Brain temperature fluctuations during physiological and pathological conditions

Characterisation of a microelectrochemical biosensor for real-time detection of brain extracellular d-serine

A modified development protocol and concomitant characterisation of a first generation biosensor for the detection of brain extracellular d-serine is reported. Functional parameters important for neurochemical monitoring, including sensor sensitivity, O2 interference, selectivity, shelf-life and biocompatibility were examined. Construction and development involved the enzyme d-amino acid oxidase (DAAO), utilising a dip-coating immobilisation method employing a new extended drying approach. The resultant Pt-based polymer enzyme composite sensor achieved high sensitivity to d-serine (0.76 ± 0.04 nA mm-2. μM-1) and a low μM limit of detection (0.33 ± 0.02 μM). The in-vitro response time was within the solution stirring time, suggesting potential sub-second in-vivo response characteristics. Oxygen interference studies demonstrated a 1 % reduction in current at 50 μM O2 when compared to atmospheric O2 levels (200 μM), indicating that the sensor can be used for reliable neurochemical monitoring of d-serine, free from changes in current associated with physiological O2 fluctuations. Potential interference signals generated by the principal electroactive analytes present in the brain were minimised by using a permselective layer of poly(o-phenylenediamine), and although several d-amino acids are possible substrates for DAAO, their physiologically relevant signals were small relative to that for d-serine. Additionally, changing both temperature and pH over possible in vivo ranges (34-40 °C and 7.2-7.6 respectively) resulted in no significant effect on performance. Finally, the biosensor was implanted in the striatum of freely moving rats and used to monitor physiological changes in d-serine over a two-week period.

Applications of flexible electronics related to cardiocerebral vascular system

Ensuring accessible and high-quality healthcare worldwide requires field-deployable and affordable clinical diagnostic tools with high performance. In recent years, flexible electronics with wearable and implantable capabilities have garnered significant attention from researchers, which functioned as vital clinical diagnostic-assisted tools by real-time signal transmission from interested targets in vivo. As the most crucial and complex system of human body, cardiocerebral vascular system together with heart-brain network attracts researchers inputting profuse and indefatigable efforts on proper flexible electronics design and materials selection, trying to overcome the impassable gulf between vivid organisms and rigid inorganic units. This article reviews recent breakthroughs in flexible electronics specifically applied to cardiocerebral vascular system and heart-brain network. Relevant sensor types and working principles, electronics materials selection and treatment methods are expounded. Applications of flexible electronics related to these interested organs and systems are specially highlighted. Through precedent great working studies, we conclude their merits and point out some limitations in this emerging field, thus will help to pave the way for revolutionary flexible electronics and diagnosis assisted tools development.

Determinants of body core temperatures at fatigue in rats subjected to incremental-speed exercise: The prominent roles of ambient temperature, distance traveled, initial core temperature, and measurement site

Understanding the factors that underlie the physical exercise-induced increase in body core temperature (T_CORE) is essential to developing strategies to counteract hyperthermic fatigue and reduce the risk of exertional heatstroke. This study analyzed the contribution of six factors to T_CORE attained at fatigue in Wistar rats (n = 218) subjected to incremental-speed treadmill running: ambient temperature (T_AMB), distance traveled, initial T_CORE, body mass, measurement site, and heat loss index (HLI). First, we ran hierarchical multiple linear regression analyses with data from different studies conducted in our laboratory (n = 353 recordings). We observed that T_AMB, distance traveled, initial T_CORE, and measurement site were the variables with predictive power. Next, regression analyses were conducted with data for each of the following T_CORE indices: abdominal (T_ABD), brain cortex (T_BRAIN), or colonic (T_COL) temperature. Our findings indicated that T_AMB, distance traveled (i.e., an exercise performance-related variable), initial T_CORE, and HLI predicted the three T_CORE indices at fatigue. Most intriguingly, HLI was inversely related to T_ABD and T_BRAIN but positively associated with T_COL. Lastly, we compared the temperature values at fatigue among these T_CORE indices, and the following descendent order was noticed - T_COL, T_ABD, and T_BRAIN - irrespective of T_AMB where experiments were conducted. In conclusion, T_CORE in rats exercised to fatigue depends primarily on environmental conditions, performance, pre-exercise T_CORE, and measurement site. Moreover, the influence of cutaneous heat loss on T_COL is qualitatively different from the influence on T_ABD and T_BRAIN, and the temperature values at fatigue are not homogenous within the body core.

Heatwave and mental health

Physical health has been associated with ambient temperature and heatwave. With the frequent occurrence of heatwave, the adaptive effects and mechanisms on mental health remain uncertain. On the basis of the China Health and Nutrition Survey, we estimated the relationship between heatwaves and self-assessed mental health scores in the Chinese population aged 50 and above. This study has identified that with each additional heatwave event, mental health scores decreased by an average of 0.027 points, which is equivalent to 0.3% of the average level. Heat is more likely to affect groups with low education, no medical insurance, and living in rural areas. In mechanistic exploration, we found that stress emotion is a fully mediating effect. Heat led to reduced health activities and more frequent drinking, which may lead to lower psychological well-being. Moreover, good dietary preference is a regulator that can help mitigate the adverse effects of heat on mental health. This study corroborates the impact of heat on spiritual welfare, and demonstrates the mechanisms and channels of impact, which can help reduce global economic losses due to mental health problems.

Nanowired Delivery of Mesenchymal Stem Cells with Antioxidant Compound H-290/51 Reduces Exacerbation of Methamphetamine Neurotoxicity in Hot Environment

Military personnel are often exposed to hot environments either for combat operations or peacekeeping missions. Hot environment is a severe stressful situation leading to profound hyperthermia, fatigue and neurological impairments. To avoid stressful environment, some people frequently use methamphetamine (METH) or other psychostimulants to feel comfortable under adverse situations. Our studies show that heat stress alone induces breakdown of the blood-brain barrier (BBB) and edema formation associated with reduced cerebral blood flow (CBF). On the other hand, METH alone induces hyperthermia and neurotoxicity. These effects of METH are exacerbated at high ambient temperatures as seen with greater breakdown of the BBB and brain pathology. Thus, a combination of METH use at hot environment may further enhance the brain damage-associated behavioral dysfunctions. METH is well known to induce severe oxidative stress leading to brain pathology. In this investigation, METH intoxication at hot environment was examined on brain pathology and to explore suitable strategies to induce neuroprotection. Accordingly, TiO₂-nanowired delivery of H-290/51 (150 mg/kg, i.p.), a potent chain-breaking antioxidant in combination with mesenchymal stem cells (MSCs), is investigated in attenuating METH-induced brain damage at hot environment in model experiments. Our results show that nanodelivery of H-290/51 with MSCs significantly enhanced CBF and reduced BBB breakdown, edema formation and brain pathology following METH exposure at hot environment. These observations are the first to point out that METH exacerbated brain pathology at hot environment probably due to enhanced oxidative stress, and MSCs attenuate these adverse effects, not reported earlier.

Invention of a non-invasive intracranial pressure (ICP) monitoring system - an enlightenment from a hydrocephalus study

BACKGROUND

Mechanical obstruction is the most common cause of shunt failure for hydrocephalic patients. However, the diagnosis is extremely challenging and often requires invasive testing methods. Thus, a simple and non-invasive technique is in urgent need to predict the intracranial pressure (ICP) of hydrocephalic patients during their post-surgical follow-up, which could help neurosurgeons to determine the conditions of the shunt system.

MATERIALS AND METHODS

Two groups of patients were enrolled in the current study. In group I, patients were enrolled as they were diagnosed with high ICP hydrocephalus and received shunt surgery. The shunt valve pressures were taken for their post-surgical ICP. Meanwhile, the participants of group II exhibited abnormally increased lumbar puncture opening pressure (LPOP; from 180 to 400 mmH₂O). Both the ICP and LPOP were used to match with their corresponding tympanic membrane temperature (TMT).

RESULTS

When patients' ICP were in the normal range (group I, from 50 to 180 mmH₂O), the TMT correlated with ICP in a linear regression model (R² = 0.59, p < 0.001). Interestingly, when patients exhibited above-normal ICP (LPOP was from 180 to 400 mmH₂O), their TMT fit well with the ICP in a third-order polynomial regression (R² = 0.88). When the ICP was 287.98 mmH₂O, the TMT approached the vertex, which was 38.54 °C. Based on this TMT-ICP algorithm, we invented a non-invasive ICP monitor system. Interestingly, a tight linear correlation was detected between the ICP data drawn from the non-invasive device and Codman ICP monitoring system (R² = 0.93, p < 0.01).

CONCLUSIONS

We believe the TMT-ICP algorithm (the Y-Jiang model) could be used for preliminary prediction of shunt malfunction as well as monitoring ICP changes.

The Effects of Temperature Management on Brain Microcirculation, Oxygenation and Metabolism

Purpose: Target temperature management (TTM) is often used in patients after cardiac arrest, but the effects of cooling on cerebral microcirculation, oxygenation and metabolism are poorly understood. We studied the time course of these variables in a healthy swine model.Methods: Fifteen invasively monitored, mechanically ventilated pigs were allocated to sham procedure (normothermia, NT; n = 5), cooling (hypothermia, HT, n = 5) or cooling with controlled oxygenation (HT-Oxy, n = 5). Cooling was induced by cold intravenous saline infusion, ice packs and nasal cooling to achieve a body temperature of 33–35 °C. After 6 h, animals were rewarmed to baseline temperature (within 5 h). The cerebral microvascular network was evaluated (at baseline and 2, 7 and 12 h thereafter) using sidestream dark-field (SDF) video-microscopy. Cerebral blood flow (laser Doppler MNP100XP, Oxyflow, Oxford Optronix, Oxford, UK), oxygenation (PbtO₂, Licox catheter, Integra Lifesciences, USA) and lactate/pyruvate ratio (LPR) using brain microdialysis (CMA, Stockholm, Sweden) were measured hourly. Results: In HT animals, cerebral functional capillary density (FCD) and proportion of small-perfused vessels (PSPV) significantly decreased over time during the cooling phase; concomitantly, PbtO₂ increased and LPR decreased. After rewarming, all microcirculatory variables returned to normal values, except LPR, which increased during the rewarming phase in the two groups subjected to HT when compared to the group maintained at normothermia. Conclusions: In healthy animals, TTM can be associated with alterations in cerebral microcirculation during cooling and altered metabolism at rewarming.

Core body temperatures of rats subjected to treadmill exercise to fatigue or exhaustion: The journal Temperature toolbox

This study systematically reviewed the literature reporting the changes in rats' core body temperature (TCORE) induced by either incremental- or constant-speed running to fatigue or exhaustion. In addition, multiple linear regression analyses were used to determine the factors contributing to the TCORE values attained when exercise was interrupted. Four databases (EMBASE, PubMed, SPORTDiscus, and Web of Science) were searched in October 2021, and this search was updated in August 2022. Seventy-two studies (n = 1,538 rats) were included in the systematic review. These studies described heterogeneous experimental conditions; for example, the ambient temperature ranged from 5 to 40°C. The rats quit exercising with TCORE values varying more than 8°C among studies, with the lowest and highest values corresponding to 34.9°C and 43.4°C, respectively. Multiple linear regression analyses indicated that the ambient temperature (p < 0.001), initial TCORE (p < 0.001), distance traveled (p < 0.001; only incremental exercises), and running speed and duration (p < 0.001; only constant exercises) contributed significantly to explaining the variance in the TCORE at the end of the exercise. In conclusion, rats subjected to treadmill running exhibit heterogeneous TCORE when fatigued or exhausted. Moreover, it is not possible to determine a narrow range of TCORE associated with exercise cessation in hyperthermic rats. Ambient temperature, initial TCORE, and physical performance-related variables are the best predictors of TCORE at fatigue or exhaustion. From a broader perspective, this systematic review provides relevant information for selecting appropriate methods in future studies designed to investigate exercise thermoregulation in rats.

Luminescence Thermometry for Brain Activity Monitoring: A Perspective

Minimally invasive monitoring of brain activity is essential not only to gain understanding on the working principles of the brain, but also for the development of new diagnostic tools. In this perspective we describe how brain thermometry could be an alternative to conventional methods (e.g., magnetic resonance or nuclear medicine) for the acquisition of thermal images of the brain with enough spatial and temperature resolution to track brain activity in minimally perturbed animals. We focus on the latest advances in transcranial luminescence thermometry introducing a critical discussion on its advantages and shortcomings. We also anticipate the main challenges that the application of luminescent nanoparticles for brain thermometry will face in next years. With this work we aim to promote the development of near infrared luminescence for brain activity monitoring, which could also benefit other research areas dealing with the brain and its illnesses.

Suicide disparities across metropolitan areas in the US: A comparative assessment of socio-environmental factors using a data-driven predictive approach

Disparity in suicide rates across various metropolitan areas in the US is growing. Besides personal genomics and pre-existing mental health conditions affecting individual-level suicidal behaviors, contextual factors are also instrumental in determining region-/community-level suicide risk. However, there is a lack of quantitative approach to model the complex associations and interplays of the socio-environmental factors with the regional suicide rates. In this paper, we propose a holistic data-driven framework to model the associations of socio-environmental factors (demographic, socio-economic, and climate) with the suicide rates, and compare the key socio-environmental determinants of suicides across the large and medium/small metros of the vulnerable US states, leveraging a suite of advanced statistical learning algorithms. We found that random forest outperforms all the other models in terms of both in-sample goodness-of-fit and out-of-sample predictive accuracy, which is then used for statistical inferencing. Overall, our findings show that there is a significant difference in the relationships of socio-environmental factors with the suicide rates across the large and medium/small metropolitan areas of the vulnerable US states. Particularly, suicides in medium/small metros are more sensitive to socio-economic and demographic factors, while that in large metros are more sensitive to climatic factors. Our results also indicate that non-Hispanics, native Hawaiian or Pacific islanders, and adolescents aged 15-29 years, residing in the large metropolitan areas, are more vulnerable to suicides compared to those living in the medium/small metropolitan areas. We also observe that higher temperatures are positively associated with higher suicide rates, with large metros being more sensitive to such association compared to that of the medium/small metros. Our proposed data-driven framework underscores the future opportunities of using big data analytics in analyzing the complex associations of socio-environmental factors and inform policy actions accordingly.

Kinetics of protein aggregation at a temperature gradient condition

The unconventional multi-sigmoidal kinetic behaviour of protein aggregation at a temperature gradient condition is reported in this study. To establish a feasible theory for protein aggregation kinetics at a temperature gradient condition, the spatial height of the protein solution is divided into hypothetical layers and the kinetic equations in those layers are solved. Furthermore, we endeavour to study numerically the effect of the temperature gradient on the kinetics of oligomer-mediated protein aggregation and protein inhibition.

The interplay of neurovasculature and adult hippocampal neurogenesis

The subgranular zone of the dentate gyrus provides a local microenvironment (niche) for neural stem cells. In the adult brain, it has been established that the vascular compartment of such niches has a significant role in regulating adult hippocampal neurogenesis. More recently, evidence showed that neurovascular coupling, the relationship between blood flow and neuronal activity, also regulates hippocampal neurogenesis. Here, we review the most recent articles on addressing the intricate relationship between neurovasculature and adult hippocampal neurogenesis and a novel pathway where functional hyperemia enhances hippocampal neurogenesis. In the end, we have further reviewed recent research showing that impaired neurovascular coupling may cause declined neurogenesis and contribute to brain damage in neurodegenerative diseases.

Brain temperature regulation in poor-grade subarachnoid hemorrhage patients - A multimodal neuromonitoring study

Elevated body temperature (T_core) is associated with poor outcome after subarachnoid hemorrhage (SAH). Brain temperature (T_brain) is usually higher than T_core. However, the implication of this difference (T_delta) remains unclear. We aimed to study factors associated with higher T_delta and its association with outcome. We included 46 SAH patients undergoing multimodal neuromonitoring, for a total of 7879 h of averaged data of T_core, T_brain, cerebral blood flow, cerebral perfusion pressure, intracranial pressure and cerebral metabolism (CMD). Three-months good functional outcome was defined as modified Rankin Scale ≤2. T_brain was tightly correlated with T_core (r = 0.948, p < 0.01), and was higher in 73.7% of neuromonitoring time (T_delta +0.18°C, IQR -0.01 - 0.37°C). A higher T_delta was associated with better metabolic state, indicated by lower CMD-glutamate (p = 0.003) and CMD-lactate (p < 0.001), and lower risk of mitochondrial dysfunction (MD) (OR = 0.2, p < 0.001). During MD, T_delta was significantly lower (0°C, IQR -0.2 - 0.1; p < 0.001). A higher T_delta was associated with improved outcome (OR = 7.7, p = 0.002). Our study suggests that T_brain is associated with brain metabolic activity and exceeds T_core when mitochondrial function is preserved. Further studies are needed to understand how T_delta may serve as a surrogate marker for brain function and predict clinical course and outcome after SAH.

Effects of Cortical Cooling on Activity Across Layers of the Rat Barrel Cortex

Moderate cortical cooling is known to suppress slow oscillations and to evoke persistent cortical activity. However, the cooling-induced changes in electrical activity across cortical layers remain largely unknown. Here, we performed multi-channel local field potential (LFP) and multi-unit activity (MUA) recordings with linear silicone probes through the layers of single cortical barrel columns in urethane-anesthetized rats under normothermia (38°C) and during local cortical surface cooling (30°C). During cortically generated slow oscillations, moderate cortical cooling decreased delta wave amplitude, delta-wave occurrence, the duration of silent states, and delta wave-locked MUA synchronization. Moderate cortical cooling increased total time spent in the active state and decreased total time spent in the silent state. Cooling-evoked changes in the MUA firing rate in cortical layer 5 (L5) varied from increase to decrease across animals, and the polarity of changes in L5 MUA correlated with changes in total time spent in the active state. The decrease in temperature reduced MUA firing rates in all other cortical layers. Sensory-evoked MUA responses also decreased during cooling through all cortical layers. The cooling-dependent slowdown was detected at the fast time-scale with a decreased frequency of sensory-evoked high-frequency oscillations (HFO). Thus, moderate cortical cooling suppresses slow oscillations and desynchronizes neuronal activity through all cortical layers, and is associated with reduced firing across all cortical layers except L5, where cooling induces variable and non-consistent changes in neuronal firing, which are common features of the transition from slow-wave synchronization to desynchronized activity in the barrel cortex.

Hyperthermia exacerbates the acute effects of psychoactive substances on neuronal activity measured using microelectrode arrays (MEAs) in rat primary cortical cultures in vitro

Hyperthermia is a well-known, potentially life-threatening, side effect of stimulant psychoactive substances that worsens the neurological outcome of hospitalized patients. However, current in vitro methods to assess the hazard of psychoactive substances do not account for hyperthermia. Therefore, this study determined the potency of five psychoactive substances (cocaine, MDMA (3,4-methylenedioxymethamphetamine), methamphetamine, 3-MMC (3-methylmethcathinone) and TFMPP (3-trifluoromethylphenylpiperazine)) to affect neuronal activity at physiological and hyperthermic conditions. Neuronal activity of rat cortical cultures grown on microelectrode arrays (MEAs) was recorded at 37 °C before exposure. Following 30 min and 4.5 h drug exposure (1-1000 μM) at 37 °C or 41 °C, neuronal activity was measured at either 37 °C or 41 °C. Without drug exposure, hyperthermia induced a modest decrease in neuronal activity. Following acute (30 min) exposure at 37 °C, all drugs concentration-dependently inhibited neuronal activity. Increasing the temperature to 41 °C significantly exacerbated the reduction of neuronal activity ~ 2-fold for all drugs compared to 37 °C. Prolonged (4.5 h) exposure at 41 °C decreased neuronal activity comparable to 37 °C. Neuronal activity (partly) recovered following drug exposure at both temperatures, although recovery from exposure at 41 °C was less pronounced for most drugs. None of the exposure conditions affected viability. Since acute exposure at hyperthermic conditions exacerbates the decrease in neuronal activity induced by psychoactive substances, effects of hyperthermia should be included in future hazard assessment of illicit drugs and new psychoactive substances (NPS).

Imaging the effect of the circadian light-dark cycle on the glymphatic system in awake rats

Homeostasis and the daily rhythms in brain function and temperature are coupled to the circadian light–dark cycle. MRI was used to study the redistribution of intraventricular contrast agent in awake rats during the night when they are active and during the day when at rest. Redistribution is lowest during the day and highest at night and parallels the gradients and regional variations in brain temperatures reported in the literature. The brain areas of low parenchymal redistribution are associated with high temperatures and have a high density of blood vessels that may be an essential part of the organization of the glymphatic system regulating brain temperature, blood gases, nutrients, metabolites, and waste products over the light–dark cycle.

The glymphatic system functions in the removal of potentially harmful metabolites and proteins from the brain. Dynamic, contrast-enhanced MRI was used in fully awake rats to follow the redistribution of intraventricular contrast agent entrained to the light–dark cycle and its hypothetical relationship to the sleep–waking cycle, blood flow, and brain temperature in specific brain areas. Brain areas involved in circadian timing and sleep–wake rhythms showed the lowest redistribution of contrast agent during the light phase or time of inactivity and sleep in rats. Global brain redistribution of contrast agent was heterogeneous. The redistribution was highest along the dorsal cerebrum and lowest in the midbrain/pons and along the ventral surface of the brain. This heterogeneous redistribution of contrast agent paralleled the gradients and regional variations in brain temperatures reported in the literature for awake animals. Three-dimensional quantitative ultrashort time-to-echo contrast-enhanced imaging was used to reconstruct small, medium, and large arteries and veins in the rat brain and revealed areas of lowest redistribution overlapped with this macrovasculature. This study raises new questions and theoretical considerations of the impact of the light–dark cycle, brain temperature, and blood flow on the function of the glymphatic system.

Temperature Rise under Two-Photon Optogenetic Brain Stimulation

In recent decades, optogenetics has been transforming neuroscience research, enabling neuroscientists to drive and read neural circuits. The recent development in illumination approaches combined with two-photon (2P) excitation, either sequential or parallel, has opened the route for brain circuit manipulation with single-cell resolution and millisecond temporal precision. Yet, the high excitation power required for multi-target photostimulation, especially under 2P illumination, raises questions about the induced local heating inside samples. Here, we present and experimentally validate a theoretical model that makes it possible to simulate 3D light propagation and heat diffusion in optically scattering samples at high spatial and temporal resolution under the illumination configurations most commonly used to perform 2P optogenetics: single- and multi-spot holographic illumination and spiral laser scanning. By investigating the effects of photostimulation repetition rate, spot spacing, and illumination dependence of heat diffusion, we found conditions that make it possible to design a multi-target 2P optogenetics experiment with minimal sample heating.

Arterial CO2 Fluctuations Modulate Neuronal Rhythmicity: Implications for MEG and fMRI Studies of Resting-State Networks

A fast emerging technique for studying human resting state networks (RSNs) is based on spontaneous temporal fluctuations in neuronal oscillatory power, as measured by magnetoencephalography. However, it has been demonstrated recently that this power is sensitive to modulations in arterial CO₂ concentration. Arterial CO₂ can be modulated by natural fluctuations in breathing pattern, as might typically occur during the acquisition of an RSN experiment. Here, we demonstrate for the first time the fine-scale dependence of neuronal oscillatory power on arterial CO₂ concentration, showing that reductions in alpha, beta, and gamma power are observed with even very mild levels of hypercapnia (increased arterial CO₂). We use a graded hypercapnia paradigm and participant feedback to rule out a sensory cause, suggesting a predominantly physiological origin. Furthermore, we demonstrate that natural fluctuations in arterial CO₂, without administration of inspired CO₂, are of a sufficient level to influence neuronal oscillatory power significantly in the delta-, alpha-, beta-, and gamma-frequency bands. A more thorough understanding of the relationship between physiological factors and cortical rhythmicity is required. In light of these findings, existing results, paradigms, and analysis techniques for the study of resting-state brain data should be revisited.

SIGNIFICANCE STATEMENT In this study, we show for the first time that neuronal oscillatory power is intimately linked to arterial CO₂ concentration down to the fine-scale modulations that occur during spontaneous breathing. We extend these results to demonstrate a correlation between neuronal oscillatory power and spontaneous arterial CO₂ fluctuations in awake humans at rest. This work identifies a need for studies investigating resting-state networks in the human brain to measure and account for the impact of spontaneous changes in arterial CO₂ on the neuronal signals of interest. Changes in breathing pattern that are time locked to task performance could also lead to confounding effects on neuronal oscillatory power when considering the electrophysiological response to functional stimulation.

Brain heating induced by near-infrared lasers during multiphoton microscopy

Two-photon imaging and optogenetic stimulation rely on high illumination powers, particularly for state-of-the-art applications that target deeper structures, achieve faster measurements, or probe larger brain areas. However, little information is available on heating and resulting damage induced by high-power illumination in the brain. In the current study we used thermocouple probes and quantum dot nanothermometers to measure temperature changes induced by two-photon microscopy in the neocortex of awake and anaesthetized mice. We characterized heating as a function of wavelength, exposure time, and distance from the center of illumination. Although total power is highest near the surface of the brain, heating was most severe hundreds of micrometers below the focal plane, due to heat dissipation through the cranial window. Continuous illumination of a 1-mm(2) area produced a peak temperature increase of ∼1.8°C/100 mW. Continuous illumination with powers above 250 mW induced lasting damage, detected with immunohistochemistry against Iba1, glial fibrillary acidic protein, heat shock proteins, and activated caspase-3. Higher powers were usable in experiments with limited duty ratios, suggesting an approach to mitigate damage in high-power microscopy experiments.

Brain Temperature in Spontaneously Hypertensive Rats during Physical Exercise in Temperate and Warm Environments

This study aimed to evaluate brain temperature (Tbrain) changes in spontaneously hypertensive rats (SHRs) subjected to two different physical exercise protocols in temperate or warm environments. We also investigated whether hypertension affects the kinetics of exercise-induced increases in Tbrain relative to the kinetics of abdominal temperature (Tabd) increases. Male 16-week-old normotensive Wistar rats (NWRs) and SHRs were implanted with an abdominal temperature sensor and a guide cannula in the frontal cortex to enable the insertion of a thermistor to measure Tbrain. Next, the animals were subjected to incremental-speed (initial speed of 10 m/min; speed was increased by 1 m/min every 3 min) or constant-speed (60% of the maximum speed) treadmill running until they were fatigued in a temperate (25°C) or warm (32°C) environment. Tbrain, Tabd and tail skin temperature were measured every min throughout the exercise trials. During incremental and constant exercise at 25°C and 32°C, the SHR group exhibited greater increases in Tbrain and Tabd relative to the NWR group. Irrespective of the environment, the heat loss threshold was attained at higher temperatures (either Tbrain or Tabd) in the SHRs. Moreover, the brain-abdominal temperature differential was lower at 32°C in the SHRs than in the NWRs during treadmill running. Overall, we conclude that SHRs exhibit enhanced brain hyperthermia during exercise and that hypertension influences the kinetics of the Tbrain relative to the Tabd increases, particularly during exercise in a warm environment.

Thermoregulatory responses in exercising rats: methodological aspects and relevance to human physiology

Rats are used worldwide in experiments that aim to investigate the physiological responses induced by a physical exercise session. Changes in body temperature regulation, which may affect both the performance and the health of exercising rats, are evident among these physiological responses. Despite the universal use of rats in biomedical research involving exercise, investigators often overlook important methodological issues that hamper the accurate measurement of clear thermoregulatory responses. Moreover, much debate exists regarding whether the outcome of rat experiments can be extrapolated to human physiology, including thermal physiology. Herein, we described the impact of different exercise intensities, durations and protocols and environmental conditions on running-induced thermoregulatory changes. We focused on treadmill running because this type of exercise allows for precise control of the exercise intensity and the measurement of autonomic thermoeffectors associated with heat production and loss. Some methodological issues regarding rat experiments, such as the sites for body temperature measurements and the time of day at which experiments are performed, were also discussed. In addition, we analyzed the influence of a high body surface area-to-mass ratio and limited evaporative cooling on the exercise-induced thermoregulatory responses of running rats and then compared these responses in rats to those observed in humans. Collectively, the data presented in this review represent a reference source for investigators interested in studying exercise thermoregulation in rats. In addition, the present data indicate that the thermoregulatory responses of exercising rats can be extrapolated, with some important limitations, to human thermal physiology.

Brief anesthesia, but not voluntary locomotion, significantly alters cortical temperature

Changes in brain temperature can alter electrical properties of neurons and cause changes in behavior. However, it is not well understood how behaviors, like locomotion, or experimental manipulations, like anesthesia, alter brain temperature. We implanted thermocouples in sensorimotor cortex of mice to understand how cortical temperature was affected by locomotion, as well as by brief and prolonged anesthesia. Voluntary locomotion induced small (∼ 0.1 °C) but reliable increases in cortical temperature that could be described using a linear convolution model. In contrast, brief (90-s) exposure to isoflurane anesthesia depressed cortical temperature by ∼ 2 °C, which lasted for up to 30 min after the cessation of anesthesia. Cortical temperature decreases were not accompanied by a concomitant decrease in the γ-band local field potential power, multiunit firing rate, or locomotion behavior, which all returned to baseline within a few minutes after the cessation of anesthesia. In anesthetized animals where core body temperature was kept constant, cortical temperature was still > 1 °C lower than in the awake animal. Thermocouples implanted in the subcortex showed similar temperature changes under anesthesia, suggesting these responses occur throughout the brain. Two-photon microscopy of individual blood vessel dynamics following brief isoflurane exposure revealed a large increase in vessel diameter that ceased before the brain temperature significantly decreased, indicating cerebral heat loss was not due to increased cerebral blood vessel dilation. These data should be considered in experimental designs recording in anesthetized preparations, computational models relating temperature and neural activity, and awake-behaving methods that require brief anesthesia before experimental procedures.

Proton resonance frequency chemical shift thermometry: experimental design and validation toward high-resolution noninvasive temperature monitoring and in vivo experience in a nonhuman primate model of acute ischemic stroke

BACKGROUND AND PURPOSE

Applications for noninvasive biologic temperature monitoring are widespread in biomedicine and of particular interest in the context of brain temperature regulation, where traditionally costly and invasive monitoring schemes limit their applicability in many settings. Brain thermal regulation, therefore, remains controversial, motivating the development of noninvasive approaches such as temperature-sensitive nuclear MR phenomena. The purpose of this work was to compare the utility of competing approaches to MR thermometry by using proton resonance frequency chemical shift. We tested 3 methodologies, hypothesizing the feasibility of a fast and accurate approach to chemical shift thermometry, in a phantom study at 3T.

MATERIALS AND METHODS

A conventional, paired approach (difference [DIFF]-1), an accelerated single-scan approach (DIFF-2), and a new, further accelerated strategy (DIFF-3) were tested. Phantom temperatures were modulated during real-time fiber optic temperature monitoring, with MR thermometry derived simultaneously from temperature-sensitive changes in the water proton chemical shift (∼0.01 ppm/°C). MR thermometry was subsequently performed in a series of in vivo nonhuman primate experiments under physiologic and ischemic conditions, testing its reproducibility and overall performance.

RESULTS

Chemical shift thermometry demonstrated excellent agreement with phantom temperatures for all 3 approaches (DIFF-1: linear regression R(2) = 0.994; P < .001; acquisition time = 4 minutes 40 seconds; DIFF-2: R(2) = 0.996; P < .001; acquisition time = 4 minutes; DIFF-3: R(2) = 0.998; P < .001; acquisition time = 40 seconds).

CONCLUSIONS

These findings confirm the comparability in performance of 3 competing approaches to MR thermometry and present in vivo applications under physiologic and ischemic conditions in a primate stroke model.

Hypothalamic temperature of rats subjected to treadmill running in a cold environment

Different strategies for cooling the body prior to or during physical exercise have been shown to improve prolonged performance. Because of ethical and methodological issues, no studies conducted in humans have evaluated the changes in brain temperature promoted by cooling strategies. Therefore, our first aim sought to measure the hypothalamic temperature (T_hyp) of rats subjected to treadmill running in a cold environment. Moreover, evidence suggests that T_hyp and abdominal temperature (T_abd) are regulated by different physiological mechanisms. Thus, this study also investigated the dynamics of exercise-induced changes in T_hyp and T_abd at two ambient temperatures: 25°C (temperate environment) and 12°C (cold). Adult male Wistar rats were used in these experiments. The rats were implanted with a guide cannula in the hypothalamus and a temperature sensor in the abdominal cavity. After recovery from this surgery, the rats were familiarized with running on a treadmill and were then subjected to the two experimental trials: constant-speed running (20 m/min) at 12°C and 25°C. Both T_hyp and T_abd increased during exercise at 25°C. In contrast, T_hyp and T_abd remained unchanged during fatiguing exercise at 12°C. The temperature differential (i.e., T_hyp - T_abd) increased during the initial min of running at 25°C and thereafter decreased toward pre-exercise values. Interestingly, external cooling prevented this early increase in the temperature differential from the 2^nd to the 8^th min of running. In addition, the time until volitional fatigue was higher during the constant exercise at 12°C compared with 25°C. Together, our results indicate that T_hyp and T_abd are regulated by different mechanisms in running rats and that external cooling affected the relationship between both temperature indexes observed during exercise without environmental thermal stress. Our data also suggest that attenuated hypothalamic hyperthermia may contribute to improved performance in cold environments.

Basal ganglia function, stuttering, sequencing, and repair in adult songbirds

A pallial-basal-ganglia-thalamic-pallial loop in songbirds is involved in vocal motor learning. Damage to its basal ganglia part, Area X, in adult zebra finches has been noted to have no strong effects on song and its function is unclear. Here we report that neurotoxic damage to adult Area X induced changes in singing tempo and global syllable sequencing in all animals, and considerably increased syllable repetition in birds whose song motifs ended with minor repetitions before lesioning. This stuttering-like behavior started at one month, and improved over six months. Unexpectedly, the lesioned region showed considerable recovery, including immigration of newly generated or repaired neurons that became active during singing. The timing of the recovery and stuttering suggest that immature recovering activity of the circuit might be associated with stuttering. These findings indicate that even after juvenile learning is complete, the adult striatum plays a role in higher level organization of learned vocalizations.

Association between the increase in brain temperature and physical performance at different exercise intensities and protocols in a temperate environment

There is evidence that brain temperature (T_brain) provides a more sensitive index than other core body temperatures in determining physical performance. However, no study has addressed whether the association between performance and increases in T_brain in a temperate environment is dependent upon exercise intensity, and this was the primary aim of the present study. Adult male Wistar rats were subjected to constant exercise at three different speeds (18, 21, and 24 m/min) until the onset of volitional fatigue. T_brain was continuously measured by a thermistor inserted through a brain guide cannula. Exercise induced a speed-dependent increase in T_brain, with the fastest speed associated with a higher rate of T_brain increase. Rats subjected to constant exercise had similar T_brain values at the time of fatigue, although a pronounced individual variability was observed (38.7-41.7°C). There were negative correlations between the rate of T_brain increase and performance for all speeds that were studied. These results indicate that performance during constant exercise is negatively associated with the increase in T_brain, particularly with its rate of increase. We then investigated how an incremental-speed protocol affected the association between the increase in T_brain and performance. At volitional fatigue, T_brain was lower during incremental exercise compared with the T_brain resulting from constant exercise (39.3±0.3 vs 40.3±0.1°C; P<0.05), and no association between the rate of T_brain increase and performance was observed. These findings suggest that the influence of T_brain on performance under temperate conditions is dependent on exercise protocol.

Methamphetamine-induced toxicity: an updated review on issues related to hyperthermia

Reports of methamphetamine-related emergency room visits suggest that elevated body temperature is a universal presenting symptom, with lethal overdoses generally associated with extreme hyperthermia. This review summarizes the available information on methamphetamine toxicity as it pertains to elevations in body temperature. First, a brief overview of thermoregulatory mechanisms is presented. Next, central and peripheral targets that have been considered for potential involvement in methamphetamine hyperthermia are discussed. Finally, future areas of investigation are proposed, as further studies are needed to provide greater insight into the mechanisms that mediate the alterations in body temperature elicited by methamphetamine.

Constancy and trade-offs in the neuroanatomical and metabolic design of the cerebral cortex

Mammalian brains span about four orders of magnitude in cortical volume and have to operate in different environments that require diverse behavioral skills. Despite these geometric and behavioral diversities, the examination of cerebral cortex across species reveals that it contains a substantial number of conserved characteristics that are associated with neuroanatomy and metabolism, i.e., with neuronal connectivity and function. Some of these cortical constants or invariants have been known for a long time but not sufficiently appreciated, and others were only recently discovered. The focus of this review is to present the cortical invariants and discuss their role in the efficient information processing. Global conservation in neuroanatomy and metabolism, as well as their correlated regional and developmental variability suggest that these two parallel systems are mutually coupled. It is argued that energetic constraint on cortical organization can be strong if cerebral blood supplied is either below or above a certain level, and it is rather soft otherwise. Moreover, because maximization or minimization of parameters associated with cortical connectivity, function and cost often leads to conflicts in design, it is argued that the architecture of the cerebral cortex is a result of structural and functional compromises.

In vivo three-dimensional molecular imaging with Biosensor Imaging of Redundant Deviation in Shifts (BIRDS) at high spatiotemporal resolution

Spectroscopic signals which emanate from complexes between paramagnetic lanthanide (III) ions (e.g. Tm(3+)) and macrocyclic chelates (e.g. 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate, or DOTMA(4-)) are sensitive to physiology (e.g. temperature). Because nonexchanging protons from these lanthanide-based macrocyclic agents have relaxation times on the order of a few milliseconds, rapid data acquisition is possible with chemical shift imaging (CSI). Thus, Biosensor Imaging of Redundant Deviation in Shifts (BIRDS) which originate from nonexchanging protons of these paramagnetic agents, but exclude water proton detection, can allow molecular imaging. Previous two-dimensional CSI experiments with such lanthanide-based macrocyclics allowed acquisition from ~12-μL voxels in rat brain within 5 min using rectangular encoding of k space. Because cubical encoding of k space in three dimensions for whole-brain coverage increases the CSI acquisition time to several tens of minutes or more, a faster CSI technique is required for BIRDS to be of practical use. Here, we demonstrate a CSI acquisition method to improve three-dimensional molecular imaging capabilities with lanthanide-based macrocyclics. Using TmDOTMA(-), we show datasets from a 20 × 20 × 20-mm(3) field of view with voxels of ~1 μL effective volume acquired within 5 min (at 11.7 T) for temperature mapping. By employing reduced spherical encoding with Gaussian weighting (RESEGAW) instead of cubical encoding of k space, a significant increase in CSI signal is obtained. In vitro and in vivo three-dimensional CSI data with TmDOTMA(-), and presumably similar lanthanide-based macrocyclics, suggest that acquisition using RESEGAW can be used for high spatiotemporal resolution molecular mapping with BIRDS.

Hemodynamic observations of tumo yoga practitioners in a Himalayan environment

BACKGROUND

Few attempts have been made to evaluate the physiology of traditional Eastern health practices. The goal of this study was to evaluate the hemodynamic effects of the mysterious Buddhist practice of tumo. Tumo is a meditative practice that produces inner heat through the alleged cultivation of body energy-channels.

METHODS

This study was performed by members of an international expedition to the Himalayan Mountains in the Republic of India. The study was performed in an unpopulated outdoor mountainous area at an altitude of 16,400 ft with ambient temperatures between -10 and -15(°)C. Two (2) cohorts of subjects were studied: healthy non-yogi volunteers and tumo practitioners. All of the subjects were stripped down to their underclothes and exposed to the subzero atmospheric temperatures for 5 minutes. The volunteers were then passively rewarmed while the tumo practitioners performed tumo for up to 10 minutes. Blood pressure, heart rate, and stroke volume index (SVI) and cardiac index were measured noninvasively using a NICOM™ hemodynamic monitor, while carotid blood flow and biventricular performance were determined echocardiographically at each stage of the experiment. The total peripheral resistance index (TPRI), left ventricular ejection fraction (LVEF), and tricuspid annular plane systolic excursion (TAPSE) were determined using standard formula.

RESULTS

Fourteen (14) subjects (six volunteers and eight tumo practitioners) completed the study. There was one female subject in each group. With cold exposure, the SVI and carotid blood flow decreased while the TPRI increased significantly in both groups. In the volunteer group, these changes retuned to baseline with rewarming. Following tumo, the cardiac index (4.8±0.6 versus 4.0±0.5 l/m(2); p<0.01), carotid blood flow (445±127 versus 325±100 mL/min/m(2), p<0.01), LVEF (68±5 versus 64±7%; p<0.05) and TAPSE (2.9±0.4 versus 2.4±0.5 cm; p<0.01) were significantly higher when compared with baseline, while the TPRI was significantly lower (1786±189 versus 2173±281; p<0.01).

CONCLUSIONS

Tumo was associated with a hyperdynamic vasodilated state with increased biventricular performance. We postulate that tumo results in a massive increase in sympathetic activity with activation of brown adipose tissue and marked heat production. The increased heat production may explain the paradoxical vasodilatation in tumo practitioners exposed to subzero temperatures.

The influence of cold temperature on cellular excitability of hippocampal networks

The hippocampus plays an important role in short term memory, learning and spatial navigation. A characteristic feature of the hippocampal region is its expression of different electrical population rhythms and activities during different brain states. Physiological fluctuations in brain temperature affect the activity patterns in hippocampus, but the underlying cellular mechanisms are poorly understood. In this work, we investigated the thermal modulation of hippocampal activity at the cellular network level. Primary cell cultures of mouse E17 hippocampus displayed robust network activation upon light cooling of the extracellular solution from baseline physiological temperatures. The activity generated was dependent on action potential firing and excitatory glutamatergic synaptic transmission. Involvement of thermosensitive channels from the transient receptor potential (TRP) family in network activation by temperature changes was ruled out, whereas pharmacological and immunochemical experiments strongly pointed towards the involvement of temperature-sensitive two-pore-domain potassium channels (K_2P), TREK/TRAAK family. In hippocampal slices we could show an increase in evoked and spontaneous synaptic activity produced by mild cooling in the physiological range that was prevented by chloroform, a K_2P channel opener. We propose that cold-induced closure of background TREK/TRAAK family channels increases the excitability of some hippocampal neurons, acting as a temperature-sensitive gate of network activation. Our findings in the hippocampus open the possibility that small temperature variations in the brain in vivo, associated with metabolism or blood flow oscillations, act as a switch mechanism of neuronal activity and determination of firing patterns through regulation of thermosensitive background potassium channel activity.

Cerebral hemodynamics: concepts of clinical importance

Cerebral hemodynamics and metabolism are frequently impaired in a wide range of neurological diseases, including traumatic brain injury and stroke, with several pathophysiological mechanisms of injury. The resultant uncoupling of cerebral blood flow and metabolism can trigger secondary brain lesions, particularly in early phases, consequently worsening the patient's outcome. Cerebral blood flow regulation is influenced by blood gas content, blood viscosity, body temperature, cardiac output, altitude, cerebrovascular autoregulation, and neurovascular coupling, mediated by chemical agents such as nitric oxide (NO), carbon monoxide (CO), eicosanoid products, oxygen-derived free radicals, endothelins, K+, H+, and adenosine. A better understanding of these factors is valuable for the management of neurocritical care patients. The assessment of both cerebral hemodynamics and metabolism in the acute phase of neurocritical care conditions may contribute to a more effective planning of therapeutic strategies for reducing secondary brain lesions. In this review, the authors have discussed concepts of cerebral hemodynamics, considering aspects of clinical importance.

Metabolic efficiency with fast spiking in the squid axon

Fundamentally, action potentials in the squid axon are consequence of the entrance of sodium ions during the depolarization of the rising phase of the spike mediated by the outflow of potassium ions during the hyperpolarization of the falling phase. Perfect metabolic efficiency with a minimum charge needed for the change in voltage during the action potential would confine sodium entry to the rising phase and potassium efflux to the falling phase. However, because sodium channels remain open to a significant extent during the falling phase, a certain overlap of inward and outward currents is observed. In this work we investigate the impact of ion overlap on the number of the adenosine triphosphate (ATP) molecules and energy cost required per action potential as a function of the temperature in a Hodgkin-Huxley model. Based on a recent approach to computing the energy cost of neuronal action potential generation not based on ion counting, we show that increased firing frequencies induced by higher temperatures imply more efficient use of sodium entry, and then a decrease in the metabolic energy cost required to restore the concentration gradients after an action potential. Also, we determine values of sodium conductance at which the hydrolysis efficiency presents a clear minimum.

Natural changes in brain temperature underlie variations in song tempo during a mating behavior

The song of a male zebra finch is a stereotyped motor sequence whose tempo varies with social context--whether or not the song is directed at a female bird--as well as with the time of day. The neural mechanisms underlying these changes in tempo are unknown. Here we show that brain temperature recorded in freely behaving male finches exhibits a global increase in response to the presentation of a female bird. This increase strongly correlates with, and largely explains, the faster tempo of songs directed at a female compared to songs produced in social isolation. Furthermore, we find that the observed diurnal variations in song tempo are also explained by natural variations in brain temperature. Our findings suggest that brain temperature is an important variable that can influence the dynamics of activity in neural circuits, as well as the temporal features of behaviors that some of these circuits generate.

Do acute phase markers explain body temperature and brain temperature after ischemic stroke?

OBJECTIVE

Both brain and body temperature rise after stroke but the cause of each is uncertain. We investigated the relationship between circulating markers of inflammation with brain and body temperature after stroke.

METHODS

We recruited patients with acute ischemic stroke and measured brain temperature at hospital admission and 5 days after stroke with multivoxel magnetic resonance spectroscopic imaging in normal brain and the acute ischemic lesion (defined by diffusion-weighted imaging [DWI]). We measured body temperature with digital aural thermometers 4-hourly and drew blood daily to measure interleukin-6, C-reactive protein, and fibrinogen, for 5 days after stroke.

RESULTS

In 44 stroke patients, the mean temperature in DWI-ischemic brain soon after admission was 38.4° C (95% confidence interval [CI] 38.2-38.6), in DWI-normal brain was 37.7° C (95% CI 37.6-37.7), and mean body temperature was 36.6° C (95% CI 36.3-37.0). Higher mean levels of interleukin-6, C-reactive protein, and fibrinogen were associated with higher temperature in DWI-normal brain at admission and 5 days, and higher overall mean body temperature, but only with higher temperature in DWI-ischemic brain on admission.

CONCLUSIONS

Systemic inflammation after stroke is associated with elevated temperature in normal brain and the body but not with later ischemic brain temperature. Elevated brain temperature is a potential mechanism for the poorer outcome observed in stroke patients with higher levels of circulating inflammatory markers.

Treatment of resistant fever: new method of local cerebral cooling

BACKGROUND

Fever in neurocritical care patients is common and has a negative impact on neurological outcome. The purpose of this prospective observational study was (1) to evaluate the practicability of cooling with newly developed neck pads in the daily setting of neurointensive care unit (NICU) patients and (2) to evaluate its effectiveness as a surrogate endpoint to indicate the feasibility of neck cooling as a new method for intractable fever.

METHODS

Nine patients with ten episodes of intractable fever and aneurysmal subarachnoid hemorrhage were treated with one of two different shapes of specifically adapted cooling neck pads. Temperature values of the brain, blood, and urinary bladder were taken close meshed after application of the cooling neck pads up to hour 8.

RESULTS

The brain, blood, and urinary bladder temperatures decreased significantly from hour 0 to a minimum in hour 5 (P < 0.01). After hour 5, instead of continuous cooling in all the patients, the temperature of all the three sites remounted.

CONCLUSION

This study showed the practicability of local cooling for intractable fever using the newly developed neck pads in the daily setting of NICU patients.

Moritz schiff (1823-1896): a physiologist in exile

Moritz Schiff was one of the pioneers of modern experimental physiology. His involvement in the liberal movement forced him out of Germany, and, because of his adherence to proper physiological research, he had to flee Italy, his first refuge. The number and importance of his contributions are outstanding. The aim of this paper is to raise interest in his biography and to present a yet unreported field of research that is regarded as the root of functional imaging of the brain.

Brain temperature: heat production, elimination and clinical relevance

Neurological insults are a leading cause of morbidity and mortality, both in adults and especially in children. Among possible therapeutic strategies to limit clinical cerebral damage and improve outcomes, hypothermia remains a promising and beneficial approach. However, its advantages are still debated after decades of use. Studies in adults have generated conflicting results, whereas in children recent data even suggest that hypothermia may be detrimental. Is it because brain temperature physiology is not well understood and/or not applied properly, that hypothermia fails to convince clinicians of its potential benefits? Or is it because hypothermia is not, as believed, the optimal strategy to improve outcome in patients affected with an acute neurological insult? This review article should help to explain the fundamental physiological principles of brain heat production, distribution and elimination under normal conditions and discuss why hypothermia cannot yet be recommended routinely in the management of children affected with various neurological insults.

Local exposure of the rat cortex to radiofrequency electromagnetic fields increases local cerebral blood flow along with temperature

Few studies have shown that local exposure to radiofrequency electromagnetic fields (RF) induces intensity-dependent physiological changes, especially in the brain. The aim of the present study was to detect reproducible responses to local RF exposure in the parietal cortex of anesthetized rats and to determine their dependence on RF intensity. The target cortex tissue was locally exposed to 2-GHz RF using a figure-eight loop antenna within a range of averaged specific absorption rates (10.5, 40.3, 130, and 263 W/kg averaged over 4.04 mg) in the target area. Local cerebral blood flow (CBF) and temperatures in three regions (target area, rectum, and calf hypodermis) were measured using optical fiber blood flow meters and thermometers during RF exposure. All parameters except for the calf hypodermis temperature increased significantly in exposed animals compared with sham-exposed ones during 18-min exposures. Dependence of parameter values on exposure intensity was analyzed using linear regression models. The elevation of local CBF was correlated with temperature rise in both target and rectum at the end of RF exposure. However, the local CBF elevation seemed to be elevated by the rise in target temperature, but not by that of the rectal temperature, in the early part of RF exposure or at low-intensity RF exposure. These findings suggest that local RF exposure of the rat cortex drives a regulation of CBF accompanied by a local temperature rise, and our findings may be helpful for discussing physiological changes in the local cortex region, which is locally exposed to RF.

Performance of Coopworth ewe lambs exposed to low levels of ryegrass endophyte (Neotyphodium lolii) alkaloids and allowed access to a mycotoxin deactivator

During February–April, Coopworth ewe lambs grazing a pasture dominated by naturalised perennial ryegrass (PRG) exhibited slight signs of ill-thrift and heat stress. PRG represented 85% of the herbage; 90% of the PRG population was infected with Neotyphodium endophyte. Concentrations of ergovaline and lolitrem B in perennial ryegrass were each within the range 0.5–1.0 mg/kg DM during this period. Two groups of 30 lambs rotated weekly between two paddocks that offered 6 t DM/ha of mature, low-quality pasture. They received an allowance of crushed barley and peas (80 : 20) at 100 g/head per day. One group was treated with a mycotoxin deactivator, Mycofix® Plus, mixed into their mash during processing (5 g/100 g). No sign of ‘staggers’ was observed in the lambs at any time. Lambs with access to Mycofix Plus made great use of shade; their occupancy of shade increased steeply with ambient temperature over the range 18−38°C (P < 0.001). For the control group, occupancy of shade was low (P < 0.001) and independent of temperature (P < 0.001). Instead of using shade on hot days, the control lambs whose respiration rate was higher than treated ewes (P < 0.001) commonly stood by the wire fence, huddled in the open. Over the first 56 days of treatment, while pasture remained dry, weight change in control and treated lambs was –13 and +16 g/day, respectively (P < 0.010). The need for greater investigation of the effects of endophyte alkaloids on livestock is discussed.

Neuroleptic malignant syndrome: mechanisms, interactions, and causality

This review focuses on new data from recent publications concerning how compounding interactions between different thermoregulatory pathways influence the development of hyperthermia and/or neuroleptic malignant syndrome (NMS), and the fundamental issue of the presumed causal role of antipsychotic drugs. The formal criteria for substantiating cause-effect relationships in medical science, established by Hill, are applied to NMS and, for comparison, also to malignant hyperthermia and serotonin toxicity. The risk of morbidities related to hyperthermia is reviewed from human and experimental data: temperatures in excess of 39.5°C cause physiological and cellular dysfunction and high mortality. The most temperature-sensitive elements of neural cells are mitochondrial and plasma membranes, in which irreversible changes occur around 40°C. Temperatures of up to 39°C are "normal" in mammals, so, the term hyperthermia should be reserved for temperatures of 39.5°C or greater. The implicitly accepted presumption that NMS is a hypermetabolic and hyperthermic syndrome is questionable and does not explain the extensive morbidity in the majority of cases, where the temperature is less than 39°C. The thermoregulatory effects of dopamine and acetylcholine are outlined, especially because they are probably the main pathways by which neuroleptic drugs might affect thermoregulation. It is notable that even potent antagonism of these mechanisms rarely causes temperature elevation and that multiple mechanisms, including the acute phase response, stress-induced hyperthermia, drugs effects, etc., involving compounding interactions, are required to precipitate hyperthermia. The application of the Hill criteria clearly supports causality for drugs inducing both MH and ST but do not support causality for NMS.

Programmable neural processing on a smartdust for brain-computer interfaces

Brain-computer interfaces (BCIs) offer tremendous promise for improving the quality of life for disabled individuals. BCIs use spike sorting to identify the source of each neural firing. To date, spike sorting has been performed by either using off-chip analysis, which requires a wired connection penetrating the skull to a bulky external power/processing unit, or via custom application-specific integrated circuits that lack the programmability to perform different algorithms and upgrades. In this research, we propose and test the feasibility of performing on-chip, real-time spike sorting on a programmable smartdust, including feature extraction, classification, compression, and wireless transmission. A detailed power/performance tradeoff analysis using DVFS is presented. Our experimental results show that the execution time and power density meet the requirements to perform real-time spike sorting and wireless transmission on a single neural channel.

Non-invasive continuous cerebral temperature monitoring in patients treated with mild therapeutic hypothermia: an observational pilot study

AIM OF THE STUDY

To investigate if body temperature as measured with a prototype of a non-invasive continuous cerebral temperature sensor using the zero-heat-flow method to reflect the oesophageal temperature (core temperature) during mild therapeutic hypothermia after cardiac arrest.

METHODS

In patients over 18 years old with restoration of spontaneous circulation after cardiac arrest, a temperature sensor that uses the zero-heat-flow principle was placed on the forehead during the periods of cooling and re-warming. This temperature was compared to oesophageal temperature as the primary temperature-monitoring site. To assess agreement, we used the Bland-Altman approach and Lin's concordance correlation coefficient.

RESULTS

From September 2008 to April 2009, data from 19 patients were analysed. The median time from restoration of spontaneous circulation until temperature sensor application was 53min (interquartile range, 31; 96). All sensors were removed when a core temperature of 36 degrees C was reached. These measurements were in agreement with oesophageal temperature measurements. No allergic reaction, rash or other irritation occurred on the skin around or under the probes. Bland-Altman results showed a bias of -0.12 degrees C and 95% limits of agreement of -0.59 and +0.36 degrees C. Lin's concordance correlation coefficient was 0.98.

CONCLUSIONS

Body temperature measurements using a non-invasive continuous cerebral temperature sensor prototype that uses the zero-heat-flow method accurately reflected oesophageal temperature measurements during mild therapeutic hypothermia in patients with restoration of spontaneous circulation after cardiac arrest.