Dyspnea induced by hemidiaphragmatic paralysis after ultrasound-guided supraclavicular brachial plexus block in a morbidly obese patient

RATIONALE

Hemidiaphragmatic paralysis (HDP) is a frequent complication of the brachial plexus block, caused by unintentional blockade of ipsilateral phrenic nerve. HDP did not rise enough alarm and attention to most anesthesiologists, because most patients with no coexisting comorbid diseases are asymptomatic and able to tolerate it. However, it may cause severe respiratory complication for patients with preexisting compromised cardiorespiratory function.

PATIENT CONCERNS

A 67-year-old woman with morbidly obesity was planned to receive opening reduction and internal fixation of right humeral shaft fracture under regional anesthesia considering less respiratory and cardiovascular system interference compared with general anesthesia.

DIAGNOSES

After ultrasound guided supraclavicular brachial plexus block, the patient developed severe hypoxia and hypercapnia.Unintentional block of phrenic nerve and diaphragm paralysis was diagnosed by diaphragm ultrasound, which was considered as the main reason of severe hypoxia.

INTERVENTIONS

It led to a conversion from regional anesthesia to general anesthesia with endotracheal intubation for patient's safety and smooth operation.

OUTCOMES

The unintentional phrenic nerve block leads to a prolonged ventilation time, length of stay in intensive care unit and length of stay in hospital.

LESSONS

This case report highlights the risk of diaphragm paralysis in morbidly obese patients. Though new diaphragm sparing brachial plexus block (BPB) methods were developed intended to reduce the risk of HDP, no approaches could absolutely spare phrenic nerve involvement. Therefore, clinicians should always consider the risk of HDP associated with BPBs. For each individual, a detailed preoperative evaluation and sufficient preparation are paramount to avoid serious complications.

Nonsteroidal anti-inflammatory drug (ketoprofen) delivery differentially impacts phrenic long-term facilitation in rats with motor neuron death induced by intrapleural CTB-SAP injections

Intrapleural injections of cholera toxin B conjugated to saporin (CTB-SAP) selectively eliminates respiratory (e.g., phrenic) motor neurons, and mimics motor neuron death and respiratory deficits observed in rat models of neuromuscular diseases. Additionally, microglial density increases in the phrenic motor nucleus following CTB-SAP. This CTB-SAP rodent model allows us to study the impact of motor neuron death on the output of surviving phrenic motor neurons, and the underlying mechanisms that contribute to enhancing or constraining their output at 7 days (d) or 28d post-CTB-SAP injection. 7d CTB-SAP rats elicit enhanced phrenic long-term facilitation (pLTF) through the Gs-pathway (inflammation-resistant in naïve rats), while pLTF is elicited though the Gq-pathway (inflammation-sensitive in naïve rats) in control and 28d CTB-SAP rats. In 7d and 28d male CTB-SAP rats and controls, we evaluated the effect of cyclooxygenase-1/2 enzymes on pLTF by delivery of the nonsteroidal anti-inflammatory drug, ketoprofen (IP), and we hypothesized that pLTF would be unaffected by ketoprofen in 7d CTB-SAP rats, but pLTF would be enhanced in 28d CTB-SAP rats. In anesthetized, paralyzed and ventilated rats, pLTF was surprisingly attenuated in 7d CTB-SAP rats and enhanced in 28d CTB-SAP rats (both p < 0.05) following ketoprofen delivery. Additionally in CTB-SAP rats: 1) microglia were more amoeboid in the phrenic motor nucleus; and 2) cervical spinal inflammatory-associated factor expression (TNF-α, BDNF, and IL-10) was increased vs. controls in the absence of ketoprofen (p < 0.05). Following ketoprofen delivery, TNF-α and IL-10 expression was decreased back to control levels, while BDNF expression was differentially affected over the course of motor neuron death in CTB-SAP rats. This study furthers our understanding of factors (e.g., cyclooxygenase-1/2-induced inflammation) that contribute to enhancing or constraining pLTF and its implications for breathing following respiratory motor neuron death.

Evaluation of Protection by Caffeic Acid, Chlorogenic Acid, Quercetin and Tannic Acid against the In Vitro Neurotoxicity and In Vivo Lethality of Crotalus durissus terrificus (South American Rattlesnake) Venom

Systemic envenomation by Crotalus durissus terrificus (South American rattlesnake) can cause coagulopathy, rabdomyolysis, acute kidney injury, and peripheral neuromuscular blockade, the latter resulting in flaccid paralysis. Previous studies have shown that plant products such as tannic acid and theaflavin can protect against the neuromuscular blockade caused by C. d. terrificus venom in vitro. In this work, we used mouse-isolated phrenic nerve-diaphragm preparations to examine the ability of caffeic acid, chlorogenic acid, and quercetin to protect against C. d. terrificus venom-induced neuromuscular blockade in vitro. In addition, the ability of tannic acid to protect against the systemic effects of severe envenomation was assessed in rats. Preincubation of venom with caffeic acid (0.5 mg/mL), chlorogenic acid (1 mg/mL), or quercetin (0.5 mg/mL) failed to protect against venom (10 μg/mL)-induced neuromuscular blockade. In rats, venom (6 mg kg⁻¹, i.p.) caused death in ~8 h, which was prevented by preincubation of venom with tannic acid or the administration of antivenom 2 h post-venom, whereas tannic acid given 2 h post-venom prolonged survival (~18.5 h) but did not prevent death. Tannic acid (in preincubation protocols or given 2 h post-venom) had a variable effect on blood creatinine and urea and blood/urine protein levels and prevented venom-induced leukocytosis. Tannic acid attenuated the histological lesions associated with renal damage in a manner similar to antivenom. The protective effect of tannic acid appeared to be mediated by interaction with venom proteins, as assessed by SDS-PAGE. These findings suggest that tannic acid could be a potentially useful ancillary treatment for envenomation by C. d. terrificus.

Effects of sevoflurane and adenosine receptor antagonist on the sugammadex-induced recovery from rocuronium-induced neuromuscular blockade in rodent phrenic nerve-hemidiaphragm tissue specimens

Sevoflurane affects on the A1 receptor in the central nervous system and potentiates the action of neuromuscular blocking agents. In the present study, we investigated whether sevoflurane (SEVO) has the ability to potentiate the neuromuscular blocking effect of rocuronium and if the specific antagonist of adenosine receptor (SLV320) can reverse this effect. In this study, phrenic nerve-hemidiaphragm tissue specimens were obtained from 40 Sprague-Dawley (SD) rats. The specimens were immersed in an organ bath filled with Krebs buffer and stimulated by a train-of-four (TOF) pattern using indirect supramaximal stimulation at 20 s intervals. The specimens were randomly allocated to control, 2-chloroadenosine (CADO), SEVO, or SLV320 + SEVO groups. In the CADO and SLV320 + SEVO groups, CADO and SLV320 were added to the organ bath from the start to a concentration of 10 μM and 10 nM, respectively. We then proceeded with rocuronium-induced blockade of >95% depression of the first twitch tension of TOF (T1) and TOF ratio (TOFR). In the SEVO and SLV320 + SEVO groups, SEVO was added to the Krebs buffer solution to concentration of 400-500 μM for 10 min. Sugammadex-induced T1 and TOFR recovery was monitored for 30 min until >95% of T1 and >0.9 of TOFR were confirmed, and the recovery pattern was compared by plotting these data. T1 recovery in the SEVO and CADO groups was significantly delayed compared with the control and SLV320 + SEVO groups (p < .05). In conclusion, sevoflurane affects on the A1 receptor at the neuromuscular junction and delays sugammadex-induced recovery from neuromuscular blockade.

Effects of acetylcholine on hypoglossal and C4 nerve activity in brainstem-spinal cord preparations from newborn rat

Effects of acetylcholine (ACh) on respiratory activity have been an intriguing theme especially in relation to central chemoreception and the control of hypoglossal nerve activity. We studied the effects of ACh on hypoglossal and phrenic (C4) nerve activities and inspiratory and pre-inspiratory neurons in the rostral ventrolateral medulla in brainstem-spinal cord preparations from newborn rats. ACh application increased respiratory rhythm, decreased inspiratory hypoglossal and C4 nerve burst amplitude, and enhanced pre-inspiratory hypoglossal activity. ACh induced membrane depolarization of pre-inspiratory neurons that might be involved in facilitation of respiratory rhythm by ACh. Effects of ACh on hypoglossal and C4 nerve activity were partially reversed by a nicotinic receptor blocker, mecamylamine. Further application of a muscarinic receptor antagonist, oxybutynin, resulted in slight increase of hypoglossal (but not C4) burst amplitude. Thus, ACh induced different effects on hypoglossal and C4 nerve activity in the brainstem-spinal cord preparation.

Methocarbamol blocks muscular Nav 1.4 channels and decreases isometric force of mouse muscles

BACKGROUND

The muscle relaxant methocarbamol is widely used for the treatment of muscle spasms and pain syndromes. To elucidate molecular mechanisms of its action, we studied its influence on neuromuscular transmission, on isometric muscle force, and on voltage-gated Na+ channels.

METHODS

Neuromuscular transmission was investigated in murine diaphragm-phrenic nerve preparations and muscle force studied on mouse soleus muscles. Nav 1.4 channels and Nav 1.7 channels were functionally expressed in eukaryotic cell lines.

RESULTS

Methocarbamol, at 2 mM, decreased the decay of endplate currents, slowed the decay of endplate potentials and reduced tetanic force of soleus muscles. The drug reversibly inhibited current flow through muscular Nav 1.4 channels, while neuronal Nav 1.7 channels were unaffected.

CONCLUSIONS

The study provides evidence for peripheral actions of methocarbamol on skeletal muscle. Muscular Na+ channels are a molecular target of methocarbamol. Since Nav 1.7 currents were unaffected, methocarbamol is unlikely to exert its analgesic effect by directly blocking Nav 1.7 channels.

Differential mechanisms are required for phrenic long-term facilitation over the course of motor neuron loss following CTB-SAP intrapleural injections

Selective elimination of respiratory motor neurons using intrapleural injections of cholera toxin B fragment conjugated to saporin (CTB-SAP) mimics motor neuron death and respiratory deficits observed in rat models of neuromuscular diseases. This CTB-SAP model allows us to study the impact of motor neuron death on the output of surviving phrenic motor neurons. After 7(d) days of CTB-SAP, phrenic long-term facilitation (pLTF, a form of respiratory plasticity) is enhanced, but returns towards control levels at 28d. However, the mechanism responsible for this difference in magnitude of pLTF is unknown. In naïve rats, pLTF predominately requires 5-HT2 receptors, the new synthesis of BDNF, and MEK/ERK signaling; however, pLTF can alternatively be induced via A2A receptors, the new synthesis of TrkB, and PI3K/Akt signaling. Since A2A receptor-dependent pLTF is enhanced in naïve rats, we suggest that 7d CTB-SAP treated rats utilize the alternative mechanism for pLTF. Here, we tested the hypothesis that pLTF following CTB-SAP is: 1) TrkB and PI3K/Akt, not BDNF and MEK/ERK, dependent at 7d; and 2) BDNF and MEK/ERK, not TrkB and PI3K/Akt, dependent at 28d. Adult Sprague Dawley male rats were anesthetized, paralyzed, ventilated, and were exposed to acute intermittent hypoxia (AIH; 3, 5 min bouts of 10.5% O2) following bilateral, intrapleural injections at 7d and 28d of: 1) CTB-SAP (25 μg), or 2) un-conjugated CTB and SAP (control). Intrathecal C4 delivery included either: 1) small interfering RNA that targeted BDNF or TrkB mRNA; 2) UO126 (MEK/ERK inhibitor); or 3) PI828 (PI3K/Akt inhibitor). Our data suggest that pLTF in 7d CTB-SAP treated rats is elicited primarily through TrkB and PI3K/Akt-dependent mechanisms, whereas BDNF and MEK/ERK-dependent mechanisms induce pLTF in 28d CTB-SAP treated rats. This project increases our understanding of respiratory plasticity and its implications for breathing following motor neuron death.

Erythropoietin as candidate for supportive treatment of severe COVID-19

In light of the present therapeutic situation in COVID-19, any measure to improve course and outcome of seriously affected individuals is of utmost importance. We recap here evidence that supports the use of human recombinant erythropoietin (EPO) for ameliorating course and outcome of seriously ill COVID-19 patients. This brief expert review grounds on available subject-relevant literature searched until May 14, 2020, including Medline, Google Scholar, and preprint servers. We delineate in brief sections, each introduced by a summary of respective COVID-19 references, how EPO may target a number of the gravest sequelae of these patients. EPO is expected to: (1) improve respiration at several levels including lung, brainstem, spinal cord and respiratory muscles; (2) counteract overshooting inflammation caused by cytokine storm/ inflammasome; (3) act neuroprotective and neuroregenerative in brain and peripheral nervous system. Based on this accumulating experimental and clinical evidence, we finally provide the research design for a double-blind placebo-controlled randomized clinical trial including severely affected patients, which is planned to start shortly.

Thrombin action on astrocytes in the hindbrain of the rat disrupts glycemic and respiratory control

Severe trauma can produce a postinjury "metabolic self-destruction" characterized by catabolic metabolism and hyperglycemia. The severity of the hyperglycemia is highly correlated with posttrauma morbidity and mortality. Although no mechanism has been posited to connect severe trauma with a loss of autonomic control over metabolism, traumatic injury causes other failures of autonomic function, notably, gastric stasis and ulceration ("Cushing's ulcer"), which has been connected with the generation of thrombin. Our previous studies established that proteinase-activated receptors (PAR1; "thrombin receptors") located on astrocytes in the autonomically critical nucleus of the solitary tract (NST) can modulate gastric control circuit neurons to cause gastric stasis. Hindbrain astrocytes have also been implicated as important detectors of low glucose or glucose utilization. When activated, these astrocytes communicate with hindbrain catecholamine neurons that, in turn, trigger counterregulatory responses (CRR). There may be a convergence between the effects of thrombin to derange hindbrain gastrointestinal control and the hindbrain circuitry that initiates CRR to increase glycemia in reaction to critical hypoglycemia. Our results suggest that thrombin acts within the NST to increase glycemia through an astrocyte-dependent mechanism. Blockade of purinergic gliotransmission pathways interrupted the effect of thrombin to increase glycemia. Our studies also revealed that thrombin, acting in the NST, produced a rapid, dramatic, and potentially lethal suppression of respiratory rhythm that was also a function of purinergic gliotransmission. These results suggest that the critical connection between traumatic injury and a general collapse of autonomic regulation involves thrombin action on astrocytes.

Olesoxime, a cholesterol-like neuroprotectant restrains synaptic vesicle exocytosis in the mice motor nerve terminals: Possible role of VDACs

Olesoxime is a cholesterol-like neuroprotective compound that targets to mitochondrial voltage dependent anion channels (VDACs). VDACs were also found in the plasma membrane and highly expressed in the presynaptic compartment. Here, we studied the effects of olesoxime and VDAC inhibitors on neurotransmission in the mouse neuromuscular junction. Electrophysiological analysis revealed that olesoxime suppressed selectively evoked neurotransmitter release in response to a single stimulus and 20 Hz activity. Also olesoxime decreased the rate of FM1-43 dye loss (an indicator of synaptic vesicle exocytosis) at low frequency stimulation and 20 Hz. Furthermore, an increase in extracellular Cl^- enhanced the action of olesoxime on the exocytosis and olesoxime increased intracellular Cl^- levels. The effects of olesoxime on the evoked synaptic vesicle exocytosis and [Cl^-]_i were blocked by membrane-permeable and impermeable VDAC inhibitors. Immunofluorescent labeling pointed on the presence of VDACs on the synaptic membranes. Rotenone-induced mitochondrial dysfunction perturbed the exocytotic release of FM1-43 and cell-permeable VDAC inhibitor (but not olesoxime or impermeable VDAC inhibitor) partially mitigated the rotenone-driven alterations in the FM1-43 unloading and mitochondrial superoxide production. Thus, olesoxime restrains neurotransmission by acting on plasmalemmal VDACs whose activation can limit synaptic vesicle exocytosis probably via increasing anion flux into the nerve terminals.

Ampakine pretreatment enables a single brief hypoxic episode to evoke phrenic motor facilitation

Phrenic long-term facilitation (LTF) is a sustained increase in phrenic motor output occurring after exposure to multiple (but not single) hypoxic episodes. Ampakines are a class of drugs that enhance AMPA receptor function. Ampakines can enhance expression of neuroplasticity, and the phrenic motor system is fundamentally dependent on excitatory glutamatergic currents. Accordingly, we tested the hypothesis that combining ampakine pretreatment with a single brief hypoxic exposure would result in phrenic motor facilitation lasting well beyond the period of hypoxia. Phrenic nerve output was recorded in urethane-anesthetized, ventilated, and vagotomized adult Sprague-Dawley rats. Ampakine CX717 (15 mg/kg iv; n = 8) produced a small increase in phrenic inspiratory burst amplitude and frequency, but values quickly returned to predrug baseline. When CX717 was followed 2 min later by a 5-min exposure to hypoxia (n = 8; PaO2 ~45 mmHg), a persistent increase in phrenic inspiratory burst amplitude (i.e., phrenic motor facilitation) was observed up to 60 min posthypoxia (103 ± 53% increase from baseline). In contrast, when hypoxia was preceded by vehicle injection (10% 2-hydroxypropyl-β-cyclodextrin; n = 8), inspiratory phrenic bursting was similar to baseline values at 60 min. Additional experiments with another ampakine (CX1739, 15 mg/kg) produced comparable results. We conclude that pairing low-dose ampakine treatment with a single brief hypoxic exposure can evoke sustained phrenic motor facilitation. This targeted approach for enhancing respiratory neuroplasticity may have value in the context of hypoxia-based neurorehabilitation strategies.NEW & NOTEWORTHY A single brief episode of hypoxia (e.g., 3-5 min) does not evoke long-lasting increases in respiratory motor output after the hypoxia is concluded. Ampakines are a class of drugs that enhance AMPA receptor function. We show that pairing low-dose ampakine treatment with a single brief hypoxic exposure can evoke sustained phrenic motor facilitation after the acute hypoxic episode.

H2S mediates carotid body response to hypoxia but not anoxia

The role of cystathionine-γ-lyase (CSE) derived H2S in the hypoxic and anoxic responses of the carotid body (CB) were examined. Experiments were performed on Sprague-Dawley rats, wild type and CSE knockout mice on C57BL/6 J background. Hypoxia (pO2 = 37 ± 3 mmHg) increased the CB sensory nerve activity and elevated H2S levels in rats. In contrast, anoxia (pO2 = 5 ± 4 mmHg) produced only a modest CB sensory excitation with no change in H2S levels. DL-propargylglycine (DL-PAG), a blocker of CSE, inhibited hypoxia but not anoxia-evoked CB sensory excitation and [Ca2+]i elevation of glomus cells. The inhibitory effects of DL-PAG on hypoxia were seen: a) when it is dissolved in saline but not in dimethyl sulfoxide (DMSO), and b) in glomus cells cultured for18 h but not in cells either soon after isolation or after prolonged culturing (72 h) requiring 1-3 h of incubation. On the other hand, anoxia-induced [Ca2+]i responses of glomus cell were blocked by high concentration of DL-PAG (300μM) either alone or in combination with aminooxyacetic acid (AOAA; 300μM) with a decreased cell viability. Anoxia produced a weak CB sensory excitation and robust [Ca2+]i elevation in glomus cells of both wild-type and CSE null mice. As compared to wild-type, CSE null mice exhibited impaired CB chemo reflex as evidenced by attenuated efferent phrenic nerve responses to brief hyperoxia (Dejours test), and hypoxia. Inhalation of 100% N2 (anoxia) depressed breathing in both CSE null and wild-type mice. These observations demonstrate that a) hypoxia and anoxia are not analogous stimuli for studying CB physiology and b) CSE-derived H2S contributes to CB response to hypoxia but not to that of anoxia.

A comparison of biological activity of commercially available purified native botulinum neurotoxin serotypes A1 to F1 in vitro, ex vivo, and in vivo

Botulinum neurotoxin (BoNT) is a major therapeutic agent. Of seven native BoNT serotypes (A to G), only A and B are currently used in the clinic. Here we compared the potency of commercially available purified native serotypes A1 to F1 across in vitro, ex vivo, and in vivo assays. BoNT potency in vitro was assessed in rat primary cells (target protein cleavage and neurotransmitter release assays) in supraspinal, spinal, and sensory systems. BoNT potency ex vivo was measured in the mouse phrenic nerve hemidiaphragm (PNHD) assay, measuring muscle contractility. In vivo, BoNT-induced muscle relaxation in mice and rats was assessed in the Digit Abduction Score (DAS) test, while effects on body weight (BW) gain were used to assess tolerability. In all assays, all BoNT serotypes were potent toxins, except serotype D1 in vivo which failed to produce significant muscle flaccidity in mice and rats. In rats, all serotypes were well-tolerated, whereas in mice, reductions in BW were detected at high doses. Serotype A1 was the most potent serotype across in vitro, ex vivo, and in vivo assays. The rank order of potency of the serotypes revealed differences among assays. For example, species-specificity was seen for serotype B1, and to a lesser extent for serotype C1. Serotypes F1 and C1, not currently in the clinic, showed preference for sensory over motor models and therefore could be considered for development in conditions involving the somatosensory system.

Determining the effect of long-term dexamethasone and prednisolone treatment on sugammadex

Background/aim: We aimed to investigate the effect of long-term use of dexamethasone and prednisolone on the reversal effect of sugammadex. Materials and methods: TTwenty-four male Wistar albino rats were divided into three groups. Dexamethasone (600 µg/kg) was given to group D, prednisolone (10 mg/kg) was given to group P, and an equivalent volume of saline per day was administered intraperitoneally to group S for 14 days, respectively. The left hemidiaphragm with attached phrenic nerve was maintained in Krebs solution. Sugammadex (30 µmol/L) was applied while rocuronium (10 µmol/L) was present in an organ bath and a single twitch was obtained. The right hemidiaphragm was used for both adult ( ε-subunit) and fetal nicotinic acetylcholine receptor (AChR) ( ε-subunit) determination using polymerase chain reaction. Results: All animals lost weight, except group S. The mean baseline single-twitch tension was lower in both group D (14.4 ± 1.7 g) and group P (12.68 ± 0.05 g) than group S (16.8 ± 0.5 g) (P < 0.001). When sugammadex was added to the organ bath while rocuronium was present, the single twitch was measured to be lower in both group D (11.7 ± 0.7 g) and group P (11.5 ± 0.78 g) than group S (16.5 ± 0.24 g) (P < 0.001). Ɣ-AChR expression was higher in both dexamethasone and prednisolone than in saline. Conclusion: Long-term medication with dexamethasone and prednisolone caused muscle weakness, resistance to neuromuscular blockers, and upregulation of immature Ɣ-AChR and reduced the neuromuscular reversal effect of sugammadex.

In vitro effects of Crotalus atrox snake venom on chick and mouse neuromuscular preparations

The neuromuscular effect of venoms is not a major clinical manifestation shared between rattlesnakes native to the Americas, which showed two different venom phenotypes. Taking into account this dichotomy, nerve muscle preparations from mice and chicks were used to investigate the ability of Crotalus atrox venom to induce in vitro neurotoxicity and myotoxicity. Unlike crotalic venoms of South America, low concentrations of C. atrox venom did not result in significant effects on mouse neuromuscular preparations. The venom was more active on avian nerve-muscle, showing reduction of twitch heights after 120 min of incubation with 10, 30 and 100 μg/mL of venom with diminished responses to agonists and KCl. Histological analysis highlighted that C. atrox was myotoxic in both species of experimental animals; as evidenced by degenerative events, including edematous cells, delta lesions, hypercontracted fibers and muscle necrosis, which can lead to neurotoxic action. These results provide key insights into the myotoxicity and low neurotoxicity of C. atrox in two animal models, corroborating with previous genomic and proteomic findings and would be useful for a deeper understanding of venom evolution in snakes belonging to the genus Crotalus.

Purification and Characterization of Recombinant Botulinum Neurotoxin Serotype FA, Also Known as Serotype H

We have purified and characterized recombinant botulinum neurotoxin serotype FA (BoNT/FA). This protein has also been named as a new serotype (serotype H), but the classification has been controversial. A lack of well-characterized, highly pure material has been a roadblock to study. Here we report purification and characterization of enzymatically active, and of inactive nontoxic, recombinant forms of BoNT/FA as tractable alternatives to purifying this neurotoxin from native Clostridium botulinum. BoNT/FA cleaves the same intracellular target proteins as BoNT/F1 and other F serotype BoNTs; the intracellular targets are vesicle associated membrane proteins (VAMP) 1, 2 and 3. BoNT/FA cleaves the same site in VAMP-2 as BoNT/F5, which is different from the cleavage site of other F serotype BoNTs. BoNT/FA has slower enzyme kinetics than BoNT/F1 in a cell-free protease assay and is less potent at inhibiting ex vivo nerve-stimulated skeletal muscle contraction. In contrast, BoNT/FA is more potent at inhibiting neurotransmitter release from cultured neurons.

The Kölliker-Fuse nucleus acts as a timekeeper for late-expiratory abdominal activity

While the transition from the inspiratory to the post-inspiratory (post-I) phase is dependent on the pons, little attention has been paid to understanding the role of the pontine respiratory nuclei, specifically the Kölliker-Fuse nucleus (KF), in transitioning from post-I to the late expiratory (late-E) activity seen with elevated respiratory drive. To elucidate this, we used the in situ working heart-brainstem preparation of juvenile male Holtzman rats and recorded from the vagus (cVN), phrenic (PN) and abdominal nerves (AbN) during baseline conditions and during chemoreflex activation [with potassium cyanide (KCN; n=13) or hypercapnia (8% CO2; n=10)] to recruit active expiration. Chemoreflex activation with KCN increased PN frequency and cVN post-I and AbN activities. The inhibition of KF with isoguvacine microinjections (10mM) attenuated the typical increase in PN frequency and cVN post-I activity, and amplified the AbN response. During hypercapnia, AbN late-E activity emerged in association with a significant reduction in expiratory time. KF inhibition during hypercapnia significantly decreased PN frequency and reduced the duration and amplitude of post-I cVN activity, while the onset of the AbN late-E bursts occurred significantly earlier. Our data reveal a negative relationship between KF-induced post-I and AbN late-E activities, suggesting that the KF coordinates the transition between post-I to late-E activity during conditions of elevated respiratory drive.

Electrophysiological Characterization of the Antarease Metalloprotease from Tityus serrulatus Venom

Scorpions are among the oldest venomous living organisms and the family Buthidae is the largest and most medically relevant one. Scorpion venoms include many toxic peptides, but recently, a metalloprotease from Tityus serrulatus called antarease was reported to be capable of cleaving VAMP2, a protein involved in the neuroparalytic syndromes of tetanus and botulism. We have produced antarease and an inactive metalloprotease mutant in a recombinant form and analyzed their enzymatic activity on recombinant VAMP2 in vitro and on mammalian and insect neuromuscular junction. The purified recombinant antarease paralyzed the neuromuscular junctions of mice and of Drosophila melanogaster whilst the mutant was inactive. We were unable to demonstrate any cleavage of VAMP2 under conditions which leads to VAMP proteolysis by botulinum neurotoxin type B. Antarease caused a reduced release probability, mainly due to defects upstream of the synaptic vesicles fusion process. Paired pulse experiments indicate that antarease might proteolytically inactivate a voltage-gated calcium channel.

Congenital Bilateral Vocal Cord Paralysis and the Role of Glycine

Objectives:

We sought to modify normal laryngeal constrictor (LC) motoneuron activity to induce a pattern of aberrant LC muscle function that may serve as a model of congenital bilateral vocal cord paralysis.

Methods:

Single unit extracellular recordings of functionally identified LC motoneurons were made in anesthetized Sprague-Dawley rats, and the response to both intravenous and iontophoretic application of the glycine antagonist strychnine was studied.

Results:

The postinspiratory firing pattern of LC motoneurons became inspiratory after intravenous injection of strychnine (4 of 5 rats), but no change was recorded in response to strychnine iontophoresis (7 of 8 rats).

Conclusions:

Blockade of glycinergic inhibitory neurotransmission by strychnine, acting above the level of the LC motoneuron, causes LC motoneurons to fire during inspiration rather than after inspiration. This observation suggests that impaired glycine neurotransmission may be an underlying mechanism that explains the clinical manifestations of congenital bilateral vocal cord paralysis.

Ultrasound-Guided Phrenic Nerve Block for Intractable Hiccups following Placement of Esophageal Stent for Esophageal Squamous Cell Carcinoma

Hiccups are actions consisting of sudden contractions of the diaphragm and intercostals followed by a sudden inspiration and transient closure of the vocal cords. They are generally short lived and benign; however, in extreme and rare cases, such as esophageal carcinoma, they can become persistent or intractable, up to and involving significant pain, dramatically impacting the patient's quality of life. This case involves a 60-year-old man with a known history of squamous cell carcinoma of the esophagus. He was considered to have high surgical risk, and therefore he received palliative care through the use of fully covered metallic esophageal self-expandable stents due to a spontaneous perforated esophagus, after which he developed intractable hiccups and associated mediastinal pain. Conservative treatment, including baclofen, chlorpromazine, metoclopramide, and omeprazole, provided no relief for his symptoms. The patient was referred to pain management from gastroenterology for consultation on pain control. He ultimately received an ultrasound-guided left phrenic nerve block with bupivacaine and depomedrol, and 3 days later underwent the identical procedure on the right phrenic nerve. This led to complete resolution of his hiccups and associated mediastinal pain. At follow-up, 2 and 4 weeks after the left phrenic nerve block, the patient was found to maintain complete alleviation of the hiccups. Esophageal dilatation and/or phrenic or vagal afferent fiber irritation can be suspected in cases of intractable hiccups secondary to esophageal stenting. Regional anesthesia of the phrenic nerve through ultrasound guidance offers a long-term therapeutic option for intractable hiccups and associated mediastinal pain in selected patients with esophageal carcinoma after stent placement.

KEY WORDS

Esophageal stent, esophageal stenting, intractable hiccups, intractable singultus, phrenic nerve block, phrenic nerve, ultrasound, palliative care, esophageal carcinoma.

Intestinal ischemia-reperfusion induced diaphragm contractility dysfunction: Electrophysiological and ultrastructural study in a neonatal rat model

AIM

To evaluate the remote effect of intestinal ischemia reperfusion (IR) injury mediated by tumor necrosis factor alpha (TNF-α) on diaphragm contractility functions and whether administration of NAC may counteract the possible detrimental effects in an experimental neonatal rat model.

METHODS

40 Wistar rat pups were randomized into four groups; ten animals in each. Intestinal ischemia was conducted by obstructing mesentery of intestines by a silk loop. In the control group; only laparotomy was performed. After 1h ischemia, reperfusion was conducted for 1h in 1h group, 24h for 24h group and 24h for 24h+NAC group but administration of NAC (150mg/kg/day) intraperitoneally twice a day was performed. Inflammatory response was evaluated by tissue TNF-α level and contractility functions by mechanic activity studies of the diaphragm. Electrophysiology of the diaphragm and the phrenic nerve was conducted to determine neuropathy or myopathy and transmission electron microscopy was performed to evaluate ultrastructural changes in the phrenic nerve.

RESULTS

Diaphragm tissue TNF-α level significantly increased in 1h and 24h groups (P=0.004, P=0.0001; respectively). Diaphragm mechanic activation force and duration significantly decreased at 1h and 24h (P=0.004, P=0.02 and P=0.0001, P=0.0001; respectively). NAC administration significantly prevented decrease in the maximal contraction and the duration (P<0.001). Phrenic nerve compound action potential (CMAP) amplitude significantly decreased in 1h group (P<0.0001) and NAC administration significantly prevented this decrease when compared with 24h group (P<0.001). In diaphragmatic needle electromyography, the duration of motor unit potentials (MUP) was prolonged significantly when compared with control group. Contractility and electrophysiological studies were indicating primarily neuropathy in diaphragm dysfunction. Histopathology revealed axonal and myelin degeneration in the 1h and 24h group, but less injury in the NAC administered group.

CONCLUSIONS

Intestinal IR induced elevation of TNF-α level in the diaphragm. Impairment in the diaphragm contractility and neuropathic changes in the phrenic nerve occurred even in the first hour of reperfusion. NAC administration prevented these detrimental effects.

Generation and Characterization of Six Recombinant Botulinum Neurotoxins as Reference Material to Serve in an International Proficiency Test

The detection and identification of botulinum neurotoxins (BoNT) is complex due to the existence of seven serotypes, derived mosaic toxins and more than 40 subtypes. Expert laboratories currently use different technical approaches to detect, identify and quantify BoNT, but due to the lack of (certified) reference materials, analytical results can hardly be compared. In this study, the six BoNT/A1–F1 prototypes were successfully produced by recombinant techniques, facilitating handling, as well as improving purity, yield, reproducibility and biosafety. All six BoNTs were quantitatively nicked into active di-chain toxins linked by a disulfide bridge. The materials were thoroughly characterized with respect to purity, identity, protein concentration, catalytic and biological activities. For BoNT/A₁, B₁ and E₁, serotypes pathogenic to humans, the catalytic activity and the precise protein concentration were determined by Endopep-mass spectrometry and validated amino acid analysis, respectively. In addition, BoNT/A₁, B₁, E₁ and F₁ were successfully detected by immunological assays, unambiguously identified by mass spectrometric-based methods, and their specific activities were assigned by the mouse LD₅₀ bioassay. The potencies of all six BoNT/A1–F1 were quantified by the ex vivo mouse phrenic nerve hemidiaphragm assay, allowing a direct comparison. In conclusion, highly pure recombinant BoNT reference materials were produced, thoroughly characterized and employed as spiking material in a worldwide BoNT proficiency test organized by the EQuATox consortium.

Acute intermittent optogenetic stimulation of nucleus tractus solitarius neurons induces sympathetic long-term facilitation

Acute intermittent hypoxia (AIH) induces sympathetic and phrenic long-term facilitation (LTF), defined as a sustained increase in nerve discharge. We investigated the effects of AIH and acute intermittent optogenetic (AIO) stimulation of neurons labeled with AAV-CaMKIIa, hChR2(H134R), and mCherry in the nucleus of the solitary tract (NTS) of anesthetized, vagotomized, and mechanically ventilated rats. We measured renal sympathetic nerve activity (RSNA), phrenic nerve activity (PNA), power spectral density, and coherence, and we made cross-correlation measurements to determine how AIO stimulation and AIH affected synchronization between PNA and RSNA. Sixty minutes after AIH produced by ventilation with 10% oxygen in balanced nitrogen, RSNA and PNA amplitude increased by 80% and by 130%, respectively (P < 0.01). Sixty minutes after AIO stimulation, RSNA and PNA amplitude increased by 60% and 100%, respectively, (P < 0.01). These results suggest that acute intermittent stimulation of NTS neurons can induce renal sympathetic and phrenic LTF in the absence of hypoxia or chemoreceptor afferent activation. We also found that while acute intermittent optogenetic and hypoxic stimulations increased respiration-related RSNA modulation (P < 0.01), they did not increase synchronization between central respiratory drive and RSNA. We conclude that mechanisms that induce LTF originate within the caudal NTS and extend to other interconnecting neuronal elements of the central nervous cardiorespiratory network.

The facilitatory effect of Casearia sylvestris Sw. (guaçatonga) fractions on the contractile activity of mammalian and avian neuromuscular apparatus

Many natural products influence neurotransmission and are used clinically. In particular, facilitatory agents can enhance neurotransmission and are potentially useful for treating neuromuscular diseases in which muscular weakness is the major symptom. In this work, we investigated the facilitatory effect of apolar to polar fractions of Casearia sylvestris Sw. (guaçatonga) on contractility in mouse phrenic nerve-diaphragm (PND) and chick biventer cervicis (BC) neuromuscular preparations exposed to indirect (via the nerve; 3 V stimuli) and direct (30 V stimuli) muscle stimulation in the absence and presence of pharmacological antagonists. Methanolic and ethyl acetate fractions, but not hexane or dichloromethane fractions, exerted a facilitatory effect on PND (indirect stimulation). The methanolic fraction was chosen for further assays to assess the involvement of: 1) presynaptic sites (axons or nerve terminals), 2) postsynaptic sites (cholinergic receptors, sarcolemma or T-tubules), and 3) the synaptic cleft (acetylcholinesterase enzyme). In preparations treated with d-tubocurarine, the methanolic fraction did not cause facilitation in response to direct stimuli; this fraction was also unable to reverse dantrolene-induced blockade (indirect stimulation). In curarized preparations, the methanolic fraction either restored neuromuscular transmission (mimicking the effect of neostigmine) or failed to cause any recovery of neurotransmission. In the presence of 3,4-diaminopyridine (3,4-DAP), the methanolic fraction decreased twitch amplitude, whereas at a high frequency of stimulation (40 Hz) there was an increase in tetanic tension. In BC preparations, the methanolic fraction did not affect contractures to exogenous acetylcholine or potassium chloride. Incubation with atropine showed there was certain modulation by prejunctional nicotinic receptors, whereas treatment with nifedipine showed that the neurofacilitation required the entry of extracellular calcium. Tetrodotoxin did not prevent the facilitatory effect of 3,4-DAP or neostigmine, but antagonized the response to the methanolic fraction. These findings indicate that neuronal sodium channels have an important role in the facilitatory response to the methanolic fraction, with extracellular calcium entry via calcium channels modulating this neurofacilitation. Possible modulation of prejunctional cholinoceptors was not excluded, particularly in view of certain antagonism by the methanolic fraction at muscarinic receptors. Since facilitation by the methanolic fraction involved enhanced acetylcholine release, use of this fraction could be potentially beneficial in neuromuscular diseases and in the reversal of residual paralysis in the post-operative period or after local anaesthesia.

The activation effect of hainantoxin-I, a peptide toxin from the Chinese spider, Ornithoctonus hainana, on intermediate-conductance Ca2+-activated K+ channels

Intermediate-conductance Ca²⁺-activated K⁺ (IK) channels are calcium/calmodulin-regulated voltage-independent K⁺ channels. Activation of IK currents is important in vessel and respiratory tissues, rendering the channels potential drug targets. A variety of small organic molecules have been synthesized and found to be potent activators of IK channels. However, the poor selectivity of these molecules limits their therapeutic value. Venom-derived peptides usually block their targets with high specificity. Therefore, we searched for novel peptide activators of IK channels by testing a series of toxins from spiders. Using electrophysiological experiments, we identified hainantoxin-I (HNTX-I) as an IK-channel activator. HNTX-I has little effect on voltage-gated Na⁺ and Ca²⁺ channels from rat dorsal root ganglion neurons and on the heterologous expression of voltage-gated rapidly activating delayed rectifier K⁺ channels (human ether-à-go-go-related gene; human ERG) in HEK293T cells. Only 35.2% ± 0.4% of the currents were activated in SK channels, and there was no effect on BK channels. We demonstrated that HNTX-I was not a phrenic nerve conduction blocker or acutely toxic. This is believed to be the first report of a peptide activator effect on IK channels. Our study suggests that the activity and selectivity of HNTX-I on IK channels make HNTX-I a promising template for designing new drugs for cardiovascular diseases.

Intermittent hypercapnia enhances CO₂ responsiveness and overcomes serotonergic dysfunction

Serotonergic dysfunction compromises ventilatory chemosensitivity and may enhance vulnerability to pathologies such as the Sudden Infant Death Syndrome (SIDS). We have shown raphé contributions to central chemosensitivity involving serotonin (5-HT)-and γ-aminobutyric acid (GABA)-mediated mechanisms. We tested the hypothesis that mild intermittent hypercapnia (IHc) induces respiratory plasticity, due in part to strengthening of GABA mechanisms. Rat pups were IHc-pretreated (eight consecutive cycles; 5 min 5% CO2 - air, 10 min air) or constant normocapnia-pretreated as a control, each day for 5 consecutive days beginning at P12. We subsequently assessed CO2 responsiveness using the in situ perfused brainstem preparation. Hypercapnic responses were determined with and without pharmacological manipulation. Results show IHc-pretreatment induces plasticity sufficient for responsiveness despite removal of otherwise critical ketanserin-sensitive mechanisms. Responsiveness following IHc-pretreatment was absent if ketanserin was combined with GABAergic antagonism, indicating that plasticity depends on GABAergic mechanisms. We propose that IHc-induced plasticity could reduce the severity of reflex dysfunctions underlying pathologies such as SIDS.

The midbrain periaqueductal grey has no role in the generation of the respiratory motor pattern, but provides command function for the modulation of respiratory activity

It has previously been shown that stimulation of cell-columns in the periaqueductal grey (PAG) triggers site-specific cardiorespiratory effects. These are believed to facilitate changes in behaviour through coordinated changes in autonomic outflow. Here, we investigated whether PAG-evoked respiratory commands can be studied in situ using the decerebrate perfused brainstem preparation. Phrenic, vagus and abdominal iliohypogastric nerves were recorded before and after microinjection of L-glutamate (30-50 nl, 10 mM) or isoguvacine (GABA-receptor agonist, 30-50 nl, 10 mM) into the PAG. L-glutamate microinjection triggered a range of site-specific respiratory modulations (n = 17 preparations). Subsequent microinjection of isoguvacine into the same PAG sites had no effect on the baseline respiratory motor pattern or rhythm. We conclude that while the PAG has no function in respiratory pattern generation, PAG-evoked respiratory modulations can be evoked in situ in the absence of higher brain centres and while homeostatic parameters that may affect respiratory drive are held static.

Identification of the synaptic vesicle glycoprotein 2 receptor binding site in botulinum neurotoxin A

Botulinum neurotoxins (BoNTs) inhibit neurotransmitter release by hydrolysing SNARE proteins. The most important serotype BoNT/A employs the synaptic vesicle glycoprotein 2 (SV2) isoforms A-C as neuronal receptors. Here, we identified their binding site by blocking SV2 interaction using monoclonal antibodies with characterised epitopes within the cell binding domain (HC). The site is located on the backside of the conserved ganglioside binding pocket at the interface of the HCC and HCN subdomains. The dimension of the binding pocket was characterised in detail by site directed mutagenesis allowing the development of potent inhibitors as well as modifying receptor binding properties.

Purinergic and glutamatergic interactions in the hypothalamic paraventricular nucleus modulate sympathetic outflow

P2X receptors are expressed on ventrolateral medulla projecting paraventricular nucleus (PVN) neurons. Here, we investigate the role of adenosine 5'-triphosphate (ATP) in modulating sympathetic nerve activity (SNA) at the level of the PVN. We used an in situ arterially perfused rat preparation to determine the effect of P2 receptor activation and the putative interaction between purinergic and glutamatergic neurotransmitter systems within the PVN on lumbar SNA (LSNA). Unilateral microinjection of ATP into the PVN induced a dose-related increase in the LSNA (1 nmol: 38 ± 6 %, 2.5 nmol: 72 ± 7 %, 5 nmol: 96 ±13 %). This increase was significantly attenuated by blockade of P2 receptors (pyridoxalphosphate-6-azophenyl-20,40-disulphonic acid, PPADS) and glutamate receptors (kynurenic acid, KYN) or a combination of both. The increase in LSNA elicited by L-glutamate microinjection into the PVN was not affected by a previous injection of PPADS. Selective blockade of non-N-methyl-D-aspartate receptors (6-cyano-7-nitroquinoxaline-2,3-dione disodium salt, CNQX), but not N-methyl-D-aspartate receptors (NMDA) receptors (DL-2-amino-5-phosphonopentanoic acid, AP5), attenuated the ATP-induced sympathoexcitatory effects at the PVN level. Taken together, our data show that purinergic neurotransmission within the PVN is involved in the control of SNA via P2 receptor activation. Moreover, we show an interaction between P2 receptors and non-NMDA glutamate receptors in the PVN suggesting that these functional interactions might be important in the regulation of sympathetic outflow.

Remifentanil reversibly abolished phrenic long term facilitation in rats subjected to acute intermittent hypoxia

The aim was to investigate whether intravenous infusion of remifentanil would depress phrenic long term facilitation (pLTF) evoked by acute intermittent hypoxia (AIH) in adult, male, urethane anaesthetized Sprague-Dawley rats, bilaterally vagotomized, paralyzed and mechanically ventilated. The experimental group received a remifentanil infusion (0.5 μg/kg/min i.v., n=12), whereas the control group (n=6) received saline. Rats were exposed to AIH protocol. Phrenic nerve amplitude (PNA), burst frequency (f) and breathing rhythm parameters (Ti, Te, Ttot) were analyzed during 5 hypoxias and at 15, 30, and 60 minutes after the final hypoxia, and compared to baseline values. At the end of the experiment, the infusion of remifentanil was stopped and phrenic nerve activity was compared to baseline values prior to remifentanil infusion. In the control group, peak phrenic nerve activity (pPNA) significantly increased at 60 min (T60, increase by 138.8±28.3%, p=0.006) after the last hypoxic episode compared to baseline values, i.e. pLTF was induced. In remifentanil treated rats, there were no significant changes in peak phrenic nerve activity at T60 compared to baseline values (decrease by 5.3±16.5%, p>0.05), i.e. pLTF was abolished. Fifteen minutes following cessation of remifentanil infusion, pPNA increased by 93.2±40.2% (p<0.05) and remained increased compared to pre-remifentanil-infusion values for more than 30 minutes, i.e. pLTF could be observed after cessation of the remifentanil infusion. In conclusion, the short acting μ-opioid receptor agonist, remifentanil, reversibly abolished phrenic long term facilitation in urethane anesthetized rats.

Bothropstoxin-I reduces evoked acetylcholine release from rat motor nerve terminals: radiochemical and real-time video-microscopy studies

Understanding the biological activity profile of the snake venom components is fundamental for improving the treatment of snakebite envenomings and may also contribute for the development of new potential therapeutic agents. In this work, we tested the effects of BthTX-I, a Lys49 PLA(2) homologue from the Bothrops jararacussu snake venom. While this toxin induces conspicuous myonecrosis by a catalytically independent mechanism, a series of in vitro studies support the hypothesis that BthTX-I might also exert a neuromuscular blocking activity due to its ability to alter the integrity of muscle cell membranes. To gain insight into the mechanisms of this inhibitory neuromuscular effect, for the first time, the influence of BthTX-I on nerve-evoked ACh release was directly quantified by radiochemical and real-time video-microscopy methods. Our results show that the neuromuscular blockade produced by in vitro exposure to BthTX-I (1 μM) results from the summation of both pre- and postsynaptic effects. Modifications affecting the presynaptic apparatus were revealed by the significant reduction of nerve-evoked [(3)H]-ACh release; real-time measurements of transmitter exocytosis using the FM4-64 fluorescent dye fully supported radiochemical data. The postsynaptic effect of BthTX-I was characterized by typical histological alterations in the architecture of skeletal muscle fibers, increase in the outflow of the intracellular lactate dehydrogenase enzyme and progressive depolarization of the muscle resting membrane potential. In conclusion, these findings suggest that the neuromuscular blockade produced by BthTX-I results from transient depolarization of skeletal muscle fibers, consequent to its general membrane-destabilizing effect, and subsequent decrease of evoked ACh release from motor nerve terminals.

Chronic serotonin-norepinephrine reuptake transporter inhibition modifies basal respiratory output in adult mouse in vitro and in vivo

Respiratory disturbances are a common feature of panic disorder and present as breathing irregularity, hyperventilation, and increased sensitivity to carbon dioxide. Common therapeutic interventions, such as tricyclic (TCA) and selective serotonin reuptake inhibitor (SSRI) antidepressants, have been shown to ameliorate not only the psychological components of panic disorder but also the respiratory disturbances. These drugs are also prescribed for generalized anxiety and depressive disorders, neither of which are characterized by respiratory disturbances, and previous studies have demonstrated that TCAs and SSRIs exert effects on basal respiratory activity in animal models without panic disorder symptoms. Whether serotonin-norepinephrine reuptake inhibitors (SNRIs) have similar effects on respiratory activity remains to be determined. Therefore, the current study was designed to investigate the effects of chronic administration of the SNRI antidepressant venlafaxine (VHCL) on basal respiratory output. For these experiments, we recorded phrenic nerve discharge in an in vitro arterially-perfused adult mouse preparation and diaphragm electromyogram (EMG) activity in an in vivo urethane-anesthetized adult mouse preparation. We found that following 28-d VHCL administration, basal respiratory burst frequency was markedly reduced due to an increase in expiratory duration (T(E)), and the inspiratory duty cycle (T(I)/T(tot)) was significantly shortened. In addition, post-inspiratory and spurious expiratory discharges were seen in vitro. Based on our observations, we suggest that drugs capable of simultaneously blocking both 5-HT and NE reuptake transporters have the potential to influence the respiratory control network in patients using SNRI therapy.

Acid sensing ion channel 1 in lateral hypothalamus contributes to breathing control

Acid-sensing ion channels (ASICs) are present in neurons and may contribute to chemoreception. Among six subunits of ASICs, ASIC1 is mainly expressed in the central nervous system. Recently, multiple sites in the brain including the lateral hypothalamus (LH) have been found to be sensitive to extracellular acidification. Since LH contains orexin neurons and innervates the medulla respiratory center, we hypothesize that ASIC1 is expressed on the orexin neuron and contributes to acid-induced increase in respiratory drive. To test this hypothesis, we used double immunofluorescence to determine whether ASIC1 is expressed on orexin neurons in the LH, and assessed integrated phrenic nerve discharge (iPND) in intact rats in response to acidification of the LH. We found that ASIC1 was co-localized with orexinA in the LH. Microinjection of acidified artificial cerebrospinal fluid increased the amplitude of iPND by 70% (pH 7.4 v.s. pH 6.5:1.05±0.12 v.s. 1.70±0.10, n = 6, P<0.001) and increased the respiratory drive (peak amplitude of iPND/inspiratory time, PA/Ti) by 40% (1.10±0.23 v.s. 1.50±0.38, P<0.05). This stimulatory effect was abolished by blocking ASIC1 with a nonselective inhibitor (amiloride 10 mM), a selective inhibitor (PcTX1, 10 nM) or by damaging orexin neurons in the LH. Current results support our hypothesis that the orexin neuron in the LH can exert an excitation on respiration via ASIC1 during local acidosis. Since central acidification is involved in breathing dysfunction in a variety of pulmonary diseases, understanding its underlying mechanism may improve patient management.

[Ultrasonographic assessment of hemidiaphragm paralysis secondary to interscalene block]

BACKGROUND

In shoulder surgery, interscalene brachial plexus block has an incidence of 100% hemidiaphragm palsy due to phrenic nerve block. Controling the hemidiaphragm becomes a security ventilation parameter.

OBJECTIVE

identify and evaluate with ultrasound hemidiaphragm paralysis after interscalene block.

METHODS

This prospective study included 50 patients scheduled for shoulder surgery with interscalene block using neurostimulation. Diaphragmatic movement was evaluated by ultrasound prior to placement of block and the end of the surgical procedure to make the comparison between the two measurements.

RESULTS

Comparing the duration of the respiratory cycle at the start and the end of the surgical procedure, both normal and forced ventilation, there is a statistically significant difference of p < 0.001, as with the depth of the hemidiaphragm was found p < 0.001. 90% of patients had no adverse events, 8% had Horner's syndrome and 2% periauricular hypoesthesia. Hemidiaphragm paralysis was found in all cases, with a volume of 30 mL local anesthetic.

CONCLUSIONS

Ultrasound is a reliable tool that allows real time viewing of the respiratory cycle and measurements of the diaphragm dome it serves to identify diaphragmatic hemiparesis.

[Effects of Bufei Jianpi Recipe on the diaphragmatic neural discharge and the diaphragmatic muscle function in rats with chronic obstructive pulmonary disease]

OBJECTIVE

To observe the effects of Bufei Jianpi Recipe (BJR) on the diaphragmatic neural discharge and the diaphragmatic muscle function in rats with chronic obstructive pulmonary disease (COPD).

METHODS

Rats were randomly divided into the normal control group, the model group, the high dose BJR group (9.68 g/kg x d(-1)), the medium dose BJR group (4.84 g/kg x d(-1)), the low dose BJR group (2.42 g/kg x d(-1)), and the aminophylline group (2.3 mg/kg x d(-1)). The stable phase COPD rat model was prepared using repeated smoke inhalations and bacterial infections. The high, medium, and low dose BJR and aminophylline was respectively administered to rats from the ninth week to the twentieth week. The sampling was taken. The lung function, diaphragmatic neural discharge time (Td), and diaphragmatic neural discharge interval (Tdi), diaphragmatic neural discharge range (Rd), diaphragmatic neural discharge area (Ad), expiratory time (Tex), inspiratory time (Tin), respiratory rate (RR), respiratory excursion (RE), respiratory area (RA), and diaphragmatic muscular tension and endurance were detected.

RESULTS

Compared with the normal control group, the tidal volume (TV), peak expiratory flow (PEF), and 50% tidal volume expiratory flow (EF50) significantly decreased in the model group (P < 0.01). Td, Tdi, Tex, and Tin were significantly prolonged (P < 0. 05, P < 0.01). Ad, Rd, RR, RE, RA, diaphragmatic muscular tension and endurance significantly decreased (P < 0.05, P < 0.01). The ratio of type I and IIA diaphragmatic fibers significantly increased and type IIB significantly decreased (P < 0.01). The activity of ATP decreased and the activity of SDH increased (P < 0.01). The aforesaid indices were improved to different degrees in BJR groups, especially in the high dose BJR group and the medium dose BJR group (P < 0.05, P < 0.01).

CONCLUSIONS

BJR could significantly improve the diaphragmatic neural discharge and the diaphragmatic muscle function. Its efficacy was better than that of aminophylline.

Increased GABA(A) receptor ε-subunit expression on ventral respiratory column neurons protects breathing during pregnancy

GABAergic signaling is essential for proper respiratory function. Potentiation of this signaling with allosteric modulators such as anesthetics, barbiturates, and neurosteroids can lead to respiratory arrest. Paradoxically, pregnant animals continue to breathe normally despite nearly 100-fold increases in circulating neurosteroids. ε subunit-containing GABA_ARs are insensitive to positive allosteric modulation, thus we hypothesized that pregnant rats increase ε subunit-containing GABA_AR expression on brainstem neurons of the ventral respiratory column (VRC). In vivo, pregnancy rendered respiratory motor output insensitive to otherwise lethal doses of pentobarbital, a barbiturate previously used to categorize the ε subunit. Using electrode array recordings in vitro, we demonstrated that putative respiratory neurons of the preBötzinger Complex (preBötC) were also rendered insensitive to the effects of pentobarbital during pregnancy, but unit activity in the VRC was rapidly inhibited by the GABA_AR agonist, muscimol. VRC unit activity from virgin and post-partum females was potently inhibited by both pentobarbital and muscimol. Brainstem ε subunit mRNA and protein levels were increased in pregnant rats, and GABA_AR ε subunit expression co-localized with a marker of rhythm generating neurons (neurokinin 1 receptors) in the preBötC. These data support the hypothesis that pregnancy renders respiratory motor output and respiratory neuron activity insensitive to barbiturates, most likely via increased ε subunit-containing GABA_AR expression on respiratory rhythm-generating neurons. Increased ε subunit expression may be critical to preserve respiratory function (and life) despite increased neurosteroid levels during pregnancy.

Chemical constituents of the bark of Dipteryx alata vogel, an active species against Bothrops jararacussu venom

The effect of four sub-extracts prepared from the lyophilized hydroalcoholic bark of Dipteryx alata (Leguminosae-Papilionoideae) dissolved in a methanol-water (80:20) mixture through a liquid-liquid partition procedure has been investigated against the neuromuscular blockade of the venom of the snake Bothrops jararacussu. The active CH₂Cl₂ sub-extract has been extensively analyzed for its chemical constituents, resulting in the isolation of four lupane-type triterpenoids: lupeol (1), lupenone (2), 28-hydroxylup-20(29)-en-3-one (3), betulin (4), nine isoflavonoids: 8-O-methylretusin (5), 7-hydroxy-5,6,4’-trimethoxyisoflavone (6), afrormosin (8), 7-hydroxy-8,3’,4’-trimethoxyisoflavone (9), 7,3’-dihydroxy-8,4’-dimethoxyisoflavone (10), odoratin (11), 7,8,3’-trihydroxy-4’-methoxyisoflavone (13), 7,8,3’-trihydroxy-6,4’-dimethoxyisoflavone (15), dipteryxin (17), one chalcone: isoliquiritigenin (7), one aurone: sulfuretin (14) and three phenolic compounds: vanillic acid (12), vanillin (16), and protocatechuic acid (18). Their chemical structures were elucidated on the basis of spectroscopic analysis, including HRMS, 1D- and 2D-NMR techniques.

In vitro antiophidian properties of Dipteryx alata Vogel bark extracts

Extracts from Dipteryx alata bark obtained with different solvents (hexane, dichloromethane, ethyl acetate and methanol) were mixed in vitro with Bothrops jararacussu (Bjssu, 40 μg/mL) and Crotalus durissus terrificus (Cdt, 15 μg/mL) snake venoms, and applied to a mouse phrenic nerve-diaphragm preparation to evaluate the possible neutralization of venom effects. Cdt venom neurotoxic effect was not inhibited by any of the extracts, while the neurotoxic and myotoxic actions of Bjssu venom were decreased by the methanolic extract. This inhibition appears to be augmented by tannins. Dichloromethane bark extract inhibited ~40% of Bjssu venom effects and delayed blockade induced by Cdt. The methodology used to determine which extract was active allows inferring that: (i) phenolic acids and flavonoids contained in the methanolic extract plus tannins were responsible mostly for neutralization of Bjssu effects; (ii) terpenoids from the dichloromethane extract may participate in the anti-Cdt and anti-Bjssu venom effects; (iii) a given extract could not inhibit venoms from different species even if those belong to the same family, so it is improper to generalize a certain plant as antiophidian; (iv) different polarity extracts do not present the same inhibitory capability, thus demonstrating the need for characterizing both venom pharmacology and the phytochemistry of medicinal plant compounds.

The neuromuscular blockade produced by pure alkaloid, mitragynine and methanol extract of kratom leaves (Mitragyna speciosa Korth.)

AIM OF THE STUDY

The effects of pure alkaloid, mitragynine and a methanolic extract of kratom leaves were investigated on neuromuscular junction and compound nerve action potential.

MATERIALS AND METHODS

Wistar rats were killed by cervical dislocation and decapitated. The phrenic nerve-hemidiaphragms, hemidiaphragms and sciatic nerve were isolated.

RESULTS

Kratom methanolic extract present at 0.1-1 mg/mL and mitragynine (0.0156 mg/mL) decreased the muscle twitch on the isolated phrenic nerve-hemidiaphragm and hemidiaphragm preparation. Muscle relaxation caused by kratom extract (1 mg/mL) was greater than the effect of mitragynine. Pancuronium and succinylcholine potentiated the effect of kratom extract. It also had a direct relaxation effect on the hemidiaphragm muscle. The muscle relaxation caused by kratom extract was not antagonized by neostigmine, tetraethylammonium and calcium chloride. High concentrations of kratom extract (10-40 mg/mL) and mitragynine (2 mg/mL) blocked the nerve conduction, amplitude and duration of compound nerve action potential.

CONCLUSIONS

The mechanism of action of kratom extract might not act as a competitive antagonist of acetylcholine yet its dominant effect was at the neuromuscular junction and not at the skeletal muscle or somatic nerve.

[Solid-phase chemical synthesis and oxidative refolding of Hainantoxin-III]

Hainantoxin-III (HNTX-III) was synthesized using solid-phase chemical method with Fmoc-protected amino acids. Reversed-phase high performance liquid chromatography (RP-HPLC) was used to monitor the oxidative refolding of linear HNTX-III. It is found that the best refolding yield for 0.1 g/L linear HNTX-III could be obtained in double-distilled aqueous solution at pH 7.5 containing 1.0 mol/L L-arginine, 1.0 mmol/L reduced glutathione (GSH), and 0.1 mmol/L oxidized glutathione (GSSG). The relative molecular mass of the refolded HNTX-III was determined to be 3 607.68 by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Only one peak was found in the RP-HPLC chromatogram for the mixed sample of native HNTX-III and refolded HNTX-III at ratio of 1 : 1, and the effect of refolded HNTX-III on neuromuscular transmission in isolated mouse phrenic nerve-diaphragm preparations was almost same as that of native HNTX-III. The results indicate that refolded HNTX-III had the same structure and biological activities as the native HNTX-III.

Influence of 5-HT2A receptor blockade on phrenic nerve discharge at three levels of extracellular K+ in arterially-perfused adult rat

Recent observations from in vitro rodent preparations suggest an important role for the serotonin-2A (5-HT(2A)) receptor in eupneic (basal) and gasping respiratory activities, although the precise role appears to be different in different preparations. Since these in vitro preparations are typically supplied with elevated (and different) levels of K(+) to increase neuronal excitability, the role of endogenous activation of 5-HT(2A) receptors in these respiratory behaviors under "normal" levels of extracellular K(+) ([K(+)](o)) requires clarification. The current study sought to evaluate the influence of [K(+)](o) on the 5-HT(2A) receptor-mediated effects on basal respiratory activity and the phases of the hypoxic ventilatory response (HVR), including ischemia-induced gasping in an arterially-perfused adult rat preparation. Our data demonstrate that at each level of [K(+)](o) examined, blockade of 5-HT(2A) receptors increases basal phrenic burst frequency, decreases basal phrenic burst amplitude, alters basal phrenic burst pattern, and eliminates the phases of the HVR. These data support an important role for 5-HT(2A) receptors in respiratory control, and indicate the their role is not dependent on the level of [K(+)](o).

[Experimental study on promotion of somato-visceral heterogenic reinnervation with nerve growth factor in rat phrenic-to-vagus anastomosis model]

OBJECTIVE

To investigate the influence of nerve growth factor (NGF) on neuronal regeneration of somato-visceral heterogenic reinnervation using a rat phrenic-to-vagus anastomosis model.

METHODS

Forty male SD rats, aging 3 months and weighing 200 g, were selected and randomly divided into 3 groups. In group A (n = 10, control group), phrenic and vagus nerves were exposed and no neurography was performed. In group B (n = 15) and group C (n = 15), both nerves were transected and proximal stump of phrenic nerves were microsurgically anastomosed to the distal stump of vagus nerves. Postoperatively, group C was intraperitoneally injected with NGF (20 microg/kg x d), while groups A and B were given matching saline solution. Twelve weeks later, cardiac function was examined under electrical stimulation of the regenerated nerve. Light and electron microscopies were used to examine the heterogenic regenerated nerve, and the passing rate of axon and thickness of myelin sheath were calculated.

RESULTS

Under electrical never stimulation in groups A, B, and C, the decreases of blood pressure were (20.12 +/- 2.57), (10.63 +/- 2.44), and (14.18 +/- 2.93) mmHg (1 mmHg = 0.133 kPa), respectively; and the decreases of heart rate were (66.77 +/- 9.96), (33.44 +/- 11.82), and (43.27 +/- 11.02)/minutes, respectively. In group B, the decrease amplitudes of blood pressure and heart rate were 52.83% and 50.08% of group A, respectively. Blood pressure and heart rate in group C also decreased dramatically; the decrease amplitudes of blood pressure and heart rate in group C were 70.48% and 64.80% of group A. There were significant differences in the decrease amplitudes of blood pressure and heart rate (P < 0.05) between group B and group C. Morphological observation showed that heterogenic nerve fibers had the structure of matured myelin sheath and their axons could regenerate into the vagus nerve. In group B and group C, the passing rates of axon were 66.83% +/- 4.46% and 81.63% +/- 3.56%, respectively; and the thicknesses of myelin sheath were (0.25 +/- 0.10) microm and (0.46 +/- 0.08) microm, respectively; showing significant differences (P < 0.05) between group B and group C.

CONCLUSION

Heterogenic nerve is primarily a somatic motor nerve; NGF can promote the axons of heterogenic nerve to regenerate into the parasympathetic nerve.

Donepezil reverses buprenorphine-induced central respiratory depression in anesthetized rabbits

Buprenorphine is a mixed opioid receptor agonist-antagonist used in acute and chronic pain management. Although this agent's analgesic effect increases in a dose-dependent manner, buprenorphine-induced respiratory depression shows a marked ceiling effect at higher doses, which is considered to be an indicator of safety. Nevertheless, cases of overdose mortality or severe respiratory depression associated with buprenorphine use have been reported. Naloxone can reverse buprenorphine-induced respiratory depression, but is slow-acting and unstable, meaning that new drug candidates able to specifically antagonize buprenorphine-induced respiratory depression are needed in order to enable maximal analgesic effect without respiratory depression. Acetylcholine is an excitatory neurotransmitter in central respiratory control. We previously showed that a long-acting acetylcholinesterase inhibitor, donepezil, antagonizes morphine-induced respiratory depression. We have now investigated how donepezil affects buprenorphine-induced respiratory depression in anesthetized, paralyzed, and artificially ventilated rabbits. We measured phrenic nerve discharge as an Index of respiratory rate and amplitude, and compared discharges following the injection of buprenorphine with discharges following the injection of donepezil. Buprenorphine-induced suppression of the respiratory rate and respiratory amplitude was antagonized by donepezil (78.4 +/- 4.8 %, 92.3% +/- 22.8 % of control, respectively). These findings indicate that systemically administered donepezil restores buprenorphine-induced respiratory depression in anesthetized rabbits.

The effect of memantine and levodopa/carbidopa on the responses of phrenic nerve-diaphragm preparations from aged rats

BACKGROUND

Alzheimer's dementia (AD) and Parkinsonism are common in geriatric patients. Skeletal muscles are important for proper function of aging animals and humans. This study focuses on the influence of memantine (used in moderate to severe AD) and levodopa/carbidopa (LD/CD) (a cornerstone of Parkinson's disease treatment) on responses of isolated phrenic nerve-diaphragms (IPNDs) of aged male rats.

MATERIAL/METHODS

Of 100 aged male albino rats, 20 were untreated to study the in vitro effects of memantine and LD/CD on IPNDs and 80 were divided into groups 1 (control), 2 (oral memantine, 1.5 mg/kg/d), 3 (twice daily intraperitoneal LD/CD, 25/2.5 mg/kg), and 4 (both drugs). After three weeks-treatment the animals were sacrificed. Ten rats from each group were used to harvest IPNDs to study the effect of gallamine and 10 rats to measure nAchR (nicotinic acetylcholine receptor) alpha subunit mRNA by PCR.

RESULTS

The heights of indirectly elicited contractions were 63.1+/-4.6, 41.5+/-4.5, 70.6+/-4.7, and 53.9+/-3.3 mm for groups 1-4, respectively, and all differences were statistically significant (p<0.05). Memantine caused a leftward shift of the gallamine concentration-response curve and LD/CD a rightward shift. Reversal of neuromuscular block required larger neostigmine concentrations in the memantine group and smaller concentrations in the LD/CD group. In vitro, memantine inhibited diaphragmatic responses to indirect stimulation. Values of nAchR alpha subunit mRNA (microg/dl) were 0.7+/-0.16 (control), 0.13+/-0.11 (memantine), 2.3+/-0.94 (LD/CD), and 1.18+/-0.71 (both drugs) (p<0.05).

CONCLUSIONS

Memantine inhibits neuromuscular transmission in vitro and with in vivo treatment. LD/CD treatment enhances neuromuscular transmission. Clinical implications need further investigation.

Blockade of 5-HT(1A) receptors in the phrenic nucleus of the rat attenuated raphe induced activation of the phrenic nerve activity

Stimulation of the raphe pallidus nucleus produces facilitatory effects on respiratory activity. Numerous serotonergic projections from the raphe pallidus have been shown to terminate in the phrenic nucleus. This study was undertaken to examine the role of 5-hydroxytryptamine 1A (5-HT(1A)) receptors in the phrenic nucleus on the excitatory response of the phrenic nerve activity elicited from the raphe pallidus. We hypothesized that blockade of 5-HT(1A) receptors in the phrenic nucleus will attenuate raphe-induced facilitation of the phrenic nerve. Chemical stimulation of the raphe pallidus by synaptic excitant D,L-homocysteic acid produced increase in the amplitude of the phrenic nerve activity. After microinjection of the specific 5-HT(1A) receptor antagonist WAY, N-(2-(4,2-methoxyphenyl)-1-piperazinyl)ethyl)-N-2-pyridinyl-cyclohexane-carboxamide maleate into the phrenic nucleus, the raphe-induced facilitation of the phrenic nerve was attenuated. These data suggest that excitation of the phrenic nerve activity elicited by activation of the neurons in the raphe pallidus is mediated by 5-HT(1A) receptors in the phrenic nucleus.

Recovery of respiratory activity after C2 hemisection (C2HS): involvement of adenosinergic mechanisms

Consequences of spinal cord injury (SCI) depend on the level and extent of injury. Cervical SCI often results in a compromised respiratory system. Primary treatment of SCI patients with respiratory insufficiency continues to be with mechanical ventilatory support. In an animal model of SCI, an upper cervical spinal cord hemisection paralyzes the hemidiaphragm ipsilateral to the side of injury. However, a latent respiratory motor pathway can be activated to restore respiratory function after injury. In this review, restoration of respiratory activity following systemic administration of theophylline, a respiratory stimulant will be discussed. Pharmacologically, theophylline is a non-specific adenosine receptor antagonist, a phosphodiesterase inhibitor and a bronchodilator. It has been used in the treatment of asthma and other respiratory-related diseases such as chronic obstructive pulmonary disease (COPD) and in treatment of apnea in premature infants. However, the clinical use of theophylline to improve respiration in SCI patients with respiratory deficits is a more recent approach. This review will focus on the use of theophylline to restore respiratory activity in an animal model of SCI. In this model, a C2 hemisection (C2HS) interrupts the major descending respiratory pathways and paralyzes the ipsilateral hemidiaphragm. The review also highlights involvement of central and peripheral adenosine receptors in functional restitution. Biochemical binding assays that highlight changes in adenosine receptors after chronic theophylline administration are discussed as they pertain to understanding adenosine receptor-mediation in functional recovery. Finally, the clinical application of theophylline in SCI patients with respiratory deficits in particular is discussed.

Neuromuscular activity of BaTX, a presynaptic basic PLA2 isolated from Bothrops alternatus snake venom

We have previously isolated a Lys49 phospholipase A(2) homolog (BaTX) from Bothrops alternatus snake venom using a combination of molecular exclusion chromatography and reverse phase HPLC and shown its ability to cause neuromuscular blockade. In this work, we describe a one-step procedure for the purification of this toxin and provide further details of its neuromuscular activity. The toxin was purified by reverse phase HPLC and its purity and molecular mass were confirmed by SDS-PAGE, MALDI-TOF mass spectrometry, amino acid analysis and N-terminal sequencing. BaTX (0.007-1.4 microM) produced time-dependent, irreversible neuromuscular blockade in isolated mouse phrenic nerve-diaphragm and chick biventer cervicis preparations (time to 50% blockade with 0.35 microM toxin: 58+/-4 and 24+/-1 min, respectively; n=3-8; mean+/-S.E.) without significantly affecting the response to direct muscle stimulation. In chick preparations, contractures to exogenous acetylcholine (55 and 110 microM) or KCl (13.4 mM) were unaltered after complete blockade by all toxin concentrations. These results, which strongly suggested a presynaptic mechanism of action for this toxin, were reinforced by (1) the inability of BaTX to interfere with the carbachol-induced depolarization of the resting membrane, (2) a significant decrease in the frequency and amplitude of miniature end-plate potentials, and (3) a significant reduction (59+/-4%, n=12) in the quantal content of the end-plate potentials after a 60 min incubation with the toxin (1.4 microM). In addition, a decrease in the organ bath temperature from 37 degrees C to 24 degrees C and/or the replacement of calcium with strontium prevented the neuromuscular blockade, indicating a temperature-dependent effect possibly mediated by enzymatic activity.

Positive inotropic effects of Tityus cambridgei and T. serrulatus scorpion venoms on skeletal muscle

Toxins that block voltage-dependent K+ channels and those that modify Na+ channel gating exhibit positive inotropic effect on skeletal muscle. We compared the effect of the venom of Tityus cambridgei (Tc) and Tityus serrulatus (Ts) scorpions on mouse diaphragm force, in vitro. In indirect and direct (using D-tubocurarine 7.3 microM) stimulation, Tc, 10microg/mL, increased the contractile force, an effect prevented by tetrodotoxin (TTX) while Ts, 0.5 microg/mL, potentiated only indirectly stimulated diaphragm, thus indicating its activity is mainly mediated through acetylcholine release from nerve terminal. This effect is prevented by TTX and attenuated by the K+ channel opener cromakalim. In conclusion, our data show that while the positive inotropic effect of both venoms appears associated to the activity of Na+ and K+ channels, only Tc venom acts also directly on skeletal muscle. This finding call for further studies on Tc venom to identify the toxin responsible for its direct inotropic activity as it may have clinical applications.

Effects of baroreceptor activation on respiratory variability in rat

Controversy surrounds the respiratory responses to baroreceptor activation. Although many reflexes that effect respiration (e.g. chemoreflexes and nociceptive reflexes) frequently affect cardiovascular parameters, the effect of baroreflex stimulation within normal physiological limits is generally considered to affect only blood pressure and heart rate. Even though previous authors have reported that baroreceptor activation can affect respiratory activity, the effects on respiratory frequency and amplitude are highly variable, and changes in perfusion evoked by blood pressure manipulation could account for the observed effects. Here, we determined the respiratory effects of activating arterial baroreceptors by intravenous injection of phenylephrine or angiotensin II, or by electrical stimulation of the aortic depressor nerve (ADN). In urethane-anesthetized vagotomized rats, 1, 2 and 4s trains of tetanic ADN stimulation evoked 3.1+/-1.1%, 11.2+/-13.6% and 21.9+/-8.9% increases in inspiratory (TI) time and 26.5+/-18%, 23.4+/-15.7% and 34.6+/-20.9% increases in expiratory (TE) time, respectively (P<0.05 in both cases), but no effect on the amplitude of bursts recorded in the phrenic nerve. Similar effects were observed following pressor trials evoked by intravenous PE (TE: +26.1+/-9.1%, P<0.01), but not Ang II. Intermittent ADN stimulation (single pulse, 1 Hz) significantly increased the variability of TI during periods of low respiratory drive (P<0.05) without significantly affecting any other parameters. We propose that a specific baroreceptor-respiratory response exists that is independent of changes in blood flow. In contrast to the effects of baroreceptor stimulation on sympathetic nerve activity, the baro-respiratory response is subtle and highly dependent on respiratory drive.

Spinal activation of the cAMP-PKA pathway induces respiratory motor recovery following high cervical spinal cord injury

The present study investigated the involvement of the adenosine 3'5'-cyclic monophosphate-dependent protein kinase A (cAMP-PKA) pathway in the activation of the crossed-phrenic pathways after left C2 spinal cord hemisection. Experiments were conducted on left C2 spinal cord hemisected, anesthetized, vagotomized, pancuronium paralyzed, and artificially ventilated male Sprague-Dawley rats. One week post-injury, the ipsilateral phrenic nerve exhibited no respiratory-related activity indicating a functionally complete hemisection. Intrathecal spinal cord administration of the cAMP analog, 8-Br-cAMP at the level of the phrenic nucleus resulted in an enhancement of contralateral phrenic nerve output and a restoration of respiratory-related activity in the phrenic nerve ipsilateral to the hemisection. Furthermore, pre-treatment with Rp-8-Br-cAMP, a PKA inhibitor, abolished the effects of 8-Br-cAMP. These results suggest that PKA activation is necessary for the cAMP-mediated respiratory recovery following high cervical spinal cord injury and that activation of intracellular signaling cascades may represent an important strategy for improving respiratory function after spinal cord injury.