Normothermic Levels Research Articles

Effects of Therapeutic Hypothermia on Inflammasome Signaling after Traumatic Brain Injury

Traumatic brain injury (TBI) activates the NALP1/NLRP1 inflammasome, which is an important component of the early innate inflammatory response to injury. We investigated the influence of therapeutic hypothermia on inflammasome activation after TBI. Adult male Sprague-Dawley rats were subjected to moderate fluid percussion brain injury. Temperature manipulation (33°C or 37°C) was initiated 30 minutes after TBI and maintained for 4 hours. At 4 or 24 hours after TBI, traumatized cortex and hippocampus were prepared for immunoblot or immunohistochemical analysis. In the normothermic groups, caspase-1, caspase-11 and expression of the purinergic receptor P2X7 increased at 24 hours after TBI. Posttraumatic hypothermia lead to decreased expression of these proteins at 24 hours compared with normothermic levels. Immunocytochemical studies showed that posttraumatic hypothermia also decreased caspase-1 staining in cerebral cortical neurons compared with normothermic TBI. Cultured cortical neurons subjected to stretch injury demonstrated significant secretion of caspase-1 into the culture medium and caspase-3 activation, both results reduced by hypothermic treatment. Posttraumatic hypothermia decreases inflammasome signaling in neurons and reduces the innate immune response to TBI at 24 hours after injury. Therapeutic hypothermia may protect the injured central nervous system by targeting the detrimental consequences of the innate immune response to injury.

Rewarming: facts and myths from the neurological perspectives

Rewarming: facts and myths from the neurological perspectives

Colloid volume loading does not mitigate decreases in central blood volume during simulated haemorrhage while heat stressed

Heat stress results in profound reductions in the capacity to withstand a simulated haemorrhagic challenge; however, this capacity is normalized if the individual is volume loaded prior to the challenge. The present study tested the hypothesis that volume loading during passive heat stress attenuates the reduction in regional blood volumes during a simulated haemorrhagic challenge imposed via lower-body negative pressure (LBNP). Seven subjects underwent 30 mmHg LBNP while normothermic, during passive heat stress (increased internal temperature ∼1◦C), and while continuing to be heated after intravenous colloid volume loading (11 ml kg⁻¹). Relative changes in torso and regional blood volumes were determined by gamma camera imaging with technetium-99m labelled erythrocytes. Heat stress reduced blood volume in all regions (ranging from 7 to 16%), while subsequent volume loading returned those values to normothermic levels. While normothermic,LBNP reduced blood volume in all regions (torso: 22 ± 8%; heart: 18 ± 6%; spleen: 15 ± 8%). During LBNP while heat stressed, the reductions in blood volume in each region were markedly greater when compared to LBNP while normothermic (torso: 73 ± 2%; heart: 72 ± 3%; spleen: 72 ± 5%, all P<0.001 relative to normothermia). Volume loading during heat stress did not alter the extent of the reduction in these blood volumes to LBNP relative to heat stress alone (torso: 73 ± 1%; heart: 72 ± 2%; spleen: 74 ± 3%, all P>0.05 relative to heat stress alone). These data suggest that blood volume loading during passive heat stress (via 11 ml kg⁻¹ of a colloid solution) normalizes regional blood volumes in the torso, but does not mitigate the reduction in central blood volume during a simulated haemorrhagic challenge combined with heat stress.

Colloid volume loading does not mitigate thorax, heart, and liver blood volume changes during combined heat and orthostatic stress

This study tests the hypothesis that volume loading during heat stress attenuates the reduction in regional blood volumes during an orthostatic challenge. 7 subjects underwent 30 mmHg lower-body negative pressure (LBNP) while normothermic, during heat stress (increased internal temperature ~1°C), and heat stress + colloid volume loading (12ml/kg). Relative thorax, heart, and liver blood volumes were determined by gamma camera imaging of 99mTc-labelled erythrocytes. Heat stress reduced blood volume in all regions, while subsequent volume infusion returned those values to normothermic levels. During LBNP, heat stress increased the magnitude of the reduction in blood volume (thorax=73±1, heart=72±1, liver=74±1%) compared to normothermia (thorax=22±3, heart=18±2, liver=14±63%; all P<0.001). Volume loading during heat stress did not alter the extent of the reduction in these blood volumes during LBNP (P>0.05). These data indicate that colloid volume loading during heat stress normalizes thorax, heart, and liver blood volumes but does not affect the magnitude of the subsequent reduction in blood volume in these regions during LBNP relative to heat stress alone. Supported by NIH-HL61388 & HL84072

Oligodendrocyte Vulnerability Following Traumatic Brain Injury in Rats: Effect of Moderate Hypothermia

The purpose of this study was to document patterns of oligodendrocyte vulnerability to TBI and determine whether posttraumatic hypothermia prevents oligodendrocyte cell loss. Sprague Dawley rats underwent moderate fluid percussion brain injury. Thirty minutes after TBI, brain temperature was reduced to 33°C for 4 hrs or maintained at normothermic levels (37°C). Animals were perfusion-fixed for quantitative immunohistochemical analysis at 3 (n=9) or 7 (n=9) days post-TBI. Within the cerebral cortex, external capsule and corpus callosum, numbers of APC-CC1 immunoreactive oligodendrocytes at 3 and 7 days following TBI were significantly decreased compared to sham operated rats (p<0.02). Double-labeling studies showed that vulnerable oligodendrocytes expressed increased Caspase 3 activation compared to sham. Posttraumatic hypothermia significantly reduced the number of CC1 positive oligodendrocytes lost after normothermia TBI in white matter tracts (p<0.01). This model of TBI leads to quantifiable regional patterns of oligodendrocyte vulnerability. Posttraumatic hypothermia protects oligodendrocytes by interfering with Caspase 3-mediated cell death mechanisms. Therapeutic hypothermia may improve functional outcome by attenuating trauma-induced oligodendrocyte cell death, subsequent demyelination and circuit dysfunction.

Effectiveness Of End-tidal Carbon Dioxide Clamping In The Heat Stressed Human

During moderate to pronounced passive heat stress end-tidal carbon dioxide tension (PETCO2) is reduced by approximately 3 - 8 mmHg, which in part contributes to the decreases in cerebral blood flow and cerebrovascular conductance that occur in this thermal condition. Clamping devices have been used to manipulate PETCO2 in normothermic humans, however, their effectiveness in clamping arterial carbon dioxide tension (PaCO2) while heat stressed is unknown. PURPOSE: The aim of this study was to test the hypothesis that in the heat stressed human PETCO2 accurately tracks PaCO2 when PETCO2 is clamped at normothermic levels. METHODS: Internal temperature (telemetry pill), PaCO2 (radial artery catheter), and PETCO2 (capnograph) were assessed in 7 healthy individuals during three conditions performed sequentially; 1) normothermia (NT), 2) passive heat stress (HS), and 3) passive heat stress when PETCO2 was clamped at normothermic levels (HS+Clamp). Clamping was achieved using a computer controlled sequential gas delivery breathing circuit (RespiractTM). RESULTS: Heat stress increased internal temperature from 37.0 ± 0.3 to 38.4 ± 0.4 °C (P < 0.001). While normothermic values of PaCO2 (40.4 ± 3.4 mmHg) and PETCO2 (38.8 ± 3.5 mmHg; P = 0.12) were similar, HS resulted in significantly greater reductions in PaCO2 (D 10.1 ± 3.0 mmHg) relative to PETCO2 (D 7.8 ± 3.5 mmHg; P = 0.04). HS+Clamp caused comparable increases in PaCO2 (D 6.6 ± 3.4 mmHg) and PETCO2 (D 7.5 ± 2.8 mmHg: P = 0.30), however, because the decrease in PaCO2 due to HS was greater than PETCO2, absolute PaCO2 during HS+Clamp remained significantly lower (PaCO2: 36.8 ± 4.9 mmHg; PETCO2: 38.5 ± 5.2 mmHg; P < 0.01). CONCLUSION: These results indicate that despite a difference in absolute PETCO2 and PaCO2 during heat stress+clamp conditions, clamping caused similar increases between PETCO2 and PaCO2. Supported by NIH Grants HL61388 & HL84072

Do Owls Use Torpor? Winter Thermoregulation in Free‐Ranging Pearl‐Spotted Owlets and African Scops‐Owls

Numerous avian taxa use torpor, which involves pronounced reductions in body temperature (T(b)) to below normothermic levels. However, the occurrence of this phenomenon in owls (Strigidae) remains largely unknown. We investigated winter patterns of thermoregulation in the crepuscular 80-g pearl-spotted owlet Glaucidium perlatum and the strictly nocturnal 61-g African scops-owl Otus senegalensis by obtaining telemetric measurements of skin temperature (T(skin)) from free-ranging individuals in the Kalahari Desert of southern Africa. Pearl-spotted owlets remained homeothermic throughout the study period, whereas African scops-owls routinely used shallow torpor, with T(skin) reduced by 3.3 degrees -8.6 degrees C (pooled mean, 5.3+/- 1.1 degrees C) below normothermic levels for 3-4 h after sunrise. The mean lowest T(skin) recorded in three African scops-owl individuals was 29.0 degrees C +/- 0.1 degrees C. The thermoregulatory differences between these two species may be related to their diets and activity patterns. African scops-owls are almost exclusively insectivorous and experience a marked reduction in food availability on cold winter nights. In contrast, pearl-spotted owlets have more flexible activity patterns and include larger or diurnal vertebrate prey in their diet.

The effects of reduced end‐tidal carbon dioxide tension on cerebral blood flow during heat stress

Passive heat stress reduces arterial carbon dioxide partial pressure (P(aCO2)) as reflected by 3 to 5 Torr reductions in end-tidal carbon dioxide tension (P(ETCO2)). Heat stress also reduces cerebrovascular conductance (CBVC) by up to 30%. While is a strong regulator of CBVC, it is unlikely that the relatively small change in during heating is solely responsible for the reductions in CBVC. This study tested the hypothesis that P(aCO2), referenced by P(ETCO2), is not the sole mechanism for reductions in CBVC during heat stress. Mean arterial blood pressure (MAP), P(ETCO2), middle cerebral artery blood velocity (MCA V(mean)), and calculated CBVC (MCA V(mean)/MAP) were assessed in seven healthy individuals, during three separate conditions performed sequentially: (1) normothemia, (2) control passive heat stress and (3) passive heat stress with P(ETCO2) clamped at the normothermic level (using a computer-controlled sequential gas delivery breathing circuit). MAP was similar in the three thermal conditions (P = 0.55). Control heat stress increased internal temperature approximately 1.3 degrees C, which resulted in decreases in P(ETCO2), MCA V(mean) and calculated CBVC (P < 0.001 for all variables). During heat stress + clamp conditions internal temperature remained similar to that during the control heat stress condition (P = 0.31). Heat stress + clamp successfully restored to the normothermic level (P = 0.99) and increased MCA V(mean) (P = 0.002) and CBVC (P = 0.008) relative to control heat stress. Despite restoration of P(ETCO2), MCA V(mean) (P = 0.005) and CBVC (P = 0.03) remained reduced relative to normothermia. These results indicate that heat stress-induced reductions in , as referenced by P(ETCO2), contribute to the decrease in MCA V(mean) and CBVC; however, other factors (e.g. perhaps elevated sympathetic nerve activity) are also involved in mediating this response.

A reappraisal on the ability of leptin to induce fever

Leptin is often regarded as a mediator of fever, even though an in-depth analysis of the dose-dependent effects of leptin on body temperature ( T b), pro-inflammatory cytokines, and circulating leptin has never been performed. In the present study, such an analysis was performed in rats that were food deprived (lower baseline levels of leptin) or free feeding (higher baseline levels of leptin). In a relatively cool environment (22 °C), rats deprived of food for 24 h exhibited mild (~ 0.5 °C) hypothermia. Leptin infusion (250 μg/kg iv) elevated the T b of the food-deprived rats to a normothermic level, an effect that peaked (120 min post-infusion) when plasma leptin was at a level (~ 8 ng/mL) often found in leptin-responsive subjects. Increasing the leptin dose to 1000 μg/kg did not produce any further (febrile) elevation in the T b of food-deprived rats. The anti-hypothermic effect of leptin in food-deprived rats was not associated with any rise in the plasma levels of the pro-inflammatory cytokines tumor necrosis factor (TNF)-α and interleukin (IL)-6. In free-feeding rats kept in a cooler (22 °C) or warmer (28 °C) environment, leptin infusion failed to alter T b or to produce any surge in plasma TNF-α or IL-6, even when the dose infused (3500 μg/kg iv) resulted in excessive, non-physiological rises in plasma leptin (~ 542 ng/mL at 30 min; ~ 75 ng/mL at 120 min post-infusion). In contrast, free-feeding rats in the same experimental set-up were able to respond to a low dose (2 μg/kg iv) of IL-1β with a typical biphasic fever, which was associated with surges in plasma TNF-α and IL-6. Collectively, our data show that an acute rise in plasma leptin to a level within or fairly above the physiological range does not induce fever. These results challenge the idea that leptin may be a mediator of fever.

Optional strategies for reduced metabolism in gray mouse lemurs

Among the order of primates, torpor has been described only for the small Malagasy cheirogaleids Microcebus and Cheirogaleus. The nocturnal, gray mouse lemur, Microcebus murinus (approx. 60 g), is capable of entering into and spontaneously arousing from apparently daily torpor during the dry season in response to reduced temperatures and low food and water sources. Mark-recapture studies indicated that this primate species might also hibernate for several weeks, although physiological evidence is lacking. In the present study, we investigated patterns of body temperature in two free-ranging M. murinus during the austral winter using temperature-sensitive data loggers implanted subdermally. One lemur hibernated and remained inactive for 4 weeks. During this time, body temperature followed the ambient temperature passively with a minimum body temperature of 11.5 degrees C, interrupted by irregular arousals to normothermic levels. Under the same conditions, the second individual displayed only short bouts of torpor in the early morning hours but maintained stable normothermic body temperatures throughout its nocturnal activity. Reduction of body temperature was less pronounced in the mouse lemur that utilized short bouts of torpor with a minimum value of 27 degrees C. Despite the small sample size, our findings provide the first physiological confirmation that free-ranging individuals of M. murinus from the humid evergreen littoral rain forest have the option to utilize short torpor bouts or hibernation under the same conditions as two alternative energy-conserving physiological solutions to environmental constraints.

Heat Shock Prevents Tissue Factor Induction after Rewarming from Lethal Hypothermia in a c-Jun-Dependent Manner.

Decrease in body core temperature is associated with life threatening coagulation disturbances in humans. Although rewarming from hypothermia is a prerequisite for survival, it can lead to mobilization of large amounts of tissue factor (TF) from damaged tissues, which in turn can induce disseminated intravascular coagulation. Using immunoblotting, In-Cell Western assay, fluorescence activated cell sorting (FACS) and TF activity assay, we studied post-rewarming TF levels, activity and surface redistribution, along with the regulation of TF gene transcription in mononuclear cells (MNCs) obtained from an in vivo rat model. Twenty-four male Wistar rats were randomly assigned into four groups: normothermic control group (n=6); hypothermic followed by rewarming group (n=6); heat shock pretreated hypothermic followed by rewarming group (n=6); and heat shock pretreated normothermic group (n=6). Rewarming after a 5-hour episode of 15oC hypothermia caused a 5-fold rise of TF protein levels and 2-fold increase in surface TF signal intensity and serface redistribution of TF antigen, judged by 2-fold increase in surface-to-total TF ratio. TF activity was enhanced from 5.6±0.7 mU 106/cells in normothermic group to 13.9±3.6 mU 106/cells after hypothermia/rewarming. This was accompanied by a dramatic elevation of c-Jun and c-Jun-N-terminal kinase (JNK) phosphorylation, and the absence of early growth response-1 and NF-kB activation. Reflecting certain limitations of the method when dealing with detection of low levels of antigens, FACS analysis of TF-positive population of MNCs failed to detect any differences between the groups. To search for a stimulus to counteract c-Jun-mediated induction of TF activity in MNCs from rewarmed rats, we applied heat shock pretreatment one day before the hypothermia/rewarming experiment. Heat shock pretreatment restored post-rewarming TF activity, protein levels and surface-to-total TF ratio in rat MNCs to normothermic levels. Furthermore, in heat shock-pretreated animals, rewarming from hypothermia failed to increase phosphorylated c-Jun and JNK levels. We attribute this to the profound overexpression of heat shock protein 70 and inhibition of JNK. Taken together, in our present study, we report an induction of TF activity, protein levels and redistribution of TF antigen to the surface of MNCs, isolated from rats rewarmed from hypothermia. This increase was counteracted by a full body heat shock 24 hours prior to hypothermia via suppression of hypothermia-induced activation of c-Jun.

The effects of hyperthermia and hypoxia on ventilation during low-intensity steady-state exercise

This study assessed whether the elevated sensitivity of ventilation to hypoxia during exercise is accounted for by an elevation of esophageal temperature (T(es)). Eleven males volunteered for two exercise sessions on an underwater, head-out cycle ergometer at a steady-state rate of oxygen consumption (V(.)(O(2))) of approximately 0.87 l/min (SD 0.07). In one exercise session, 31.5 degrees C (SD 1.4) water held T(es) at a normothermic level of approximately 37.1 degrees C, and in the other exercise session, water at 38.2 degrees C (SD 0.1) maintained a hyperthermic T(es) of approximately 38.5 degrees C. After a 30-min rest and 20-min warm-up, exercising participants inhaled air for 10 min [Euoxia 1 (E1)], an isocapnic hypoxic gas mixture with 12% O(2) in N(2) (H1) for the next 10 min and air again [Euoxia 2 (E2)] for the last 10 min. A significant increase in V(.)(E) during all hyperthermia conditions (0.01< P < 0.048) was evident; however, during hyperthermic hypoxia, there was a disproportionate and significant (P = 0.017) increase in V(.)(E) relative to normothermic hypoxia. This was the main explanation for a significant esophageal temperature and gas type interaction (P = 0.012) for V(.)(E). Significant effects of hyperthermia, isocapnic hypoxia, and their positive interaction remained evident after removing the influence of (V(.)(O(2))) on V(.)(E). Serum lactate and potassium concentrations, as well as hemoglobin oxygen saturation, were each not significantly different between normothermic and hyperthermic-hypoxic conditions. In conclusion, the elevated sensitivity of exercise ventilation to hypoxia during exertion appears to be modulated by elevations in esophageal temperature, potentially because of a temperature-mediated stimulation of the peripheral chemoreceptors.

Induction of Monocytic Tissue Factor Expression After Rewarming From Hypothermia In Vivo Is Counteracted by Heat Shock in c-Jun–Dependent Manner

Triggering of tissue factor (TF)-mediated blood coagulation leads to the development of disseminated intravascular coagulation during rewarming from hypothermia. We studied post-rewarming TF levels, activity, and surface redistribution, along with the regulation of TF gene transcription in mononuclear cells (MNCs) obtained from an in vivo rat model. Rewarming after a 5-hour episode of 15 degrees C hypothermia caused an increase in TF activity, protein levels, and externalization of TF antigen in rat MNCs. This was accompanied by a dramatic elevation of c-Jun and JNK phosphorylation, and the absence of EGR-1 and NF-kappaB activation. To search for a stimulus to counteract c-Jun-mediated induction of TF activity in MNCs from rewarmed rats, we applied heat shock pretreatment one day before the hypothermia/rewarming experiment. This restored post-rewarming TF activity, protein levels, and surface-to-total TF ratio in rat MNCs to normothermic levels. Furthermore, in heat shock-pretreated animals, rewarming failed to increase phosphorylated c-Jun and JNK levels. We attribute this to the profound overexpression of heat shock protein 70 and inhibition of JNK. MNCs respond to rewarming from hypothermia by an induction of active TF antigen. This effect is dependent on c-Jun activation and is abolished by heat shock pretreatment.

The Ginkgo biloba extract, EGb 761, fails to reduce brain infarct size in rats after transient, middle cerebral artery occlusion in conditions of unprevented, ischemia‐induced fever

There is much biochemical evidence, but very few studies in animal models of stroke in vivo, to suggest that Ginkgo biloba (EGb 761) may offer neuroprotection against regional, ischemic brain damage; additional investigations are needed to ensure future clinical trials. This study reports the effects of EGb 761 given acutely or chronically before ischemia. Rats were subjected to middle cerebral artery occlusion (MCAO) for 2 h and the brain infarct size was assessed 24 h later. Dipyrone (100 mg/kg, i.p.) was injected 30 min before ischemia, and 2.5 and 5.5 h after ischemia, to reduce ischemia-induced fever. EGb 761 (Tebonin) was given acutely (200 mg/kg, p.o., 60 min before ischemia) or chronically (100 mg/kg, p.o., once daily, for 14 days before ischemia). Acute or chronic treatment with EGb 761, either alone or in combination with dipyrone, did not reduce the infarct size compared with saline alone (p > 0.05). Dipyrone failed to prevent ischemia-induced fever during the intra-ischemic period (p > 0.05 vs saline; p < 0.001 vs sham). In the reperfusion phase, dipyrone reduced fever to normothermic levels in the group treated acutely with EGb 761 (p < 0.01 vs saline, p > 0.05 vs sham) but not after chronic EGb 761 (p < 0.01 vs sham), indicating possible pharmacokinetic interaction. In conclusion, within the context of unprevented, ischemia-induced fever, the present results demonstrate that EGb 761 has no significant effect on brain infarct size.

Hypothermia-induced respiratory arrest and recovery in neonatal rats.

To examine the changes in breathing that occur during progressive hypothermia and rewarming in neonatal rats, we cooled and rewarmed rat pups during the first 6 days of life. During cooling, breathing stopped when rectal temperature (Tr) fell below 10.7+/-0.24 degrees C, and recovered spontaneously during rewarming when Tr reached 13.3+/-0.38 degrees C, regardless of age. During cooling, breathing frequency declined progressively, whereas tidal volume increased until Tr fell below 15 degrees C whence it declined to, but never below, normothermic levels. These data support suggestions that failure occurs at the level of the central rhythm generator for breathing and is not due to an inability to sustain the level of motor output. During rewarming, following respiratory arrest, the pattern of change was reversed, but with a significant thermal hysteresis, resulting in slower breathing and cardiac frequencies at any given rectal temperature during rewarming. There were no effects of age observed over the range studied on the changes in respiratory variables associated with hypothermia or rewarming. Breathing restarted spontaneously on rewarming with no evidence that gasping was required to initiate this process. The overall breathing pattern was episodic during the early stages of rewarming, however, suggesting that the respiratory rhythm is only periodically expressed during the initial stages of recovery from hypothermia.

Posttraumatic hypothermia is neuroprotective in a model of traumatic brain injury complicated by a secondary hypoxic insult

Human traumatic brain injury frequently results in secondary complications, including hypoxia. In previous studies, we have reported that posttraumatic hypothermia is neuroprotective and that secondary hypoxia exacerbates histopathologic outcome after fluid-percussion brain injury. The purpose of this study was to assess the therapeutic effects of mild (33 degrees C) hypothermia after fluid-percussion injury combined with secondary hypoxia. In addition, the importance of the rewarming period on histopathologic outcome was investigated. Prospective experimental study in rats. Experimental laboratory in a university teaching hospital. Intubated, anesthetized rats underwent normothermic parasagittal fluid-percussion brain injury (1.8-2.1 atmospheres) followed by either 30 mins of normoxia (n = 6) or hypoxic (n = 6) gas levels and by 4 hrs of normothermia (37 degrees C). In hypothermic rats, brain temperature was reduced immediately after the 30-min hypoxic insult and maintained for 4 hrs. After hypothermia, brain temperature was either rapidly (n = 6) or slowly (n = 5) increased to normothermic levels. Rats were killed 3 days after traumatic brain injury, and contusion volumes were quantitatively assessed. As previously shown, posttraumatic hypoxia significantly increased contusion volume compared with traumatic brain injury-normoxic animals (p <.02). Importantly, although posttraumatic hypothermia followed by rapid rewarming (15 mins) failed to decrease contusion volume, those animals undergoing a slow rewarming period (120 mins) demonstrated significantly (p <.03) reduced contusion volumes, compared with hypoxic normothermic rats. These data emphasize the beneficial effects of posttraumatic hypothermia in a traumatic brain injury model complicated by secondary hypoxia and stress the importance of the rewarming period in this therapeutic intervention.

Exacerbation of traumatically induced axonal injury by rapid posthypothermic rewarming and attenuation of axonal change by cyclosporin A.

Although considerable attention has been focused on the use of posttraumatic hypothermia, little consideration has been given to the issue of posthypothermic rewarming and its potentially damaging consequences. In this communication, the authors examine the issue of rapid posthypothermic rewarming compared with gradual rewarming while exploring the potential utility of cyclosporin A (CsA) administration for attenuating any rapid rewarming-induced axonal change. Male Sprague-Dawley rats were subjected to impact-acceleration injury and then their body temperature was lowered to 32 degrees C for 1 hour postinjury. After hypothermia, rewarming to normothermic levels was accomplished either within a 20-minute period (rapid rewarming) or over a 90-minute period (slow rewarming). Some animals in the rapid rewarming group received intrathecal infusion of either CsA or its vehicle, whereas the rats in the slow rewarming group received vehicle alone. Both the CsA and its vehicle were administered immediately before initiation of rewarming. Twenty-four hours postinjury the animals' brains were processed for visualization of amyloid precursor protein (APP), a marker of traumatic axonal injury. The APP-positive axonal density in the gradually rewarmed group receiving vehicle was statistically significantly reduced in comparison with the rapidly rewarmed, vehicle-treated group. For the group undergoing rapid rewarming and treatment with CsA, a statistically significant reduction was also found in the density of the APP profiles compared with the rapidly rewarmed, vehicle-treated group. The results of this study show that rapid rewarming exacerbates traumatically induced axonal injury, which can be significantly attenuated by administering CsA.

Relative humidity at moderate ambient temperatures: Its effect on male broiler chickens and turkeys

1. The effect of relative humidity (RH, 40% to 75%) at moderate ambient temperatures (T a , 28° and 30°C) on the performance and thermoregulation of male broiler chickens and turkeys was studied at the age of 4 to 8 weeks. 2. Weight gain and food intake of male broiler chickens were significantly higher at 60% to 65% RH but food conversion efficiency was not affected by RH. In male turkeys, no effect of RH on performance was recorded. 3. Both chickens and turkeys controlled body temperature at normothermic levels during exposure to the experimental environmental conditions. 4. The rate of panting estimated from blood pH and p CO 2 was lower in chickens exposed to 28°C than to 30°C. In turkeys, the rate was lower than that recorded in chickens at both T a s. 5. Plasma T 3 was positively and significantly correlated with food intake. 6. It may be concluded that RH plays a role in the performance of chickens exposed to 30° and 28°C. whereas male turkeys must respond to RH at T a >30°C.

Moderate Posttraumatic Hypothermia Decreases Early Calpain-Mediated Proteolysis and Concomitant Cytoskeletal Compromise in Traumatic Axonal Injury

Traumatic brain injury (TBI) in animals and man generates widespread axonal injury characterized by focal axolemmal permeability changes, induction of calpain-mediated proteolysis, and neurofilament side-arm modification associated with neurofilament compaction (NFC) evolving to axonal disconnection. Recent observations have suggested that moderate hypothermia is neuroprotective in several models of TBI. Nevertheless, the pathway by which hypothermia prevents traumatic axonal injury (TAI) is still a matter of debate. The present study was conducted to evaluate the effects of moderate, early posttraumatic hypothermia on calpain-mediated spectrin proteolysis (CMSP), implicated in the pathogenesis of TAI. Using moderate (32°C) hypothermia of 90 min duration without rewarming, the density of CMSP immunoreactive/damaged axons was quantified via LM analysis in vulnerable brain stem fiber tracts of hypothermic and normothermic rats subjected to impact acceleration TBI (90 min postinjury survival). To assess the influence of posthypothermic rewarming, a second group of animals was subjected to 90 min of hypothermia followed by 90 min of rewarming to normothermic levels when CMSP was analyzed to detect if any purported CMSP prevention persisted (180 min postinjury survival). Additionally, to determine if this protection translated into comparable cytoskeletal protection in the same foci showing decreased CMSP, antibodies targeting altered/compacted NF subunits were also employed. Moderate hypothermia applied in the acute postinjury period drastically reduced the number of damaged axons displaying CMSP at both time points and significantly reduced NFC immunoreactivity at 180 min postinjury. These results suggest that the neuroprotective effects of hypothermia in TBI are associated with the inhibition of axonal/cytoskeletal damage.

Posttreatment with high-dose albumin reduces histopathological damage and improves neurological deficit following fluid percussion brain injury in rats.

We have recently shown that high-dose human serum albumin (HSA) therapy confers marked histological protection in experimental middle cerebral artery occlusion. Thus, the purpose of this study was to determine whether treatment with high-dose HSA would protect in a rat model of traumatic brain injury (TBI). Twenty-four hours prior to TBI, the fluid percussion interface was positioned parasagittally over the right cerebral cortex. On the following day, fasted rats were anesthetized with 3% halothane, 70% nitrous oxide, and 30% oxygen and received right parieto-occipital parasagittal fluid-percussion injury (1.5-2.0 atm). Cranial and rectal temperatures were monitored throughout the experiment and held at normothermic levels (36.5-37.5 degrees C) by a warming lamp above the animal's head. The agent (25% human serum albumin, HSA) or vehicle (sodium chloride 0.9%) was administered i.v. (1% of body weight) 15 min after trauma. Behavioral function was evaluated in all rats before and after TBI (at 2 h, 24 h, 48 h, 72 h, and 7 days). Neurological function was graded on a scale of 0-12 (normal score = 0; maximal score = 12). Seven days after TBI, brains were perfusion-fixed, coronal sections at various levels were digitized, and contusion areas in the superficial, middle and deep layers of cortex and in the underlying fimbria were measured. HSA significantly improved the neurological score compared to saline at 24 h, 72 h, and 7 days after TBI (6.0 +/- 0.6 [albumin] versus 8.4 +/- 0.5 [saline]; 3.6 +/- 0.7 versus 6.8 +/- 1.0; and 2.6 +/- 0.6 versus 5.7 +/- 0.8, respectively; p < 0.05). HSA therapy also significantly reduced total contusion area (0.89 +/- 0.2 versus 1.82 +/- 0.3 mm2; p = 0.02). Our findings document that high-concentration albumin therapy instituted 15 min after trauma significantly improves the neurological score and reduces histological damage. We believe that this pharmacological agent may have promising potential for the clinical treatment of brain injury.