| 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 |
| 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 |
| 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 |
| 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 |
| 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 |
| 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 |
| 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 |
| 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 |
| 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 |
| 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 |
| 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 |
| 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 |
| 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 |
| 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 |
| 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 |
| 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 |
| 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 |
| 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 |
| 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 |
| 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 |
| 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 |
| 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 |
| 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 |
| 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 |
| 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 |
| 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 |
| 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 |
| 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 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 |
| 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 |
| 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 |
| 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 |
| 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 |
| 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 |
| 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 |
| [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 |
| 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 |
| 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 |
| 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 |
| 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 |
| 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 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 |
| 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 |
| 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 |
| 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 |
| 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 |
| 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 |
| 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 |
| 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 |
| 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 |
| 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 |
| enzymatic control of glycogenolysis during anoxic submergence in the freshwater turtle trachemys scripta. | freshwater turtles trachemys scripta elegans endure prolonged severe hypoxia, and even complete anoxia, while diving or hibernating underwater. metabolic adaptations supporting survival include the activation of glycogenolysis and glucose output from liver, as well as strong metabolic rate depression. the present study analyzes the enzymes of both the phosphorolytic (glycogen phosphorylase, phosphorylase b kinase, camp-dependent protein kinase) and glucosidic (alpha-glucosidase) pathways of glyc ... | 1995 | 7584617 |
| upregulation of the gabaa/benzodiazepine receptor during anoxia in the freshwater turtle brain. | the freshwater turtle brain survives anoxia by decreasing its energy expenditure. during this anoxic period there is a sustained release of the inhibitory neurotransmitter gamma-aminobutyric acid (gaba). this study investigated whether there was a corresponding change in the binding properties of the gabaa/benzodiazepine (gaba/bdz) receptor. turtles (trachemys scripta) were subjected to a 100% n2 atmosphere for up to 24 h. after exposure, the cerebral cortex was dissected out, and saturation bin ... | 1995 | 7771598 |
| conservation and dynamics of microsatellite loci over 300 million years of marine turtle evolution. | microsatellite loci consisting of (ca)n repetitive arrays were obtained from three species of marine turtle, and primers were designed to test for polymorphism within species and the persistence of microsatellites across species. homologous loci were found in each test of six marine species within two families (cheloniidae and dermochelyidae), as well as in a freshwater species (emydidae, trachemys scripta), which indicates a conservation of flanking sequences spanning approximately 300 million ... | 1995 | 7739385 |
| short-term effects of dopamine on photoreceptors, luminosity- and chromaticity-horizontal cells in the turtle retina. | the effects of dopamine on luminosity-type horizontal cells have been documented in different vertebrate retinas, both in vivo and in vitro. some of these effects may reflect direct action of dopamine onto these cells, but indirect effects mediated by presynaptic neurons cannot be ruled out. furthermore, direct effects of dopamine on horizontal cells may affect other, postsynaptic neurons in the outer plexiform layer. to test these possibilities, we studied the effects of dopamine on photorecept ... | 2013 | 7654600 |
| camp-dependent protein kinase and anoxia survival in turtles: purification and properties of liver pka. | the catalytic subunit of turtle (trachemys scripta elegans) liver cyclic amp-dependent protein kinase (pkac) was purified to homogeneity with a final specific activity of 65,783 pmol phosphate transferred.min-1.mg protein-1. subunit molecular weight was 42-43 kda as determined by sds-page and sephacryl s-300 chromatography. the isolectric point was ph 6.41 +/- 0.02. turtle liver pkac showed highest activity with kemptide as its substrate; activity with other artificial substrates, histone iia an ... | 1995 | 7659081 |
| spectral properties of turtle cones. | microelectrodes were used to record from red and green cones of the turtle pseudemys scripta elegans. the purpose of this study was to determine the action spectra of the red and green cone photopigments, and to look closely for direct interactions between the two cone classes. an isolated retina preparation was employed so that cones could be stimulated from the outer segment side, thereby avoiding the oil droplets that reside in the inner segments of many cones and normally filter incident lig ... | 2008 | 7786854 |
| the slider turtle as an environmental sentinel: multiple tissue assays using flow cytometric analysis. | we used flow cytometry (fcm) to conduct a multiple-tissue assay on slider turtles (trachemys scripta) inhabiting radioactive seepage basins. duplicate samples of blood, heart, spleen and kidney were analysed on two different cytometers (leitz mpv and coulter profile ii), each employing distinct staining protocols (dapi and pi, respectively). both dapi and pi assays of spleen cells demonstrated significantly greater variation in dna content for the basin turtles than for 'control' animals from ne ... | 1995 | 24197546 |
| effects of anoxia on protein phosphatase in turtle organs: purification and properties of protein phosphatase type-1 from turtle liver. | protein phosphatase type 1 (pp-1) was analyzed in organs of the red-eared slider turtle, trachemys scripta elegans, a species capable of long-term anoxia survival. during anoxic submergence at 7 degrees c, pp-1 activity in liver rapidly decreased to 63% of the control value within the first hour and remained suppressed over the subsequent 20 h of anoxia. pp-1 activity was also suppressed in red skeletal muscle during anoxia and dropped transiently (after 1 h) in brain but did not change in heart ... | 1995 | 7864641 |
| electrocardiography in anaesthetised red-eared sliders (trachemys scripta elegans). | electrocardiographic (ecg) values were measured in nine red-eared sliders (trachemys scripta elegans), anaesthetised with either ketamine, ketamine/xylazine or ketamine/midazolam, for the purpose of cardiocentesis. lead ii traces were then recorded through three cutaneous electrodes. the ecg complexes consisted of small upright p waves, larger r waves and no q or s wave deflections, very long qt intervals, small upright t waves, and a short tp interval. no sv waves were recorded. this pattern wa ... | 1995 | 7709064 |
| effect of anoxia on isolated turtle tissues: is the response to anoxia mediated by protein kinase second messengers? | organ slices from the turtle trachemys scripta elegans were incubated under aerobic and anoxic conditions to examine the effect of protein kinase (prk) second messengers in potentiating the biochemical responses to anoxia exposure. incubating liver slices from aerobic animals under anoxic conditions produced biochemical changes exactly similar to those observed in vivo: phosphofructokinase (pfk) was more sensitive to citrate inhibition and the percentage of glycogen phosphorylase (gp) in the act ... | 1994 | 7696998 |
| role of reductase and aromatase in sex determination 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. in the red-eared slider turtle (trachemys scripta), an incubation temperature of 26 degrees c results in all male offspring, whereas an incubation temperature of 31 degrees c results in all female offspring; at temperatures intermediate to these (e.g. 29, 29.2, 29.4 degrees c) a mixed sex ratio is obtained. administration of exogenous oestrogens will overcome the effects of an all-male pr ... | 1994 | 7829992 |
| nitric oxide synthase in the brain of the turtle pseudemys scripta elegans. | the distribution pattern of nitric oxide synthase (nos) was investigated in the brain of the turtle by nadph-diaphorase histochemistry. the specificity of the histochemical staining was tested by immunocytochemical colocalization with an antiserum specific for nos. in the forebrain, neurons staining intensely for nitric oxide synthase were localized in the olfactory tubercle, the basal ganglia complex, the basal amygdaloid nucleus, suprapeduncular nucleus, and the posterior hypothalamic area. ma ... | 1994 | 7529267 |
| time course of anoxia-induced increase in cerebral blood flow rate in turtles: evidence for a role of adenosine. | the exceptional ability of the turtle brain to survive prolonged anoxia makes it a unique model for studying anoxic survival mechanisms. we have used epi-illumination microscopy to record blood flow rate in venules on the cortical surface of turtles (trachemys scripta). during anoxia, blood flow rate increased 1.7 times after 45-75 min, whereupon it fell back, reaching preanoxic values after 115 min of anoxia. topical superfusion with adenosine (50 microm) during normoxia caused a 3.8-fold incre ... | 1994 | 8063883 |
| a tetraethylammonium-insensitive inward rectifier k+ channel in müller cells of the turtle (pseudemys scripta elegans) retina. | ion channels present in isolated glial (müller) cells from the retina of the turtle (pseudemys scripta elegans) were studied with the patch clamp technique. the predominant conductance in these cells was due to an inward rectifying potassium current. the whole-cell conductance of the inward rectifier was 20.2 +/- 1.9 ns (n = 7 cells) in a standard extracellular saline solution (3 mm extracellular potassium). this conductance was dependent on the extracellular potassium concentration, with a 2.88 ... | 1994 | 7807523 |
| regulation of central vascular blood flow in the turtle. | the purpose of this study was to determine the effects of vagal nerve stimulation on the pulmonary and systemic circulations in the turtle pseudemys scripta. the heart rate (hr), systemic vascular resistance (rsys), pulmonary vascular resistance (rpul), total pulmonary blood flow (qpul), and total systemic blood flow (qsys) were measured during electrical stimulation of the vagal efferent and the vagal afferent nerves. vagal efferent nerve stimulation resulted in a bradycardia, increased rsys an ... | 1994 | 8067470 |
| anatomical characterization of retinal ganglion cells that project to the nucleus of the basal optic root in the turtle (pseudemys scripta elegans). | there is little detailed information about retinal ganglion cells which project to specific central targets in the brain. the present study examined retinal ganglion cells projecting to the nucleus of the basal optic root, a major accessory retinal target in the turtle. these ganglion cells were first selectively labeled using retrograde transport of rhodamine injected stereotaxically into the nucleus of the basal optic root. the number and distribution of the retrogradely labeled cells in the r ... | 1994 | 7969940 |
| functional architecture of vestibular primary afferents from the posterior semicircular canal of a turtle, pseudemys (trachemys) scripta elegans. | physiological studies in many vertebrates indicate that vestibular primary afferents are not a homogeneous population. such data raise the question of what structural mechanisms underlie these physiological differences and what functional role is played by afferents of each type. we have begun to answer these questions by characterizing the architecture of 110 afferents innervating the posterior canal of pseudemys scripta. we emphasize their spatial organization because experimental evidence sug ... | 1994 | 7929889 |
| distribution of target cells for 1,25-dihydroxyvitamin d3 in the brain of the yellow bellied turtle trachemys scripta. | five h after injection of tritiated 1,25-dihydroxyvitamin d3 into trachemys scripta, neurons with nuclear concentrations of radioactivity were identified in distinct regions within the central nervous system. coinjection of a 100-fold excess of non-labeled 1,25-dihydroxyvitamin d3 abolished or reduced the specific nuclear binding of tracer. target neurons were present in ventral periventricular brain regions including tuberculum olfactorium, nucleus accumbens, cortex piriformis, primordium hippo ... | 1994 | 8004456 |
| light adaptation and photopigment bleaching in cone photoreceptors in situ in the retina of the turtle. | light adaptation and photopigment bleaching in cone photoreceptors were studied in the intact, superfused retina of the turtle (pseudemys scripta elegans). a new method for measuring changes in the photopigment of cones is described. action spectrum measurements indicate that the signals arise from the red-sensitive cones. measurements of steady-state bleaching are well described by the monomolecular bleaching equation with a half-bleaching constant of about 5.5 log photons sec-1 microns-2. quan ... | 1994 | 8120614 |
| temperature and cerebral blood flow regulation in the freshwater turtle, pseudemys scripta. | chemical regulation of cerebral blood flow (cbf) by co2 has been demonstrated in an ectohermic vertebrate (davies, am. j. physiol. 260: r382, 1991). cerebrovascular sensitivity to co2 (delta cbf/delta paco2), a measure of the vascular reactivity of the cerebral blood vessels to co2, was found to be 0.7 ml.min-1.100 g-1.torr-1 during normoxia and 3.4 during anoxia in the freshwater turtle, pseudemys scripta. in the present study, the effect of body temperature on delta cbf/delta paco2 was studied ... | 1994 | 8059076 |
| glucuronidation of flumequine by the turtle pseudemys scripta elegans. | | 1994 | 8196100 |
| glucuronidation of naproxen by the turtle pseudemys scripta elegans. | | 1994 | 8196098 |
| 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 |
| 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 |
| role of aromatization in testosterone-induced inhibition of luteinizing hormone secretion in female turtles, trachemys scripta. | both 17 beta-estradiol (e2) and testosterone (t) were shown to inhibit in vitro pituitary lh secretion in the turtle trachemys scripta. since t was approximately 500 times less potent than e2, and 5 alpha-dihydrotestosterone was even less active than t, the inhibitory action of t may result from its aromatization to estrogen. we utilized both in vivo and in vitro approaches to elucidate the roles of t and estrogen in the negative feedback of pituitary lh secretion. gonadectomy of adult (vitellog ... | 1994 | 8312438 |
| anoxia induces changes in translatable mrna populations in turtle organs: a possible adaptive strategy for anaerobiosis. | the effects of anoxic submergence (16 h at 15 degrees c) on cellular mrna contents were assessed in five organs of anoxia tolerant turtles trachemys scripta elegans. poly(a)+ rna was extracted from liver, red and white skeletal muscle, kidney and heart of control and anoxic turtles, as well as from heart and kidney of turtles allowed 24 h aerobic recovery (at 15 degrees c) after anoxia exposure. poly(a)+ rna content increased by 30% in white muscle from anoxic turtles relative to control animals ... | 1994 | 7983251 |
| de novo protein synthesis and protein phosphorylation during anoxia and recovery in the red-eared turtle. | changes in de novo protein synthesis and protein phosphorylation were monitored during anoxia and recovery in the red-eared slider trachemys (= pseudemys) scripta elegans. time courses of 35s-radiolabeled methionine incorporation into acid-precipitable material showed an increase up to 5 h postinjection and remained constant after this time. comparison of the total and acid-precipitable 35s label incorporation into tissues from 20-h control, anoxic, and recovering animals showed differences betw ... | 1993 | 8285280 |
| estrogen- and temperature-induced medullary cord regression during gonadal differentiation in a turtle. | gonadal differentiation associated with estrogen-induced female sex determination was examined in a turtle with temperature-dependent sex determination, and was compared to ovarian differentiation at a female-producing temperature. freshly ladi eggs of the red-eared slider, trachemys scripta, were incubated at a male-producing temperature (26 degrees c) and were experimentally manipulated at one of three embryonic stages: stage 15, 17, or 20 (i.e. early, midway, or late in the temperature-sensit ... | 1993 | 8405765 |
| differential n-acetylation of alpha-msh and beta-endorphin in the intermediate pituitary of the turtle, pseudemys scripta. | steady-state analyses of the intermediate pituitary of the turtle, pseudemys scripta, indicated that alpha-msh-sized immunoreactive forms and beta-endorphin-sized immunoreactive forms are major end products of melanotropic cells. three forms of alpha-msh-related immunoreactivity were detected. the two major forms had the same reversed-phase hplc properties as synthetic n,o-diacetyl-acth(1-13)-nh2 and n-acetyl-acth(1-13)-nh2. these forms accounted for 97% of the total alpha-msh-related immunoreac ... | 2007 | 8234035 |
| synaptic microcircuitry of bipolar and amacrine cells with serotonin-like immunoreactivity in the retina of the turtle, pseudemys scripta elegans. | although serotonin is thought to be a neurotransmitter in a number of retinal systems, much of the precise synaptic connectivity of serotonergic neurons is unknown. to address this issue, we used an antiserum directed against serotonin to label serotonergic bipolar and amacrine cells in the turtle retina. light-microscopic analysis of labeled amacrine and bipolar cells indicated that both had bistratified dendritic arborizations primarily in stratum 1 and in strata 4/5 of the inner plexiform lay ... | 2013 | 8494799 |
| monoaminergic systems in the brainstem and spinal cord of the turtle pseudemys scripta elegans as revealed by antibodies against serotonin and tyrosine hydroxylase. | with the aim of gaining more insight into the monoaminergic regulation of spinal motor systems in the turtle, we have studied the distribution of 5-ht (5-htir) and tyrosine hydroxylase immunoreactivity (thir) in the brainstem and spinal cord of pseudemys scripta elegans. 5-htir cell bodies were located in the midline in nucleus raphe inferior, nucleus raphe superior, and laterally in nuclei reticularis superior and inferior and nucleus reticularis isthmi. thir cell bodies were located in the com ... | 1992 | 1361496 |
| design and control of the head retractor muscle in a turtle, pseudemys (trachemys) scripta: ii. efferent innervation. | the head retractor muscle (rccq) of pseudemys scripta is a useful model in which to study the mechanisms animals use to vary the force and timing of movement. single fibers in this muscle differ significantly in attachments, length, diameter, taper characteristics, and histochemical properties, suggesting that they may be energetically and architecturally specialized for different roles in head movement. in the present paper, we report the peripheral and central efferent innervation of these div ... | 1992 | 1280283 |
| gabaa, gabab, and benzodiazepine binding sites in the cerebellar cortex of the red-eared turtle (pseudemys scripta). | we used receptor autoradiography to ascertain the distribution of gabaa and gabab binding sites in the cerebellar cortex of the red-eared turtle (pseudemys scripta). gabaa binding sites were found in both molecular and granule cell layers with highest levels in the granule cell layer. gabab binding sites were found at highest level in the molecular layer. benzodiazepine binding sites were found in approximately equal abundance in both layers. little binding of any ligand was seen in the purkinje ... | 1992 | 1334769 |
| barbiturate sensitive components of visual erps in a reptile. | the selective effects of methohexital anesthesia were used to differentiate components of visual event-related brain potentials (erps) in pond turtles (pseudemys scripta). tectal and forebrain omitted stimulus potentials (osps) were found to be particularly sensitive to the barbiturate; they are reversibly abolished while the large early wave of the forebrain flash visual evoked potential (vep; 110-120 ms) is reduced by only 27 +/- 11% and that of the tectal vep (55-65 ms) is increased by 40 +/- ... | 1992 | 1330066 |
| glutamate antagonists that block hyperpolarizing bipolar cells increase the release of dopamine from turtle retina. | some neurochemical features of the neuronal circuitry regulating dopamine release were examined in the retina of the turtle, pseudemys scripta elegans. glutamate antagonists that block hyperpolarizing bipolar cells, such as 2,3 piperidine dicarboxylic acid (pda), produced dose-dependent dopamine release. in contrast, the glutamate agonist 2-amino-4-phosphonobutyric acid (apb), which blocks depolarizing bipolar cell responses with high specificity, had no effect on the release of dopamine. the ga ... | 2017 | 1327088 |
| vestibular afferents innervating the posterior ampullae in a turtle, pseudemys scripta. | | 1992 | 1599219 |
| specificity of steroid hormone-induced sex determination in a turtle. | the specificity of steroid hormone-induced sex determination was investigated in the red-eared slider, trachemys scripta, a turtle with temperature-dependent sex determination. all eggs were incubated at either a female-producing temperature (31 degrees c) or a male-producing temperature (26 degrees c) and received control or experimental treatments at stage 17-18 of embryonic development. a variety of treatments induced female sex determination at the male-producing temperature. oestradiol-17 b ... | 1992 | 1517701 |
| sites of estrogen uptake in embryonic trachemys scripta, a turtle with temperature-dependent sex determination. | female sex determination can be induced in embryonic red-eared slider turtles (trachemys scripta) by exogenous estrogen, as well as by incubation at warm temperature. in the present study, estrogen target areas were identified in embryos before (stage 15), during (stage 18), and after (stage 22) the critical period for sex determination. both hyperfilm and emulsion autoradiography were used to localize tritium accumulation after the injection of radiolabeled 17 beta-estradiol. site-specific trit ... | 1992 | 1617018 |
| effects of temperature and anoxia on regional cerebral blood flow in turtles. | regional cerebral blood flow (cbf) was measured in isoflurane-anesthetized turtles (pseudemys scripta) by the hydrogen clearance method. teflon-coated platinum electrodes (25 microns) were implanted in the olfactory bulbs, midcerebral cortex and cerebellum in eight adult turtles. the electrodes were voltage clamped at +0.30 v relative to a ag-agcl electrode implanted in the dorsal neck muscles. washout kinetics of h2 gas administered via controlled ventilation was used to calculate local blood f ... | 1992 | 1558224 |
| subcellular enzyme binding and the regulation of glycolysis in anoxic turtle brain. | the association of glycolytic enzymes with the particulate fraction of the cell was assessed in the brain of the freshwater turtle, pseudemys scripta elegans, using three different methodologies. each method showed that a large percentage of each of eight enzymes was bound in brain. the effect of environmental anoxia (5 or 20 h submergence in n2-bubbled water at 7 degrees c) on the distribution of enzymes between free and bound states was analyzed. all three techniques showed a significant incre ... | 1992 | 1532698 |
| norepinephrine activates potassium conductance in neurons of the turtle cerebral cortex. | whole-cell voltage and current clamp recordings were obtained from cortical neurons of the pond turtle, pseudemys scripta elegans. norepinephrine (ne) induced an outward current in 50% of pyramidal neurons. this current had a reversal potential of -88.3 +/- 3.2 mv, consistent with a k+ conductance increase, and had a mean amplitude of 18.3 +/- 7.2 pa at -40 mv. the ionic dependence and pharmacological analyses are both consistent with alpha 2 adrenergic receptor stimulation. inhibition of na(+)- ... | 1992 | 1617428 |
| hydroxysteroid dehydrogenase activity associated with sexual differentiation in embryos of the turtle trachemys scripta. | many turtles exhibit temperature-dependent sex determination. we have examined the hypothesis that incubation temperature causes a differential expression of steroidogenic enzymes in embryonic turtles. the activities of three steroidogenic enzymes were studied histochemically in turtle (trachemys scripta) embryos at different developmental stages: sexually undifferentiated (stage 15), differentiating (stage 17), and differentiated (stage 26; i.e., hatchling). steroidogenic enzymes were detected ... | 1992 | 1547311 |
| a "beat-to-beat" interval generator for optokinetic nystagmus. | an analysis of optokinetic responses was used to derive an iterative model that reproduces the duration of nystagmus slow phases and eye position control during optokinetic nystagmus. optokinetic nystagmus was recorded with magnetic search coils from red-eared turtles (pseudemys scripta elegans) during monocular, random dot pattern stimulation at constant velocities ranging from 0.25-63 degrees/s. the beat-to-beat behavior of slow phase durations was consistent with the existence of an underlyin ... | 1992 | 1540673 |
| refractive state, contrast sensitivity, and resolution in the freshwater turtle, pseudemys scripta elegans, determined by tectal visual-evoked potentials. | visual-evoked potentials (veps) were recorded from the surface of the optic tectum of the freshwater turtle, pseudemys scripta elegans, in response to phase reversal of square-wave gratings of different spatial frequency and contrast. the refractive state of a group of 12 turtles in air was assessed from veps by placing trial lenses in front of the eye. the group mean refraction did not differ significantly from emmetropia, as compared to 4.8 diopters of hyperopia when refracted retinoscopically ... | 1991 | 1772808 |
| chronology and morphology of temperature-dependent sex determination. | temperature sensitivity and gonadal differentiation were studied in a turtle, trachemys scripta, with temperature-dependent sex determination. sex determination was sensitive to both the duration and magnitude of incubation temperature. temperature exerted an "all or none" effect on the ovarian or testicular nature of most gonads, but affected the length of ovaries in a graded fashion. collectively, the results indicate that sex determination is controlled by the quantitative effect of temperatu ... | 1991 | 1744617 |
| localization of aspartate-like immunoreactivity in the retina of the turtle (pseudemys scripta). | aspartate has been reported to be a putative excitatory neurotransmitter in the retina, but little detailed information is available concerning its anatomical distribution. we used an antiserum directed against an aspartate-albumin conjugate to analyze the anatomy, dendritic stratification, and regional distribution of cell types with aspartate-like immunoreactivity in the turtle retina. the results showed dramatic differences in immunoreactivity in the peripheral versus the central retina. stro ... | 1991 | 1761744 |
| synergism between temperature and estradiol: a common pathway in turtle sex determination? | in many reptiles, the temperature at which the eggs are incubated determines the sex of the hatchlings. administration of estradiol will counteract the masculinizing effects of a male-producing temperature, resulting in female hatchlings. to address whether temperature and estrogen are biologically equivalent, two experiments were conducted with the red-eared slider turtle, trachemys scripta. in the first experiment, varying dosages of estrogen were administered at stage 17 (the middle of the te ... | 1991 | 1791420 |