Allosteric inhibition of muscle-type nicotinic acetylcholine receptors by a neuromuscular blocking agent pancuronium.

Muscle relaxants are indispensable for surgical anesthesia. Early studies suggested that a classical non-depolarizing muscle relaxant pancuronium competitively binds to the ligand binding site to block nicotinic acetylcholine receptors (nAChR). Our group recently showed that nAChR which has two distinct subunit combinations are expressed in zebrafish muscles, αßδε and αßδ, for which potencies of pancuronium are different. Taking advantage of the distinct potencies, we generated chimeras between two types of nAChRs and found that the extracellular ACh binding site is not associated with the pancuronium sensitivity. Furthermore, application of either 2 µM or 100 µM ACh in native αßδε or αßδ subunits yielded similar IC50 of pancuronium. These data suggest that pancuronium allosterically inhibits the activity of zebrafish nAChRs.

Effect of preoperative ivabradine on hemodynamics during elective off-pump CABG.

Background: Ivabradine is a specific heart rate (HR)-lowering agent which blocks the cardiac pacemaker If channels. It reduces the HR without causing a negative inotropic or lusitropic effect, thus preserving ventricular contractility. The authors hypothesized that its usefulness in lowering HR can be utilized in patients undergoing off-pump coronary artery bypass (OPCAB) surgery. Objective: To study the effects of preoperative ivabradine on hemodynamics (during surgery) in patients undergoing elective OPCAB surgery. Methods: Fifty patients, New York Heart Association (NYHA) class I and II, were randomized into group I (control, n = 25) and group II (ivabradine group, n = 25). In group I, patients received the usual anti-anginal medications in the preoperative period, as per the institutional protocol. In group II, patients received ivabradine 5 mg twice daily for 3 days before surgery, in addition to the usual anti-anginal medications. Anesthesia was induced with fentanyl, thiopentone sodium, and pancuronium bromide as a muscle relaxant and maintained with fentanyl, midazolam, pancuronium bromide, and isoflurane. The hemodynamic parameters [HR and mean arterial pressure (MAP)] and pulmonary artery (PA) catheter-derived data were recorded at the baseline (before induction), 3 min after the induction of anesthesia at 1 min and 3 min after intubation and at 5 min and 30 min after protamine administration. Intraoperatively, hemodynamic data (HR and MAP) were recorded every 10 min, except during distal anastomosis of the coronary arteries when it was recorded every 5 min. Post-operatively, at 24 hours, the levels of troponin T and brain natriuretic peptide (BNP) were measured. This trial's CTRI registration number is CTRI/005858. Results: The HR in group II was lower when compared to group I (range 59.6-72.4 beats/min and 65.8-80.2 beats/min, respectively) throughout the study period. MAP was comparable [range (78.5-87.8 mm Hg) vs. (78.9-88.5 mm Hg) in group II vs. group I, respectively] throughout the study period. Intraoperatively, 5 patients received metoprolol in group I to control the HR, whereas none of the patients in group II required metoprolol. The incidence of preoperative bradycardia (HR <60 beats/min) was higher in group II (20%) vs. group I (8%). There was no difference in both the groups in terms of troponin T and BNP level after 24 hours, time to extubation, requirement of inotropes, incidence of arrhythmias, in-hospital morbidity, and 30-day mortality. Conclusion: Ivabradine can be safely used along with other anti-anginal agents during the preoperative period in patients undergoing OPCAB surgery. It helps to maintain a lower HR during surgery and reduces the need for beta-blockers in the intraoperative period, a desirable and beneficial effect in situations where the use of beta-blockers may be potentially harmful. Further studies are needed to evaluate the beneficial effects of perioperative Ivabradine in patients with moderate-to-severe left ventricular dysfunction.

Deep Tissue Incision Enhances Spinal Dorsal Horn Neuron Activity During Static Isometric Muscle Contraction in Rats.

Translational correlates to pain with activities after deep tissue injury have been rarely studied. We hypothesized that deep tissue incision causes greater activation of nociception-transmitting neurons evoked by muscle contraction. In vivo neuronal activity was recorded in 203 dorsal horn neurons (DHNs) from 97 rats after sham, skin-only, or skin + deep muscle incision. We evaluated DHN responses to static, isometric muscle contractions induced by direct electrical stimulation of the muscle. The effect of pancuronium on DHN response to contractions was also examined. Approximately 50% of DHNs with receptive fields in the hindpaw were excited during muscle contraction. One-second .5- and 1.0-g muscle contractions produced greater DHN activity after skin + deep muscle incision (median [interquartile range], 32 [5-39] impulses, P = .021; and 36 [26-46] impulses, P = .006, respectively) than after sham (6 [0-21] and 15 [8-32] impulses, respectively). Neuromuscular blockade with pancuronium inhibited the muscle contractions and DHN activation during electrical stimulation, demonstrating contraction-induced activation. The greater response of spinal DHNs to static muscle contraction after skin + deep muscle incision may model and inform mechanisms of dynamic pain after surgery. PERSPECTIVE: Completion of various activities is an important milestone for recovery and hospital discharge after surgery. Skin + deep muscle incision caused greater activation of nociception-transmitting DHNs evoked by muscle contraction compared with skin-only incision. This result suggests an important contribution of deep muscle injury to activity-evoked hyperalgesia after surgery.

Association between levobupivacaine and pancuronium. Interference in neuromuscular transmission and blockade in rats.

PURPOSE: To evaluate the effects of levobupivacaine on neuromuscular transmission and neuromuscular blockade produced by pancuronium in vitro. METHODS: Thirty rats were distributed into groups (n = 5) according to the drug used alone or in combination: Group I - levobupivacaine (5 µg.mL-1); Group II - pancuronium (2 µg.mL-1); Group III - pancuronium (2 µg.mL-1) + levobupivacaine (5µg.mL-1). The following parameters were evaluated: 1) amplitude of diaphragmatic response to indirect stimulation, before and 60 minutes after the addition of levobupivacaine and pancuronium alone, and after the addition of levobupivacaine combined with pancuronium; 2) membrane potentials (MP) and miniature endplate potentials (MEPP). RESULTS: Levobupivacaine alone did not alter the amplitude of muscle response and MP. In preparations previoulsy exposed to levobupivacaine, the block with pancuronium was significantly denser (90.2 ± 15.2%), showing a significant difference (p=0.031) in comparison to the block produced by pancuronium alone (48.9% ± 9.8%). There was a decrease in the frequency and amplitude of MEPPs. CONCLUSION: Levobupivacaine potentiated the neuromuscular blockade produced by pancuronium, confirming a presynaptic action by a decrease in miniature endplate potentials.

Association between levobupivacaine and pancuronium. Interference in neuromuscular transmission and blockade in rats

ABSTRACT PURPOSE: To evaluate the effects of levobupivacaine on neuromuscular transmission and neuromuscular blockade produced by pancuronium in vitro. METHODS: Thirty rats were distributed into groups (n = 5) according to the drug used alone or in combination: Group I - levobupivacaine (5 µg.mL-1); Group II - pancuronium (2 µg.mL-1); Group III - pancuronium (2 µg.mL-1) + levobupivacaine (5µg.mL-1). The following parameters were evaluated: 1) amplitude of diaphragmatic response to indirect stimulation, before and 60 minutes after the addition of levobupivacaine and pancuronium alone, and after the addition of levobupivacaine combined with pancuronium; 2) membrane potentials (MP) and miniature endplate potentials (MEPP). RESULTS: Levobupivacaine alone did not alter the amplitude of muscle response and MP. In preparations previoulsy exposed to levobupivacaine, the block with pancuronium was significantly denser (90.2 ± 15.2%), showing a significant difference (p=0.031) in comparison to the block produced by pancuronium alone (48.9% ± 9.8%). There was a decrease in the frequency and amplitude of MEPPs. CONCLUSION: Levobupivacaine potentiated the neuromuscular blockade produced by pancuronium, confirming a presynaptic action by a decrease in miniature endplate potentials.

Modulation of medial geniculate nucleus neuronal activity by electrical stimulation of the nucleus accumbens.

Dysfunctional sensory gating has been proposed to result in the generation of phantom perceptions. In agreement, it has been recently suggested that tinnitus, a phantom perception of sound commonly associated with hearing loss, is the result of a breakdown of circuitry involving the limbic system and the medial geniculate nucleus (MGN) of the thalamus. In humans with tinnitus, structural changes and abnormal activity have been found to occur in the auditory pathway as well as parts of the limbic system such as the nucleus accumbens (NAc). However, at present, no studies have been conducted on the influence of the NAc on the MGN. We investigated the functional connectivity between the NAc and MGN single neurons. Bipolar electrical stimulation was delivered to the NAc while recording single neuron activity in MGN in anesthetized Wistar rats. Histological analysis was used to confirm placement of electrodes. NAc electrical stimulation generally decreased spontaneous firing rates in MGN neurons and, in a limited number of neurons, caused an increase in firing rate. This suggests that NAc can modulate the activity of auditory neurons in the MGN and may play a role in the development of tinnitus.

Effect of ropivacaine combined with pancuronium on neuromuscular transmission and effectiveness of neostigmine and 4-aminopyridine for blockade reversal: experimental study / Efeito da associação ropivacaina-pancurônio na transmissão neuromuscular e eficácia da neostigmine e 4-aminopiridina na reversão do bloqueio: estudo experimental / Efecto de la asociación ropivacaína-pancuronio en la transmisión neuromuscular. Eficacia de la neostigmina y 4-aminopiridina en la reversión del bloqueo. Estudio experimental

BACKGROUND AND OBJECTIVES: The local anesthetic effects on neuromuscular junction and its influence on blockade produced by nondepolarizing neuromuscular blockers are still under-investigated; however, this interaction has been described in experimental studies and in humans. The aim of this study was to evaluate in vitro the interaction between ropivacaine and pancuronium, the influence on transmission and neuromuscular blockade, and the effectiveness of neostigmine and 4-aminopyridine to reverse the blockade. METHODS: Rats were divided into groups (n = 5) according to the study drug: ropivacaine (5 µg mL-1); pancuronium (2 µg mL-1); ropivacaine + pancuronium. Neostigmine and 4-aminopyridine were used at concentrations of 2 µg mL-1 and 20 µg mL-1, respectively. The effects of ropivacaine on membrane potential and miniature endplate potential, the amplitude of diaphragm responses before and 60 min after the addition of ropivacaine (degree of neuromuscular blockade with pancuronium and with the association of pancuronium-ropivacaine), and the effectiveness of neostigmine and 4-aminopyridine on neuromuscular block reversal were evaluated. RESULTS: Ropivacaine did not alter the amplitude of muscle response (the membrane potential), but decreased the frequency and amplitude of the miniature endplate potential. Pancuronium blockade was potentiated by ropivacaine, and partially and fully reversed by neostigmine and 4-aminopyridine, respectively. CONCLUSIONS: Ropivacaine increased the neuromuscular block produced by pancuronium. The complete antagonism with 4-aminopyridine suggests presynaptic action of ropivacaine. .

JUSTIFICATIVA E OBJETIVOS: Os efeitos dos anestésicos locais na junção neuromuscular e sua influência no bloqueio produzido por bloqueadores neuromusculares não-despolarizantes é ainda alvo de pouca investigação, no entanto esta interação tem sido descrita em trabalhos experimentais e em humanos. O objetivo deste estudo foi avaliar in vitro, a interação da ropivacaína com o pancurônio, a influência na transmissão e bloqueio neuromuscular e a efetividade da neostigmina e 4-aminopiridina na reversão do bloqueio. MÉTODO: Ratos foram distribuídos em grupos (n = 5) de acordo com o fármaco estudado: ropivacaína (5 µg mL-1); pancurônio (2 µg mL-1); ropivacaína + pancurônio. A neostigmina e a 4-aminopiridina foram usadas nas concentrações de 2 µg mL-1 e 20 µg.mL-1, respectivamente. Avaliou-se: 1) efeitos da ropivacaína sobre o potencial de membrana e potenciais de placa terminal em miniatura; 2) a amplitude das respostas do diafragma antes e 60 minutos após a adição da ropivacaína; o grau de bloqueio neuromuscular com o pancurônio e com a associação pancurônio - ropivacaína; 3) a efetividade da neostigmina e 4-aminopiridina na reversão do bloqueio neuromuscular. RESULTADOS: A ropivacaína não alterou a amplitude das respostas musculares, os potenciais de membrana, mas diminuiu a frequência e a amplitude dos potenciais de placa terminal em miniatura. O bloqueio produzido pelo pancurônio foi potencializado pela ropivacaína, e parcial e totalmente revertido pela neostigmina e 4-aminopiridina, respectivamente. CONCLUSÕES: A ropivacaína potencializou o bloqueio neuromuscular produzido pelo pancurônio. O antagonismo completo com a 4-aminopiridina sugere ação pré-sináptica da ropivacaína. .

JUSTIFICACIÓN Y OBJETIVOS: Los efectos de los anestésicos locales en la unión neuromuscular y su influencia en el bloqueo producido por bloqueantes neuromusculares no-despolarizantes todavía son poco investigados, sin embargo, esta interacción ha sido descrita en trabajos experimentales y en seres humanos. El objetivo de este estudio fue evaluar in vitro la interacción de la ropivacaína con el pancuronio, la influencia en la transmisión y bloqueo neuromuscular y la efectividad de la neostigmina y 4-aminopiridina en la reversión del bloqueo. MÉTODO: Unos ratones fueron distribuidos en grupos (n = 5) de acuerdo con el fármaco estudiado: ropivacaína (5 µg/ml-1); pancuronio (2 µg/ml-1); ropivacaína + pancuronio. La neostigmina y la 4-aminopiridina fueron usadas en concentraciones de 2 µg/ml-1 y 20 µg/ml-1, respectivamente. Evaluamos: 1) efectos de la ropivacaína sobre el potencial de membrana y potenciales de placa terminal en miniatura; 2) la amplitud de las respuestas del diafragma antes y 60 min después de la adición de la ropivacaína; el grado de bloqueo neuromuscular con el pancuronio y con la asociación pancuronio-ropivacaína; 3) la efectividad de la neostigmina y 4-aminopiridina en la reversión del bloqueo neuromuscular. RESULTADOS: La ropivacaína no alteró la amplitud de las respuestas musculares, los potenciales de membrana, pero disminuyó la frecuencia y la amplitud de los potenciales de placa terminal en miniatura. El bloqueo producido por el pancuronio fue potenciado por la ropivacaína, y parcial y totalmente revertido por la neostigmina y 4-aminopiridina, respectivamente. CONCLUSIONES: La ropivacaína potenció el bloqueo neuromuscular producido por el pancuronio. El antagonismo completo con la 4-aminopiridina muestra una acción presináptica de la ropivacaína. .

Novel strategy for biofilm inhibition by using small molecules targeting molecular chaperone DnaK.

Biofilms are complex communities of microorganisms that attach to surfaces and are embedded in a self-produced extracellular matrix. Since these cells acquire increased tolerance against antimicrobial agents and host immune systems, biofilm-associated infectious diseases tend to become chronic. We show here that the molecular chaperone DnaK is important for biofilm formation and that chemical inhibition of DnaK cellular functions is effective in preventing biofilm development. Genetic, microbial, and microscopic analyses revealed that deletion of the dnaK gene markedly reduced the production of the extracellular functional amyloid curli, which contributes to the robustness of Escherichia coli biofilms. We tested the ability of DnaK inhibitors myricetin (Myr), telmisartan, pancuronium bromide, and zafirlukast to prevent biofilm formation of E. coli. Only Myr, a flavonol widely distributed in plants, inhibited biofilm formation in a concentration-dependent manner (50% inhibitory concentration [IC50] = 46.2 µM); however, it did not affect growth. Transmission electron microscopy demonstrated that Myr inhibited the production of curli. Phenotypic analyses of thermosensitivity, cell division, intracellular level of RNA polymerase sigma factor RpoH, and vulnerability to vancomycin revealed that Myr altered the phenotype of E. coli wild-type cells to make them resemble those of the isogenic dnaK deletion mutant, indicating that Myr inhibits cellular functions of DnaK. These findings provide insights into the significance of DnaK in curli-dependent biofilm formation and indicate that DnaK is an ideal target for antibiofilm drugs.

Haemodynamic differences between pancuronium and vecuronium in an experimental pig model.

OBJECTIVE: To compare baseline cardiovascular function in anesthetised pigs using either pancuronium or vecuronium as a neuromuscular blocker. STUDY DESIGN: Retrospective, non-randomized comparison. ANIMALS: Norwegian Land Race pigs (Sus scrofa domesticus) weighing mean 42 ± SD 3 kg. METHODS: One hundred and sixteen animals from four different research protocols premedicated with identical doses of ketamine, diazepam, atropine and isoflurane, and anaesthetised with pentobarbital, fentanyl, midazolam and N(2)O were arranged into three uniform groups with respect to neuromuscular blocking agent: pancuronium bolus of 0.063 mg kg(-1) followed by 0.14 mg kg(-1) hour(-1) (n = 54), low-dose vecuronium 0.4 mg kg(-1) /0.2 mg kg(-1) hour(-1) (n = 29) and high-dose vecuronium 0.6 mg kg(-1) /0.3 mg kg(-1) hour(-1) (n = 33). RESULTS: The majority of cardiovascular parameters demonstrated no significant differences between groups. For heart rate, there was an overall group difference, p = 0.036. Dromotropy was low in the pancuronium group, with an increased normalised PR-interval compared to the high-dose vecuronium group, median 0.200 interquartile range (0.190, 0.215) versus 0.182 (0.166, 0.199), p < 0.05. Left ventricular compliance was increased in pancuronium-treated animals, demonstrated as a reduction in the nonlinear end-diastolic pressure volume relationship ß compared to both vecuronium groups, 0.021 (0.016, 0.025) versus 0.031 (0.025, 0.046) and 0.031 (0.022, 0.048), p < 0.05. The linear end-diastolic pressure volume relationship EDPVR(lin) was reduced as well in the pancuronium group, compared to the low-dose vecuronium group, 0.131 (0.116, 0.169) versus 0.181 (0.148, 0.247), p < 0.05. CONCLUSIONS: There are only minor haemodynamic differences when using pancuronium compared to vecuronium in the fentanyl-pentobarbital-midazolam-N(2)O anesthetised domestic pigs. Furthermore, increasing doses of vecuronium have minimal haemodynamic effects. CLINICAL RELEVANCE: Experimental studies in pigs using either pancuronium or vecuronium as a neuromuscular blocking agent are comparable with regard to cardiac and haemodynamic performance.

The comparison of spontaneous breathing and muscle paralysis in two different severities of experimental lung injury.

OBJECTIVES: The benefits of spontaneous breathing over muscle paralysis have been proven mainly in mild lung injury; no one has yet evaluated the effects of spontaneous breathing in severe lung injury. We investigated the effects of spontaneous breathing in two different severities of lung injury compared with muscle paralysis. DESIGN: Prospective, randomized, animal study. SETTING: University animal research laboratory. SUBJECTS: Twenty-eight New Zealand white rabbits. INTERVENTIONS: Rabbits were randomly divided into the mild lung injury (surfactant depletion) group or severe lung injury (surfactant depletion followed by injurious mechanical ventilation) group and ventilated with 4-hr low tidal volume ventilation with spontaneous breathing or without spontaneous breathing (prevented by a neuromuscular blocking agent). Inspiratory pressure was adjusted to control tidal volume to 5-7 mL/kg, maintaining a plateau pressure less than 30 cm H2O. Dynamic CT was used to evaluate changes in lung aeration and the regional distribution of tidal volume. MEASUREMENTS AND RESULTS: In mild lung injury, spontaneous breathing improved oxygenation and lung aeration by redistribution of tidal volume to dependent lung regions. However, in severe lung injury, spontaneous breathing caused a significant increase in atelectasis with cyclic collapse. Because of the severity of lung injury, this group had higher plateau pressure and more excessive spontaneous breathing effort, resulting in the highest transpulmonary pressure and the highest driving pressure. Although no improvements in lung aeration were observed, muscle paralysis with severe lung injury resulted in better oxygenation, more even tidal ventilation, and less histological lung injury. CONCLUSIONS: In animals with mild lung injury, spontaneous breathing was beneficial to lung recruitment; however, in animals with severe lung injury, spontaneous breathing could worsen lung injury, and muscle paralysis might be more protective for injured lungs by preventing injuriously high transpulmonary pressure and high driving pressure.

Adenosine A(2A) receptor antagonists are broad facilitators of antinicotinic neuromuscular blockade monitored either with 2 Hz train-of-four or 50 Hz tetanic stimuli.

1. The 2 Hz train-of-four ratio (TOF(ratio)) is used to monitor the degree of patient curarization. Using a rat phrenic nerve-hemidiaphragm preparation, we showed that antinicotinic agents, such as hexamethonium, d-tubocurarine and pancuronium, but not cisatracurium, decreased contractions produced by physiological nerve activity patterns (50 Hz) more efficiently than those caused by 2 Hz trains. Uncertainty about the usefulness of the TOF(ratio) to control safe recovery from curarization prompted us to investigate the muscarinic and adenosine neuromodulation of tetanic (50 Hz) fade induced by antinicotinic agents at concentrations that cause a 25% reduction in the TOF(ratio) (TOF(fade)). 2. Tetanic fade caused by d-tubocurarine (1.1 µmol/L), pancuronium (3 µmol/L) and hexamethonium (5.47 mmol/L) was attenuated by blocking presynaptic inhibitory muscarinic M(2) and adenosine A(1) receptors with methoctramine (1 µmol/L) and 1,3-dipropyl-8-cyclopentylxanthine (2.5 nmol/L), respectively. These compounds enhanced rather than decreased tetanic fade induced by cisatracurium (2.2 µmol/L), but they consistently attenuated cisatracurium-induced TOF(fade). The effect of the M(1) receptor antagonist pirenzepine (10 nmol/L) on fade produced by antinicotinic agents at 50 Hz was opposite to that observed with TOF stimulation. Blockade of adenosine A(2A) receptors with ZM 241385 (10 nmol/L) attenuated TOF(fade) caused by all antinicotinic drugs tested, with the exception of the 'pure' presynaptic nicotinic antagonist hexamethonium. ZM 241385 was the only compound tested in this series that facilitated recovery from tetanic fade produced by cisatracurium. 3. The data suggest that distinct antinicotinic relaxants interfere with fine-tuning neuromuscular adaptations to motor nerve stimulation patterns via activation of presynaptic muscarinic and adenosine receptors. These results support the use of A(2A) receptor antagonists together with atropine to facilitate recovery from antinicotinic neuromuscular blockade.

Pancuronium dose refinement in experimental pigs used in cardiovascular research.

OBJECTIVE: To quantify the dose of pancuronium required to obtain moderate neuromuscular blockade as monitored by acceleromyography (NMB(mod) : train-of-four count of ≤2) as a part of a balanced anaesthetic protocol in pigs used in cardiovascular research. STUDY DESIGN: Prospective cross-sectional study. ANIMALS: Five pigs (median body weight: 60 (range 60-63) kg). METHODS: Anaesthesia was induced with xylazine, ketamine, atropine and midazolam and maintained with isoflurane in O(2) :air and fentanyl. Pigs received 0.1 mg kg(-1) pancuronium initial bolus to reach NMB(mod) followed by 0.1 mg kg(-1) hour(-1) constant rate infusion (CRI). During anaesthesia a twitch count of 3 or measureable T4/T1 ratio indicated unsatisfactory NMB. In this case additional 0.4 mg boluses of pancuronium were administered IV to effect in addition to the CRI. Descriptive statistical analysis was performed to express the median and range of the bolus and CRI dose of pancuronium in pigs. Cardiovascular parameters were analyzed at selected time points with Friedman Repeated Measures Analysis on Ranks. Spearman Rank test was used to evaluate correlation between parameters. RESULTS: Acceleromyographic monitoring of NMB is feasible in anaesthetized pigs. The median initial dose and rate of pancuronium required to achieve NMB(mod) were 0.10 (range 0.10-0.13) mg kg(-1) and 0.11 (range 0.10-0.21) mg kg(-1) hour(-1) , respectively. The administration rate showed considerable individual variation. CONCLUSIONS AND CLINICAL RELEVANCE: These pancuronium doses can be used as a guideline to achieve NMB(mod) in pigs as part of a balanced anaesthetic protocol. Instrumental NMB monitoring is essential because of individual kinetic variations and compliance to monitoring guidelines.

Variability in the muscle composition of rat esophagus and neural pathway of lower esophageal sphincter relaxation.

Several studies from our laboratory show that axial stretch of the lower esophageal sphincter (LES) in an oral direction causes neurally mediated LES relaxation. Under physiological conditions, axial stretch of the LES is caused by longitudinal muscle contraction (LMC) of the esophagus. Because longitudinal muscle is composed of skeletal muscle in mice, vagal-induced LMC and LES relaxation are both blocked by pancuronium. We conducted studies in rats (thought to have skeletal muscle esophagus) to determine if vagus nerve-mediated LES relaxation is also blocked by pancuronium. LMC-mediated axial stretch on the LES was monitored using piezoelectric crystals. LES and esophageal pressures were monitored with a 2.5-Fr solid-state pressure transducer catheter. Following bilateral cervical vagotomy, the vagus nerve was stimulated electrically. LES, along with the esophagus, was harvested after in vivo experiments and immunostained for smooth muscle (smooth muscle α-actin) and skeletal muscle (fast myosin heavy chain). Vagus nerve-stimulated LES relaxation and esophageal LMC were reduced in a dose-dependent fashion and completely abolished by pancuronium (96 µg/kg) in six rats (group 1). On the other hand, in seven rats, LES relaxation and LMC were only blocked completely by a combination of pancuronium (group 2) and hexamethonium. Immunostaining revealed that the longitudinal muscle layer was composed of predominantly skeletal muscle in the group 1 rats. On the other hand, the longitudinal muscle layer of group 2 rats contained a significant amount of smooth muscle (P < 0.05). Our study shows tight coupling between axial stretch on the LES and relaxation of the LES, which suggests a cause and effect relationship between the two. We propose that the vagus nerve fibers that cause LMC induce LES relaxation through the stretch-sensitive activation of inhibitory motor neurons.

Intact internal dynamics of the neocortex in acutely paralyzed mice.

Animals collect sensory information through self-generated movements. Muscle movements drive active feedback of sensory information and determine large parts of the sensory inputs the animal receives; however, little is known about how this active feedback process modulates the ongoing dynamics of the brain. We made electrophysiological recordings from layer 2/3 neurons of the mouse neocortex and compared spontaneous cortical activity in local field potentials and intracellular potential fluctuations between normal and hypomyotonic conditions. We found that pancuronium-induced paralysis did not affect the electrophysiological properties of ongoing cortical activity and its perturbation evoked by visual and tactile stimuli. Thus, internal cortical dynamics are not much affected by active muscle movements, at least, in an acute phase.

SUGAMADEX: novos horizontes para a reversão do bloqueio neuromuscular / SUGAMMADEX: new horizons for the reversal of neuromuscular blockade

O sugamadex é uma droga nova e revolucionária desenvolvida como antagonista seletivo dos agentes bloqueadores neuromusculares (ABNM) esteroides (rocurônio > vecurônio ¼ pancurônio). O medicamento é uma y-ciclodextrina modificada e hidrossolúvel que forma um composto estável com o ABNM na razão de 1:1. Ele se liga ao ABNM livre no plasma, criando um gradiente de concentração que desloca o ABNM dos receptores nicotínicos na junção neuromuscular, levando à reversão completa e duradoura do BNM. O sugamadex não se liga às proteínas ou a qualquer outro receptor no organismo, o que lhe confere ótimo perfil de tolerância. O sugamadex pode ser usado na reversão do BNM profundo, promovendo recuperação mais rápida em relação à succinilcolina. Seu emprego pode diminuir a necessidade de monitorização do BNM, a incidência de bloqueio residual e ainda evitar os efeitos adversos causados pelos anticolinesterásicos e anticolinérgicos. Entretanto, também há limitações em relação à utilização 00 sugamadex. Ele impede o uso dos AB- NMs esteroides durante 24 horas, caso seja necessário novo BNM, e pode aumentar o risco do emprego desnecessário e indiscriminado dos ABNMs. Além disso, faltam dados da sua utilização em alguns grupos populacionais e de seu uso em larga escala. Por fim, deve-se considerar também o fator econômico, visto que se trata de uma droga nova e de valor ainda elevado no mercado...

Sugammadex is a novel and unique compaund designed as a selective antaganist ot steroidal neuromuscular blaeking agents (NMBA) (rocuronium>vecuronium¼pancuronium). The drug is a modified water-saluble y-cyclodextrin that forms a stable complex at a 1:1 ratio with the NMBA. It combines with the NMBA creating a concentration gradient favoring the movement ot the NMBA from the nicotine receptors ot the neuromuscular junction leading to the complete and lasting reversal af the neuromuscular blockade (NMB). Sugamadex does not bind to plasma proteins or any other receptors system in the body what provides him a great tolerance profile. Sugamadex can be used in the reversal af deep neuromuscular blockade with a faster recovery time in relation to succinylcholine. Its use can diminish the necessity af monitoring af the NMB, the incidence ot residual blockade and still prevent the adverse effects caused by the antiecholinesterase and anticholinergic drugs. However, there are limitatians regarding the use af Sugammadex. It hinders the use ot the steroidal NMBA during 24 hours if a new NMB must be restablished and it can increase the risk ot unnecessary and indiscriminate use af the NMBA. Mareaver, there is a laek ot data regarding the its use in some population groups and in large scale. Final/y, the economic factor must be also considered, since it is a new drug with a still raised value in market...

Effects of common anesthetics on eye movement and electroretinogram.

High-resolution magnetic resonance imaging (MRI) provides non-invasive images of retinal anatomy, physiology, and function with depth-resolved laminar resolution. Eye movement and drift, however, could limit high spatial resolution imaging, and anesthetics that minimize eye movement could significantly attenuate retinal function. The aim of this study was to determine the optimal anesthetic preparations to minimize eye movement and maximize visual-evoked retinal response in rats. Eye movements were examined by imaging of the cornea with a charge-coupled device (CCD) camera under isoflurane, urethane, ketamine/xylazine, and propofol anesthesia at typical dosages in rats. Combination of the paralytic pancuronium bromide with isoflurane or ketamine/xylazine anesthesia was also examined for the eye movement studies. Visual-evoked retinal responses were evaluated using full-field electroretinography (ERG) under isoflurane, ketamine/xylazine, urethane, and ketamine/xylazine + pancuronium anesthesia in rats. The degree of eye movement, measured as displacement per unit time, was the smallest under 1% isoflurane + pancuronium anesthesia. The ketamine/xylazine groups showed larger dark-adapted ERG a- and b-waves than other anesthetics tested. The isoflurane group showed the shortest b-wave implicit times. Photopic ERGs in the ketamine/xylazine groups showed the largest b-waves with the isoflurane group showing slightly shorter implicit times at the higher flash intensities. Oscillatory potentials revealed an early peak in the isoflurane group compared with ketamine/xylazine and urethane groups. Pancuronium did not affect the a- and b-wave, but did increase oscillatory potential amplitudes. Compared with the other anesthetics tested here, ketamine/xylazine + pancuronium was the best combination to minimize eye movement and maximize retinal function. These findings should set the stage for further development and application of high-resolution functional imaging techniques, such as MRI, to study retinal anatomy, physiology, and function in anesthetized rats.

Presynaptic facilitatory adenosine A2A receptors mediate fade induced by neuromuscular relaxants that exhibit anticholinesterase activity.

1. Pancuronium, cisatracurium and vecuronium are antinicotinic agents that, in contrast with d-tubocurarine and hexamethonium, exhibit anticholinesterase activity. Pancuronium-, cisatracurium- and vecuronium-induced fade results from blockade of facilitatory nicotinic receptors on motor nerves, but fade produced by such agents also depends on the presynaptic activation of inhibitory muscarinic M2 receptors by acetylcholine released from motor nerve terminals and activation of inhibitory adenosine A1 receptors by adenosine released from motor nerves and muscles. The participation of presynaptic facilitatory A2A receptors in fade caused by pancuronium, cisatracurium and vecuronium has not yet been investigated. In the present study, we determined the effects of ZM241385, an antagonist of presynaptic facilitatory A2A receptors, on fade produced by these neuromuscular relaxants in the rat phrenic nerve-diaphragm (PND) preparation. 2. The muscles were stimulated indirectly at 75±3Hz to induce a sustained tetanizing muscular contraction. The lowest concentration at which each antinicotinic agent produced fade without modifying initial tetanic tension (presynaptic action) was determined. 3. d-Tubocurarine-induced fade occurred only at 55 nmol/L, a concentration that also reduced maximal tetanic tension (post-synaptic action). At 10 nmol/L, ZM 241385 alone did not produce fade, but it did attenuate pancuronium (0.32 µmol/L)-, cisatracurium (0.32 µmol/L)- and vecuronium (0.36 µmol/L)-induced fade. 4. The fade induced by the 'pure' antinicotinic agents d-tubocurarine (55 nmol/L) and hexamethonium (413 µmol/L) was not altered by 10 nmol/L ZM 241385, indicating that presynaptic adenosine A2A receptors play a significant role in the fade produced by antinicotinic agents when such agents have anticholinesterase activity.

Ivermectin effects on motor coordination and contractions of isolated rat diaphragm.

Ivermectin, the antiparasitic drug from the macrocyclic lactones class raises attention due to its high efficiency against nematodes and arthropods and very specific toxic and side effects that it may produce in host. Dominant clinical symptoms of adverse effects and toxicity of ivermectin in animals are tremor, ataxia, CNS depression and coma which often results in mortality. In our study increasing intravenous doses of ivermectin, (6 or more times higher than therapeutic dose: 1.25, 2.5, 3.75, 5.0, 6.25 and 7.5 mg/kg), caused dose-dependent disturbance of motor coordination in treated rats. The median effective dose (ED50) that was able to impair the rota-rod performance in rats treated 3 min before testing was 2.52 mg/kg. This effect weakens over time, while in the rats treated 60 min before the rota-rod test, ED50 of ivermectin was 4.21 mg/kg. Whereas, all tested doses of ivermectin did not cause any other clinical symptoms of toxicity. Ivermectin has no effect on the contractions of isolated diaphragm caused by the EFS, which effectively blocked mecamylamine (100 µM) and pancuronium (1 and 2 µM). Effect on motor coordination is the first detectable clinical symptom of ivermectin toxicity and apparently is a result of its central effects.

Role of 5-HT1A receptors in control of lower urinary tract function in anesthetized rats.

The role of 5-hydroxytryptamine (5-HT) 1A (5-HT1A) receptors in lower urinary tract function was examined in urethane-anesthetized female Sprague-Dawley rats. Bladder pressure and the external urethral sphincter electromyogram (EUS EMG) activity were recorded during continuous-infusion transvesical cystometrograms (TV-CMGs) to allow voiding and during transurethral-CMGs (TU-CMGs) which prevented voiding and allowed recording of isovolumetric bladder contractions. 8-Hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT), a 5-HT1A receptor agonist, decreased volume threshold (VT) for initiating voiding and increased contraction amplitude (CA) during TU-CMGs but decreased CA during TV-CMGs. 8-OH-DPAT prolonged EUS bursting as well as the intrabursting silent periods (SP) during voiding. N-[2-[4-(2-methoxyphenyl)-1- piperazinyl]ethyl]-N-(2-pyridinyl)cyclohexanecarboxamine trihydrochloride (WAY-100635), a 5-HT1A antagonist, increased VT, increased residual volume, markedly decreased voiding efficiency, decreased the amplitude of micturition contractions recorded under isovolumetric conditions, and decreased the SP of EUS bursting. These results indicate that activation of 5-HT1A receptors by endogenous 5-HT lowers the threshold for initiating reflex voiding and promotes voiding function by enhancing the duration of EUS relaxation, which should reduce urethral outlet resistance.