Respiratory Reflexes Research Articles

Modulation of Sensory Irritation Responsiveness by Adenosine and Malodorants

Respiratory tract reflex responses are an important defense mechanism against noxious airborne materials. This study was aimed at defining the effects of adenosine on sensory irritation responsiveness and its role in odorant-irritant interactions. These experiments were aimed at testing the hypothesis that adenosine, through the A2 receptor, enhances trigeminal nerve responses to multiple irritants and that odorants enhance responsiveness to irritants through A2 pathways in the female C57Bl/6 mouse. The adenosine precursor, AMP, immediately and markedly increased the sensory irritation response to capsaicin, cyclohexanone, and styrene, irritants that activate chemosensory nerves through differing receptor pathways. The neuromodulatory effect was blocked by the general adenosine receptor antagonist theophylline and by the A2 receptor-specific antagonist DMPX. Multiple odorants were examined, including R-carvone (spearmint), linalool (lavender), trimethylamine (rotting fish), mercaptoethanol, and ethyl sulfide (stench and rotten eggs). Of these, only mercaptoethanol and ethyl sulfide exhibited neuromodulatory effects, enhancing the sensory irritation response to styrene or cyclohexanone. This effect was blocked by theophylline and DMPX indicating the importance of adenosine A2 receptor pathways in this effect. These results highlight that trigeminal chemosensory responsiveness is not static, but can be quickly modulated by adenosine and select odors resulting in hyperresponsive states.

The effect of intravenous lidocaine on laryngeal and respiratory reflex responses in anaesthetised children*

We studied the effect of intravenous lidocaine on laryngeal and respiratory reflex responses in children anaesthetised with sevoflurane. We tested the hypothesis that the incidence of laryngospasm evoked by laryngeal stimulation is temporarily diminished after the administration of lidocaine. Forty children, aged between 25 and 84months, were anaesthetised with sevoflurane and breathed spontaneously through a laryngeal mask airway. Respiratory reflex responses were elicited by spraying distilled water onto the laryngeal mucosa at three time intervals: (i) before lidocaine was administered (baseline); (ii) at 2min and (iii) at 10min following the intravenous administration of a bolus of lidocaine 2mg.kg(-1) . A blinded reviewer assessed the evoked responses. The incidence of laryngospasm was reduced from 38% at baseline to 15% 2min after lidocaine administration (p<0.02) and 18% 10min after lidocaine administration (p=0.10). We conclude that intravenous lidocaine significantly reduced the incidence of laryngospasm but that the effect was short-lived.

Small patients, big ethics

Small patients, big ethics

Apparent Life-Threatening Events

Apparent Life-Threatening Events

Opioids inhibit visceral afferent activation of catecholamine neurons in the solitary tract nucleus

Brainstem A2/C2 catecholamine (CA) neurons within the solitary tract nucleus (NTS) influence many homeostatic functions, including food intake, stress, respiratory and cardiovascular reflexes. They also play a role in both opioid reward and withdrawal. Injections of opioids into the NTS modulate many autonomic functions influenced by catecholamine neurons including food intake and cardiac function. We recently showed that NTS-CA neurons are directly activated by incoming visceral afferent inputs. Here we determined whether opioid agonists modulate afferent activation of NTS-CA neurons using transgenic mice with EGFP expressed under the control of the tyrosine hydroxylase promoter (TH-EGFP) to identify catecholamine neurons. The opioid agonist Met-enkephalin (Met-Enk) significantly attenuated solitary tract-evoked excitatory postsynaptic currents (ST-EPSCs) in NTS TH-EGFP neurons by 80%, an effect reversed by wash or the mu opioid receptor-specific antagonist D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2 (CTOP). Met-Enk had a significantly greater effect to inhibit afferent inputs onto TH-EGFP-positive neurons than EGFP-negative neurons, which were only inhibited by 50%. The mu agonist, DAMGO, also inhibited the ST-EPSC in TH-EGFP neurons in a dose-dependent manner. In contrast, neither the delta agonist DPDPE, nor the kappa agonist, U69,593, consistently inhibited the ST-EPSC amplitude. Met-Enk and DAMGO increased the paired pulse ratio, decreased the frequency, but not amplitude, of mini-EPSCs and had no effect on holding current, input resistance or current–voltage relationships in TH-EGFP neurons, suggesting a presynaptic mechanism of action on afferent terminals. Met-Enk significantly reduced both the basal firing rate of NTS TH-EGFP neurons and the ability of afferent stimulation to evoke an action potential. These results suggest that opioids inhibit NTS-CA neurons by reducing an excitatory afferent drive onto these neurons through presynaptic inhibition of glutamate release and elucidate one potential mechanism by which opioids could control autonomic functions and modulate reward and opioid withdrawal symptoms at the level of the NTS.

Contribution of central μ-receptors to switching pulmonary C-fibers-mediated rapid shallow breathing into an apnea by fentanyl in anesthetized rats

Our previous study has shown that activating peripheral μ-receptors is necessary for switching the bronchopulmonary C-fibers (PCFs)-mediated rapid shallow breathing (RSB) into an apnea by systemic administration of fentanyl. The brainstem nuclei, such as the medial nucleus tractus solitarius (mNTS) and the pre-Botzinger complex (PBC), are required for completing the PCF-mediated respiratory reflexes. Moreover, these areas contain abundant μ-receptors and their activation prolongs expiratory duration (TE). Thus, we asked if central μ-receptors, especially those in the mNTS and PBC, are involved in fully expressing this RSB-apnea switch by fentanyl. In anesthetized rats, the cardiorespiratory responses to right atrial injection of phenylbiguanide (PBG, 3–6μg/kg) were repeated after: (1) fentanyl (iv), a μ-receptor agonist, alone (8μg/kg, iv); (2) fentanyl following microinjection of naloxone methiodide (NXM, an opioid receptor antagonist) into the cisterna magna (10μg/4μl); (3) the bilateral mNTS (10mM, 20nl); or (4) PBC (10mM, 20nl). Our results showed that PBG shortened TE by 37±6% (RSB, from 0.41±0.05 to 0.26±0.03s, P<0.01), but it markedly prolonged TE by 5.8-fold (an apnea, from 0.50±0.04s to 2.9±0.57s, P<0.01) after fentanyl (iv). Pretreatment with NXM injected into the cisterna magna or the PBC, but not the mNTS, prevented the fentanyl-induced switch. This study, along with our previous results mentioned above, suggests that although peripheral μ-receptors are essential for triggering the fentanyl-induced switch, central μ-receptors, especially those in the PBC, are required to fully exhibit such switch.Summary statement: Our results suggest that the activation of central μ-receptors, especially those in the pre-Botzinger complex, is required for switching the pulmonary C-fiber-mediated rapid shallow breathing into an apnea by systemic administration of fentanyl.

Effect of sublingual nitrate on respiratory reflexes arising from stimulation of juxta-pulmonary capillary (J) receptors by i.v. lobeline and short duration exercise

Juxta-pulmonary capillary (J or pulmonary C fiber) receptors are stimulated by an increase in pulmonary blood flow and give rise to respiratory acceleration and related sensations and inhibit exercise. However, the reverse, i.e., the effect of reducing pulmonary blood flow on their reflexes, is as yet not known. This was investigated by carrying out a placebo-controlled study on the acute effects of a single dose (0.4mg) of sublingual glyceryl nitrate (GTN), known to shift blood from the central to the peripheral circulation, on the respiratory parameters of exercising healthy subjects and on their responses to i.v. lobeline.In 10 subjects, GTN use delayed the first appearance of respiratory sensations from 9.08±0.9min to 11min (P=0.002), reduced the increase in minute ventilation by the end of 10min of exercise (P=0.003) and increased its duration by 1–4s and doubled it in the remaining one subject. In a majority of 8 of them, the effect of GTN on i.v. lobeline-induced respiratory reflexes and sensations was a significant increase in the dose required (P=0.006) for producing threshold effects and in the latency of their appearance (P=0.003). The latter feature points to a reduction in blood flow in the lung parenchyma where these receptors are located and to which they are sensitive. As this would have led to a reduced stimulation of these receptors, it would account for the delayed appearance of respiratory symptoms, a reduction in ventilatory increase and prolongation of exercise duration.We demonstrated a mechanism of reducing the stimulus level of J receptors by reducing pulmonary blood flow by means of pharmacological sequestration with GTN use, which then led to a reduction in the magnitude of respiratory and viscerosomatic reflexes, while noting at the same time that changes in blood flow in the pulmonary bed do not directly influence limb muscles, tendons and joints which also determine exercise output.

Respiration drives phase synchronization between blood pressure and R‐R interval following loss of cardiovagal baroreflex during vasovagal syncope

Thoracic hypovolemia and hyperpnea contribute to the nonlinear time‐dependent hemodynamic instability of vasovagal syncope. We used a phase synchronization index (PhSI) to describe coupling between systolic BP (SBP), RR‐interval (RR), and ventilation, and a directional index (DI) of coupling. We hypothesized normal AP‐RR PhSI during early 70° head‐up tilt, indicating intact cardiovagal baroreflex (CVB), but decrease as faint approached. Data were recorded supine and upright in 15 control (C) and 15 fainters (F). Data were evaluated during baseline, early tilt, late tilt, faint, and recovery. During late tilt to faint, F but not C showed SBP‐RR PhSI decrease (from 0.65±0.04 to 0.24±0.03) which increased at faint (0.80±0.03) coinciding with a change in phase difference from positive to negative. Starting in late tilt and through faint, F but not C exhibited increasing phase coupling between respiration and AP and between respiration and RR. DI indicated respiratory driven AP and RR in F. The initial drop in the SBP‐RR PhSI and directional change of phase difference at late tilt indicates loss of cardiovagal baroreflex. The subsequent increase in SBP‐RR PhSI is due to a respiratory synchronization and drive on both AP and RR. Cardiovagal baroreflex is lost prior to syncope and supplanted by respiratory reflexes, producing hypotension and bradycardia.

313 Psychogenic Intractable Sneezing. Case Report

BackgroundSneezing is a coordinated protective respiratory reflex which occurs due to stimulation of the upper respiratory tract, and frequently accompanies allergic or nonallergic rhinitis. Sneezing can also arise due to bright light or sun (ACHOO syndrome), physical stimulants of the trigeminal nerve, psychogenic or central nervous system pathologies, sexual ideation and psychogenic sneezing. There are few case reports in the literature of patients with psychogenic sneezing.Methods14-year-old girl who had incessant sneezing for over 4 days. The patient was initially seen in a rural hospital, were it was prescribed prednisone and antihistamines but the patient did not show any improvement. She was refered to 3rd level Hospital and treated with nasal steroids, antihistamines, and isotonic sodium chloride solution nasal spray; sneezing remitted in 2 hours. During a follow up visit nasal endoscopy was normal. Had a similar episode a month after that, and was referred to our service. She didn´t have either personal or family history of allergies.ResultsThere were not abnormalities in physical examination but obesity; nasal cytology and skin tests to aeroallergens were negatives. Received the same management with isotonic sodium chloride solution nasal and the symptoms remitted. Consultation with psychiatry is requested by probable psychogenic sneezing. The interrogation relates to the loss of father 3 years also suffered from bullying for obesity. Combined treatment was initiated by psychiatry and psychology.ConclusionsPsychogenic Sneezing is a rare disorder, but should be considered in the differential diagnosis of sneezing. May have suspect if inspiratory phase is quite short and the amount of nasal mucosal secretion expelled very low. Eyes may remain open during sneezing. It usually develops due to psychogenic factors and is refractory to medical treatment. It is important to assess the patient in a holistic manner through a medical history and physical examination. Psychosocial environmental conditions should be investigated, and once identified the trigger requires a multidisciplinary treatment.

Effects of Bupivacaine on the Isolated Rat Tracheal Smooth Muscle

Background Bupivacaine is an amide-linked local anesthetic that has been used in subcutaneous infiltration, epidural and peripheral nerve block for surgery over three decades. Several studies have suggested that inhaled local anesthetics can reduce respiratory reflexes. To assess the direct actions of bupivacaine on airway smooth muscle we used our preparation to examine the effectiveness of bupivacaine on isolated rat trachea. Methods A 5-mm-long portion of rat trachea was mounted in Krebs solution at 37 °C. Changes in tracheal contractility in response to a parasympathetic mimetic agent and electrical stimulation were measured using a transducer connected to a Pentium III computer equipped with polygraphy software. The following assessments were done: (1) effect of bupivacaine on the resting tension of tracheal smooth muscle; (2) effect of bupivacaine on contraction caused by exposure to 10 −6 M methacholine as a parasympathetic mimetic; (3) effect of bupivacaine on electrically induced contraction of tracheal smooth muscle. Results Bupivacaine had a negligible effect on the basal tracheal tension as the concentration increased. Bupivacaine inhibited the tracheal smooth muscle contraction in response to methacholine and electrical stimulation in a concentration-dependent manner. Conclusion The study indicates that bupivacaine might inhibit cholinergic neurotransmission and have an anti-spasmic effect on the trachea, in that it inhibited the contractions elicited by electrical field stimulation and a depolarizing agent.

Functional expression of the α7 and α4-containing nicotinic acetylcholine receptors on the neonatal rat carotid body

The carotid bodies (CBs) are chemosensory organs that respond to hypoxemia with transmitter neurosecretion, leading to a respiratory reflex response. It has been proposed that acetylcholine is a key regulator of transmitter release through activation of presynaptic nicotinic acetylcholine receptors (nAChRs). In the present work, we studied the identity of such nAChRs and their contribution to catecholamine release from CBs.Neonatal rat CBs were placed in a recording chamber for electrochemical recordings or disassociated for voltage-clamp studies on isolated cells. Fast nicotine superfusion increases catecholamine release from intact CBs. This response was diminished reversibly by the non-selective nAChR blocker hexamethonium, by the selective α7 blocker α-bungarotoxin and by the α4-containing nAChR blocker erysodine.In isolated CB cells the nAChR agonists nicotine, acetylcholine and cytisine all evoke inward currents with similar potencies. The nicotine-evoked current was fully blocked by mecamylamine and partially inhibited by α-bungarotoxin or erysodine. However, the combination of both α-bungarotoxin an erysodine failed to suppress this response. Immunodetection studies confirm the presence of α7 and α4 subunits in isolated dopaminergic CB cells. Our results show that activation of α7 and/or α4-containing nAChR subtypes have the ability to regulate catecholamine release from intact CB due to activation of fast inward currents expressed in chemoreceptor cells. Therefore, our results suggest that both nAChR subtypes contribute to the cholinergic nicotinic regulation of catecholamine signaling in the carotid body system.

Propofol facilitated excitatory postsynaptic currents frequency on nucleus tractus solitarii (NTS) neurons

Propofol, an intravenous anesthetic, is broadly used for general anesthesia and diagnostic sedations due to its fast onset and recovery. Propofol depresses respiratory and cardiovascular reflex responses, however, their underlying mechanisms are not well known. Cardiorespiratory information from visceral afferent vagus nerves is integrated in the nucleus tractus solitarii (NTS). Cardiac and respiratory signals transducing vagal afferent neurons release the excitatory neurotransmitter glutamate onto NTS neurons in an activity dependent manner and trigger negative feedback reflex responses. In this experiment, the effects of propofol on glutamatergic synaptic responses at NTS neurons was tested using patch clamp methods. Glutamatergic excitatory postsynaptic currents (EPSC) were recorded at chloride reversal potential (− 49 mV) without γ-aminobutyric acid type A (GABA A) receptor antagonists. Propofol (≥ 3 μM) facilitated frequency of the spontaneous EPSCs in a concentration dependent manner without altering amplitude and decay time. The GABA A receptor selective antagonist, gabazine (6 μM), attenuated propofol effects on glutamate release. Propofol (10 μM) evoked glutamate release was also blocked in the presence of the voltage dependent Na + and Ca 2+ channel blockers TTX (0.3 μM) and Cd 2+ (0.2 mM), respectively. In addition, the Na +–K +–Cl − cotransporter type 1 antagonist bumetanide (10 μM) also inhibited propofol evoked increase in sEPSC frequency. These results suggest that propofol evoked glutamate release onto NTS neurons by GABA A receptor-mediated depolarization of the presynaptic excitatory terminals.

Spinal blocks

SummaryEvery anesthetist should have the expertise to perform lumbar puncture that is the prerequisite to induce spinal anesthesia. Spinal anesthesia is easy and effective technique: small amount of local anesthetic injected in the lumbar cerebrospinal fluid provides highly effective anesthesia, analgesia, and sympathetic and motor block in the lower part of the body. The main limitation of spinal anesthesia is a variable and relatively short duration of the block with a single‐injection of local anesthetic. With appropriate use of adjuvant or combining spinal anesthesia with epidural anesthesia, the analgesic action can be controlled in case of early recovery of initial block or in patients with prolonged procedures. Contraindications are rare. Bleeding disorders and any major dysfunction in coagulation system are rare in children, but spinal anesthesia should not be used in children with local infection or increased intracranial pressure. Children with spinal anesthesia may develop the same adverse effects as has been reported in adults, but in contrast to adults, cardiovascular deterioration is uncommon in children even with high blocks. Most children having surgery with spinal anesthesia need sedation, and in these cases, close monitoring of sufficient respiratory function and protective airway reflexes is necessary. Postdural puncture headache and transient neurological symptoms have been reported also in pediatric patients, and thus, guardians should be provided instructions for follow‐up and contact information if symptoms appear or persist after discharge. Epidural blood patch is effective treatment for prolonged, severe headache, and nonopioid analgesic is often sufficient for transient neurological symptoms.

Disparate purinergic modulation of respiration in rats and mice

Disparate purinergic modulation of respiration in rats and mice

Sidney Hilton (1921–2011) physiologist

Sidney Hilton (1921–2011) physiologist

Hydrogen sulfide augments synaptic neurotransmission in the nucleus of the solitary tract.

Within the brain stem, the nucleus tractus solitarii (NTS) serves as a principal central site for sensory afferent integration from the cardiovascular and respiratory reflexes. Neuronal activity and synaptic transmission in the NTS are highly pliable and subject to neuromodulation. In the central nervous system, hydrogen sulfide (H₂S) is a gasotransmitter generated primarily by the enzyme cystathionine-β-synthase (CBS). We sought to determine the role of H₂S, and its generation by CBS, in NTS excitability. Real-time RT-PCR, immunoblot, and immunohistochemistry analysis identified the presence of CBS in the NTS. Patch-clamp electrophysiology in brain stem slices examined excitatory postsynaptic currents (EPSCs) and membrane properties in monosynaptically driven NTS neurons. Confocal imaging of labeled afferent synaptic terminals in NTS slices monitored intracellular calcium. Exogenous H₂S significantly increased the amplitude of evoked solitary tract (TS)-EPSCs, frequency of miniature (m)EPSCs, and presynaptic terminal calcium fluorescence in the NTS. H₂S did not alter action potential discharge or postsynaptic properties. On the other hand, the CBS inhibitor aminooxyacetate (AOA) significantly reduced the amplitude of TS-EPSCs and presynaptic terminal calcium fluorescence in the NTS without altering postsynaptic properties. Taken together, these data support a presynaptic role for endogenous H₂S in modulation of excitatory neurotransmission in the NTS.

Total intravenous anaesthesia by boluses or by continuous rate infusion of propofol in mute swans (Cygnus olor)

ObjectiveTo investigate intravenous (IV) propofol given by intermittent boluses or by continuous rate infusion (CRI) for anaesthesia in swans. Study designProspective randomized clinical study. AnimalsTwenty mute swans (Cygnus olor) (eight immature and 12 adults) of unknown sex undergoing painless diagnostic or therapeutic procedures. MethodsInduction of anaesthesia was with 8 mg kg−1 propofol IV. To maintain anaesthesia, ten birds (group BOLI) received propofol as boluses, whilst 10 (group CRI) received propofol as a CRI. Some physiological parameters were measured. Anaesthetic duration was 35 minutes. Groups were compared using Mann–Whitney U-test. Results are median (range). ResultsAnaesthetic induction was smooth and tracheal intubation was achieved easily in all birds. Bolus dose in group BOLI was 2.9 (1.3–4.3) mg kg−1; interval between and number of boluses required were 4 (1–8) minutes and 6 (4–11) boluses respectively. Total dose of propofol was 19 (12.3–37.1) mg kg−1. Awakening between boluses was very abrupt. In group CRI, propofol infusion rate was 0.85 (0.8–0.9) mg kg−1 minute−1, and anaesthesia was stable. Body temperature, heart and respiratory rates, oxygen saturation (by pulse oximeter) and reflexes did not differ between groups. Oxygen saturations (from pulse oximeter readings) were low in some birds. Following anaesthesia, all birds recovered within 40 minutes. In 55 % of all, transient signs of central nervous system excitement occurred during recovery. Conclusions and clinical relevance8 mg kg−1 propofol appears an adequate induction dose for mute swans. For maintenance, a CRI of 0.85 mg kg−1 minute−1 produced stable anaesthesia suitable for painless clinical procedures. In contrast bolus administration, was unsatisfactory as birds awoke very suddenly, and the short intervals between bolus requirements hampered clinical procedures. Administration of additional oxygen throughout anaesthesia might reduce the incidence of low arterial haemoglobin saturation.

Caudal nuclei of the rat nucleus of the solitary tract differentially innervate respiratory compartments within the ventrolateral medulla

A substantial array of respiratory, cardiovascular, visceral and somatic afferents are relayed via the nucleus of the solitary tract (NTS) to the brainstem (and forebrain). Despite some degree of overlap within the NTS, specificity is maintained in central respiratory reflexes driven by second order afferent relay neurons in the NTS. While the topographic arrangement of respiratory-related afferents targeting the NTS has been extensively investigated, their higher order brainstem targets beyond the NTS has only rarely been defined with any precision. Nonetheless, the various brainstem circuits serving blood gas homeostasis and airway protective reflexes must clearly receive a differential innervation from the NTS in order to evoke stimulus appropriate behavioral responses. Accordingly, we have examined the question of which specific NTS nuclei project to particular compartments within the ventral respiratory column (VRC) of the ventrolateral medulla. Our analyses of NTS labeling after retrograde tracer injections in the VRC and the nearby neuronal groups controlling autonomic function indicate a significant distinction between projections to the Bötzinger complex and preBötzinger complex compared to the remainder of the VRC. Specifically, the caudomedial NTS, including caudal portions of the medial solitary nucleus and the commissural division of NTS project relatively densely to the region of the retrotrapezoid nucleus and rostral ventrolateral medullary nucleus as well as to the rostral ventral respiratory group while avoiding the intervening Bötzinger and preBötzinger complexes. Area postrema appears to demonstrate a pattern of projections similar to that of caudal medial and commissural NTS nuclei. Other, less pronounced differential projections of lateral NTS nuclei to the various VRC compartments are additionally noted.

Effects of loading on upper airway and respiratory pump muscle motoneurons

The functional outcomes of respiratory muscle loading by chemical (e.g. hypercapnia), mechanical (i.e. external mechanical loading) or ventilatory (e.g. exercise) factors can be either positive, such as through an increase in pressure-generating capacity of the inspiratory muscles or detrimental, such as by fatigue. Neurophysiological responses to respiratory muscle loading can occur at one or more points along the pathway from motor cortex to muscle. This paper describes the respiratory pump and upper airway motoneuron responses to the imposition of acute loads including processes of pre-activation, respiratory reflexes, potentiation and fatigue. It also considers changes suggestive of adaptation to chronic loading either from specific respiratory muscle training programs or as part of disease processes such as chronic obstructive pulmonary disease or obstructive sleep apnoea.

Menthol and related cooling compounds.

Menthol and related cooling compounds such as 'coolant agent 10', are widely used in products ranging from common cold medications to toothpastes, confectionery, cosmetics and pesticides. The review brings together a range of information on production and chemistry of menthol, and its metabolism, mechanism of action, structure-activity relationships, pharmacology and toxicology. In particular, the coolant action and carminative actions of menthol are discussed in terms of actions on calcium conductance in sensory nerves and smooth muscle. The actions of menthol on the nose, respiratory reflexes, oral cavity, skin and gastrointestinal tract are reviewed.