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At least 685 records · Page 38Linked to original sources
PubMed1988

A monoclonal antibody that binds to photoreceptors in the turtle retina.

We have raised monoclonal antibodies to photoreceptor cells in the retina of the turtle (Pseudemys scripta elegans). One of these antibodies, 15-18 (an IgG1), was studied by immunoelectron microscopy using colloidal gold, and found to bind to the outer segments of all rods and some single cones, but did not stain turtle double cones. Immunoblotting and immunoprecipitation show that antibody 15-18 binds to an antigen of apparent Mr approximately 34,5000 which is probably turtle opsin. Antibody 15-18 binds visual pigments from several species, including bovine opsin. In order to determine the antigenic site bound by 15-18 in bovine opsin, synthetic peptides were used as competitors in an enzyme-linked immunoassay (ELISA). The antigenic site is located in the surface loop connecting rhodopsin helices IV-V, in the sequence 190-197. Antibody 15-18 binds to the external surface of rod cell outer segments, thus providing direct evidence for the predicted orientation of rhodopsin in the plasma membrane.

Animals↗
PubMed1992

Neurons immunoreactive to choline acetyltransferase in the turtle retina.

Light microscopic immunocytochemistry using anti-choline acetyltransferase (ChAT) was performed to stain putative cholinergic amacrine cells in turtle retina. ChAT-immunoreactive somata lie in the inner nuclear (INL) and ganglion cell (GCL) layers. Three types of amacrine cells were found according to the location of their somata and their dendritic stratification pattern in the inner plexiform layer (IPL). Type I amacrines lie in the row of cells closest to the INL/IPL limits and they branch along the s1/s2 border of the IPL. Type II amacrines are displaced to the GCL and they ramify along the s3/s4 border of the IPL. Type III amacrines lie in the middle of the INL, 2-3 rows away from the IPL limits and their dendrites appear to be bi- or tri-stratified in s1 and s3-s4 of the IPL. The turtle ChAT-IR amacrines are thus similar to the types described in chicken retina. A regular, non-random mosaic formed by stained type II amacrine cells was observed in the GCL. Their density in mid-central retina was 750 cells/mm2, tapering off to 393 cells/mm2 in peripheral retina. Our study indicates that a pair of cholinergic amacrine cell types in turtle retina is arranged in mirror-image symmetry contributing to sublamina "a" and sublamina "b" of the IPL, like in other vertebrate retinas.

Animals↗
PubMed1987

Frogs and turtles: different ectotherm overwintering strategies.

The ability of frogs and turtles to overwinter and to survive hypoxia and anoxia has long been a topic of interest. While data remains scant, the emerging picture shows fundamentally different approaches to overwintering in these two groups of ectotherms. Frogs are far more limited by availability of oxygen than are turtles, even at near-freezing ambient temperatures. The reasons for this probably involve the vastly greater cutaneous permeability of the former. With their extreme tolerance of anoxia and profound suppression of metabolism, overwintering in turtles should not be viewed as simply prolonged diving but rather as ectotherm hibernation. Their incredible diving capabilities are merely a spin-off of a successful overwintering strategy. The following discussion reviews the major physiological mechanisms involved in the overwintering strategies of these two ectotherm groups.

Acclimatization↗
PubMed1988

Metabolic rate of feeding and fasting juvenile midland painted turtles, Chrysemys picta marginata.

1. Resting metabolic rates at 25 degrees C were determined for juvenile midland painted turtles that had recently been fed or fasted for 1, 2, 4, 6, 10, 14 or 19 days. 2. Recently fed turtles had an oxygen consumption rate of 211 microliter O2/g/hr. This decreased by 32% on the first day of the fast and by 69% by the 19th day. 3. Mass of the turtles (4.91-14.30 g) did not affect the rate of oxygen consumption (VO2).

Animals↗
PubMed1991

Anoxia-resistant turtle brain maintains ascorbic acid content in vitro.

The isolated turtle brain maintains intra- and extracellular concentrations of ascorbate when incubated in ascorbate-free physiological saline for as long as 24 h. After incubation for 1 h, total tissue content of ascorbate in the turtle cerebellum was the same as in unincubated controls. After 20-24 h, tissue ascorbate content remained at 65% of control levels, while extracellular ascorbate concentration, measured with carbon fiber voltammetric microelectrodes, was 56% of the initial value. For an intermediate incubation period of 6 h, reduced ascorbate content was maintained at about 80% of control levels, regardless of whether incubation was under normal conditions or in the absence of glucose or oxygen. By contrast, only 4% of the ascorbate content of guinea pig brain slices remained after a 6 h incubation. Maintenance of high levels of ascorbate by the anoxia-resistant turtle brain could be an important factor in the amelioration of oxidative injury in this tissue. Inclusion of ascorbate in media used for in vitro studies of mammalian brain tissue is recommended.

Animals↗
PubMed1996

Identification of central 5-HT and 5-HT1A receptors in the turtle brain (Chrysemys picta).

Radiologand binding studies were undertaken in the turtle whole brain, cerebellum and raphe using the selective radioligands [3H]5-hydroxytryptamine trifluoroacetate ([3H]5-HT) amd [3H]+/-8-hydroxy-2-(di-N-propylamino) tetralin hydrobromide ([3H]DPAT) to identify serotonin (5-HT) receptors and the specific 5-HT1A receptor subtype. Scatchard analysis identified a nanomolar affinity binding site for [3H]5-HT (12 nM) in turtle whole brain assays. A low affinity 5-HT1A site (102 nM) was also identified in turtle whole brain assays, with a higher affinity site noted in binding studies performed with tissue from the inferior raphe (20 nM). The difference in affinity for 5-HT receptors in reptilian versus mammalian brain may prove characteristic of lower vertebrate brains with implications for the physiologic effects of this neurotransmitter in the central nervous system.

Animals↗
PubMed1977

Some comparative aspects of the organ distribution of superoxide dismutase activity in the freshwater turtle, Pseudemys scripta elegans.

1. Superoxide dismutase activities in five tissues of the relatively anaerobic freshwater turtle were compared with SOD activities in the same tissues of two mammalian species (mouse and rabbit) with a more usual pattern of dependence on O2 availability. 2. SOD activities in brain, lung and skeletal muscle, but not liver or cardiac muscle, are significantly lower in the turtle. The turtle also shows differences in the pattern of relative SOD activities in various tissues as compared to the two mammalian species. 3. The data indicate that a relationship does exist between SOD activities and O2 exposure in intact vertebrate systems, and is consistent with a physiological role for SOD in tissue O2 metabolism.

Animals↗
PubMed1985

Steroid biosynthesis in turtle testes.

Testicular metabolism of radiolabelled substrates (pregnenolone, progesterone and androstenedione) was examined in two species of turtles, Pseudemys scripta and Sternotherus odoratus. Chemical methods (chromatography, derivative formation and crystallization) identified testosterone (in both species) and 5 alpha-androstane-3 beta,17 beta-diol (in S. odoratus) as products. Tentative identifications were also made of 20 beta-hydroxypregn-4-en-3-one in both turtles. Chromatographic profiles indicated the presence of several other C19- and C21-steroids. In S. odoratus, changes in proportions of the two major C19-compounds (testosterone and the 5 alpha-androstanediol) suggest a "switch" in the enzymatic pathways which resembles that associated with maturation in the rat. This enzymatic switch may be associated with the annual testicular cycle of the adult turtle.

Androstenedione↗
PubMed1989

pH regulation of calcium efflux by turtle liver mitochondria.

1. Turtle liver mitochondria are capable of taking up calcium in a pattern similar to that described from rat liver mitochondria. 2. Turtle liver mitochondria also possess a system for calcium efflux which is extremely sensitive to changes in extramitochondrial pH. A decrease in extramitochondrial pH by addition of HCl or by gassing with CO2 caused a rapid release of calcium. 3. The profound changes in pH and pCO2 during deep diving likely affects Ca efflux from mitochondria in the turtle liver.

Animals↗
PubMed1983

Do retinal and spinal projections overlap within the turtle thalamus?

The spinal and retinal projections to the turtle thalamus were studied using the autoradiographic tracing technique. Particular attention is given to the regions receiving both spinal and retinal projections: the ovalis complex and a perirotundal stripe. Spinal and retinal projections do not overlap significantly in either of these regions. In the perirotundal stripe there appears to be little likelihood of convergence of these projections on single neurons. In the ovalis complex, the most densely and the most consistently innervated thalamic region, however, the respective spinal and retinal target areas are located immediately adjacent to each other and low order somatosensory and visual projections may converge on single neurons with dendrites extending into both the spinal and retinal terminal arborizations. The ovalis complex in the turtle may be compared with the ventral part of the mammalian lateral geniculate nucleus. Both these nuclei receive spinal and retinal projections and both, reportedly, do not project to the telencephalon. The findings are discussed in relation to the possible evolution of the specific thalamic sensory nuclei in higher mammals as well as to the prosencephalic processing of somatosensory and visual information in turtles and mammals.

Animals↗
PubMed1988

The nucleus magnocellularis in the red-eared turtle, Chrysemys scripta elegans: eighth nerve endings and neuronal types.

Eighth nerve endings and neuronal types in the nucleus magnocellularis were analyzed in the red-eared turtle (Chrysemys scripta elegans). One group of turtles had horseradish peroxidase (HRP) injected into the surgically exposed inner ear. Following injection the animals survived for 3-5 days and then their 8th nerve fibers and endings were analyzed. A second group of turtles were impregnated by the Golgi-Kopsch technique. This also demonstrated 8th nerve endings and neurons in the nucleus magnocellularis. A third group had brains stained with cresyl violet to demonstrate normal morphology. Two types of neurons were present in the nucleus magnocellularis; bushy and stellate. Bushy neurons had a single primary dendrite with little branching and spines. Stellate neurons had 3-5 primary dendrites with secondary order branching and dendritic spines. Thick 8th nerve axons gave rise to endbulbs of Held and their axons formed bouton-type ending. Endbulbs of Held were presently only on bushy neurons while bouton-type terminals were only on stellate neurons. Endbulbs of Held had two patterns; one group was cup-shaped and surrounded approximately 1/2 of the soma without appendages. A second type had a smaller cup with 3-5 extensions to other parts of the cell. Stellate neurons had terminal boutons adjacent to the cell membrane. They appeared in some situations as a necklace surrounding the neuron.

Animals↗
PubMed1995

Laser-feedback measurements of turtle basilar membrane motion using direct reflection.

In mammalian hearing, the frequency-dependent spatial pattern of movement in the basilar membrane/organ of Corti complex forms the basis of frequency discrimination. This is not necessarily the case in lower vertebrates; the turtle, for example, has an electrical resonance mechanism in its auditory receptor cells that varies in best frequency from cell to cell. But how much, if any, of the frequency separation by the turtle is done mechanically by the basilar membrane complex? Attempts to find an investigative approach that avoided placing objects on the basilar membrane led to the rediscovery of laser-feedback interferometry. Laser-feedback interferometric investigations of the vibrational amplitude and phase of the turtle basilar membrane in response to imposed nanometer displacements of the eardrum reveal that the membrane reflects the broadly-tuned middle-ear filter characteristics. Phase-angle measurements of the basilar membrane as a function of frequency, and the best frequency of the obtained amplitude tuning curves, did not vary as a function of position within each specimen. Input-output functions of the basilar membrane were generally linear. The middle ear demonstrates a negative gain of 2-6 while the central region of the basilar membrane has a positive gain of 4-18 dependent on location and biological variability.

Acoustic Stimulation↗
PubMed1983

Absence of purinoceptors in the heart of the turtle (Emys orbicularis).

The effects of adenosine, adenosine 5'-triphosphate (ATP), a slowly degradable ATP analogue beta,gamma-methylene ATP (APPCP) and a degradation resistant ATP analogue alpha,beta-methylene ATP (APCPP) were examined on the turtle heart. Adenosine, ATP, APPCP and APCPP had no effect on the rate or force of contraction of either the atrium or ventricle. The effects of acetylcholine and noradrenaline were also examined on the turtle heart. Acetylcholine decreased the force and rate of contraction of turtle atria in a concentration-dependent manner. Noradrenaline increased the rate of contraction but caused a slight decrease in the force of contraction of the atrium. Neither acetylcholine nor noradrenaline produced an inotropic effect on the ventricle.

Acetylcholine↗
PubMed1988

Evolution of neurotransmitter-related markers in the vertebrate telencephalon. Comparative microchemical study in discrete brain regions of a frog and a turtle.

1. Neurochemical markers related to cholinergic, GABAergic and glutamatergic/aspartatergic neurotransmission have been measured in telencephalic areas obtained by microdissection from frog (Rana esculenta) and turtle (Pseudemys scripta elegans) brain. 2. In both species, pallial areas showed remarkably higher levels of synaptosomal D-3H-aspartate high affinity uptake than basal regions. Conversely, striatal and septal areas possessed higher levels of the GABAergic marker glutamate decarboxylase (GAD) than the pallium. 3. A differential distribution of GAD was noticed in striatal regions, highest levels of the enzyme being present in the ventral striatum, followed by the nucleus accumbens and the dorsal striatum. 4. Cholinergic markers choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) were rather uniformly distributed in the frog telencephalon, while, in the turtle, cholinergic markers were several-fold higher in the basal telencephalon, particularly in the striatum, than in the pallium. 5. The turtle dorsal ventricular ridge possessed ChAT levels more similar to the striatal than to the cortical ones. On the contrary, D-3H-aspartate uptake in the dorsal ventricular ridge was close to the highest levels found in cortical areas. 6. The quantitative neurochemical approach adopted for the present study appears to be a useful tool to investigate the problem of homologies and to gain new information on the evolution of neuron populations and neuronal connections in the vertebrate telencephalon.

Acetylcholinesterase↗
PubMed1989

Binding of [3H] muscimol to the retina of rabbit and turtle.

1. We studied the binding of [3H]muscimol to membrane preparations of the retina of rabbit (Lepus cuniculus) and turtle (Pseudemys scripta elegans). 2. In both species, [3H]muscimol binding was maximal at 0 degrees C and decreased with increasing temperature, it was saturable, protein concentration dependent and specific. Muscimol, GABA and bicuculline were the most effective displacers, whereas baclofen and diaminobutyric acid were ineffective. 3. In the turtle retina, Scatchard analysis indicated the presence of a single site with a KD of 20.81 nM, and a Bmax of 3.620 pmol/mg prot. 4. In the rabbit, a single site could be identified in the nanomolar concentration range (KD of 12.8 nM, Bmax of 1.327). A study of the association rate of [3H]muscimol binding revealed a faster kinetics in turtle, as compared to rabbit.

Animals↗
PubMed1990

Beta-endorphin-like and adrenocorticotropin-like materials in turtle heart and intestine.

1. Turtle heart and intestine acetone powders were extracted with an acetone-water-HCl mixture. An acid acetone powder resulted by adding a copious volume of acetone to the extract. The powder was subjected to gel filtration on Sephadex G-25 and ion exchange chromatography on CM-cellulose. 2. In turtle heart, corticotropin-like bioactivity was distributed among chromatographic fractions (derived from material unretarded on Sephadex G-25) unadsorbed and adsorbed on CM-cellulose. The highest opiate receptor binding activity and beta-endorphin-like immunoreactivity were adsorbed on CM-cellulose. 3. In turtle intestine, corticotropin-like bioactivity was absent. Opiate receptor binding activity was present in fractions unretarded as well as in fractions retarded on Sephadex G-25, indicating a molecular weight of greater and smaller than 5000 respectively. 4. The highest opiate receptor binding activity and beta-endorphin-like immunoreactivity were found in a fraction adsorbed on CM-cellulose.

Adrenal Medulla↗
PubMed1990

Comparative studies on the effects of some enkephalin agonists on the ERG of frog and turtle.

1. Effects of mu-agonist morphine in a concentration of 1.10(-5)-1.10(-6) M and delta-agonist Dalargin in a concentration of 1.10(-5)-1.10(-8) M on electroretinogram (ERG) of frog (mixed type of retina) and turtle (predominantly cone retina) were investigated. 2. The enkephalin agonists studied influenced both types of retina in a different manner, producing mainly inhibitory effects. 3. Variability in mu-receptors sensitivity in the turtle retina, most probably depending on the seasons, was observed. 4. The data obtained show that opiate-sensitive mechanisms control the bioelectric activity of the distal layers of frog and turtle retina. 5. Species specificity and variability in sensitivity of the opiate receptors are discussed.

Animals↗
PubMed1988

Polymerization of turtle alpha-macroglobulin through newly exposed sulfhydryls reveals the location of ex-thiolester bonds.

Green turtle alpha-macroglobulin, which has previously been shown to contain thiolester bonds, formed linear polymers after being treated with proteinases. Biochemical analyses showed that the polymerization proceeded through disulfide-bond formation between monomers. The only sulfhydryl groups available for such polymerization after proteinase treatment were those created as the product of thiolester hydrolysis. Electron micrographs of polymers revealed H-shaped monomeric units aligned lengthwise in linear polymers. The average length per monomeric unit in the polymer estimated from the discrete distribution of polymer lengths was approximately 80% of the average length of free monomers, indicating that monomers overlapped each other within a region of about 4 nm. From such observations we concluded that the newly produced sulfhydryl groups were located on the four arms of the H-shaped molecule. The location of sulfhydryls can be taken as the site of the exposure of thiolesters which were originally sequestered in the hydrophobic interior of the molecule. Since the structure of turtle alpha-macroglobulin is very similar to that of human serum alpha 2-macroglobulin the results predict a similar location of sulfhydryls in human alpha 2-macroglobulin after proteinase treatment. The observed polymerization property is unique to sea turtle alpha-macroglobulin and has not been observed with human alpha 2-macroglobulin or other homologous proteins.

Animals↗