Continuous positive airway pressure increases CSF flow and glymphatic transport

Respiration can positively influence cerebrospinal fluid (CSF) flow in the brain, yet its effects on central nervous system (CNS) fluid homeostasis, including waste clearance function via glymphatic and meningeal lymphatic systems, remain unclear. Here, we investigated the effect of supporting respiratory function via continuous positive airway pressure (CPAP) on glymphatic-lymphatic function in spontaneously breathing anesthetized rodents. To do this, we used a systems approach combining engineering, MRI, computational fluid dynamics analysis, and physiological testing. We first designed a nasal CPAP device for use in the rat and demonstrated that it functioned similarly to clinical devices, as evidenced by its ability to open the upper airway, augment end-expiratory lung volume, and improve arterial oxygenation. We further showed that CPAP increased CSF flow speed at the skull base and augmented glymphatic transport regionally. The CPAP-induced augmented CSF flow speed was associated with an increase in intracranial pressure (ICP), including the ICP waveform pulse amplitude. We suggest that the augmented pulse amplitude with CPAP underlies the increase in CSF bulk flow and glymphatic transport. Our results provide insights into the functional crosstalk at the pulmonary-CSF interface and suggest that CPAP might have therapeutic benefit for sustaining glymphatic-lymphatic function

Normothermic mouse functional MRI of acute focal thermostimulation for probing nociception

Combining mouse genomics and functional magnetic resonance imaging (fMRI) provides a promising tool to unravel the molecular mechanisms of chronic pain. Probing murine nociception via the blood oxygenation level-dependent (BOLD) effect is still challenging due to methodological constraints. Here we report on the reproducible application of acute noxious heat stimuli to examine the feasibility and limitations of functional brain mapping for central pain processing in mice. Recent technical and procedural advances were applied for enhanced BOLD signal detection and a tight control of physiological parameters. The latter includes the development of a novel mouse cradle designed to maintain whole-body normothermia in anesthetized mice during fMRI in a way that reflects the thermal status of awake, resting mice. Applying mild noxious heat stimuli to wildtype mice resulted in highly significant BOLD patterns in anatomical brain structures forming the pain matrix, which comprise temporal signal intensity changes of up to 6% magnitude. We also observed sub-threshold correlation patterns in large areas of the brain, as well as alterations in mean arterial blood pressure (MABP) in response to the applied stimulus

Doctor of Philosophy

dissertationThe goal of this study was to investigate the bioavailability, efficacy, and safety of inhaled remifentanil, inhaled remimazolam, and combinations of both drugs in mouse, rat, and pig models. Anesthesiology could benefit from efficacious, noninvasively delivered, short acting, and thereby easily titratable analgesic/sedative agents. Remifentanil and remimazolam are potentially advantageous due to their esterase-based metabolism and rapid elimination profiles, particularly to high-risk populations such as obese, elderly, and pediatric populations. Dosing via spontaneous respiration can inherently and safely control the duration and level of sedation and analgesia via patient minute ventilation. There is no inhaled opioid or benzodiazepine currently available for clinical use as an anesthetic agent. It was our hypothesis that remifentanil and remimazolam delivered by inhalation would be rapidly absorbed, pharmacologically active, rapidly cleared, and noninjurious to rodent airways and lungs. We also hypothesized that the pharmacokinetics of inhaled remifentanil in pigs would exhibit similar rapid onset and recovery. Inhaled remifentanil in rats induced profound analgesia with rapid recovery. Inhaled remimazolam in mice produced sedation, while inhaled remimazolam in rats did not produce sedation at the maximum dose able to be achieved in aerosols. Remimazolam delivered in combination with remifentanil potentiated the analgesic response. Pulmonary mechanics and histology showed no irritation or injury by either drug or the combination. Pharmacokinetic analysis of both drugs in rodents were consistent with the pharmacological effects and a study of inhaled remifentanil in pigs demonstrated rapid absorption and clearance of the drug consistent with those reported for intravenous dosing in humans and animals. We have shown that remifentanil and remimazolam, administered alone or in combination, can be a clinically relevant method of anesthesia. These fundamental experiments and results are critical for the future development of formulations for inhalation delivery of these drugs for clinical use. These inhaled drugs could eventually revolutionize the ease and practicality of administering inhaled anesthetic agents, both inside and outside of the operating room

Acute and long-term effects of isoflurane and sevoflurane anaesthesia in laboratory mice

Isoflurane is to date the most common volatile anaesthetic in laboratory rodents whereas the modern sevoflurane is usual for inhalation anaesthesia in human medicine. In this study it was aimed to characterize and compare the clinical properties and safety of both anaesthetics for anaesthetizing mice. In an approach that mirrors the laboratory routine (spontaneous breathing, gas supply via nose mask, preventing hypothermia by a warming mat) a 50-minutes anaesthesia was performed. Anaesthetics were administered at standardized dosages of 1.5 X minimum alveolar concentrations (1.85% for isoflurane, 3.25% for sevoflurane) in 100% oxygen. Induction and recovery from anaesthesia proceeded quickly, within 1 and 2 minutes respectively. During anaesthesia, all reflex testing were negative and no serious impairment of vital functions was found; all animals survived. Most prominent side effect during anaesthesia was the respiratory depression with marked decrease of respiration rate, hypercapnia and acidosis. Under anaesthesia, heart rate and core body temperature remained stable and within normal range, but were significantly increased for 12 hours after anaesthesia. Locomotor activity, food and water consumption and body weight progression showed no abnormalities after anaesthesia. No relevant differences between the two anaesthetics were found. In conclusion, both anaesthetics equally provide high safety margin with acceptable side effects and are therefore recommended for anaesthesia in laboratory mice

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\u27 recommendation based on the authors\u27 clinical experiences

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

Sestrins are evolutionarily conserved mediators of exercise benefits.

Exercise is among the most effective interventions for age-associated mobility decline and metabolic dysregulation. Although long-term endurance exercise promotes insulin sensitivity and expands respiratory capacity, genetic components and pathways mediating the metabolic benefits of exercise have remained elusive. Here, we show that Sestrins, a family of evolutionarily conserved exercise-inducible proteins, are critical mediators of exercise benefits. In both fly and mouse models, genetic ablation of Sestrins prevents organisms from acquiring metabolic benefits of exercise and improving their endurance through training. Conversely, Sestrin upregulation mimics both molecular and physiological effects of exercise, suggesting that it could be a major effector of exercise metabolism. Among the various targets modulated by Sestrin in response to exercise, AKT and PGC1α are critical for the Sestrin effects in extending endurance. These results indicate that Sestrin is a key integrating factor that drives the benefits of chronic exercise to metabolism and physical endurance

Occupational exposure to isoflurane anesthetic gas in the research environment

This dissertation is a compilation of studies related to the halogenated anesthetic gas isoflurane. Historically, halogenated anesthetic gases have been used in the health care industry. In 1977 the National Institute for Occupational Safety and Health (NIOSH) issued a recommended exposure limit (REL) of two parts per million (ppm) averaged over one hour of exposure for halogenated anesthetic gases (NIOSH 1977). The purpose of the standard was to protect healthcare workers from exposure to halothane, methoxyflurane, and chloroform. However, isoflurane only became available after the NIOSH REL was adopted. Therefore, the NIOSH REL is not directly applicable to isoflurane. Moreover, use of isoflurane in healthcare has diminished over the years, and it is now more widely used in medical research laboratories and veterinary clinics. The purpose of this dissertation is to demonstrate the need for an updated occupational exposure limit for isoflurane. Four studies were conducted toward the completion of this goal; a systematic review of the literature to investigate human health effects associated with occupational exposure to isoflurane, a case study of a high exposure to isoflurane and its control, an assessment of occupational exposure of isoflurane to researchers, and a comparison of the effectiveness of control methods in reducing isoflurane waste anesthetic gas (WAG). In the first study, we searched the PubMed and Embase databases were searched for articles with data on health effects associated with occupational isoflurane exposure. Thirteen studies were found during the search that fit the review criteria. Five of the studies reported no adverse human health effects. Eight of the studies reported human health effects ranging from genetic mutations, changes in cellular function, symptoms of acute exposure, and congenital anomalies in the offspring of exposed women. In the second study, we found that researchers working with isoflurane in a small unventilated space had exposures close to 30 ppm over a short-time period (0.48 and 1.15 hours) for the main researcher. Other members of the group had exposures above 2 parts per million (ppm). An active scavenging ventilation control which reduced isoflurane exposure by an average of 86%. In the third study, we showed that isoflurane exposure to researchers at a medical research institution was significantly associated with scavenging technique and role of the investigator (p = 0.02 and 0.04, respectively). Researchers using passive scavenging canisters were exposed to a mean concentration of 3.18 ppm (%CV = 123) and researchers using active scavenging were exposed to a mean isoflurane concentration of 0.83 ppm (% CV = 89). Researchers who performed the greater part of the procedures were exposed to a mean of 2.71 ppm (%CV = 108) and researchers who assisted were exposed to a mean of 1.18 ppm (%CV = 97). In the final study, we evaluated isoflurane exposures when using active scavengers, passive canister scavengers, and combinations of both scavenging techniques. We also evaluated isoflurane exposures with no scavenging control. Isoflurane concentration was significantly associated with control method (p \u3c 0.0001). Post hoc Tukey’s comparison showed the significant difference (p = 0.05) in isoflurane concentration between no scavenging and active scavenging conditions, no scavenging and combination active and passive scavenging conditions, and passive and active scavenging conditions. There was no difference between no scavenging and passive scavenging conditions or active scavenging and combination scavenging conditions. The mean isoflurane concentration while using no scavenging controls was 10.23 ppm (%CV = 12), and was 10.35 ppm (%CV = 58) while using passive scavenging. Isoflurane concentration using active scavenging was 1.43 ppm (%CV = 15) and 0.59 ppm (%CV = 46) while using the combination scavenging method. Researchers who use passive scavenging methods are more likely to be at risk for isoflurane exposure above 2 ppm. Researchers should use active scavenging to control isoflurane WAG

Inhalation exposure methodology.

Modern man is being confronted with an ever-increasing inventory of potentially toxic airborne substances. Exposures to these atmospheric contaminants occur in residential and commercial settings, as well as in the workplace. In order to study the toxicity of such materials, a special technology relating to inhalation exposure systems has evolved. The purpose of this paper is to provide a description of the techniques which are used in exposing laboratory subjects to airborne particles and gases. The various modes of inhalation exposure (whole body, head only, nose or mouth only, etc.) are described at length, including the advantages and disadvantages inherent to each mode. Numerous literature citations are included for further reading. Among the topics briefly discussed are the selection of appropriate animal species for toxicological testing, and the types of inhalation studies performed (acute, chronic, etc.)