Sex effects on behavioral markers of emergence from propofol and isoflurane anesthesia in rats

Exogenous Ketone Supplement Administration Abrogated Isoflurane-Anesthesia-Induced Increase in Blood Glucose Level in Female WAG/Rij Rats

It has been demonstrated that isoflurane-induced anesthesia can increase the blood glucose level, leading to hyperglycemia and several adverse effects. The administration of a mix of ketone diester (KE) and medium-chain triglyceride (MCT) oil, named KEMCT, abolished the isoflurane-anesthesia-induced increase in blood glucose level and prolonged the recovery time from isoflurane anesthesia in a male preclinical rodent model, Wistar Albino Glaxo/Rijswijk (WAG/Rij) rats. While most preclinical studies use exclusively male animals, our previous study on blood glucose changes in response to KEMCT administration showed that the results can be sex-dependent. Thus, in this study, we investigated female WAG/Rij rats, whether KEMCT gavage (3 g/kg/day for 7 days) can change the isoflurane (3%)-anesthesia-induced increase in blood glucose level and the recovery time from isoflurane-evoked anesthesia using the righting reflex. Moreover, KEMCT-induced ketosis may enhance both the extracellular level of adenosine and the activity of adenosine A1 receptors (A1Rs). To obtain information on the putative A1R mechanism of action, the effects of an A1R antagonist, DPCPX (1,3-dipropyl-8-cyclopentylxanthine; intraperitoneal/i.p. 0.2 mg/kg), on KEMCT-generated influences were also investigated. Our results show that KEMCT supplementation abolished the isoflurane-anesthesia-induced increase in blood glucose level, and this was abrogated by the co-administration of DPCPX. Nevertheless, KEMCT gavage did not change the recovery time from isoflurane-induced anesthesia. We can conclude that intragastric gavage of exogenous ketone supplements (EKSs), such as KEMCT, can abolish the isoflurane-anesthesia-induced increase in blood glucose level in both sexes likely through A1Rs in WAG/Rij rats, while recovery time was not affected in females, unlike in males. These results suggest that the administration of EKSs as an adjuvant therapy may be effective in mitigating metabolic side effects of isoflurane, such as hyperglycemia, in both sexes.

Hormonal basis of sex differences in anesthetic sensitivity

General anesthesia-a pharmacologically induced reversible state of unconsciousness-enables millions of life-saving procedures. Anesthetics induce unconsciousness in part by impinging upon sexually dimorphic and hormonally sensitive hypothalamic circuits regulating sleep and wakefulness. Thus, we hypothesized that anesthetic sensitivity should be sex-dependent and modulated by sex hormones. Using distinct behavioral measures, we show that at identical brain anesthetic concentrations, female mice are more resistant to volatile anesthetics than males. Anesthetic sensitivity is bidirectionally modulated by testosterone. Castration increases anesthetic resistance. Conversely, testosterone administration acutely increases anesthetic sensitivity. Conversion of testosterone to estradiol by aromatase is partially responsible for this effect. In contrast, oophorectomy has no effect. To identify the neuronal circuits underlying sex differences, we performed whole brain c-Fos activity mapping under anesthesia in male and female mice. Consistent with a key role of the hypothalamus, we found fewer active neurons in the ventral hypothalamic sleep-promoting regions in females than in males. In humans, we demonstrate that females regain consciousness and recover cognition faster than males after identical anesthetic exposures. Remarkably, while behavioral and neurocognitive measures in mice and humans point to increased anesthetic resistance in females, cortical activity fails to show sex differences under anesthesia in either species. Cumulatively, we demonstrate that sex differences in anesthetic sensitivity are evolutionarily conserved and not reflected in conventional electroencephalographic-based measures of anesthetic depth. This covert resistance to anesthesia may explain the higher incidence of unintended awareness under general anesthesia in females.

GABAergic Neurons in the Nucleus Accumbens are Involved in the General Anesthesia Effect of Propofol

The mechanism underlying the hypnosis effect of propofol is still not fully understood. In essence, the nucleus accumbens (NAc) is crucial for regulating wakefulness and may be directly engaged in the principle of general anesthesia. However, the role of NAc in the process of propofol-induced anesthesia is still unknown. We used immunofluorescence, western blotting, and patch-clamp to access the activities of NAc GABAergic neurons during propofol anesthesia, and then we utilized chemogenetic and optogenetic methods to explore the role of NAc GABAergic neurons in regulating propofol-induced general anesthesia states. Moreover, we also conducted behavioral tests to analyze anesthetic induction and emergence. We found out that c-Fos expression was considerably dropped in NAc GABAergic neurons after propofol injection. Meanwhile, patch-clamp recording of brain slices showed that firing frequency induced by step currents in NAc GABAergic neurons significantly decreased after propofol perfusion. Notably, chemically selective stimulation of NAc GABAergic neurons during propofol anesthesia lowered propofol sensitivity, prolonged the induction of propofol anesthesia, and facilitated recovery; the inhibition of NAc GABAergic neurons exerted opposite effects. Furthermore, optogenetic activation of NAc GABAergic neurons promoted emergence whereas the result of optogenetic inhibition was the opposite. Our results demonstrate that NAc GABAergic neurons modulate propofol anesthesia induction and emergence.

Estrogen Receptor-A in Medial Preoptic Area Contributes to Sex Difference of Mice in Response to Sevoflurane Anesthesia

A growing number of studies have identified sex differences in response to general anesthesia; however, the underlying neural mechanisms are unclear. The medial preoptic area (MPA), an important sexually dimorphic structure and a critical hub for regulating consciousness transition, is enriched with estrogen receptor alpha (ERα), particularly in neuronal clusters that participate in regulating sleep. We found that male mice were more sensitive to sevoflurane. Pharmacological inhibition of ERα in the MPA abolished the sex differences in sevoflurane anesthesia, in particular by extending the induction time and facilitating emergence in males but not in females. Suppression of ERα in vitro inhibited GABAergic and glutamatergic neurons of the MPA in males but not in females. Furthermore, ERα knockdown in GABAergic neurons of the male MPA was sufficient to eliminate sex differences during sevoflurane anesthesia. Collectively, MPA ERα positively regulates the activity of MPA GABAergic neurons in males but not in females, which contributes to the sex difference of mice in sevoflurane anesthesia.

Propofol ameliorates acute postoperative fatigue and promotes glucagon-regulated hepatic gluconeogenesis by activating CREB/PGC-1α and accelerating fatty acids beta-oxidation

Postoperative fatigue (POF) is the most common and long-lasting complication after surgery, which brings heavy burden to individuals and society. Recently, hastening postoperative recovery receives increasing attention, but unfortunately, the mechanisms underlying POF remain unclear. Propofol is a wildly used general anesthetic in clinic, and inspired by the rapid antidepressant effects induced by ketamine at non-anesthetic dose, the present study was undertaken to investigate the anti-fatigue effects and underlying mechanisms of propofol at a non-anesthetic dose in 70% hepatectomy induced POF model in rats. We first showed here that single administration of propofol at 0.1 mg/kg ameliorated acute POF in hepatectomy induced POF rats. Based on metabonomics analysis, we hypothesized that propofol exerted anti-fatigue activity in POF rats by facilitating free fatty acid (FFA) oxidation and gluconeogenesis. We further confirmed that propofol restored the deficit in FFA oxidation and gluconeogenesis in POF rats, as evidenced by the elevated FFA utilization, acetyl coenzyme A content, pyruvic acid content, phosphoenolpyruvic acid content, hepatic glucose output and glycogen storage. Moreover, propofol stimulated glucagon secretion and up-regulated expression of cAMP-response element binding protein (CREB), phosphorylated CREB, peroxlsome prolifeator-activated receptor-γ coactivator-1α (PGC-1α), phosphoenolpyruvate carboxykinade1 and carnitine palmitoltransferase 1A. In summary, our study suggests for the first time that propofol ameliorates acute POF by promoting glucagon-regulated gluconeogenesis via CREB/PGC-1α signaling and accelerating FFA beta-oxidation.

Brain networks and endogenous pain inhibition are modulated by age and sex in healthy rats

Endogenous pain inhibition is less efficient in chronic pain patients. Diffuse noxious inhibitory control (DNIC), a form of endogenous pain inhibition, is compromised in women and older people, making them more vulnerable to chronic pain. However, the underlying mechanisms remain unclear. Here, we used a capsaicin-induced DNIC test and resting-state functional MRI to investigate the impact of aging and sex on endogenous pain inhibition and associated brain circuitries in healthy rats. We found that DNIC was less efficient in young females compared with young males. Diffuse noxious inhibitory control response was lost in old rats of both sexes, but the brain networks engaged during DNIC differed in a sex-dependent manner. Young males had the most efficient analgesia with the strongest connectivity between anterior cingulate cortex (ACC) and periaqueductal gray (PAG). The reduced efficiency of DNIC in young females seemed to be driven by widespread brain connectivity. Old males showed increased connectivity between PAG, raphe nuclei, pontine reticular nucleus, and hippocampus, which may not be dependent on connections to ACC, whereas old females showed increased connectivity between ACC, PAG, and more limbic regions. These findings suggest that distinct brain circuitries including the limbic system may contribute to higher susceptibility to pain modulatory deficits in the elderly population, and sex may be a risk factor for developing age-related chronic pain.

Repetitive Anodal Transcranial Direct Current Stimulation Hastens Isoflurane-Induced Emergence and Recovery and Enhances Memory in Healthy Rats

BACKGROUND

Attaining a rapid and smooth return to consciousness after general anesthesia is a goal for clinical anesthesiologists. This study aimed to investigate the effects of repeated anodal transcranial direct current stimulation (atDCS) on emergence and recovery from isoflurane anesthesia in rats.

METHODS

Four days after surgery for atDCS socket implantation, rats received either sham stimulation or repetitive anodal direct electrical current of 0.2 mA intensity applied to the right motor cortex for 20 minutes/d for 10 consecutive days. Isoflurane potency and emergence and recovery from a 2-hour isoflurane challenge were evaluated 24 hours after the last atDCS session. Cognitive performance on novel object recognition and spontaneous alternation Y-maze tests were measured 48 hours after the last atDCS session. Locomotor activity was assessed via automated counting of electric infrared beam crossings.

RESULTS

Data are expressed as mean ± standard error of mean (SEM). Isoflurane potency was not affected by atDCS (sham: 1.69% ± 0.06%, transcranial direct current stimulation [tDCS]: 1.73% ± 0.11%, mean difference [MD]: 0.045, 95% confidence interval [CI]: -0.22 to 0.30; P = .72). However, the time to appearance of emergence behavioral marker (eg, return of righting reflex) was hastened in rats receiving atDCS (sham: 486 ± 31 seconds, tDCS: 330 ± 45 seconds, MD: 157, 95% CI: 30-284; P = .008). Similarly, time to acknowledgment of adhesive tape ("sticky dot" applied while anesthetized) was also decreased in atDCS-treated rats as compared to sham (sham: 1374 ± 179 seconds, tDCS: 908 ± 151 seconds, MD: 466, 95% CI: 73-858; P = .015), indicating a faster recovery of isoflurane anesthesia. Rats treated with atDCS spent more time exploring the novel object and environment when compared to sham without affecting activity cycles, indicating visual and working memory can be enhanced by atDCS.

CONCLUSIONS

Taken together, our findings suggest that atDCS over cortical areas might hasten recovery from isoflurane anesthesia and could potentially be used as a preventative strategy for disruptions in higher order functions related to sedation/anesthesia.

Prehabilitative exercise hastens recovery from isoflurane in diabetic and non-diabetic rats

Diabetes has been demonstrated to be one of the strongest predictors of risk for postoperative delirium and functional decline in older patients undergoing surgery. Exercise is often prescribed as a treatment for diabetic patients and regular physical activity is hypothesized to decrease the risk of postoperative cognitive impairments. Prior studies suggest that anesthetic emergence trajectories and recovery are predictive of risk for later postoperative cognitive impairments. Therapeutic strategies aimed at improving emergence and recovery from anesthesia may therefore be beneficial for diabetic patients. Wistar (n = 32) and Goto-Kakizaki (GK) type 2 diabetic (n = 32) rats between 3-4 months old underwent treadmill exercise for 30 min/day for ten days or remained inactive. Pre-anesthesia spontaneous alternation behavior was recorded with a Y-maze. Rats then received a 2-h exposure to 1.5-2 % isoflurane or oxygen only. The time to reach anesthetic emergence and post-anesthesia recovery behaviors was recorded for each rat. Postsynaptic density protein-95 (PSD-95), an important scaffolding protein required for synaptic plasticity, protein levels were quantified from hippocampus using western blot. Spontaneous alternation behavior (p = 0.044) and arm entries (p < 0.001) were decreased in GK rats. There was no difference between groups in emergence times from isoflurane, but exercise hastened the recovery time (p = 0.008) for both Wistar and GK rats. Following 10 days of exercise, both Wistar and GK rats show increased levels of PSD-95 in the hippocampus. Prehabilitation with moderate intensity exercise, even on a short timescale, is beneficial for recovery from isoflurane in rats, regardless of metabolic disease status.

Sex differences in the elevated plus-maze test and large open field test in adult Wistar rats

There is a growing need for a better understanding of sex differences in animal models of psychiatric disorders. The elevated plus-maze (EPM) test and large open field (LOF) test are widely used to study anxiety-like behavior in rodents. Our studies explored sex differences in anxiety and activity parameters in the LOF and EPM and determined whether these parameters correlate within and between tests. Drug naïve adult male and female Wistar rats (n = 47/sex) were used for the studies, and the rats were tested for 5 min in the EPM and 10 min in the LOF. The females spent more time on the open arms of the EPM and made more open arms entries than the males. The females also spent more time in the center zone of the LOF and made more center zone entries. The females traveled a greater distance in the LOF and EPM. There was a moderate positive correlation between time on the open arms of the EPM and time in the center zone of the LOF. There was also a moderate positive correlation between open arms entries in the EPM and center zone entries in the LOF. A hierarchical cluster analysis revealed one cluster with LOF parameters, one cluster with EPM parameters, and one cluster with parameters related to the avoidance of open spaces. In conclusion, these findings indicate that female rats display less anxiety-like behavior in the EPM and LOF. Furthermore, there are sex differences for almost all behavioral parameters in these anxiety tests.

Intravenous infusion of rocuronium bromide prolongs emergence from propofol anesthesia in rats

BACKGROUND

Neuromuscular blocking agents induce muscle paralysis via the prevention of synaptic transmission at the neuromuscular junction and may have additional effects at other sites of action. With regard to potential effects of neuromuscular blocking agents on the central nervous system, a definitive view has not been established. We investigated whether intravenous infusion of rocuronium bromide affects the emergence from propofol anesthesia.

METHODS

Using an in vivo rat model, we performed propofol infusion for 60 minutes, along with rocuronium bromide at various infusion rates or normal saline. Sugammadex or normal saline was injected at the end of the infusion period, and we evaluated the time to emergence from propofol anesthesia. We also examined the neuromuscular blocking, circulatory, and respiratory properties of propofol infusion along with rocuronium bromide infusion to ascertain possible factors affecting emergence.

RESULTS

Intravenous infusion of rocuronium bromide dose-dependently increased the time to emergence from propofol anesthesia. Sugammadex administered after propofol infusion not containing rocuronium bromide did not affect the time to emergence. Mean arterial pressure, heart rate, partial pressures of oxygen and carbon dioxide, and pH were not affected by rocuronium bromide infusion. Neuromuscular blockade induced by rocuronium bromide, even at the greatest infusion rate in the emergence experiment, was rapidly antagonized by sugammadex.

CONCLUSIONS

These results suggest that intravenous infusion of rocuronium bromide dose-dependently delays the emergence from propofol anesthesia in rats. Future studies, such as detection of rocuronium in the cerebrospinal fluid or central nervous system, electrophysiologic studies, microinjection of sugammadex into the brain, etc., are necessary to determine the mechanism of this effect.

Objective and graded calibration of recovery of consciousness in experimental models

PURPOSE OF REVIEW

Experimental preclinical models of recovery of consciousness (ROC) and anesthesia emergence are crucial for understanding the neuronal circuits restoring arousal during coma emergence. Such models can also potentially help to better understand how events during coma emergence facilitate or hinder recovery from brain injury. Here we provide an overview of current methods used to assess ROC/level of arousal in animal models. This exposes the need for objective approaches to calibrate arousal levels. We outline how correlation of measured behaviors and their reestablishment at multiple stages with cellular, local and broader neuronal networks, gives a fuller understanding of ROC.

RECENT FINDINGS

Animals emerging from diverse coma-like states share a dynamic process of cortical and behavioral recovery that reveals distinct states consistently sequenced from low-to-high arousal level and trackable in nonhuman primates and rodents. Neuronal activity modulation of layer V-pyramidal neurons and neuronal aggregates within the brainstem and thalamic nuclei play critical roles at specific stages to promote restoration of a conscious state.

SUMMARY

A comprehensive, graded calibration of cortical, physiological, and behavioral changes in animal models is undoubtedly needed to establish an integrative framework. This approach reveals the contribution of local and systemic neuronal circuits to the underlying mechanisms for recovering consciousness.

Deficiency of Mitochondrial Functions and Peroxidation of Frontoparietal Cortex Enhance Isoflurane Sensitivity in Aging Mice

Background: Hypersensitivity to general anesthetics may predict poor postoperative outcomes, especially among the older subjects. Therefore, it is essential to elucidate the mechanism underlying hypersensitivity to volatile anesthetics in the aging population. Given the fact that isoflurane sensitivity increases with aging, we hypothesized that deficiencies of mitochondrial function and elevated oxidative levels in the frontoparietal cortex may contribute to the enhanced sensitivity to isoflurane in aging mice. Methods: Isoflurane sensitivity in aging mice was determined by the concentration of isoflurane that is required for loss of righting reflex (LORR). Mitochondrial bioenergetics of the frontoparietal cortex was measured using a Seahorse XFp analyzer. Protein oxidation and lipid oxidation in the frontoparietal cortex were assessed using the Oxyblot protein oxidation detection kit and thiobarbituric acid reactive substance (TBARS) assay, respectively. Contributions of mitochondrial complex II inhibition by malonate and peroxidation by ozone to isoflurane sensitivity were tested in vivo. Besides, effects of antioxidative therapy on mitochondrial function and isoflurane sensitivity in mice were also measured. Results: The mean concentration of isoflurane that is required for LORR in aging mice (14-16 months old) was 0.83% ± 0.13% (mean ± SD, n = 80). Then, the mice were divided into three groups as sensitive group (S group, mean - SD), medium group (M group), and resistant group (R group, mean + SD) based on individual concentrations of isoflurane required for LORR. Activities of mitochondrial complex II and complex IV in mice of the S group were significantly lower than those of the R group, while frontoparietal cortical malondialdehyde (MDA) levels were higher in the mice of S group. Both inhibition of mitochondrial complexes and peroxidation significantly decreased the concentration of isoflurane that is required for LORR in vivo. After treatment with idebenone, the levels of lipid oxidation were alleviated and mitochondrial function was restored in aging mice. The concentration of isoflurane that required for LORR was also elevated after idebenone treatment. Conclusions: Decreased mitochondrial functions and higher oxidative stress levels in the frontoparietal cortex may contribute to the hypersensitivity to isoflurane in aging mice.

Robust alternative to the righting reflex to assess arousal in rodents

The righting reflex (RR) is frequently used to assess level of arousal and applied to animal models of a range of neurological disorders. RR produces a binary result that, when positive, is used to infer restoration of consciousness, often without further behavioral corroboration. We find that RR is an unreliable metric for arousal/recovery of consciousness. Instead, cortical activity and motor behavior that accompany RR are a non-binary, superior criterion that accurately calibrates and establishes level of arousal in rodents.