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PubMed2001

Broadly tuned spinal neurons for each form of fictive scratching in spinal turtles.

Behavioral choice can be mediated either by a small number of sharply tuned neurons or by large populations of broadly tuned neurons. This issue can be conveniently examined in the turtle spinal cord, which generates each of three forms of scratching-rostral, pocket, and caudal-in response to mechanical stimulation in each of three adjacent regions of the body surface. Previous research showed that many propriospinal neurons are broadly tuned to either the rostral scratch region or the pocket scratch region, but responses to caudal scratch stimulation could not be examined in that reduced preparation. In the current study, individual spinal neurons were recorded extracellularly from the gray matter of the turtle spinal cord hindlimb enlargement, while sites in the rostral, pocket, and caudal scratch regions were mechanically stimulated. Many neurons were broadly tuned to the caudal scratch region; other neurons were broadly tuned to either the pocket scratch or rostral scratch region. All three types were typically found within a single animal. These data are consistent with the hypothesis that the turtle spinal cord relies on large populations of broadly tuned neurons to select each of the three forms of scratching. In addition, neurons that were broadly tuned to each of the scratch regions were typically found in each spinal cord segment and within the same range of mediolateral and dorsoventral locations. Providing that these neurons are related to the selection and generation of the three forms of scratching, this would indicate that cells of this type are not segregated into distinct regions of the spinal cord gray matter.

Animals↗
PubMed2004

Noradrenaline decreases spike voltage threshold and induces electrographic sharp waves in turtle medial cortex in vitro.

The noradrenergic modulation of neuronal properties has been described at different levels of the mammalian brain. Although the anatomical characteristics of the noradrenergic system are well known in reptiles, functional data are scarce. In our study the noradrenergic modulation of cortical electrogenesis in the turtle medial cortex was studied in vitro using a combination of field and intracellular recordings. Turtle EEG consists of a low voltage background interspersed by spontaneous large sharp waves (LSWs). Noradrenaline (NA, 5-40 microM) induced (or enhanced) the generation of LSWs in a dose-dependent manner. Pharmacological experiments suggest the participation of alpha and beta receptors in this effect. In medial cortex neurons NA induced a hyperpolarization of the resting potential and a decrease of input resistance. Both effects were observed also after TTX treatment. Noradrenaline increased the response of the cells to depolarizing pulses, resulting in an upward shift of the frequency/current relation. In most cells the excitability change was mediated by a decrease of the spike voltage threshold resulting in the reduction of the amount of depolarization needed to fire the cell (voltage threshold minus resting potential). As opposed to the mechanisms reported in mammalian neurons, no changes in the frequency adaptation or the post-train afterhyperpolarization were observed. The NA effects at the cellular level were not reproduced by noradrenergic agonists. Age- and species-dependent properties in the pharmacology of adrenergic receptors could be involved in this result. Cellular effects of NA in turtle cortex are similar to those described in mammals, although the increase in cellular excitability seems to be mediated by a different mechanism.

Action Potentials↗
PubMed1988

Planar relations of semicircular canals in awake, resting turtles, Pseudemys scripta.

As part of a project aimed at elucidating mechanisms of vestibulocollic control in the red-eared turtle Pseudemys scripta, we have calculated the planar relations of its semicircular canals using principal-components analysis. This information is prerequisite to understanding the pattern of canal activation that is set up by head movement of any spatial form. In addition, we have developed a method for monitoring canal orientation in an awake, behaving animal, and we have used this technique to assess canal position in resting turtles. Our results indicate that ipsilateral canals in Pseudemys are not mutually orthogonal, nor are complementary canals precisely coplanar, although they approach this idealized condition more closely than do the canals of several other vertebrates for which quantitative data exist. One significant departure from the perfectly orthogonal configuration is that both verical canals are rotated slightly toward the frontal plane; thus, Pseudemys should be somewhat more sensitive to head roll than to head rotation in other planes. Radiographic analyses of awake, resting turtles indicate that the anterior interparietal suture is held aligned with the earth horizontal and midsagittal plane. The horizontal canal is pitched up (open anterior) 3-4 degrees relative to the earth horizontal.

Animals↗
PubMed1987

Distribution of dopamine in the forebrain and midbrain of the red-eared turtle, Pseudemys scripta elegans, reinvestigated using antibodies against dopamine.

The distribution of dopamine (DA) immunoreactivity in the forebrain and midbrain of the red-eared turtle, Pseudemys scripta elegans, was studied using recently developed antibodies against DA. DA-containing cells were found around the glomeruli of the olfactory bulb but not in the telencephalon proper. In the diencephalon DA cells were observed in the preoptic region, several parts of the periventricular hypothalamic nucleus, the periventricular organ, the ependymal wall of the infundibular recess, the lateral hypothalamic area and the pretectal posterodorsal nucleus. In the midbrain DA cells were found in the ventral tegmental area, the substantia nigra and the presumed reptilian homologue of the mammalian A8 cell group. Dopaminergic fibers and terminals were observed throughout the whole brain, particularly in the telencephalon and diencephalon. The olfactory tubercle, the striatum and the nucleus accumbens appear to have the most dense innervation, but the anterior olfactory nucleus and the septal area also show numerous DA fibers and terminals. Cortical areas are in general not densely innervated by DA fibers. Compared to the results obtained for a lizard, Gekko gecko, with the same antibodies, the results of the present study are very similar as regards the distribution of DA neurons, fibers and terminals. In having better developed DA cell groups in the midbrain and a stronger innervation of the striatum, Pseudemys resembles mammals more than does Gekko. In contrast, the many cerebrospinal fluid-contacting DA neurons in the hypothalamus of Pseudemys are a primitive feature of the diencephalon. The previous immunohistochemical study of Gekko, a lizard, and the present account of Pseudemys, a turtle, indicate that at least two different lines of evolution exist within the reptiles with regard to the DA innervation of the dorsal ventricular ridge. One, including turtles and, probably, crocodilians with a weak DA innervation; and another, represented by lizards, with a strong DA immunoreactivity.

Animals↗
PubMedDate not supplied

Omeprazole and SCH 28080 inhibit acid secretion by the turtle urinary bladder.

There is now convincing evidence that in addition to the vacuolar-type H(+)-ATPase, a gastric-type H+/K(+)-ATPase participates in acidification by the distal nephron. To determine whether a similar pump exists in the turtle bladder, we examined the dependence of acid secretion on mucosal K+, and the effects of supposedly specific inhibitors of the gastric H+/K(+)-ATPase, omeprazole and SCH 28080. In CO2-stimulated bladders both drugs produced dose-dependent inhibition of electrogenic H+ secretion measured as the reverse short-circuit current (RSCC). At the highest concentrations tested, H+ secretion decreased 45 +/- 16% with mucosal and 20 +/- 7% with serosal omeprazole (P < 0.01). SCH 28080 at 400 microM produced essentially complete inhibition of H+ secretion with either mucosal or serosal application. When H+ secretion was purposefully inhibited by DIDS or an adverse mucosal pH gradient, SCH 28080 had no effect on RSCC. Removing mucosal K+ (measured K+ < 50 microM), with or without mucosal barium, had no effect on RSCC. The inhibition of RSCC by omeprazole was reversed by mercaptoethanol. Finally, HCO3 secretion, as measured by either RSCC or pH-stat titration, increased significantly in response to 400 microM SCH 28080. The results demonstrate that these compounds inhibit acid secretion by the turtle bladder but stimulate the secretion of base. In view of the total independence of acid secretion on potassium, it is unlikely that any of the bladder's acid secretion is mediated by an H+/K(+)-ATPase. The most reasonable interpretation of the data is that omeprazole and SCH 28080, previously thought to be specific inhibitors of the H+/K(+)-ATPase, also inhibit the vacuolar H(+)-ATPase of the turtle bladder. The results also indicate that HCO3 secretion by the bladder employ a different mechanism of H+ transport than is used for acid secretion; there is no simple reversal of polarity in the acid- versus base-secreting cells.

Animals↗
PubMed2004

Homogeneity and diversity of color-opponent horizontal cells in the turtle retina: Consequences for potential wavelength discrimination.

Color information processing in fish and turtles starts with the transformation of the tetra-chromatic cone system into two types of color-opponent horizontal cells (C-type). Few studies reported on large variability between C-type horizontal cells of the same class, suggesting it might improve color vision. However, such variability is contradictory with the tight coupling between horizontal cells that tends to average intercellular differences. We addressed this apparent discrepancy, and studied the spectral properties of C-type horizontal cells in the turtle retina. Photoresponses were recorded in the eyecup preparation, using light stimuli of different wavelengths and intensities. The spectral properties of each cell were defined by the neutral points (wavelengths at which response polarity reversed), which were derived from sensitivity data and from large-amplitude photoresponses. For each C-type horizontal cell, a linear relationship between log stimulus intensity needed for polarity reversal and wavelength was found. With this definition, homologous C-type horizontal cells from the same retina were practically identical in their spectral properties, indicating that the averaging effects of the horizontal cell syncytium eliminated any intercellular variability. In contrast, C-type horizontal cells of the same class exhibited large inter-retina variability. We tested the potential for wavelength discrimination by applying the line element theory to the action spectra of the two chromatic (Red/Green & Yellow/Blue) horizontal cell channels, and found good agreement with behavioral data from a similar species of turtles.

Animals↗
PubMed1990

Isolation and biological activity of a novel kinin ([Thr6] bradykinin) from the turtle, Pseudemys scripta.

Incubation of plasma from the red-eared turtle with glass beads in the presence of the kininase inhibitor 1,10-phenanthroline resulted in activation of the kallikrein-kinin system and generation of bradykinin-like immunoreactivity. The immunoreactive material comprised a single molecular form that was purified to homogeneity by reverse phase HPLC. The primary structure of the peptide was determined by automated Edman degradation and fast atom bombardment mass spectrometry. The amino acid sequence of the turtle kinin Arg-Pro-Pro-Gly-Phe-Thr-Pro-Phe-Arg contains the substitution Thr for Ser at position 6 compared with mammalian bradykinin. [Thr6] bradykinin was synthesized using solid phase methodology, and bolus injections of the peptide into the left atrium of the anaesthetized turtle produced rapid vasodilation. A dose-dependent increase in blood flow in the left aortic arch was accompanied by a decrease in peripheral vascular resistance, so that systemic blood pressure did not change. The data suggest that the kallikrein-kinin system may play an important physiological role in the regulation of cardiovascular function in reptiles.

Amino Acid Sequence↗
PubMed2003

Metabolic and cardiovascular adjustments of juvenile green turtles to seasonal changes in temperature and photoperiod.

We measured activity levels, oxygen consumption, metabolic enzyme activity, breathing frequency, heart rate and blood chemistry variables of juvenile green turtles exposed to a laboratory simulation of subtropical winter and summer temperatures (17-26 degrees C) and photoperiod (10.25 h:13.75 h to 14 h:10 h light:dark). The activity level of turtles had a significant effect on oxygen consumption and breathing frequency but there was no significant change in activity level between the summer and winter simulations. There was a moderate 24-27% decrease in oxygen consumption during exposure to winter conditions compared with summer conditions, but this difference was not statistically significant. Likewise, there was no statistically significant difference in breathing frequency between summer and winter simulations. Exposure to winter conditions did result in a significant decrease in activity of the aerobic enzyme citrate synthase. By contrast, activities of the glycolytic enzymes pyruvate kinase and lactate dehydrogenase were significantly higher in tissue collected during exposure to winter conditions compared with summer conditions. Citrate synthase, pyruvate kinase and lactate dehydrogenase had relatively low thermal dependence over the range of assay temperatures (15-30 degrees C; Q10=1.44-1.69). Heart rate was 46-48% lower during the winter simulation compared with the summer simulation, and this difference was statistically significant. Exposure to winter conditions resulted in a significant decrease in plasma thyroxine and plasma proteins and a significant increase in plasma creatine phosphokinase and hematocrit. Overall, our results suggest that green turtles have a relatively low thermal dependence of metabolic rate over the range of temperatures commonly experienced at tropical to subtropical latitudes, a trait which allows them to maintain activity year-round.

Animals↗
PubMed2005

Patterns of variation in glycogen, free glucose and lactate in organs of supercooled hatchling painted turtles (Chrysemys picta).

Hatchling painted turtles (Chrysemys picta) typically spend their first winter of life in a shallow, subterranean hibernaculum (the natal nest), where they may be exposed for extended periods to ice and cold. The key to their survival seems to be to avoid freezing and to sustain a state of supercooling. As temperature declines below 0 degrees C, however, the heart of an unfrozen turtle beats progressively slower, the diminished perfusion of peripheral tissues with blood induces a functional hypoxia, and anaerobic glycolysis assumes ever greater importance as a source of ATP. We hypothesized that diminished circulatory function in supercooled turtles also reduces the delivery of metabolic substrates to peripheral tissues from central stores in the liver, so that the tissues depend increasingly on endogenous stores to fuel their metabolism. We discovered in the current investigation that part of the glycogen reserve in hearts and brains of hatchlings is mobilized during the first 10 days of exposure to -6 degrees C but that glucose from hepatic glycogen supports metabolism of the organs thereafter. Hatchlings that were held at -6 degrees C for 10 days and then at +3 degrees C for another 10 days were able to reconstitute some of the reserve of glycogen in heart and liver but not the glycogen reserve in brain. Patterns of accumulation of lactate in individual organs were very similar to those reported for whole animals in a companion study, and point to a high degree of reliance on anaerobic metabolism at -6 degrees C and to a lesser degree of reliance on anaerobiosis at higher subzero temperatures. Lactate had returned to baseline levels in organs of animals that were held for 10 days at -6 degrees C and for another 10 days at +3 degrees C, but free glucose remained elevated. Indeed, carbohydrate metabolism probably does not return to the pre-exposure state in any of the major organs until well after the exposure to subzero temperatures has ended, circulatory sufficiency has been restored, and aerobic respiration has fully supplanted anaerobic respiration as a source of ATP.

Analysis of Variance↗
PubMed2006

Vomeronasal sensory neurons from Sternotherus odoratus (stinkpot/musk turtle) respond to chemosignals via the phospholipase C system.

The mammalian signal transduction apparatus utilized by vomeronasal sensory neurons (VSNs) in the vomeronasal organ (VNO) has been richly explored, while that of reptiles, and in particular, the stinkpot or musk turtle Sternotherus odoratus, is less understood. Given that the turtle's well-known reproductive and mating behaviors are governed by chemical communication, 247 patch-clamp recordings were made from male and female S. odoratus VSNs to study the chemosignal-activated properties as well as the second-messenger system underlying the receptor potential. Of the total neurons tested, 88 (35%) were responsive to at least one of five complex natural chemicals, some of which demonstrated a degree of sexual dimorphism in response selectivity. Most notably, male VSNs responded to male urine with solely outward currents. Ruthenium Red, an IP3 receptor (IP3R) antagonist, failed to block chemosignal-activated currents, while the phospholipase C (PLC) inhibitor, U73122, abolished the chemosignal-activated current within 2 min, implicating the PLC system in the generation of a receptor potential in the VNO of musk turtles. Dialysis of several second messengers or their analogues failed to elicit currents in the whole-cell patch-clamp configuration, negating a direct gating of the transduction channel by cyclic adenosine monophosphate (cAMP), inositol 1,4,5-trisphosphate (IP3), arachidonic acid (AA), or diacylglycerol (DAG). Reversal potential analysis of chemosignal-evoked currents demonstrated that inward currents reversed at -5.7+/-7.8 mV (mean +/- s.e.m.; N=10), while outward currents reversed at -28.2+/-2.4 mV (N=30). Measurements of conductance changes associated with outward currents indicated that the outward current represents a reduction of a steady state inward current by the closure of an ion channel when the VSN is exposed to a chemical stimulus such as male urine. Chemosignal-activated currents were significantly reduced when a peptide mimicking a domain on canonical transient receptor potential 2 (TRPC2), to which type 3 IP3 receptor (IP3R3) binds, was included in the recording pipette. Collectively these data suggest that there are multiple transduction cascades operational in the VSNs of S. odoratus, one of which may be mediated by a non-selective cation conductance that is not gated by IP3 but may be modulated by the interaction of its receptor with the TRPC2 channel.

Action Potentials↗
PubMed1985

Partitioning of body fluids and cardiovascular responses to circulatory hypovolaemia in the turtle, Pseudemys scripta elegans.

Investigations were conducted (1) to measure the steady state compartmentation of body fluids and (2) to assess the efficacy of blood volume and pressure maintenance during haemorrhage-induced hypovolaemia in the pond turtle, Pseudemys scripta elegans. The pre-haemorrhage blood volume, as determined by tracer dilution of 51Cr-labelled erythrocytes, averaged 6.89 +/- 0.33% of the body mass, and was part of comparatively large extracellular (40.2 +/- 0.70%) and total body fluid volumes (75.25 +/- 1.48%). Turtles exhibited progressive reductions in systemic arterial pressure throughout a cumulative haemorrhage of -48% of their original blood volume, despite dramatic increases in heart rate and comparatively large magnitudes of transcapillary fluid transfer from interstitial to intravascular spaces. Arterial blood pressure returned to pre-haemorrhage values 2h after experimental haemorrhage ceased, concomitant with the restoration of the original blood volume. Our results support arguments made in previous studies that the resistance to fluid movement between vascular and extravascular locations in reptiles is comparatively low. Furthermore, the haemodynamic responses of turtles to experimental hypovolaemia suggest that barostasis through adjustments in vascular tone is less effective than that observed in other reptiles.

Animals↗
PubMed1988

Predominance of vagal bradycardia mechanism in the brain stem of turtles.

Cardiovascular parameters of spontaneously breathing pond turtles (Cyclemys flavomarginata) anaesthetized with chloralose (4 mg 100 g-1) and urethane (40 mg 100 g-1), were examined during exploratory electrical stimulation of the brain stem. Turtles exhibited a low mean systemic arterial blood pressure (MSAP, average 25 mmHg) and slow heart rate (average 24 beats min-1). Upon stimulation, pressor (sympathetic), depressor (sympathetic inhibition), bradycardia and hypotensive (vagal) responses were elicited from regions of the brain stem extending from the hypothalamus to the medulla, principally in the medial region. The pressor response appeared after a longer latency than did the bradycardia and hypotensive responses. It developed rather slowly, and rarely attained a magnitude double its resting value. In contrast, stimulation of many points in the brain stem produced marked slowing or even cessation of the heart beat, and thus resulted in an immediate fall of the blood pressure even to zero. This cardio-inhibitory response depended on the integrity of the vagus nerves and was particularly marked upon stimulation in the caudal medulla, the areas of the ambiguus, solitary and dorsomotor nuclei of the vagus and the midline structures. When such an area was stimulated continuously the heart stopped beating throughout the stimulation. The longest period of cardiac arrest before the appearance of escape was 35 min. With continuous stimulation of the peripheral end of the cut vagus, the earliest escape beat occurred even later (65 min). Epinephrine given intravenously produced an increase of MSAP and force of cardiac contraction, although the slope of pressor rise was shallow. Reflex bradycardia, however, was not observed. These experiments show that a very prominent vagal bradycardia can be evoked from the turtle brain stem, which may contribute to its well-known capacity for tolerating anoxia.

Animals↗
PubMed1989

Control of metabolism and growth in embryonic turtles: a test of the urea hypothesis.

We performed two experiments to determine (1) whether the metabolism and growth of embryonic snapping turtles (Chelydra serpentina) incubating in wet and dry environments are correlated inversely with the concentration of urea inside their eggs, and (2) whether urea accumulating inside eggs might be the cause of reductions in metabolism and growth by embryos. Eggs in the first experiment were incubated in different hydric environments to induce different patterns of net water exchange between the eggs and their surroundings. Turtles hatching from eggs that were in positive water balance had larger carcasses, smaller residual yolks and lower concentrations of urea in their blood than animals emerging from eggs that were in negative water balance. Thus, we confirmed the existence of correlations among water exchange by eggs, concentrations of urea in fluid compartments inside eggs, and metabolism and growth of embryos. In the second experiment, eggs were injected with solutions of urea at the mid-point of incubation to induce different levels of uremia in developing embryos. The injection protocol induced variation in the concentration of urea in blood of hatchlings similar to that observed in the first experiment for turtles hatching in wet and dry environments. However, the injection protocol did not induce variation in size of hatchlings or in mass of their residual yolk. Thus, the reduction in metabolism and growth of chelonian embryos developing in dry environments does not result from an inhibition of intermediary metabolism caused by urea, and the 'urea hypothesis' for control of metabolism cannot be accepted in its present form.

Animals↗
PubMed1992

Responses to freezing exposure of hatchling turtles Trachemys scripta elegans: factors influencing the development of freeze tolerance by reptiles.

Hatchling red-eared turtles Trachemys (= Pseudemys) scripta elegans (Wied) from a Louisiana population display a significant ability to withstand the freezing of extracellular body fluids. All animals survived at least 2 h of freezing at -2.5 or -4 degrees C. At -2.5 degrees C, survival declined to 50% after 6 h of freezing and no animals recovered after 24 h or longer, when mean ice content reached 54.7 +/- 1.4% of total body water. At -4 degrees C, all turtles recovered from 4 h of freezing exposure with a mean ice content of 49.6 +/- 2.4%, but survival dropped sharply thereafter with no animals recovering after 8 h, when ice content had reached 64.5 +/- 0.7%. Survival times were substantially shorter and percentage ice values greater than comparable values for hatchling painted turtles (Chrysemys picta (Schneider)) from northern populations subjected to identical freezing exposures. The ability to synthesize cryoprotectants in response to freezing was poorly developed in T. s. elegans; maximal accumulation of glucose was only 3.2 mumol g-1 wet mass in liver. Lactate content increased two- to threefold in oxygen-sensitive organs (heart and brain) during freezing, but levels of lactate and other putative cryoprotectants were unchanged in other organs. Total free amino acid content rose significantly in liver, muscle and blood during freezing; increased taurine concentration was primarily responsible for the changes in liver and blood. The capacity for freezing survival by T. s. elegans hatchlings from southern populations would be of limited use for hibernation in a cold climate, but the metabolic responses to freezing displayed by these animals might be enhanced by northern populations to increase their freeze tolerance.

Acclimatization↗
PubMed1996

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 synchrony in free-diving and fully recovered turtles (Trachemys scripta). During breath-holds lasting longer than 5 min, Qpul averaged 15 ml min-1 kg-1 and increased more than threefold to a maximum value of 50 ml min-1 kg-1 during ventilation. Qsys also increased during ventilation compared with during breath-holds lasting longer than 5 min (from 44 to 73 ml min-1 kg-1 during ventilation). Neither Qpul nor Qsys was affected by the number of breaths in the ventilatory periods. Changes in Qpul and Qsys were accomplished entirely through a significant increase in heart rate during ventilation, while total stroke volume (systemic+pulmonary) remained constant. Irrespective of the ventilatory state, Qsys exceeded Qpul by 20-30 ml min-1 kg-1. Nevertheless, because Qpul increased relatively more than Qsys during ventilation, Qpul/Qsys increased from 0.29 during apnoea to 0.80 during lung ventilation. This study confirms cardiorespiratory synchrony in the turtle Trachemys scripta but, in contrast to earlier studies, a net right-to-left cardiac shunt prevailed regardless of ventilatory state.

Animals↗
PubMed1997

Effects of anoxia, acidosis and temperature on the contractile properties of turtle cardiac muscle strips.

The responses to anoxia and acidosis of cardiac ventricular muscle strips from the anoxia-tolerant turtle Chrysemys picta bellii were investigated at 10 degrees C and 20 degrees C. Force-velocity curves were determined by quick isotonic releases at 85% of the time to peak isometric force under control, anoxia, lactate acidosis and anoxic lactate acidosis conditions. The isotonic forces during quick releases spanned 5-95% of the measured isometric force at each conditions. Superfusion solution pH was 7.8 and 7.95 for non-acidosis experiments, and 7.0 and 7.15 for acidosis experiments, at 20 degrees C and 10 degrees C, respectively. After normalizing force data to control isometric force, the values of maximum isometric force (P0), maximum velocity of shortening (Vmax) and maximal power output (Powermax) were evaluated by fitting the curves using the hyperbolic Hill equation. The maximum rate of force development (dF/dtmax), time-to-peak force (TPF) and half-relaxation time (T1/2) were also determined. At 20 degrees C, during acidosis, anoxia and anoxic acidosis, P0 decreased significantly to 81%, 40% and 24% of control values, dF/dtmax decreased significantly to 67%, 53% and 23% of control values, and Powermax decreased significantly to 75%, 40% and 14% of control values, respectively. Vmax, however, was not significantly affected by acidosis, anoxia or even anoxia acidosis. TPF was significantly shortened by anoxia, but prolonged by acidosis. The effects were similar at 10 degrees C, Temperature did not affect P0, but Vmax decreased by a factor of 1.6-1.8 at all corresponding conditions when temperature was reduced from 20 degrees C to 10 degrees C. We conclude that acidosis and anoxia inhibit isometric force production and Powermax of turtle cardiac muscle, but have no effect on Vmax, and the insensitivity of Vmax indicates that the rate of cross-bridge cycling is not affected by these conditions. Our observations indicate that the reduced power outputs of the hearts of submerged anoxic turtles at low temperature are due in part to inhibition of force production by anoxia and acidosis, and to a reduction of contraction velocity at low temperature.

Acidosis, Lactic↗
PubMed1997

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 PSRs in the regulation of central vascular blood flows, we examined the effect of manipulating lung volume (and therefore PSR stimulation) on blood flows and heart rate in the freshwater turtle Trachemys scripta. Turtles were instrumented with blood flow probes on the left aortic arch and the left pulmonary artery for measurements of blood flow, and catheters were inserted into both lungs for manipulation of lung volume. In both anaesthetized and fully recovered animals, reductions or increases in lung volume by withdrawal of lung gas or injection of air, N2, O2 or 10% CO2 (in room air) had no effect on blood flows. Furthermore, simulations of normal breathing bouts by withdrawal and injection of lung gas did not alter Qpul or fH. We conclude that stimulation of PSRs is not sufficient to elicit cardiovascular changes and that the large increase in Qpul and fH normally observed during spontaneous ventilation are probably caused by a simultaneous feedforward control of central origin.

Animals↗
PubMed2000

Seasonal changes in physiology and development of cold hardiness in the hatchling painted turtle Chrysemys picta.

Hatchling painted turtles (Chrysemys picta) commonly hibernate in shallow, natal nests where winter temperatures may fall below -10 degrees C. Although hatchlings are moderately freeze-tolerant, they apparently rely on supercooling to survive exposure to severe cold. We investigated seasonal changes in physiology and in the development of supercooling capacity and resistance to inoculative freezing in hatchling Chrysemys picta exposed in the laboratory to temperatures that decreased from 22 to 4 degrees C over a 5.5 month period. For comparison, we also studied hatchling snapping turtles (Chelydra serpentina), a less cold-hardy species that usually overwinters under water. Although Chrysemys picta and Chelydra serpentina differed in some physiological responses, both species lost dry mass, catabolized lipid and tended to gain body water during the acclimation regimen. Recently hatched, 22 degrees C-acclimated Chrysemys picta supercooled only modestly (mean temperature of crystallization -6.3+/-0.2 degrees C; N=6) and were susceptible to inoculation by ice nuclei in a frozen substratum (mean temperature of crystallization -1.1+/-0.1 degrees C; N=6) (means +/- s.e.m.). In contrast, cold-acclimated turtles exhibited pronounced capacities for supercooling and resistance to inoculative freezing. The development of cold hardiness reflected the elimination or deactivation of potent endogenous ice nuclei and an elevation of blood osmolality that was due primarily to the retention of urea, but was not associated with accumulation of the polyols, sugars or amino acids commonly found in the cryoprotection systems of other animals. Also, Chrysemys picta (and Chelydra serpentina) lacked both antifreeze proteins and ice-nucleating proteins, which are used by some animals to promote supercooling and to initiate freezing at the high temperatures conducive to freezing survival, respectively.

Acclimatization↗