Effects of nitrous oxide and ketamine on electrophysiological and molecular responses in the prefrontal cortex of mice: A comparative study

Nitrous oxide (N2O; laughing gas) has recently reported to produce rapid antidepressant effects, but little is known about the underlying mechanisms. We performed transcriptomics, in situ hybridization, and electrophysiological studies to examine the potential shared signatures induced by 1 h inhalation of 50% N2O and a single subanesthetic dose of ketamine (10 mg/kg, i.p.) in the medial prefrontal cortex (mPFC) in adult mice. Both treatments similarly affected the transcription of several negative regulators of mitogen-activated protein kinases (MAPKs), namely, dual specificity phosphatases (DUSPs). The effects were primarily located in the pyramidal cells. Notably, the overall effects of N2O on mRNA expression were much more prominent and widespread compared to ketamine. Ketamine caused an elevation of the spiking frequency of putative pyramidal neurons and increased gamma activity (30-100 Hz) of cortical local field potentials. However, N2O produced no such effects. Spiking amplitudes and spike-to-local field potential phase locking of putative pyramidal neurons and interneurons in this brain area showed no uniform changes across treatments. Our findings suggest that N2O and subanesthetic-dose ketamine target MAPK pathway in the mPFC but produce varying acute electrophysiological responses.

Practical Use of Self-Adjusted Nitrous Oxide During Transrectal Prostate Biopsy: A Double-Blind Randomized Controlled Trial

PURPOSE

Transrectal prostate biopsy is a common ambulatory procedure that can result in pain and anxiety for some men. Low-dose, adjustable nitrous oxide is increasingly being used to improve experience of care for patients undergoing painful procedures. This study seeks to evaluate the efficacy and safety of low-dose (<45%) nitrous oxide, which has not been previously established for transrectal prostate biopsies.

MATERIALS AND METHODS

A single-institution, prospective, double-blind, randomized, controlled trial was conducted on patients undergoing transrectal prostate biopsies. Patients were randomized to receive either self-adjusted nitrous oxide or oxygen, in addition to routine periprostatic bupivacaine block. Nitrous oxide at levels between 20% and 45% were adjusted to patients' desired effect. Patients completed a visual analog scale for anxiety, State Trait Anxiety Inventory, and a visual analog scale for pain immediately before and after biopsy. The blinded operating urologist evaluated ease of procedure. Periprocedural vitals and complications were assessed. Patients were allowed to drive home independently.

RESULTS

A total of 133 patients received either nitrous oxide (66) or oxygen (67). There was no statistically significant difference in the primary anxiety end point of State Trait Anxiety Inventory or the visual analog scale for anxiety scores between the nitrous oxide and oxygen groups. However, patients in the nitrous oxide group reported significantly lower visual analog scale for pain scores compared to the oxygen group (P = .026). The operating urologists' rating of tolerance of the procedure was better in the nitrous oxide group (P = .03). There were no differences in biopsy performance time. Complications were similarly low between the 2 groups.

CONCLUSIONS

Patient-adjusted nitrous oxide at levels of 20% to 45% is a safe adjunct during transrectal prostate biopsy. Although there was not an observed difference in the primary end point of anxiety, nitrous oxide was associated with lower patient-reported pain scores.

Safety and efficacy of a nitrous oxide procedural sedation programme in a paediatric emergency department: a decade of outcomes

BACKGROUND

Nitrous oxide (N2O) has multiple benefits in paediatric procedural sedation (PPS), but use is restricted by its limited analgesic properties. Analgesic potency could be increased by combining N2O and intranasal fentanyl (INF). We assessed safety and efficacy data from 10 years (2011-2021) of our N2O PPS programme.

METHODS

Prospectively collected data from a sedation registry at a paediatric emergency department (PED) were reviewed. Total procedures performed with N2O alone or with INF, success rate, sedation depth and adverse events were determined. Contributing factors for these outcomes were assessed via regression analysis and compared between different N2O concentrations, N2O in combination with INF, and for physician versus nurse administered sedation. A post hoc analysis on factors associated with vomiting was also performed.

RESULTS

831 N2O procedural sedations were performed, 358 (43.1%) involved a combination INF and N2O. Nurses managed sedation in 728 (87.6%) cases. Median sedation depth on the University of Michigan Sedation Scale was 1 (IQR 1-2). Sedation was successful in 809 (97.4%) cases. Combination INF/N2O demonstrated higher median sedation scores (2 vs 1, p<0.001) and increased vomiting (RR 1.8, 95% CI 1.3 to 2.5), with no difference in sedation success compared with N2O alone. No serious adverse events (SAEs) were reported (desaturation, apnoea, aspiration, bradycardia or hypotension) regardless of N2O concentration or use of INF. 137 (16.5%) minor adverse events occurred. Vomiting occurred in 113 (13.6%) cases and was associated with higher concentrations of N2O and INF use, but not associated with fasting status. There were no differences in adverse events (RR 0.98, 95% CI 0.97 to 1.04) or success rates (RR 0.93, 95% CI 0.56 to 1.7) between physician provided and nurse provided sedation.

CONCLUSION

N2O can provide effective PED PPS. No SAEs were recorded. INF may be an effective PPS adjunct but remains limited by increased rates of vomiting.

Nitrous Oxide, a Rapid Antidepressant, Has Ketamine-like Effects on Excitatory Transmission in the Adult Hippocampus

BACKGROUND

Nitrous oxide (N2O) is a noncompetitive inhibitor of NMDA receptors that appears to have ketamine-like rapid antidepressant effects in patients with treatment-resistant major depression. In preclinical studies, ketamine enhances glutamate-mediated synaptic transmission in the hippocampus and prefrontal cortex. In this study, we examined the effects of N2O on glutamate transmission in the hippocampus and compared its effects to those of ketamine.

METHODS

Glutamate-mediated synaptic transmission was studied in the CA1 region of hippocampal slices from adult albino rats using standard extracellular recording methods. Effects of N2O and ketamine at subanesthetic concentrations were evaluated by acute administration.

RESULTS

Akin to 1 μM ketamine, 30% N2O administered for 15-20 minutes resulted in persistent enhancement of synaptic responses mediated by both AMPA receptors and NMDA receptors. Synaptic enhancement by both N2O and ketamine was blocked by co-administration of a competitive NMDA receptor antagonist at saturating concentration, but only ketamine was blocked by an AMPA receptor antagonist. Synaptic enhancement by both agents involved TrkB (tropomyosin receptor kinase B), mTOR (mechanistic target of rapamycin), and NOS (nitric oxide synthase) with some differences between N2O and ketamine. N2O potentiation occluded enhancement by ketamine, and in vivo N2O exposure occluded further potentiation by both N2O and ketamine.

CONCLUSIONS

These results indicate that N2O has ketamine-like effects on hippocampal synaptic function at a subanesthetic, but therapeutically relevant concentration. These 2 rapid antidepressants have similar, but not identical mechanisms that result in persisting synaptic enhancement, possibly contributing to psychotropic actions.

Procedural analgesia with nitrous oxide at home for epidermolysis bullosa: A case report

RATIONALE

Epidermolysis bullosa (EB) is an inherited disease characterized by fragile skin with painful blistering, which requires lifelong skin and wound care. This case report describes the use of inhaled nitrous oxide (N2O) for procedural pain control at home during wound care in a young man with severe dystrophic EB. To our knowledge, only 1 case was reported by Ingelmo et al in 2017 regarding the use of N2O at home in a 4-year-old-child. To date, no such attempt has been made in adult patients.

PATIENT CONCERNS

Our patient was a 28-year-old man. Frequent blisters appear spontaneously, and are often preceded by erythema and itching. Patient required daily treatment daily consisting of lancing blisters with a needle and emptying them by compression.

DIAGNOSES

Severe recessive dystrophic EB diagnosed at the time of delivery.

INTERVENTIONS

Procedural pain control was managed by the auto-administration of an inhaled N2O and air gas mixture.

OUTCOMES

Conscious sedation with N2O leads to beneficial effects, such as reduction in dressing duration, acute procedural pain, local antibiotic needing, medication memory, anxiety, anticipatory pain, and fatigue after the dressing session.

LESSONS

N2O analgesia is safe and effective, resulting in a significant reduction in procedural pain and an improvement in the quality of life of patients and their caregivers.

Combination of nitrous oxide and the modified inflation-deflation method for identifying the intersegmental plane in segmentectomy: A randomized controlled trial

Background

During thoracoscopic segmentectomy, accurately and rapidly identifying the intersegmental plane (ISP) is of great importance. This study aimed to investigate the effect and safety of a nitrous oxide (N₂O)/oxygen (O₂) inspired mixture on the appearance time of the ISP (T_ISP) via the modified inflation‐deflation method.

Methods

A total of 65 participants who underwent segmentectomy were randomized into three groups: 75% N₂O (n = 24), 50% N₂O (n = 23) or 0% N₂O (n = 18). The 75% N₂O group received a gas mixture of N₂O/O₂ (Fio₂ = 0.25), the 50% N₂O group received N₂O/O₂ (Fio₂ = 0.5), and the 0% N₂O group received 100% oxygen during lung expansion. The appearance time of satisfactory and ideal planes was recorded. Furthermore, arterial blood gas at breathing room air, one‐lung ventilation (OLV) before lung expansion, 5 and 15 min after lung expansion were also recorded.

Results

T_ISP was significantly shorter in the 75% N₂O group (320.2 ± 65.9 s) compared with that of the 50% N₂O group (552.4 ± 88.9 s, p < 0.001) and the 0% N₂O group (968.3 ± 85.5 s, p < 0.001), while the 50% N₂O group was shorter than that of the 0% N₂O group (p < 0.001). Arterial oxygenation was significantly improved in the 0% N₂O group only after lung expansion, before which there were no differences in mean PaO₂ values among groups.

Conclusions

The use of N₂O in the inspired gas mixture during lung expansion is an applicable strategy to rapidly identify the ISP via the modified inflation‐deflation method without any adverse effect on OLV related arterial oxygenation during segmentectomy.

Inhalation Sedation During the COVID-19 Outbreak: An Expert Opinion

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), the pathogen that causes coronavirus disease-2019 (COVID-19), is thought to be transmitted via droplets and aerosols, and was detected in saliva of infected individuals. These droplets from the upper airway may infect the inhalation sedation mask and tubing. The authors determined the adequate measures needed to prevent the transmission of COVID-19 by nitrous-oxide (N2O) system during inhalation sedation in dentistry and provided evidence on mask and tubing sterilization. Additional measures to protect patients and healthcare workers from COVID-19 that may be transmitted by the inhalation sedation system are discussed. The authors recommend minimal use of a N2O system during inhalation sedation in dentistry. In case of need, the practitioners should have more than one scavenger kit and nasal masks for each N2O/O2 mixer. Biologic barriers should be mounted between the scavenger's tubing and the central evacuation system. Strict cleansing and sterilization should be performed for all parts of the N2O system. The use a disposable scavenger system and nasal mask should be considered as a viable option.

Effects of nitrous oxide on glycinergic transmission in rat spinal neurons

We investigated the effects of nitrous oxide (N₂O) on glycinergic inhibitory whole-cell and synaptic responses using a "synapse bouton preparation," dissociated mechanically from rat spinal sacral dorsal commissural nucleus (SDCN) neurons. This technique can evaluate pure single- or multi-synaptic responses from native functional nerve endings and enable us to accurately quantify how N₂O influences pre- and postsynaptic transmission. We found that 70 % N₂O enhanced exogenous glycine-induced whole-cell currents (I_Gly) at glycine concentrations lower than 3 × 10^-5 M, but did not affect I_Gly at glycine concentrations higher than 10^-4 M. N₂O did not affect the amplitude and 1/e decay-time of both spontaneous and miniature glycinergic inhibitory postsynaptic currents recorded in the absence and presence of tetrodotoxin (sIPSCs and mIPSCs, respectively). The decrease in frequency induced by N₂O was observed in sIPSCs but not in mIPSCs, which was recorded in the presence of both tetrodotoxin and Cd²⁺, which block voltage-gated Na⁺ and Ca²⁺ channels, respectively. N₂O also decreased the amplitude and increased the failure rate and paired-pulse ratio of action potential-evoked glycinergic inhibitory postsynaptic currents. N₂O slightly decreased the Ba²⁺ currents mediated by voltage-gated Ca²⁺ channels in SDCN neurons. We found that N₂O suppresses glycinergic responses at synaptic levels with presynaptic effect having much more predominant role. The difference between glycinergic whole-cell and synaptic responses suggests that extrasynaptic responses seriously modulate whole-cell currents. Our results strongly suggest that these responses may thus in part explain analgesic effects of N₂O via marked glutamatergic inhibition by glycinergic responses in the spinal cord.

[Frostbite due to recreational nitrous oxide use]

BACKGROUND

There is a new type of injury that is observed increasingly often: frostbite of the thighs that has occurred as result of holding a cylinder containing nitrous oxide in position between the legs during recreational use of said substance. Because skin symptoms are often mild in the first few days after the event, the severity of the injury is often not recognized. However, patients can suffer serious scarring from this type of injury.

CASE DESCRIPTION

We present two cases involving young patients who were referred to the burns unit with lesions sustained through nitrous oxide use. Upon inspection we observed deep frostbite wounds, which necessitated operative treatment. The patients had to undergo multiple operations and remained under our care for management of their scars.

CONCLUSION

It is important to recognize this injury and to consult one of the burns units to treat these patients in a timeline and appropriate manner.

Changes in CO-oximetry values and pulse oximetry in isoflurane-anesthetized dogs with and without nitrous oxide

Concentrations of 64% to 70% nitrous oxide (N₂O) provide intra-operative analgesia. Clinically, pulse oximeter estimation (SpO₂) of oxygen (O₂) hemoglobin saturation (SaO₂) was observed to decrease with N₂O. Absorption atelectasis from breathing O₂ was thought to decrease arterial partial pressure of O₂ (PaO₂) below 70 mmHg and reduce SaO₂ and SpO₂ when N₂O was used. Administering N₂O from the beginning of the anesthesia might prevent atelectasis development and low PaO₂. The study was done in 2 parts (P < 0.05). In Part 1, isoflurane-anesthetized dogs undergoing ovariohysterectomy (n = 15 each group) breathed N₂O from anesthesia start (N₂O_early) or 1 hour later (N₂O_late). SpO₂, CO-oximetry values, and PaO₂ were compared to dogs breathing O₂ throughout anesthesia (control). Timing of N₂O introduction did not affect PaO₂ (lowest = 94 mmHg), SaO₂, or SpO₂. With N₂O, the lowest SpO₂ value was 91% and corresponded to a PaO₂ of 151 mmHg. Carboxyhemoglobin increased (highest = 2.7%) and SaO₂ decreased with N₂O (lowest = 96.7%). In Part 2, to replicate findings, 10 isoflurane-anesthetized dogs breathed N₂O, then O₂. With N₂O, SaO₂ did not decrease, but carboxyhemoglobin increased and returned to baseline once N₂O was discontinued. The dog with the highest carboxyhemoglobin (2%) had an SaO₂ of 96.8% (PaO₂ = 93 mmHg). Carboxyhemoglobin and SaO₂ changes were not clinically significant. Pulse oximetry did not reliably estimate SaO₂ but N₂O was not always a factor.

Use of nitrous oxide in children

BACKGROUND

In July 2013, the Department of Paediatric and Adolescent Medicine at Østfold Hospital Trust introduced nitrous oxide as an option for procedural sedation of children and adolescents.

MATERIAL AND METHOD

During the period 13 July 2013-25 August 2017, 311 procedures were performed with nitrous oxide in 238 patients aged 4-17 years. Age, sex, type and duration of procedure, any supplementary medications, complications and whether the procedure would previously have required general anaesthesia, were recorded in a form. The child rated the effectiveness of nitrous oxide using a graded age-appropriate 10-point pain scale, and the nurse rated it as good, moderate or none.

RESULTS

The children reported a median pain score of 2/10 (interquartile range 0-4), and nurses rated effectiveness as good in 247 of 304 (81 %) cases. For 43 % of procedures, the nurse felt that general anaesthesia would have been necessary had the department not had access to nitrous oxide. Adverse effects, most often dizziness, were reported in 110 of 311 procedures (35 %). In 7 of 311 procedures (2 %), the patient experienced adverse effects that resulted in stoppage of the procedure. The procedure was completed in 286 (92 %) children.

INTERPRETATION

Nitrous oxide is a useful option for children who require procedural sedation, and means that more procedures can be performed without general anaesthesia.

Influence of nitrous oxide on granule cell migration in the dentate gyrus of the neonatal rat

For several decades, the neurotoxicities of anesthetics to the developing brain have been reported by many researchers focusing on various phenomena such as apoptosis, neurodegeneration, electrophysiological aberrations, and behavioral abnormalities. According to these reports, signals via N-methyl-D-aspartate receptors (NMDA-r) and/or γ-aminobutyric acid type A receptors (GABA_A-r) are implicated in the anesthetic neurotoxicity. On the other hand, during brain development, NMDA-r and GABA_A-r are also recognized to play primary roles in neural cell migration. Therefore, anesthetics exposed in this period may influence the neural cell migration of neonates, and increase the number of hilar ectopic granule cells, which are reported to be a cause of continuous neurological deficits. To examine this hypothesis, we investigated immunohistochemically granule cell distribution in the hippocampal dentate gyrus of Wistar/ST rats after nitrous oxide (N₂O) exposure. At postnatal day (P) 6, 5-bromo-2'-deoxyuridine (BrdU) was administered to label newly generated cells. Then, rats were divided into groups (n = 6 each group), exposed to 50% N₂O at P7, and evaluated at P21. As a result, we found that ectopic ratios (ratio of hilar/total granule cells generated at P6) were decreased in rats at P21 compared with those at P7, and increased in N₂O exposed rats for over 120 min compared with the other groups. These results suggest that 50% N₂O exposure for over 120 min increases the ratios of ectopic granule cells in the rat dentate gyrus.

Plasma corticosterone, epinephrine, and norepinephrine levels increase during administration of nitrous oxide in rats

Nitrous oxide (N2O) is a gaseous drug with abuse potential. Despite its common clinical use, little is known about whether N2O administration activates the HPA axis and/or the sympathetic adrenomedullary system. The goal of this study was to determine whether 60% N2O alters plasma concentrations of corticosterone (CORT), epinephrine (EPI), and norepinephrine (NE) in male Long-Evans rats. A gas-tight swivel assembly in the lid of a gas administration chamber allowed the remote collection of blood samples from an indwelling jugular vein catheter at four time-points: baseline and at 30, 60, and 120 min during a two-hour administration of 60% N2O. Relative to baseline, plasma CORT (n = 9) was significantly elevated at all three time-points during N2O inhalation (mixed model analysis, p = .001) and plasma EPI and NE levels were each significantly elevated (n = 8, p ≤ .001) at the 30 min assessment. EPI then declined and did not differ from baseline at the 60 and 120 min assessments (p > .05) whereas NE remained elevated (120 min, p = .001). Administration of 60% N2O increases circulating CORT, EPI, and NE, supporting N2O as a physiological stressor. An N2O-induced increase in CORT is consistent with the observation that addictive drugs typically activate the HPA axis causing increased plasma levels of glucocorticoids. Allostatic models of drug addiction typically involve stress systems and the possible role of stress hormones in N2O-induced allostatic dysregulation is discussed.

Nitrous oxide-based vs. nitrous oxide-free general anaesthesia and accidental awareness in surgical patients: an abridged Cochrane systematic review

Accidental awareness during general anaesthesia can arise from a failure to deliver sufficient anaesthetic agent, or from a patient's resistance to an expected sufficient dose of such an agent. Awareness is 'explicit' if the patient is subsequently able to recall the event. We conducted a systematic review into the effect of nitrous oxide used as part of a general anaesthetic on the risk of accidental awareness in people over the age of five years undergoing general anaesthesia for surgery. We included 15 randomised controlled trials, 14 of which, representing a total of 3439 participants, were included in our primary analysis of the frequency of accidental awareness events. The awareness incidence rate was rare within these studies, and all were considered underpowered with respect to this outcome. The risk of bias across all studies was judged to be high, and 76% of studies failed adequately to conceal participant allocation. We considered the available evidence to be of very poor quality. There were a total of three accidental awareness events reported in two studies, one of which reported that the awareness was the result of a kink in a propofol intravenous line. There were insufficient data to conduct a meta- or sub-group analysis and there was insufficient evidence to draw outcome-related conclusions. We can, however, recommend that future studies focus on potentially high-risk groups such as obstetric or cardiac surgery patients, or those receiving neuromuscular blocking drugs or total intravenous anaesthesia.

Flow Analysis and Sorting of Plant Chromosomes

Analysis and sorting of plant chromosomes (plant flow cytogenetics) is a special application of flow cytometry in plant genomics and its success depends critically on sample quality. This unit describes the methodology in a stepwise manner, starting with the induction of cell cycle synchrony and accumulation of dividing cells in mitotic metaphase, and continues with the preparation of suspensions of intact mitotic chromosomes, flow analysis and sorting of chromosomes, and finally processing of the sorted chromosomes. Each step of the protocol is described in detail as some procedures have not been used widely. Supporting histograms are presented as well as hints on dealing with plant material; the utility of sorted chromosomes for plant genomics is also discussed. © 2016 by John Wiley & Sons, Inc.

Microbial Community and Greenhouse Gas Fluxes from Abandoned Rice Paddies with Different Vegetation

The area of rice paddy fields has declined continuously in East Asian countries due to abandonment of agriculture and concurrent socioeconomic changes. When they are abandoned, rice paddy fields generally transform into wetlands by natural succession. While previous studies have mainly focused on vegetation shifts in abandoned rice paddies, little information is available about how these changes may affect their contribution to wetland functions. As newly abandoned fields proceed through succession, their hydrology and plant communities often change. Moreover, the relationships between these changes, soil microbial characteristics, and emissions of greenhouse gasses are poorly understood. In this study, we examined changes over the course of secondary succession of abandoned rice paddies to wetlands and investigated their ecological functions through changes in greenhouse gas fluxes and microbial characteristics. We collected gas and soil samples in summer and winter from areas dominated by Cyperaceae, Phragmites, and Sphagnum in each site. We found that CO2 emissions in summer were significantly higher than those in winter, but CH4 and N2O emission fluxes were consistently at very low levels and were similar among seasons and locations, due to their low nutrient conditions. These results suggest that microbial activity and abundance increased in summer. Greenhouse gas flux, soil properties, and microbial abundance were not affected by plant species, although the microbial community composition was changed by plant species. This information adds to our basic understanding of the contribution of wetlands that are transformed from abandoned rice paddy systems.

Nitrous oxide speeds the reduction of distressing intrusive memories in an experimental model of psychological trauma

BACKGROUND

Post-traumatic stress disorder (PTSD) involves maladaptive long-term memory formation which underlies involuntary intrusive thoughts about the trauma. Preventing the development of such maladaptive memory is a key aim in preventing the development of PTSD. We examined whether the N-methyl d-aspartate receptor (NMDAR) antagonist gas nitrous oxide (N2O) could reduce the frequency of intrusive memories by inhibiting NMDAR-dependent memory consolidation in a laboratory analogue of psychological trauma.

METHOD

Participants were randomized to inhale N2O (N = 25) or medical air (N = 25) after viewing a negatively valenced emotional film clip ('trauma film'). Participants subsequently completed a daily diary assessing frequency of intrusive thoughts relating to the film clip. A week later, participants completed an explicit memory recall task related to the film.

RESULTS

Post-encoding N2O sped the reduction in intrusive memory frequency, with a significant reduction by the next day in the N2O group compared to 4 days later in the air group. N2O also interacted with post-film dissociation, producing increased intrusion frequency in those who were highly dissociated at baseline. Sleep length and quality the night after viewing the film did not differ between the groups.

CONCLUSION

N2O speeds the reduction of intrusive analogue trauma memory in a time-dependent manner, consistent with sleep-dependent long-term consolidation disruption. Further research with this drug is warranted to determine its potential to inoculate against enduring effects of psychological trauma; however, caution is also urged in dissociated individuals where N2O may aggravate PTSD-like symptomatology.

OC30 - Fracture reduction with nitrous oxide at the children's emergency department shortens the length of stay and reduces the use of full anaesthesia in the operating department

Theme: Accreditation and quality improvement.

AIM

Dislocated fractures are common in the children's emergency department (ER). All forms of fracture reduction are very painful requiring nitrous oxide. The purpose is to shorten the length of stay in the hospital as well as sustain a high quality of care.

METHODS

All nurses received theoretical and practical training in the use of nitrous oxide. Evaluations with the families were made by telephone.

RESULT

A total of 40 enclosed fracture reductions were made at the ER, leading to a reduction of 33 patients in the operating department and the length of stay was shortened - this compared to the same time in 2014. No adverse event was reported and no patient felt any increase in pain during the treatment. All patients would repeat the procedure if necessary.

CONCLUSION

The treatment has reduced the length of stay in the hospital without affecting the other patients in the ER or the quality of care.

Pain reduction in patients after applying a nitrous oxide/oxygen mixture (Livopan) during photodynamic therapy: study protocol for an observational study (Livopan study)

INTRODUCTION

Photodynamic therapy (PDT) is an effective treatment option for extensively photodamaged skin with multiple actinic kerastosis. However, the main drawback of PDT is the intensive pain experienced during its application, which makes it frequently necessary to interrupt or even terminate the process resulting in incomplete treatment. Several strategies for controlling pain during PDT have been studied but few effective methods are currently available. Alternative options are urgently needed. Livopan, a nitrous oxide/oxygen mixture, is indicated for the treatment of short-term pain conditions when rapid analgesic onset and offset effects are wanted. But so far, there are no studies evaluating the effect of Livopan on pain intensity during PDT. Therefore, it remains unclear whether patients benefit from this inhalation analgesia. Within the Livopan study, this issue will be evaluated for the first time.

METHODS AND ANALYSIS

The Livopan study is a prospective, single-centre, explorative, controlled, observational study to investigate the pain reduction in patients after applying a nitrous oxide/oxygen mixture (Livopan) during PDT according to the visual analogue scale in 60 patients.

ETHICS AND DISSEMINATION

Ethics approval was provided by the ethics committee of the medical faculty of the University of Heidelberg. Ethics approval number S-169/2014.

TRIAL REGISTRATION NUMBER

German Clinical Trial Register (DRKS): DRKS00006054.

The interaction of nitrous oxide and fentanyl on the minimum alveolar concentration of sevoflurane blocking motor movement (MACNM) in dogs

The study objective was to determine the effects of 70% nitrous oxide (N2O) and fentanyl on the end-tidal concentration of sevoflurane necessary to prevent movement (MACNM) in response to noxious stimulation in dogs. Six healthy, adult, intact male, mixed-breed dogs were used on 3 occasions in a randomized crossover design. After induction of anesthesia with sevoflurane, each of the following treatments was randomly administered: fentanyl loading dose (Ld) of 15 μg/kg and infusion of 6 μg/kg per hour [treatment 1 (T1)], 70% N2O (T2), or fentanyl (Ld of 15 μg/kg and infusion of 6 μg/kg per hour) combined with 70% N2O (T3). Each dog received each of the 3 treatments once during the 3-week period. Determination of MACNM was initiated 90 min after the start of each treatment. The values were compared using the baseline MACNM, which had been determined in a previous study on the same group of dogs. Data were analyzed using a mixed-model analysis of variance (ANOVA) and Tukey-Kramer tests, and expressed as least squares mean ± SEM. The baseline MACNM decreased by 36.6 ± 4.0%, 15.0 ± 4.0%, and 46.0 ± 4.0% for T1, T2, and T3, respectively (P < 0.05), and differed (P < 0.05) among treatments. Mean fentanyl plasma concentrations did not differ (P ≥ 0.05) between T1 (3.70 ± 0.56 ng/mL) and T3 (3.50 ± 0.56 ng/mL). The combination of fentanyl and N2O resulted in a greater sevoflurane MACNM sparing effect than either treatment alone.

Effect of High-Pressure Gas on Yeast Growth

Microcalorimetry is a useful tool for monitoring the growth behavior of microorganisms. In this study, microcalorimetry was used to investigate the effects of nitrogen, air, oxygen, nitrous oxide, argon, and krypton at high pressure on the growth of the yeast Saccharomyces cerevisiae. Growth thermograms (metabolic heat vs. incubation time) were generated to estimate metabolic activity under compressed gases and to determine the 50% inhibitory pressure (IP(50)) and minimum inhibitory pressure (MIP), which are regarded as indices of the toxicity of compressed gases. Based on MIP values, the most toxic to the least toxic gases were found to be: O(2) > N(2)O > air > Kr > N(2) > Ar.

Exploitation of induced 2n-gametes for plant breeding

Unreduced gamete formation derived via abnormal meiotic cell division is an important approach to polyploidy breeding. This process is considered the main driving force in spontaneous polyploids formation in nature, but the potential application of these gametes to plant breeding has not been fully exploited. An effective mechanism for their artificial induction is needed to attain greater genetic variation and enable efficient use of unreduced gametes in breeding programs. Different approaches have been employed for 2n-pollen production including interspecific hybridization, manipulation of environmental factors and treatment with nitrous oxide, trifluralin, colchicine, oryzalin and other chemicals. These chemicals can act as a stimulus to produce viable 2n pollen; however, their exact mode of action, optimum concentration and developmental stages are still not known. Identification of efficient methods of inducing 2n-gamete formation will help increase pollen germination of sterile interspecific hybrids for inter-genomic recombination and introgression breeding to develop new polyploid cultivars and increase heterozygosity among plant populations. Additionally, the application of genomic tools and identification and isolation of genes and mechanisms involved in the induction of 2n-gamete will enable increased exploitation in different plant species, which will open new avenues for plant breeding.

Comparison of disinfection effect of pressurized gases of CO2, N2O, and N2 on Escherichia coli

Based on the production of gas bubbles with the support of a liquid film-forming apparatus, a device inducing contact between gas and water was used to inactivate pathogens for water disinfection. In this study, the inactivation effect of CO2 against Escherichia coli was investigated and compared with the effects of N2O and N2 under the same pressure (0.3-0.9 MPa), initial concentration, and temperature. The optimum conditions were found to be 0.7 MPa and an exposure time of 25 min. Under identical treatment conditions, a greater than 5.0-log reduction in E. coli was achieved by CO2, while 3.3 log and 2.4 log reductions were observed when N2O and N2 were used, respectively. Observation under scanning electron microscopy and measurement of bacterial cell substances by UV-absorbance revealed greater cell rupture of E. coli following treatment with CO2 than when treatment was conducted using N2O, N2 and untreated water. The physical effects of the pump, acidified characteristics and the release of intracellular substances caused by CO2 were bactericidal mechanism of this process. Overall, the results of this study indicate that CO2 has the disinfection potential without undesired by-product forming.

Nitrous oxide and oxygen sedation: an update

This course will teach the desirable characteristics of nitrous oxide, indications and contraindications for N2O/O2 use, as well as facts and myths surrounding chronic exposure to nitrous oxide, the biologic effects associated with high levels of the gas, and ways to assess and minimize trace gas contamination in an outpatient setting.

[The comparative effects on hemodynamics and bispectral index score of the addition of remifentanil or nitrous oxide to sevoflurane/epidural anesthesia in patients undergoing lower abdominal surgery]

BACKGROUND

The effects of the addition of remifentanil or nitrous oxide (N2O) on hemodynamics and bispectral index score (BIS) during surgery were exam-ined.

METHODS

Twenty-four patients for total hysterectomy were allocated into three groups; 1) 8 patients who received neither remifentanil nor N2O (C group), 2) 8 patients who received remifentanil 0.085 microg kg-1 . min-1 (R group) and 3) 8 patients who received 66% of N2O (G group). They were anesthetized with sevoflurane/epidural anesthesia. Mean arterial pressure (MAP), heart rate (HR) and BIS were recorded 3 times (5 minutes after the skin incision, at the moment of uterine extraction and during retroperitoneal closure).

RESULTS

No significant differences were found in MAP and HR between the C and G group throughout the study, while MAP during retroperitoneal closure and HR at any time points in the R groups were lower than those in the C group. Although BIS in the G group was always lower than that in the C group, no significant differences were found in BIS between the C and R group throughout the study.

CONCLUSIONS

The effects of remifentanil on hemodynamics and bispectral index score in patients during surgery under sevoflurane/epidural anesthesia were completely different from those of N2O.

The effect of nitrous oxide on the minimum alveolar concentration (MAC) and MAC derivatives of isoflurane in dogs

This study investigated the effects of 70% nitrous oxide (N2O) on the minimum alveolar concentration (MAC) of isoflurane (ISO) that prevents purposeful movement, the MAC of ISO at which there is no motor movement (MACNM), and the MAC of ISO at which autonomic responses are blocked (MACBAR) in dogs. Six adult, healthy, mixed-breed, intact male dogs were anesthetized with ISO delivered via mask. Baseline MAC, MACNM, and MACBAR of ISO were determined for each dog using a supra-maximal electrical stimulus (50 V, 50 Hz, 10 ms). Nitrous oxide (70%) was then administered and MAC and its derivatives (N2O-MAC, N2O-MACNM, and N2O-MACBAR) were determined using the same methodology. The values for baseline MAC, MACNM, and MACBAR were 1.39 ± 0.14, 1.59 ± 0.10, and 1.72 ± 0.16, respectively. The addition of 70% N2O decreased MAC, MACNM, and MACBAR by 32%, 15%, and 25%, respectively.

Modulation of functional EEG networks by the NMDA antagonist nitrous oxide

Parietal networks are hypothesised to play a central role in the cortical information synthesis that supports conscious experience and behavior. Significant reductions in parietal level functional connectivity have been shown to occur during general anesthesia with propofol and a range of other GABAergic general anesthetic agents. Using two analysis approaches (1) a graph theoretic analysis based on surrogate-corrected zero-lag correlations of scalp EEG, and (2) a global coherence analysis based on the EEG cross-spectrum, we reveal that sedation with the NMDA receptor antagonist nitrous oxide (N₂O), an agent that has quite different electroencephalographic effects compared to the inductive general anesthetics, also causes significant alterations in parietal level functional networks, as well as changes in full brain and frontal level networks. A total of 20 subjects underwent N₂O inhalation at either 20%, 40% or 60% peak N₂O/O₂ gas concentration levels. N₂O-induced reductions in parietal network level functional connectivity (on the order of 50%) were exclusively detected by utilising a surface Laplacian derivation, suggesting that superficial, smaller spatial scale, cortical networks were most affected. In contrast reductions in frontal network functional connectivity were optimally discriminated using a common-reference derivation (reductions on the order of 10%), indicating that the NMDA antagonist N₂O induces spatially coherent and widespread perturbations in frontal activity. Our findings not only give important weight to the idea of agent invariant final network changes underlying drug-induced reductions in consciousness, but also provide significant impetus for the application and development of multiscale functional analyses to systematically characterise the network level cortical effects of NMDA receptor related hypofunction. Future work at the source space level will be needed to verify the consistency between cortical network changes seen at the source level and those presented here at the EEG sensor space level.

[Volatile anaesthesias' molecular biological course of action]

Anaesthesia is extensively used worldwide and in Denmark alone more than 400,000 anaesthesias are performed each year. In spite of that the molecularly mechanism of anaesthesia has not been proven. Hypotheses have been suggested (lipid versus protein theory), but none has yet been able to explain the whole mechanism. Molecular targets for volatile anaesthetics (e.g. potassium and calcium channels) affected areas in the central nervous system and the impact on the cerebral metabolism versus the cerebral blood flow are discussed.

Time-dependent middle ear pressure changes under general anaesthesia in children: N2O-O2 mixture versus air-oxygen mixture

OBJECTIVES

The aim of this study was to investigate the effects of N2O-O2 mixture (Inspired O2 30%) on middle ear pressure (MEP) in children compared with the effects of an air-oxygen mixture (Inspired O2 50%).

METHOD

The study included thirty child patients who underwent general anaesthesia for different reasons, with the exception of ENT problems and ear interventions. They were randomly divided into two groups. Group 1 (15 children: 10 male and 5 female) received a N2O-O2 mixture (Inspired O2 30%); and group 2 (15 children: 10 male and 5 female) were given an air-oxygen mixture (Inspired O2 50%). MEP was measured using a portable impedance analyser before the operation (PreO),10 minutes after intubation (10AEn), 30 minutes after intubation (30AEn), 10 minutes before extubation (10BEx), 15 minutes after the operation (PO15), 30 minutes after the operation (PO30), 1 hour after the operation (PO1h) and 6 hours after the operation (PO6h).

RESULTS

The pressure and compliance values were the same in groups 1 and 2. The pressure-time graphs for the two groups were different: in Group 2, MEP rose quickly at 10AEn and positive pressure values were seen in the middle ear. MEP then fell rapidly until the end of the surgery and lower and negative pressures (Mean -50 daPa) were observed at PO6h. In Group 1, MEP was elevated at 10AEn and positive pressure was found (but not as high as in Group 2). MEP then fell more slowly. In other words, positive pressure in the middle ear persisted longer and the middle ear was subjected to positive pressure and nitrogen over a longer period. Separate analyses were made in Groups 1 and 2 of pressure differences and of compliance values at eight measurement points using the Friedman test. Differences in pressure values were found to be statistically significant in both Group 1 (p = 0.000) and Group 2 (p = 0.000). In Group 1, all the 10AEn and 30AEn values were significantly higher than the PreO, PO30, PO1h and PO6h values. The 10BEx value was significantly higher than the PreO and PO1h values. The PO15 value was significantly higher than the PreO value. In Group 2, the PO6h value was significantly lower than the 10BEx, 10AEn and 30AEn values. The PO1h value was significantly lower than the 30AEn values. The MEP values increased in Group 1 in younger and taller children and in children receiving anaesthesia for shorter periods. MEP values increased in Group 2 in younger and taller children, and in heavier children. MEP values fell with the length of anaesthesia.

CONCLUSION

In brief anaesthesia, nitrogen was not removed from the middle ear quickly in Group 1: middle ear pressure values were higher. The nitrous oxide remained in the middle ear longer and so the possibility of ear toxicity may increase. In Group 2, 50% O2 was rapidly absorbed and removed from the middle ear and so middle ear pressure was not as high. It may be concluded that air-oxygen mixture (Inspired O2 50%) anaesthesia should be recommended as being more reliable in tympanoplasties and other middle ear interventions than a N2O-O2 mixture (Inspired O2 30%).

[Is nitrous oxide useful for laryngeal mask airway insertion under 8% sevoflurane?]

BACKGROUND

The usefulness of nitrous oxide for laryngeal mask airway insertion under 8% sevoflurane anesthesia was investigated.

METHODS

One hundred and fifty patients aged 40 to 60 years for general anesthesia were divided into GOS (nitrous oxide, oxygen, sevoflurane) and OS (oxygen, sevoflurane) groups. Anesthesia was induced with 8% sevoflurane and nitrous oxide 3 l x min(-1) and oxygen 3 l x min(-1) in the GOS group, or oxygen 6 l x min(-1) in the OS group. When verbal response disappeared, sevoflurane concentration was reduced to 3%. Five min after the start of induction, laryngeal mask airway was inserted.

RESULTS

The changes in blood pressure and heart rate were significantly smaller and times to disappearance of eyelash response and verbal response were significantly shorter in the GOS group than those in the OS group. The frequencies of postoperative nausea, vomiting, and headache were not different between the groups.

CONCLUSIONS

Nitrous oxide shortened induction time, decreased hemodynamic changes, but did not increase postoperative nausea, vomiting and headache when used for anesthesia induction with 8% sevoflurane to insert laryngeal mask airway.

Psychomotor function during mild narcosis induced by subanesthetic level of nitrous oxide: individual susceptibility beyond gender effect

OBJECTIVE

We investigated the effect of narcosis induced by subanesthetic concentrations of nitrous oxide (N2O), a behavioral analogue for hyperbaric nitrogen, on psychomotor performance. In particular, we assessed individual susceptibility to narcosis.

METHODS

The participants were 12 female and 12 male undergraduate students. Psychomotor assessment was conducted with a computerized Visual Simple Reaction Time (VSRT) test, and Trail Making Tests Part A (TMTA) and Part B (TMT-B). The tests were conducted on two separate occasions in the following order: VSRT, TMT-A, TMT-B. On the first occasion participants conducted the tests breathing room air (air trial), and during the second test they conducted the tests while breathing a normoxic mixture containing 30% N2O (N2O trial).

RESULTS

Males had significantly (p = 0.036) shorter VSRT in the air trials. There was no effect of gender on psychomotor performance in the N2O trials. Overall, mean performance in the N2O trials degraded significantly (p = 0.004) only in VSRT. Performance of individual participants exhibited different and inconsistent direction of change in the N2O trials.

CONCLUSION

N2O-induced alterations in psychomotor function are primarily dependent on individual susceptibility to narcosis (i.e., concentration threshold).

Comparison of cuff-pressure changes in silicone and PVC laryngeal masks during nitrous oxide anaesthesia in spontaneously breathing children

BACKGROUND

The purpose of this study was to evaluate the cuff pressures of four different laryngeal masks in paediatric patients undergoing routine surgery and to determine whether there is a substantial increase in cuff pressure when silicone masks are used compared to PVC laryngeal mask airways.

METHODS

Hundred and forty patients aged < 16 yr were randomly allocated to receive one of four extra glottic airway devices: LMA-Classic; LMA-Unique; Soft Seal; or Cobra-PLA. Intracuff pressure was monitored continuously throughout the operative intervention. The primary outcome was measurement of an increase in cuff pressure. First attempt success rate, effective airway time, anatomical position of the airway and incidence of airway morbidity data were monitored.

RESULTS

Mean cuff pressure increased within 5 min of N2O exposure, and was substantially higher in the silicone LMA-C,compared to the PVC-based extra glottic airway devices tested, reaching a plateau of the cuff pressure after 45 min.The overall first attempt success rate (97%) and the mean effective airway time (24 ± 9 sec) were very satisfactory and all patients underwent successful surgery. Anatomical position was adequate in most airways, although in 34%of the patients in the Cobra group herniation of either the epiglottis or arytenoids were detected. Airway morbidity due to the devices was insignificant.

CONCLUSIONS

This study demonstrated a substantial increase in cuff pressure during anaesthesia for children in whom a silicone-based LMA-C was used, whereas PVC-based extra glottic airway devices showed a much lower increase.

[The correlation of middle ear pressure variations with mastoid pneumatization during nitrous oxide administration]

BACKGROUND

The present study evaluated the relationship between the middle ear (ME) pressure increase rate (PIR) and the mastoid size as well as the effect of mastoid size on the incidence of nausea and vomiting during nitrous oxide (N2O) anesthesia.

METHODS

Twelve healthy male volunteers were recruited. The extent of mastoid pneumatization was measured planimetrically using a mastoid X-ray (Schuller's view). The ears were then divided into a small or large mastoid group according to the median value. The ME pressure was compared just before each increase to 33%, 50%, and 67% N2O. Using the ME pressure curve, the PIR for the first peak of the curve steepness was calculated.

RESULTS

Increasing the end-tidal N2O concentration to 50% and 67% in the large mastoid group and to 33%, 50%, and 67% in the small mastoid group significantly increased the ME pressure. The PIR in the ears in the large mastoid group was significantly lower and the incidence of nausea was 33% in the small mastoid group during 33% N2O anesthesia.

CONCLUSIONS

A higher PIR in the ears and a higher incidence of nausea were observed in the small mastoid group, compared with the large mastoid group.

[Mechanism of general anesthesia and antinociception]

Nitrous oxide exhibits antinociceptive effects by inhibition of transmission of nociceptive information from the primary afferent neuron to the spinal cord neuron through the activation of the descending inhibitory pathway. Furthermore, nitrous oxide might directly modulate the nociceptive transmission at the dorsal horn of the spinal cord. Analysis of knockout mice and pharmacological analysis suggest that the K -opioid receptor and the nociceptin receptor are involved in the antinociceptive effects of nitrous oxide. To elucidate the molecular mechanism in pharmacological effects of nitrous oxide, further investigation is necessary.

[How far has our understanding of mechanisms of general anesthesia advanced?: preface and comments]

Although the great advance has been made in clinical anesthesia practice, the fundamental mechanisms of anesthetic action still remain to be an unsolved mystery. The early lipid membrane theory based on Meyer and Overton's law was taken over by the proteo-centric view of mechanism. Studies at the molecular and cellular level have shown that anesthetics act on a wide rage of functional proteins, including ligand-gated ion channels (GABA, glycine, NMDA receptors), two pore domain K channels and other ion channels. The effects on the individual channels, however, differ among various types of anesthetics. Elucidating how anesthetics work on the neuronal pathways is important to find the link between the molecular studies and in vivo action of anesthetics. Anesthesia disrupts the linkages between cortical and thalamic neurons and those among the cortical neurons, as well as depression and activation of the arousal and sleep nuclei, respectively. Functional brain imaging has revealed the global effects of general anesthetics on the human brain. Taken together, the disruption of thalamocortical connectivity and the integrative properties of the cerebral cortex might be an essential common feature of anesthetic action.

Direct animal calorimetry, the underused gold standard for quantifying the fire of life

Direct animal calorimetry, the gold standard method for quantifying animal heat production (HP), has been largely supplanted by respirometric indirect calorimetry owing to the relative ease and ready commercial availability of the latter technique. Direct calorimetry, however, can accurately quantify HP and thus metabolic rate (MR) in both metabolically normal and abnormal states, whereas respirometric indirect calorimetry relies on important assumptions that apparently have never been tested in animals with genetic or pharmacologically-induced alterations that dysregulate metabolic fuel partitioning and storage so as to promote obesity and/or diabetes. Contemporary obesity and diabetes research relies heavily on metabolically abnormal animals. Recent data implicating individual and group variation in the gut microbiome in obesity and diabetes raise important questions about transforming aerobic gas exchange into HP because 99% of gut bacteria are anaerobic and they outnumber eukaryotic cells in the body by ∼10-fold. Recent credible work in non-standard laboratory animals documents substantial errors in respirometry-based estimates of HP. Accordingly, it seems obvious that new research employing simultaneous direct and indirect calorimetry (total calorimetry) will be essential to validate respirometric MR phenotyping in existing and future pharmacological and genetic models of obesity and diabetes. We also detail the use of total calorimetry with simultaneous core temperature assessment as a model for studying homeostatic control in a variety of experimental situations, including acute and chronic drug administration. Finally, we offer some tips on performing direct calorimetry, both singly and in combination with indirect calorimetry and core temperature assessment.

Nitrous oxide-induced NO-dependent neuronal release of β-endorphin from the rat arcuate nucleus and periaqueductal gray

Nitrous oxide (N(2)O)-induced antinociception is thought to result from nitric oxide (NO)-dependent neuronal release of endogenous opioid peptides in the central nervous system. The present study employed microdialysis to determine whether exposure to N(2)O stimulates proopiomelanocortin (POMC) neurons to release β-endorphin in the arcuate nucleus (ARC) of the hypothalamus and the periaqueductal gray (PAG) of the midbrain. Male Sprague-Dawley rats were stereotaxically implanted with microdialysis probes in the ARC or PAG. Exposure to 70% N(2)O significantly increased dialysate levels of oxidation products of NO as well as β-endorphin, compared to levels in fractions collected under room air. These increases in the ARC and PAG were abolished by systemic pretreatment with L-N(G)-nitro arginine methyl ester (L-NAME). These findings suggest an association between increased NO activity and the stimulated release of β-endorphin during exposure of rats to N(2)O.

[A comparative analysis of haemodynamics and oxygen transport during xenon and nitrous oxide anaesthesia in endoscopic surgery in gynaecology]

A comparative analysis of haemodynamics and blood gases has been performed in patients during either low-flow anaesthesia with xenon and nitrous oxide and high-flow nitrous oxide anaesthesia. Ninety five patients scheduled for endoscopic surgery were included and divided into three groups: a combined low-flow anaesthesia (30 women), a low-flow nitrous oxide anaesthesia (30 women) and a high-flow nitrous oxide anaesthesia using a semi-closed circuit (35 women). The study has shown a stimulating effect of xenon on haemodynamics during carboxyperitoneum and Trendelenburg position, a better oxygen transport performance and a lower consumption of opioids in this group. Those favourable changes enable the optimization of the oxygen transport in endoscopic surgery in gynaecology, and reduce the contraindications to endoscopic surgery.

Nitrous oxide discretely up-regulates nNOS and p53 in neonatal rat brain

AIM

Animal studies suggest that neuronal cell death often results from anesthetic administration during synaptogenesis. Volatile anesthetics are strongly involved in triggering neuronal apoptosis, whereas other inhalational agents (xenon) demonstrate protective effects. Nitrous oxide (N2O) has modest pro-apoptotic effects on its own and potent, synergistic toxic effects when combined with volatile agents. Recent findings suggest that, during periods of rapid brain development, the enhanced neurodegeneration triggered by anesthetic drugs may be caused by a compensatory increase in intracellular free calcium, a potent activator of neuronal nitric oxide synthase (nNOS). Anesthesia-induced neuro-apoptosis is also activated via the intrinsic and the extrinsic apoptotic pathways because both pathways involve p53, a key regulatory gene. The molecular events related to neuronal cell apoptosis are not completely understood. To gain further insight into the events underlying neuro-apoptosis, we analyzed the transcriptional consequences of N2O exposure on nNOS, iNOS and p53 mRNA levels.

METHODS

The study used 2 groups of postnatal day seven Sprague/Dawley rats (N=6 each) that were exposed for 120 minutes to air (75% N2, 25% O2) or N2O (75% N2O, 25% O2; this N2O concentration is commonly used to induce anesthesia and has been demonstrated to trigger neurodegeneration in postnatal day seven rats). Total RNA was isolated from each brain and expression analyses on iNOS and nNOS transcripts were performed using relative Real-Time C-reactive protein PCR (using G3PDH as a housekeeping gene). A semi-quantitative RT-PCR analysis was performed on the p53 transcript (using Ciclophylin A as a housekeeping gene).

RESULTS

Statistical analysis (REST 2005) revealed a significant, 11-fold up-regulation (P=0.026) of the nNOS transcript but no significant changes in iNOS transcription. The p53 mRNA was up-regulated almost 2-fold (P=0.0002; Student's t-Test; GraphPad Prism 4.00) in N2O-treated samples relative to room-air samples.

CONCLUSION

Our preliminary data show that N2O induced a selective increase in nNOS and p53 transcription. These new findings provide evidence of pro-apoptotic action by N2O and may shed new insight on its toxic effects; however, further investigations are necessary.

Quality of fresh-cut baby spinach grown under a floating trays system as affected by nitrogen fertilisation and innovative packaging treatments

BACKGROUND

Alternative techniques for cultivation of leafy vegetables such as a floating tray system and unconventional gas mixtures for post-harvest active modified atmosphere packaging (MAP) could be of interest in the minimally processed vegetable industry.

RESULTS

The combined effect of three pre-harvest fertilisation doses (8, 12 or 16 mmol N L(-1)) and three post-harvest MAP conditions (passive, super-atmospheric or N2O-enriched) on the main quality attributes of fresh-cut baby spinach leaves throughout 10 days at 5 degrees C was studied. After 8 days of shelf life, spinach leaves fertilised with 8 and 16 mmol N L(-1) and stored under N2O-enriched MAP showed the lowest microbial growth, with good sensory quality. Such combined treatments also preserved the total antioxidant capacity sampled at harvest (8 g ascorbic acid equivalent antioxidant capacity kg(-1) f.w.). A decrease of 10-20% in total vitamin C content regardless of N fertilisation and packaging treatment was found during shelf life. Total phenolics content at harvest was 2 g gallic acid equivalents kg(-1) f.w., which was slightly decreased or preserved during shelf life while total chlorophylls were preserved for all treatments assayed around 550 mg kg(-1) f.w.

CONCLUSION

No clear effect of fertilisation doses was observed during post-harvest storage on overall quality of fresh-cut baby spinach leaves, while N2O-enriched atmospheres seems to be a promising alternative to passive MAP for extending shelf life.

Reduced immobilizing properties of isoflurane and nitrous oxide in mutant mice lacking the N-methyl-D-aspartate receptor GluR(epsilon)1 subunit are caused by the secondary effects of gene knockout

BACKGROUND

Until recently, the N-methyl-D-aspartate (NMDA) receptor was considered to possibly mediate the immobility produced by inhaled anesthetics such as isoflurane and nitrous oxide. However, new evidence suggests that the role of this receptor in abolition of the movement response may be less important than previously thought. To provide further evidence supporting or challenging this view, we examined the anesthetic potencies of isoflurane and nitrous oxide in genetically modified animals with established NMDA receptor dysfunction caused by GluRepsilon1 subunit knockout.

METHODS

The immobilizing properties of inhaled anesthetics in mice quantitated by the minimum alveolar anesthetic concentration (MAC) were evaluated using the classic tail clamp method.

RESULTS

Compared with wild-type controls, NMDA receptor GluRepsilon1 subunit knockout mice displayed larger isoflurane MAC values indicating a resistance to the immobilizing action of isoflurane. Knockout mice were previously shown to have enhanced monoaminergic tone as a result of genetic manipulation, and this increase in MAC could be abolished in our experiments by pretreatment with the serotonin 5-hydroxytryptamine type 2A receptor antagonist ketanserin or with the dopamine D2 receptor antagonist droperidol at doses that did not affect MAC values in wild-type animals. Mutant mice also displayed resistance to the isoflurane MAC-sparing effect of nitrous oxide, but this resistance was similarly abolished by ketanserin and droperidol. Thus, resistance to the immobilizing action of inhaled anesthetics in knockout mice seems to be secondary to increased monoaminergic activation after knockout rather than a direct result of impaired NMDA receptor function.

CONCLUSIONS

Our results confirm recent findings indicating no critical contribution of NMDA receptors to the immobility induced by isoflurane and nitrous oxide. In addition, they demonstrate the ability of changes secondary to genetic manipulation to affect the results obtained in global knockout studies.

Effects of sevoflurane on cognitive deficit, motor function, and histopathology after cerebral ischemia in rats

BACKGROUND

The volatile anesthetic sevoflurane exhibits neuroprotective properties when assessed for motor function and histopathology after cerebral ischemia in rats. Damage of hippocampal neurons after ischemia relates to a number of cognitive deficits that are not revealed by testing animals for motor function. Therefore, the present study evaluates cognitive and behavioral function as well as hippocampal damage in rats subjected to cerebral ischemia under sevoflurane compared with fentanyl/nitrous oxide (N(2)O)/O(2) anesthesia.

METHODS

Thirty-four rats were trained for 10 days using a hole-board test to detect changes in cognitive and behavioral function. Rats were randomly assigned to the following groups: (A) sham/fentanyl/N(2)O/O(2) (n=7); (B) ischemia/fentanyl/N(2)O/O(2) (n=10); (C) sham/2.0 vol% sevoflurane in O(2)/air (n=7); and (D) ischemia/2.0 vol% sevoflurane in O(2)/air (n=10). Cerebral ischemia was produced by unilateral common carotid artery occlusion combined with hemorrhagic hypotension (mean arterial blood pressure 40 mmHg for 45 min). Temperature, arterial blood gases, and pH were maintained constant. Cerebral blood flow was measured using laser-Doppler flowmetry. After surgery, cognitive and behavioral function was re-evaluated for 10 days. On day 11, the brains were removed for histopathologic evaluation (hematoxylin/eosin-staining).

RESULTS

Cognitive testing revealed deficits in declarative and working memory in ischemic rats anesthetized with fentanyl/N(2)O. Rats anesthetized with sevoflurane during ischemia showed a significantly better outcome. Hippocampal damage was significantly worse with fentanyl/N(2)O.

CONCLUSION

The present data add to previous investigations showing that sevoflurane prevents a deficit in cognitive function and histopathological damage induced by cerebral ischemia in rats.

Sevoflurane and nitrous oxide exert cardioprotective effects against hypoxia-reoxygenation injury in the isolated rat heart

It is unclear whether nitrous oxide (N(2)O) has a protective effect on cardiac function in vitro. In addition, little is known about the cardioprotective effect of anesthesia administered during hypoxia or ischemia. We therefore studied the cardioprotective effects of N(2)O and sevoflurane administered before or during hypoxia in isolated rat hearts. Rat hearts were excised and perfused using the Langendorff technique. For hypoxia-reoxygenation, hearts were made hypoxic (95% N(2), 5% CO(2)) for 45 min and then reoxygenated (95% O(2), 5% CO(2)) for 40 min (control: CT group). Preconditioning was achieved through three cycles of application of 4% sevoflurane (sevo-pre group) or 50% N(2)O (N(2)O-pre group) for 5 min with 5-min washouts in between. Hypoxic conditions were achieved by administering the 4% sevoflurane (sevo-hypo group) or 50% N(2)O (N(2)O-hypo group) during the 45-min hypoxic period. L-type calcium channel currents (I(Ca,L)) were recorded on rabbit myocytes. (1) Both 4% sevoflurane and 50% N(2)O significantly reduced left ventricular developed pressure (LVDP). Sevoflurane also increased left ventricular end-diastolic pressure, though N(2)O did not. (2) The recoveries of LVDP and pressure-rate product (PRP) after hypoxia-reoxygenation were better in the sevo-pre group than in the CT or N(2)O-pre group. (3) Application of either sevoflurane or N(2)O during hypoxia improved recovery of LVDP and PRP, and GOT release was significantly lower than in the CT group. (4) Sevoflurane and N(2)O reduced I(Ca,L) to similar extents. Although sevoflurane administered before or during hypoxia exerts a cardioprotective effect, while N(2)O shows a cardioprotective effect only when administered during hypoxia.