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

Recent advances in the study of anesthesia-and analgesia-related mechanisms of S-ketamine

Ketamine is a racemic mixture of equal amounts of R-ketamine and S-ketamine and is well known to anesthesiologists for its unique dissociative anesthetic properties. The pharmacological properties of ketamine, namely, its sympathetic excitation, mild respiratory depression, and potent analgesia, are still highly valued in its use as an anesthetic for some patients. In particular, since its advent, S-ketamine has been widely used as an anesthetic in many countries due to its increased affinity for NMDA receptors and its enhanced anesthetic and analgesic effects. However, the anesthetic and analgesic mechanisms of S-ketamine are not fully understood. In addition to antagonizing NMDA receptors, a variety of other receptors or channels may be involved, but there are no relevant mechanistic summaries in the literature. Therefore, the purpose of this paper is to review the mechanisms of action of S-ketamine on relevant receptors and systems in the body that result in its pharmacological properties, such as anesthesia and analgesia, with the aim of providing a reference for its clinical applications and research.

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.

Exploring Nitrous Oxide as Treatment of Mood Disorders: Basic Concepts

Nitrous oxide (laughing gas) has shown early promise as a rapidly acting antidepressant in patients with treatment-resistant major depression and is currently investigated in several clinical trials. Because nitrous oxide is rarely administered outside operating rooms or dental practices, most psychiatrists are not familiar with how nitrous oxide is administered in a medical setting and what regulations guide its use. The goal of this brief review was to educate psychiatrists about the basic concepts of nitrous oxide administration and pharmacology. Furthermore, common misconceptions about nitrous oxide will be discussed.

Anesthetic synergy between two n-alkanes

OBJECTIVE

N-butane and n-pentane can both produce general anesthesia. Both compounds potentiate γ-aminobutyric acid type A (GABA_A) receptor function, but only butane inhibits N-methyl-d-aspartate (NMDA) receptors. It was hypothesized that butane and pentane would exhibit anesthetic synergy due to their different actions on ligand-gated ion channels.

STUDY DESIGN

Prospective experimental study.

ANIMALS

A total of four Xenopus laevis frogs and 43 Sprague-Dawley rats.

METHODS

Alkane concentrations for all studies were determined via gas chromatography. Using a Xenopus oocyte expression model, standard two-electrode voltage clamp techniques were used to measure NMDA and GABA_A receptor responses in vitro as a function of butane and pentane concentrations relevant to anesthesia. The minimum alveolar concentrations (MAC) of butane and pentane were measured separately in rats, and then pentane MAC was measured during coadministration of 0.25, 0.50 or 0.75 times MAC of butane. An isobole with 95% confidence intervals was constructed using regression analysis. A sum of butane and pentane that was statistically less than the lower-end confidence bound isobole indicated a synergistic interaction.

RESULTS

Both butane and pentane dose-dependently potentiated GABA_A receptor currents over the study concentration range. Butane dose-dependently inhibited NMDA receptor currents, but pentane did not modulate NMDA receptors. Butane and pentane MAC in rats was 39.4±0.7 and 13.7±0.4 %, respectively. A small but significant (p<0.03) synergistic anesthetic effect with pentane was observed during administration of either 0.50 or 0.75×MAC butane.

CONCLUSIONS

Butane and pentane show synergistic anesthetic effects in vivo consistent with their different in vitro receptor effects.

CLINICAL RELEVANCE

Findings support the relevance of NMDA receptors in mediating anesthetic actions for some, but not all, inhaled agents.

N-methyl-D-aspartate receptor channel blocker-like discriminative stimulus effects of nitrous oxide gas

Nitrous oxide (N2O) gas is a widely used anesthetic adjunct in dentistry and medicine that is also commonly abused. Studies have shown that N2O alters the function of the N-methyl-d-aspartate (NMDA), GABAA, opioid, and serotonin receptors among others. However, the receptors systems underlying the abuse-related central nervous system effects of N2O are unclear. The present study explores the receptor systems responsible for producing the discriminative stimulus effects of N2O. B6SJLF1/J male mice trained to discriminate 10 minutes of exposure to 60% N2O + 40% oxygen versus 100% oxygen served as subjects. Both the high-affinity NMDA receptor channel blocker (+)-MK-801 maleate [(5S,10R)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate] and the low-affinity blocker memantine partially mimicked the stimulus effects of N2O. Neither the competitive NMDA antagonist, CGS-19755 (cis-4-[phosphomethyl]-piperidine-2-carboxylic acid), nor the NMDA glycine-site antagonist, L701-324 [7-chloro-4-hydroxy-3-(3-phenoxy)phenyl-2(1H)-quinolinone], produced N2O-like stimulus effects. A range of GABAA agonists and positive modulators, including midazolam, pentobarbital, muscimol, and gaboxadol (4,5,6,7-tetrahydroisoxazolo[4,5-c]pyridine-3-ol), all failed to produce N2O-like stimulus effects. The μ-, κ-, and δ-opioid agonists, as well as 5-hydroxytryptamine (serotonin) 1B/2C (5-HT1B/2C) and 5-HT1A agonists, also failed to produce N2O-like stimulus effects. Ethanol partially substituted for N2O. Both (+)-MK-801 and ethanol but not midazolam pretreatment also significantly enhanced the discriminative stimulus effects of N2O. Our results support the hypothesis that the discriminative stimulus effects of N2O are at least partially mediated by NMDA antagonist effects similar to those produced by channel blockers. However, as none of the drugs tested fully mimicked the stimulus effects of N2O, other mechanisms may also be involved.

Treatment-Resistant Major Depression: Rationale for NMDA Receptors as Targets and Nitrous Oxide as Therapy

Major depressive disorder (MDD) remains a huge personal and societal encumbrance. Particularly burdensome is a virulent subtype of MDD, treatment resistant major depression (TMRD), which afflicts 15-30% of MDD patients. There has been recent interest in N-methyl-d-aspartate receptors (NMDARs) as targets for treatment of MDD and perhaps TMRD. To date, most pre-clinical and clinical studies have focused on ketamine, although psychotomimetic and other side effects may limit ketamine's utility. These considerations prompted a recent promising pilot clinical trial of nitrous oxide, an NMDAR antagonist that acts through a mechanism distinct from that of ketamine, in patients with severe TRMD. In this paper, we review the clinical picture of TRMD as a subtype of MDD, the evolution of ketamine as a fast-acting antidepressant, and clinical and basic science studies supporting the possible use of nitrous oxide as a rapid antidepressant.

A novel upregulation of glutathione peroxidase 1 by knockout of liver-regenerating protein Reg3β aggravates acetaminophen-induced hepatic protein nitration

Murine regenerating islet-derived 3β (Reg3β) represents a homologue of human hepatocarcinoma-intestine-pancreas/pancreatic-associated protein and enhances mouse susceptibility to acetaminophen (APAP)-induced hepatotoxicity. Our objective was to determine if and how knockout of Reg3β (KO) affects APAP (300 mg/kg, ip)-mediated protein nitration in mouse liver. APAP injection produced greater levels of hepatic protein nitration in the KO than in the wild-type mice. Their elevated protein nitration was alleviated by a prior injection of recombinant mouse Reg3β protein and was associated with an accelerated depletion of the peroxynitrite (ONOO(-)) scavenger glutathione by an upregulated hepatic glutathione peroxidase-1 (GPX1) activity. The enhanced GPX1 production in the KO mice was mediated by an 85% rise (p<0.05) in the activity of selenocysteine lyase (Scly), a key enzyme that mobilizes Se for selenoprotein biosynthesis. Knockout of Reg3β enhanced AP-1 protein and its binding activity to the Scly gene promoter, upregulating its gene transcription. However, knockout of Reg3β did not affect gene expression of other key factors for selenoprotein biosynthesis. In conclusion, our findings unveil a new metabolic role for Reg3β in protein nitration and a new biosynthesis control of GPX1 by a completely "unrelated" regenerating protein, Reg3β, via transcriptional activation of Scly in coping with hepatic protein nitration. Linking selenoproteins to tissue regeneration will have profound implications in understanding the mechanism of Se functions and physiological coordination of tissue regeneration with intracellular redox control.

Anesthetics and control of breathing

An important side effect of general anesthetics is respiratory depression. Anesthetics have multiple membrane targets of which ionotropic receptors such as gamma-aminobutyric acid-A (GABA(A)), glycine, N-methyl-D-aspartate and nicotinic acetylcholinergic (nACh) receptors are important members. GABA, glutamate and ACh are crucial neurotransmitters in the respiratory neuronal network, and the ability of anesthetics to modulate their release and interact with their receptors implies complex effects on respiration. Metabotropic receptors and intracellular proteins are other important targets for anesthetics suggesting complex effects on intracellular signaling pathways. Here we briefly overview the effects of general anesthetics on protein targets as far as these are relevant for respiratory control. Subsequently, we describe some methods with which the overall effect of anesthetics on the control of breathing can be measured, as well as some promising in vivo approaches to study their synaptic effects. Finally, we summarize the most important respiratory effects of volatile anesthetics in humans and animals and those of some intravenous anesthetics in animals.

Molecular approaches to improving general anesthetics

Over the last several decades, the average age of patients has steadily increased, whereas the use of general anesthesia and deep sedation has grown largely outside the operating room environment. Currently available general anesthetics and delivery models represent limitations in addressing these trends. At the same time, research has tremendously expanded the knowledge of how general anesthetics produce their beneficial effects and also revealed evidence of previously unappreciated general anesthetic toxicities. The goal of this review is to highlight these important developments and describe translational research on new general anesthetics with the potential to improve and reshape clinical care.