The diving behaviour of green turtles undertaking oceanic migration to and from Ascension Island: dive durations, dive profiles and depth distribution.
(57/445)
Satellite telemetry was used to record the submergence duration of green turtles (Chelonia mydas) as they migrated from Ascension Island to Brazil (N=12 individuals) while time/depth recorders (TDRs) were used to examine the depth distribution and dive profiles of individuals returning to Ascension Island to nest after experimental displacement (N=5 individuals). Satellite telemetry revealed that most submergences were short (<5 min) but that some submergences were longer (>20 min), particularly at night. TDRs revealed that much of the time was spent conducting short (2-4 min), shallow (approximately 0.9-1.5 m) dives, consistent with predictions for optimisation of near-surface travelling, while long (typically 20-30 min), deep (typically 10-20 m) dives had a distinctive profile found in other marine reptiles. These results suggest that green turtles crossing the Atlantic do not behave invariantly, but instead alternate between periods of travelling just beneath the surface and diving deeper. These deep dives may have evolved to reduce silhouetting against the surface, which would make turtles more susceptible to visual predators such as large sharks. (+info)
The archaeogastropod mollusc Haliotis iris: tissue and blood metabolites and allosteric regulation of haemocyanin function.
(58/445)
We investigated divalent cation and anaerobic end-product concentrations and the interactive effects of these substances and pH on haemocyanin oxygen-binding (Hc-O(2)) in the New Zealand abalone Haliotis iris. During 24 h of environmental hypoxia (emersion), D-lactate and tauropine accumulated in the foot and shell adductor muscles and in the haemolymph of the aorta, the pedal sinus and adductor muscle lacunae, whereas L-lactate was not detected. Intramuscular and haemolymph D-lactate concentrations were similar, but tauropine accumulated to much higher levels in muscle tissues. Repeated disturbance and short-term exposure to air over 3 h induced no accumulation of D- or L-lactate and no change in [Ca(2+)], [Mg(2+)], pH and O(2)-binding properties of the native haemolymph. The haemolymph showed a low Hc-O(2) affinity, a large reverse Bohr effect and marked cooperativity. Dialysis increased Hc-O(2) affinity, obliterated cooperativity and decreased the pH-sensitivity of O(2) binding. Replacing Mg(2+) and Ca(2+) restored the native O(2)-binding properties and the reverse Bohr shift. L- and D-lactate exerted minor modulatory effects on O(2)-affinity. At in vivo concentrations of Mg(2+) and Ca(2+), the cooperativity is dependent largely on Mg(2+), which modulates the O(2) association equilibrium constants of both the high-affinity (K(R)) and the low-affinity (K(T)) states (increasing and decreasing, respectively). This allosteric mechanism contrasts with that encountered in other haemocyanins and haemoglobins. The functional properties of H. iris haemocyanin suggest that high rates of O(2) delivery to the tissues are not a priority but are consistent with the provision of a large O(2) reserve for facultatively anaerobic tissues during internal hypoxia associated with clamping to the substratum. (+info)
Corrosion behavior of pure titanium and titanium alloys in fluoride-containing solutions.
(59/445)
The effects of fluoride concentrations and pH on the corrosion behavior of pure titanium, Ti-6Al-4V, Ti-6Al-7Nb alloys and a new Ti alloy adding palladium, which is expected to promote a repassivation of Ti were examined by anodic polarization and corrosion potential measurements. The amount of dissolved Ti was analyzed by inductively coupled plasma mass spectroscopy. The surface of the specimen was analyzed by X-ray photoelectron spectroscopy before and after the measurement. Pure Ti, Ti-6Al-4V and Ti-6Al-7Nb alloys were easily corroded even in a low fluoride concentration in an acidic environment. The corrosion resistance of Ti-0.2Pd alloy was greater than those of pure Ti, Ti-6Al-4V and Ti-6Al-7Nb alloys in the wide range of pH and fluoride concentrations. The high corrosion resistance of Ti-0.2Pd alloy was caused by the surface enrichment of Pd promoting a repassivation of Ti. The Ti-0.2Pd alloy is expected to be useful as a new Ti alloy with high corrosion resistance in dental use. (+info)
Change in the bisphenol A content in a polycarbonate orthodontic bracket and its leaching characteristics in water.
(60/445)
The change in the bisphenol A (BPA) content in a polycarbonate (PC) orthodontic bracket and its leaching characteristics were studied by immersing the bracket in water because BPA has been the matter of controversy in dentistry due to its estrogenic potential. PC brackets were placed in water at 37 degrees C and 60 degrees C and the BPA content in the bracket and the amount of BPA released into the water were analyzed at appropriate intervals by high performance liquid chromatography. The BPA content increased in the water with time and was 3.8-fold after 12 months at 37 degrees C and 12.4-fold after 14 weeks at 60 degrees C compared with the virgin value. The rate of BPA release also increased with time. The results suggested that BPA was released from the bracket time-dependently in the oral cavity. However, it was assessed that little or no estrogenic effect due to the released BPA is expected in the human body. (+info)
Two different mechanisms underlie reversible, intrinsic optical signals in rat hippocampal slices.
(61/445)
Intrinsic optical signals (IOSs) induced by synaptic stimulation and moderate hypotonic swelling in brain tissue slices consist of reduced light scattering and are usually attributed to cell swelling. During spreading depression (SD), however, light-scattering increases even though SD has been shown to cause strong cell swelling. To understand this phenomenon, we recorded extracellular voltage, light transmission (LT), which is inversely related to light scattering, and interstitial volume (ISV) simultaneously from the same site (stratum radiatum of CA1) in both interface and submerged hippocampal slices. As expected, moderate lowering of bath osmolarity caused concentration-dependent shrinkage of ISV and increase in LT, while increased osmolarity induced opposite changes in both variables. During severe hypotonia, however, after an initial increase of LT, the direction of the IOS reversed to a progressive decrease in spite of continuing ISV shrinkage. SD caused by hypotonia, by microinjection of high-K(+) solution, or by hypoxia, was associated with a pronounced LT decrease, during which ISV shrinkage indicated maximal cell swelling. If most of the extracellular Cl(-) was substituted by the impermeant anion methylsulfate and also in strongly hypertonic medium, the SD-related decrease in LT was suppressed and replaced by a monotonic increase. Nevertheless, the degree of ISV shrinkage was similar in low and in normal Cl(-) conditions. The optical signals and ISV changes were qualitatively identical in interface and submerged slices. We conclude that there are at least two mechanisms that underlie reversible optical responses in hippocampal slices. The first mechanism underlies light-scattering decrease (hence enhancing LT) when ISV shrinks (cell swelling) under synaptic stimulation and mild hypotonia. Similarly, as result of this mechanism, expansion of ISV (cell shrinkage) during mild hypertonia leads to an increased light scattering (and decreased LT). Thus optical signals associated with this first mechanism show expected cell-volume changes and are linked to either cell swelling or shrinkage. A different mechanism causes the light-scattering increase (leading to a LT decrease) during severe hypotonia and various forms of SD but with a severely decreased ISV. This second mechanism may be due to organelle swelling or dendritic beading but not to cell-volume increase. These two mechanisms can summate, indicating that they are independent in origin. Suppression of the SD-related light-scattering increase by lowering [Cl(-)](o) or severe hypertonia unmasks the underlying swelling-related scattering decrease. The simultaneous IOS and ISV measurements clearly distinguish these two mechanisms of optical signal generation. (+info)
Baroreflex modulation of muscle sympathetic nerve activity during cold pressor test in humans.
(62/445)
The purpose of this project was to test the hypothesis that baroreceptor modulation of muscle sympathetic nerve activity (MSNA) and heart rate is altered during the cold pressor test. Ten subjects were exposed to a cold pressor test by immersing a hand in ice water for 3 min while arterial blood pressure, heart rate, and MSNA were recorded. During the second and third minute of the cold pressor test, blood pressure was lowered and then raised by intravenous bolus infusions of sodium nitroprusside and phenylephrine HCl, respectively. The slope of the relationship between MSNA and diastolic blood pressure was more negative (P < 0.005) during the cold pressor test (-244.9 +/- 26.3 units x beat(-1) x mmHg(-1)) when compared with control conditions (-138.8 +/- 18.6 units x beat(-1) x mmHg(-1)), whereas no significant change in the slope of the relationship between heart rate and systolic blood pressure was observed. These data suggest that baroreceptors remain capable of modulating MSNA and heart rate during a cold pressor test; however, the sensitivity of baroreflex modulation of MSNA is elevated without altering the sensitivity of baroreflex control of heart rate. (+info)
Clearing mechanisms of Vibrio vulnificus biotype I in the black tiger shrimp Penaeus monodon.
(63/445)
Vibrio species' infections are a common sequelae to environmental stress or other disease processes in shrimp, but the mechanism by which the shrimp eliminate the bacteria is poorly understood. In this study, the penetration, fate and the clearing of V. vulnificus were investigated in Penaeus monodon. A bacterial disease isolate from a shrimp farm was identified as V. vulnificus biotype I. Polyclonal antiserum was raised in rabbits against the bacterium and the specificity was verified by ELISA and immunoblot against a range of Vibrio spp. and other gram-negative bacteria. The bacteria were then administered to P. monodon juveniles by injection, immersion and oral intubation. An indirect immunoperoxidase technique was employed in a time course study to follow the bacteria and bacterial antigens in the tissue of the shrimp. Bacteria were cleared by a common route, regardless of the method of administration. Observations in immersion challenge were similar to a combination of those for oral and injection challenges. With immersion, bacteria entered the shrimp through damaged cuticle or via insertion points of cuticular setae. Shortly after entry, whole bacterial cells were observed in the haemolymph and connective tissue. They were either phagocytosed by haemocytes, or broken down outside host cells. Haemocytes containing bacterial cells or antigens (HCB) were observed in the connective tissue and haemolymph. HCB accumulated around the hepatopancreas, midgut, midgut-caecum, gills, heart and lymphoid organ. Free bacterial antigens also accumulated in the heart and lymphoid organ. Bacteria entering through the mouth by oral intubation or immersion were broken down so that only soluble or very fine particles entered the hepatopancreas. Bacterial antigens passed through the hepatopancreas into the haemolymph. Antigens were initially observed in the haemolymph sinuses and subsequently accumulated in the heart and lymphoid organ. Bacterial antigens were released from the shrimp, initially through the gills and subsequently through hepatopancreatic B-cells, branchial podocytes and sub-cuticular podocytes. (+info)
Autonomic nervous activity during hand immersion in cold water in patients with vibration-induced white finger.
(64/445)
Autonomic nervous function in response to cold was investigated in 21 patients with vibration-induced white finger (VWF) and 17 healthy controls of similar age, using power spectral analysis of heart rate variability. In a supine position, electrocardiogram and skin temperature of both index fingers were measured during immersion of right hand in cold water at 10 degrees C for 10 minutes. Autonomic nervous activity was evaluated from the power of the low-frequency component (LF: 0.02-0.15 Hz), the high-frequency component (HF: 0.15-0.40 Hz) and the ratio of the LF to the HF power (LF/HF ratio). The LF/HF ratio, an index of sympathetic nervous activity, significantly increased during the immersion in the VWF patients, but did not significantly increase in the controls. The LF/HF ratio was then significantly greater in the patients than in the controls during the first 1-2 minutes of the immersion. The HF power related to parasympathetic nervous activity did not change significantly in either group. Finger skin temperature of the immersed right hand was significantly lower in the VWF patients than in the controls during the last five minutes of the immersion and in the recovery period. The present results indicate that sympathetic nervous response to cold is significantly enhanced in VWF patients. The exaggerated sympathetic response to cold in these patients is considered to contribute to the enhanced vasoconstriction of their extremities. (+info)