Absence of selective brain cooling in unrestrained baboons exposed to heat

To test whether baboons are capable of implementing selective brain cooling, we measured, every 5 min, the temperature in their hypothalamus, carotid arterial bloodstream, and abdominal cavity. The baboons were unrestrained and exposed to 22 degrees C for 7 days and then to a cyclic environment with 15 degrees C at night and 35 degrees C during the day for a further 7 days. During the latter 7 days some of the baboons also were exposed to radiant heat during the day. For three days, during heat exposure, water was withheld. At no time was the hypothalamus cooler than carotid arterial blood, despite brain temperatures above 40 degrees C. With little variation, the hypothalamus was consistently 0.5 degrees C warmer than arterial blood. At high body temperatures, the hypothalamus was sometimes cooler than the abdomen. Abdominal temperature was more variable than arterial blood and tended to exceed arterial blood temperature at higher body temperatures. Hypothalamic temperature cooler than a warm abdomen is not evidence for selective brain cooling. In species that can implement selective brain cooling, the brain is most likely to be cooler than carotid arterial blood when an animal is hyperthermic, during heat exposure, and also dehydrated and undisturbed by human presence. When we exposed baboons to high ambient temperatures while they were water deprived and undisturbed, they never implemented selective brain cooling. We conclude that baboons cannot implement selective brain cooling and can find no convincing evidence that any primate species can do so.     

A test of biochemical symmorphosis in a heterothermic tissue: bluefin tuna white muscle

Selective brain cooling (SBC) is defined as a brain temperature cooler than the temperature of arterial blood from the trunk. Surrogate measures of arterial blood temperature have been used in many published studies on SBC. The use of a surrogate for arterial blood temperature has the potential to confound proper identification of SBC. We have measured brain, carotid blood, and rectal temperatures in conscious sheep exposed to 40, 22, and 5 degrees C. Rectal temperature was consistently higher than arterial blood temperature. Brain temperature was consistently cooler than rectal temperature during all exposures. Brain temperature only fell below carotid blood temperature during the final few hours of 40 degrees C exposure and not at all during the 5 degrees C exposure. Consequently, using rectal temperature as a surrogate for arterial blood temperature does not provide a reliable indication of the status of the SBC effector. We also show that rapid suppression of SBC can result if the animals are disturbed.     

The BIORACK facility and its performance during the IML-2 Spacelab mission

The configuration and performance of the Biorack facility during the Second International Microgravity Laboratory mission (IML-2; 8-23 July 1995) is described in detail. During this Spacelab mission, Biorack flew with two incubators (22 degrees C and 37 degrees C), glovebox, cooler (5 degrees C) and four passive thermal conditioning units (PTCU; 5 degrees C and 10 degrees C) in the stowage. The crew worked more than 40 h to perform 19 Biorack experiments originating from seven European countries. Almost 200 Biorack experiment containers had to be translocated in about 1500 predetermined steps before the Space Shuttle Columbia returned after nearly 14 days: 18 h or 236 orbits in space to Kennedy Space Center, Florida.     

Variation in subsurface seawater temperature off Discovery Bay, Jamaica and the U.S. Virgin Islands

Long-term, high accuracy seawater temperature data sets are essential in studies assessing environmental changes that may alter coral reef communities. Located at the approximately the same latitude, the subsurface seawater temperature (S3T) off Discovery Bay, Jamaica (DBJ) and the U.S. Virgin Islands (USVI) had the same overall mean temperature. The USVI S3T during the winter months is approximately 0.5 degrees C warmer than DBJ, while May - July at DBJ is approximately 1 degrees C warmer than USVI S3T. With the passing of tropical storms in 1995 and 1997 in the USVI S3T dropped as much as 1.5 degrees C within a 20 hr period and did not revert to the previous temperature during that calendar year. Mean monthly S3T during 2000 and 2001 in the USVI was > 0.5 degrees C warmer than during similar periods in the early 1990s. Mean monthly S3T during 1999-2002 at DBJ was 0.27 degrees C cooler than during 1994-1995.     

Temperature regulation of microtiter plates for enzyme assays

To facilitate the use of microtiter plates as vessels for enzyme assays, an incubator has been designed to maintain the wells of the microtiter plates at the appropriate temperature. The temperature variation within a single well was +/- 0.02 degrees (standard error of the mean) at 25 degrees C and +/- 0.02 degrees at 37 degrees C. The temperature variation was the same for internal and peripheral wells within the plates, although the internal wells were approximately 0.14 degrees C warmer than the outer wells at 25 degrees C and 0.68 degrees C cooler at 37 degrees C. The overall uncertainty (95% confidence interval) of the well temperature in a typical plate was +/- 0.4 degrees C at 25 degrees C and +/- 0.7 degrees C at 37 degrees C. This uncertainty is realistic for routine enzyme determinations, as opposed to precise studies. The incubator was designed to allow access to the plates from above so that additions could be made during the incubation. To demonstrate the suitability of microtiter plates and the incubator for enzyme determinations, this method was used to measure the activity of myeloperoxidase and alpha-naphthylbutyryl esterase.     

A preovulatory temperature gradient between the isthmus and ampulla of pig oviducts during the phase of sperm storage

Fine thermistor probes positioned in each end of the same oviduct and connected to the same scale were used to measure temperature gradients in the lumen before and after spontaneous ovulation in normally-cyclic gilts. Readings were taken after full surgical closure of a mid-ventral incision and a subsequent period of stabilization, but whilst animals remained under general anaesthesia. A small but consistent difference in temperature was recorded between the proximal ampulla and distal isthmus of the same oviduct in each of 20 preovulatory gilts. In 10 of these animals that had not mated, the isthmus was a mean of 0.43 degree C cooler than the ampulla (range 0.2-0.7 degree C) whereas in 10 mated animals the isthmus was 0.69 degree C cooler (range 0.2-1.6 degree C); 3 animals in the latter group had within-oviduct differences of greater than or equal to 1 degrees C. By contrast, in 12 animals that had recently ovulated, the isthmus was a mean of only 0.1 degree C cooler than the ampulla; there was no measurable temperature gradient in 3 of the animals, whilst the isthmus was 0.1 degree C warmer in 2 animals. The preovulatory temperature differences are thought primarily to reflect the extent and activity of the vascular and lymphatic beds in the oviduct tissues and, together with specific chemical microenvironments, may facilitate the relatively prolonged period of sperm storage in the distal portion of the isthmus.     

Respiratory Q10 varies between populations of two species of Myrmica ants according to the latitude of their sites

Metabolic respiration by groups of resting Myrmica ruginodis and M. scabrinodis worker ants from five sites representing a range of latitudes, have been compared by measuring rates of CO(2) production-standardised by fat-free weight-at 5 and 25 degrees C. M. ruginodis which lives in cooler habitats than M. scabrinodis consistently produced more CO(2). At 5 degrees C ants of both species from southern latitudes were metabolically more active than those from more northerly latitudes, whereas at 25 degrees C the situation was reversed. Estimates of Q10 were positively correlated with latitude indicating that the respiratory metabolism of northern populations increases relatively more in response to rising temperatures than southern populations. Values of Q10 at different latitudes were the same for both species. The results are discussed in terms of seasonal fluctuations of temperature at different latitudes.     

Temperature and humidity of expired air of sheep

The temperature and humidity of expired air from three adult Merino sheep were measured at air temperatures of 20, 30 and 40 degrees C before and after the animals were shorn. Expired air was apparently always saturated with water vapour. At the higher air temperatures the temperature of expired air was close to deep body temperature; at lower air temperatures, expired air had been significantly cooled, e.g. to 32.3 degrees C in shorn sheep at 20 degrees C air temperature. Expired air was cooler from shorn than from unshorn animals at 20 and 30 degrees C air temperature, possibly due to thermally induced vasomotor changes in the upper respiratory tract. Cooling of expired air would be expected to lead to recovery of some of the water evaporated during inspiration; at 20 degrees C air temperature, this fraction was estimated to be 25% in unshorn sheep and 36% in shorn sheep.     

Quantification of the expression of a temperature-sensitive pigment allele in sailfin mollies (Poecilia latipinna) by image analysis

Image analysis was used to quantify the activity of a temperature-sensitive macromelanophore-determining allele in sailfin mollies as the percentage of the body surface area covered by macromelanophores. Fish heterozygous for the macromelanophore-determining allele produced very few macromelanophores when raised at either 25 or 28 degrees C, even after more than 200 days. In contrast, the mean percent coverage for genetically identical fish raised at 22 degrees C increased steadily throughout the course of the experiment. Production of macromelanophores was sex influenced, with greater expressivity seen in males. At 22 degrees C, the mean percent coverages had significantly diverged between males and females by the age of 201 days. From that point on, the percent macromelanophore coverage of the males was consistently significantly higher than that of the females. The tendency to produce greater melanization at cooler temperatures is not the result of a heat-sensitive tyrosinase enzyme, as is the case in mammals carrying the Himalayan allele. In mollies, the activity of tyrosinase increases between 22 and 29 degrees C. We hypothesize that production of macromelanophores is under the control of a proto-oncogene.     

Minimal changes in hypothalamic temperature accompany microwave-induced alteration of thermoregulatory behavior

This study probed the mechanisms underlying microwave-induced alterations of thermoregulatory behavior. Adult male squirrel monkeys (Saimiri sciureus), trained to regulate the temperature of their immediate environment (Ta) behaviorally, were chronically implanted with Teflon reentrant tubes in the medical preoptic/anterior hypothalamic area (PO/AH), the brainstem region considered to control normal thermoregulatory processes. A Vitek temperature probe inserted into the tube measured PO/AH temperature continuously while changes in thermoregulatory behavior were induced by either brief (10-min) or prolonged (2.5-h) unilateral exposures to planewave 2,450-MHz continuous wave (CW) microwaves (E polarization). Power densities explored ranged from 4 to 20 mW/cm2 (rate of energy absorption [SAR] = 0.05 [W/kg]/cm2]). Rectal temperature and four representative skin temperatures were also monitored, as was the Ta selected by the animal. When the power density was high enough to induce a monkey to select a cooler Ta (8 mW/cm2 and above), PO/AH temperature rose approximately 0.3 degrees C but seldom more. Lower power densities usually produced smaller increases in PO/AH temperature and no reliable change in thermoregulatory behavior. Rectal temperature remained constant while PO/AH temperature rose only 0.2-0.3 degrees C during 2.5-h exposures at 20 mW/cm2 because the Ta selected was 2-3 degrees C cooler than normally preferred. Sometimes PO/AH temperature increments greater than 0.3 degrees C were recorded, but they always accompanied inadequate thermoregulatory behavior. Thus, a PO/AH temperature rise of 0.2-0.3 degrees C, accompanying microwave exposure, appears to be necessary and sufficient to alter thermoregulatory behavior, which ensures in turn that no greater temperature excursions occur in this hypothalamic thermoregulatory center.     

An implantable nerve cooler for the exercising dog

An implantable nerve cooler has been constructed to block cervical vago-sympathetic activity in the exercising dog reversibly. An insulated gilt brass container implanted around the nerve is perfused with cooled alcohol via silicone tubes. The flow of alcohol is controlled by an electromagnetic valve to keep nerve temperature at the required value. Nerve temperature is measured by a thermistor attached to the housing and in contact with the nerve. It is shown that, during cooling, temperature at this location differs less than 2 degrees C from nerve core temperature. Measurement of changes in heart rate revealed that complete vagal block in the conscious animal is obtained at a nerve temperature of 2 degrees C and can be achieved within 50 s. During steady-state cooling in the exercising animal nerve temperature varied less than 0.5 degree C. When the coolers after 2 weeks of implantation were removed they showed no oxydation and could be used again.     

The effect of surface cooling on blood flow distribution in infant pigs with mature left to right shunts

Surface cooling as an adjunct to cardiopulmonary bypass, core cooling, and circulatory arrest has been effectively used to produce more homogeneous cooling and better tissue preservation. A previous study, using pigs with newly created aortopulmonary shunts, revealed a redistribution of blood flow away from the kidneys and viscera during surface cooling that did not occur in normal pigs. The present study tests the hypothesis that pigs with mature aortopulmonary shunts behave in a similar manner. Group I (N = 7, unshunted pigs) and Group II (N = 7, shunted pigs) underwent surface cooling and blood flow distribution measurements by microspheres at 37, 32, 28, and 25 degrees C. Both Groups I and II experienced a decrease in cardiac output with hypothermia. Group II had decreased absolute tissue flow to the viscera, kidneys, muscle, and skin at 37 degrees C compared with Group I, even before the onset of hypothermia. During hypothermia, Group I experienced a decrease in all tissue flows, but Group II had a decrease only in visceral and renal flows at 25 degrees C. Blood flow distribution, as a percentage of cardiac output, showed little change (decrease only in skin) in Group I with hypothermia. In Group II, however, a maldistribution of cardiac output developed resulting in decreased percentage of cardiac output to the kidneys and viscera and an increased percentage of cardiac output to the lungs that was confirmed by an increase in the Qp/Qs ratio.(ABSTRACT TRUNCATED AT 250 WORDS)     

Acute cold exposure and the metabolism of glucose and some of its precursors in the liver of the fed and fasted sheep.

Measurements of total body oxygen consumption, visceral and hepatic blood flow, oxygen consumption, exchanges of amino acids, lactate, pyruvate and glucose were made on sheep fed 3--6 h or 21 h before the experiment and exposed for 3 h to a neutral environment (15 degrees C) or a cold environment (0.5 to 4 degrees C with clipped coat and wind speed 2 m.s-1). Recent feeding significantly increasedd the total oxygen consumption and the oxygen consumption of the viscera and liver. No general release of amino acids from the viscera or uptake by the liver after feeding was detected although the arterial plasma concentration of essential amino acids did increase significantly after feeding. The plasma concentration of most non-essential amino acids also increased except that of glycine, which decreased significantly. Cold exposure increased the total oxygen consumption and reduced the respiratory quotient significantly. Release of amino acids from the viscera was stimulated by cold exposure. There was a variable increase in the hepatic uptake of lactate and alanine when the sheep were fasted and cold-exposed. The liver's glucose output doubled and the blood (arterial) glucose concentration significantly increased in the cold.     

Metabolic and cardiovascular adjustment to work in air and water at 18, 25, and 33 degrees C.

By use of successive increments of discontinuous work with an arm-leg cycle ergometer the VO2, Q, SV, and HR were studied in six male subjects at rest and during exercise in air and in water at 18, 25, and 33 degrees C. The Q values obtained by CO2 rebreathing were reproducible. VO2 was linearly related to work with the plots for air and 33 degrees C water being similar. However, during work in 25 and 18 degrees C water, the VO2 averaged 9.0% (150 ml) and 25.3% (400 ml) higher, respectively, than values observed in 33 degrees C water, with the largest differences observed in leaner subjects. The plot of HR-VO2 was linear and almost identical during work in air and 33 degrees C water, but shifted significantly to the right in cooler water. VO2 averaged 250-700 ml higher in cold water compared to air and 33 degrees C water at a given mean heart rate. The Q vs. VO2 line was similar during work in air and in water with no effect of water or temperature. At similar levels of VO2, SV was significantly larger (P less than 0.05) in 25 and 18 degrees C water than in air or 33 degrees C water. Consequently, the reduction in heart rate during work in cold water was entirely compensated for by a proportionate increase in the SV of the heart. Q was therefore maintained at similar levels of energy expenditure in air and in 18, 25, and 30 degrees C water.     

人胚胎干细胞程序降温保存的实验研究

本文采用升降式程序降温仪对人胚胎干细胞进行了程序降温保存,并探讨和比较了降温速率、置核温度、保护剂和投入液氮前温度对冻存复苏后胚胎干细胞的存活率、活力及分化特性的影响。结果表明：采用Me2SO 血清 DMEM(体积比为1：3：6)的保护剂,从0℃开始,以0．5℃／min的速率对细胞悬液降温;至-10℃时对其进行置核,并于-35℃时将其快速投入液氮中保存,复温后效果最佳。冻存复温后细胞存活率可达81．8％,复苏后的胚胎干细胞形态和集落生长方式都与冻前的生长形态相同,且胚胎干细胞标志之一碱性磷酸酶(AKP)反应阳性,同时染色体组型仍正常。     

Effect of water temperature on the ability of Diplostomum spathaceum miracidia to establish in lymnaeid snails

The effects of water temperature on the ability of Diplostomum spathaceum miracida to infect and establish patent infections in Lymnaea peregra and L. stagnalis were investigated. Snails were infected over a range of temperatures (6-20 degrees C) and kept thereafter at 20 degrees C or were infected at 20 degrees C and kept at either 14, 20, or 25 degrees C. Infection success was determined after 8 weeks by either observing cercarial shedding or examining snail viscera for sporocysts. The establishment of miracidia declined at lower water temperatures despite maintenance for 8 weeks at 20 degrees C while exposure of snails to miracidia at 20 degrees C and maintenance at different temperatures had little apparent effect. Infection success under these conditions was related more to the numbers of miracidia to which the snails were exposed. However, under this latter experimental regime, the time taken for the infection to become patent clearly depended upon maintenance temperature.     

Synthesis of 70K stress protein by human leukocytes: effect of exercise in the heat

To determine whether reinduction of 70,000-Da (70K) stress protein synthesis could be used as an assay for thermal history and/or cellular levels of 70K stress protein in hyperthermic humans, leukocytes were obtained before and after 2 h of exercise and then incubated at 37 or 41 degrees C. Five healthy males completed 2 h of treadmill exercise consisting of running at 4-6 km/h for 30-45 min followed by 75-90 min of walking up a 2-10% grade. This exercise bout was performed by two subjects in hot (46 degrees C, 15% relative humidity) and by five subjects in cooler (30 degrees C, 40% relative humidity) environmental conditions. Exercise resulting in rectal temperature (Tre) less than 40 degrees C did not alter the amount of 70K stress protein synthesized by leukocytes incubated at 41 degrees C. In contrast, exercise resulting in Tre greater than 40 degrees C reduced the amount of 70K stress protein synthesized by leukocytes incubated at 41 degrees C. A protein immunoblot, probed with an antibody specific for the inducible 72K stress protein, showed that the reduction of 35S-labeled 70K stress protein in these postexercise leukocyte samples occurred without marked elevations of this protein. In vitro incubation of human leukocytes at 40 degrees C for 15-120 min reduced, in a time-dependent manner, the amount of 70K stress protein synthesized during a subsequent 41 degrees C heat stress. This reduction of 70K stress protein synthesis in 41 degrees C-treated leukocytes was abolished when cycloheximide was present during the 40 degrees C preincubation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of cryoprotective diluent on post-thaw viability and acrosomal integrity of spermatozoa of the African elephant (Loxodonta africana)

Electroejaculates from free-ranging, African elephants were frozen to test various seminal diluents, freezing methods and thawing media on post-thaw sperm viability and structural integrity. In Study I, each ejaculate was tested with each of 7 cryoprotective diluents. After cooling to 5 degrees C and equilibration on ice (4 degrees C) for 120 min, each aliquant was pellet frozen on solid CO2, stored in liquid nitrogen and thawed (37 degrees C) in saline or tissue culture solution. Amongst all diluents, post-thaw sperm motility, motility duration in vitro (37 degrees C) and acrosomal integrity were greatest (P less than 0.05) when diluent BF5F was used. Thawing medium had no effect on results. In Study II, the optimal diluent from Study I (BF5F) was compared with the diluent SGI. Results were not affected by a 90- or a 150-min cooling-equilibration interval in an electronic cooler (5 degrees C); however, post-thaw sperm motility rating and duration of motility in vitro were greater (P less than 0.01) with the pellet than the straw container freezing method. When the pelleting method was used, diluents BF5F and SGI provided comparable cryoprotection. Duration of post-thaw motility was enhanced 2-fold and up to 12 h by maintaining thawed semen at 21 rather than 37 degrees C (P less than 0.05). All diluents provided some protection on acrosomal integrity, but the overall proportion of intact acrosomes after thawing was markedly less in Study II, apparently as a result of the slower initial cooling rate (approximately 1.5 degrees C/min) compared to that of Study I (approximately 6.5 degrees C/min). This study demonstrates the feasibility of cryopreserving semen from free-ranging African elephants and indicates that spermatozoa must effectively survive freezing when the BF5F or SGI diluent is used in conjunction with the pelleting method.     

Influence of long-term changes in incubation temperature on catecholamine levels in plasma of chicken embryos (Gallus gallus f. domestica)

Catecholamine concentrations were determined from day 18 to 21 of incubation (D18, D21) in developing chicken embryos. The control group was continuously incubated at 37.5 degrees C. The eggs of the two other groups were incubated at 37.5 degrees C until day 14. In the cold group, temperature was decreased to 35.0 degrees C and in the warm group, incubation temperature was increased to 38.5 degrees C for the remainder of incubation. Plasma catecholamine concentrations were measured in eggs exposed to a change in incubation temperature for 4, 5, 6 and 7 days. Embryos in the warm group had dopamine (DA) and noradrenaline (NA) concentrations that were significantly higher than in the control group. On the contrary, eggs incubated at the cooler temperature had hormone levels that were significantly lower than in the control group. Adrenaline (A) levels in the two experimental treatments were significantly lower compared to control eggs. Temperature modulated the time needed for development. Chicken embryos are supposed to hatch on day 21. However, on day 20, NA concentration in the cold-incubated group was too low to fulfill its essential physiological function, whereas in the warm group, the NA concentration seems to be sufficient. Long-term exposure to altered incubation temperature affects the quantitative catecholamine concentration during development, but the relative proportion of each catecholamine remained constant.     

Strongyloides ratti: thermokinetic behavior of third-stage larvae on a temperature gradient

We examined the thermokinetic behaviors of infective third-stage larvae (L3) of the rodent parasitic nematode Strongyloides ratti on temperature gradients using an in vitro agarose tracking assay method. Observed behaviors included both negative and positive thermokineses, the direction of movement depending both on the gradient temperature at which larvae were initially placed and on prior experience of culture temperature. Larvae isolated from rat feces cultured at 25 degrees C and placed on a gradient at temperatures between 22 degrees and 29 degrees C tended to move toward higher temperatures. At higher placement temperatures, most larvae moved little and showed no directional response, whereas at lower placement temperatures, many migrated toward cooler temperatures. At placement temperatures of 20 degrees C or below, few or no larvae moved toward the zone of higher temperature. Larvae isolated from rat feces cultured at 20 degrees C tended to migrate to a high temperature area regardless of placed temperature. Those cultured at 30 degrees C did not respond to the temperature gradient. L3 cultured at 30 degrees C were significantly less infective to rats than those cultured at 25 degrees or 20 degrees C. Additional experiments were designed to demonstrate thermokinetic behaviors during the period after reaching the L3 stage. Larvae incubated in double distilled water (DDW) for 24 h at 37 degrees C lost their ability to respond to lower temperatures, while in those incubated in DDW at 15 degrees and 25 degrees C, responses were still apparent. The thermokinetic behavior of S. ratti L3 is affected by surrounding environmental temperatures and this may have an important role in host finding.