Pentobarbitone modulation of NMDA receptors in neurones isolated from the rat olfactory brain

The Neuroprotective Effect of Thiopental on the Postoperative Neurological Complications in Patients Undergoing Surgical Clipping of Unruptured Intracranial Aneurysm: A Retrospective Analysis

Although thiopental improved neurological outcomes in several animal studies, there are still insufficient clinical data examining the efficacy of thiopental for patients undergoing surgical clipping of unruptured intracranial aneurysm (UIA). This study validated the effect of thiopental and investigated risk factors associated with postoperative neurological complications in patients undergoing surgical clipping of UIA. In total, 491 patients who underwent aneurysm clipping were included in this retrospective cohort study. Data regarding demographics, aneurysm characteristics, and use of thiopental were collected from electronic medical records. Propensity score matching and logistic regression analysis were used. After propensity score matching, the thiopental group showed a lower incidence of the postoperative neurological complications than non-thiopental group (5.5% vs. 17.1%, p = 0.001). In multivariate analysis, thiopental reduced the risk of postoperative neurological complications (odds ratio (OR) 0.26, 95% confidence interval (CI) 0.13 to 0.51, p < 0.001) while aneurysm size ≥ 10 mm (OR 4.48, 95% CI 1.69 to 11.87, p = 0.003), and hyperlipidemia (OR 2.24, 95% CI 1.16 to 4.32, p = 0.02) increased the risk of postoperative neurological complications. This study showed that thiopental was associated with the lower risk of neurological complications after clipping of UIA.

Effects of anesthetics, sedatives, and opioids on ventilatory control

This article provides a comprehensive, up to date summary of the effects of volatile, gaseous, and intravenous anesthetics and opioid agonists on ventilatory control. Emphasis is placed on data from human studies. Further mechanistic insights are provided by in vivo and in vitro data from other mammalian species. The focus is on the effects of clinically relevant agonist concentrations and studies using pharmacological, that is, supraclinical agonist concentrations are de-emphasized or excluded.

Which anesthetic should be used in the treatment of refractory status epilepticus?

While the treatment of refractory status epilepticus (SE) relies on the use of anesthetic agents, mostly barbiturates, propofol, or midazolam, the study of the available literature discloses that the evidence level is low. Therapeutic coma induction appears straightforward for generalized convulsive or subtle SE, but this approach is debated for complex partial SE. Each anesthetic has its own advocates, and specific advantages and risks; furthermore, several different protocols have been reported regarding the duration and depth of sedation. However, it seems that the biological background of the patient (especially the etiology) remains the main prognostic determinant in SE. There is a clear need of controlled trials regarding this topic.

Robust ligand-based modeling of the biological targets of known drugs

Systematic annotation of the primary targets of roughly 1000 known therapeutics reveals that over 700 of these modulate approximately 85 biological targets. We report the results of three analyses. In the first analysis, drug/drug similarities and target/target similarities were computed on the basis of three-dimensional ligand structures. Drug pairs sharing a target had significantly higher similarity than drug pairs sharing no target. Also, target pairs with no overlap in annotated drug specificity shared lower similarity than target pairs with increasing overlap. Two-way agglomerative clusterings of drugs and targets were consistent with known pharmacology and suggestive that side effects and drug-drug interactions might be revealed by modeling many targets. In the second analysis, we constructed and tested ligand-based models of 22 diverse targets in virtual screens using a background of screening molecules. Greater than 100-fold enrichment of cognate versus random molecules was observed in 20/22 cases. In the third analysis, selectivity of the models was tested using a background of drug molecules, with selectivity of greater than 80-fold observed in 17/22 cases. Predicted activities derived from crossing drugs against modeled targets identified a number of known side effects, drug specificities, and drug-drug interactions that have a rational basis in molecular structure.

Barbiturates induce mitochondrial depolarization and potentiate excitotoxic neuronal death

Barbiturates are widely used as anesthetics, anticonvulsants, and neuroprotective agents. However, barbiturates may also inhibit mitochondrial respiration, and mitochondrial inhibitors are known to potentiate NMDA receptor-mediated neurotoxicity. Here we used rat cortical cultures to examine the effect of barbiturates on neuronal mitochondria and responses to NMDA receptor stimulation. The barbiturates tested, secobarbital, amobarbital, and thiamylal, each potentiated NMDA-induced neuron death at barbiturate concentrations relevant to clinical and experimental use (100-300 microm). By using rhodamine-123 under quenching conditions, barbiturates in this concentration range were shown to depolarize neuronal mitochondria and greatly amplify NMDA-induced mitochondrial depolarization. Barbiturate-induced mitochondrial depolarization was increased by the ATP synthase inhibitor oligomycin, indicating that barbiturates act by inhibiting electron transport sufficiently to cause ATP synthase reversal. Barbiturates similarly amplified the effects of NMDA on cytoplasmic free calcium concentrations. The cell-impermeant barbiturate N-glucoside amobarbital did not influence mitochondrial potential or potentiate NMDA neurotoxicity or calcium responses. However, all of the barbiturates attenuated NMDA-induced calcium elevations and cell death when present at millimolar concentrations. Whole-cell patch-clamp studies showed that these effects may be attributable to actions at the cell membrane, resulting in a block of NMDA-induced current flux at millimolar barbiturate concentrations. Together, these findings reconcile previous reports of opposing effects on barbiturates on NMDA neurotoxicity and show that barbiturate effects on neuronal mitochondria can be functionally significant. Effects of barbiturates on neuronal mitochondria should be considered in experimental and clinical application of these drugs.

Barbiturates induce mitochondrial depolarization and potentiate excitotoxic neuronal death

Barbiturates are widely used as anesthetics, anticonvulsants, and neuroprotective agents. However, barbiturates may also inhibit mitochondrial respiration, and mitochondrial inhibitors are known to potentiate NMDA receptor-mediated neurotoxicity. Here we used rat cortical cultures to examine the effect of barbiturates on neuronal mitochondria and responses to NMDA receptor stimulation. The barbiturates tested, secobarbital, amobarbital, and thiamylal, each potentiated NMDA-induced neuron death at barbiturate concentrations relevant to clinical and experimental use (100-300 microm). By using rhodamine-123 under quenching conditions, barbiturates in this concentration range were shown to depolarize neuronal mitochondria and greatly amplify NMDA-induced mitochondrial depolarization. Barbiturate-induced mitochondrial depolarization was increased by the ATP synthase inhibitor oligomycin, indicating that barbiturates act by inhibiting electron transport sufficiently to cause ATP synthase reversal. Barbiturates similarly amplified the effects of NMDA on cytoplasmic free calcium concentrations. The cell-impermeant barbiturate N-glucoside amobarbital did not influence mitochondrial potential or potentiate NMDA neurotoxicity or calcium responses. However, all of the barbiturates attenuated NMDA-induced calcium elevations and cell death when present at millimolar concentrations. Whole-cell patch-clamp studies showed that these effects may be attributable to actions at the cell membrane, resulting in a block of NMDA-induced current flux at millimolar barbiturate concentrations. Together, these findings reconcile previous reports of opposing effects on barbiturates on NMDA neurotoxicity and show that barbiturate effects on neuronal mitochondria can be functionally significant. Effects of barbiturates on neuronal mitochondria should be considered in experimental and clinical application of these drugs.

The role of the NMDA synapse in general anesthesia

A theory of anesthesia is presented. It consists of four hypotheses. (1) The occurrence of states of consciousness causally depends on the formation of transient higher-order, self-referential mental representations. The occurrence of such states is identical with the appearance of conscious phenomena. Loss of consciousness will occur, if the brain's representational activity falls below a critical threshold. (2) Higher-order mental representations are instantiated by neural cell assemblies. (3) The formation of such assemblies involves the activation of the NMDA receptor channel complex. The activation state of this receptor determines the rate at which such assemblies are generated. (4) Modification of NMDA-dependent computational processes is the final common pathway of anesthetic action. Agents that directly inactivate the NMDA synapse necessarily have anesthetic properties; agents that do not directly affect the NMDA synapse will exert an anesthetic action, if they inhibit NMDA-dependent processes.

What the actions of anaesthetics on fast synaptic transmission reveal about the molecular mechanism of anaesthesia

1. Synapses with the brain are important components of the networks responsible for higher nervous function and current evidence suggests that general anaesthetics modulate synaptic transmission in the brain. 2. Analysis of anaesthetic action on these synapses not only defines the cellular mechanisms involved in anaesthesia but also reveals much about the molecular targets of anaesthetic action. 3. It appears that while anaesthetics affect a wide variety of processes, the most sensitive are those which are directly linked to the activity of ligand-gated ion channels. Moreover, both single channel patch clamp studies and the molecular biological investigations of the sub-unit specificity of the sensitivity to anaesthetics indicate that anaesthetics interact directly with these functional proteins.

Effects of anticonvulsive drugs on pentylenetetrazol kindling and long-term potentiation in freely moving rats

Drugs with anticonvulsive properties and different mechanisms of action were compared for their influence on long-term potentiation and pentylenetetrazol kindling in freely moving animals. Rats were chronically implanted with a stimulation electrode in the angular bundle and a recording electrode in the dentate gyrus. Field potentials in the dentate gyrus were elicited and long-term potentiation was induced by stimulation of the perforant pathway. The clinically used drugs or the potentially anticonvulsive drugs, diphenylhydantoin (50 mg/kg), diazepam (0.5 mg/kg), pentobarbital (10 mg/kg), dizocilpine (MK 801, 0.2 mg/kg) and CGP 43487 (2-amino-4-methyl-5-phosphono-3-pentenoic acid-carboxyethylester, 10 mg/kg), were injected before tetanization. In behavioural experiments pentylenetetrazol kindling was performed with pretreatment with the substances in dosages indicated above (except MK 801, 0.3 mg/kg). Field potentials recorded in the interval between drug administration and tetanization were influenced only by diphenylhydantoin which enhanced the population spike amplitude to 128% of control values. However, the substances showed different effects on long-term potentiation. MK 801, CGP 43487 and pentobarbital depressed potentiation; diazepam was without effect. Diphenylhydantoin had a minor influence on induction but significantly impaired maintenance of long-term potentiation. Furthermore, MK 801, CGP 43487, diazepam and pentobarbital differentially depressed kindling whereas phenytoin only slightly influenced it. The consequences as to hypothetical common cellular mechanisms for kindling development and long-term potentiation are discussed.

Thiopental induced cerebral protection during ischemia in gerbils

Temporary interruption or reduction of cerebral blood flow during cerebrovascular surgery may rapidly result in ischemia or cerebral infarction. Thiopental has been shown to have cerebroprotective effects. However, the cerebroprotective dose of thiopental causes burst suppression of the EEG, thus this parameter cannot be used continuously for the detection of metabolic changes in the brain during thiopental anaesthesia. This study was performed in order to examine whether the multiparametric assembly (MPA), which measures energy metabolism CBF and mitochondrial (NADH) as well as extracellular ion concentrations (K+), can shed light on the mechanism of the cerebroprotective effects of thiopental. The MPA was placed on the brain of Mongolian gerbils and burst suppression of the ECoG was induced by thiopental. Cerebral ischemia was induced by occlusion of carotid arteries after burst suppression. Burst suppression of the ECoG was accompanied by a significant decrease in cerebral blood flow. In animals that received thiopental prior to ischemia, NADH increased to a lesser degree and extracellular potassium ion concentration increased to a lesser degree than in the control animals, indicating that thiopental affords protection of the brain under ischemic conditions due to improved energy metabolism. This study also demonstrates that the MPA can monitor changes occurring in the cerebral cortex even after the ECoG can no longer be used. Those findings have a significant value in the development of a new clinical monitoring device.