Comparing the Effects of Isoflurane and Alpha Chloralose upon Mouse Physiology

Reactivated thalamocortical plasticity alters neural activity in sensory-motor cortex during post-critical period

Neuroplasticity in sensory brain areas supports adaptation after nerve injury and fundamentally impacts sensation and movement. However, limited neuroplasticity in somatosensory areas due to the early critical period makes determining the role of thalamocortical (TC) inputs in sensorimotor signal processing challenging. Here, we demonstrated that reactivation of TC neuroplasticity was associated with an increase in the number of neurons in layer IV (L4) of the whisker primary somatosensory cortex (wS1) with a stable excitation-inhibition ratio. Highly synchronized neural activity in L4 propagated throughout the wS1 column and to the downstream areas, including whisker secondary somatosensory, primary motor cortices, and contralateral wS1. These results provide crucial evidence that TC inputs can alter the neural activity of sensory-motor pathways even after the critical period. Altogether, these enormous changes in sensorimotor circuit activity are important for adaptation following an injury such as limb loss, stroke, or other forms of neural injury.

Enhancing anesthetic techniques for improving whisker stimulation response in the barrel cortex

This study adopts and validates an anesthetic protocol designed for rat whisker stimulation experiments, achieving significant enhancements in the neural response of the barrel field cortex. By combining alpha-chloralose, low-dose Isoflurane (0.5%) and Dexdomitor, the protocol not only maintains a stable anesthetic state but also markedly improves the amplitude and latency of local field potential (LFP) signals. Experimental results reveal that LFP amplitudes in the barrel field under this protocol are twice as high as those achieved with Isoflurane and four times as high as those with Ketamine-Xylazine, with significantly shortened latencies and reduced noise interference. For the first time, power spectral analysis reveals a distinct enhancement of oscillatory power in the alpha (8-13 Hz) and beta (13-30 Hz) bands under alpha-chloralose anesthesia, diverging from the traditional dominance of delta (0.5-4 Hz) oscillations observed with other anesthetics. Mechanistically, this phenomenon may be attributed to alpha-chloralose's unique modulation of GABAergic and glutamatergic pathways, promoting cortical desynchronization and enhanced sensory processing. This protocol offers new insights into optimizing sensory-evoked neural signal acquisition and provides a reference for future studies exploring neural modulation in sensory neuroscience.

High-resolution awake mouse fMRI at 14 tesla

High-resolution awake mouse functional magnetic resonance imaging (fMRI) remains challenging despite extensive efforts to address motion-induced artifacts and stress. This study introduces an implantable radio frequency (RF) surface coil design that minimizes image distortion caused by the air/tissue interface of mouse brains while simultaneously serving as a headpost for fixation during scanning. Furthermore, this study provides a thorough acclimation method used to accustom animals to the MRI environment minimizing motion-induced artifacts. Using a 14 T scanner, high-resolution fMRI enabled brain-wide functional mapping of visual and vibrissa stimulation at 100 µm×100 µm×200 µm resolution with a 2 s per frame sampling rate. Besides activated ascending visual and vibrissa pathways, robust blood oxygen level-dependent (BOLD) responses were detected in the anterior cingulate cortex upon visual stimulation and spread through the ventral retrosplenial area (VRA) with vibrissa air-puff stimulation, demonstrating higher-order sensory processing in association cortices of awake mice. In particular, the rapid hemodynamic responses in VRA upon vibrissa stimulation showed a strong correlation with the hippocampus, thalamus, and prefrontal cortical areas. Cross-correlation analysis with designated VRA responses revealed early positive BOLD signals at the contralateral barrel cortex (BC) occurring 2 s prior to the air-puff in awake mice with repetitive stimulation, which was not detected using a randomized stimulation paradigm. This early BC activation indicated a learned anticipation through the vibrissa system and association cortices in awake mice under continuous exposure of repetitive air-puff stimulation. This work establishes a high-resolution awake mouse fMRI platform, enabling brain-wide functional mapping of sensory signal processing in higher association cortical areas.

Cardiovascular function and autonomic regulation in urethane-anesthetized and conscious mice

Urethane is widely used for its ability to induce prolonged anesthesia. Variability in previously reported cardiovascular parameters in murine models makes it challenging to definitively evaluate the cardiovascular effects of urethane anesthesia. We aimed to address these challenges, thereby advancing our understanding of urethane's effects on cardiovascular function in mice. In this study, we investigated how urethane anesthesia, with and without supplemental oxygen, impacts heart rate, arterial oxygen saturation ([Formula: see text]), blood pressure, and heart rate variability in mice. First, we conducted a literature review and found that data in mice were both limited and lacking in reproduction. Next, we conducted a series of physiological measurements to address gaps in the literature and subjected C57BL/6J mice to three conditions: 1) conscious, 2) urethane-anesthetized, and 3) urethane-anesthetized with supplemental oxygen. Blood pressure, heart rate, [Formula: see text], and heart rate variability (via time, frequency, and M-curve analyses) were assessed. We observed an increase in heart rate with urethane anesthesia (P = 0.012) compared with the conscious state. Urethane caused a decrease in heart rate variability, which was independent of oxygen supplementation. Urethane anesthesia caused a significant reduction in arterial blood pressure (P < 0.001) with oxygen-supplemented mice remained hypotensive. Urethane decreased [Formula: see text] (P = 0.001), which was restored by oxygen supplementation (P < 0.001). We did not observe sex effects of urethane anesthesia on blood pressure, heart rate, heart rate variability, or [Formula: see text]. Taken together, these results underscore the importance of a cautious approach when using urethane in mice, as urethane significantly impacts arterial blood pressure, heart rate, oxygen saturation, and heart rate variability.NEW & NOTEWORTHY This investigation documents cardiovascular outcomes in mice receiving urethane anesthesia, emphasizing sex as a biological variable, and considering oxygen supplementation during anesthesia. This is the first report of M-curve analysis in rodents as a heart rate-independent variability analysis.

Local wakefulness-like activity of layer 5 cortex under general anaesthesia

Consciousness, defined as being aware of and responsive to one's surroundings, is characteristic of normal waking life and typically is lost during sleep and general anaesthesia. The traditional view of consciousness as a global brain state has evolved toward a more sophisticated interplay between global and local states, with the presence of local sleep in the awake brain and local wakefulness in the sleeping brain. However, this interplay is not clear for general anaesthesia, where loss of consciousness was recently suggested to be associated with a global state of brain-wide synchrony that selectively involves layer 5 cortical pyramidal neurons across sensory, motor and associative areas. According to this global view, local wakefulness of layer 5 cortex should be incompatible with deep anaesthesia, a hypothesis that deserves to be scrutinised with causal manipulations. Here, we show that unilateral chemogenetic activation of layer 5 pyramidal neurons in the sensorimotor cortex of isoflurane-anaesthetised mice induces a local state transition from slow-wave activity to tonic firing in the transfected hemisphere. This wakefulness-like activity dramatically disrupts layer 5 interhemispheric synchrony with mirror-image locations in the contralateral hemisphere, but does not reduce the level of unconsciousness under deep anaesthesia, nor in the transitions to/from anaesthesia. Global layer 5 synchrony may thus be a sufficient condition for anaesthesia-induced unconsciousness, but is not a necessary one, at least under isoflurane anaesthesia. Local wakefulness-like activity of layer 5 cortex can be induced and maintained under deep anaesthesia, encouraging further investigation into the local vs. global aspects of anaesthesia-induced unconsciousness. KEY POINTS: The neural correlates of consciousness have evolved from global brain states to a nuanced interplay between global and local states, evident in terms of local sleep in awake brains and local wakefulness in sleeping brains. The concept of local wakefulness remains unclear for general anaesthesia, where the loss of consciousness has been recently suggested to involve brain-wide synchrony of layer 5 cortical neurons. We found that local wakefulness-like activity of layer 5 cortical can be chemogenetically induced in anaesthetised mice without affecting the depth of anaesthesia or the transitions to and from unconsciousness. Global layer 5 synchrony may thus be a sufficient but not necessary feature for the unconsciousness induced by general anaesthesia. Local wakefulness-like activity of layer 5 neurons is compatible with general anaesthesia, thus promoting further investigation into the local vs. global aspects of anaesthesia-induced unconsciousness.

High-resolution awake mouse fMRI at 14 Tesla

High-resolution awake mouse fMRI remains challenging despite extensive efforts to address motion-induced artifacts and stress. This study introduces an implantable radiofrequency (RF) surface coil design that minimizes image distortion caused by the air/tissue interface of mouse brains while simultaneously serving as a headpost for fixation during scanning. Furthermore, this study provides a thorough acclimation method used to accustom animals to the MRI environment minimizing motion induced artifacts. Using a 14T scanner, high-resolution fMRI enabled brain-wide functional mapping of visual and vibrissa stimulation at 100×100×200μm resolution with a 2s per frame sampling rate. Besides activated ascending visual and vibrissa pathways, robust BOLD responses were detected in the anterior cingulate cortex upon visual stimulation and spread through the ventral retrosplenial area (VRA) with vibrissa air-puff stimulation, demonstrating higher-order sensory processing in association cortices of awake mice. In particular, the rapid hemodynamic responses in VRA upon vibrissa stimulation showed a strong correlation with the hippocampus, thalamus, and prefrontal cortical areas. Cross-correlation analysis with designated VRA responses revealed early positive BOLD signals at the contralateral barrel cortex (BC) occurring 2 seconds prior to the air-puff in awake mice with repetitive stimulation, which was not detected using a randomized stimulation paradigm. This early BC activation indicated a learned anticipation through the vibrissa system and association cortices in awake mice under continuous training of repetitive air-puff stimulation. This work establishes a high-resolution awake mouse fMRI platform, enabling brain-wide functional mapping of sensory signal processing in higher association cortical areas.

Existence of multiple transitions of the critical state due to anesthetics

Scale-free statistics of coordinated neuronal activity, suggesting a universal operating mechanism across spatio-temporal scales, have been proposed as a necessary condition of healthy resting-state brain activity. Recent studies have focused on anesthetic agents to induce distinct neural states in which consciousness is altered to understand the importance of critical dynamics. However, variation in experimental techniques, species, and anesthetics, have made comparisons across studies difficult. Here we conduct a survey of several common anesthetics (isoflurane, pentobarbital, ketamine) at multiple dosages, using calcium wide-field optical imaging of the mouse cortex. We show that while low-dose anesthesia largely preserves scale-free statistics, surgical plane anesthesia induces multiple dynamical modes, most of which do not maintain critical avalanche dynamics. Our findings indicate multiple pathways away from default critical dynamics associated with quiet wakefulness, not only reflecting differences between these common anesthetics but also showing significant variations in individual responses. This is suggestive of a non-trivial relationship between criticality and the underlying state of the subject.

RUNX1-PDIA5 Axis Promotes Malignant Progression of Glioblastoma by Regulating CCAR1 Protein Expression

PDIA5 is responsible for modification of disulfide bonds of proteins. However, its impact on the malignant progression of glioblastoma multiforme (GBM) remains unknown. We analyzed the expression and prognostic significance of PDIA5 in cohorts of GBM and clinical samples. The PDIA5 protein was significantly overexpressed in GBM tissues, and higher expression of PDIA5 was statistically associated with a worse prognosis in patients with GBM. Transcriptional data from PDIA5 knockdown GBM cells revealed that downstream regulatory genes of PDIA5 were enriched in malignant regulatory pathways and PDIA5 enhanced the proliferative and invasive abilities of GBM cells. By constructing a PDIA5 CXXC motif mutant plasmid, we found CCAR1 was the vital downstream factor of PDIA5 in regulating GBM malignancy in vitro and in vivo. Additionally, RUNX1 bound to the promoter region of PDIA5 and regulated gene transcription, leading to activation of the PDIA5/CCAR1 regulatory axis in GBM. The RUNX1/PDIA5/CCAR1 axis significantly influenced the malignant behavior of GBM cells. In conclusion, this study comprehensively elucidates the crucial role of PDIA5 in the malignant progression of GBM. Downregulating PDIA5 can mitigate the malignant biological behavior of GBM both in vitro and in vivo, potentially improving the efficacy of treatment for clinical patients with GBM.

Anesthesia-related brain microstructure modulations detected by diffusion magnetic resonance imaging

Recent studies have shown significant changes to brain microstructure during sleep and anesthesia. In vivo optical microscopy and magnetic resonance imaging (MRI) studies have attributed these changes to anesthesia and sleep-related modulation of the brain's extracellular space (ECS). Isoflurane anesthesia is widely used in preclinical diffusion MRI (dMRI) and it is therefore important to investigate if the brain's microstructure is affected by anesthesia to an extent detectable with dMRI. Here, we employ diffusion kurtosis imaging (DKI) to assess brain microstructure in the awake and anesthetized mouse brain (n = 22). We find both mean diffusivity (MD) and mean kurtosis (MK) to be significantly decreased in the anesthetized mouse brain compared with the awake state (p < 0.001 for both). This effect is observed in both gray matter and white matter. To further investigate the time course of these changes we introduce a method for time-resolved fast DKI. With this, we show the time course of the microstructural alterations in mice (n = 5) as they transition between states in an awake-anesthesia-awake paradigm. We find that the decrease in MD and MK occurs rapidly after delivery of gas isoflurane anesthesia and that values normalize only slowly when the animals return to the awake state. Finally, time-resolved fast DKI is employed in an experimental mouse model of brain edema (n = 4), where cell swelling causes the ECS volume to decrease. Our results show that isoflurane affects DKI parameters and metrics of brain microstructure and point to isoflurane causing a reduction in the ECS volume. The demonstrated DKI methods are suitable for in-bore perturbation studies, for example, for investigating microstructural modulations related to sleep/wake-dependent functions of the glymphatic system. Importantly, our study shows an effect of isoflurane anesthesia on rodent brain microstructure that has broad relevance to preclinical dMRI.

Jiaohong pills attenuate neuroinflammation and amyloid-β protein-induced cognitive deficits by modulating the mitogen-activated protein kinase/nuclear factor kappa-B pathway

BACKGROUND

Jiaohong pills (JHP) consist of Pericarpium Zanthoxyli (PZ) and Radix Rehmanniae, two herbs that have been extensively investigated over many years due to their potential protective effects against cognitive decline and memory impairment. However, the precise mechanisms underlying the beneficial effects remain elusive. Here, research studies were conducted to investigate and validate the therapeutic effects of JHP on Alzheimer's disease.

METHODS

BV-2 cell inflammation was induced by lipopolysaccharide. AD mice were administered amyloid-β (Aβ). Behavioral experiments were used to evaluate learning and memory ability. The levels of nitric oxide (NO), tumor necrosis factor-alpha (TNF-α), interleukin-1β (IL-1β), and interleukin-10 (IL-10) were detected using enzyme-linked immunosorbent assay (ELISA). The protein expressions of inducible nitric oxide synthase (iNOS) and the phosphorylation level of mitogen-activated protein kinase (MAPK) and nuclear factor kappa-B (NF-κB) were detected using Western blot. Nissl staining was used to detect neuronal degeneration.

RESULTS

The results demonstrated that an alcoholic extract of PZ significantly decreased the levels of NO, IL-1β, TNF-α, and iNOS; increased the expression level of IL-10; and significantly decreased the phosphorylation levels of MAPK and NF-κB. These inhibitory effects were further confirmed in the AD mouse model. Meanwhile, JHP improved learning and memory function in AD mice, reduced neuronal damage, and enriched the Nissl bodies in the hippocampus. Moreover, IL-1β and TNF-α in the cortex were significantly downregulated after JHP administration, whereas IL-10 showed increased expression.

CONCLUSIONS

It was found that JHP reduced neuroinflammatory response in AD mice by targeting the MAPK/NF-κB signaling pathway.

Lactate as a supplemental fuel for synaptic transmission and neuronal network oscillations: Potentials and limitations

Lactate shuttled from the blood circulation, astrocytes, oligodendrocytes or even activated microglia (resident macrophages) to neurons has been hypothesized to represent a major source of pyruvate compared to what is normally produced endogenously by neuronal glucose metabolism. However, the role of lactate oxidation in fueling neuronal signaling associated with complex cortex function, such as perception, motor activity, and memory formation, is widely unclear. This issue has been experimentally addressed using electrophysiology in hippocampal slice preparations (ex vivo) that permit the induction of different neural network activation states by electrical stimulation, optogenetic tools or receptor ligand application. Collectively, these studies suggest that lactate in the absence of glucose (lactate only) impairs gamma (30-70 Hz) and theta-gamma oscillations, which feature high energy demand revealed by the cerebral metabolic rate of oxygen (CMRO2, set to 100%). The impairment comprises oscillation attenuation or moderate neural bursts (excitation-inhibition imbalance). The bursting is suppressed by elevating the glucose fraction in energy substrate supply. By contrast, lactate can retain certain electric stimulus-induced neural population responses and intermittent sharp wave-ripple activity that features lower energy expenditure (CMRO2 of about 65%). Lactate utilization increases the oxygen consumption by about 9% during sharp wave-ripples reflecting enhanced adenosine-5'-triphosphate (ATP) synthesis by oxidative phosphorylation in mitochondria. Moreover, lactate attenuates neurotransmission in glutamatergic pyramidal cells and fast-spiking, γ-aminobutyric acid (GABA)ergic interneurons by reducing neurotransmitter release from presynaptic terminals. By contrast, the generation and propagation of action potentials in the axon is regular. In conclusion, lactate is less effective than glucose and potentially detrimental during neural network rhythms featuring high energetic costs, likely through the lack of some obligatory ATP synthesis by aerobic glycolysis at excitatory and inhibitory synapses. High lactate/glucose ratios might contribute to central fatigue, cognitive impairment, and epileptic seizures partially seen, for instance, during exhaustive physical exercise, hypoglycemia and neuroinflammation.

Central Artery Hemodynamics in Angiotensin II-Induced Hypertension and Effects of Anesthesia

Systemic hypertension is a strong risk factor for cardiovascular, neurovascular, and renovascular diseases. Central artery stiffness is both an initiator and indicator of hypertension, thus revealing a critical relationship between the wall mechanics and hemodynamics. Mice have emerged as a critical animal model for studying effects of hypertension and much has been learned. Regardless of the specific mouse model, data on changes in cardiac function and hemodynamics are necessarily measured under anesthesia. Here, we present a new experimental-computational workflow to estimate awake cardiovascular conditions from anesthetized data, which was then used to quantify effects of chronic angiotensin II-induced hypertension relative to normotension in wild-type mice. We found that isoflurane anesthesia had a greater impact on depressing hemodynamics in angiotensin II-infused mice than in controls, which led to unexpected results when comparing anesthetized results between the two groups of mice. Through comparison of the awake simulations, however, in vivo relevant effects of angiotensin II-infusion on global and regional vascular structure, properties, and hemodynamics were found to be qualitatively consistent with expectations. Specifically, we found an increased in vivo vascular stiffness in the descending thoracic aorta and suprarenal abdominal aorta, leading to increases in pulse pressure in the distal aorta. These insights allow characterization of the impact of regionally varying vascular remodeling on hemodynamics and mouse-to-mouse variations due to induced hypertension.

Oxygen imaging of hypoxic pockets in the mouse cerebral cortex

Consciousness is lost within seconds upon cessation of cerebral blood flow. The brain cannot store oxygen, and interruption of oxidative phosphorylation is fatal within minutes. Yet only rudimentary knowledge exists regarding cortical partial oxygen tension (Po2) dynamics under physiological conditions. Here we introduce Green enhanced Nano-lantern (GeNL), a genetically encoded bioluminescent oxygen indicator for Po2 imaging. In awake behaving mice, we uncover the existence of spontaneous, spatially defined "hypoxic pockets" and demonstrate their linkage to the abrogation of local capillary flow. Exercise reduced the burden of hypoxic pockets by 52% compared with rest. The study provides insight into cortical oxygen dynamics in awake behaving animals and concurrently establishes a tool to delineate the importance of oxygen tension in physiological processes and neurological diseases.

Regulation of vagally-evoked respiratory responses by the lateral parabrachial nucleus in the mouse

Vagal sensory inputs to the brainstem can alter breathing through the modulation of pontomedullary respiratory circuits. In this study, we set out to investigate the localised effects of modulating lateral parabrachial nucleus (LPB) activity on vagally-evoked changes in breathing pattern. In isoflurane-anaesthetised and instrumented mice, electrical stimulation of the vagus nerve (eVNS) produced stimulation frequency-dependent changes in diaphragm electromyograph (dEMG) activity with an evoked tachypnoea and apnoea at low and high stimulation frequencies, respectively. Muscimol microinjections into the LPB significantly attenuated eVNS-evoked respiratory rate responses. Notably, muscimol injections reaching the caudal LPB, previously unrecognised for respiratory modulation, potently modulated eVNS-evoked apnoea, whilst muscimol injections reaching the intermediate LPB selectively modulated the eVNS-evoked tachypnoea. The effects of muscimol on eVNS-evoked breathing rate changes occurred without altering basal eupneic breathing. These results highlight novel roles for the LPB in regulating vagally-evoked respiratory reflexes.

Simultaneous magnetic resonance imaging of pH, perfusion and renal filtration using hyperpolarized 13C-labelled Z-OMPD

pH alterations are a hallmark of many pathologies including cancer and kidney disease. Here, we introduce [1,5-13C2]Z-OMPD as a hyperpolarized extracellular pH and perfusion sensor for MRI which allows to generate a multiparametric fingerprint of renal disease status and to detect local tumor acidification. Exceptional long T1 of two minutes at 1 T, high pH sensitivity of up to 1.9 ppm per pH unit and suitability of using the C1-label as internal frequency reference enables pH imaging in vivo of three pH compartments in healthy rat kidneys. Spectrally selective targeting of both 13C-resonances enables simultaneous imaging of perfusion and filtration in 3D and pH in 2D within one minute to quantify renal blood flow, glomerular filtration rates and renal pH in healthy and hydronephrotic kidneys with superior sensitivity compared to clinical routine methods. Imaging multiple biomarkers within a single session renders [1,5-13C2]Z-OMPD a promising new hyperpolarized agent for oncology and nephrology.

Telemetric electroencephalography recording in anesthetized mice-A novel system using minimally-invasive needle electrodes with a wireless OpenBCI™ Cyton Biosensing Board

Telemetric electroencephalography (EEG) recording, using subdermal needle electrodes, is a minimally-invasive method to investigate mammalian neurophysiology during anesthesia. These inexpensive systems may streamline experiments examining global brain phenomena during surgical anesthesia or disease. We utilized the OpenBCI™ Cyton board with subdermal needle electrodes to extract EEG features in six C57BL/6J mice undergoing isoflurane anesthesia. Burst suppression ratio (BSR) and spectral features were compared for a verification of our method. Following an increase from 1.5% to 2.0% isoflurane, the BSR increased (Wilcoxon-signed-rank statistic; p = 0.0313). Furthermore, although the absolute EEG spectral power decreased, the relative spectral power remained comparable (Wilcoxon-Mann-Whitney U-Statistic; 95% CI exclusive AUC=0.5; p < 0.05). Compared to tethered systems, this method confers several improvements for anesthesia specific protocols: 1-Avoiding electrode implant surgical procedures, 2-Anatomical non-specificity for needle electrode placement to monitor global cortical activity representative of anesthetic state, 3-Facility to repeat recordings in the same animal, 4-User-friendly for non-experts, 5-Rapid set-up time, and 6-Lower costs.•Minimally-invasive telemetric EEG recording systems ergonomically improve tethered systems for anesthesia protocols.•Using this method, we verified that higher isoflurane concentrations resulted in an increased EEG burst suppression ratio and decreased EEG absolute spectral power, with no change in frequency distribution.

Intrinsic, widefield optical imaging of hemodynamics in rodent models of Alzheimer's disease and neurological injury

The complex cerebrovascular network is critical to controlling local cerebral blood flow (CBF) and maintaining brain homeostasis. Alzheimer's disease (AD) and neurological injury can result in impaired CBF regulation, blood-brain barrier breakdown, neurovascular dysregulation, and ultimately impaired brain homeostasis. Measuring cortical hemodynamic changes in rodents can help elucidate the complex physiological dynamics that occur in AD and neurological injury. Widefield optical imaging approaches can measure hemodynamic information, such as CBF and oxygenation. These measurements can be performed over fields of view that range from millimeters to centimeters and probe up to the first few millimeters of rodent brain tissue. We discuss the principles and applications of three widefield optical imaging approaches that can measure cerebral hemodynamics: (1) optical intrinsic signal imaging, (2) laser speckle imaging, and (3) spatial frequency domain imaging. Future work in advancing widefield optical imaging approaches and employing multimodal instrumentation can enrich hemodynamic information content and help elucidate cerebrovascular mechanisms that lead to the development of therapeutic agents for AD and neurological injury.

Protective effect of isoflurane preconditioning on neurological function in rats with HIE

Hypoxic-ischemic encephalopathy (HIE) is an important cause of neonatal death and disability, which can lead to long-term neurological and motor dysfunction. Currently, inhalation anesthetics are widely used in surgery, and some studies have found that isoflurane (ISO) may have a positive effect on neuroprotection. In this paper, we investigated whether ISO pretreatment has a neuroprotective effect on the neurological function of HIE rats. Here, 7-day-old neonatal rats were randomly divided into a sham group, a hypoxic-ischemic (HI) group, and an ISO pretreatment (pretreatment) group. The pretreatment group was pretreated with 2% ISO for 1 h, followed by the HI group to establish an HI animal model. The HI‑induced neurological injury was evaluated by Zea‑Longa scores and triphenyltetrazolium (TTC) staining. Neuronal number and histomorphological changes were observed with Nissl staining and Hematoxylin-eosin (HE) staining. In addition, motor learning memory function was evaluated by the Morris water maze (MWM), the Y-maze, and the rotarod tests. HI induced severe neurological dysfunction, brain infarction, and cell apoptosis as well as obvious neuron loss in neonatal rats. In the MWM, the rats in the pretreatment group showed a decrease in escape latency (p = 0.042), indicating that pretreatment with ISO could improve the learning ability of HI rats. The results of Nissl staining showed that in the HI group, there was an irregular arrangement of neurons and nuclear fixation; however, the cell damage was significantly reduced and the total number of neurons was increased after ISO pretreatment (p < 0.001). In conclusion, ISO pretreatment improved cognitive function and attenuated HI-induced reduction of Nissl-positive cells and spatial memory impairment, suggesting that pretreatment with ISO before HI modeling could reduce neuronal cell death in the hippocampus after HI.

Anesthetic modulations dissociate neuroelectric characteristics between sensory-evoked and spontaneous activities across bilateral rat somatosensory cortical laminae

Spontaneous neural activity has been widely adopted to construct functional connectivity (FC) amongst distant brain regions. Although informative, the functional role and signaling mechanism of the resting state FC are not intuitive as those in stimulus/task-evoked activity. In order to bridge the gap, we investigated anesthetic modulation of both resting-state and sensory-evoked activities. We used two well-studied GABAergic anesthetics of varying dose (isoflurane: 0.5–2.0% and α-chloralose: 30 and 60 mg/kg∙h) and recorded changes in electrophysiology using a pair of laminar electrode arrays that encompass the entire depth of the bilateral somatosensory cortices (S1fl) in rats. Specifically, the study focused to describe how varying anesthesia conditions affect the resting state activities and resultant FC between bilateral hemispheres in comparison to those obtained by evoked responses. As results, isoflurane decreased the amplitude of evoked responses in a dose-dependent manner mostly due to the habituation of repetitive responses. However, α-chloralose rather intensified the amplitude without exhibiting habituation. No such diverging trend was observed for the spontaneous activity, in which both anesthetics increased the signal power. For α-chloralose, overall FC was similar to that obtained with the lowest dose of isoflurane at 0.5% while higher doses of isoflurane displayed increased FC. Interestingly, only α-chloralose elicited relatively much greater increases in the ipsi-stimulus evoked response (i.e., in S1fl ipsilateral to the stimulated forelimb) than those associated with the contra-stimulus response, suggesting enhanced neuronal excitability. Taken together, the findings demonstrate modulation of the FC profiles by anesthesia is highly non-linear, possibly with a distinct underlying mechanism that affects either resting state or evoked activities differently. Further, the current study warrants thorough investigation of the basal neuronal states prior to the interpretation of resting state FC and evoked activities for accurate understanding of neural signal processing and circuitry.

Continuous long-term recording and triggering of brain neurovascular activity and behaviour in freely moving rodents

A minimally invasive, microchip-based approach enables continuous long-term recording of brain neurovascular activity, heart rate, and head movement in freely behaving rodents. This approach can also be used for transcranial optical triggering of cortical activity in mice expressing channelrhodopsin. The system uses optical intrinsic signal recording to measure cerebral blood volume, which under baseline conditions is correlated with spontaneous neuronal activity. The arterial pulse and breathing can be quantified as a component of the optical intrinsic signal. Multi-directional head movement is measured simultaneously with a movement sensor. A separate movement tracking element through a camera enables precise mapping of overall movement within an enclosure. Data is processed by a dedicated single board computer, and streamed from multiple enclosures to a central server, enabling simultaneous remote monitoring and triggering in many subjects. One application of this system described here is the characterization of changes in of cerebral blood volume, heart rate and behaviour that occur with the sleep-wake cycle over weeks. Another application is optical triggering and recording of cortical spreading depression (CSD), the slowly propagated wave of neurovascular activity that occurs in the setting of brain injury and migraine aura. The neurovascular features of CSD are remarkably different in the awake vs. anaesthetized state in the same mouse. With its capacity to continuously and synchronously record multiple types of physiological and behavioural data over extended time periods in combination with intermittent triggering of brain activity, this inexpensive method has the potential for widespread practical application in rodent research. KEY POINTS: Recording and triggering of brain activity in mice and rats has typically required breaching the skull, and experiments are often performed under anaesthesia A minimally invasive microchip system enables continuous recording and triggering of neurovascular activity, and analysis of heart rate and behaviour in freely behaving rodents over weeks This system can be used to characterize physiological and behavioural changes associated with the sleep-wake cycle over extended time periods This approach can also be used with mice expressing channelrhodopsin to trigger and record cortical spreading depression (CSD) in freely behaving subjects. The neurovascular responses to CSD are remarkably different under anaesthesia compared with the awake state. The method is inexpensive and straightforward to employ at a relatively large scale. It enables translational investigation of a wide range of physiological and pathological conditions in rodent models of neurological and systemic diseases.

Prolonged isoflurane anesthesia-induced acidosis decreases penile intracavernous pressure in rats

BACKGROUND

Intracavernous pressure measurement following cavernous nerve electrostimulation has been extensively adopted for the evaluation of erectile function in animals. However, the effect of measurement time and acidosis during anesthesia is still lacking.

OBJECTIVE

To explore the effect of measurement time and acidosis during anesthesia.

MATERIALS AND METHODS

Fifty-six male Sprague-Dawley rats were used and anesthetized by a spontaneous inhalation of isoflurane. In the first step, rats were randomly divided into four groups: a control group and three time-delayed measurement groups (intracavernous pressure measurement beginning at 15, 30, and 45 min after cavernous nerve exposure). In the second step, rats were randomly divided into three groups: a control group and two time-delayed measurement groups. Two intravenous fluid support strategies were used in time-delayed measurement groups: a normal saline solution and an isotonic Na₂ CO₃ solution.

RESULTS

Isoflurane-anesthetized rats developed systemic acidosis that worsens with time during intracavernous pressure measurement, which results in a significant decrease in the maximum intracavernous pressure value, intracavernous pressure/mean arterial pressure ratio, and total intracavernous pressure measured. The Na₂ CO₃ infusion could effectively correct acidosis. The decrease in intracavernous pressure was related to the reduced nitric oxide synthase activity, decreased cyclic guanosine monophosphate concentration, and reactive oxygen species activation in rat penis under acidosis conditions.

DISCUSSION AND CONCLUSION

Prolonged isoflurane anesthesia-induced acidosis markedly depresses the erectile response to cavernous nerve electrostimulation in rats. In this situation, it is recommended to supplement with a Na₂ CO₃ infusion to maintain a normal acid-base balance.

Mouse Anesthesia: The Art and Science

There is an art and science to performing mouse anesthesia, which is a significant component to animal research. Frequently, anesthesia is one vital step of many over the course of a research project spanning weeks, months, or beyond. It is critical to perform anesthesia according to the approved research protocol using appropriately handled and administered pharmaceutical-grade compounds whenever possible. Sufficient documentation of the anesthetic event and procedure should also be performed to meet the legal, ethical, and research reproducibility obligations. However, this regulatory and documentation process may lead to the use of a few possibly oversimplified anesthetic protocols used for mouse procedures and anesthesia. Although a frequently used anesthetic protocol may work perfectly for each mouse anesthetized, sometimes unexpected complications will arise, and quick adjustments to the anesthetic depth and support provided will be required. As an old saying goes, anesthesia is 99% boredom and 1% sheer terror. The purpose of this review article is to discuss the science of mouse anesthesia together with the art of applying these anesthetic techniques to provide readers with the knowledge needed for successful anesthetic procedures. The authors include experiences in mouse inhalant and injectable anesthesia, peri-anesthetic monitoring, specific procedures, and treating common complications. This article utilizes key points for easy access of important messages and authors’ recommendation based on the authors’ clinical experiences.

Preclinical techniques to investigate exercise training in vascular pathophysiology

Atherosclerosis is a dynamic process starting with endothelial dysfunction and inflammation and eventually leading to life-threatening arterial plaques. Exercise generally improves endothelial function in a dose-dependent manner by altering hemodynamics, specifically by increased arterial pressure, pulsatility, and shear stress. However, athletes who regularly participate in high-intensity training can develop arterial plaques, suggesting alternative mechanisms through which excessive exercise promotes vascular disease. Understanding the mechanisms that drive atherosclerosis in sedentary versus exercise states may lead to novel rehabilitative methods aimed at improving exercise compliance and physical activity. Preclinical tools, including in vitro cell assays, in vivo animal models, and in silico computational methods, broaden our capabilities to study the mechanisms through which exercise impacts atherogenesis, from molecular maladaptation to vascular remodeling. Here, we describe how preclinical research tools have and can be used to study exercise effects on atherosclerosis. We then propose how advanced bioengineering techniques can be used to address gaps in our current understanding of vascular pathophysiology, including integrating in vitro, in vivo, and in silico studies across multiple tissue systems and size scales. Improving our understanding of the antiatherogenic exercise effects will enable engaging, targeted, and individualized exercise recommendations to promote cardiovascular health rather than treating cardiovascular disease that results from a sedentary lifestyle.

A quantitative analysis of cell-specific contributions and the role of anesthetics to the neurovascular coupling

The neurovascular coupling (NVC) connects neuronal activity to hemodynamic responses in the brain. This connection is the basis for the interpretation of functional magnetic resonance imaging data. Despite the central role of this coupling, we lack detailed knowledge about cell-specific contributions and our knowledge about NVC is mainly based on animal experiments performed during anesthesia. Anesthetics are known to affect neuronal excitability, but how this affects the vessel diameters is not known. Due to the high complexity of NVC data, mathematical modeling is needed for a meaningful analysis. However, neither the relevant neuronal subtypes nor the effects of anesthetics are covered by current models. Here, we present a mathematical model including GABAergic interneurons and pyramidal neurons, as well as the effect of an anesthetic agent. The model is consistent with data from optogenetic experiments from both awake and anesthetized animals, and it correctly predicts data from experiments with different pharmacological modulators. The analysis suggests that no downstream anesthetic effects are necessary if one of the GABAergic interneuron signaling pathways include a Michaelis-Menten expression. This is the first example of a quantitative model that includes both the cell-specific contributions and the effect of an anesthetic agent on the NVC.

The (Un)Conscious Mouse as a Model for Human Brain Functions: Key Principles of Anesthesia and Their Impact on Translational Neuroimaging

In recent years, technical and procedural advances have brought functional magnetic resonance imaging (fMRI) to the field of murine neuroscience. Due to its unique capacity to measure functional activity non-invasively, across the entire brain, fMRI allows for the direct comparison of large-scale murine and human brain functions. This opens an avenue for bidirectional translational strategies to address fundamental questions ranging from neurological disorders to the nature of consciousness. The key challenges of murine fMRI are: (1) to generate and maintain functional brain states that approximate those of calm and relaxed human volunteers, while (2) preserving neurovascular coupling and physiological baseline conditions. Low-dose anesthetic protocols are commonly applied in murine functional brain studies to prevent stress and facilitate a calm and relaxed condition among animals. Yet, current mono-anesthesia has been shown to impair neural transmission and hemodynamic integrity. By linking the current state of murine electrophysiology, Ca2+ imaging and fMRI of anesthetic effects to findings from human studies, this systematic review proposes general principles to design, apply and monitor anesthetic protocols in a more sophisticated way. The further development of balanced multimodal anesthesia, combining two or more drugs with complementary modes of action helps to shape and maintain specific brain states and relevant aspects of murine physiology. Functional connectivity and its dynamic repertoire as assessed by fMRI can be used to make inferences about cortical states and provide additional information about whole-brain functional dynamics. Based on this, a simple and comprehensive functional neurosignature pattern can be determined for use in defining brain states and anesthetic depth in rest and in response to stimuli. Such a signature can be evaluated and shared between labs to indicate the brain state of a mouse during experiments, an important step toward translating findings across species.

Interactions between stimuli-evoked cortical activity and spontaneous low frequency oscillations measured with neuronal calcium

Spontaneous brain activity has been widely used to map brain connectivity. The interactions between task-evoked brain responses and the spontaneous cortical oscillations, especially within the low frequency range of ~0.1 ​Hz, are not fully understood. Trial-to-trial variabilities in brain's response to sensory stimuli and the ability for brain to detect under noisy conditions suggest an appreciable impact of the brain state. Using a multimodality imaging platform, we simultaneously imaged neuronal Ca²⁺ and cerebral hemodynamics at baseline and in response to single-pulse forepaw stimuli in rat's somatosensory cortex. The high sensitivity of this system enables detection of responses to very weak and strong stimuli and real time determination of low frequency oscillations without averaging. Results show that the ongoing neuronal oscillations inversely modulate Ca²⁺ transients evoked by sensory stimuli. High intensity stimuli reset the spontaneous neuronal oscillations to an unpreferable excitability following the stimulus. Cerebral hemodynamic responses also inversely interact with the spontaneous hemodynamic oscillations, correlating with the neuronal Ca²⁺ transient changes. The results reveal competing interactions between spontaneous oscillations and stimulation-evoked brain activities in somatosensory cortex and the resultant hemodynamics.

The effect of caffeine on cerebral metabolism during alpha-chloralose anesthesia differs from isoflurane anesthesia in the rat brain

RATIONALE

Caffeine is a widely studied psychostimulant, even though its exact effect on brain activity remains to be elucidated. Positron emission tomography (PET) allows studying mechanisms underlying cerebral metabolic responses to caffeine in caffeine-naïve rats. Rodent studies are typically performed under anesthesia. However, the anesthesia may affect neurotransmitter systems targeted by tested drugs.

OBJECTIVES

The scope of the present study was to address the impairing or enhancing effect of two common anesthetics, alpha-chloralose and isoflurane, on the kinetics of caffeine.

METHODS

The first group of rats (n = 15) were anesthetized under 1.5% isoflurane anesthesia. The second group of rats (n = 15) were anesthetized under alpha-chloralose (80 mg/kg). These rats received an intravenous injection of saline (n = 5) or of 2.5 mg/kg (n = 5) or 40 mg/kg (n = 5) caffeine for both groups.

RESULTS

With 2.5 mg/kg or 40 mg/kg caffeine, whole-brain cerebral metabolism was significantly reduced by 17.2% and 17% (both P < 0.01), respectively, under alpha-chloralose anesthesia. However, the lower dose of caffeine (2.5 mg/kg) had a limited effect on brain metabolism, whereas its higher dose (40 mg/kg) produced enhancements in brain metabolism in the striatum, hippocampus, and thalamus (all P < 0.05) under isoflurane anesthesia.

CONCLUSION

These findings demonstrate significant differences in brain responses to caffeine on the basic of the anesthesia regimen used, which highlights the importance of attention to the anesthetic used when interpreting findings from animal pharmacological studies because of possible interactions between the anesthetic and the drug under study.

Altered neurovascular coupling and brain arginine metabolism in endothelial nitric oxide synthase deficient mice

Nitric oxide (NO) produced by endothelial NO synthase (eNOS) is a key regulator of cerebral blood flow (CBF) dynamics. Mice with eNOS deficiency (eNOS^-/-) display age-related increases in amyloid beta in the brain and memory deficits, implicating eNOS dysfunction in the neuropathogenesis and/or development of Alzheimer's disease (AD). The present study systematically investigated behavioural, CBF and brain arginine metabolic profile changes in male and female wildtype (WT) and eNOS^-/- mice at 14 months of age. eNOS^-/- mice displayed altered behaviour in the Y-maze and open field tests. A real-time microcirculation imager revealed a significant sex difference in the basal CBF and significantly increased perfusion response to whisker stimulations in the Barrel cortex in both male and female eNOS^-/- mice relative to their sex-matched WT controls. The treatment of 7-nitroindazole blocked the increased perfusion response to whisker stimulations in eNOS^-/- mice. Neurochemically, the most intriguing changes were markedly reduced glutamine levels in both male and female eNOS^-/- mice in the frontal cortex, hippocampus, parahippocampal region and cerebellum. These findings demonstrate altered behavioural function, neurovascular coupling and brain arginine metabolism (glutamine in particular) under the condition of eNOS deficiency, which further supports the role of eNOS dysfunction in the AD neuropathogenesis.

How to monitor breathing in laboratory rodents: a review of the current methods

Accurately measuring respiration in laboratory rodents is essential for many fields of research, including olfactory neuroscience, social behavior, learning and memory, and respiratory physiology. However, choosing the right technique to monitor respiration can be tricky, given the many criteria to take into account: reliability, precision, and invasiveness, to name a few. This review aims to assist experimenters in choosing the technique that will best fit their needs, by surveying the available tools, discussing their strengths and weaknesses, and offering suggestions for future improvements.

Brain tumors disrupt the resting-state connectome

Brain tumor patients often experience functional deficits that extend beyond the tumor site. While resting-state functional MRI (rsfMRI) has been used to map such functional connectivity changes in brain tumor patients, the interplay between abnormal tumor vasculature and the rsfMRI signal is still not well understood. Therefore, there is an exigent need for new tools to elucidate how the blood‑oxygenation-level-dependent (BOLD) rsfMRI signal is modulated in brain cancer. In this initial study, we explore the utility of a preclinical model for quantifying brain tumor-induced changes on the rsfMRI signal and resting-state brain connectivity. We demonstrate that brain tumors induce brain-wide alterations of resting-state networks that extend to the contralateral hemisphere, accompanied by global attenuation of the rsfMRI signal. Preliminary histology suggests that some of these alterations in brain connectivity may be attributable to tumor-related remodeling of the neurovasculature. Moreover, this work recapitulates clinical rsfMRI findings from brain tumor patients in terms of the effects of tumor size on the neurovascular microenvironment. Collectively, these results lay the foundation of a preclinical platform for exploring the usefulness of rsfMRI as a potential new biomarker in patients with brain cancer.

The effects of hypercapnia on cortical capillary transit time heterogeneity (CTH) in anesthetized mice

Capillary flow patterns are highly heterogeneous in the resting brain. During hyperemia, capillary transit-time heterogeneity (CTH) decreases, in proportion to blood's mean transit time (MTT) in passive, compliant microvascular networks. Previously, we found that functional activation reduces the CTH:MTT ratio, suggesting that additional homogenization takes place through active neurocapillary coupling mechanisms. Here, we examine changes in the CTH:MTT ratio during hypercapnic hyperemia in anesthetized mice (C57Bl/6NTac), expecting that homogenization is smaller than during functional hyperemia. We used an indicator-dilution technique and multiple capillary scans by two-photon microscopy to estimate CTH and MTT. During hypercapnia, MTT and CTH decreased as derived from indicator-dilution between artery and vein, as well as between arterioles and venules. The CTH:MTT ratio, however, increased. The same tendency was observed in the estimates from capillary scans. The parallel reductions of MTT and CTH are consistent with previous data. We speculate that the relative increase in CTH compared to MTT during hypercapnia represents either or both capillary constrictions and blood passage through functional thoroughfare channels. Intriguingly, hemodynamic responses to hypercapnia declined with cortical depth, opposite previous reports of hemodynamic responses to functional activation. Our findings support the role of CTH in cerebral flow-metabolism coupling during hyperemia.

Neural and metabolic basis of dynamic resting state fMRI

Resting state fMRI (rsfMRI) as a technique showed much initial promise for use in psychiatric and neurological diseases where diagnosis and treatment were difficult. To realize this promise, many groups have moved towards examining "dynamic rsfMRI," which relies on the assumption that rsfMRI measurements on short time scales remain relevant to the underlying neural and metabolic activity. Many dynamic rsfMRI studies have demonstrated differences between clinical or behavioral groups beyond what static rsfMRI measured, suggesting a neurometabolic basis. Correlative studies combining dynamic rsfMRI and other physiological measurements have supported this. However, they also indicate multiple mechanisms and, if using correlation alone, it is difficult to separate cause and effect. Hypothesis-driven studies are needed, a few of which have begun to illuminate the underlying neurometabolic mechanisms that shape observed differences in dynamic rsfMRI. While the number of potential noise sources, potential actual neurometabolic sources, and methodological considerations can seem overwhelming, dynamic rsfMRI provides a rich opportunity in systems neuroscience. Even an incrementally better understanding of the neurometabolic basis of dynamic rsfMRI would expand rsfMRI's research and clinical utility, and the studies described herein take the first steps on that path forward.

Demonstration of impaired neurovascular coupling responses in TG2576 mouse model of Alzheimer's disease using functional laser speckle contrast imaging

Increasing evidence from epidemiological, clinical, and experimental studies indicates that cerebromicrovascular dysfunction and microcirculatory damage play critical roles in the pathogenesis of many types of dementia in the elderly, including both vascular cognitive impairment (VCI) and Alzheimer's disease. Vascular contributions to cognitive impairment and dementia (VCID) include impairment of neurovascular coupling responses/functional hyperemia ("neurovascular uncoupling"). Due to the growing interest in understanding and pharmacologically targeting pathophysiological mechanisms of VCID, there is an increasing need for sensitive, easy-to-establish methods to assess neurovascular coupling responses. Laser speckle contrast imaging (LSCI) is a technique that allows rapid and minimally invasive visualization of changes in regional cerebromicrovascular blood perfusion. This type of imaging technique combines high resolution and speed to provide great spatiotemporal accuracy to measure moment-to-moment changes in cerebral blood flow induced by neuronal activation. Here, we provide detailed protocols for the successful measurement in neurovascular coupling responses in anesthetized mice equipped with a thinned-skull cranial window using LSCI. This method can be used to evaluate the effects of anti-aging or anti-AD treatments on cerebromicrovascular health.

Acute cardiac support with intravenous milrinone promotes recovery from early brain injury in a murine model of severe subarachnoid haemorrhage

Early brain injury/ischaemia (EBI) is a serious complication early after subarachnoid haemorrhage (SAH) that contributes to development of delayed cerebral ischaemia (DCI). This study aimed to determine the role of inotropic cardiac support using milrinone (MIL) on restoring acute cerebral hypoperfusion attributable to EBI and improving outcomes after experimental SAH. Forty-three male C57BL/6 mice were assigned to either sham surgery (SAH-sham), SAH induced by endovascular perforation plus postconditioning with 2% isoflurane (Control), or SAH plus isoflurane combined with MIL with and without hypoxia-inducible factor inhibitor (HIF-I) pretreatment. Cardiac output (CO) during intravenous MIL infusion (0.25-0.75 μg/kg/min) between 1.5 and 2.5 hours after SAH induction was monitored with Doppler echocardiography. Magnetic resonance imaging (MRI)-continuous arterial spin labelling was used for quantitative cerebral blood flow (CBF) measurements. Neurobehavioral function was assessed daily by neurological score and open field test. DCI was analyzed 3 days later by determining infarction on MRI. Mild reduction of cardiac output (CO) and global cerebral blood flow (CBF) depression were notable early after SAH. MIL increased CO in a dose-dependent manner (P<.001), which was accompanied by improved hypoperfusion, incidence of DCI and functional recovery than Control (P<.05). The neuroprotective effects afforded by MIL or Control were attenuated by hypoxia-inducible factor (HIF) inhibition (P<.05). These results suggest that MIL improves acute hypoperfusion by its inotropic effect, leading to neurobehavioral improvement in mice after severe SAH, in which HIF may be acting as a critical mediator.

High-density speckle contrast optical tomography (SCOT) for three dimensional tomographic imaging of the small animal brain

High-density speckle contrast optical tomography (SCOT) utilizing tens of thousands of source-detector pairs, was developed for in vivo imaging of blood flow in small animals. The reduction in cerebral blood flow (CBF) due to local ischemic stroke in a mouse brain was transcanially imaged and reconstructed in three dimensions. The reconstructed volume was then compared with corresponding magnetic resonance images demonstrating that the volume of reduced CBF agrees with the infarct zone at twenty-four hours.

Altered regional connectivity reflecting effects of different anaesthesia protocols in the mouse brain

Studies in mice using resting-state functional magnetic resonance imaging (rs-fMRI) have provided opportunities to investigate the effects of pharmacological manipulations on brain function and map the phenotypes of mouse models of human brain disorders. Mouse rs-fMRI is typically performed under anaesthesia, which induces both regional suppression of brain activity and disruption of large-scale neural networks. Previous comparative studies using rodents investigating various drug effects on long-distance functional connectivity (FC) have reported agent-specific FC patterns, however, effects of regional suppression are sparsely explored. Here we examined changes in regional connectivity under six different anaesthesia conditions using mouse rs-fMRI with the goal of refining the framework of understanding the brain activation under anaesthesia at a local level. Regional homogeneity (ReHo) was used to map local synchronization in the brain, followed by analysis of several brain areas based on ReHo maps. The results revealed high local coherence in most brain areas. The primary somatosensory cortex and caudate-putamen showed agent-specific properties. Lower local coherence in the cingulate cortex was observed under medetomidine, particularly when compared to the combination of medetomidine and isoflurane. The thalamus was associated with retained local coherence across anaesthetic levels and multiple nuclei. These results show that anaesthesia induced by the investigated anaesthetics through different molecular targets promote agent-specific regional connectivity. In addition, ReHo is a data-driven method with minimum user interaction, easy to use and fast to compute. Given that examination of the brain at a local level is widely applied in human rs-fMRI studies, our results show its sensitivity to extract information on varied neuronal activity under six different regimens relevant to mouse functional imaging. These results, therefore, will inform future rs-fMRI studies on mice and the type of anaesthetic agent used, and will help to bridge observations between this burgeoning research field and ongoing human research across analytical scales.

Neurocardiac protection with milrinone for restoring acute cerebral hypoperfusion and delayed ischemic injury after experimental subarachnoid hemorrhage

BACKGROUND AND PURPOSE

Acute cerebral hypoperfusion following subarachnoid hemorrhage (SAH) is highly related to the pathogenesis of delayed cerebral ischemia (DCI), but the therapeutic option is poorly available. This study aimed to clarify the effect of milrinone (MIL) on cerebral blood flow (CBF) and related outcomes after experimental SAH.

METHODS

Twenty-seven male C57BL/6 mice were assigned to either sham surgery (SAH-sham; n=6), SAH induced by endovascular perforation (control; n=10), or SAH followed by cardiac support with intravenous MIL (n=11) performed 1.5-h after SAH induction. CBF, neurobehavioral function, occurrence of DCI were assessed by MR-continuous arterial spin labeling, daily neurological score testing, and diffusion- and T2-weighted MR images on days 1 and 3, respectively.

RESULTS

Initial global CBF depression was notable in mice of control and MIL groups as compared to the SAH-sham group (P<0.05). MIL raised CBF in a dose-dependent manner (P<0.001), resulted in lower incidence of DCI (P=0.008) and better recovery from neurobehavioral decline than control (P<0.001). The CBF values on day 1 predicted DCI with a cut-off of 42.5ml/100g/min (82% specificity and 83% sensitivity), which was greater in mice treated with MIL than those of control (51.7 versus 37.6ml/100g/min; P<0.001).

CONCLUSION

MIL improves post-SAH acute hypoperfusion that can lead to the prevention of DCI and functional worsening, acting as a neurocardiac protective agent against EBI.

Inotropic support against early brain injury improves cerebral hypoperfusion and outcomes in a murine model of subarachnoid hemorrhage

Early brain injury/ischemia is a recent therapeutic target that contributes to triggering delayed cerebral ischemia (DCI) in the setting of subarachnoid hemorrhage (SAH). This study aimed to determine the role of dobutamine for inotropic cardiac support in improving cerebral blood flow (CBF) and outcomes after experimental SAH, mediated by hypoxia-inducible factor (HIF). Thirty-one mice were subjected to SAH by endovascular perforation, and assigned to either 2% isoflurane postconditioning performed between 1 and 2.5h after SAH induction or concomitant intravenous dobutamine infusion (15μg/kg/min) with or without HIF inhibitor 2-methoxyestradiol (2ME2) (10mg/kg) administered intraperitoneally. Neurobehavioral function was assessed daily by neurological scores and open field testing. DCI was defined 3days later by detecting a new infarction on MRI. Global CBF depression was notable early after SAH, but dobutamine showed significant improvement in CBF, lower incidence of DCI, and better recovery of neuroscores and open field test variables compared with isoflurane postconditioning (P<0.05). CBF over the entire brain on day 1 predicted DCI with a cut-off of 36.5ml/100g/min (80% specificity and 67% sensitivity), with a better area under the curve (0.83 versus 0.75) than the hemispheric CBF measured on the perforated side. The dobutamine-mediated outcomes were attenuated (P<0.05) by 2ME2 pretreatment. The data suggest that cardiac support with dobutamine improves global CBF depression induced by early brain injury, leading to reduced prevalence of DCI and better functional outcomes after experimental SAH, in which HIF may be acting as a critical mediator.