregulation of mitochondrial genes for nadh-ubiquinone oxidoreductase subunit 5 and cytochrome c oxidase subunit 1. | a cdna library constructed from heart of anoxia-exposed adult turtles (trachemys scripta elegans) was differentially screened with 32p-labeled single-stranded cdna probes from heart of control versus anoxic animals to clone genes induced by anoxia stress. four cdna clones, pbtar20, pbtar34, pbtar63 and pbtar914 were obtained and confirmed to be upregulated in response to anoxic submergence (20 h in n2-bubbled water at 7 degrees c). two clones, pbtar20 and pbtar63, were characterized by sequence ... | 1996 | 8898892 |
| correspondence between visually evoked voltage-sensitive dye signals and synaptic activity recorded in cortical pyramidal cells with intracellular microelectrodes. | fast, multiple-site optical recording of voltage-sensitive dye (vsd) signals and intracellular microelectrode recordings were combined to characterize visually evoked neuronal responses in the visual cortex of the pond turtle, pseudemys scripta. by using an in vitro, eye-brain preparation stained with the merocyanine oxazolone voltage-sensitive dye, nk-2495 or a close analog, nk-2761, large vsd signals relatively free of vibrational noise could be recorded in single trials following a stroboscop ... | 2015 | 8903037 |
| the influence of center-surround antagonism on light adaptation in cones in the retina of the turtle. | the influence of center-surround antagonism on light adaptation in cone photoreceptors was investigated by intracellular recording from red-sensitive cones in the retina of the turtle, pseudemys scripta elegans. test flashes of 0.15-mm diameter were applied at the center of background fields of 0.25-mm or 2.2-mm diameter. immediately upon expanding the background from 0.25 to 2.2 mm, the membrane potential depolarized by about 1-4 mv. the test flash response was enhanced if the depolarization wa ... | 1995 | 8924411 |
| metabolic adaptations supporting anoxia tolerance in reptiles: recent advances. | animal survival during severe hypoxia and/or anoxia is enhanced by a variety of biochemical adaptations including adaptations of fermentative pathways of energy production and, most importantly, the ability to sharply reduce metabolic rate by 5-20 fold and enter a hypometabolic state. the biochemical regulation of metabolic arrest is proving to have common molecular principles that extend across phylogenetic lines and that are conserved in different types of arrested states (not only anaerobiosi ... | 1996 | 8936040 |
| purification and characterization of plasma vitamin d binding protein from the snapping turtle, chelydra serpentina. | vitamin d binding protein (dbp) was isolated from the plasma of the snapping turtle, chelydra serpentina (mixed sex adult), and compared with the previously characterized dual function binding plasma protein that binds both thyroxine (t4) and vitamin d (tstdbp) in an emydid turtle, trachemys scripta. purification of chelydra serpentina dbp (csdbp) was accomplished by ion exchange chromatography, preparative polyacrylamide gel electrophoresis, and reverse-phase high-performance liquid chromatogra ... | 1996 | 8954770 |
| use of the sensitive anterograde tracer cholera toxin fragment b reveals new details of the central retinal projections in turtles. | previous anterograde degeneration and autoradiographic studies have yielded inconsistent results on the extent and target areas of the central retinal projections in turtles. we used the highly sensitive anterograde and retrograde tracer, cholera toxin b fragment (ctb), to re-examine the central retinal projections in pseudemys scripta elegans. in contrast to the results of the previous anterograde degeneration studies and autoradiographic studies, immunohistochemical detection of ctb-labeled ce ... | 1996 | 8955961 |
| the pupillary response to light in the turtle. | when intense adapting lights are turned off, the pupil of the turtle, pseudemys scripta elegans, enlarges. the recovery functions for pupillary dilation have different time constants that are defined by red- and green-sensitive cones and rods as they are affected by prior light adaptation and time in the dark. pupillary area related to dilation responds over at least a three- to four-fold range. following white-light adaptation, the course of pupil dilation in the dark shows a three-legged curve ... | 2008 | 8962831 |
| kainic acid blocks a ttx-sensitive sodium channel in retinal horizontal cells of the turtle (pseudemys scripta elegans). | the aim of this study was to investigate the effects of excitatory amino acids on channels found in horizontal cell membranes using patch-clamp techniques. we unexpectedly found that the excitatory amino acid receptor agonist, kainic acid, reversibly inhibited the transient tetrodotoxin (ttx)-sensitive na+ current in isolated horizontal cell bodies and axons from the retina of the turtle (pseudemys scripta elegans). the effect of kainic acid was antagonized by the glutamate receptor antagonist 6 ... | 1996 | 8981397 |
| atrial natriuretic peptide, bradykinin, and angiotensin ii-like immunoreactivity in the harderian gland of the terrapin pseudemys scripta: response to osmotic stress. | the harderian gland of the terrapin pseudemys scripta has four types of acinar cells. type iv cells are very similar to the salt secreting cells of the salt secretory glands of various marine vertebrates. the presence and localization of the ile5-angiotensin ii, atrial natriuretic peptide, and bradykinin has been investigated by immunohistochemical methods. immunoreactivity is confined to the type iv cells. changes in the environmental salinity resulted in different patterns in the immunoreactiv ... | 1996 | 8986047 |
| decreased total ventricular and mitochondrial protein synthesis during extended anoxia in turtle heart. | the turtle heart provides a model system to study the effects of anoxia on protein synthesis without the potentially confounding factor of contractile failure and decreased atp levels. protein synthesis, as measured by 3h-labeled phenylalanine incorporation, was studied under conditions of normoxia and anoxia in isolated perfused turtle [trachemys (= pseudemys) scripta elegans] hearts at 15 degrees c. heart rate, cardiac output, and ventricular pressure development were unaffected by 2 or 3 h of ... | 1996 | 8997367 |
| liver protein kinase c isozymes: properties and enzyme role in a vertebrate facultative anaerobe. | protein kinase c was purified to homogeneity from liver of the anoxia-tolerant turtle (trachemys scripta elegans). two isozymes were present and were identified as pkc alpha and pkc beta by hydroxylapatite chromatography and cross-reaction with specific antibodies to the mammalian isozymes. kinetic characterization of the isozymes showed that both required phospholipids and ca2+ for activation and both were inhibited by low concentrations of pkc inhibitors. the pkc alpha was activated more stron ... | 1996 | 9022285 |
| shell disease in river cooters (pseudemys concinna) and yellow-bellied turtles (trachemys scripta) in a georgia (usa) lake. | a disfiguring shell disease was detected in river cooters (pseudemys concinna) and yellow-bellied turtles (trachemys scripta) from lake blackshear, georgia (usa). the turtles used were part of a mark-recapture study conducted from september 1991 to june 1993. histologic changes on four turtles included acute segmental necrosis of the epidermis, followed by ulceration, necrosis of the underlying dermis and dermal bone, and exaggerated remodeling of bone. additional findings included visceral infl ... | 1997 | 9027694 |
| effects of inhibition of nitric oxide synthesis and of hypercapnia on blood pressure and brain blood flow in the turtle. | in the mammalian brain, nitric oxide (no) is responsible for a vasodilatory tonus as well as the elevation of cerebral blood flow (cbf) induced by hypercapnia. there have been few comparative studies of cerebral vasoregulation in lower vertebrates. using epi-illumination microscopy in vivo to observe cbf velocity on the brain surface (cerebral cortex), we show that turtles (trachemys scripta) exposed to hypercapnia (inspired pco2 = 4.9 kpa) displayed a 62% increase in cbf velocity, while systemi ... | 1997 | 9076965 |
| analysis of cardiac shunting in the turtle trachemys (pseudemys) scripta: application of the three outflow vessel model. | blood distribution within the ventricle was analysed in acutely prepared turtles trachemys scripta by measuring the oxygen concentration and flow rates of blood in the central vessels. pulmonary (qp) and systemic (qs) blood flow rates were similar when total cardiac output (qtot) was below 40 ml min-1 kg-1. above this value, increments of qtot were directed to the pulmonary circuit, with qs levelling off at approximately 20 ml min-1 kg-1. when qtot was larger than 40 ml min-1 kg-1, the systemic ... | 1996 | 9110953 |
| antioxidant systems and anoxia tolerance in a freshwater turtle trachemys scripta elegans. | the effects of anoxic submergence (20 h at 5 degrees c) and subsequent 24 h aerobic recovery on the antioxidant systems of six organs were examined in freshwater turtles, trachemys scripta elegans. both xanthine oxidase and xanthine dehydrogenase were detected in turtle tissues with xanthine oxidase composing 36-75% of the total activity. turtle organs displayed high constitutive activities of catalase (cat), superoxide dismutase (sod), and alkyl hydroperoxide reductase (ahr). measurements of li ... | 1997 | 9144333 |
| energy turnover in the normoxic and anoxic turtle heart. | we examined the possibility that the heart of the tuttle chrysemys scripta is an exceptional anaerobic performer, by measuring myocardial power output, lactate output, and estimated atp turnover in perfused heart preparations. over a range of myocardial power outputs at 5 and 15 degrees c we find that turtle hearts perfused with anoxic saline do not show a particularly outstanding ability to produce atp anaerobically. furthermore, at 15 degrees c anoxia reduced the atp turnover rate to 50% of th ... | 1997 | 9185339 |
| protein synthesis under conditions of anoxia and changing workload in ventricle strips from turtle heart. | an earlier study determined that protein synthesis in isolated perfused turtle (trachemys [= pseudemys] scripta elegans) hearts was three-fold lower under conditions of anoxia than under conditions of normoxia. however, the earlier study did not attempt to define the role of work in the isolated perfused preparation. in this study, the effects of varying workload, as defined by changing frequency of contraction, and anoxia on protein synthesis were examined. the ventricle strip preparation allow ... | 1997 | 9216073 |
| epithelial localization of a reptilian na+/h+ exchanger homologous to nhe-1. | basolateral membranes of turtle (pseudemys scripta) colon epithelial cells exhibit robust na+/h+ exchange activity that can be activated by cell shrinkage and is blocked by amiloride [m. a. post and d. c. dawson. am. j. physiol. 262 cell physiol. 31):c1089-c1094, 1992]. the colonic epithelium actively absorbs na+ and secretes k+ and hco3-, but the role of basolateral na+/h+ exchange, if any, in transepithelial transport is unknown. the current studies were undertaken to identify the gene product ... | 1997 | 9227498 |
| role for adenosine in channel arrest in the anoxic turtle brain. | the remarkable ability of the turtle brain to survive anoxia is based on its ability to match energy demand flexibly to energy production. earlier studies indicate that reduced ion leakage is an important mechanism for energy conservation during anoxia. we tested the hypothesis that extracellular adenosine plays a role in the reduction of k+ flux (channel arrest) that occurs in the anoxic turtle brain. changes in extracellular k+ concentration ([k+]o in the in situ brain of the turtle trachemys ... | 1997 | 9232005 |
| energy metabolism in liver of anoxia-tolerant turtle species (pseudemys scripta): a model for studying hepatic tolerance to cold hypoxia. | we have studied biochemical markers of energy metabolism and glycolysis by enzyme analyses and 1h nmr spectroscopy in livers of the freshwater turtle, pseudemys scripta, after vascular flush and cold storage. values for hepatic atp content and energy charge remained unchanged for 24 h and showed only small declines between 24 and 48 h of cold hypoxia. lactate and glucose levels increased over the 48-h period, demonstrating, respectively, progressive glycolysis and glycogenolysis. these observati ... | 1997 | 9245506 |
| glutathione systems and anoxia tolerance in turtles. | effects of anoxic submergence (20 h at 5 degrees c) and subsequent 24 h aerobic recovery on glutathione levels and the activities of glutathione-related enzymes were examined in six tissues of trachemys scripta elegans. anoxia exposure resulted in tissue-specific changes in enzyme maximal activities, the most dramatic being suppression of gamma-glutamyl transpeptidase (gamma-gtpase) activity in anoxic kidney to only 2% of control. anoxia exposure also caused significant decreases in activities o ... | 1997 | 9249553 |
| abundant synthesis of transthyretin in the brain, but not in the liver, of turtles. | the binding of thyroxine to proteins in the blood plasma of the turtle, trachemys scripta, was analyzed by incubation with radioactive thyroxine, electrophoresis and autoradiography. albumin and an alpha-globulin were found to bind thyroxine; no thyroxine-binding transthyretin was detected in the prealbumin region. in contrast to blood plasma, a thyroxine-binding prealbumin was observed in medium from t. scripta choroid plexus incubated in vitro. rna was extracted from brain tissue containing ch ... | 1997 | 9253180 |
| postnatal neurogenesis in the telencephalon of turtles: evidence for nonradial migration of new neurons from distant proliferative ventricular zones to the olfactory bulbs. | postnatal neurogenesis in the the turtle telencephalon was investigated by using bromodeoxyuridine immunocytochemistry and [3h]thymidine autoradiography. red-eared slider turtles trachemys scripta elegans (cryptodira, emydidae) 2-3 months old were injected with the thymidine analogue 5'-bromodeoxyuridine (brdu) and allowed to survive for 7, 30, 90, and 180 days. results indicate that cells in the walls of the lateral ventricles continue to proliferate postnatally. shortly after brdu treatment (s ... | 1997 | 9263587 |
| comparison between oogenesis and related ovarian structures in a reptile, pseudemys scripta elegans (turtle) and in a bird coturnix coturnix japonica (quail). | the aspect of the oogonia during their premitotic dna synthesis and of the premeiocytes during their premeiotic dna synthesis was studied in turtles by autoradiography, after injection of 3h-thymidine. as in the adult laying quail, the intrafollicular oocytes of the adult turtle go through three successive stages: prelampbrush, lampbrush and postlampbrush. during the prelampbrush and lampbrush stage two kinds of nucleoli exist: peripheral and central. in contrast to avian yolk, during its final ... | 2006 | 9269708 |
| membrane properties and monosynaptic retinal excitation of neurons in the turtle accessory optic system. | using an eye-attached isolated brain stem preparation of a turtle, pseudemys scripta elegans, in conjunction with whole cell patch techniques, we recorded intracellular activity of accessory optic system neurons in the basal optic nucleus (bon). this technique offered long-lasting stable recordings of individual synaptic events. in the reduced preparation (most of the dorsal structures were removed), large spontaneous excitatory synaptic inputs [excitatory postsynaptic potentials (epsps)] were f ... | 1997 | 9307099 |
| on the presence of dendrite bundles in the cerebral cortex of the madagascan lesser hedgehog tenrec and the red-eared pond turtle. | in mammals with a well-differentiated neocortex apical dendrites of pyramidal cells form vertical bundles. little is known about the presence of dendrite bundles in animals with a poorly differentiated cortex. in this paper the presence of dendrite bundles has been investigated in the lesser hedgehog tenrec, echinops telfairi, a basal insectivore with a very low degree of neocorticalization. in a further step the arrangement of dendrites has been analyzed in the cerebral cortex of the red-eared ... | 1997 | 9310312 |
| vagal regulation of intracardiac shunting in the turtle pseudemys scripta | two principal hypotheses account for intracardiac shunting in reptiles. the 'pressure shunting' hypothesis proposes that there is no fuctional separation between the ventricular cava during systole. the 'washout shunting' hypothesis suggests that the cavum pulmonale is functionally separated from the rest of the ventricle during systole. the purpose of this study was to test the two principal hypotheses in a turtle, pseudemys scripta, after inducing a right-to-left shunt by electrical stimulatio ... | 1994 | 9317438 |
| mechanical performance of an in situ perfused heart from the turtle chrysemys scripta during normoxia and anoxia at 5 c and 15 c | we developed an in situ perfused turtle (chrysemys scripta) heart preparation to study its intrinsic mechanical properties at 5°c and 15°c using normoxic and anoxic perfusion conditions. the in situ preparation proved durable and stable. at 15°c and a spontaneous heart rate of 23.4 beats min-1, maximum stroke volume was 2.54 ml kg-1 body mass, maximum cardiac output was 62.5 ml min-1 kg-1 and maximum cardiac myocardial power output was 1.50 mw g-1 ventricular mass. there was good agr ... | 1994 | 9317650 |
| [embryonic mortality and hatching rate of trachemys scripta (testudines: emydidae) eggs artificially grown in a protected natural area]. | in the northeast of costa rica, illegal collecting, habitat destruction and heavy predation on adult females, young and eggs of trachemys scripta produced a population decline in recent years. the slider turtle has a high reproductive potential and nests were relocated. between january and march 1991, 179 nests (3220 eggs) were collected from natural areas of caño negro national wildlife refuge, costa rica and relocated for incubation under natural conditions in a protected site. the mean of num ... | 1996 | 9332615 |
| the effects of artificial lung inflation on pulmonary blood flow and heart rate in the turtle trachemys scripta. | as for most ectothermic vertebrates, the breathing pattern of turtles is episodic, and pulmonary blood flow (qpul) and heart rate (fh) normally increase several-fold during spontaneous ventilation. while some previous studies suggest that these cardiovascular changes are caused by stimulation of pulmonary stretch receptors (psrs) during ventilation, it has been noted in other studies that blood flows often change prior to the initiation of breathing. given the uncertainty regarding the role of p ... | 1997 | 9366085 |
| release of adenosine and atp in the brain of the freshwater turtle (trachemys scripta) during long-term anoxia. | extracellular adenosine and atp levels were monitored by microdialysis in the striatum of the freshwater turtle trachemys scripta during long-term n2 respiration. after an initial rise in extracellular adenosine, a second peak of longer duration and higher in intensity, followed. the frequencies of these adenosine cycles varied considerably between individual turtles, such that the shortest time between the peaks was 80 min and the longest was 300 min (mean 151 min). after about 60 min anoxia, t ... | 1997 | 9374196 |
| brain na+/k+-atpase activity in two anoxia tolerant vertebrates: crucian carp and freshwater turtle. | the crucian carp (carassius carassius) and freshwater turtles (trachemys scripta) are among the very few vertebrates that can survive extended periods of anoxia. the major problem for an anoxic brain is energy deficiency. in the brain, the na+/k+-atpase is the single most atp consuming enzyme, being responsible for maintaining ion gradients. we here show that the na+/k+-atpase activity in the turtle brain is reduced by 31% in telencephalon and by 34% in cerebellum after 24 h of anoxia. both chan ... | 1997 | 9389603 |
| corticosterone secretion in response to capture and handling in free-living red-eared slider turtles. | the corticosterone response to capture and handling was measured in free-living red-eared slider turtles, trachemys scripta elegans. to determine the ability of this species to exhibit this endocrine response, slider turtles were bled at the time of removal from hoop nets and again at 30 and 60 min following capture to create plasma profiles of acute corticosterone secretion from individuals. plasma corticosterone concentration increased significantly with handling time. the greatest rise in cor ... | 1997 | 9405119 |
| synaptic inputs to identified color-coded amacrine and ganglion cells in the turtle retina. | previous studies have proposed models of the specific synaptic circuitry responsible for color processing in the turtle retina. to determine the accuracy of these models of the circuits underlying color opponency in the inner retina of the turtle (pseudemys scripta), we have studied the physiology, morphology, and synaptic connectivity of identified amacrine and ganglion cells. these cells were first characterized electrophysiologically and were then stained with horseradish peroxidase. postembe ... | 1997 | 9416919 |
| surfactant regulates pulmonary fluid balance in reptiles. | reptilian lungs are potentially susceptible to fluid disturbances because they have very high pulmonary fluid filtration rates. in mammals, pulmonary surfactant protects the lung from developing alveolar edema. reptiles also have an order of magnitude more surfactant per square centimeter of respiratory surface area compared with mammals. we investigated the role of reptilian surfactant 1) in the entry of vascularly derived fluid into the alveolar space of the isolated perfused lizard (pogona vi ... | 1997 | 9435656 |
| purification and partial amino acid sequences of two distinct albumins from turtle plasma. | two putative albumins, denoted alb-1 (apparent molecular mass of 67 kda) and alb-2 (68 kda), were purified from plasma of the emydid turtle (trachemys scripta). concentrations in serum or plasma were determined by radioimmunoassay using 125i-labeled alb-1. in juvenile turtles (less than 2 years of age), serum concentrations of alb-1 and alb-2 were 2.72 +/- 0.23 mg/ml and 1.68 +/- 0.22 mg/ml, respectively, while concentrations in plasma pooled from adult turtles were 4.2 mg/ml and 2.6 mg/ml, resp ... | 1997 | 9440230 |
| cellular bioavailability of natural hormones and environmental contaminants as a function of serum and cytosolic binding factors. | environmental contaminants have been reported to function as hormone mimics in various wildlife species. to investigate a potential mechanism for the interaction of contaminants with the endocrine system, we evaluated the cellular bioavailability of numerous chemicals. hormone binding proteins from oviductal cytosol of the american alligator (alligator mississippiensis) and yellow-bellied turtle (trachemys scripta) were used in competitive binding assays with [3h] 17 beta-estradiol. most of the ... | 1998 | 9460179 |
| cardiovascular regulation during anoxia in the turtle: an in vivo study. | this study describes the integrated cardiovascular response of instrumented turtles to acute anoxic exposure (approximately 2 h) and also determines the factors that regulate these responses. trachemys scripta were chronically implanted with ultrasonic blood flow probes for the measurement of total pulmonary and systemic blood flows and heart rate. in addition, catheters were implanted into the right aortic arch for the measurement of systemic blood pressure, arterial blood gases, and ph. animal ... | 2016 | 9472807 |
| fine structure of the dorsal lingual epithelium of trachemys scripta elegans (chelonia: emydidae). | turtles are adapted to different environments, such as freshwater, marine, and terrestrial habitats. examination of histological and ultrastructural features of the dorsal lingual epithelium of the red-eared turtle, trachemys scripta elegans, and comparison of the results with those of other turtles should elucidate the relationship between the morphology of tongues as well as the fine structure of lingual epithelia and chelonian feeding mechanisms. | 1998 | 9489772 |
| 31p-nmr determinations of cytosolic phosphodiesters in turtle hearts. | as part of our ongoing research on cardiac hypoxia tolerance we have conducted 31p nuclear magnetic resonance (nmr) studies of isolated, perfused, working hearts from freshwater turtles, animals that are well known for their ability to tolerate prolonged periods of anoxia. a striking feature of turtle heart spectra is an extremely high concentration of nmr visible phosphodiesters (pdes). cardiac spectra from mammals, on the other hand, typically exhibit only a small resonance in the pde region. ... | 1997 | 9505428 |
| nomenclature, filling and angioarchitecture of lymph vessels in organs. scanning electron microscopy of the stomach of the turtle pseudemys scripta elegans using different injection methods. | the gastric lymph vessel network of pseudemys scripta elegans shows all the characteristics of initial lymphatics. a differentiation of initial lymphatics in lymphatic capillaries and precollectors is not possible in the turtle. the scanning electron microscopic examination shows that ultrastructural analysis of initial lymphatics is possible after manual subserous injection of glutaraldehyde or application with the vacuum chamber. in the stomach of the turtle all characteristics of initial lymp ... | 1998 | 9505440 |
| the anatomy and perfusion of the renal portal system in the red-eared slider (trachemys scripta elegans). | the anatomy of the renal portal system of the red-eared slider (trachemys scripta elegans) is described, based on dissection of six double latex-injected specimens (three males, three females). the anatomy of these vessels, which had not previously been described in this species, was found not to differ significantly from the fundamental chelonian pattern. fluoroscopic radioangiography revealed that venous blood returning from the hindlimbs flowed predominantly to the liver and bypassed the kidn ... | 1997 | 9523630 |
| the effect of the renal portal system on pharmacokinetic parameters in the red-eared slider (trachemys scripta elegans). | the premise that drugs not be injected into the caudal body of reptiles because they will be carried by the renal portal system to the kidneys, where they may be nephrotoxic or rapidly excreted, was tested by comparing the pharmacokinetics of gentamicin (excreted via glomerular filtration in mammals) and carbenicillin (excreted partly via renal tubular secretion in mammals) following injection into the forelimb or hindlimb of red-eared sliders (trachemys scripta elegans). ten sliders received in ... | 1997 | 9523631 |
| trace elements in egg contents and egg shells of slider turtles (trachemys scripta) from the savannah river site. | in this paper we examine the levels of trace elements in the egg contents and egg shells of slider turtles (trachemys scripta) from the savannah river site, near aiken, south carolina. trace elements have seldom been examined in the tissues or eggs of reptiles, although some turtles and large snakes occupy a high trophic level. lead, mercury, cadmium, selenium, chromium, and manganese levels were examined in one egg and its egg shell collected from each of 16 females that laid in late may and ju ... | 1998 | 9543509 |
| morphology of basal optic tract terminals in the turtle, pseudemys scripta elegans. | the morphologies of axon terminals of retinal ganglion cells projecting to the basal optic nucleus (bon) via the basal optic tract (bot) were studied in the red-eared turtle. the bot was visualized on the ventral surface of the brainstem in vitro, and either biotinylated dextran amine was injected extracellularly or neurobiotin was injected into physiologically identified axons during intracellular recordings. up to 16 hours after tracer injection, the brains were fixed, sectioned parasagittally ... | 1998 | 9548549 |
| cloning and in situ hybridization analysis of estrogen receptor in the developing gonad of the red-eared slider turtle, a species with temperature-dependent sex determination. | many reptiles exhibit temperature-dependent sex determination where the incubation temperature of the egg determines the gonadal sex of the individual. if exogenous estrogen is administered during the temperature-sensitive period to embryos incubating at a male-producing temperature, the temperature effects can be overridden and females will be produced. inhibiting production of endogenous estrogens at female-biased incubation temperatures results in embryos developing as males rather than femal ... | 1998 | 9572366 |
| comparison of blood viscosity in red-eared sliders (trachemys scripta) adapted to cold and room temperature. | red-eared sliders (trachemys scripta) in their northern range undergo hibernation at temperatures of about 5 degrees c, which may result in a profound bradycardia and a drop in blood pressure leading to very slow blood flows. blood viscosity increases with decreasing temperature and at low shear rates associated with slow blood flows. to investigate the effects of temperature on the blood viscosity of these animals, 20 red-eared sliders were randomly assigned to each of two groups, cold environm ... | 1998 | 9621436 |
| temperature-dependent sex determination in the red-eared slider turtle, trachemys scripta. | temperature-dependent sex determination (tsd) in the red-eared slider turtle, trachemys scripta, has been the subject of a variety of past studies. incubation temperature appears to affect sex determination in a dose-dependent fashion. this suggests that temperature could be affecting a dosage-sensitive element in the sex-determination cascade. sex determination in t. scripta is sensitive to estrogen, and data from many studies support the hypothesis that endogenous estrogen production may be in ... | 1998 | 9662828 |
| sequence and expression analysis of wt1 and sox9 in the red-eared slider turtle, trachemys scripta. | temperature-dependent sex-determination (tsd) is a phenomenon that has been characterized at the ecological, morphological, and endocrinological levels in some reptilian species. we have begun to investigate tsd at the level of molecular development by cloning, sequencing, and analyzing the expression of two genes, wt1 and sox9, in the red-eared slider turtle trachemys scripta. we obtained almost full-length cdna clones for wt1 and sox9 that were greater than 73% identical to the human homologue ... | 1998 | 9662829 |
| low extracellular dopamine levels are maintained in the anoxic turtle (trachemys scripta) striatum. | the uncontrolled increase of extracellular dopamine (da) has been implicated in the pathogenesis of hypoxic/ischemic damage in the mammalian brain. but unlike the harmful release of excitatory neurotransmitters such as glutamate and aspartate, which occurs on brain depolarization, excessive extracellular da levels occur even with mild hypoxia in the mammalian brain. the purpose of this study was to determine whether hypoxia/anoxia provokes a similar increase in the anoxic tolerant turtle brain. ... | 1998 | 9663509 |
| endogenous yolk steroid hormones in turtles with different sex-determining mechanisms. | maternal transfer of nutrients, including steroid hormones, to embryos during gestation in viviparous amniotes is well known, but the concordant process in oviparous amniotes is poorly understood. recent evidence suggests that steroid hormones are present in freshly laid eggs of archosaurs and that their concentrations may influence offspring phenotypes. this process might be especially important in reptiles with temperature-dependent sex determination (tsd), because embryonic sex determination ... | 1998 | 9707477 |
| species recognition of congeneric acanthocephalans in slider turtles by random-amplified polymorphic dna (rapd) markers. | species recognition of acanthocephalans of the genus neoechinorhynchus (hamann, 1892) found in the freshwater turtle trachemys scripta (wied, 1838) has previously been based primarily on female body and egg morphology. observed morphological plasticity within and among species may lead to the misclassification of female specimens and leaves males of different species completely indistinguishable. here, random-amplified polymorphic dna (rapd) analysis was used to genetically characterize samples ... | 1998 | 9714226 |
| uv-sensitive input to horizontal cells in the turtle retina. | microspectrophotometry, electroretinography and behavioural studies have indicated that ultraviolet (uv) light contributes to functional vision in various vertebrate species. based on behavioural evidence, this was also suggested for turtle vision. in order to reveal the interactions underlying detection of uv light in the distal retina, we recorded intracellularly the photoresponses of cones and horizontal cells in retinas of pseudemys scripta elegans and mauremys caspica and calculated the act ... | 1998 | 9751127 |
| expression of a new rna-splice isoform of wt1 in developing kidney-gonadal complexes of the turtle, trachemys scripta. | wt1 is a tumor suppressor gene encoding a zinc finger dna-binding protein required for normal vertebrate kidney and gonad development. although the sequence and function of this gene has been studied mostly in mammals, comparative analysis in other vertebrates may suggest regions of conservation of function as well as evolution of function. we have initiated a study of this gene in the freshwater turtle, trachemys scripta, a species that demonstrates temperature dependent sex determination. the ... | 1998 | 9787767 |
| oviductal sperm storage as a reproductive tactic of turtles. | the oviducts of two species of freshwater turtles were examined throughout the year to determine the distribution of sperm within the oviduct, the locations of stored sperm, and the onset of mating. sperm were stored in undifferentiated tubules and ducts of submucosal glands at the periphery of large glandular segments of the albumen and uterine regions of the oviduct. sperm transfer to females commenced in october in sternotherus odoratus and in january in trachemys scripta. the role of sperm s ... | 2006 | 9803538 |
| hypoxia elicits an increase in pulmonary vasculature resistance in anaesthetised turtles (trachemys scripta). | in mammals and birds, low oxygen levels in the lungs cause a constriction of the pulmonary vasculature. this response is locally mediated and is considered to be important for local matching of perfusion and ventilation. it is not known whether reptiles respond in a similar fashion. the present study describes the effects of altering lung oxygen levels (at a constant fco2 of 0.03) on systemic and pulmonary blood flows and pressures in anaesthetised (nembumal, 50 mg kg-1) and artificially ventila ... | 1998 | 9817833 |
| n-methyl-d-aspartate-mediated bulbospinal respiratory drive is ph/p(co2)-insensitive in turtle brainstem-spinal cord. | a split-bath in vitro brainstem-spinal cord preparation from adult turtles (pseudemys scripta) was used to test the hypotheses that: (1) bulbospinal respiratory synaptic transmission is mediated, at least in part, by n-methyl-d-aspartate (nmda) glutamatergic receptors, and (2) this transmission is suppressed by low spinal ph (induced by hypercapnea). recordings from intact pectoralis (expiratory) and serratus (inspiratory) nerves showed that the in vitro turtle brainstem-spinal cord preparation ... | 1998 | 9840329 |
| atp-sensitive k+ channel activation provides transient protection to the anoxic turtle brain. | there is wide speculation that atp-sensitive k+ (katp) channels serve a protective function in the mammalian brain, being activated during periods of energy failure. the aim of the present study was to determine if katp channels also have a protective role in the anoxia-tolerant turtle brain. after ouabain administration, rates of change in extracellular k+ were measured in the telencephalon of normoxic and anoxic turtles (trachemys scripta). the rate of k+ efflux was reduced by 50% within 1 h o ... | 1998 | 9843892 |
| effects of lead on behavior, growth, and survival of hatchling slider turtles. | in this study the effects of lead on behavioral development of hatchling slider turtles (trachemys scripta) from the savannah river site, near aiken, sc, were examined. it was of interest to determine whether dose or size affects survival, growth, or behavior. hatchlings from 1995 showed no significant differences in growth, survival, or behavior between control and lead-injected animals at a dose of 0.05 and 0.1 mg/g (n = 10 per group). in 1996, 48 hatchlings were divided into four groups injec ... | 1998 | 9860323 |
| response to dietary dilution in an omnivorous freshwater turtle: implications for ontogenetic dietary shifts. | several species of freshwater turtles in the family emydidae undergo an ontogenetic dietary shift; as juvenile turtles mature, they change from a primarily carnivorous to a primarily herbivorous diet. it has been hypothesized that this shift results from an unfavorable ratio of gut capacity to metabolic rate that prevents small reptiles from processing adequate volumes of plant material to meet their energetic demands. effects of dietary dilution on intake were evaluated in two size classes of r ... | 2010 | 9882608 |
| exercise and forced submergence in the pond slider (trachemys scripta) and softshell turtle (apalone ferox): influence on bimodal gas exchange, diving behaviour and blood acid-base status | the dynamics of bimodal respiration, diving behaviour and blood acid-base status in the softshell turtle trachemys scripta and the pond slider apalone ferox were investigated at rest and under conditions of stress induced by exercise and forced submergence. during periods of forced submergence, only a. ferox doubled its aquatic gas exchange rate. both a. ferox and t. scripta increased their aerial gas exchange profoundly following exercise and forced submergence, a pattern indicative of increase ... | 1999 | 9882639 |
| developmental synergism of steroidal estrogens in sex determination. | gonadal sex in the red-eared slider turtle, trachemys scripta, is determined by incubation temperature during embryonic development. evidence suggests that temperature determines sex by influencing steroid hormone metabolism and/or sensitivity: steroidogenic enzyme inhibitors or exogenous sex steroid hormones and their man-made analogs override (or enhance) temperature effects on sex determination. specifically, nonaromatizable androgens and aromatase inhibitors induce testis differentiation at ... | 1999 | 9924002 |
| no threshold dose for estradiol-induced sex reversal of turtle embryos: how little is too much? | risk assessments for nongenotoxic chemicals assume a threshold below which no adverse outcomes are seen. however, when an endogenous chemical, such as 17ss-estradiol (e2), occurs at a concentration sufficient to cause an effect, the threshold is already exceeded. under these circumstances, exogenous estradiol is not expected to provide a threshold dose. this principle is demonstrated for e2 in the red-eared slider, a turtle with temperature-dependent sex determination. in this species, gonadal s ... | 1999 | 9924012 |
| identification and structural characterization of a novel member of the vitamin d binding protein family. | the apparent high degree of homology of a blood protein with a unique dual binding affinity for two distinct hormones, thyroxin (t4) and vitamin d, isolated from a turtle, trachemys scripta (family emydidae) and mammalian vitamin d binding protein (dbp) prompted further interspecific comparison to better understand the structure of functional binding sites. using polymerase-chain reaction (pcr) with primers derived from the putative nucleotide sequences encoding peptides from the degradation of ... | 1998 | 9972311 |
| spatiotemporal structure of depolarization spread in cortical pyramidal cell populations evoked by diffuse retinal light flashes. | the spatiotemporal structure of cortical activity evoked by diffuse light flashes was investigated in an isolated eyecup-brain preparation of the pond turtle, pseudemys scripta. by combining a photomicroscopic image of the preparation with voltage-sensitive dye signals recorded by a 464-element photodiode array, the spread of depolarization within different cortical areas could be directly visualized with millisecond temporal resolution. diffuse stimulation of the contralateral eyecup initially ... | 2007 | 10022479 |
| the effects of dietary vitamin c on growth rates of juvenile slider turtles (trachemys scripta elegans). | seventeen juvenile red-eared slider turtles (trachemys scripta elegans) were separated into two groups: one group received a diet that included vitamin c supplementation, the other group received a similar diet devoid of supplemental vitamin c. overall body mass and carapace length were measured monthly for a period of 1 yr. no significant differences were observed between the growth rates of the two experimental groups, suggesting that dietary vitamin c is not essential for normal growth and de ... | 1998 | 10065850 |
| characterization of thyroid hormone 5'-monodeiodinase activity in the turtle (trachemys scripta). | thyroid hormone metabolism by 5'-monodeiodinase enzymes (5'md) was characterized in peripheral tissues of the turtle, trachemys scripta, and compared with activity measured in the rat. based on differences in ph dependence, sensitivity to inhibitors, substrate affinity, and cofactor requirements, at least two types of enzyme activities have been identified in the turtle. a 5'md activity was measured in liver and kidney microsomal fractions that exhibits inhibition by 2n-propyl-6-thiouracil (ptu) ... | 1999 | 10068496 |
| sex reversal effects of environmentally relevant xenobiotic concentrations on the red-eared slider turtle, a species with temperature-dependent sex determination. | xenobiotics suspected of being estrogenic-the pcb aroclor 1242 and the pesticides toxaphene, dieldrin, p,p'-ddd, cis-nonachlor, trans-nonachlor, p,p'-dde, and chlordane-were examined for their ability to override a male-producing incubation temperature and result in female hatchlings in the red-eared slider, a turtle with temperature-dependent sex determination. compounds were assayed in the environmentally relevant concentrations detected in alligator eggs from lake apopka, florida, singly, in ... | 1999 | 10068503 |
| co2 excretion and postcapillary ph equilibration in blood-perfused turtle lungs | turtles possess a significant postcapillary co2 partial pressure (pco2) disequilibrium between arterial blood and alveolar gas. there are several possible explanations for this blood disequilibrium including a slow rate of erythrocyte physiological anion shift (cl-/hco3- exchange) or inaccessibility of plasma hco3- to red blood cell or pulmonary carbonic anhydrase. the present study characterized the contribution of erythrocyte anion exchange and pulmonary and erythrocyte carbonic anhydrase to c ... | 1999 | 10085269 |
| fatal trematodiasis in research turtles. | during a 5-year period, 16 freshwater turtles (trachemys scripta elegans and chrysemys picta) that were purchased for research purposes died spontaneously. clinical signs of disease included lethargy, constant swimming, swimming sideways, hemiplegia, and ulcerative lesions on the carapace. at necropsy, subcutaneous edema, hepatic necrosis, pancreatic necrosis, splenic necrosis, and intestinal parasites were identified. histologically, trematode eggs were seen within the liver, brain, spleen, kid ... | 1998 | 10090039 |
| identification of renal podocytes in multiple species: higher vertebrates are vimentin positive/lower vertebrates are desmin positive. | we sought to characterize podocytes in the kidneys of numerous species from amphibians to mammals because of the pivotal function of these cells in renal diseases. for this purpose, intermediate filament (if) proteins of podocytes were examined by immunofluorescence microscopy using antibodies against vimentin, cytokeratins, and desmin. these staining patterns were then compared to those of parietal cells of bowman's capsule and tubular cells of the first portion of the proximal tubule from the ... | 1999 | 10090571 |
| multiplicity of glutamic acid decarboxylases (gad) in vertebrates: molecular phylogeny and evidence for a new gad paralog. | the evolution of chordate glutamic acid decarboxylase (gad; ec 4.1.1.15), a key enzyme in the central nervous system synthesizing the neurotransmitter gamma-amino-butyric acid (gaba) from glutamate, was studied. prior to this study, molecular data of gad had been restricted to mammals, which express two distinct forms, gad65 and gad67. these are the products of separate genes and probably are derived from a common ancestral gad following gene duplication at some point during vertebrate evolution ... | 1999 | 10331265 |
| hypoxic hypometabolism in the anesthetized turtle, trachemys scripta. | a hypometabolic response during acute exposure to hypoxia has been measured in both endothermic and ectothermic vertebrates. in the turtle, we determined the metabolic response to normocapnic hypoxia and hypercapnic hypoxia. in addition, we tested the hypothesis that hypoxic hypometabolism was a regulated response that did not depend on o(2) availability. metabolic, cardiovascular, and blood gas measurements were collected in anesthetized turtles under two conditions: during normocapnic hypoxia ... | 1999 | 10409253 |
| embryonic development of connections in turtle pallium. | we are interested in similarities and conserved mechanisms in early development of the reptilian and mammalian thalamocortical connections. we set out to analyse connectivity in embryonic turtle brains (pseudemys scripta elegans, between stages 17 and 25), by using carbocyanine dye tracing. from the earliest stages studied, labelling from dorsal and ventral thalamus revealed backlabelled cells among developing thalamic fibres within the lateral forebrain bundle and striatum, which had similar mo ... | 1999 | 10464368 |
| temporal dispersion windows in cortical neurons. | a temporal dispersion window is the time required for a volley of action potentials on presynaptic axons to cross the dendritic arbor of a postsynaptic neuron. the volley produces a series of unitary postsynaptic potentials (psps) on the postsynaptic neuron. temporal dispersion is, thus, one factor that can influence the integration of unitary psps and the production of action potentials in cortical neurons. temporal dispersion windows for neurons in the visual cortex of the freshwater turtle, p ... | 2013 | 10482003 |
| incubation temperature influences sex-steroid levels in juvenile red-eared slider turtles, trachemys scripta, a species with temperature-dependent sex determination. | incubation temperature determines gonadal sex in the red-eared slider turtle, trachemys scripta. however, little is known about the long-term effects of incubation temperature on traits other than gonadal sex in this species. to investigate the hypothesis that incubation temperature (independent of gonadal sex) influences sex steroid levels after hatching, we incubated eggs of the red-eared slider turtle at three temperatures (26, 28.6, and 31 degrees c). we then measured plasma levels of dihydr ... | 1999 | 10529274 |
| effects of exogenous corticosterone on locomotor activity in the red-eared slider turtle, trachemys scripta elegans. | we investigated the effects of exogenous corticosterone on the locomotor activity of captive red-eared slider turtles, trachemys scripta elegans. an increase in plasma corticosterone often increases locomotor activity in mammals and birds, but there are no reported findings for turtles. in this study turtles implanted with corticosterone-filled silastic((r)) implants showed a significant increase in caged locomotor activity when compared to control animals with empty implants. corticosterone-tre ... | 1999 | 10531550 |
| cardiorespiratory response to progressive hypoxia and hypercapnia in the turtle trachemys scripta | the ventilatory responses of chelonian reptiles to hypoxic and hypercapnic stress have been fairly well described. as turtles are capable of large cardiac shunts, changes in pulmonary perfusion may be an equally viable and potent response to these stressors. to test this hypothesis, conscious unrestrained turtles were unidirectionally ventilated while blood flow in the left pulmonary artery ( q_dot (lpa)) and left aortic arch ( q_dot (lao)) was monitored. turtles were exposed to step changes (2. ... | 1999 | 10539969 |
| warm-blooded isochore structure in nile crocodile and turtle. | the genomes of warm-blooded vertebrates are characterized by a strong heterogeneity in base composition, with gc-rich and gc-poor isochores. the gc content of sequences, especially in third codon positions, is highly correlated with that of the isochore they are embedded in. in amphibian and fish genomes, gc-rich isochores are nearly absent. thus, it has been proposed that the gc increase in a part of mammalian and avian genomes represents an adaptation to homeothermy. to test this selective hyp ... | 1999 | 10555283 |
| identification and expression of gastrin and cholecystokinin mrnas from the turtle, pseudemys scripta: evidence of tissue-specific tyrosyl sulfation(1). | gastrin and cholecystokinin (cck) are related peptide hormones expressed in the brain and gut of vertebrates. in this study, complementary dnas have been characterised from the red-eared slider turtle, pseudemys scripta. the encoded preprocck contains mono and dibasic endoproteolytic processing sites for formation of the previously identified cck-70, cck-40 and cck-8 products, whereas preprogastrin contains two dibasic processing sites for the generation of gastrin-52. alignment of the predicted ... | 1999 | 10561540 |
| morphological changes induced by prolonged darkness in the retinal pigment epithelium of the turtle (pseudemys scripta elegans). | the retinal pigment epithelium of vertebrates was shown to be sensitive to cyclic oscillations of light and darkness. the morphological changes induced by prolonged darkness on the retinal epithelial cells of the freshwater turtle were studied, with particular regard to their localization and to their reversibility if animals are recovered under cyclic light. the eyes were processed for light and electron microscopy and a morphological and morphometric analysis was performed on the specimens. af ... | 2003 | 10575821 |
| discordant responses of mitogen-activated protein kinases to anoxia and freezing exposures in hatchling turtles. | the role of two vertebrate mitogen-activated protein kinases (mapks) in mediating responses to in vivo anoxia or freezing exposures was examined in four organs (liver, heart, kidney and brain) of hatchling red-eared turtles, trachemys scripta elegans, which are naturally tolerant of these stresses. the extracellular signal-regulated kinases were not stress-activated except in brain of frozen turtles. the c-jun nh2-terminal kinases (jnks) were transiently activated by anoxia exposure in all four ... | 1999 | 10595322 |
| developmental expression of steroidogenic factor 1 in a turtle with temperature-dependent sex determination. | a variety of reptiles possess temperature-dependent sex determination (tsd) in which the incubation temperature of a developing egg determines the gonadal sex. current evidence suggests that temperature signals may be transduced into steroid hormone signals with estrogens directing ovarian differentiation. steroidogenic factor 1 (sf-1) is one component of interest because it regulates the expression of steroidogenic enzymes in mammals and is differentially expressed during development of testis ... | 1999 | 10603272 |