Increase In Cortical Temperature Research Articles

Photostimulation of lymphatic clearance of β-amyloid from mouse brain: a new strategy for the therapy of Alzheimer’s disease

Alzheimer’s disease (AD) is an age-related neurodegenerative disorder that poses a significant burden on socio-economic and healthcare systems worldwide. However, the currently available therapy of AD is limited, and new strategies are needed to enhance the clearance of β-amyloid (Aβ) protein and improve cognitive function. Photobiomodulation (PBM) is a non-invasive and effective therapeutic method that has shown promise in treating various brain diseases. Here, we demonstrate that 1267-nm PBM significantly alleviates cognitive decline in the 5xFAD mouse model of AD and is safe as it does not induce a significant increase in cortical temperature. Moreover, with the combination of 3D tissue optical clearing imaging and automatic brain region segmentation, we show that PBM-mediated reductions of Aβ plaques in different subregions of prefrontal cortex and the hippocampus are different. The PBM-induced lymphatic clearance of Aβ from the brain is associated with improvement of memory and cognitive functions in 5xFAD mice. Our results suggest that the modulation of meningeal lymphatic vessels (MLVs) should play an important role in promoting Aβ clearance. Collectively, this pilot study demonstrates that PBM can safely accelerate lymphatic clearance of Aβ from the brain of 5xFAD mice, promoting improvement of neurocognitive status of AD animals suggesting that PBM can be an effective and bedside therapy for AD.Graphical

Epileptic seizure-related changes in electrocorticogram, cortical temperature, and cerebral hemodynamics obtained via an implantable multimodal multichannel probe during preoperative monitoring: illustrative case.

BACKGROUNDElectrocorticography (EcoG) plays an essential role in the preoperative evaluation of epilepsy, despite its high invasiveness. Brain temperature and cerebral hemodynamics also reflect brain activity. This study examined whether a multimodal multichannel probe that simultaneously records EcoG, cortical temperature, and cerebral hemodynamics can contribute to improving the assessment of epileptic seizures. After preoperative monitoring was performed in a patient with epilepsy, three generalized seizures and two focal seizures were observed.OBSERVATIONSA short-term power increase in the alternating current spectrogram, high-amplitude slow waves in direct current potential, an increase in cortical temperature, an increase in oxyhemoglobin (HbO2) concentration and total hemoglobin (HbT) concentration, and a decrease in deoxyhemoglobin (HHb) concentration, followed by a decrease in HbO2 and HbT concentrations and an increase in HHb concentration, were observed in generalized seizures. However, no changes in these pathophysiological signals were observed in focal seizures.LESSONSSeizure-related changes regarding generalized seizures were consistent with the results of previous studies. The results of generalized and focal seizures indicate that epileptic brain activity propagated from the epileptic focus in the right frontal lobe to the measurement area near the motor cortex in generalized seizures but not in focal seizures.

Physiological and Pathological Brain Activation in the Anesthetized Rat Produces Hemodynamic-Dependent Cortical Temperature Increases That Can Confound the BOLD fMRI Signal.

Anesthetized rodent models are ubiquitous in pre-clinical neuroimaging studies. However, because the associated cerebral morphology and experimental methodology results in a profound negative brain-core temperature differential, cerebral temperature changes during functional activation are likely to be principally driven by local inflow of fresh, core-temperature, blood. This presents a confound to the interpretation of blood-oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) data acquired from such models, since this signal is also critically temperature-dependent. Nevertheless, previous investigation on the subject is surprisingly sparse. Here, we address this issue through use of a novel multi-modal methodology in the urethane anesthetized rat. We reveal that sensory stimulation, hypercapnia and recurrent acute seizures induce significant increases in cortical temperature that are preferentially correlated to changes in total hemoglobin concentration (Hbt), relative to cerebral blood flow and oxidative metabolism. Furthermore, using a phantom-based evaluation of the effect of such temperature changes on the BOLD fMRI signal, we demonstrate a robust inverse relationship between both variables. These findings suggest that temperature increases, due to functional hyperemia, should be accounted for to ensure accurate interpretation of BOLD fMRI signals in pre-clinical neuroimaging studies.

Polysilicon-based flexible temperature sensor for brain monitoring with high spatial resolution

Temperature is one of the most important variables in brain monitoring, since changes of focal brain temperature are closely coupled to cerebral physiology and pathophysiological phenomena in injured brain. In this work, a highly accurate temperature sensor with polysilicon thermistors has been developed on flexible polyimide for monitoring brain temperature with high spatial resolution. The temperature sensors have a response time of 1.5 s and sensitivity of −0.0031 °C−1. Thermal hysteresis of the sensor in the physiological temperature range of 30–45 °C was found to be less than 0.1 °C. With silicon nitride as the passivation layer, the temperature sensor exhibits drift of less than 0.3 °C for 3 d in water. In vivo tests of the sensor show a low noise level of 0.025 ± 0.03 °C, and the expected transient increases in cortical temperature associated with cortical spreading depolarization. The temperature sensor developed in this work is suitable for monitoring brain temperature with the desired high sensitivity and resolution.

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.

Intramedullary pressure increase and increase in cortical temperature during reaming of the femoral medullary cavity: the effect of draining the medullary contents before reaming.

Reaming is regarded as the most adverse aspect of the intramedullary nailing procedure since it leads not only to impairment of the vessels but also to an increase in intramedullary pressure and cortical temperatures which may in turn lead to aseptic cortical necroses and pulmonary dysfunction. Intramedullary pressure increase is considered to be the most detrimental of these factors. The aim of this study was to investigate the effect on intramedullary pressure and cortical temperature of removing the medullary fat before reaming. The fat was removed through a suction tube inserted proximally. The measurements were made on pairs of human femora whereby in one group the contents of the medulla were drained by suction before reaming. The pressure was measured in the mid diaphysis and in the metaphysis. The temperature was measured in the mid diaphysis. The femora were reamed in a water bath at 37 degrees C and at a constant insertion force. In comparison to the group which was not drained, the pressure for the 9.0 mm reamer in previously drained femora was reduced as follows: positive diaphyseal pressure by 88% (reamer insertion); positive metaphyseal pressure by 78% (reamer insertion); negative diaphyseal pressure by 84% (reamer withdrawal); negative metaphyseal pressure by 65% (reamer withdrawal). No significant difference was determined for temperature increase (median suction, 39.7 degrees C; median without suction, 39.4 degrees C). The removal of the medullary contents by suction before inserting reaming instruments leads to a considerable and statistically significant pressure reduction. If the medullary contents are not sucked out before reaming or insertion of unreamed nails, high intramedullary pressure and the risk of embolization is unaltered. Consequently new instruments should be developed to facilitate the removal of the medullary contents before commencing the reaming procedure or insertion of unreamed nails.

Interleukin-1 induces changes in sleep, brain temperature, and serotonergic metabolism.

Simultaneous recordings of sleep-wake activity and of serotonergic metabolism in the medial preoptic area were performed in freely moving rats after the intracerebroventricular injection of interleukin-1 (IL-1) at dark onset. IL-1 (2.5 ng) induced a biphasic increase in slow-wave sleep and an early increase in serotonergic metabolism starting 30 min postinjection. Phasic, state-specific changes (which have been described in spontaneous sleep) were superimposed on this tonic, overall increase in serotonergic metabolism. IL-1 (25 ng) induced an increase in wakefulness and a delayed increase in serotonergic metabolism, which started 120 min postinjection. This suggests that the time course of the serotonergic activation could play a role in mediating IL-1 effects on sleep. Both doses of IL-1 induced a similar and significant increase in brain cortical temperature, suggesting that IL-1 effects on sleep are not a secondary effect of the increase in cortical temperature and that the serotonergic system is not involved in IL-1-induced fever.

Changes in regional cortical temperature and cerebral blood flow after cortical spreading depression.

Regional cerebral blood flow (rCBF) measurement by laser Doppler flowmetry and cortical temperature measurement using thermoencephaloscopy (TES) were performed to investigate the relationship between the changes in rCBF and cortical temperature after induced cortical spreading depression (CSD) in rats. TES showed a gradually expanding thermoresponse like an extending circular wave after CSD induced by application of KCl. Similarly, a transient increase in rCBF spread from the site of stimulation with a velocity of propagation of 2.5 mm/min. Simultaneous monitoring of rCBF and cortical temperature showed that the transient increase in rCBF was associated with an initial decrease in cortical temperature, followed by an increase in cortical temperature. We suggest that the cortical temperature is regulated mainly by neurogenic control of the pial microvascular blood supply that is precisely adjusted to the metabolic needs of the cerebral cortex. Non-injured cortex with the fine vascular architecture must be preserved during neurosurgery to allow heat transfer from deep areas of the cortex.

Intramedullary pressure, strain on the diaphysis and increase in cortical temperature when reaming the femoral medullary cavity — a comparison of blunt and sharp reamers

Clinical application has shown intramedullary nailing to be a safe therapeutic procedure, although damage to the vascular system and fat embolism have been demonstrated in animal experiments. The main negative factors were presumed to be the increase in intramedullary pressure and the increase in cortical temperature. In this study, the effect of the blunting of the reamers on the increase in intramedullary pressure, the tangential strain on the diaphysis and the increase in cortical temperature was to be clarified. The measurements were carried out on pairs of human femora reamed with sharp and blunt AO reamers. The pressure was measured in the middle of the diaphysis and in the metaphysis, the strain in the middle of the femur and the temperature on four aspects of the femur. The femora were reamed with identical compression and traction forces in a water bath at 37 °C. In comparison with the sharp reamer, the blunt reamer develops 2.1 times the positive diaphyseal pressure, 1.7 times the positive metaphyseal pressure, 1.6 times the negative diaphyseal pressure, 1.5 times the positive tangential strain, 55 times the negative tangential strain and 2.8 times the increase in cortical temperature. There is no difference in the negative metaphyseal pressure. Since blunt reamers produce greater intramedullary pressure values, greater tangential strain on the diaphysis and a greater increase in cortical temperature, the attention of surgeons and operating staff must be drawn to the fact that they should treat the reamers gently and replace them whenever necessary.

Extent of bluntness and damage to reamers from hospitals

The negative effects of intramedullary nailing, such as aseptic cortical necroses and fat embolisms, are mainly caused by an increase in intramedullary pressure and an increase in cortical temperature during the reaming process. The degree of bluntness of the reamers has a negative influence on these two parameters. The objective of this study was to examine the degree of bluntness and damage to intramedullary reamers in clinical use. 10 sets of intramedullary reamers returned from Swiss clinics were examined with regard to the radius of the cutting edge and the degree of damage. The following results were established (MN = medullary nailings): Sharpest reamers: hospitals with 300–400 beds. Hospitals with <5 MN per year. Bluntest reamers: hospitals with >1000 beds. Hospitals with 40–60 MN/year. Least damaged reamers: hospitals with 300–400 beds. Hospitals with 40–60 MN/year Most damaged reamers: hospitals with >1000 beds. Hospitals with 40–60 MN/year Due to the fact that some of the reamers in clinical use are of inadequate quality both with regard to the sharpness of the milling lips and the degree of damage, doctors and operating staff should be instructed to check the quality of cutting tools before using them, to treat them carefully and to replace them if necessary.

Temperatures Measured in Human Cortical Bone when Drilling

Temperature measurements have been made in cortical bone while drilling under controlled laboratory conditions. Cortical temperatures greater than 100 degrees centigrade were frequently recorded when drilling if no specific provisions for cooling were made. The force applied to the drill was found to be much more important than drilling speed as a factor in both the magnitude and duration of cortical temperature elevations. Increases in the force applied to the drill were associated with decreases in the maximum temperatures and the durations of temperature elevation. Worn drills caused much greater temperature changes than new drills. All forms of irrigation that allowed the stream of irrigating fluid to be directed to the point of penetration of the cortex were effective in limiting the increases in cortical temperature. Tapping did not appear to cause significant temperature elevations.