Endozepines in recurrent stupor

Frequency and characteristics of patients with bispectral index values of 60 or higher during the induction and maintenance of general anesthesia with remimazolam

In Korea, the approved anesthetic regimen of remimazolam starts with 6 mg/kg/h or 12 mg/kg/h until loss of consciousness, followed by maintenance at 1-2 mg/kg/h. Some patients receiving remimazolam for general anesthesia experience occasional difficulty maintaining bispectral index (BIS) value ˂ 60. This retrospective study aimed to analyze the data from patients undergoing elective surgery under remimazolam based-general anesthesia to determine the frequency and physical characteristics of patients with BIS values ˂ 60. The criterion was established for patients with a poorly maintained BIS value < 60. The frequency and physical characteristics of patients who satisfied this criterion were investigated through their medical records. The modified Brice interview was conducted within 24 h after surgery. Among the 1500 patients included in the analysis, 61 (4.1%) met the criteria for BIS ˂ 60. Based on the modified Brice interview, none of the patients with poorly maintained BIS ˂ 60 complained of intraoperative awareness based on the modified Brice interview or exhibit specific physical characteristics. These patients accounted for less than 5% of the total population studied. Notably, physical characteristics alone are insufficient to predict such patients before surgery.

The Possible Role of Endozepines in Sleep Regulation and Biomarker of Process S of the Borbély Sleep Model

The well-known Two-Process Model of Sleep Regulation describes the integration of the circadian rhythm of arousal and sleep - Process C, and the homeostatic pressure to sleep - Process S. Presently, the known biological markers for Process C are melatonin and core body temperature; whereas, for Process S, there is no biological marker except that of aspects of the electroencephalogram (EEG). Endozepines are a class of endogenous compounds that act like benzodiazepines (BZ), i.e., serving as ligands for the BZ binding sites on GABA_A receptors. Not much is known about the role of endozepines, in particular non-peptide endozepines, in the sleep field except very few reports about high concentrations observed in endozepine stupor, a rare phenomenon of idiopathic recurring stupor. We focused on hypoxanthine and thromboxane A2, which are considered to have endozepine function. This study aimed to examine the effect of 24 h of acute sleep deprivation on blood levels of hypoxanthine and thromboxane A2 of healthy subjects without sleep problems or disorders. The results showed a significant decrease of both compounds in the morning after sleep deprivation in comparison to the unrestricted normal sleep condition, thereby suggesting that these endozepines are secreted regularly while asleep, and, thus, are necessary for the sleep process. This study is the first to suggest a connection between specific biological markers - endozepines and Process S - in the Two-Process Model of Sleep Regulation and, furthermore, it sheds light on the possible role of endozepines in sleepiness and fatigue.

Kleine-Levin syndrome: A neuropsychiatric disorder

Kleine-Levin syndrome (KLS) is a rare, relapsing-remitting disease that affects mostly adolescents. It is characterized by episodes lasting from 1 to several weeks, and comprises neurological (hypersomnia, confusion, slowness, amnesia) and neuropsychiatric symptoms (derealization and apathy). Some psychiatric symptoms (megaphagia, hypersexuality, anxiety, depressed mood, hallucinations, delusions) arise during episodes, albeit less frequently, while patients are normal between episodes. However, sudden severe (>18h/day of sleep) and recurrent hypersomnia helps to differentiate KLS from other psychiatric mimics. Derealization, the striking feeling of unreality or of being in a dream-like environment, is strongly associated with hypoperfusion of the associative temporoparietal junction cortex, whereas apathy is almost complete loss of autoactivation: teenagers stop using their cell phones and their only spontaneous initiative is to sleep. The cause of KLS is not known, but evidence suggests it could be a recurrent inflammatory encephalitis. Up to 5% of cases are familial, although no abnormal gene has yet been found. Hypersomnia episodes tend to become less frequent and to disappear with advancing age. However, 28% of patients have long-lasting episodes (>30 days), and around 15% have no signs of recovery after >20 years of living with the disorder. Patients' cognitive and psychiatric status should be regularly checked during asymptomatic periods, as 20-40% develop long-term mild cognitive impairment or mood disorders. Lithium therapy is beneficial for reducing episode frequency, and intravenous steroids can reduce the duration of long episodes.

Endozepines

Since their introduction in the 1960s, benzodiazepines (BZs) remain one of the most commonly prescribed medications, acting as potent sedatives, hypnotics, anxiolytics, anticonvulsants, and muscle relaxants. The primary neural action of BZs and related compounds is augmentation of inhibitory transmission, which occurs through allosteric modulation of the gamma-aminobutyric acid (GABA)-induced current at the gamma-aminobutyric acid receptor (GABAAR). The discovery of the BZ-binding site on GABAARs encouraged many to speculate that the brain produces its own endogenous ligands to this site (Costa & Guidotti, 1985). The romanticized quest for endozepines, endogenous ligands to the BZ-binding site, has uncovered a variety of ligands that might fulfill this role, including oleamides (Cravatt et al., 1995), nonpeptidic endozepines (Rothstein et al., 1992), and the protein diazepam-binding inhibitor (DBI) (Costa & Guidotti, 1985). Of these ligands, DBI, and affiliated peptide fragments, is the most extensively studied endozepine. The quest for the "brain's Valium" over the decades has been elusive as mainly negative allosteric modulatory effects have been observed (Alfonso, Le Magueresse, Zuccotti, Khodosevich, & Monyer, 2012; Costa & Guidotti, 1985), but recent evidence is accumulating that DBI displays regionally discrete endogenous positive modulation of GABA transmission through activation of the BZ receptor (Christian et al., 2013). Herein, we review the literature on this topic, focusing on identification of the endogenous molecule and its region-specific expression and function.

Professor Elio Lugaresi's contributions to neurology and sleep disorders

The authors present a brief historical review of the most important contributions by Professor Elio Lugaresi, of the University of Bologna, Italy, to neurology and sleep disorders.

Modulation of vigilance in the primary hypersomnias by endogenous enhancement of GABAA receptors

The biology underlying excessive daytime sleepiness (hypersomnolence) is incompletely understood. After excluding known causes of sleepiness in 32 hypersomnolent patients, we showed that, in the presence of 10 μM γ-aminobutyric acid (GABA), cerebrospinal fluid (CSF) from these subjects stimulated GABA(A) receptor function in vitro by 84.0 ± 40.7% (SD) relative to the 35.8 ± 7.5% (SD) stimulation obtained with CSF from control subjects (Student's t test, t = 6.47, P < 0.0001); CSF alone had no effect on GABA(A) signaling. The bioactive CSF component had a mass of 500 to 3000 daltons and was neutralized by trypsin. Enhancement was greater for α2 subunit- versus α1 subunit-containing GABA(A) receptors and negligible for α4 subunit-containing ones. CSF samples from hypersomnolent patients also modestly enhanced benzodiazepine (BZD)-insensitive GABA(A) receptors and did not competitively displace BZDs from human brain tissue. Flumazenil--a drug that is generally believed to antagonize the sedative-hypnotic actions of BZDs only at the classical BZD-binding domain in GABA(A) receptors and to lack intrinsic activity--nevertheless reversed enhancement of GABA(A) signaling by hypersomnolent CSF in vitro. Furthermore, flumazenil normalized vigilance in seven hypersomnolent patients. We conclude that a naturally occurring substance in CSF augments inhibitory GABA signaling, thus revealing a new pathophysiology associated with excessive daytime sleepiness.

Metabolic encephalopathies

Kinnier Wilson coined the term metabolic encephalopathy to describe a clinical state of global cerebral dysfunction induced by systemic stress that can vary in clinical presentation from mild executive dysfunction to deep coma with decerebrate posturing; the causes are numerous. Some mechanisms by which cerebral dysfunction occurs in metabolic encephalopathies include focal or global cerebral edema, alterations in transmitter function, the accumulation of uncleared toxic metabolites, postcapillary venule vasogenic edema, and energy failure. This article focuses on common causes of metabolic encephalopathy, and reviews common causes, clinical presentations and, where relevant, management.

Context dependent benzodiazepine modulation of GABA(A) receptor opening frequency

The anxiolytic, hypnotic, and anti-convulsant properties of benzodiazepines (BDZs) require modulation of distinct GABA_A receptor α-subtypes. BDZ modulation of GABA_A receptors is often described in terms of increased opening frequency, and contrasted with the increased open durations occurring with barbiturate modulation. Several studies spanning single channel, rapid kinetic, and whole cell techniques have suggested that BDZs effect this observed change in frequency through increased affinity for GABA. BDZ-sensitive αβγ isoforms exist at extrasynaptic as well as synaptic locations, where they encounter markedly different concentration and time-course of GABA exposure. Interestingly, this affinity-based mechanism (specifically, decreasing the GABA unbinding rate) is only predicted to increase opening frequency under conditions that allow the unbinding and rebinding cycles typical of prolonged exposure to low GABA concentrations, which are more likely to occur at extrasynaptic GABA_A receptors. In contrast, when rebinding is less likely, such as may occur in certain synaptic conditions, the number, but not the frequency, of channel openings increases in response to BDZ modulation. In conclusion, not only can multiple kinetic mechanisms alter channel opening frequency, but a single mechanism – increased affinity – impacts opening frequency differently under different contexts of GABA_A receptor activation.

The pharmacology of anxiety

Understanding the neurochemistry of anxiety is of fundamental importance in the development and use of novel anxiolytics. Through measuring peripheral markers of brain biochemistry, direct pharmacological challenges and brain neuroimaging techniques our understanding of this field has increased substantially in the past few decades. We review the four most studied neurotransmitter systems with respect to in anxiety disorders: gamma amino-butyric acid, serotonin, noradrenaline and dopamine. We have focussed upon clinical studies to highlight the current techniques used to determine brain neurochemistry in vivo. Future research in this field will greatly benefit from recent advances in neuroimaging techniques and the discovery of novel ligands targeting specific receptors.

Natural endogenous ligands for benzodiazepine receptors in hepatic encephalopathy

Benzodiazepines of natural origin (NBZDs) have been found in human blood and brains as well as in medicinal plants and foods. In plasma and brain tissue there are i.e. diazepam and nordiazepam equal to commercial drugs but there are also other benzodiazepine-like compounds termed "endozepines", which act as agonists at the benzodiazepine receptors of central type (CBR). A synthetic pathway for the production of NBZDs has not yet been found, but it has been suggested that micro-organisms may synthesize molecules with benzodiazepine-like structures. Hence NBZDs could be of both endogenous and exogenous source and be considered as natural anxyolitic and sedative. Interestingly there are also natural compounds, such as the polypeptide Diazepam Binding Inhibitor (DBI) acting as an "inversive agonist" implicated in fair and panic disorders. It has been suggested that NBZDs may play a role in the pathogenesis of hepatic encephalopathy (HE). Multidirectional studies evaluated NBZDs levels (1) in the blood of normal subjects, of cirrhotic with or without HE and in commercial benzodiazepine consumers; (2) in the blood of cirrhotic treated or not with a non-absorbable antibiotic; (3) in several constituents of our diet. In conclusion, NBZDs increase sometime in cirrhotics with or without HE but they reach concentrations not higher than those found in commercial benzodiazepines consumers. Hence NBZDs must be considered as occasional precipitating factor of HE and benzodiazepine antagonists only symptomatic drugs. The finding that NBZDs may be in part synthesized by intestinal bacterial flora and in part constituent of our diet underlines the importance to feed cirrhotic patients with selected food.