Effects of volatile anesthetics on the circadian rhythms of rat hippocampal acetylcholine release and locomotor activity

Magnitude and Mechanism of Phrenic Long-term Facilitation Shift Between Daily Rest Versus Active Phase

Plasticity is a fundamental property of the neural system controlling breathing. One key example of respiratory motor plasticity is phrenic long-term facilitation (pLTF), a persistent increase in phrenic nerve activity elicited by acute intermittent hypoxia (AIH). pLTF can arise from distinct cell signaling cascades initiated by serotonin versus adenosine receptor activation, respectively, and interact via powerful cross-talk inhibition. Here, we demonstrate that the daily rest/active phase and the duration of hypoxic episodes within an AIH protocol have profound impact on the magnitude and mechanism of pLTF due to shifts in serotonin/adenosine balance. Using the historical "standard" AIH protocol (3, 5-min moderate hypoxic episodes), we demonstrate that pLTF magnitude is unaffected by exposure in the midactive versus midrest phase, yet the mechanism driving pLTF shifts from serotonin-dominant (midrest) to adenosine-dominant (midactive). This mechanistic "flip" results from combined influences of hypoxia-evoked adenosine release and daily fluctuations in basal spinal adenosine. Since AIH evokes less adenosine with shorter (15, 1-min) hypoxic episodes, midrest pLTF is amplified due to diminished adenosine constraint on serotonin-driven plasticity; in contrast, elevated background adenosine during the midactive phase suppresses serotonin-dominant pLTF. These findings demonstrate the importance of the serotonin/adenosine balance in regulating the amplitude and mechanism of AIH-induced pLTF. Since AIH is emerging as a promising therapeutic modality to restore respiratory and nonrespiratory movements in people with spinal cord injury or ALS, knowledge of how time-of-day and hypoxic episode duration impact the serotonin/adenosine balance and the magnitude and mechanism of pLTF has profound biological, experimental, and translational implications.

Improved method for surgical induction of chronic hypertension in mice

Chronic hypertension can be induced in mice by one-kidney one-clip (1K1C) or two-kidney one-clip surgery, transgenic overexpression of angiotensinogen and renin, administration of deoxycorticosterone acetate-salt, supplying Nitro-L-arginine methyl-ester in the drinking water and Angiotensin-II infusion. Although each model has its own pros and cons, selection of a model that mimics human hypertensive disease accurately is essential to ensure rigor and reproducibility in hypertension research. 1K1C mice represent an efficient, budget-friendly, and translationally capable model; however, their use in preclinical research has remained largely hindered due to concerns about potential technical complexity and lack of reported information regarding procedure-related mortality rates. Here, we describe in detail an improved version of the 1K1C surgery in mice that has zero intraoperative mortality and excellent survival rates in a long-term setting and permits the development of stable chronic hypertension and its target organ complications. Key to this outcome is unilateral nephrectomy 1 week after renal artery clipping to decelerate the blood pressure (BP) increase, which allows the organism to adapt better to the BP rise. The technical and animal welfare improvements presented here may promote the acceptance of the 1K1C model.

Melatonin pretreatment prevents propofol-induced sleep disturbance by modulating circadian rhythm in rats

Postoperative sleep disorder frequently occurs in patients after surgery. Sleep disturbance aggravates pain, anxiety, and delirium, which is an important risk factor for poor recovery. Circadian rhythm disorder induced by general anesthesia plays important role in postoperative sleep disorders. A large number of clinical studies have shown that various forms and duration of general anesthesia can lead to postoperative sleep disorders. In this study, the effect of prolonged propofol anesthesia on biological rhythm was comprehensively evaluated by wireless physiological telemetry system, and the therapeutic effect of exogenous melatonin pretreatment was further investigated. The results showed that prolonged propofol anesthesia had significant impacts on the circadian rhythm of sleep, body temperature, locomotor activity and endogenous melatonin secretion within 24 h following anesthesia, resulting in diminished oscillation amplitude. In hypothalamus, the expression of circadian factor PER and CRY were inhibited by propofol, possibly through activation of CAMK-CREB signaling pathway. Post-translational factors GSK-3β, SIRT1, AMPK were also involved in the regulation of circadian factors after propofol anesthesia. Melatonin pretreatment could restore circadian rhythm process by regulating circadian factor expression through post-translational modulation and prohibit the over-synthesis of melatonin in pineal gland. This study verified the effects of anesthetics on circadian rhythm and further evaluated the potential therapeutic effect of melatonin on postoperative circadian rhythm and sleep disorders.

Adult Neurogenesis under Control of the Circadian System

The mammalian circadian system is a hierarchically organized system, which controls a 24-h periodicity in a wide variety of body and brain functions and physiological processes. There is increasing evidence that the circadian system modulates the complex multistep process of adult neurogenesis, which is crucial for brain plasticity. This modulatory effect may be exercised via rhythmic systemic factors including neurotransmitters, hormones and neurotrophic factors as well as rhythmic behavior and physiology or via intrinsic factors within the neural progenitor cells such as the redox state and clock genes/molecular clockwork. In this review, we discuss the role of the circadian system for adult neurogenesis at both the systemic and the cellular levels. Better understanding of the role of the circadian system in modulation of adult neurogenesis can help develop new treatment strategies to improve the cognitive deterioration associated with chronodisruption due to detrimental light regimes or neurodegenerative diseases.

Dissecting the Roles of the Autonomic Nervous System and Physical Activity on Circadian Heart Rate Fluctuations in Mice

Heart rate (HR) and blood pressure as well as adverse cardiovascular events show clear circadian patterns, which are linked to interdependent daily variations in physical activity and cardiac autonomic nerve system (ANS) activity. We set out to assess the relative contributions of the ANS (alone) and physical activity to circadian HR fluctuations. To do so, we measured HR (beats per minute, bpm) in mice that were either immobilized using isoflurane anesthesia or free-moving. Nonlinear fits of HR data to sine functions revealed that anesthetized mice display brisk circadian HR fluctuations with amplitudes of 47.1±7.4bpm with the highest HRs in middle of the dark (active) period (ZT 18: 589±46bpm) and lowest HRs in the middle of the light (rest) period (ZT 6: 497±54bpm). The circadian HR fluctuations were reduced by ~70% following blockade of cardiac parasympathetic nervous activity (PNA) with atropine while declining by <15% following cardiac sympathetic nerve activity (SNA) blockade with propranolol. Small HR fluctuation amplitudes (11.6±5.9bpm) remained after complete cardiac ANS blockade. Remarkably, circadian HR fluctuation amplitudes in freely moving, telemetrized mice were only ~32% larger than in anesthetized mice. However, after gaining access to running wheels for 1week, circadian HR fluctuations increase to 102.9±12.1bpm and this is linked directly to increased O₂ consumption during running. We conclude that, independent of physical activity, the ANS is a major determinant of circadian HR variations with PNA playing a dominant role compared to SNA. The effects of physical activity to the daily HR variations are remarkably small unless mice get access to running wheels.

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.

Effect of inhalation anesthesia with isoflurane on circadian rhythm of murine intraocular pressure

PURPOSE

For research on circadian intraocular pressure (IOP), rebound tonometers are widely used with or without general anesthesia as a non-invasive approach to obtain IOP values. However, whether general anesthesia such as inhalation anesthesia with isoflurane affects the circadian rhythm of IOP and in turn IOP measurements is currently unclear. As such, data reporting IOP values obtained under general anesthesia should be interpreted with caution. The purpose of this study was to evaluate how general anesthesia with isoflurane inhalation affects the circadian rhythm of IOP.

METHODS

C57Bl/6J strain mice maintained using a 12h:12h light/dark cycle (lights on and off at ZT0 and ZT12, respectively) were used. IOPs were measured using a rebound tonometer (Icare TonoLab) before and 3, 5, 10, 15, and 30 min after initiating anesthesia in both light and dark phases (ZT 2-6 and ZT 14-18, respectively). Awake IOPs and IOPs at 3 and 5 min after anesthesia initiation were also obtained at ZT5, 8, 11, 14, 17, and 20 to assess IOP diurnal curves under gas anesthesia.

RESULTS

IOP values gradually decreased after anesthesia initiation in both light and dark phases (P < 0.001) and there was no interaction between light/dark phase and anesthesia time (P = 0.88). There was a slight, but not significant, reduction in IOP 3 min after initiating anesthesia (P = 0.23), and significant decreases in IOP occurred at subsequent timepoints (P ≤ 0.001). Both awake and anesthetized mice showed a robust IOP rhythm that reached a peak and trough in the dark and light phase, respectively. Awake IOP levels did not significantly differ from those for anesthetized mice at 3 min after anesthesia initiation at all time points (P ≥ 0.07).

CONCLUSIONS

Both awake and anesthetized mice demonstrated a robust circadian rhythm for IOP. Murine IOP showed similar gradual decreases under inhalation anesthesia with isoflurane in both the light and dark phases. IOPs measured using a rebound tonometer within 3 min of initiating isoflurane anesthesia were comparable to awake IOPs, and thus may be useful to monitor the circadian rhythm of IOP in mice.

Desflurane anesthesia shifts the circadian rhythm phase depending on the time of day of anesthesia

Desflurane is one of the most frequently used inhalational anesthetics in clinical practice. A circadian rhythm phase-shift after general anesthesia with sevoflurane or isoflurane has been reported in mice, but few studies have reported this effect with desflurane. In the present study, we examined the rest/activity rhythm of mice by counting the number of running wheel rotations, and we found that desflurane anesthesia caused a phase shift in the circadian rhythm that was dependent on the time of day of anesthesia. We also found that desflurane anesthesia altered the relative mRNA expression of four major clock genes (Per2, Bmal, Clock, and Cry1) in the suprachiasmatic nucleus (SCN). These results are important for elucidating the effects of desflurane on the SCN, which is the master clock for the mammalian circadian rhythm. Further studies on the relationship between anesthesia and circadian rhythm may lead to the prevention and treatment of postoperative complications related to circadian rhythms.

Effects of Euterpe oleracea to Enhance Learning and Memory in a Conditioned Nicotinic and Muscarinic Receptor Response Paradigm by Modulation of Cholinergic Mechanisms in Rats

Euterpe oleracea (EO) includes a large number of polyphenolic compounds such as phenolics, flavonoids, and anthocyanins that have antioxidant activities. E. oleracea was suggested to ease the oxidative stress and inflammation in brain cells. Our aim was to analyze the effects of E. oleracea on learning and memory. Seventy-two (250 ± 25 g) male Wistar albino rats were used for this study. The groups consisted of control, EO100 mg/kg, EO300 mg/kg, scopolamine 1.5 mg/kg, mecamylamine 7.5 mg/kg, combinations of scopolamine with EO100 mg/kg, EO300 mg/kg, and rivastigmine 1.5 mg/kg; and mecamylamine combined with EO100 mg/kg. Before the start of the study, E. oleracea doses were provided once a day for a period of 15 days and for a 6-day experimental period. Thirty minutes after intraperitoneal scopolamine and mecamylamine injections, gastrogavage was applied to each group. Ninety minutes after the drug treatments, locomotor activity and Morris water maze tests were performed. Rats were killed and each hippocampus was used for the quantification of acetylcholine (Ach). Statistical analyses were calculated using one-way and two-way analyses of variance (ANOVA), and a value of P < .05 was considered significant. In groups EO100 mg/kg and EO300 mg/kg the results did not show any significant changes on learning and memory compared with the control group. Mecamylamine and scopolamine enhanced the latency for the escape platform, and decreased the time spent in escape platform quadrant when the memory tests were applied in reference to the control value of P < .05. Scopolamine and mecamylamine combinations of EO100 mg/kg, EO300 mg/kg, and rivastigmine were proven to improve the memory. There was significant difference between the first and fifth days of the learning tests in all the groups, but no significant difference occurred between the groups. Ach levels in hippocampi supported all memory tests. We suggest that E. oleracea made no alterations on learning and memory, but still improved nicotinic and muscarinic receptor-mediated and impaired memory just as rivastigmine.

Impact of anaesthesia on circadian rhythms and implications for laboratory experiments

General anaesthesia is a widely used tool to enable surgery in animal experimentation. There is now convincing evidence that general anaesthesia can cause profound and strongly time-dependant shifts in circadian rhythms of behaviour (sleep-wake cycles), physiology (core body temperature, blood pressure, heart rate and hormone release) and cognitive parameters (learning and memory) in a range of species. These effects have the potential to confound laboratory experiments, and may lead to misinterpretation of results. Here, we summarise these effects and advise caution to those conducting laboratory experiments in which anaesthesia forms part of the protocol.

Severity classification of repeated isoflurane anesthesia in C57BL/6JRj mice-Assessing the degree of distress

According to the EU Directive 2010/63, the severity of a procedure has to be classified as mild, moderate or severe. General anesthesia is thought to be mild, but the Directive does not differentiate between single and repeated anesthesia. Therefore, we investigated the impact of repeated administration of isoflurane, the most commonly used inhalation anesthetic, on the well-being of adult C57BL/6JRj mice, in comparison to single administrations and to untreated animals, when applied six times for 45 min at an interval of 3–4 days. For the animals anesthetized, excitations, phases of anesthesia, and vital parameters were monitored. Well-being after anesthesia was assessed using a behavioral test battery including luxury behavior like burrowing and nest building behavior, the Mouse Grimace Scale (MGS), the free exploratory paradigm for anxiety-related behavior, home cage activity and the rotarod test for activity, as well as food intake and body weight. Additionally, hair corticosterone and fecal corticosterone metabolites were measured. Our results show that nest building behavior, home cage activity, body weight, and corticosterone concentrations were not influenced by anesthesia, whereas changes in burrowing behavior, the MGS, food intake, and the free exploratory behavior indicated that the well-being of the mice was more affected by repeated than single isoflurane anesthesia. This effect depended on the sex of the animals, with female mice being more susceptible than male mice. However, repeated isoflurane anesthesia caused only short-term mild distress and impairment of well-being, mainly in the immediate postanesthetic period. Well-being stabilized at 8 days after the last anesthesia, at the latest. Therefore, we conclude that when using our anesthesia protocol, the severity of both single and repeated isoflurane anesthesia in C57BL/6JRj mice can be classified as mild. However, within the mild severity category, repeated isoflurane anesthesia ranks higher than single isoflurane anesthesia. Additionally, our results imply that male and female mice can differently perceive the severity of a procedure.

Effect of day/night administration of three different inhalational anesthetics on melatonin levels in rats

The nocturnal peak of melatonin can be altered after anesthesia and surgery. We aimed to examine the melatonin levels during the day and night after anesthesia with three commonly used inhalational anesthetics. Forty-eight male Wistar albino rats were randomized into eight groups. Rats were administered anesthesia between 7:00 am and 1:00 pm (day groups) or 7:00 pm and 1:00 am (night groups) for 6 hours. At the end of the anesthesia, blood samples were collected for assessing melatonin levels. Mean values of melatonin levels after 6 hours of anesthesia during daytime were 43.17±12.95 for control, 59.79±27.83 for isoflurane, 50.75±34.28 for sevoflurane and 212.20±49.56 pg/mL for desflurane groups. The night groups' mean melatonin levels were 136.12±33.20 for control, 139.85±56.29 for isoflurane, 117.48±82.39 for sevoflurane and 128.70±44.63 pg/mL for desflurane groups. Desflurane anesthesia between 7:00 am and 1:00 pm significantly increased melatonin levels (p<0.001). Sevoflurane and desflurane anesthesia between 7:00 pm and 1:00 am decreased the melatonin levels but there were no significant differences (p=0.904 and p>0.99, respectively). Isoflurane anesthesia did not significantly change melatonin levels during day or night (p=0.718 and p>0.99, respectively). Our results demonstrate that during daytime desflurane anesthesia can alter melatonin levels. Altered melatonin rhythm following inhalational anesthesia can be related to sleep disorders observed after anesthesia.

The effects of the general anaesthetic isoflurane on the honey bee (Apis mellifera) circadian clock

General anaesthesia administered during the day has previously been shown to phase shift the honey bee clock. We describe a phase response curve for honey bees (n=105) to six hour isoflurane anaesthesia. The honey bee isoflurane PRC is "weak" with a delay portion (maximum shift of -1.88 hours, circadian time 0 - 3) but no advance zone. The isoflurane-induced shifts observed here are in direct opposition to those of light. Furthermore, concurrent administration of light and isoflurane abolishes the shifts that occur with isoflurane alone. Light may thus provide a means of reducing isoflurane-induced phase shifts.

State-dependent alterations in sleep/wake architecture elicited by the M4 PAM VU0467154 - Relation to antipsychotic-like drug effects

Accumulating evidence indicates direct relationships between sleep abnormalities and the severity and prevalence of other symptom clusters in schizophrenia. Assessment of potential state-dependent alterations in sleep architecture and arousal relative to antipsychotic-like activity is critical for the development of novel antipsychotic drugs (APDs). Recently, we reported that VU0467154, a selective positive allosteric modulator (PAM) of the M4 muscarinic acetylcholine receptor (mAChR), exhibits robust APD-like and cognitive enhancing activity in rodents. However, the state-dependent effects of VU0467154 on sleep architecture and arousal have not been examined. Using polysomnography and quantitative electroencephalographic recordings from subcranial electrodes in rats, we evaluated the effects of VU0467154, in comparison with the atypical APD clozapine and the M1/M4-preferring mAChR agonist xanomeline. VU0467154 induced state-dependent alterations in sleep architecture and arousal including delayed Rapid Eye Movement (REM) sleep onset, increased cumulative duration of total and Non-Rapid Eye Movement (NREM) sleep, and increased arousal during waking periods. Clozapine decreased arousal during wake, increased cumulative NREM, and decreased REM sleep. In contrast, xanomeline increased time awake and arousal during wake, but reduced slow wave activity during NREM sleep. Additionally, in combination with the N-methyl-d-aspartate subtype of glutamate receptor (NMDAR) antagonist MK-801, modeling NMDAR hypofunction thought to underlie many symptoms in schizophrenia, both VU0467154 and clozapine attenuated MK-801-induced elevations in high frequency gamma power consistent with an APD-like mechanism of action. These findings suggest that selective M4 PAMs may represent a novel mechanism for treating multiple symptoms of schizophrenia, including disruptions in sleep architecture without a sedative profile.

Redox Changes Induced by General Anesthesia in Critically Ill Patients with Multiple Traumas

The critically ill polytrauma patient is a constant challenge for the trauma team due to the complexity of the complications presented. Intense inflammatory response and infections, as well as multiple organ dysfunctions, significantly increase the rate of morbidity and mortality in these patients. Moreover, due to the physiological and biochemical imbalances present in this type of patients, the bioproduction of free radicals is significantly accelerated, thus installing the oxidative stress. In the therapeutic management of such patients, multiple surgical interventions are required and therefore they are being subjected to repeated general anesthesia. In this paper, we want to present the pathophysiological implications of oxidative stress in critically ill patients with multiple traumas and the implications of general anesthesia on the redox mechanisms of the cell. We also want to summarize the antioxidant treatments able to reduce the intensity of oxidative stress by modulating the biochemical activity of some cellular mechanisms.

Effects of isoflurane, ketamine-xylazine and a combination of medetomidine, midazolam and fentanyl on physiological variables continuously measured by telemetry in Wistar rats

BACKGROUND

This study investigated effects on cardiovascular parameters during anaesthesia with isoflurane (ISO, 2-3 Vol%), ketamine-xylazine (KX, 100 mg•kg(-1) + 5 mg•kg(-1)) or a combination of medetomidine-midazolam-fentanyl (MMF, 0.15 mg•kg(-1) + 2.0 mg•kg(-1) + 0.005 mg•kg(-1)) in rats throughout induction, maintenance and recovery from anaesthesia. Rats were instrumented with a telemetric system for the measurement of systolic, diastolic and mean arterial pressure (SAP, DAP, MAP), pulse pressure (PP), heart rate (HR) and core body temperature (BT). The parameters were continuously measured before, during and after each type of anaesthesia. Forty minutes after induction, ISO delivery was terminated and MMF was antagonized with atipamezole-flumazenil-naloxone (AFN, 0.75 mg•kg(-1) + 0.2 mg•kg(-1) + 0.12 mg•kg(-1)) whereas KX was not antagonized.

RESULTS

Differences were observed between anaesthesias with KX (301 min) lasting much longer than MMF (45 min) and ISO (43 min). HR in ISO ([Formula: see text] = 404 ± 25 bpm) increased during the time of surgical tolerance whereas a HR decrease was observed in KX ([Formula: see text] = 255 ± 26 bpm) and MMF ([Formula: see text] = 209 ± 24 bpm). In ISO (MAP during time of surgical tolerance: [Formula: see text] = 89 ± 12.3 mmHg) and KX (MAP during wake-up period: [Formula: see text] = 84 ± 8.5 mmHg) mild hypotensive values were observed, whereas blood pressure (BP) in MMF (MAP during time of surgical tolerance: [Formula: see text] = 138 ± 9.9 mmHg) increased. Despite keeping animals on a warming pad, a loss of BT of about 1°C was seen in all groups. Additionally, we observed a peaked increase of HR ([Formula: see text] = 445 ± 20 bpm) during the wake-up period with ISO and an increase of PP ([Formula: see text] = 59 ± 8.5 mmHg) in MMF during the time of surgical tolerance.

CONCLUSION

The anaesthesias influenced very differently the cardiovascular parameters measured in Wistar rats. ISO caused mild hypotension and increased HR whereas MMF produced a marked hypertension and a significant decrease of HR. The slightest alterations of BP, HR and BT were observed using KX, but the long wake-up and recovery period suggest the need for prolonged monitoring.