Merits and Limitations of Studying Neuronal Depolarization-Dependent Processes Using Elevated External Potassium

Elevated extracellular potassium chloride is widely used to achieve membrane depolarization of cultured neurons. This technique has illuminated mechanisms of calcium influx through L-type voltage sensitive calcium channels, activity-regulated signaling, downstream transcriptional events, and many other intracellular responses to depolarization. However, there is enormous variability in these treatments, including durations from seconds to days and concentrations from 3mM to 150 mM KCl. Differential effects of these variable protocols on neuronal activity and transcriptional programs are underexplored. Furthermore, potassium chloride treatments in vitro are criticized for being poor representatives of in vivo phenomena and are questioned for their effects on cell viability. In this review, we discuss the intracellular consequences of elevated extracellular potassium chloride treatment in vitro, the variability of such treatments in the literature, the strengths and limitations of this tool, and relevance of these studies to brain functions and dysfunctions.

A Chronology for the Identification and Disclosure of Adverse Effects of Succinylcholine

BACKGROUND

New therapies are created to address specific problems and enjoy popularity as they enter widespread clinical use. Broader use can reveal unknown adverse effects and impact the life cycle significantly. Succinylcholine, a depolarizing neuromuscular blocker, was the product of decades of research surrounding the ancient compound, curare. It was introduced into practice in the 1950s by Burroughs Wellcome and Company (BW Co) and was welcomed due to its rapidly acting muscle relaxation effects. Global clinical use revealed adverse effects, both minor and major, in particular, hyperkalemia and malignant hyperthermia. We investigated when practitioners and the manufacturer became aware of these adverse effects, how information about these side effects was disseminated, and whether the manufacturer met the regulatory requirements of the time, specifically regarding the timely reporting of adverse effects.

SOURCES

Primary literature search using online and archived documents was conducted at the Wood Library-Museum of Anesthesiology, Schaumburg, IL. We consulted documents submitted by BW Co to federal authorities, through the Freedom of Information Act (FOIA), Food and Drug Administration (FDA) reports, promotional advertisements, package inserts, published articles, and textbooks.

RESULTS

Initial clinical testing in humans in 1952 found no adverse effects on cardiovascular or respiratory systems. Fasciculations and myalgia were early side effects described in case reports in 1952. Large-scale clinical trials in 1953 found abnormally long recovery times among some patients; the discovery of abnormal pseudocholinesterase enzyme activity was not fully demonstrated until the early 1960s. Bradycardia was first reported in 1957 in children, and in 1959 in adults. In 1960, animal studies reported a transient increase in plasma potassium; further experiments in 1969 clearly demonstrated succinylcholine-induced hyperkalemia in burn patients. Malignant hyperthermia was first described in 1966. Similar cases of elevated temperatures and muscle rigidity were described globally but the underlying mechanism was not elucidated until the 1990s. Standard anesthesia textbooks did not report major side effects of succinylcholine until 1960 and included newly documented side effects with each edition. BW Co's packaging contained warnings as early as the 1950s but were later updated in 1962 and beyond to reflect the newly discovered hyperkalemia and malignant hyperthermia.

CONCLUSION

Particularly given the regulatory environment of the time, BW Co appropriately reported the adverse effects of succinylcholine after market entry; it updated promotional and packaging material in a timely manner to reflect newly discovered adverse effects. The toxicity, though alarming and put clinicians on alert, did not seem to heavily impact succinylcholine's use, given its various desirable properties. It is still a choice muscle relaxant used today, although there are efforts to develop superior agents to replace succinylcholine.

Magnesium sulfate - An effective agent could delay the progression of fulminant malignant hyperthermia

Malignant hyperthermia (MH) is a life-threatening disease that occurs during general anaesthesia following exposure to succinylcholine (SCh), a depolarizing muscle relaxant, and volatile anaesthetics. Susceptibility to MH most commonly arises from mutations in the RyR1 gene, the Ca²⁺ release channel of skeletal muscle. Fulminant MH (f-MH) is the most dangerous form of MH, which presents a hypermetabolic cascade state, including very high temperature and carbon dioxide production, increased heart rate and oxygen consumption, mixed acidosis, rigid muscles, and rhabdomyolysis. Dantrolene is the only specific drug therapy for MH on the market. Without dantrolene, the reported mortality of f-MH is as high as 42.3%. Based on the participation of catecholamine in the hyperhaemodynamic response of f-MH and the demonstrated effective control of catecholamine release of magnesium sulfate, combined with the fact that magnesium and calcium have opposite effects on muscle contraction, I hypothesized that magnesium sulfate could be a choice for delaying the progression of f-MH while waiting for dantrolene treatment.

Growth of Staphylococcus epidermidis in Anaesthetic Resuscitative Drugs: Implications for Potential Contamination

This controlled laboratory study investigated the survival of Staphylococcus epidermidis (S. epidermidis) over a 24 hour period in four commonly drawn-up anaesthetic resuscitative drugs: suxamethonium, atropine, metaraminol and ephedrine. These drugs were prepared in typical therapeutic concentrations and then inoculated with S. epidermidis. Samples of the inoculated drug preparations were cultured on horse blood agar plates at 0, 2, 6, 12 and 24 hourly intervals and incubated for 24 hours.

Colony counts were performed at the end of the incubation period. Suxamethonium, atropine and metaraminol all showed an inhibitory effect on colony counts within the first six hours. There was a more gradual decline of colony counts over a 24 hour period in the ephedrine solution. This decline was similar to that occurring in the normal saline. It is concluded that suxamethonium, atropine and metaraminol do not support the survival of the common skin contaminant, S. epidermidis over a 24 hour period.

A study of intubating conditions: Sevoflurane versus propofol-suxamethonium in children

BACKGROUND

Endotracheal intubation is an integral part of general anaesthesia in children, and the choice of induction agents and technique may affect the ease of intubation and thus the outcome of paediatric patients. We compared the ease of endotracheal intubation following sevoflurane and propofol-suxamethonium induction using Helbo-Hansen score.

PATIENTS AND METHODS

A prospective, randomized double-blinded comparative study conducted on sixty-six children (two groups of 33 each) between the ages of 3-10 years undergoing different elective surgeries. Group I received intravenous propofol and intravenous suxamethonium while Group II had inhalational induction with sevoflurane in 60% nitrous oxide and oxygen. Data including intubating conditions, time to tracheal intubation and haemodynamic changes were analysed using SPSS version 18, with statistical significance set at P < 0.05.

RESULTS

Using the Helbo-Hansen intubation score, the study reveals that 28 patients (85%) scored 4, 5 (15.2%) scored 5 and no patient scored 6 in Group I whereas 15 (45.5%) scored 4, 16 (48.5%) scored 5 and 2 (6.1%) scored 6 in Group II with P = 0.002. The mean time taken from induction to laryngoscopy was 91.27 ± 29.96 s in Group I and 219.09 ± 63.88 s in Group II (with P < 0.0001); mean time taken from laryngoscopy to completion of intubation was 29.03 ± 10.61 s and 28.09 ± 9.48 s which was not statistically significant with P = 0.71.

CONCLUSION

Sevoflurane provides clinically acceptable intubating conditions and can be a suitable alternative to propofol-suxamethonium for endotracheal intubation in children. We recommend the use of sevoflurane to facilitate intubation in elective procedures in children.

[Danish Cholinesterase Research Unit diagnoses patients with prolonged paralysis after succinylcholine and mivacurium]

The Danish Cholinesterase Research Unit (DCRU) is a nationwide unit for patients carrying mutations in the butyrylcholinesterase enzyme (BChE). BChE hydrolyzes the neuromuscular blocking drugs succinylcholine and mivacurium. Patients with mutations in the butyrylcholinesterase gene are at risk of experiencing a prolonged effect of the drugs, such as weakness or paralysis for hours. In order to diagnose the referred patients correctly, DCRU combines results such as BChE activity, genotyping, pedigree and clinical reactions to succinylcholine or mivacurium.

[Danish Cholinesterase Research Unit diagnoses patients with prolonged paralysis after succinylcholine and mivacurium]

The Danish Cholinesterase Research Unit (DCRU) is a nationwide unit for patients carrying mutations in the butyrylcholinesterase enzyme (BChE). BChE hydrolyzes the neuromuscular blocking drugs succinylcholine and mivacurium. Patients with mutations in the butyrylcholinesterase gene are at risk of experiencing a prolonged effect of the drugs, such as weakness or paralysis for hours. In order to diagnose the referred patients correctly, DCRU combines results such as BChE activity, genotyping, pedigree and clinical reactions to succinylcholine or mivacurium.

Comparison of muscle paralysis after intravenous and intraosseous administration of succinylcholine in Swine

AIM

To compare the onset and duration of intravenous (IV) and intraosseous (IO) administration of succinylcholine in swine.

METHODS

Electromyographic (EMG) amplitudes were used to characterize muscle paralysis following administration of succinylcholine via the IV or IO route in four Yorkshire-cross swine.

RESULTS

The onset of action of succinylcholine was statistically longer after IO administration (0.97±0.40) compared with IV administration (0.55±0.26) (p=.048). Duration of action was unaffected by route of administration: IO, 11.4±4.2, and IV, 12.9±3.8 (p=.65).

CONCLUSIONS

Succinylcholine can be effectively administered via the IO route. However, an increased dose may be necessary when administering succinylcholine via the IO route to achieve the same rapid onset as standard IV dosing.

Inhibition of cholinergic signaling causes apoptosis in human bronchioalveolar carcinoma

Recent case-controlled clinical studies show that bronchioalveolar carcinomas (BAC) are correlated with smoking. Nicotine, the addictive component of cigarettes, accelerates cell proliferation through nicotinic acetylcholine receptors (nAChR). In this study, we show that human BACs produce acetylcholine (ACh) and contain several cholinergic factors including acetylcholinesterase (AChE), choline acetyltransferase (ChAT), choline transporter 1 (CHT1, SLC5A7), vesicular acetylcholine transporter (VAChT, SLC18A3), and nACh receptors (AChRs, CHRNAs). Nicotine increased the production of ACh in human BACs, and ACh acts as a growth factor for these cells. Nicotine-induced ACh production was mediated by α7-, α3β2-, and β3-nAChRs, ChAT and VAChT pathways. We observed that nicotine upregulated ChAT and VAChT. Therefore, we conjectured that VAChT antagonists, such as vesamicol, may suppress the growth of human BACs. Vesamicol induced potent apoptosis of human BACs in cell culture and nude mice models. Vesamicol did not have any effect on EGF or insulin-like growth factor-II-induced growth of human BACs. siRNA-mediated attenuation of VAChT reversed the apoptotic activity of vesamicol. We also observed that vesamicol inhibited Akt phosphorylation during cell death and that overexpression of constitutively active Akt reversed the apoptotic activity of vesamicol. Taken together, our results suggested that disruption of nicotine-induced cholinergic signaling by agents such as vesamicol may have applications in BAC therapy.

The effect of electroconvulsive therapy using propofol and succinylcholine on the intraocular pressure

PURPOSE

Electroconvulsive therapy (ECT) is a therapeutic procedure in many mood and psychiatric disorders. After induction of general anesthesia by administering an induction dose of an intravenous anesthetic such as Propofol, intravenous succinylcholine is often used to prevent bone fractures and joint dislocations during ECT. Intraocular pressure (IOP) is raised by succinylcholine and tonic-colonic convulsion,and decreased by propofol administration. To our knowledge, there is no published paper on the effect of ECT using propofol and succinylcholine on the IOP. This study for the first time shows the effect of ECT on IOP. The source of the financial support is a grant allocation of Zahedan University of Medical Sciences. There is no financial relationship between authors and commercial interest with a vested interest in the outcome of the study.

METHODS

One hundred patients 20 to 40 years old ASA class 1 or 2 without any ophthalmic disorders were enrolled. All of the psychiatric medications were discontinued 48 hours before ECT treatment. The baseline IOP values of the patients were checked after application of sterile eye drop tetracaine 0.5% by an applanation tonometer, and then the patients received atropine 0.5 mg, propofol 0.75 mg/kg, succinylcholine 1 mg/kg intravenously, with intervals of 1 minute. Then electrical stimulation was delivered via bi-frontal electrodes. IOPs were checked before any drug administration, before electrical application, as well as 1, 5 and 10 minutes after termination of the convulsion.

RESULTS

The baseline IOP (14.81 +/- 3.6 mmHg) decreased significantly after administration of propofol (13.18 +/- 3.55 mmHg) but increased significantly after succinylcholine (15.52 +/- 3.58 mmHg), one minute (18.32 +/- 3.49 mmHg) and 5 minutes after convulsion (15.41 +/- 3.46 mmHg). However, IOP returned to the baseline 10 minutes after convulsion (14.68 +/- 3.57 mmHg).

CONCLUSION

IOP increased after ECT but the IOP levels never reached to pathologic range in this study. Therefore, regarding IOP, ECT is a safe procedure in patients with normal eye condition. Further studies are recommended in older patients with ophthalmic diseases.

The effects of succinylcholine or low-dose rocuronium to aid endotracheal intubation of adult sows

This randomized, prospective, blinded study compared the use of succinylcholine or rocuronium to aid endotracheal intubation of 27 adult sows [mean body weight 261 ± 28 (standard deviation) kg]. Preliminary trials allowed development of the intubation technique and skills. The sows were premedicated with azaperone, atropine, and morphine, and anesthesia was induced with thiopental [6 mg/kg body weight (BW)]. Nine sows each received succinylcholine (1.0 mg/kg BW), rocuronium (0.5 mg/kg BW), or saline (15 mL) after induction. Increments of thiopental (1 mg/kg BW) were used if swallowing impaired intubation. Intubation was performed 45 s after injection of the test drug and was timed and scored. The intubation scores were analyzed with Kruskal-Wallis analysis of variance (ANOVA). Time taken for intubation, body weight, and total dose of thiopental were analyzed with ANOVA and Bonferroni's multiple-comparisons test. No significant differences (at P < 0.05) were found between the groups with regard to intubation score, time taken for intubation, or total thiopental dose. Thus, neuromuscular blocking agents did not aid endotracheal intubation of adult sows anesthetized with thiopental.

Modulation of neurite outgrowth by activation of calcium-permeable kainate receptors expressed by rat nociceptive-like dorsal root ganglion neurons

Neurite outgrowth is a fundamental step in establishing proper neuronal connections in the developing central nervous system. Dynamic control of outgrowth has been attributed to changes in growth cone Ca2+ levels in response to extracellular cues. Here we have investigated a possible role for Ca2+ permeable kainate (KA) receptors in regulating neurite outgrowth of nociceptive-like dorsal root ganglion (DRG) neurons. To identify KA receptor subunits likely to be involved, we used quantitative RT-PCR on acutely dissociated DRG and dorsal horn neurons. DRG neurons expressed more GluK1, particularly the GluK1b spice variant, than dorsal horn neurons. Conversely, dorsal horn neurons expressed more GluK2, particularly GluK2a, than DRG neurons. Further, an RNA editing assay indicated that the majority of GluK1 and GluK2 mRNA transcripts in DRG were unedited. Imaging Ca2+ transients following application of a KA receptor agonist to DRG and dorsal horn co-cultures revealed increases in intracellular Ca2+ in the growth cones of DRG neurons. In the majority of cases, this increase in Ca2+ was partly or completely blocked by Joro spider toxin (JSTX), an antagonist for Ca2+-permeable AMPA and KA receptors. Treatment of DRG/dorsal horn co-cultures with KA for 18 hours suppressed neurite outgrowth while application of the rapidly desensitizing KA receptor agonist SYM 2081, the competitive AMPA/KA receptor antagonist, CNQX, and JSTX or philanthotoxin enhanced neurite outgrowth and prevented KA effects on neurite outgrowth. Thus, Ca2+ entry through KA receptors at the growth cone of DRG neurons may be an important regulator of neurite outgrowth.

[Resistance to vecuronium induced muscle relaxation in a patient with mental retardation receiving phenytoin for chronic anticonvulsant therapy]

A 36-year-old woman weighing 31.7 kg with mental retardation was scheduled for dental treatment under general anesthesia. She had undergone anticonvulsant therapy (phenytoin, clonazepam, zonisamide) for years. Standard monitors and bispectral index (BIS) monitor were applied except for an accelomyography. Anesthesia was induced with propofol and vecuronium, and maintained with nitrous oxide in oxygen, with 1.5-2.0% end-tidal concentration of sevoflurane. Forty minutes after induction of anesthesia, spontaneous respiration (SR) started suddenly despite adequate depth of anesthesia (BIS value 35-40). Vecuronium 1 mg was administered and SR stopped immediately. After the event, however, SR started repeatedly and then additional vecuronium was administered every 30-40 minutes to stop SR until the end of the treatment. During the treatment, no factors (hypercapnia, hypoxemia, hyperthermia and so on) to shorten the muscle relaxation were observed. The treatment finished uneventfully She became awake rapidly and extubated. Post-extubation period was also uneventful. In this case, chronic phenytoin therapy induced resistance to vecuronium was highly suspected; however, since clonazepam and zonisamide have elevation effects on blood concentration of phenytoin, they might be also cofactors in resistance to vecuronium. Therefore, patients undergoing chronic anticonvulsant therapy should be paid more attention because they have resistance to neuromuscular blocking drugs.

Succinylcholine activation of human horizontal eye muscles

PURPOSE

Succinylcholine (Sch) can induce contracture in slow, multiply innervated muscle fibres of the extraocular muscles in animals of different species. Slow muscle fibres also exist in human eye muscle but their physiological properties have not been studied.

METHODS

Isometric tension development was recorded in the lateral and medial rectus muscles in 12 patients operated under general anaesthesia. A strain gauge probe was attached with 5-0 silk sutures to the muscle tendon. Recordings were made in 12 eye muscles with the tendon attached to the globe and in four muscles detached from the globe. Muscle activation was produced by i.v. injection of Sch at a dose of 0.2-0.3 mg/kg bodyweight.

RESULTS

  A single injection of Sch induced slow contractures lasting for several minutes. In the muscles attached to the globe, mean maximal isometric tension was 12.2 g in the lateral rectus and 12.8 g in the medial rectus. Similar tension was shown in the muscles detached from the globe.

CONCLUSIONS

The contracture of eye muscles in response to Sch showed characteristics typical of slow muscle fibre activation in amphibian and avian muscle and confirmed the participation of slow fibre systems in ocular motor control.

Emergency airway management

Emergency airway management is associated with a high complication rate. Evaluating the patient prior to airway management is important to identify patients with increased risk of failed airways. Pre-oxygenation of critically ill patients is less effective in comparison to less sick patients. Induction agents are often required, but most induction agents are associated with hypotension during emergency intubation. Use of muscle relaxants is controversial for emergency intubation, but they are commonly used in the emergency department. Supervision of emergency airway management by attending physicians significantly decreases complications. Standardized algorithms may increase the success of emergency intubation. Attention should be paid to cardiopulmonary stability in the immediate post-intubation period.

Depolarizing stimuli cause persistent and selective loss of orexin in rat hypothalamic slice culture

A hypothalamic neuropeptide orexin (hypocretin) is a critical regulator of physiological processes including sleep/wakefulness and feeding. Using organotypic slice culture of rat hypothalamus, we found that exposure to elevated extracellular concentration of K(+) (+10-30 mM) for 24-72h led to a substantial decrease in the number of neurons immunoreactive for orexin and a co-existing neuropeptide dynorphin-A. In contrast, the same treatment affected neither the number of melanin-concentrating hormone-immunoreactive neurons nor the number of total neurons. A substantial decrease of orexin-immunoreactive neurons was also induced by 72h treatment with 1-10 microM veratridine, a Na(+) channel activator. The effect of elevated K(+) was only partially reversible, and that of veratridine was virtually irreversible, although the decrease in orexin immunoreactivity was not associated with signs of cell damage assessed by propidium iodide uptake and Hoechst 33342 nuclear staining. In addition, the level of preproorexin mRNA did not decrease during treatment with elevated K(+) or veratridine. After treatment with elevated K(+) and veratridine, c-Fos immunoreactivity appeared in orexin-immunoreactive neurons but not in melanin-concentrating hormone-immunoreactive neurons, suggesting selective excitation of orexin neurons. However, the amount of orexin released extracellularly was paradoxically decreased by treatment with elevated K(+) and veratridine. Overall, these characteristics of orexin neurons may be taken into consideration to understand the behaviors of these neurons under physiological and pathophysiological conditions.

Carbachol regulates pacemaker activities in cultured interstitial cells of Cajal from the mouse small intestine

We studied the effect of carbachol on pacemaker currents in cultured interstitial cells of Cajal (ICC) from the mouse small intestine by muscarinic stimulation using a whole cell patch clamp technique and Ca2+-imaging. ICC generated periodic pacemaker potentials in the current-clamp mode and generated spontaneous inward pacemaker currents at a holding potential of-70 mV. Exposure to carbachol depolarized the membrane and produced tonic inward pacemaker currents with a decrease in the frequency and amplitude of the pacemaker currents. The effects of carbachol were blocked by 1-dimethyl-4-diphenylacetoxypiperidinium, a muscarinic M(3) receptor antagonist, but not by methotramine, a muscarinic M(2) receptor antagonist. Intracellular GDP-beta-S suppressed the carbachol-induced effects. Carbachol-induced effects were blocked by external Na+-free solution and by flufenamic acid, a non-selective cation channel blocker, and in the presence of thapsigargin, a Ca2+-ATPase inhibitor in the endoplasmic reticulum. However, carbachol still produced tonic inward pacemaker currents with the removal of external Ca2+. In recording of intracellular Ca2+ concentrations using fluo 3-AM dye, carbachol increased intracellular Ca2+ concentrations with increasing of Ca2+ oscillations. These results suggest that carbachol modulates the pacemaker activity of ICC through the activation of non-selective cation channels via muscarinic M(3) receptors by a G-protein dependent intracellular Ca2+ release mechanism.

Malignant hyperthermia and its implications in general dentistry

Malignant hyperthermia (MH) is an uncommon and potentially life-threatening pharmacogenetic disorder. This abnormality in muscle metabolism can be triggered by a variety of agents (particularly general anesthetics and stress), resulting in a rapid heart rate increase, muscle rigidity, acidosis, temperature elevation, rhabdomyolysis, and renal failure. Immediate discontinuing of triggering agents, oxygenation, cooling, and dantrolene are necessary to treat an episode. MH-susceptible patients often indicate a positive family history of experiencing an adverse event during anesthesia. Few diagnostic tests are available to screen patients; the most accurate test is a skeletal muscle biopsy. MH-susceptible patients can undergo surgical procedures as necessary. Careful exploration of the medical history will allow the clinician to make the necessary modifications to treat and manage an episode expediently.

[Does rocuronium displace the position of suxamethonium?]

A full stomach patient often requires a rapid sequence induction (RSI) technique to protect against gastric aspiration. Suxamethonium is the most common muscle relaxant used because it has a fast onset and a short duration. Unfortunately it can have serious side effects as a result of its membrane depolarizing effect and release of potassium. Rocuronium has been suggested to create intubating conditions similar to suxamethonium. However, it has been proved that suxamethonium creates superior intubation conditions to rocuronium in a large meta-analysis comparing intubation conditions. Once Org 25969 (sugammadex) is available to rapidly bind rocuronium and reverse its action, rocuronium may replace succinylcholine for rapid-sequence induction.

[Basic and clinical importance of nicotinic acetylcholine receptors]

Shortly after encountering the muscle surface, the motor axon releases agrin to the postsynaptic muscle membrane to regulate postsynaptic differentiation. Neural agrin activates postsynaptic muscle-specific kinase to induce aggregation of muscle nicotinic acetylcholine receptors (nAChR) expressed throughout the muscle surface into the subsynaptic area. Agrin also regulates the distribution of other synaptic proteins, including rapsyn, ErbB receptor. Rapsyn, 43-kd cytoplasmic protein, attaches to the beta subunit of synaptic nAChR and anchors it at the neuromuscular junction. Neureglin binds to ErbB receptors to activate a pathway that leads to enhance mature nAChR gene transcription in synaptic nuclei. While, a voltage change evoked by binding of acetylcholine to nAChR leads to down-regulate fetal nAChR expression in extrasynaptic nuclei. Denervation causes destruction of normal neuromuscular synapse and induces up-regulation of immature nAChR at extrajunctional sites. Importantly in clinical settings, the immature nAChR is resistant to non-depolarizing neuromuscular blocking agents and more sensitive to depolarizing muscle relaxants.

Effects of succinylcholine on the recovery of block produced by mivacurium in rats

This study investigates the effects of succinylcholine on the recovery of neuromuscular blockade produced by mivacurium in rats. In 48 anesthetized animals, the sciatic nerve was prepared and stimulated, and twitches of the flexor digitorum longus muscle were recorded. Animals were randomly divided into four groups (n = 12 each): bolus dose of succinylcholine 0.1 mg/kg (GroupSch), bolus dose of mivacurium 0.15 mg/kg (GroupMiv), bolus dose of mivacurium 0.15 mg/kg, followed by succinylcholine 0.1 mg/kg at 25% neuromuscular recovery from mivacurium (Group-MivSch(25)), or bolus dose of mivacurium 0.15 mg/kg, followed by succinylcholine 0.1 mg/kg at 75% neuromuscular recovery from mivacurium (GroupMivSch(75)). Onset times of neuromuscular block following succinylcholine in mivacurium-treated groups were comparable and significantly shorter than in GroupSch (p < 0.001). Duration of action of succinylcholine was more prolonged when it was given in the presence of deeper neuromuscular block induced by mivacurium (p < 0.001 in GroupMivSch(25) and p < 0.01 in GroupMivSch(75)). Our results suggest that, in rats, mivacurium administration has a significant potentiating effect on a subsequent succinylcholine-induced neuromuscular block.

[Anesthesia in malignant hyperthermia]

Malignant hyperthermia is a condition for which the anesthesiologist must be prepared to take specific measures. Associated mortality is high despite correct diagnosis and, occasionally, the right treatment. Malignant hyperthermia is rare in Spain, however, and perhaps for this reason the Spanish public health authorities have not made an effort to respond to persistent calls for a national reference center for study and diagnosis, such as can be found in other European countries. The problem of malignant hyperthermia may become worse in the near future due to changes in the population brought about by immigration. It is therefore necessary to establish appropriately revised protocols and action plans to cope with this possibility. A reference center cannot be created by individuals, but we can become more aware of the need to establish up-to-date protocols in our departments in order to be prepared for this situation.

Low dose domoic acid in neonatal rats abolishes nicotine induced conditioned place preference during late adolescence

In this study, neonatal rats were chronically exposed to low, non-convulsive doses of the kainate receptor agonist domoic acid (DOM), or saline. Later, as adolescents, all animals were tested in a nicotine-induced conditioned place preference (CPP) paradigm. As expected, a nicotine-induced CPP was evident in the adolescent control rats, but surprisingly, not in the DOM animals. This study demonstrates the importance of KA receptors in the development of normal adolescent behaviors manifested in response to the rewarding properties of nicotine.

Synaptic transmission and plasticity in an active cortical network

BACKGROUND

The cerebral cortex is permanently active during both awake and sleep states. This ongoing cortical activity has an impact on synaptic transmission and short-term plasticity. An activity pattern generated by the cortical network is a slow rhythmic activity that alternates up (active) and down (silent) states, a pattern occurring during slow wave sleep, anesthesia and even in vitro. Here we have studied 1) how network activity affects short term synaptic plasticity and, 2) how synaptic transmission varies in up versus down states.

METHODOLOGY/PRINCIPAL FINDINGS

Intracellular recordings obtained from cortex in vitro and in vivo were used to record synaptic potentials, while presynaptic activation was achieved either with electrical or natural stimulation. Repetitive activation of layer 4 to layer 2/3 synaptic connections from ferret visual cortex slices displayed synaptic augmentation that was larger and longer lasting in active than in silent slices. Paired-pulse facilitation was also significantly larger in an active network and it persisted for longer intervals (up to 200 ms) than in silent slices. Intracortical synaptic potentials occurring during up states in vitro increased their amplitude while paired-pulse facilitation disappeared. Both intracortical and thalamocortical synaptic potentials were also significantly larger in up than in down states in the cat visual cortex in vivo. These enhanced synaptic potentials did not further facilitate when pairs of stimuli were given, thus paired-pulse facilitation during up states in vivo was virtually absent. Visually induced synaptic responses displayed larger amplitudes when occurring during up versus down states. This was further tested in rat barrel cortex, where a sensory activated synaptic potential was also larger in up states.

CONCLUSIONS/SIGNIFICANCE

These results imply that synaptic transmission in an active cortical network is more secure and efficient due to larger amplitude of synaptic potentials and lesser short term plasticity.

Age-related physiological and morphological changes of muscle spindles in rats

Age-related physiological and morphological changes of muscle spindles were examined in rats (male Fischer 344/DuCrj: young, 4-13 months; middle-aged, 20-22 months; old, 28-31 months). Single afferent discharges of the muscle spindles in gastrocnemius muscles were recorded from a finely split dorsal root during ramp-and-hold (amplitude, 2.0 mm; velocity, 2-20 mm s(-1)) or sinusoidal stretch (amplitude, 0.05-1.0 mm; frequency, 0.5-2 Hz). Respective conduction velocities (CVs) were then measured. After electrophysiological experimentation, the muscles were dissected. The silver-impregnated muscle spindles were teased and then analysed using a light microscope. The CV and dynamic response to ramp-and-hold stretch of many endings were widely overlapped in old rats because of the decreased CV and dynamic response of primary endings. Many units in old rats showed slowing of discharge during the release phase under ramp-and-hold stretch and continuous discharge under sinusoidal stretch, similarly to secondary endings in young and middle-aged rats. Morphological studies revealed that primary endings of aged rat muscle spindles were less spiral or non-spiral in appearance, but secondary endings appeared unchanged. These results suggest first that primary muscle spindles in old rats are indistinguishable from secondary endings when determined solely by previously used physiological criteria. Secondly, these physiological results reflect drastic age-related morphological changes in spindle primary endings.

Depolarization-induced Rapid Generation of 2-Arachidonoylglycerol, an Endogenous Cannabinoid Receptor Ligand, in Rat Brain Synaptosomes

2-arachidonoylglycerol (2-AG) is an endogenous ligand for the cannabinoid receptors with a variety of potent biological activities. In this study, we first examined the effects of potassium-induced depolarization on the level of 2-AG in rat brain synaptosomes. We found that a significant amount of 2-AG was generated in the synaptosomes following depolarization. Notably, depolarization did not affect the levels of other molecular species of monoacylglycerols. Furthermore, the level of anandamide was very low and did not change markedly following depolarization. It thus appeared that the depolarization-induced accelerated generation is a unique feature of 2-AG. We obtained evidence that phospholipase C is involved in the generation of 2-AG in depolarized synaptosomes: U73122, a phospholipase C inhibitor, markedly reduced the depolarization-induced generation of 2-AG, and the level of diacylglycerol was rapidly elevated following depolarization. A significant amount of 2-AG was released from synaptosomes upon depolarization. Interestingly, treatment of the synaptosomes with SR141716A, a CB1 receptor antagonist, augmented the release of glutamate from depolarized synaptosomes. These results strongly suggest that the endogenous ligand for the cannabinoid receptors, i.e. 2-AG, generated through increased phospholipid metabolism upon depolarization, plays an important role in attenuating glutamate release from the synaptic terminals by acting on the CB1 receptor.

A comparison of intubating conditions in children following induction of anaesthesia with propofol and suxamethonium or propofol and remifentanil

Sixty ASA 1 and 2 children aged between 2 and 16 years who required tracheal intubation as part of anaesthesia for elective surgery were studied. We evaluated intubating conditions, haemodynamic responses and duration of apnoea following propofol 4 mg.kg-1 combined with either remifentanil 1.25 microg.kg-1 (group R), or suxamethonium 1 mg.kg-1 (group S). Tracheal intubation was graded as excellent, good or poor according to ease of laryngoscopy, vocal cord position, coughing, and jaw relaxation and limb movement. Thirty of group S and 28 of group R children were successfully intubated on the first attempt. Overall, intubation conditions were excellent or good in 26/30 (87%) patients in group S and 20/30 (67%) in group R (p<0.05). Mean apnoea time was 190 s in group S, and 362 s in group R (p<0.001). Heart rate increased in response to suxamethonium (p<0.01) and both systolic and diastolic blood pressure decreased in the remifentanil group (p<0.01).

Hippocampal mossy fiber sprouting and elevated trkB receptor expression following systemic administration of low dose domoic acid during neonatal development

We have previously reported that serial systemic injections of low-dose (subconvulsive) domoic acid (DOM) during early postnatal development produces changes in both behavior and hippocampal cytoarchitecture in aged rats (17 months) that are similar to those seen in existing animal models of temporal lobe epilepsy. Herein we report further hippocampal changes, consisting of mossy fiber sprouting and associated changes in the trkB receptor population in young adult (3 months) rats, and further, report that these changes show regional variation throughout the septo-temporal axis of the hippocampus. Groups of Sprague Dawley rat pups were injected daily from postnatal day 8-14 with either saline (n = 23) or 20 microg/kg DOM (n = 25), tested for key indicators of neonatal neurobehavioral development, and then left undisturbed until approximately 90 days of age, at which time brain tissue was removed, hippocampi were dissected, fixed and processed using either Timm's stain to visualize hippocampal mossy fiber sprouting (MFS) or trkB immunohistochemistry to visualize full length trkB receptors. Multiple sections from dorsal, mid, and ventral hippocampus were analyzed separately and all measures were conducted using image analysis software. The results indicate significant increases in MFS in the inner molecular layer in treated animals with corresponding changes in trkB receptor density. Further we identified significant increases in trkB receptor density in the hilus of the dentate gyrus and area CA3 and report increased mossy fiber terminal density in the stratum lucidum in treated rats. The magnitude of these changes differed between sections from dorsal, mid, and ventral hippocampus. We conclude that low dose neonatal DOM produces cytoarchitectural changes indicative of abnormal development and/or synaptic plasticity that are progressive with age and show regional variation within the hippocampal formation.

Neuromuscular block

Descriptions of the South American arrow poisons known as curares were reported by explorers in the 16th century, and their site of action in producing neuromuscular block was determined by Claude Bernard in the mid-19th century. Tubocurarine, the most important curare alkaloid, played a large part in experiments to determine the role of acetylcholine in neuromuscular transmission, but it was not until after 1943 that neuromuscular blocking drugs became established as muscle relaxants for use during surgical anaesthesia. Tubocurarine causes a number of unwanted effects, and there have been many attempts to replace it. The available drugs fall into two main categories: the depolarising blocking drugs and the nondepolarising blocking drugs. The former act by complex mixed actions and are now obsolete with the exception of suxamethonium, the rapid onset and brief duration of action of which remain useful for intubation at the start of surgical anaesthesia. The nondepolarising blocking drugs are reversible acetylcholine receptor antagonists. The main ones are the atracurium group, which possess a built-in self-destruct mechanism that makes them specially useful in kidney or liver failure, and the vecuronium group, which are specially free from unwanted side effects. Of this latter group, the compound rocuronium is of special interest because its rapid onset of action allows it to be used for intubation, and there is promise that its duration of action may be rapidly terminated by a novel antagonist, a particular cyclodextrin, that chelates the drug, thereby removing it from the acetylcholine receptors.

Amino acid release at the spinomedullary junction after inflammation of the TMJ region in male and female rats

Temporomandibular joint (TMJ) disorders are painful conditions that are more prevalent in women than men. This study tested the hypothesis that acute inflammation of the TMJ region evoked sex-related changes in amino acid transmitter concentrations at the trigeminal subnucleus/upper cervical cord (Vc/C2) junction, the major terminal zone for TMJ sensory afferents. Microdialysis samples were collected in male, intact and ovariectomized (OvX) female rats after injection of mustard oil into the TMJ region (TMJ-MO) under barbiturate anesthesia. Males displayed increases in glutamate, aspartate and serine at 5 min and secondary increases 40-45 min after TMJ-MO. Intact and OvX females given low dose estrogen (LE2) displayed increases in glutamate, aspartate and serine at 5 min but no secondary increase at 40 min, while OvX females given high dose estrogen (HE2) revealed no increases after TMJ-MO. Glycine increased 20 min after TMJ-MO in males and cycling females, but not in OvX rats. Perfusion of high potassium through the probe evoked similar increases in glutamate, aspartate and glycine in all groups. In separate experiments, perfusion of the glutamate-aspartate reuptake inhibitor, L-trans-2,4-pyrrolidine dicarboxylate (PDC), through the probe caused a prompt elevation in glutamate that was significantly greater in HE2 than LE2 females or males. These results suggested sex hormone status affects glutamatergic neurotransmission at the Vc/C2 junction by acting, in part, through modulation of glutamate reuptake. Altered amino acid transmitter release and/or availability at the Vc/C2 junction may contribute to differential processing of sensory input from the TMJ region in males and females.

Neuromuskuläre Blockade

Currently, the main aims of using neuromuscular blocking agents during general anaesthesia are the improvement of surgical and intubation conditions. Neuromuscular blocking agents themselves are neither analgesic nor anaesthetic. All agents interact with the acetylcholinergic receptor at the neuromuscular junction and induce a blockade either through a continuous activation imitating the effect of acetylcholine or through a competitive antagonism against acetylcholine. Succinylcholine is the only depolarizing muscle relaxant that is in clinical use. Non-depolarizing neuromuscular blockers may be grouped by their chemical structure into benzylisoquinolines or aminosteroids, and cover the complete range from short and intermediate, to long acting agents. Possible adverse drug reactions to the single agents are also related to their mechanism of action. Moreover, pharmacokinetic properties and effects such as histamine liberation could play an important role when choosing a myorelaxant. The depth of a neuromuscular block and recovery from paralysis can be monitored using qualitative and quantitative techniques. Therefore, the monitoring of neuromuscular recovery plays an important role in the prevention of postoperative complications due to residual paralysis. In case of residual paralysis, cholinesterase inhibitors are suitable for reversal.

Presynaptic inhibition by kainate receptors converges mechanistically with presynaptic inhibition by adenosine and GABAB receptors

Kainate receptors are widely reported to regulate the release of neurotransmitter in the CNS, but the mechanisms involved remain controversial. Previous studies have found that the kainate receptor agonist ATPA, which selectively activates Glu(K5)-containing kainate receptors, depresses glutamate release at Schaffer-collateral synapses in the hippocampus. In the present study, we provide pharmacological evidence that this depressant effect is mediated by Glu(K5)-containing heteromers, but is distinct from a similar depressant effect engaged by the kainate receptor agonist domoate. The depressant effect of ATPA is insensitive to antagonists for GABA(A), GABA(B), and adenosine receptors, and is also unaffected by lowering the release probability by reducing extracellular calcium. However, the effect of ATPA is partly occluded by prior activation of GABA(B) receptors and completely occluded by prior activation of adenosine receptors, suggesting a mechanistic convergence of heteromeric Glu(K5) kainate receptor signaling with GABA(B) receptors and adenosine receptors. The effects of domoate are partially occluded by both adenosine and GABA(B) receptor agonists, indicating at least a partial convergence of Glu(K5)-lacking kainate receptor signaling with these other pathways. The depressant effect of ATPA is not blocked by inhibition of serine/threonine protein kinases. These results suggest that ATPA and domoate inhibit glutamate release through mechanisms that converge with those of classical metabotropic receptor agonists, although they do so through different receptors.

Role of the plasma membrane calcium adenosine triphosphatase on domoate-induced intracellular acidification in primary cultures of cerebelar granule cells

Changes in intracellular pH (pH(i)) and cytosolic calcium concentration ([Ca(2+)](c)) caused by the glutamate agonist domoate (DOM) were studied in single cultured mouse cerebellar granule cells (CGC) by using the fluorescent probes 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein acetoxymethyl ester (BCECF-AM) and simultaneous evaluation of cytosolic calcium concentration with the fluorescent dye Fura-2 acetoxymethyl ester (Fura-2 AM). DOM caused a concentration-dependent increase in [Ca(2+)](c) and a concentration-dependent intracellular acidification of CGC. DOM-induced intracellular acidification was completely abolished by the use of Ca(2+)-free medium, suggesting that it was due mostly to an influx of extracellular calcium. The pH(i) decrease caused by DOM was also completely blocked in the presence of the AMPA/kainate receptor antagonist CNQX, indicating that the DOM-induced intracellular acidification was caused by DOM activation of the AMPA/kainate subtype of glutamate receptors. Different mechanisms that could be involved in DOM-induced pH(i) decrease, such as displacement of H(+) by Ca(2+) from a common intracellular binding site, DOM-induced alteration of pH(i) regulation mechanisms, and a possible acidification caused by DOM-induced increase of mitochondrial Ca(2+) uptake, were excluded. DOM-induced intracellular acidification was completely prevented by inhibitors of the plasma membrane calcium adenosine triphosphatase (ATPase) (PMCA), including orthovanadate, lanthanum extracellular pH of 8.5, and the specific PMCA inhibitor caloxin 2A1. Our results therefore indicate that PMCA is involved in DOM-induced intracellular acidification in primary cultures of CGC. Simultaneous recording of [Ca(2+)](c) and pH(i) indicates that the increase in intracellular calcium evoked by DOM will activate the calcium extrusion mechanisms through the calcium pump, which, in turn, will decrease intracellular pH by countertransport of H(+) ions.

The effect of lidocaine and sufentanil in preventing intraocular pressure increase due to succinylcholine and endotracheal intubation

BACKGROUND AND OBJECTIVE

Succinylcholine administration, laryngoscopy and tracheal intubation are followed by increased intraocular pressure. Various premedications have been advocated for preventing increases in intraocular pressure, especially in patients undergoing surgical repair of open globe due to penetrating eye trauma. Results of studies in this area have been controversial.

METHODS

In this double-blind study, three groups of 70 patients receiving sufentanil, lidocaine and placebo 90 s prior to intubation were evaluated and compared for intraocular pressure changes following succinylcholine administration, laryngoscopy and tracheal intubation.

RESULTS

Mean intraocular pressure measured 2 and 3 min after succinylcholine administration in groups receiving sufentanil and lidocaine was significantly lower than in the placebo group. Mean intraocular pressure changes in the three groups were -1.84, -2.03 and +2.82 mmHg, respectively in minute 2; -4.78, -4.73 and +1.35 mmHg, respectively in minute 5. There was a significant intraocular pressure decrease in the sufentanil and lidocaine groups, compared to the placebo group. The eye surgeons' satisfaction was also significantly higher with the sufentanil and lidocaine groups.

CONCLUSION

Previous studies have yielded controversial results as to the effect of sufentanil and lidocaine in preventing intraocular pressure following succinylcholine administration, laryngoscopy and tracheal intubation. The present study affirms the preventive effect of these drugs on intraocular pressure increase.

Increase of insulin secretion by ginsenoside Rh2 to lower plasma glucose in Wistar rats

1. The aim of the present study was to clarify the role of ginsenoside Rh2 as the active compound in Panax ginseng root for lowering plasma glucose in animals. 2. Plasma glucose was assessed using the glucose oxidase method. Changes in the levels of insulin and C-peptide in plasma were measured by ELISA using commercially available kits. 3. After intravenous injection into fasting Wistar rats for 60 min, ginsenoside Rh2 (0.1-1.0 mg/kg) decreased plasma glucose in a dose-dependent manner. In parallel with the decrease in plasma glucose, increases in plasma insulin levels, as well as plasma C-peptide, were observed in rats receiving the same treatment. These effects of Rh2 were reversed by atropine (0.1-1.0 mg/kg), but not affected by the ganglionic nicotinic antagonists pentolinium or hexamethonium (both at 7.5 mg/kg). 4. Disruption of synaptically available acetylcholine (ACh) using an inhibitor of choline uptake (hemicholinium-3; 1-10 microg/kg) or an inhibitor of vesicular ACh transport (vesamicol; 1.5-3.5 mg/kg) abolished the actions of Rh2. In addition, physostigmine (0.1-0.5 mg/kg), at a concentration sufficient to inhibit acetylcholinesterase, enhanced the actions of the ginsenoside Rh2. Thus, mediation of the effects of Rh2 to enhance insulin secretion by ACh released from nerve terminals can be considered. 5. Blockade of the increase in plasma insulin and the plasma glucose-lowering action of Rh2 by 4-diphenylacetoxy-N-methylpiperdine methiodide (4-DAMP; 5-10 microg/kg) indicates the participation of muscarinic M(3) receptors. Increases in plasma C-peptide level induced by Rh2 were also sensitive to 4-DAMP. 6. The results of the present study suggest that ginsenoside Rh2 has the ability to increase insulin secretion as a result of the release of ACh from nerve terminals that then stimulates muscarinic M(3) receptors in pancreatic cells. This finding shows the mechanism for the plasma glucose-lowering action of ginsenoside Rh2, that is one of the major principles contained in P. ginseng root. Thus, ginsenoside Rh2 may be applied as an adjuvant for the management of diabetes.

Activation and Inhibition of Human Muscular and Neuronal Nicotinic Acetylcholine Receptors by Succinylcholine

Background

Succinylcholine is one of the most widely used muscle relaxants in clinical anesthesia and emergency medicine. Although the clinical advantages and cardiovascular side effects are well known, its mechanism of action within the human nicotinic cholinergic receptor system remains to be understood. The aim of this study was to investigate the effect of succinylcholine on human muscle and neuronal nicotinic acetylcholine receptor (nAChR) subtypes.

Methods

Xenopus laevis oocytes were injected with human messenger RNA for muscle and neuronal nAChR subunits. Receptor activation, desensitization, and inhibition induced by the natural ligand acetylcholine or by succinylcholine was studied using a multichannel two-electrode voltage clamp setup. Responses were measured as peak current and net charge.

Results

Succinylcholine concentration-dependently activated the muscle-type nAChR with an EC50 value of 10.8 microm (95% confidence interval, 9.8-11.9 microm), and after the initial activation, succinylcholine desensitized the muscle-type nAChR. Succinylcholine did not activate the neuronal nAChR subtypes alpha3beta2, alpha3beta4, alpha4beta2, or alpha7 at concentrations up to 1 mm and was a poor inhibitor at these receptor subtypes, with IC50 values above 100 microm.

Conclusion

Succinylcholine activates the muscle-type nAChR followed by desensitization. The observation that succinylcholine does not inhibit the presynaptic alpha3beta2 autoreceptor at clinically relevant concentrations provides a possible mechanistic explanation for the typical lack of tetanic fade in succinylcholine-induced neuromuscular blockade. Finally, cardiovascular side effects (e.g., tachyarrhythmias) of succinylcholine are not mediated via direct activation of the autonomic ganglionic alpha3beta4 subtype because succinylcholine does not activate the neuronal nAChRs.

[Interaction between mivacurium and succinylcholine from a different point of view]

OBJECTIVES

Succinylcholine (SCH) may first be used and continue with mivacurium (MIV). MIV has been suggested as a pretreatment. Conflicting results arises from studies on SCH-MIV interaction. The following trial revisits this interaction.

PATIENTS AND METHODS

The patients were intubated after randomized administration of 100 microg x Kg(-1) of mivacurium (group 1) or 1 mg x Kg(-1) of succinylcholine and, after 50% recovery, 100 microg x Kg(-1) of mivacurium (group 2). A third group received the same regimen as group 2, preceded by pretreatment with 10 microg x Kg(-1) of mivacurium. Maximum effect (MAX), onset time, the 10%-25% recovery index, and duration of effect of mivacurium were determined by electromyography. In groups 2 and 3, the corrected MAX was defined as the difference between the actual MAX effect and the residual block after administration of succinylcholine, and speed of action was defined as the ratio between MAX or corrected MAX and onset time. Data were subjected to analysis of variance and Student-Newman-Keuls and t tests for bivariate comparisons. A value of P less than 0.05 was considered significant.

RESULTS

Groups 2 and 3 had significantly greater MAX effects (97% and 98%, respectively) in comparison with group 1 (93%), shorter onset times (135 and 158 seconds in groups 2 and 3 vs 279 seconds in group 1), and greater speed of action without changes in duration of effect. MAX was halved when corrected (to 47% and 49% in groups 2 and 3, respectively), and speed of action was significantly reduced (from 1.34 and 1.62 seconds/% in groups 2 and 3 respectively, to 2.69 and 3.36 seconds/%). Mivacurium pretreatment did not produce relevant clinical changes.

CONCLUSIONS

When mivacurium is used before the effects of succinylcholine disappear, a residual effect is not usually taken into consideration. This study corrected MAX and calculated speed of action, demonstrating a reduction in net block and speed of action, consistent with an antagonistic action when the 2 blockers are administered sequentially.

Rocuronium Versus Succinylcholine for Rapid Sequence Induction of Anesthesia and Endotracheal Intubation: A Prospective, Randomized Trial in Emergent Cases

When anesthesia is induced with propofol in elective cases, endotracheal intubation conditions are not different between succinylcholine and rocuronium approximately 60 s after the injection of the neuromuscular relaxant. In the present study, we investigated whether, in emergent cases, endotracheal intubation conditions obtained at the actual moment of intubation under succinylcholine differ from those obtained 60 s after the injection of rocuronium. One-hundred-eighty adult patients requiring rapid sequence induction of anesthesia for emergent surgery received propofol (1.5 mg/kg) and either rocuronium (0.6 mg/kg; endotracheal intubation 60 s after injection) or succinylcholine (1 mg/kg; endotracheal intubation as soon as possible). The time from beginning of the induction until completion of the intubation was shorter after the administration of succinylcholine than after rocuronium (median time 95 s versus 130 s; P < 0.0001). Endotracheal intubation conditions, rated with a 9-point scale, were better after succinylcholine administration than after rocuronium (8.6 +/- 1.1 versus 8.0 +/- 1.5; P < 0.001). There was no significant difference in patients with poor intubation conditions (7 versus 12) or in patients with failed first intubation attempt (4 versus 5) between the groups. We conclude that during rapid sequence induction of anesthesia in emergent cases, succinylcholine allows for a more rapid endotracheal intubation sequence and creates superior intubation conditions compared with rocuronium.

Depolarization-induced release of ethanolamine from brain synaptic preparations in vitro

The release of ethanolamine from mouse brain synaptosomes and synaptoneurosomes has been investigated. The depolarizing agents veratridine (50 microM), KCl (35 mM) and 4-aminopyridine (2 mM) enhanced the release of [3H]ethanolamine from preloaded synaptosomes under superfusion conditions. Tetrodotoxin (2 microM) strongly inhibited veratridine- and 4-aminopyridine-stimulated release of [3H]ethanolamine but had no effect on KCl-evoked or resting release. In the absence of calcium, a reduction in the resting release of [3H]ethanolamine occurred and release evoked by veratridine, and KCl was markedly reduced. Exposure of preloaded synaptosomes to 5 mM ethanolamine (but not 5 mM serine or 5 mM choline) calcium-dependently increased the efflux of [3H]ethanolamine, however, this was not accompanied by membrane depolarization. When these experiments were performed using synaptoneurosomes, qualitatively similar results were obtained. The resting and evoked release of [3H]ethanolamine was however approximately 2.5-fold higher compared to synaptosomes on a brain equivalent basis, suggesting that uptake and release occur at sites in addition to the nerve ending. Our data are consistent with the idea that a significant amount of ethanolamine accumulates presynaptically and undergoes calcium-dependent release upon depolarization possibly via classical exocytosis. In contrast, ethanolamine-induced release of [3H]ethanolamine likely involves mostly diffusional exchange across the neuronal membrane rather than base exchange. The present results add support to the concept that ethanolamine may play a role as a synaptic signaling molecule in mammalian brain.

Vesicles in snake motor terminals comprise one functional pool and utilize a single recycling strategy at all stimulus frequencies

At a variety of fast chemical synapses, spent synaptic vesicles are recycled via a large 'reserve' vesicle pool at high stimulus frequencies, and via fast 'local cycling' near release sites (e.g. 'kiss and run' transmitter release) at low stimulus frequencies. We have investigated recycling at the snake neuromuscular junction (NMJ), specifically seeking evidence for local cycling. Activity-dependent staining and destaining of the endocytic probe FM1-43 were directly compared to transmitter release over a range of stimulus frequencies. We found a fixed proportionality between staining/destaining and summed endplate potentials (EPPs) representing total transmitter release. There was no direct dependence of staining or destaining on stimulus frequency, as would be expected if local cycling (and consequent altered FM1-43 retention) were more prevalent at one frequency than another. In other experiments the drug vesamicol was used to abolish refilling of vesicles with transmitter, thereby blocking EPPs contributed by recycled vesicles. Control and vesamicol-treated NMJs had identical quantal content for the first 10 min of 1 Hz stimulation. Afterwards EPP amplitudes at vesamicol-treated NMJs declined at a rate consistent with use of a large pool containing approximately 130,000 vesicles. Finally, calibrated paired stimulations show that regenerated vesicles have poorer than random probability of re-release. Our findings are inconsistent with local cycling and suggest that the snake motor terminal utilizes exclusively a single large vesicle pool.

The use of the rat isolated vagus nerve for functional measurements of the effect of drugs in vitro

In this article we describe how to dissect, set up and use the rat isolated vagus nerve in a 'grease gap' apparatus which provides a simple and practical method for measuring the effects of drugs on the membrane potential of axons in the nerve in vitro. Some discussion of the origins and development of the technique as well as the strengths and disadvantages of the preparation as a neuropharmacological tool are included. The vagus nerve conducts action potentials in at least three distinct types of axons that can be measured extracellularly as compound action potentials and distinguished on the basis of their conduction velocity and excitability. Activity in myelinated A fibres and unmyelinated C fibres can be measured separately easily. The axons express receptors for a wide range of putative neurotransmitter agents including 5-HT, GABA and ATP as well as other agents such as capsaicin, anandamide, bradykinin and prostanoids. Responses to all of these chemicals can be measured as a depolarization of the nerve fibres. The vagus nerve is an important target for a wide range of drugs and the isolated preparation provides a fairly simple preparation for studying their effects. The isolated vagus nerve is also a convenient system in which the effects of drugs that have been discovered using heterologous expression systems can be assayed on receptors and ion channels that are expressed in a native neural system.