Intravenous anaesthetics inhibit nicotinic acetylcholine receptor-mediated currents and Ca2+ transients in rat intracardiac ganglion neurons

Cholinergic modulation in the vertebrate auditory pathway

Acetylcholine (ACh) is a prevalent neurotransmitter throughout the nervous system. In the brain, ACh is widely regarded as a potent neuromodulator. In neurons, ACh signals are conferred through a variety of receptors that influence a broad range of neurophysiological phenomena such as transmitter release or membrane excitability. In sensory circuitry, ACh modifies neural responses to stimuli and coordinates the activity of neurons across multiple levels of processing. These factors enable individual neurons or entire circuits to rapidly adapt to the dynamics of complex sensory stimuli, underscoring an essential role for ACh in sensory processing. In the auditory system, histological evidence shows that acetylcholine receptors (AChRs) are expressed at virtually every level of the ascending auditory pathway. Despite its apparent ubiquity in auditory circuitry, investigation of the roles of this cholinergic network has been mainly focused on the inner ear or forebrain structures, while less attention has been directed at regions between the cochlear nuclei and midbrain. In this review, we highlight what is known about cholinergic function throughout the auditory system from the ear to the cortex, but with a particular emphasis on brainstem and midbrain auditory centers. We will focus on receptor expression, mechanisms of modulation, and the functional implications of ACh for sound processing, with the broad goal of providing an overview of a newly emerging view of impactful cholinergic modulation throughout the auditory pathway.

The role of nitric oxide on the antiarrhythmic effects of ketamine/xylazine in a rat model of acute cardiac ischemia-reperfusion

The prevalence of ventricular arrhythmias during general anesthesia is about 70%. In experimental studies on the antiarrhythmic effects of different agents, using anesthetic drugs that do not have any protective properties are preferable. The present study was conducted to investigate molecular mechanisms involved in the antiarrhythmic effects of ketamine/xylazine (K/X).

Sixty male rats were assigned to eight groups: K/X, L -NAME (25–35 mg/kg) with thiopental (TP), L-NAME (25–35 mg/kg) with ketamine/xylazine, L arginine (100 mg/kg) with thiopental, L-arginine (100 mg/kg) with ketamine/xylazine. After anesthetic induction using TP or K/X, the animals were subjected to 30 min of ischemia. Hemodynamic parameters, ventricular arrhythmias during ischemia, the incidence of ventricular tachycardia (VT), and ventricular fibrillation (VF) were measured. Additionally, in order to assess nitrite/nitrate ratio and LDH after ischemia, serum samples were collected and used.

Our results showed that in the K/X group, the number of VT and VF, duration of VT (p = 0.006), the severity of arrhythmias (p = 0.0179). There was no VF incidence in this group.

These protective effects were faded by administration of L-NAME with K/X. The combination of L- Arginine in the TP group decreased the number and duration of VT (p < 0.001, p = 0.0013) with no incidence of VF in comparison with TP. L-arginine with K/X groups increased the number and duration of VT (p < 0.0001, p < 0.001) compared to K/X and VF was seen (100%). However, there was no significant difference between TP and K/X groups in terms of this nitrite/nitrate ratio. These findings suggest that the antiarrhythmic effects of ketamine/xylazine might be partially relative to the nitric oxide synthesis pathway.

•

The prevalence of ventricular arrhythmias during general anesthesia is about 70%. ketamine/xylazine as common anesthetic agents have antiarrhythmic properties.

•

The antiarrhythmic effects of ketamine/xylazine might be partially relative to the nitric oxide synthesis pathway.

[Etomidate reduces excitability of the neurons and suppresses the function of nAChR ventral horn in the spinal cord of neonatal rats]

OBJECTIVE

To investigate the effects of etomidate on electrophysiological properties and nicotinic acetylcholine receptors (nAChRs) of ventral horn neurons in the spinal cord.

METHODS

The spinal cord containing lumbosacral enlargement was isolated from 19 neonatal SD rats aged 7-12 days. The spinal cord were sliced and digested with papain (0.18 g/30 mL artificial cerebrospinal fluid) and incubated for 40 min. At the ventral horn, acute mechanical separation of neurons was performed with fire-polished Pasteur pipettes, and perforated patch-clamp recordings combined with pharmacological methods were employed on the adherent healthy neurons. In current-clamp mode, the spontaneous action potential (AP) of the ventral horn neurons in the spinal cord was recorded. The effects of pretreatment with different concentrations of etomidate on AP recorded in the ventral horn neurons were examined. In the voltage-clamp mode, nicotine was applied to induce inward currents in the ventral horn neurons, and the effect of pretreatment with etomidate on the inward currents induced by nicotine were examined with different etomidate concentrations, different holding potentials and different use time.

RESULTS

The isolated ventral horn neurons were in good condition with large diverse somata and intact processes. The isolated spinal ventral horn neurons (n=21) had spontaneous action potentials, and were continuously perfused for 2 min with 0.3, 3.0 and 30.0 μmol/L etomidate. Compared with those before administration, the AP amplitude, spike potential amplitude and overshoot were concentration-dependently suppressed (P < 0.01), and spontaneous discharge frequency was obviously reduced (P < 0.01, n=12). The APs of the other 9 neurons were completely abolished by etomidate at 3.0 or 30 μmol/L. At the same holding potential (VH=-70 mV), pretreatment with 0.3, 3.0 or 30.0 μmol/L etomidate for 2 min concentration-dependently suppressed the current amplitude induced by 0.4 mmol/L nicotine (P < 0.01, n=7). At the holding potentials of - 30, - 50, and - 70 mV, pretreatment with 30.0 μmol/L etomidate for 2 min voltage-dependently suppressed the current amplitude induced by 0.4 mmol/L nicotine (P < 0.01, n=6 for each holding potential). During the 6 min of 30.0 μmol/L etomidate pretreatment, the clamped cells were exposed to 0.4 mmol/L nicotine for 4 times at 0, 2, 4, and 6 min (each exposure time was 2 s), and the nicotinic current amplitude decreased gradually as the number of exposures increased. But at the same concentration, two nicotine exposures (one at the beginning and the other at the end of the 6 min pretreatment) resulted in a significantly lower inhibition rate compared with 4 nicotine exposures (P < 0.01, n=6).

CONCLUSIONS

etomidate reduces the excitability of the spinal ventral neurons in a concentration-dependent manner and suppresses the function of nAChR in a concentration-, voltage-, and use-dependent manner.

Ketamine inhibits synaptic transmission and nicotinic acetylcholine receptor-mediated responses in rat intracardiac ganglia in situ

The intravenous anaesthetic ketamine, has been demonstrated to inhibit nicotinic acetylcholine receptor (nAChR)-mediated currents in dissociated rat intracardiac ganglion (ICG) neurons (Weber et al., 2005). This effect would be predicted to depress synaptic transmission in the ICG and would account for the inhibitory action of ketamine on vagal transmission to the heart (Inoue and König, 1988). This investigation was designed to examine the activity of ketamine on (i) postsynaptic responses to vagal nerve stimulation, (ii) the membrane potential, and (iii) membrane current responses evoked by exogenous application of ACh and nicotine in ICG neurons in situ. Intracellular recordings were made using sharp intracellular microelectrodes in a whole mount ICG preparation. Preganglionic nerve stimulation and recordings in current- and voltage-clamp modes were used to assess the action of ketamine on ganglionic transmission and nAChR-mediated responses. Ketamine attenuated the postsynaptic responses evoked by nerve stimulation. This reduction was significant at clinically relevant concentrations at high frequencies. The excitatory membrane potential and current responses to focal application of ACh and nicotine were inhibited in a concentration-dependent manner by ketamine. In contrast, ketamine had no effect on either the directly-evoked action potential or excitatory responses evoked by focal application of γ-aminobutyric acid (GABA). Taken together, ketamine inhibits synaptic transmission and nicotine- and ACh-evoked currents in adult rat ICG. Ketamine inhibition of synaptic transmission and nAChR-mediated responses in the ICG contributes significantly to its attenuation of the bradycardia observed in response to vagal stimulation in the mammalian heart.

Mechanism and Development of Modern General Anesthetics

BACKGROUND

Before October 1846, surgery and pain were synonymous but not thereafter. Conquering pain must be one of the very few strategies that has potentially affected every human being in the world of all milestones in medicine.

METHODS

This review article describes how various general anesthetics were discovered historically and how they work in the brain to induce sedative, hypnosis and immobility. Their advantages and disadvantages will also be discussed.

RESULTS

Anesthesia is a relatively young field but is rapidly evolving. Currently used general anesthetics are almost invariably effective, but nagging side effects, both short (e.g., cardiac depression) and long (e.g., neurotoxicity) term, have reawakened the call for new drugs.

CONCLUSION

Based on the deepening understanding of historical development and molecular targets and actions of modern anesthetics, novel general anesthetics are being investigated as potentially improved sedative-hypnotics or a key to understand the mechanism of anesthesia.

Challenges in anesthesia personalization: resolving the pharmacogenomic puzzle

Clinicians are witnessing differences in the doses required for induction and maintenance of anesthesia, as well as prolonged recovery in some patients. Predictable factors like patient characteristics, factors related to the procedure, pharmacological characteristics of anesthetics and adjunctive drugs, might explain some of the observed differences. However, the role of various polymorphisms of genes encoding for drugs’ molecular targets, transporters and metabolic enzymes can have a significant impact on anesthesia outcome, too. In the present paper, we critically discuss pharmacological characteristics of the most common drugs used in anesthesia, with a focus on the possible genetic background of unpredictable diversities in anesthesia outcomes.

Design and Applications of Small Molecular Probes for Calcium Detection

The physiological significance of calcium ions such as the role in cellular signalling, cell growth, etc. have driven the development of methods to detect and monitor the level of Ca²⁺ ions, both in vivo and in vitro. Although various approaches for the detection of calcium ions have been reported, methods based on small molecular fluorescent probes have unique advantages including small probe size, easy monitoring of detection processes and applicability in biological systems. In this review article, we will discuss the progress in the development of Ca²⁺ -binding fluorescent probes by taking into account the types of chelating groups that have been employed for Ca²⁺ binding.

Surgical stress and cancer progression: the twisted tango

Surgical resection is an important avenue for cancer treatment, which, in most cases, can effectively alleviate the patient symptoms. However, accumulating evidence has documented that surgical resection potentially enhances metastatic seeding of tumor cells. In this review, we revisit the literature on surgical stress, and outline the mechanisms by which surgical stress, including ischemia/reperfusion injury, activation of sympathetic nervous system, inflammation, systemically hypercoagulable state, immune suppression and effects of anesthetic agents, promotes tumor metastasis. We also propose preventive strategies or resolution of tumor metastasis caused by surgical stress.

Effect of cholinergic crisis on the potency of different emergency anaesthesia protocols in soman-poisoned rats

BACKGROUND

In a military or terrorist scenario, combination of organophosphorus compounds (OP) poisoning with physical trauma requiring surgical treatment and thus general anaesthesia are possible. Previous in vitro studies showed an altered potency of relevant anaesthetics during cholinergic crisis. Hence, it is not clear, which anaesthetics are suitable to achieve the necessary stage of surgical anaesthesia in OP poisoning.

METHODS

In the present study, different anaesthetic regimens (ketamine-midazolam, propofol-fentanyl, thiopental-fentanyl), relevant in military emergency medicine, were examined in soman-poisoned rats. Clinical signs and cardiovascular variables were recorded continuously. Blood samples for acetylcholinesterase (AChE) activity were drawn. After euthanasia or death of the animals, brain and diaphragm were collected for cholinesterase assays.

RESULTS

Propofol-fentanyl and thiopental-fentanyl resulted in surgical anaesthesia throughout the experiments. With ketamine-midazolam, surgical anaesthesia without respiratory impairment could not be achieved in pilot experiments (no soman challenge) and was therefore not included in the study. Soman-poisoned and control animals required a comparable amount of propofol-fentanyl or thiopental-fentanyl. In combination with atropine, significantly less propofol was needed. Survival rate was higher with thiopental compared to propofol. Atropine improved survival in both groups. Blood and tissue AChE activities were strongly inhibited after soman administration with and without atropine treatment.

DISCUSSION

The current in vivo study did not confirm concerns of altered potency of existing anaesthetic protocols for the application of propofol or thiopental with fentanyl due to soman poisoning. Despite severe cholinergic crisis, sufficient anaesthetic depth could be achieved in all animals.

CONCLUSION

Further experiments in in vivo models closer to human pharmaco- and toxicokinetics (e.g., swine) are required for confirmation of the initial findings and for improving extrapolation to humans.

Effect fingerprinting of new psychoactive substances (NPS): What can we learn from in vitro data?

The use of new psychoactive substances (NPS) is increasing and currently >600 NPS have been reported. However, limited information on neuropharmacological and toxicological effects of NPS is available, hampering risk characterization. We reviewed the literature on the in vitro neuronal modes of action to obtain effect fingerprints of different classes of illicit drugs and NPS. The most frequently reported NPS were selected for review: cathinones (MDPV, α-PVP, mephedrone, 4-MEC, pentedrone, methylone), cannabinoids (JWH-018), (hallucinogenic) phenethylamines (4-fluoroamphetamine, benzofurans (5-APB, 6-APB), 2C-B, NBOMes (25B-NBOMe, 25C-NBOMe, 25I-NBOMe)), arylcyclohexylamines (methoxetamine) and piperazine derivatives (mCPP, TFMPP, BZP). Our effect fingerprints highlight the main modes of action for the different NPS studied, including inhibition and/or reversal of monoamine reuptake transporters (cathinones and non-hallucinogenic phenethylamines), activation of 5-HT₂receptors (hallucinogenic phenethylamines and piperazines), activation of cannabinoid receptors (cannabinoids) and inhibition of NDMA receptors (arylcyclohexylamines). Importantly, we identified additional targets by relating reported effect concentrations to the estimated human brain concentrations during recreational use. These additional targets include dopamine receptors, α- and β-adrenergic receptors, GABA_Areceptors and acetylcholine receptors, which may all contribute to the observed clinical symptoms following exposure. Additional data is needed as the number of NPS continues to increase. Also, the effect fingerprints we have obtained are still incomplete and suffer from a large variation in the reported effects and effect sizes. Dedicated in vitro screening batteries will aid in complementing specific effect fingerprints of NPS. These fingerprints can be implemented in the risk assessments of NPS that are necessary for eventual control measures to reduce Public Health risks.

Effects of Ketamine and Ketamine Metabolites on Evoked Striatal Dopamine Release, Dopamine Receptors, and Monoamine Transporters

Following administration at subanesthetic doses, (R,S)-ketamine (ketamine) induces rapid and robust relief from symptoms of depression in treatment-refractory depressed patients. Previous studies suggest that ketamine's antidepressant properties involve enhancement of dopamine (DA) neurotransmission. Ketamine is rapidly metabolized to (2S,6S)- and (2R,6R)-hydroxynorketamine (HNK), which have antidepressant actions independent of N-methyl-d-aspartate glutamate receptor inhibition. These antidepressant actions of (2S,6S;2R,6R)-HNK, or other metabolites, as well as ketamine's side effects, including abuse potential, may be related to direct effects on components of the dopaminergic (DAergic) system. Here, brain and blood distribution/clearance and pharmacodynamic analyses at DA receptors (D1-D5) and the DA, norepinephrine, and serotonin transporters were assessed for ketamine and its major metabolites (norketamine, dehydronorketamine, and HNKs). Additionally, we measured electrically evoked mesolimbic DA release and decay using fast-scan cyclic voltammetry following acute administration of subanesthetic doses of ketamine (2, 10, and 50 mg/kg, i.p.). Following ketamine injection, ketamine, norketamine, and multiple hydroxynorketamines were detected in the plasma and brain of mice. Dehydronorketamine was detectable in plasma, but concentrations were below detectable limits in the brain. Ketamine did not alter the magnitude or kinetics of evoked DA release in the nucleus accumbens in anesthetized mice. Neither ketamine's enantiomers nor its metabolites had affinity for DA receptors or the DA, noradrenaline, and serotonin transporters (up to 10 μM). These results suggest that neither the side effects nor antidepressant actions of ketamine or ketamine metabolites are associated with direct effects on mesolimbic DAergic neurotransmission. Previously observed in vivo changes in DAergic neurotransmission following ketamine administration are likely indirect.

BPC 157 antagonized the general anaesthetic potency of thiopental and reduced prolongation of anaesthesia induced by L-NAME/thiopental combination

AIM

We hypothesized that certain effects of the general anaesthetic thiopental are dependent on NO-related mechanisms, which were consequently counteracted by stable gastric pentadecapeptide BPC 157.

MAIN METHODS

(1) All rats intraperitoneally received thiopental (20, 30, 40, and 50 mg/kg) while medication BPC 157 (10 μg/kg, 10 ng/kg, and 10 pg/kg) was given intraperitoneally at 5 min before thiopental. (2) To determine NO-related mechanisms, all rats received intraperitoneally thiopental 40 mg/kg while BPC 157 (10 μg/kg), L-NAME (10 mg/kg) and L-arginine (30 mg/kg) were applied alone and/or combined. BPC 157 was given at 25 min before thiopental while L-NAME, L-arginine, alone and/or combined, were applied at 20 min before thiopental.

KEY FINDINGS

(1) BPC 157 own effect on thiopental anaesthesia: BPC 157 (10 ng/kg and 10 μg/kg) caused a significant antagonism of general anaesthesia produced by thiopental with a parallel shift of the dose-response curve to the right. (2) L-NAME-L-arginine-BPC 157 interrelations: L-NAME: Thiopental-induced anaesthesia duration was tripled. L-arginine: Usual thiopental anaesthesia time was not influenced. Active only when given with L-NAME or BPC 157: potentiating effects of L-NAME were lessened, not abolished; shortening effect of BPC 157: abolished. BPC 157 and L-NAME: Potentiating effects of L-NAME were abolished. BPC 157 and L-NAME and L-arginine: BPC 157 +L-NAME +L-arginine rats exhibited values close to those in BPC 157 rats.

SIGNIFICANCE

Thiopental general anaesthesia is simultaneously manipulated in both ways with NO system activity modulation, L-NAME (prolongation) and BPC 157 (shortening/counteraction) and L-arginine (interference with L-NAME and BPC 157).

Ketamine and other glutamate receptor modulators for depression in adults

BACKGROUND

Considering the ample evidence of involvement of the glutamate system in the pathophysiology of depression, pre-clinical and clinical studies have been conducted to assess the antidepressant efficacy of glutamate inhibition, and glutamate receptor modulators in particular. This review focuses on the use of glutamate receptor modulators in unipolar depression.

OBJECTIVES

To assess the effects - and review the acceptability - of ketamine and other glutamate receptor modulators in comparison to placebo (or saline placebo), other pharmacologically active agents, or electroconvulsive therapy (ECT) in alleviating the acute symptoms of depression in people with unipolar major depressive disorder.

SEARCH METHODS

We searched the Cochrane Depression, Anxiety and Neurosis Review Group's Specialised Register (CCDANCTR, to 9 January 2015). This register includes relevant randomised controlled trials (RCTs) from: the Cochrane Library (all years), MEDLINE (1950 to date), EMBASE (1974 to date), and PsycINFO (1967 to date). We did not apply any restrictions to date, language or publication status.

SELECTION CRITERIA

Double- or single-blind RCTs comparing ketamine, memantine, or other glutamate receptor modulators with placebo (or saline placebo), other active psychotropic drugs, or electroconvulsive therapy (ECT) in adults with unipolar major depression.

DATA COLLECTION AND ANALYSIS

Three review authors independently identified studies, assessed trial quality and extracted data. The primary outcomes for this review were response rate and adverse events.

MAIN RESULTS

We included 25 studies (1242 participants) on ketamine (9 trials), memantine (3), AZD6765 (3), D-cycloserine (2), Org26576 (2), atomoxetine (1), CP-101,606 (1), MK-0657 (1), N-acetylcysteine (1), riluzole (1) and sarcosine (1). Twenty-one studies were placebo-controlled and the majority were two-arm studies (23 out of 25). Twenty-two studies defined an inclusion criteria specifying the severity of depression; 11 specified at least moderate depression; eight, severe depression; and the remaining three, mild-moderate depression. Nine studies recruited only treatment-resistant patients.We rated the risk of bias as low or unclear for most domains, though lack of detail regarding masking of treatment in the studies reduced our certainty in the effect for all outcomes. We rated three studies as having high risk for selective outcome reporting. Many trials did not provide information on all the prespecified outcomes and we found no data, or very limited data, on very important issues like suicidality, cognition, quality of life, costs to healthcare services and dropouts due to lack of efficacy.Among all glutamate receptor modulators, only ketamine (administered intravenously) proved to be more efficacious than placebo, though the quality of evidence was limited by risk of bias and small sample sizes. There was low quality evidence that treatment with ketamine increased the likelihood of response after 24 hours (odds ratio (OR) 10.77, 95% confidence interval (CI) 2.00 to 58.00; 3 RCTs, 56 participants), 72 hours (OR 12.59, 95% CI 2.38 to 66.73; 3 RCTs, 56 participants), and one week (OR 2.58, 95% CI 1.08 to 6.16; 4 RCTs, 131 participants). The effect of ketamine was even less certain at two weeks, as data were available from only one trial (OR 0.93, 95% CI 0.31 to 2.83; 51 participants, low quality evidence). This was consistent across all efficacy outcomes. Ketamine caused more confusion and emotional blunting compared to placebo. There was insufficient evidence to determine if this increased the likelihood of leaving the study early (OR 1.90, 95% CI 0.43 to 8.47; 5 RCTs, 139 participants, low quality evidence).One RCT with 72 participants reported higher numbers of responders on ketamine than midazolam at 24 hours (OR 0.36, 95% CI 0.14 to 0.58), 72 hours (OR 0.37, 95% CI 0.16 to 0.59), and one week (OR 0.29, 95% CI 0.08 to 0.49). However, midazolam was better tolerated than ketamine in terms of blurred vision, dizziness, general malaise and nausea/vomiting at 24 hours post-infusion. The evidence contributing to these outcomes was of low quality.We found better efficacy of sarcosine over citalopram at four weeks (OR 6.93, 95% CI 1.53 to 31.38; 1 study, 40 participants), but not at two weeks (OR: 8.14, 95% CI 0.88 to 75.48); fewer participants in the sarcosine group experienced adverse events (OR 0.04, 95% CI 0.00 to 0.68; P = 0.03, 1 study, 40 participants). This was based on low quality evidence. No significant results were found for the remaining glutamate receptor modulators.In one study with 18 participants, ketamine was more effective than ECT at 24 hours (OR 28.00, 95% CI 2.07 to 379.25) and 72 hours (OR 12.25, 95% CI 1.33 to 113.06), but not at one week (OR 3.35, 95% CI 0.12 to 93.83), or two weeks (OR 3.35, 95% CI 0.12 to 93.83). No differences in terms of adverse events were found between ketamine and ECT, however the only adverse events reported were blood pressure and heart rate. This study was rated as very low quality.

AUTHORS' CONCLUSIONS

We found limited evidence for ketamine's efficacy over placebo at time points up to one week in terms of the primary outcome, response rate. The effects were less certain at two weeks post-treatment. No significant results were found for the remaining ten glutamate receptor modulators, except for sarcosine being more effective than citalopram at four weeks. In terms of adverse events, the only significant differences in favour of placebo over ketamine were in regards to confusion and emotional blunting. Despite the promising nature of these preliminary results, our confidence in the evidence was limited by risk of bias and the small number of participants. Many trials did not provide information on all the prespecified outcomes and we found no data, or very limited data, on very important issues like suicidality, cognition, quality of life, costs to healthcare services and dropouts due to lack of efficacy.All included studies administered ketamine intravenously, which can pose practical problems in clinical practice. Very few trials were included in the meta-analyses for each comparison; the majority of comparisons contained only one study. Further RCTs (with adequate blinding) are needed to explore different modes of administration of ketamine with longer follow-up, which test the comparative efficacy of ketamine and the efficacy of repeated administrations.

Dehydroepiandrosterone, its metabolites and ion channels

This review is focused on the physiological and pathophysiological relevance of steroids influencing the activities of the central and peripheral nervous systems with regard to their concentrations in body fluids and tissues in various stages of human life like the fetal development or pregnancy. The data summarized in this review shows that DHEA and its unconjugated and sulfated metabolites are physiologically and pathophysiologically relevant in modulating numerous ion channels and participate in vital functions of the human organism. DHEA and its unconjugated and sulfated metabolites including 5α/β-reduced androstane steroids participate in various physiological and pathophysiological processes like the management of GnRH cyclic release, regulation of glandular and neurotransmitter secretions, maintenance of glucose homeostasis on one hand and insulin insensitivity on the other hand, control of skeletal muscle and smooth muscle activities including vasoregulation, promotion of tolerance to ischemia and other neuroprotective effects. In respect of prevalence of steroid sulfates over unconjugated steroids in the periphery and the opposite situation in the CNS, the sulfated androgens and androgen metabolites reach relevance in peripheral organs. The unconjugated androgens and estrogens are relevant in periphery and so much the more in the CNS due to higher concentrations of most unconjugated steroids in the CNS tissues than in circulation and peripheral organs. This article is part of a Special Issue entitled "Essential role of DHEA".

Paying attention to smell: cholinergic signaling in the olfactory bulb

The tractable, layered architecture of the olfactory bulb (OB), and its function as a relay between odor input and higher cortical processing, makes it an attractive model to study how sensory information is processed at a synaptic and circuit level. The OB is also the recipient of strong neuromodulatory inputs, chief among them being the central cholinergic system. Cholinergic axons from the basal forebrain modulate the activity of various cells and synapses within the OB, particularly the numerous dendrodendritic synapses, resulting in highly variable responses of OB neurons to odor input that is dependent upon the behavioral state of the animal. Behavioral, electrophysiological, anatomical, and computational studies examining the function of muscarinic and nicotinic cholinergic receptors expressed in the OB have provided valuable insights into the role of acetylcholine (ACh) in regulating its function. We here review various studies examining the modulation of OB function by cholinergic fibers and their target receptors, and provide putative models describing the role that cholinergic receptor activation might play in the encoding of odor information.

How theories evolved concerning the mechanism of action of barbiturates

The barbiturate phenobarbital has been in use in the treatment of epilepsy for 100 years. It has long been recognized that barbiturates act by prolonging and potentiating the action of γ-aminobutyric acid (GABA) on GABA(A) receptors and at higher concentrations directly activating the receptors. A large body of data supports the concept that GABA(A) receptors are the primary central nervous system target for barbiturates, including the finding that transgenic mice with a point mutation in the β3 GABA(A) -receptor subunit exhibit diminished sensitivity to the sedative and immobilizing actions of the anesthetic barbiturate pentobarbital. Although phenobarbital is only modestly less potent as a GABA(A) -receptor modulator than pentobarbital, phenobarbital is minimally sedating at effective anticonvulsant doses. Possible explanations for the reduced sedative effect of phenobarbital include more regionally restricted action; partial agonist activity; reduced propensity to directly activate GABA(A) receptors (possibly including extrasynaptic receptors containing δ subunits); and reduced activity at other ion channel targets, including voltage-gated calcium channels. In recent years, substantial progress has been made in defining the structural features of GABA(A) receptors responsible for gating and allosteric modulation by drugs. Although the precise sites of action of barbiturates have not yet been defined, the second and third transmembrane domains of the β subunit appear to be critical; binding may involve a pocket formed by β-subunit methionine 286 as well as α-subunit methionine 236. In addition to effects on GABA(A) receptors, barbiturates block AMPA/kainate receptors, and they inhibit glutamate release through an effect on P/Q-type high-voltage activated calcium channels. The combination of these various actions likely accounts for their diverse clinical activities. Despite the remarkable progress of the last century, there is still much to learn about the actions of barbiturates that can be applied to the discovery of new, more therapeutically useful agents.

Ketamine for treatment-resistant unipolar depression: current evidence

Currently available drugs for unipolar major depressive disorder (MDD), which target monoaminergic systems, have a delayed onset of action and significant limitations in efficacy. Antidepressants with primary pharmacological targets outside the monoamine system may offer the potential for more rapid activity with improved therapeutic benefit. The glutamate system has been scrutinized as a target for antidepressant drug discovery. The purpose of this article is to review emerging literature on the potential rapid-onset antidepressant properties of the glutamate NMDA receptor antagonist ketamine, an established anaesthetic agent. The pharmacology of ketamine and its enantiomer S-ketamine is reviewed, followed by examples of its clinical application in chronic, refractory pain conditions, which are commonly co-morbid with depression. The first generation of studies in patients with treatment-resistant depression (TRD) reported the safety and acute efficacy of a single subanaesthetic dose (0.5 mg/kg) of intravenous ketamine. A second generation of ketamine studies is focused on testing alternate routes of drug delivery, identifying methods to prevent relapse following resolution of depressive symptoms and understanding the neural basis for the putative antidepressant actions of ketamine. In addition to traditional depression rating endpoints, ongoing research is examining the impact of ketamine on neurocognition. Although the first clinical report in MDD was published in 2000, there is a paucity of adequately controlled double-blind trials, and limited clinical experience outside of research settings. Given the potential risks of ketamine, safety considerations will ultimately determine whether this old drug is successfully repositioned as a new therapy for TRD.

Effects of NMDA receptor antagonists on visceromotor reflexes and on intestinal motility, in vivo

Antagonists of NMDA receptors can inhibit both the transmission of pain signals from the intestine and enteric reflexes. However, it is unknown whether doses of the NMDA antagonist, ketamine, that are used in anaesthetic mixtures suppress motility reflexes and visceromotor responses (VMRs). In fact, whether intestinal motility is affected by NMDA receptor blockers in vivo has been little investigated. We studied the effects of ketamine and memantine, administered intravenously or intrathecally. Rats were maintained under alpha-chloralose plus xylazine or pentobarbitone anaesthesia; VMR and jejunal motility were measured. Under alpha-chloralose/xylazine anaesthesia, i.v. ketamine inhibited VMRs at 6 mg kg h(-1), but not at 3 mg kg h(-1). It did not inhibit propulsive reflexes in the jejunum at 10 mg kg h(-1), but reduced them by 30% at 20 mg kg h(-1). Under alpha-chloralose/pentobarbitone anaesthesia, i.v. ketamine reduced propulsive reflexes at 40 mg kg h(-1) and VMR at 10 mg kg h(-1). Memantine inhibited VMRs at 20 mg kg h(-1) and propulsion at 2 mg kg h(-1). Ketamine and memantine, intrathecally, prevented VMRs, but not jejunal propulsion. We conclude that peripherally administered ketamine reduces both VMR and motility reflexes, but not at doses used in anaesthetic mixes (1.8-2.4 mg kg h(-1)). Effects on motility reflexes are likely to be due to non-NMDA receptor actions, possibly on nicotinic receptors.

The effect of ketamine on intraspinal acetylcholine release: involvement of spinal nicotinic receptors

The general anaesthetic ketamine affects the central cholinergic system in several manners, but its effect on spinal acetylcholine release, which may be an important transmitter in spinal antinociception, is unknown. This study aimed to investigate the effect of ketamine on spinal acetylcholine release. Microdialysis probes were placed intraspinally in male rats, and acetylcholine was quantified with HPLC. Anaesthesia was switched from isoflurane (1.3%) to ketamine (150 mg/kg h), which resulted in a 500% increased acetylcholine release. The increase was attenuated during nicotinic receptor blockade (50 microM mecamylamine). The nicotinic receptor agonist epibatidine (175 microM) produced a ten-fold higher relative increase of acetylcholine release during isoflurane anaesthesia compared to ketamine anaesthesia (270% to 27%). Intraspinal administration of ketamine and norketamine both increased the acetylcholine release in high concentrations (100 microM to 10 mM). The results indicate that spinal nicotinic receptors are important for the ketamine-induced acetylcholine release, and that the effect is partly mediated at the spinal level.