Nitrous oxide (laughing gas) is an NMDA antagonist, neuroprotectant and neurotoxin

Repurposing General Anesthetic Drugs to Treat Depression: A New Frontier for Anesthesiologists in Neuropsychiatric Care

During the last 100 years, the role of anesthesiologists in psychiatry has focused primarily on facilitating electroconvulsive therapy and mitigating postoperative delirium and other perioperative neurocognitive disorders. The discovery of the rapid and sustained antidepressant properties of ketamine, and early results suggesting that other general anesthetic drugs (including nitrous oxide, propofol, and isoflurane) have antidepressant properties, has positioned anesthesiologists at a new frontier in the treatment of neuropsychiatric disorders. Moreover, shared interest in understanding the biologic underpinnings of anesthetic drugs as psychotropic agents is eroding traditional academic boundaries between anesthesiology and psychiatry. This article presents a brief overview of anesthetic drugs as novel antidepressants and identifies promising future candidates for the treatment of depression. The authors issue a call to action and outline strategies to foster collaborations between anesthesiologists and psychiatrists as they work toward the common goals of repurposing anesthetic drugs as antidepressants and addressing mood disorders in surgical patients.

Stroke and Translational Research - Review of Experimental Models with a Focus on Awake Ischaemic Induction and Anaesthesia

Animal models are an indispensable tool in the study of ischaemic stroke with hundreds of drugs emerging from the preclinical pipeline. However, all of these drugs have failed to translate into successful treatments in the clinic. This has brought into focus the need to enhance preclinical studies to improve translation. The confounding effects of anaesthesia on preclinical stroke modelling has been raised as an important consideration. Various volatile and injectable anaesthetics are used in preclinical models during stroke induction and for outcome measurements such as imaging or electrophysiology. However, anaesthetics modulate several pathways essential in the pathophysiology of stroke in a dose and drug dependent manner. Most notably, anaesthesia has significant modulatory effects on cerebral blood flow, metabolism, spreading depolarizations, and neurovascular coupling. To minimise anaesthetic complications and improve translational relevance, awake stroke induction has been attempted in limited models. This review outlines anaesthetic strategies employed in preclinical ischaemic rodent models and their reported cerebral effects. Stroke related complications are also addressed with a focus on infarct volume, neurological deficits, and thrombolysis efficacy. We also summarise routinely used focal ischaemic stroke rodent models and discuss the attempts to induce some of these models in awake rodents.

Pharmacotherapeutic advances in fibromyalgia: what's new on the horizon?

INTRODUCTION

This review delves into Fibromyalgia Syndrome (FMS), a chronic pain condition demanding thorough understanding for precise diagnosis and treatment. Yet, a definitive pharmacological solution for FMS remains elusive.

AREAS COVERED

In this article, we systematically analyze various pharmacotherapeutic prospects for FMS treatment, organized into sections based on the stage of drug development and approval. We begin with an overview of FDA-approved drugs, discussing their efficacy in FMS treatment. Next, we delve into other medications currently used for FMS but still undergoing further study, including opioids and muscle relaxants. Further, we evaluate the evidence behind medications that are currently under study, such as cannabinoids and naltrexone. Lastly, we explore new drugs that are in phase II trials. Our research involved a thorough search on PUBMED, Google Scholar, and clinicaltrials.gov. We also discuss the action mechanisms of these drugs and their potential use in specific patient groups.

EXPERT OPINION

A focus on symptom-driven, combination therapy is crucial in managing FMS. There is also a need for ongoing research into drugs that target neuroinflammation, immunomodulation, and the endocannabinoid system. Bridging the gap between benchside research and clinical application is challenging, but it holds potential for more targeted and effective treatment strategies.

Neurobiological basis of emergence from anesthesia

The suppression of consciousness by anesthetics and the emergence of the brain from anesthesia are complex and elusive processes. Anesthetics may exert their inhibitory effects by binding to specific protein targets or through membrane-mediated targets, disrupting neural activity and the integrity and function of neural circuits responsible for signal transmission and conscious perception/subjective experience. Emergence from anesthesia was generally thought to depend on the elimination of the anesthetic from the body. Recently, studies have suggested that emergence from anesthesia is a dynamic and active process that can be partially controlled and is independent of the specific molecular targets of anesthetics. This article summarizes the fundamentals of anesthetics' actions in the brain and the mechanisms of emergence from anesthesia that have been recently revealed in animal studies.

The boon and bane of nitrous oxide

Nitrous oxide (N2O) has been known since the end of the eighteenth century. Today, N2O plays a huge role as a greenhouse gas and an ozone-depleting stratospheric molecule. The main sources of anthropogenic N2O emissions are agriculture, fuel combustion, wastewater treatment, and various industrial processes. By contrast, the contribution of medical N2O to the greenhouse effect appears to be small. The recreational and medical uses of N2O gradually diverged over time. N2O has analgesic and anesthetic effects, making it widely used in modern dentistry and surgery. New research has also begun studying N2O's antidepressant actions. N-methyl-D-aspartate (NMDA) antagonism and opioid effects are believed to be the main underlying biochemical mechanisms. At this point, numerous questions remain open and, in particular, the conduct of larger clinical trials will be essential to confirm N2O's use as a rapid-acting antidepressant. The N2O concentration delivered, the duration of a single inhalation, as well as the number of inhalations ultimately required, deserve to be better understood. Finally, the non-medical use of N2O has gained significant attention in recent years. Sudden deaths directly attributed to N2O are primarily due to asphyxia. Heavy, chronic N2O use may result in vitamin B12 deficiency, which, among other things, may cause megaloblastic anemia, venous thrombosis, myeloneuropathy, and skin pigmentation. Helpful biochemical tests include homocysteine and methylmalonic acid. The centerpiece of treatment is complete cessation of N2O use together with parenteral administration of vitamin B12.

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.

Plasma neurological biomarkers as a measure of neurotoxicity in pediatric dental general anesthesia: a prospective observational feasibility study

PURPOSE

Neurotoxicity concerns have been raised over general anesthesia and sedation medication use in children. Such concerns are largely based on animal studies, historical anesthetic agents, and assessment tools, thus warranting further investigations. Blood biomarkers in detecting neuronal inflammation and apoptosis are novel methods for detecting neuronal damage. Therefore, the aim of this feasibility study was to assess the usefulness of the levels of four plasma biomarkers in dental general anesthesia (DGA) as surrogate markers of neurotoxicity in children. The secondary aim was to compare changes in motor manipulative skills pre- and post-anesthetic exposure.

METHODS

This single-center prospective observational study included 22 healthy children aged between 3 and 6 years old who underwent DGA. Subclinical neurotoxicity was measured with a panel of four plasma biomarkers: Caspase-3, neuron-specific enolase (NSE), neurofilament light chain, and S100B at three time points (1; at start, 2; end and 3; on recovery from DGA). The Skillings-Mack test was used to identify the difference in the biomarker levels at three time points. Motor manipulative score assessment, prior and two weeks after DGA was also performed.

RESULTS

A total of 22 study participants (mean age = 5 ± 1 years) were included with a median DGA duration of 106 ± 28 min. A reduction in Caspase-3 levels was recorded, with pairwise comparison over three time points, reporting a statistical significance between time point 2 vs. 1 and time point 3 vs. 1. Although fluctuations in NSE levels were recorded, no significant changes were found following pairwise comparison analysis. Among other biomarkers, no significant changes over the three periods were recorded. Furthermore, no significant changes in manipulative motor scores were reported.

CONCLUSION

Caspase-3 reduced significantly in the short time frames during day-care DGA; this might be due to the relatively short anesthesia duration associated with dental treatment as compared with more extensive medical-related treatments. Therefore, further studies on Caspase-3 as a potential biomarker in pediatric DGA neurotoxicity are required to further ascertain results of this study.

Nitrous oxide induced subacute combined degeneration of the spine cord: A case report

RATIONALE

In recent years, recreational use of inhaled nitrous oxide (N2O) is on the increase among young people, accompanied by a corresponding rise in reports about its toxicity. Subacute combined degeneration of the spine cord (SCD) is the typical clinical picture of the nervous system disorder caused by N2O intoxication, as a result of metabolic disturbance of vitamin B12.

PATIENT CONCERNS, DIAGNOSES, INTERVENTIONS AND OUTCOMES

We report a 28-year-old female of SCD due to prolonged use of N2O, presented with paresthesia and unsteady in walking progressing within 1 month. Symptoms gradually improved with the treatment of intramuscular injections of hydroxocobalamin combined with N2O abstinence, and the patient recovered completely with normal neurological examination after 4 months of follow-up.

LESSONS

Clinicians should be aware of the clinical features and pathogenesis of SCD caused by N2O intoxication in order to lead effective treatment as soon as possible. Recreational N2O use should always be considered as an etiology when dealing with patients presented with myelopathy and/or neuropathy suspected of vitamin B12 deficiency.

Vision Threatening Raised Intracranial Pressure Associated with Recreational Nitrous Oxide Use

Nitrous oxide is used as an anaesthetic and analgesic agent in the medical setting and is known to cause raised intracranial pressure. The use of nitrous oxide recreationally for the drug's euphoric and relaxant properties has been linked to multiple neurological and psychiatric sequelae including neuropathy, myelopathy, and psychosis. We describe a case of a young person who declared heavy nitrous oxide use resulting in vision-threatening papilloedema secondary to raised intracranial pressure. He underwent emergency lumbar drainage alongside high-dose acetazolamide and parenteral vitamin B12 injections. To our knowledge, there have yet to be other reports of cases where heavy nitrous oxide use has caused secondary pseudotumor cerebri syndrome.

Psychedelic concentrations of nitrous oxide reduce functional differentiation in frontoparietal and somatomotor cortical networks

Despite the longstanding use of nitrous oxide and descriptions of its psychological effects more than a century ago, there is a paucity of neurobiological investigation of associated psychedelic experiences. We measure the brain's functional geometry (through analysis of cortical gradients) and temporal dynamics (through analysis of co-activation patterns) using human resting-state functional magnetic resonance imaging data acquired before and during administration of 35% nitrous oxide. Both analyses demonstrate that nitrous oxide reduces functional differentiation in frontoparietal and somatomotor networks. Importantly, the subjective psychedelic experience induced by nitrous oxide is inversely correlated with the degree of functional differentiation. Thus, like classical psychedelics acting on serotonin receptors, nitrous oxide flattens the functional geometry of the cortex and disrupts temporal dynamics in association with psychoactive effects.

Neuropathy with Cerebral Features Induced by Nitrous Oxide Abuse-A Case Report

Nitrous oxide abuse may cause functional cobalamin deficiency and subsequent damage to the peripheral nerves, the spinal cord, and the brain, a symptom complex best described by the term cobalamin neuropathy. Here, we report a case of cobalamin neuropathy with uncommon cerebral symptomatology following nitrous oxide intoxication and contextualize the symptomatology. A 22-year-old male with a history of mixed drug dependency presented at the emergency room after inhaling six 615 g cylinders, equal to ~1800 L, of nitrous oxide daily for two weeks. His main complaints were rapidly progressing paresthesias and gait difficulties, but he was also found to suffer from memory impairment and signs of extrapyramidal pathology in the form of dystonic posturing and athetosis. Neuroimaging demonstrated spinal cord hyperintensities consistent with subacute combined degeneration. The patient had low serum cobalamin and high plasma homocysteine, suggesting cobalamin neuropathy. After commencing treatment with parenteral hydroxocobalamin, plasma homocysteine normalized. The extrapyramidal symptoms disappeared during the first days of treatment, whereas the cognitive and peripheral symptoms only partially resolved over the following 20 days. This case highlights how neurological symptoms such as hyperkinetic movements and memory impairment may be associated with chronic nitrous oxide abuse. It is unclear to what extent these and other symptoms of cobalamin neuropathy are reversible, which underscores the public health concern.

Lethal nitrous oxide (N2O) intoxication during surgery: the contribution of immunohistochemistry in identifying the cause of death: a case report

BACKGROUND

Nitrous oxide (N2O) is a gas used in medicine for its analgesic, anxiolytic and amnesic properties. It is a drug considered safe if adequately administered. In the literature, accidental N2O-related deaths are rare. They are mostly related to inhalation of this substance for recreational and autoerotic purposes; rarely are reported deaths due to incorrect administration of medical gas in anesthesia. The diagnosis of death from acute N2O intoxication is complex and is generally an exclusion diagnosis: the macroscopic and microscopic post-mortem signs are entirely nonspecific. Furthermore, the circumstantial data are not always supportive and can even be confusing, mainly if the death occurred inside a hospital.

CASE PRESENTATION

We describe a particular case of death from acute nitrous oxide poisoning in a hospital environment, of a Caucasian male of 72-years-old. The intoxication occurred during a minimally invasive vascular surgery due to an incorrect assembly of the supply lines of medical gases (O2 and N2O). The identification of the cause of death resulted from the analysis of circumstantial data, macroscopic and microscopic autoptic findings, and immunohistochemical investigations based on the search for antibodies anti E-selectin, P-selectin, and HIF 1-α.

CONCLUSION

Although not pathognomonic of asphyxiation by N2O, the latter molecules are a valid and early marker of hypoxic insult. Therefore, in concert with all other findings, it may constitute valid support for the forensic pathologist to ascertain the cause of death in case of suspected intoxication by N2O.

The efficacy and tolerability of inhaled nitrous oxide in major depressive disorder: a systematic review and meta-analysis

BACKGROUND

Nitrous oxide (N2O) has been initially confirmed by clinical trials to benefit to patients with major depressive disorder (MDD). However, there needs to be a meta-analysis to compare the efficacy and tolerability of N2O in MDD.

METHODS

PubMed, EMBASE, and Cochrane Library were searched for relevant studies up to Jan 1st, 2023. The meta-analysis mainly compared the outcome of the change in depression severity scores, response, remission, and adverse events in patients with MDD receiving 50% N2O and placebo.

RESULTS

Four studies with 133 patients were eventually identified. We found that the N2O group and control group showed an overall significant difference in the change in depression severity score for patients at 2 h, 24 h, and 2 weeks or more (2 h, SMD =  - 0.64, 95% CI - 0.01 to - 0.28, p < 0.0001) (24 h, SMD =  - 0.65, 95% CI - 1.01 to - 0.29, p < 0.0001) (2 weeks, SMD =  - 0.76, 95% CI - 1.16 to - 0.36, p < 0.0001). For the response and remission rate, the long-term effect of N2O was also statistically significant (for the response, RR = 2.33, 95% CI 1.23 to 4.44, p = 0.01) (for the remission, RR = 4.68, 95% CI 1.49 to 14.68, p = 0.008). For safety outcomes, patients treated with N2O had higher odds of nausea or vomiting (RR = 10.15, 95% CI 1.96 to 52.59, p = 0.009).

CONCLUSION

Our study suggested that N2O has a rapid and long-lasting antidepressant effect in patients with MDD. However, the efficacy of lower or titrated concentration of N2O should be further investigated.

Over-expression of miR-3584-5p Represses Nav1.8 Channel Aggravating Neuropathic Pain caused by Chronic Constriction Injury

Nav1.8, a tetrodotoxin-resistant voltage-gated sodium channels (VGSCs) subtype encoded by SCN10A, which plays an important role in the production and transmission of peripheral neuropathic pain signals. Studies have shown that VGSCs may be key targets of MicroRNAs (miRNAs) in the regulation of neuropathic pain. In our study, bioinformatics analysis showed that the targeting relationship between miR-3584-5p and Nav1.8 was the most closely. The purpose of this study was to investigate the roles of miR-3584-5p and Nav1.8 in neuropathic pain. The effects of miR-3584-5p on chronic constriction injury (CCI)-induced neuropathic pain in rats was investigated by intrathecal injection of miR-3584-5p agomir (an agonist, 20 μM, 15 μL) or antagomir (an antagonist, 20 μM, 15 μL). The results showed that over-expression of miR-3584-5p aggravated neuronal injury by hematoxylin-eosin (H&E) staining and mechanical/thermal hypersensitivity in CCI rats. MiR-3584-5p indirectly inhibited the expression of Nav1.8 by up-regulating the expression of key proteins in the ERK5/CREB signaling pathway, and also inhibited the current density of the Nav1.8 channel, changed its channel dynamics characteristic, thereby accelerating the transmission of pain signals, and further aggravating pain. Similarly, in PC12 and SH-SY5Y cell cultures, miR-3584-5p increased the level of reactive oxygen species (ROS) and inhibited mitochondrial membrane potential (Δψm) in the mitochondrial pathway, decreased the ratio of apoptosis-related factor Bcl-2/Bax, and thus promoted neuronal apoptosis. In brief, over-expression of miR-3584-5p aggravates neuropathic pain by directly inhibiting the current density of Nav1.8 channel and altering its channel dynamics, or indirectly inhibiting Nav1.8 expression through ERK5/CREB pathway, and promoting apoptosis through mitochondrial pathway.

Classical and non-classical psychedelic drugs induce common network changes in human cortex

The neurobiology of the psychedelic experience is not fully understood. Identifying common brain network changes induced by both classical (i.e., acting at the 5-HT2 receptor) and non-classical psychedelics would provide mechanistic insight into state-specific characteristics. We analyzed whole-brain functional connectivity based on resting-state fMRI data in humans, acquired before and during the administration of nitrous oxide, ketamine, and lysergic acid diethylamide. We report that, despite distinct molecular mechanisms and modes of delivery, all three psychedelics reduced within-network functional connectivity and enhanced between-network functional connectivity. More specifically, all three drugs increased connectivity between right temporoparietal junction and bilateral intraparietal sulcus as well as between precuneus and left intraparietal sulcus. These regions fall within the posterior cortical "hot zone," posited to mediate the qualitative aspects of experience. Thus, both classical and non-classical psychedelics modulate networks within an area of known relevance for consciousness, identifying a biologically plausible candidate for their subjective effects.

Neonatal exposure to a neuroactive steroid alters low-frequency oscillations in the subiculum

Preclinical studies have established that neonatal exposure to contemporary sedative/hypnotic drugs causes neurotoxicity in the developing rodent and primate brains. Our group recently reported that novel neuroactive steroid (3β,5β,17β)-3-hydroxyandrostane-17-carbonitrile (3β-OH) induced effective hypnosis in both neonatal and adult rodents but did not cause significant neurotoxicity in vulnerable brain regions such as subiculum, an output region of hippocampal formation particularly sensitive to commonly used sedatives/hypnotics. Despite significant emphasis on patho-morphological changes, little is known about long-term effects on subicular neurophysiology after neonatal exposure to neuroactive steroids. Hence, we explored the lasting effects of neonatal exposure to 3β-OH on sleep macrostructure as well as subicular neuronal oscillations in vivo and synaptic plasticity ex vivo in adolescent rats. At postnatal day 7, we exposed rat pups to either 10 mg/kg of 3β-OH over a period of 12 h or to volume-matched cyclodextrin vehicle. At weaning age, a cohort of rats was implanted with a cortical electroencephalogram (EEG) and subicular depth electrodes. At postnatal day 30-33, we performed in vivo assessment of sleep macrostructure (divided into wake, non-rapid eye movement, and rapid eye movement sleep) and power spectra in cortex and subiculum. In a second cohort of 3β-OH exposed animals, we conducted ex vivo studies of long-term potentiation (LTP) in adolescent rats. Overall, we found that neonatal exposure to 3β-OH decreased subicular delta and sigma oscillations during non-rapid eye movement sleep without altering sleep macrostructure. Furthermore, we observed no significant changes in subicular synaptic plasticity. Interestingly, our previous study found that neonatal exposure to ketamine increased subicular gamma oscillations during non-rapid eye movement sleep and profoundly suppressed subicular LTP in adolescent rats. Together these results suggest that exposure to different sedative/hypnotic agents during a critical period of brain development may induce distinct functional changes in subiculum circuitry that may persist into adolescent age.

Use of the Rehabilitation Treatment Specification System (RTSS) in the management of nitrous oxide (N2O)-induced spinal cord injury

Nitrous oxide (N₂O) is an inhaled anaesthetic gas and a popular intoxicant. Excessive recreational use can cause spinal cord myelopathy. Previous studies have discussed the medical management. However, none have specified the sensorimotor rehabilitation management. This case report documents the investigations, physical rehabilitation and functional outcomes in two cases of N₂O-associated myelopathy. Both presented with lower limb strength and sensorimotor integration impairments resulting in ataxic ambulation. Dorsal column signal abnormality was observed on T2-weighted MRI in one case. Myelopathy was diagnosed based on clinical presentation and both were treated with vitamin B₁₂ Rehabilitation was conceived and specified using the Rehabilitation Treatment Specification System (RTSS). Both cases achieved independent indoor gait on hospital discharge, and full function at 9 months in one case. Appropriate and timely medical management and reasoned rehabilitation provided excellent functional outcomes for N₂O-related myelopathy. By using the RTSS, reasoned rehabilitation efficacy can be tested in the future.

Nitrous oxide-induced myeloneuropathy: an emerging public health issue

Increasing use of nitrous oxide as a recreational drug has been reported among young adults in western countries over the past decade. We present two cases of young males presenting to the Emergency Department (ED) of a large urban university hospital in Dublin with progressive neurological dysfunction related to nitrous oxide use. We review the pathophysiology, clinical features and treatment of nitrous oxide neurotoxicity. It is important that clinicians are aware of this evolving public health issue and are able to recognize the clinical features of this rare presentation, which may become more common in Irish EDs and GP surgeries as nitrous oxide abuse becomes more prevalent.

Depression of Synaptic N-methyl-D-Aspartate Responses by Xenon and Nitrous Oxide

In "synapse bouton preparation" of rat hippocampal CA3 neurons, we examined how Xe and N₂O modulate N-methyl-D-aspartate (NMDA) receptor-mediated spontaneous and evoked excitatory post-synaptic currents (sEPSC_NMDA and eEPSC_NMDA). This preparation is a mechanically isolated single neuron attached with nerve endings (boutons) preserving normal physiologic function and promoting the exact evaluation of sEPSC_NMDA and eEPSC_NMDA responses without influence of extrasynaptic, glial, and other neuronal tonic currents. These sEPSCs and eEPSCs are elicited by spontaneous glutamate release from many homologous glutamatergic boutons and by focal paired-pulse electric stimulation of a single bouton, respectively. The s/eEPSC_AMPA/KA and s/eEPSC_NMDA were isolated pharmacologically by their specific antagonists. Thus, independent contributions of pre- and postsynaptic responses could also be quantified. All kinetic properties of s/eEPSC_AMPA/KA and s/eEPSC_NMDA were detected clearly. The s/eEPSC_NMDA showed smaller amplitude and slower rise and 1/e decay time constant (τ _Decay) than s/eEPSC_AMPA/KA Xe (70%) and N₂O (70%) significantly decreased the frequency and amplitude without altering the τ _Decay of sEPSC_NMDA They also decreased the amplitude but increased the Rf and PPR without altering the τ _Decay of the eEPSC_NMDA These data show clearly that "synapse bouton preparation" can be an accurate model for evaluating s/eEPSC_NMDA Such inhibitory effects of gas anesthetics are primarily due to presynaptic mechanisms. Present results may explain partially the powerful analgesic effects of Xe and N₂O. SIGNIFICANCE STATEMENT: We could record pharmacologically isolated NMDA receptor-mediated spontaneous and (action potential-evoked) excitatory postsynaptic currents (sEPSC_NMDA and eEPSC_NMDA) and clearly detect all kinetic parameters of sEPSC_NMDA and eEPSC_NMDA at synaptic levels by using "synapse bouton preparation" of rat hippocampal CA3 neurons. We found that Xe and N₂O clearly suppressed both sEPSC_NMDA and eEPSC_NMDA. Different from previous studies, present results suggest that Xe and N₂O predominantly inhibit the NMDA responses by presynaptic mechanisms.

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.

Mechanisms Involved in the Neurotoxicity and Abuse Liability of Nitrous Oxide: A Narrative Review

The recreational use of nitrous oxide (N₂O) has increased over the years. At the same time, more N₂O intoxications are presented to hospitals. The incidental use of N₂O is relatively harmless, but heavy, frequent and chronic use comes with considerable health risks. Most importantly, N₂O can inactivate the co-factor cobalamin, which, in turn, leads to paresthesia's, partial paralysis and generalized demyelinating polyneuropathy. In some patients, these disorders are irreversible. Several metabolic cascades have been identified by which N₂O can cause harmful effects. Because these effects mostly occur after prolonged use, it raises the question of whether N₂O has addictive properties, explaining its prolonged and frequent use at high dose. Several lines of evidence for N₂O's dependence liability can be found in the literature, but the underlying mechanism of action remains controversial. N₂O interacts with the opioid system, but N₂O also acts as an N-methyl-D-aspartate (NMDA) receptor antagonist, by which it can cause dopamine disinhibition. In this narrative review, we provide a detailed description of animal and human evidence for N₂O-induced abuse/dependence and for N₂O-induced neurotoxicity.

General anesthesia and sleep: like and unlike

General anesthesia and sleep have long been discussed in the neurobiological context owingto their commonalities, such as unconsciousness, immobility, non-responsiveness to externalstimuli, and lack of memory upon returning to consciousness. Sleep is regulated bycomplex interactions between wake-promoting and sleep-promoting neural circuits. Anestheticsexert their effects partly by inhibiting wake-promoting neurons or activating sleep-promotingneurons. Unconscious but arousable sedation is more related to sleep-wake circuitries,whereas unconscious and unarousable anesthesia is independent of them. Generalanesthesia is notable for its ability to decrease sleep propensity. Conversely, increasedsleep propensity due to insufficient sleep potentiates anesthetic effects. Taken together, it isplausible that sleep and anesthesia are closely related phenomena but not the same ones.Further investigations on the relationship between sleep and anesthesia are warranted.

General anesthesia in children and long-term neurodevelopmental deficits: A systematic review

Background

Millions of children experienced surgery procedures requiring general anesthesia (GA). Any potential neurodevelopmental risks of pediatric anesthesia can be a serious public health issue. Various animal studies have provided evidence that commonly used GA induced a variety of morphofunctional alterations in the developing brain of juvenile animals.

Methods

We conducted a systematic review to provide a brief overview of preclinical studies and summarize the existing clinical studies. Comprehensive literature searches of PubMed, EMBASE, CINAHL, OVID Medline, Web of Science, and the Cochrane Library were conducted using the relevant search terms “general anesthesia,” “neurocognitive outcome,” and “children.” We included studies investigating children who were exposed to single or multiple GA before 18, with long-term neurodevelopment outcomes evaluated after the exposure(s).

Results

Seventy-two clinical studies originating from 18 different countries published from 2000 to 2022 are included in this review, most of which are retrospective studies (n = 58). Two-thirds of studies (n = 48) provide evidence of negative neurocognitive effects after GA exposure in children. Neurodevelopmental outcomes are categorized into six domains: academics/achievement, cognition, development/behavior, diagnosis, brain studies, and others. Most studies focusing on children &lt;7 years detected adverse neurocognitive effects following GA exposure, but not all studies consistently supported the prevailing view that younger children were at greater risk than senior ones. More times and longer duration of exposures to GA, and major surgeries may indicate a higher risk of negative outcomes.

Conclusion

Based on current studies, it is necessary to endeavor to limit the duration and numbers of anesthesia and the dose of anesthetic agents. For future studies, we require cohort studies with rich sources of data and appropriate outcome measures, and carefully designed and adequately powered clinical trials testing plausible interventions in relevant patient populations.

Effects of Low-Concentration Nitrous Oxide Anesthesia on Patient Anxiety During Cataract Surgery: A Retrospective Cohort Study

Purpose

We investigated the effects of 30% low-concentration nitrous oxide (N₂O) anesthesia on anxiety, pain, and vital signs and the patient population that would benefit from low-concentration N₂O anesthesia during cataract surgery.

Patients and Methods

Sixty-three patients who underwent cataract surgery due to visual impairment from cataracts were included in this single-center retrospective cohort study conducted at the Ophthalmology Department of Shinseikai Toyama Hospital, Japan. Fifty eyes of 39 patients received a combination of local and N₂O anesthesia (N₂O group), and 30 eyes of 24 patients received local anesthesia without N₂O anesthesia (Air group). The primary outcome measures were visual analogue scale (VAS) scores for patient anxiety, pain, and vital signs. The secondary outcome measures were the patient population.

Results

The change in the VAS scores for anxiety and pain decreased significantly (p = 0.002 and p = 0.014, respectively) in the N₂O group (−15.6 ± 22.9 and 12.4 ± 14.9, respectively) compared with that in the Air group (1.2 ± 20.6 and 24.2 ± 22.4, respectively). The systolic and diastolic blood pressure changes did not significantly differ between both groups (p = 0.093 and p = 0.23, respectively). The change in heart rate decreased significantly (p = 0.001) in the N₂O group (−4.8 ± 4.8 bpm) compared with that in the Air group (−0.6 ± 5.8 bpm). Multivariate analyses demonstrated that the change in anxiety level in the N₂O group correlated significantly with patient age (p = 0.045) and preoperative VAS score for anxiety (p = 0.0001), whereas the change in anxiety level in the Air group did not correlate with any factor.

Conclusion

Low-concentration N₂O anesthesia showed beneficial effects on intraoperative anxiety and pain during cataract surgery; this may aid the stabilization of intraoperative vital signs. Moreover, low-concentration N₂O anesthesia during cataract surgery could benefit young patients and patients with high levels of preoperative anxiety.

Does hyperbaric oxygen cause narcosis or hyperexcitability? A quantitative EEG analysis

Divers breathe higher partial pressures of oxygen at depth than at the surface. The literature and diving community are divided on whether or not oxygen is narcotic. Conversely, hyperbaric oxygen may induce dose-dependent cerebral hyperexcitability. This study evaluated whether hyperbaric oxygen causes similar narcotic effects to nitrogen, and investigated oxygen's hyperexcitability effect. Twelve human participants breathed "normobaric" air and 100% oxygen, and "hyperbaric" 100% oxygen at 142 and 284 kPa, while psychometric performance, electroencephalography (EEG), and task load perception were measured. EEG was analyzed with functional connectivity and temporal complexity algorithms. The spatial functional connectivity, estimated using mutual information, was summarized with the global efficiency network measure. Temporal complexity was calculated with a "default-mode-network (DMN) complexity" algorithm. Hyperbaric oxygen-breathing caused no change in EEG global efficiency or in the psychometric test. However, oxygen caused a significant reduction of DMN complexity and a reduction in task load perception. Hyperbaric oxygen did not cause the same changes in EEG global efficiency seen with hyperbaric air, which likely related to a narcotic effect of nitrogen. Hyperbaric oxygen seemed to disturb the time evolution of EEG patterns that could be taken as evidence of early oxygen-induced cortical hyperexcitability. These findings suggest that hyperbaric oxygen is not narcotic and will help inform divers' decisions on suitable gas mixtures.

Thromboembolic complications of recreational nitrous oxide (ab)use: a systematic review

The recreatinal use of nitrous oxide has become more common in recent years, especially in adolescents and young adults. It has been mainly associated with medical conditions like megaloblastic anemia and (myelo)neuropathy. We report on the thromboembolic complications, a less known side effect, associated with recreational inhalation of nitrous oxide. An extensive literature search was performed for publications reporting on the thromboembolic complications associated with recreational nitrous oxide abuse. Data about sex, age, location of thrombosis, laboratory findings, therapy and outcome were collected. A total of 13 case reports or case series were identified comprising a total of 14 patients. The reported thromboembolic side effects included deep venous thrombosis, pulmonary embolism, mesenterial-, portal and splenic vein thrombosis, cerebral sinus thrombosis, cortical vein thrombosis, stroke, acute myocardial infarction and peripheral artery thromboembolism. These side effects are possibly mediated by the interaction of nitrous oxide with vitamin B12, a cofactor of the methionine synthase complex, which eventually results in elevation of plasma levels of homocysteine. Despite being a known risk factor for cardiovascular disease, the exact pathophysiological mechanism remains unclear. Cessation of nitrous oxide inhalation is necessary to prevent recurrent thrombosis. Nitrous oxide abuse may thus result in a wide spectrum of thromboembolic complications. One should be aware of this etiology, especially in a young person with no obvious risk factors for cardiovascular disease. Spreading awareness is important to inform people about the potentially serious side effects associated with nitrous oxide inhalation.

Acute nitrous oxide-induced neuropathy mimicking Guillain-Barré Syndrome

BACKGROUND AND OBJECTIVE

The early clinical features of nitrous oxide (N₂ O)-induced neuropathy were mimicking that of Guillain-Barré Syndrome (GBS). We aimed to explore clinical and laboratory characteristics of N₂ O-induced neuropathy in comparison with GBS.

METHODS

We retrospectively reviewed data of 15 patients with N₂ O-induced neuropathy and compared them with 15 GBS patients.

RESULTS

The age of the N₂ O-induced neuropathy group was significantly younger than that in the GBS group (22 ± 5 vs 45 ± 17). Paresthesia was more common in N₂ O-induced neuropathy group (100% vs 53.3%). The proportion of distal upper limbs weakness was lower than that in GBS group (20.0% vs 93.3%). There was no significant difference in distal weakness of the lower limbs (100% vs 80.0%). The incidence of motor conduction block and compound muscle action potential amplitude reduction in upper limbs was lower than that in GBS group (6.7% vs 60.0%; 26.7% vs 80.0%). The sensory nerve action potential amplitude drop in the lower limbs was more severe than that in GBS group (53.3% vs 0). The increase of Mean corpuscular volume (MCV) was more pronounced compared to GBS group (96.97 ± 6.00 vs 88.55 ± 5.41). High homocysteine levels were more common in N₂ O-related group [29.80(11.60, 70.50) vs 14.35(9.22, 19.30)].

CONCLUSION

Typical clinical features of the acute N₂ O neuropathy appears to be a myeloneuropathy, affecting the lower limbs more than the upper limbs, mixed axonal-demyelinating electrophysiological performance, higher homocysteine level and larger MCV and common posterior spinal cord involvement in cervical segment. This article is protected by copyright. All rights reserved.

SCH 23390 inhibits the acquisition of nitrous oxide-induced conditioned place preference and the changes in ERK phosphorylation expression in nucleus accumbens of mice

Nitrous oxide (N₂O) has a long history of abuse, but its abuse mechanism has not been clear yet. This research aimed at the possibility of mesolimbic dopaminergic system (MLDS) involved in the rewarding effect of N₂O. In this work, the rewarding behavior of N₂O in mice was evaluated using a typical gas-administered conditioned place preference (CPP) procedure. SCH 23390, a Dopamine D1 receptor (D1R) antagonist, and Haloperidol, a Dopamine D2 receptor (D2R) antagonist were administered during CPP to evaluate the role of dopamine receptors in the N₂O-induced CPP. The accompanying changes in phosphorylation of extracellular signal-regulated kinase (ERK) in MLDS related brain regions, including the ventral tegmental area (VTA), caudate putamen (CPu), prefrontal cortex (PFC), and nucleus accumbens (NAc) were measured to assess the neural plasticity changes in the CPP mice by Western blot analysis. Results revealed that 60% N₂O induced CPP in the gas-administered mice and promoted the ERK phosphorylation (p-ERK) in the NAc and CPu during the test session of the CPP test. Pretreatment of SCH 23390 (0.5mg/kg) inhibited the acquisition of N₂O-induced CPP and the enhanced p-ERK in NAc.It suggested that Dopamine D1 receptor may play an important role in the acquisition of N₂O-induced CPP and the accompanied ERK activation in the NAc, which provide insight into the molecular mechanism in the rewarding properties of nitrous oxide.

A review of potential neuropathological changes associated with ketamine

INTRODUCTION

: Ketamine is an established intervention for treatment resistant depression (TRD). However, long-term adverse effects with repeated doses remain insufficiently characterized. Although several animal models have shown N-methyl-D-aspartate glutamate receptor antagonists to produce various neuropathological reactions, attention surrounding the risk of brain lesions has been minimal.

AREAS COVERED

: The current review focuses on potential neuropathological changes associated with ketamine. Search terms included variations of ketamine, Olney lesions, tau hyperphosphorylation, and parvalbumin interneurons.

EXPERT OPINION

: Daily high-dose ketamine use in substance use disorder (SUD) populations was associated with clear neurotoxic effects, while no studies specifically evaluated effects of ketamine protocols used for TRD. It is difficult to discern effects directly attributable to ketamine due to methodological factors, such as comorbidities and dramatic differences in dose in SUD populations versus infrequent sub-anesthetic doses typically prescribed for TRD. Taken together, animal models and human ketamine SUD populations suggest potential neuropathology with chronic high-dose ketamine exposure exceeding those recommended for adults with TRD. It is unknown whether repeat sub-anesthetic dosing of ketamine in adults with TRD is associated with Olney lesions or other neuropathologies. In the interim, practitioners should be vigilant for this possibility recognizing that the condition itself is associated with neurodegenerative processes.

Analysis of clinical characteristics and prognostic factors in 110 patients with nitrous oxide abuse

PURPOSE

To review the clinical symptoms, auxiliary examination findings, and outcomes of patients with nitrous oxide (N₂ O) abuse, and analyze the factors that affect outcomes.

METHODS

Patients with N₂ O abuse treated in the Department of Neurology between January 2018 and December 2020 were included. The clinical data of these patients were collected, and follow-up was conducted to determine the outcomes.

RESULTS

The average age of the 110 patients with N₂ O abuse was 21.4 ± 4.2 years (range: 14-33 years). Clinical presentation primarily included neurological symptoms, such as limb numbness and/or weakness (97%), psychiatric symptoms, changes in appetite, and skin hyperpigmentation. Laboratory test results were characterized by vitamin B₁₂ deficiency (60%, 34 out of 57 cases) and high homocysteine level (69%, 31 out of 45 cases). Electromyography indicated mixed axonal and demyelination injury (92%, 80 out of 87 cases). Motor and sensory nerves were simultaneously involved, and injury primarily involved the lower limbs. One hundred and seven (97%) patients were clinically diagnosed with peripheral neuropathy, of whom 26 (24%) exhibited spinal abnormalities on magnetic resonance imaging, supporting a diagnosis of subacute combined degeneration. Treatment included N₂ O withdrawal and vitamin B₁₂ supplementation. Reexamination of six patients indicated that treatment was effective. Follow-up was completed for 51 patients. Thirty-four patients (67%) recovered completely, 17 patients (33%) had residual limb numbness, and only one patient experienced relapse. Sex was an independent prognostic factor; the outcomes of female patients were better than that of male patients.

CONCLUSION

The recreational use of N₂ O has largely expanded among youth in recent decades, which has become a growing public health concern in China. It highlights the importance of the recognition of various clinical symptoms, particularly limb numbness and/or weakness related to the cases of N₂ O abuse. The therapeutic administration of vitamin B₁₂ supplementation and N₂ O withdrawal can make the overall prognosis good, especially for female patients.

The Use of a Fixed 50:50 Mixture of Nitrous Oxide and Oxygen to Reduce Lumbar Puncture-Induced Pain in the Emergency Department: A Randomized Controlled Trial

Lumbar puncture (LP) is stressful and often painful. We evaluated the efficacy of a fixed 50% nitrous oxide−oxygen mixture (50%N2O-O2) versus placebo to reduce immediate procedural pain and anxiety during LP performed in an emergency setting. We conducted a randomized controlled trial involving adults who needed a cerebrospinal fluid analysis in an emergency department. Patients were randomly assigned to inhale either 50%N2O-O2 or medical air. The primary endpoint, assessed using a numerical scale, was the maximum pain felt by the patient during the procedure and the maximum anxiety and satisfaction as secondary outcomes. Eighty-eight patients were randomized and analyzed (ITT). The maximal pain was 5.0 ± 2.9 for patients receiving air and 4.2 ± 3.0 for patients receiving 50%N2O-O2 (effect-size = −0.27 [−0.69; 0.14], p = 0.20). LP-induced anxiety was 4.7 ± 2.8 vs. 3.7 ± 3.7 (p = 0.13), and the proportion of patients with significant anxiety (score ≥ 4/10) was 72.7% vs. 50.0% (p = 0.03). Overall satisfaction was higher among patients receiving 50%N2O-O2 (7.4 ± 2.4 vs. 8.9 ± 1.6, p < 0.001). No serious adverse events were attributable to 50%N2O-O2 inhalation. Although inhalation of 50%N2O-O2 failed to reduce LP-induced pain in an emergency setting, it tended to reduce anxiety and significantly increased patient satisfaction.

Nitrous oxide abuse induced subacute combined degeneration despite patient initiated B12 supplementation

INTRODUCTION

Nitrous oxide (N₂O) is a commonly used inhaled anesthetic that is legal to purchase as a food additive and is popular as a recreational euphoric drug. Abuse causes a functional B12 deficiency, leading to clinical features and imaging consistent with subacute combined spinal cord degeneration (SCD).

CASES

Poison Center medical records from four patients are reviewed in this series. Four patients presented with lower extremity weakness, paresthesias and gait abnormalities in the setting of chronic N₂O abuse. Each reported using 50-150 N₂O cartridges ("whippets") almost daily for months to years, and reported supplementing with oral B12 at the recommendation of other users and online forums. None reported prior B12 deficiency or dietary restrictions, and none exhibited hematologic abnormalities.

RESULTS

All patients had clinical signs of neurotoxicity including weakness and ataxia. Additionally, all had elevated methylmalonic acid and homocysteine concentrations with normal B12 indicating a functional B12 deficiency. Three had imaging consistent with SCD despite home supplementation The MRI in the fourth case was inconclusive due to movement artifact.

CONCLUSION

We report four cases of subacute combined degeneration induced by recreational nitrous oxide abuse despite self-administered vitamin B12 supplementation.

General Anesthesia and the Young Brain: The Importance of Novel Strategies with Alternate Mechanisms of Action

Over the past three decades, we have been grappling with rapidly accumulating evidence that general anesthetics (GAs) may not be as innocuous for the young brain as we previously believed. The growing realization comes from hundreds of animal studies in numerous species, from nematodes to higher mammals. These studies argue that early exposure to commonly used GAs causes widespread apoptotic neurodegeneration in brain regions critical to cognition and socio-emotional development, kills a substantial number of neurons in the young brain, and, importantly, results in lasting disturbances in neuronal synaptic communication within the remaining neuronal networks. Notably, these outcomes are often associated with long-term impairments in multiple cognitive-affective domains. Not only do preclinical studies clearly demonstrate GA-induced neurotoxicity when the exposures occur in early life, but there is a growing body of clinical literature reporting similar cognitive-affective abnormalities in young children who require GAs. The need to consider alternative GAs led us to focus on synthetic neuroactive steroid analogues that have emerged as effective hypnotics, and analgesics that are apparently devoid of neurotoxic effects and long-term cognitive impairments. This would suggest that certain steroid analogues with different cellular targets and mechanisms of action may be safe alternatives to currently used GAs. Herein we summarize our current knowledge of neuroactive steroids as promising novel GAs.

CPP impairs contextual learning at concentrations below those that block pyramidal neuron NMDARs and LTP in the CA1 region of the hippocampus

Drugs that block N-methyl-d-aspartate receptors (NMDARs) suppress hippocampus-dependent memory formation; they also block long-term potentiation (LTP), a cellular model of learning and memory. However, the fractional block that is required to achieve these effects is unknown. Here, we measured the dose-dependent suppression of contextual memory in vivo by systemic administration of the competitive antagonist (R,S)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP); in parallel, we measured the concentration-dependent block by CPP of NMDAR-mediated synapses and LTP of excitatory synapses in hippocampal brain slices in vitro. We found that the dose of CPP that suppresses contextual memory in vivo (EC50 = 2.3 mg/kg) corresponds to a free concentration of 53 nM. Surprisingly, applying this concentration of CPP to hippocampal brain slices had no effect on the NMDAR component of evoked field excitatory postsynaptic potentials (fEPSPNMDA), or on LTP. Rather, the IC50 for blocking the fEPSPNMDA was 434 nM, and for blocking LTP was 361 nM - both nearly an order of magnitude higher. We conclude that memory impairment produced by systemically administered CPP is not due primarily to its blockade of NMDARs on hippocampal pyramidal neurons. Rather, systemic CPP suppresses memory formation by actions elsewhere in the memory-encoding circuitry.

Pharmacological modelling of dissociation and psychosis: an evaluation of the Clinician Administered Dissociative States Scale and Psychotomimetic States Inventory during nitrous oxide ('laughing gas')-induced anomalous states

RATIONALE

A significant obstacle to an improved understanding of pathological dissociative and psychosis-like states is the lack of readily implemented pharmacological models of these experiences. Ketamine has dissociative and psychotomimetic effects but can be difficult to use outside of medical and clinical-research facilities. Alternatively, nitrous oxide (N₂O) - like ketamine, a dissociative anaesthetic and NMDAR antagonist - has numerous properties that make it an attractive alternative for modelling dissociation and psychosis. However, development and testing of such pharmacological models relies on well-characterized measurement instruments.

OBJECTIVES

To examine the factor structures of the Clinician Administered Dissociative States Scale (CADSS) and Psychotomimetic States Inventory (PSI) administered during N₂O inhalation in healthy volunteers.

METHODS

Secondary analyses of data pooled from three previous N₂O studies with healthy volunteers.

RESULTS

Effect sizes for N₂O-induced dissociation and psychotomimesis were comparable to effects reported in experimental studies with sub-anaesthetic ketamine in healthy volunteers. Although, like ketamine, a three-factor representation of N₂O-induced dissociation was confirmed, and a more parsimonious two-factor model might be more appropriate. Bayesian exploratory factor analysis suggested that N₂O-induced psychosis-like symptoms were adequately represented by two negative and two positive symptom factors. Hierarchical cluster analysis indicated minimal item overlap between the CADSS and PSI.

CONCLUSION

N₂O and ketamine produce psychometrically similar dissociative states, although parallels in their psychosis-like effects remain to be determined. The CADSS and PSI tap largely non-overlapping experiences under N₂O and we propose the use of both measures (or similar instruments) to comprehensively assess anomalous subjective states produced by dissociative NMDAR antagonists.

What is better for psychiatry: Titrated or fixed concentrations of nitrous oxide?

Medication dosages are crucial-no single dose fits all. My paper compares the safety, scientific and practical applicability of fixed 25-50% concentrations of nitrous oxide (N₂O) with the variable titrated concentrations of Psychotropic Analgesic N₂O (PAN), as used in dentistry, and neuropsychiatry. A crucial difference is that PAN is always titrated, via an open circuit (nasal mask), to the minimum concentration (dose), which ensures full consciousness, cooperation, comfort and relaxation. With PAN, the goal is subject comfort, not dose. In contrast, fixed goal concentrations are usually given via relatively closed circuits (full facial mask/similar) without account for individual patient's dose-response. Hence, fixed concentrations, in N₂O sensitive subjects, could result in unconsciousness and other adverse effects (nausea, vomiting, anxiety, aspiration, might occur; requiring an anaesthesiologist for patient safety. PAN is titrated using each subject's subjective and objective responses as the guide to the ideal concentration. Thus, when PAN is used, there is no fixed concentration even for a single subject, nor is an anaesthesiologist required. Furthermore, there is a greater scientific rationale for using PAN, because the receptor systems involved are better known, whilst those for fixed concentrations are not. The PAN or dental titration method has been safely used in general dentistry for over 70 years and as an investigative, diagnostic and therapeutic tool for neuropsychiatry for over 40 years. Clinical applications include substance abuse detoxification, ameliorating depression, and investigations of schizophrenia, human orgasm, pain perception and basic neuroscience. By contrast, the experience with fixed doses in psychiatry is limited.

Evaluation of antihyperalgesic and analgesic effects of 35% nitrous oxide when combined with remifentanil: A randomised phase 1 trial in volunteers

BACKGROUND

Remifentanil is an effective drug in peri-operative pain therapy, but it can also induce and aggravate hyperalgesia. Supplemental administration of N2O may help to reduce remifentanil-induced hyperalgesia.

OBJECTIVE

To evaluate the effect of 35 and 50% N2O on hyperalgesia and pain after remifentanil infusion.

DESIGN

Single site, phase 1, double-blind, placebo-controlled, randomised crossover study.

SETTING

University Hospital, Germany from January 2012 to April 2012.

PARTICIPANTS

Twenty-one healthy male volunteers.

INTERVENTIONS

Transcutaneous electrical stimulation induced spontaneous acute pain and stable areas of hyperalgesia. Each volunteer underwent the following four sessions in a randomised order: 50 to 50% N2-O2 and intravenous (i.v.) 0.9% saline infusion (placebo); 50 to 50% N2-O2 and i.v. remifentanil infusion at 0.1 μg kg-1 min-1 (remifentanil); 35 to 15 to 50% N2O-N2-O2 and i.v. remifentanil infusion at 0.1 μg kg-1 min-1 (tested drug) and 50 to 50% N2O-O2 and i.v. remifentanil infusion at 0.1 μg kg-1 min-1 (gas active control). Gas mixtures were inhaled for 60 min; i.v. drugs were administered for 30 min.

MAIN OUTCOME MEASURES

Areas of pin-prick hyperalgesia, areas of touch-evoked allodynia and pain intensity on a visual analogue scale were assessed repeatedly for 160 min.

RESULTS

Data from 20 volunteers were analysed. There were significant treatment and treatment-by-time effects regarding areas of hyperalgesia (P < 0.001). After the treatment period, the area of hyperalgesia was significantly reduced (P < 0.001) in the tested drug and in the gas active control (30.6 ± 9.25 and 24.4 ± 7.3 cm2, respectively) compared with remifentanil (51.0 ± 17.0 cm2). There was also a significant difference between the gas active control and the tested drug sessions (P < 0.001). For the area of allodynia and pain rating, results were consistent with the results for hyperalgesia.

CONCLUSIONS

Administration of 35% N2O significantly reduced hyperalgesia, allodynia and pain intensity induced after remifentanil. It might therefore be suitable in peri-operative pain relief characterised by hyperalgesia and allodynia, such as postoperative pain, and may help to reduce opioid demand.

TRIAL REGISTRATION

EudraCT-No.: 2011-000966-37.

[Volatile anesthetics for prehospital analgesia by paramedics-An overview]

Treatment of acute pain is a central task in emergency medicine. Yet, prehospital pain relief is often insufficient or delayed since the administration of potent intravenous analgesic drugs (such as opioids) is mostly limited to physicians due to legal restrictions or training deficiencies in Germany and Austria. Frequently, prehospitally operating emergency physicians have to be demanded later for anguished patients limiting disposability of physicians for patients who are in a potentially life-threatening condition. Thus, inhaled analgesics could represent an interesting alternative.A mixture of 50% nitrous oxide and 50% oxygen (N₂O, Livopan®) has been available in Germany and Austria for several years; however, prehospital use of Livopan has been merely realized and only one trial has been published. In addition, methoxyflurane (Penthrop®), a volatile anesthetic from the group of the dialkyl esters (2-dichloro-1:1-difluoroethyl-methyl-ester) was approved for the treatment of moderate to severe pain following trauma in adults in many European countries in recent years and was brought onto the market in Austria in 2018. Several in-hospital trials demonstrated high effectiveness in this setting.This article discusses the effects and prehospital areas of application of both substances in the light of the existing literature. We provide a narrative overview of the current study situation and report on a recently performed prehospital application study of methoxyflurane (Penthrop®) from Austria.The need for pressurized gas cylinders for the use of N₂O represents a certain limitation in prehospital use. Furthermore, in certain injuries such as of the inner ear or a pneumothorax N₂O should not be used and the risk of diffusion hypoxemia has to be addressed. Users should be particularly careful and limit the use in alcohol addicts and vegans. The advances of N₂O are that it is odorless, has a fast onset of action, the usability in patients over 1 month old and has stabilizing effects on the circulation. Plenty of literature regarding prehospital as well as in-hospital use of nitrous oxide in emergency, obstetric and pediatric settings show its effectiveness as a single drug as well as in combination with other analgesics, such as paracetamol or various opioids. Its long tradition in Anglo-American countries is also based on its safety and low rate of side effects.Methoxyflurane is easier to store and handle and may be slightly more effective in severe pain after trauma; however, its approval is restricted to adults, where it works significantly better with increasing age, based on the declining minimal alveolar concentration (MAC) of all inhaled anesthetics with increasing age. Furthermore, decades of use of inhaled methoxyflurane in Australia have shown the drug is effective, safe and low in side effects and has a broad spectrum of applications. The use of methoxyflurane is limited in patients with severe hepatic or renal insufficiency and the characteristic odor has been described as unpleasant by some patients. In Europe, three large in-hospital trials showed strong pain relief in trauma patients, even comparable to opioids.Overall, based on the current evidence, the use of nitrous oxide and even more of methoxyflurane may be recommended also for prehospital use by skilled paramedics.

Best clinical practice guidance for conscious sedation of children undergoing dental treatment: an EAPD policy document

BACKGROUND

Due to fear and/or behaviour management problems, some children are unable to cooperate for dental treatment using local anaesthesia and psychological support alone. Sedation is required for these patients in order for dentists to be able to deliver high quality, pain-free dental care. The aim of this guideline is to evaluate the efficacy and relative efficacy of conscious sedation agents and dosages for behaviour management in paediatric dentistry and to provide guidance as to which sedative agents should be used.

METHODS

These guidelines were developed using a multi-step approach adapted from that outlined by the National Institute for Clinical Excellence (NICE (2020) Developing NICE Guidelines: the manual. https://www.nice.org.uk/process/pmg20/chapter/introduction#main-stages-of-guideline-development . Accessed 7 Oct 2020). Evidence for this guideline was provided from a pre-existing Cochrane review (Ashley et al. Cochrane Database Syst Rev 12:CD003877, 2018) supplemented by an updated search and data extraction up to May 2020.

RESULTS

Studies were from 18 different countries and had recruited 4131 participants overall with an average of 70 participants per study. Ages ranged from 0 to 16 years with an average age of 5.6 years across all included studies. A wide variety of drugs or combinations of drugs (n = 38) were used and delivered orally, intranasally, intravenously, rectally, intramuscularly, submucosally, transmucosally or by inhalation sedation. Twenty-four different outcome measures for behaviour were used. The wide range of drug combinations and outcome measures used greatly complicated description and analysis of the data.

CONCLUSION

Oral midazolam is recommended for conscious dental sedation. Midazolam delivered via other methods or nitrous oxide/oxygen sedation could be considered, but the evidence for both was very low.

Towards Quantum-Chemical Modeling of the Activity of Anesthetic Compounds

The modeling of the activity of anesthetics is a real challenge because of their unique electronic and structural characteristics. Microscopic approaches relevant to the typical features of these systems have been developed based on the advancements in the theory of intermolecular interactions. By stressing the quantum chemical point of view, here, we review the advances in the field highlighting differences and similarities among the chemicals within this group. The binding of the anesthetics to their partners has been analyzed by Symmetry-Adapted Perturbation Theory to provide insight into the nature of the interaction and the modeling of the adducts/complexes allows us to rationalize their anesthetic properties. A new approach in the frame of microtubule concept and the importance of lipid rafts and channels in membranes is also discussed.

Does vitamin B12 deficiency explain psychiatric symptoms in recreational nitrous oxide users? A narrative review

Background Recreational use of nitrous oxide (N₂O) is associated with many side effects, of which neurological complications are most common. Nitrous oxide abuse is also associated with psychiatric symptoms, but these have received less attention so far. Vitamin B12 deficiency may play a role in the development of these psychiatric symptoms.Aims To explore the relationship among the occurrence of recreational nitrous oxide-induced psychiatric symptoms, accompanying neurological symptoms, vitamin B12 status and choice of treatment.Methods A retrospective search for case reports was conducted across multiple databases (Pubmed, Embase, Web of Science, PsycINFO and CINAHL). Keywords included variants of "nitrous oxide", "case report" and "abuse". No restrictions to language or publication date were applied.Results The search retrieved 372 articles. A total of 25 case reports were included, representing 31 patients with psychiatric complications following nitrous oxide abuse. The most often reported symptoms were: hallucinations (n = 16), delusions (n = 11), and paranoia (n = 11). When neurological symptoms were present, patients were treated more frequently with vitamin B12 supplementation.Conclusions This review highlights the need to recognize that psychiatric symptoms may appear in association with nitrous oxide use. Approximately half of the cases that presented with nitrous oxide-induced psychiatric complaints did not show neurological symptoms, and their vitamin B12 concentration was often within the hospital's reference range. Psychiatrists and emergency physicians should be aware of isolated psychiatric symptoms caused by recreational nitrous oxide abuse. We suggest asking all patients with new psychiatric symptoms about nitrous oxide use and protocolizing the management of nitrous oxide-induced psychiatric symptoms.

Effects of general anesthetics on synaptic transmission and plasticity

General anesthetics depress excitatory and/or enhance inhibitory synaptic transmission principally by modulating the function of glutamatergic or GABAergic synapses, respectively, with relative anesthetic agent-specific mechanisms. Synaptic signaling proteins, including ligand- and voltage-gated ion channels, are targeted by general anesthetics to modulate various synaptic mechanisms, including presynaptic neurotransmitter release, postsynaptic receptor signaling, and dendritic spine dynamics to produce their characteristic acute neurophysiological effects. As synaptic structure and plasticity mediate higher-order functions such as learning and memory, long-term synaptic dysfunction following anesthesia may lead to undesirable neurocognitive consequences depending on the specific anesthetic agent and the vulnerability of the population. Here we review the cellular and molecular mechanisms of transient and persistent general anesthetic alterations of synaptic transmission and plasticity.

Neural Dynamics in Primate Cortex during Exposure to Subanesthetic Concentrations of Nitrous Oxide

Nitrous oxide (N₂O) is a hypnotic gas with antidepressant and psychedelic properties at subanesthetic concentrations. Despite long-standing clinical use, there is insufficient understanding of its effect on neural dynamics and cortical processing, which is important for mechanistic understanding of its therapeutic effects. We administered subanesthetic (70%), inhaled N₂O and studied the dynamic changes of spiking rate, spectral content, and somatosensory information representation in primary motor cortex (M1) in two male rhesus macaques implanted with Utah microelectrode arrays in the hand area of M1. The average sorted multiunit spiking rate in M1 increased from 8.1 ± 0.99 to 10.6 ± 1.3 Hz in Monkey W (p < 0.001) and from 5.6 ± 0.87 to 7.0 ± 1.1 Hz in Monkey N (p = 0.003). Power spectral densities increased in beta- and gamma-band power. To evaluate somatosensory content in M1 as a surrogate of information transfer, fingers were lightly brushed and classified using a naive Bayes classifier. In both monkeys, the proportion of correctly classified fingers dropped from 0.50 ± 0.06 before N₂O inhalation to 0.34 ± 0.03 during N₂O inhalation (p = 0.018), although some fingers continued to be correctly classified (p = 0.005). The decrease in correct classifications corresponded to decreased modulation depth for the population (p = 0.005) and fewer modulated units (p = 0.046). However, the increased single-unit firing rate was not correlated with its modulation depth (R² < 0.001, p = 0.93). These data suggest that N₂O degrades information transfer, although no clear relationship was found between neuronal tuning and N₂O-induced changes in firing rate.

Neonatal Anesthesia and dysregulation of the Epigenome

Each year, millions of infants and children are anesthetized for medical and surgical procedures. Yet, a substantial body of preclinical evidence suggests that anesthetics are neurotoxins that cause rapid and widespread apoptotic cell death in the brains of infant rodents and non-human primates. These animals have persistent impairments in cognition and behavior many weeks or months after anesthesia exposure, leading us to hypothesize that anesthetics do more than simply kill brain cells. Indeed, anesthetics cause chronic neuropathology in neurons that survive the insult, which then interferes with major aspects of brain development, synaptic plasticity, and neuronal function. Understanding the phenomenon of anesthesia-induced developmental neurotoxicity is of critical public health importance because clinical studies now report that anesthesia in human infancy is associated with cognitive and behavioral deficits. In our search for mechanistic explanations for why a young and pliable brain cannot fully recover from a relatively brief period of anesthesia, we have accumulated evidence that neonatal anesthesia can dysregulate epigenetic tags that influence gene transcription such as histone acetylation and DNA methylation. In this review, we briefly summarize the phenomenon of anesthesia-induced developmental neurotoxicity. We then discuss chronic neuropathology caused by neonatal anesthesia, including disturbances in cognition, socio-affective behavior, neuronal morphology, and synaptic plasticity. Finally, we present evidence of anesthesia-induced genetic and epigenetic dysregulation within the developing brain that may be transmitted intergenerationally to anesthesia-naïve offspring.

A phase 2 trial of inhaled nitrous oxide for treatment-resistant major depression

Nitrous oxide at 50% inhaled concentration has been shown to improve depressive symptoms in patients with treatment-resistant major depression (TRMD). Whether a lower concentration of 25% nitrous oxide provides similar efficacy and persistence of antidepressant effects while reducing the risk of adverse side effects is unknown. In this phase 2 clinical trial (NCT03283670), 24 patients with severe TRMD were randomly assigned in a crossover fashion to three treatments consisting of a single 1-hour inhalation with (i) 50% nitrous oxide, (ii) 25% nitrous oxide, or (iii) placebo (air/oxygen). The primary outcome was the change on the Hamilton Depression Rating Scale (HDRS-21). Whereas nitrous oxide significantly improved depressive symptoms versus placebo (P = 0.01), there was no difference between 25 and 50% nitrous oxide (P = 0.58). The estimated differences between 25% and placebo were -0.75 points on the HDRS-21 at 2 hours (P = 0.73), -1.41 points at 24 hours (P = 0.52), -4.35 points at week 1 (P = 0.05), and -5.19 points at week 2 (P = 0.02), and the estimated differences between 50% and placebo were -0.87 points at 2 hours (P = 0.69), -1.93 points at 24 hours (P = 0.37), -2.44 points at week 1 (P = 0.25), and -7.00 points at week 2 (P = 0.001). Adverse events declined substantially with dose (P < 0.001). These results suggest that 25% nitrous oxide has comparable efficacy to 50% nitrous oxide in improving TRMD but with a markedly lower rate of adverse effects.