Pseudemys Scripta Elegans Research Articles

Oxygen transfer kinetics of red blood cells of the turtle Pseudemys scripta elegans

The kinetics of O 2 uptake into, and release from, the red blood cells (RBC) of the turtle Pseudemys scripta elegans were determined with a stopped-flow technique at varied temperature (10–30°C) and pH (7.5–7.9). The results were compared to those obtained for RBC of other vertebrates and related to morphometric and physiological data on gas/blood diffusion in turtle lungs. The O 2 transfer conductance of RBC, G, for O 2 release into high concentrations of dithionite, considered to represent the best estimate of true RBC transfer conductance for O 2 uptake and release, averaged 0.17 ± 0.01 at 30°C, 0.13 ± 0.01 at 20°C, 0.09 ± 0.01 at 10°C (mean ± SSD, in mmol·min −1·Torr −1·(mlRBC) −1). These values are about one half the corresponding value for human RBC, and this difference may be due to the larger size of turtle RBC (volume, 327 μm 3) compared to human RBC (90μm 3). The temperature dependence of G, Q 10 = 1.3 indicates that, as in human RBC, diffusion through aqueous media is the main limiting factor for O 2 exchange. Morphometric data on the lungs of Pseudemys scripta suggest that the resistance to O 2 transfer by RBC is lower than that offered by the gas-blood barrier. The total apparent transfer resistance to CO, obtained from previous measurements of pulmonary diffusing capacity for CO in the same species, is much higher than that predicted from the combination of RBC O 2 kinetics and morphometric data on gas-blood barrier.

Excretion and metabolism of a series of xanthines by the turtle Pseudemys scripta elegans.

The xanthines paraxanthine, xanthine, and uric acid are absorbed completely by the turtle Pseudemys scripta elegans and metabolised presumably into CO2 and NH3. No intermediate metabolites are excreted. Caffeine, hydroxycaffein, theobromine, hydroxytheobromine, and hydroxypraxanthine are absorbed and excreted in different amounts or percentages of the dose administered. Intermediate metabolites of these compounds are not excreted. The turtle Pseudemys scripta elegans may, therefore, be ammonotelic.

Diving increases atrial natriuretic factor-like peptide in freshwater diving turtles

1. 1. Prolonged anoxic dives in the freshwater turtle, Pseudemys scripta elegans, are associated with increased serum osmolality and a decreased serum chloride, suggesting a diuresis that might be secondary to the newly described diuresis-producing hormone, atrial natriuretic factor (ANF). 2. 2. An ANF-like peptide was found to circulate in nearly equal concentrations in male [48 ± 3 (SD) pg/'ml] and female (46 ± 4 pg/ ml) turtles. 3. 3. In six turtles that remained submerged for 1 hr there was a four-fold increase in the circulating plasma concentration of ANF (i.e.205 ± 16 pg/ml). 4. 4. In turtles exposed to 100% N 2 for 1 hr, ANF concentration increased to 76.4 pg/ml indicating that only a small part of the ANF increase with diving is explained by hypoxia.

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°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 K D of 20.81 nM, and a B max of 3.620 pmol/mg prot. 4. In the rabbit, a single site could be identified in the nanomolar concentration range ( K D of 12.8 nM, B max of 1.327). A study of the association rate of [ 3H]muscimol binding revealed a faster kinetics in turtle, as compared to rabbit.

Permeability of the urinary bladder of the turtle, Pseudemys scripta elegans, to ammonia

1. 1. The permeability of the isolated turtle urinary bladder to ammonia was investigated by varying the ratio of NH 3 to HN + 4 concentration in the serosal bath and measuring the flux of ammonia into the mucosal bath. 2. 2. The permeability of the turtle bladder to NH 3 was in the range of 5.4–6.1 × 10 −3cm/sec and the permeability of the unstirred layer to NH + 4 was in the range of 1.1–2.1 × 10 −5 cm/sec. 3. 3. The flux of ammonia calculated from the permeability of NH 3 can account for the decrease in mucosal H + secretion observed with addition of NH 4Cl to the serosal bath.

Prolonged depolarization in turtle cones evoked by current injection and stimulation of the receptive field surround.

1. Responses evoked by stimulation of the receptive field surround were recorded intracellularly from cone photoreceptors in the retina of the turtle (Pseudemys scripta elegans). 2. A distinctive depolarizing response was evoked by flashing an annulus of light while steadily illuminating the centre of the receptive field. The response, here called 'the prolonged depolarization', was found in 67% of a sample of 125 cones and could reach some 20 mV in amplitude. 3. The prolonged depolarization is characterized by a set of properties which include: the capacity to persist up to 17 s after the flash, a stereotypical waveform, a long period of temporal facilitation, a very narrow dynamic range, and a long refractory period (30-45 s). 4. Depolarizing current pulses (0.01-0.1 nA) evoke a prolonged depolarization which is similar to and functionally interchangeable with that evoked by light. The prolonged depolarization is thus apparently generated by a voltage-sensitive mechanism intrinsic to the cone. 5. Brief depolarizing spikes were recorded in a small fraction of cones. The spikes appear to be dissociable from the prolonged depolarization although both might arise for similar regenerative mechanisms. 6. The prolonged depolarization is typically preceded by a graded, stimulus-locked depolarization which can also be recorded in isolation by flashing annuli of low intensity. The graded depolarization is probably a manifestation of the depolarizing influence arising from synaptic feed-back from horizontal cells first described by Baylor, Fuortes & O'Bryan (1971). 7. It is suggested that the graded depolarization triggers the prolonged depolarization and that complex responses arise from the interaction of these disparate components.

Bipolar cells in the turtle retina are strongly immunoreactive for glutamate.

Strong glutamate immunoreactivity was observed by both light and electron microscopy in bipolar cells of the turtle (Pseudemys scripta elegans) retina after postembedding immunohistochemistry. Virtually all bipolar cells showed strong labeling, on average 18 times that of the Müller (glial) cells. The data suggest that both on- and off-center bipolar cells are glutamatergic. Photoreceptors were also labeled, but with a labeling intensity about half that of the bipolar cells. Other types of retinal neurons showed less immunoreactivity, except for a small population of strongly labeled amacrine cells.

N-oxidation, N-demethylation, and excretion of pefloxacin by the turtle Pseudemys scripta elegans.

Pefloxacin is minimally absorbed by the gastrointestinal tract of the turtle Pseudemys scripta elegans and then N-oxidised and N-demethylated. Pefloxacin is excreted within one hour after being given orally to the turtles.

Mesencephalic innervation of the turtle retina by a single serotonin-containing neuron

Co-localization of retrograde transported Nuclear yellow and serotonin immunoreactivity revealed the existence of a central serotonergic projection to the retina in the turtle Pseudemys scripta elegans. This serotonergic retinopetal system consists of only one fiber originating in the contralateral caudal mesencephalon. In the retina, the fiber arborizes exclusively in the temporal hemisphere, covering about one third of the total retinal surface. Interestingly this projecting area lies in the part of the retina, to which binocular perception can be attributed.

Thyroid hormones act at the level of the pituitary to regulate thyrotropin and growth hormone secretion in hatchling slider turtles (Pseudemys scripta elegans)

AbstractPituitaries from hatchling turtles (Pseudemys scripta elegans) were incubated with different doses of L‐thyroxine (T4: 1–500 ng/ml) or 3,5,3′‐triiodothyronine (T3: 1–50 ng/ml) for various times (1–48 hr) to assess their effects on basal thyrotropin (TSH) and growth hormone (GH) secretion and responsiveness to thyrotropin‐releasing hormone (TRH: 10 ng/ml). Pretreatment with a pharmacological dose of T4 (500 ng/ml) for 1 hr inhibited the TSH response to TRH, and physiological doses were effective after slightly longer times. The TRH effect was reduced by exposure to 50 ng/ml T4 for 1 hr, and abolished after 4 hr. Pretreatment with 50 ng/ml T4 or T3 for 6 hr did not affect basal TSH secretion, but the attenuation of the TRH response persisted for at least 20 hr after removal of thyroid hormones. Longer exposure (16 hr) to 50 ng/ml T4 or T3 reduced both TSH basal secretion and the response to TRH. A low dose (1 ng/ml) of T4 or T3 for the same amount of time had no effect on basal TSH secretion and only slightly reduced the TRH response; T3 was more potent than T4. Basal secretion and TRH responses of glands pretreated with 5 ng/ml T4 were not different from controls after 4 and 6 hr, but were significantly reduced after 24 hr of exposure; 15 ng/ml T4 reduced the TRH response after 6 hr, but basal secretion was not affected until 24 hr. Treatment with 2 ng/ml T4 for 48 hr reduced the response to TRH but did not affect the baseline. Basal and TRH‐stimulated GH secretion was also inhibited by thyroid hormones, but the onset of these effects were delayed (16 to 24 hr after exposure) and required a relatively high dose (50 ng/ml).These data are consistent with an earlier report from this laboratory (Denver and Licht: J. Exp. Zool. [in press], '88) that in vivo treatment with thyroid hormone or a goitrogen alters in vitro pituitary hormone secretion in turtles and provide evidence for a direct action of thyroid hormones at the level of the pituitary.

Organization of the inner plexiform layer of the turtle retina: an electron microscopic study.

We have performed a serial-section electron microscopic study of the inner plexiform layer (IPL) of the retina of the turtle Pseudemys scripta elegans. A qualitative and quantitative assessment of the neuropil of the IPL has been done from photomontages taken from the linear visual streak area and peripheral retina. Counts of conventional, ribbon, serial, and reciprocal synapses, of ganglion cell dendrites, and of profiles containing large, dense-cored vesicles were made in five equal-thickness strata in each montage. Averages of these different features were plotted for each stratum in the linear visual streak and compared with peripheral retina. The trend was for stratum 2 to have the highest overall absolute number of amacrine and bipolar interactions, and also of serial synapses, both in the linear visual streak and in peripheral regions. Stratum 4 tended to have the second-highest number of synapses. The total number of synapses for the entire thickness of the IPL, regardless of stratification, is higher in the streak than in the periphery. The total amacrine-to-bipolar-synapse ratio in the IPL is the highest of any vertebrate studied to date (11.0 in the streak and 14.5 in the periphery) but the number of synapses/micron 2 was found to be similar to that reported for other vertebrates. Amacrine-to-amacrine synaptic contacts greatly outnumber other types of synapses; amacrines constitute the principal input to ganglion cells, whereas bipolar output is mainly onto amacrines. The trend for higher numbers of synaptic interactions in strata 2 and 4 of the streak region of the turtle IPL can be correlated with the branching of small-field amacrine and ganglion cells described in Golgi studies (Kolb: Philos. Trans. R. Soc. Lond. B 298:355-393, '82). In peripheral retina, branching of large-field amacrines and a lower number of bipolar pathways may account for the trend for larger numbers of amacrine synapses in strata 2 and 4. Profiles having large, dense-cored vesicles tend to occur most frequently in strata 1 and 5, which correlates well with the stratification in the IPL of the processes of immunoreactive amacrine cells described in other studies.

Thyroid status influences in vitro thyrotropin and growth hormone responses to thyrotropin‐releasing hormone by pituitary glands of hatchling slider turtles (Pseudemys scripta elegans)

AbstractThe effects of thyroidal feedback on thyrotropin (TSH), growth hormone (GH) and prolactin (PRL) secretion by pituitary glands, and on TSH responsiveness of thyroids in hatchling turtles, Pseudemys scripta elegans, were investigated by in vitro techniques. Pituitaries were stimulated in culture with 0, 1, 10, or 100 ng/ml thyrotropin‐releasing hormone (TRH) at intervals up to 36 hr; hormones were estimated by RIA. TSH release was elevated by all doses of TRH during the first 2 hr of stimulation (1.8 to 3.6‐fold) and secretion rates increased further during the following 4 hr, with a dose response between 1 and 10 ng/ml TRH. TSH release then returned to initial basal levels and showed the same response to TRH on the second day. GH secretion was also elevated by all doses of TRH tested. A progressive increase in basal GH secretion over time in vitro suggested that GH might normally be under inhibitory control. Medium concentrations of PRL were nondetectable at all times and thus were not measured in subsequent experiments. In vitro thyroxine (T4) secretion by thyroids from these same turtles showed a dose response when stimulated with 5–20 ng/ml purified sea turtle TSH for 8 or 20 hr.Treatment of turtles in vivo with 0.5 μg T4 at 2 hr or daily for up to 2 wk prior to sacrifice greatly reduced in vitro basal TSH secretion and the response to 10 ng/ml TRH. In contrast, several of the T4treatments significantly elevated basal GH secretion. Plasma TSH was markedly elevated after 4 wk treatment with a goitrogen, methimazole, and this was accompanied by increased basal TSH secretion and responsiveness to TRH by pituitaries in vitro; basal GH secretion was reduced but the response of GH to TRH was unaffected. The response of in vitro thyroidal T4 output to TSH was augmented in hyperthyroid animals (⩾ 1 wk T4) and was abolished by methimazole treatment. These data demonstrate a clear thyroidal feedback in the regulation of chelonian TSH secretion and are consistent with an involvement of TRH in the control of pituitary TSH and GH. While the site(s) of the inhibitory actions of T4 are unknown, changes in the functional properties of the pituitary thyrotropes are involved; the somatotropes appear to be less dependent on T4.

Neuropeptide Y-immunoreactive amacrine cells in the retina of the turtle Pseudemys scripta elegans.

Antiserum directed against neuropeptide Y selectively labeled certain amacrine cells in the turtle retina. The cell types, sizes, dendritic stratification, regional distribution, and degrees of immunolabeling were examined. The results indicated that three morphologically distinct cell types were labeled: types A, B, and C. Computer rotation of digitized data from camera lucida drawings was used to study dendritic stratification. The type A somata were large (11.5 micron in diameter), well-stained, and located in the third tier of the inner nuclear layer. Type A somata gave rise to well-stained processes which arborized within the inner plexiform layer in strata 1 and 3 and at the border between strata 4 and 5. Processes in stratum 1 were sparse and delicate with small boutons. Processes in stratum 3 were numerous and often coarse, with many large and small boutons. At the border between strata 4 and 5 the processes were frequently numerous but slender, with many small boutons. Occasional immunolabeled processes were found in the ganglion cell layer. The somata of the type B cells were smaller (9.0 micron in diameter) and gave rise to single labeled processes which descended into the inner plexiform layer and divided quickly into two secondary processes. These secondary processes gave rise to lightly labeled dendritic fields which arborized primarily in strata 2 and 4. The type C cells were usually observed at the periphery of the retina and had large somata (12.0 micron in diameter) with simple, but very elongated, dendritic arborizations in strata 1, 4, and 5. Observations also showed that type A and B cells were often found in close proximity to each other and suggested that dendrites of these cells made contact with each other. The labeled neurons were distributed relatively evenly throughout the retina except for the visual streak where they were sparse. This study indicates that neuropeptide Y-like immunoreactivity is found in more than one anatomically distinct class of amacrine cells in the turtle retina.

The vascularization of the choroid plexus of the lateral ventricle of the turtle Pseudemys scripta elegans (Reptilia)

The vascularization of the choroid plexus of the lateral ventricle of the turtle (Pseudemys scripta elegans) has been studied by means of vascular corrosion casts and transmission electron microscopy (TEM). A single arterial supply via the choroidal artery and a two‐fold venous drainage was found. By its form the plexus was subdivided into two parts: the body, and numerous villi projecting out of the body. The body consists of large convoluted arteries and veins which are covered by a network of vessels always greater than 15 μm in diameter. The villi are composed of a head consisting of vessels with a diameter of 16–50 μm and a stalk represented by one arteriole and one or two veins, which unite at the base of the stalk. An arteriovenous shunt occurs occasionally at the base of the stalk. By their angioarchitecture, six types of villi can be discerned: simple, club‐shaped, flat, wrinkled, glomus‐like and basket‐like villi. Garland vessels were present around arteries only. In ultrathin sections the vessels of the head of a villus possess a thin endothelium with tentacle‐like flaps which protrude into the lumen and many pinocytotic vesicles. These vessels were surrounded by a very fragmentary basement membrane and a dense layer of collagen fibrils.It is suggested that the different areas in the plexus, i.e. the various villi and the body, represent areas with different physiological functions

Hydroxylation and oxidation of nalidixic acid in the turtle Pseudemys scripta elegans.

The turtle Pseudemys scripta elegans hydroxylates nalidixic acid into 7-hydroxynalidixic acid; this latter metabolite is oxidised into 7-carboxynalidixic acid. The elimination half-life of nalidixic acid in the turtle is 30 h. No glucuronides of nalidixic- and 7-hydroxynalidixic acid are formed, as they are in man.

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 IgG 1), 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 M r ~ 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.

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.

Ganglion cells in the turtle retina contain the neuropeptide LANT-6

This study investigated the presence of the neurotensin-related hexapeptide, LANT-6, in retinal ganglion cells and their central projections in the turtle Pseudemys scripta elegans. Immunocytochemical techniques demonstrated that many of the cells in the ganglion cell layer of the turtle retina could be labeled with an antiserum specific for LANT-6. Radioimmunoassay and chromatographic analysis confirmed the presence of LANT-6-related peptides in retina, as well as brain. Several molecular forms of LANT-6 were observed, some larger than LANT-6. Characterization of the cells labeled in the ganglion cell layer in terms of their cell body size and their dendritic arborization patterns revealed that at least 6 specific LANT-6-positive cell types were present in the ganglion cell layer. Morphologically, the LANT-6-positive cells strongly resembled turtle ganglion cells, as previously described. In addition, two other lines of evidence supported this interpretation. First, double-label studies were performed in which retinal ganglion cells projecting to the tectum were retrogradely labeled by HRP injected into the tectum (using a cobalt chloride color-modified DAB reaction product) and immunocytochemically labeled with DAB using the antiserum against LANT-6. These double-label studies revealed that many of the LANT-6-positive cells in the ganglion cell layer in the portion of the retina labeled retrogradely by the HRP injection did project to the tectum. Within the retrogradely labeled portion of the retina, LANT-6-positive cells that were not labeled retrogradely, as well as neurons labeled retrogradely that did not contain LANT-6 were also observed. Second, the central projections of LANT-6-positive cells of the ganglion cell layer were examined by studying the effects of monocular enucleation on the distribution of LANT-6-positive fibers in the central projection targets of the turtle retina. Two to 8 weeks after enucleation, a substantial reduction in LANT-6-positive fibers was observed in all retinal target areas contralateral to the enucleated eye. Radioimmunoassay and chromatographic studies confirmed the presence of LANT-6-related peptides in the turtle brain and corroborated the reduction of LANT-6 observed in the contralateral tectum following monocular enucleation. Previous studies have demonstrated that LANT-6-related material is present in cells of the ganglion cell layer in a variety of vertebrates. The present results indicate that LANT-6 is in ganglion cells and that it may play a role in neurotransmission between retinal ganglion cells and their central target areas.

Distribution and morphology of dopaminergic amacrine cells in the retina of the turtle (Pseudemys scripta elegans).

A light microscopical study of the cell types that stain by immunohistochemistry for the synthesizing enzyme for dopamine, tyrosine hydroxylase, has been performed on the retina of the turtle Pseudemys scripta elegans. The immunostain can be localized to a single morphological type of amacrine cell. The cells are like A28 cells of a Golgi classification. They have medium sized dendritic fields that range in diameter from 200 to 700 micron with eccentricity from the visual streak. The amacrines have a tri-stratified dendritic tree with tiers of fine, curved dendrites ramifying in strata S1, lower S2 and the S4/5 border of the inner plexiform layer. We, like others, can find no good evidence that these cells are interplexiform cells. The dopaminergic amacrine cells have a low frequency (approximately 1300-1500 total cells in 130 mm2 retina), with their highest density occurring in the visual streak (60 cells per mm2). The density profiles fall in elliptical isodensity rings from the visual streak towards the peripheral retina. At all points on the retina the dendritic fields maintain a constant coverage factor independent of eccentricity. A comparison of the dopaminergic amacrine cells in the turtle and other vertebrate retinae is made.

Acetylation, deacetylation and hydroxylation of sulphamethoxazole and N4-acetylsulphamethoxazole in the turtle Pseudemys scripta elegans.

The turtle Pseudemys scripta elegans is able to hydroxylate and acetylate Sulphamethoxazole in a way that is comparable to man, i.e. the rate and yield of hydroxylation equals that of the acetylation. The hydroxy metabolites 5-hydroxy- and N4-acetyl-5-hydroxysulphamethoxazole are not glucuronidated. N4-acetylsulphamethoxazole is neither deacetylated nor hydroxylated.