Nicotinic acetylcholine receptors on vagal afferent neurons

Nicotinic receptors as SARS-CoV-2 spike co-receptors?

Nicotinic acetylcholine receptors (nAChRs) play an important role in homeostasis and respiratory diseases. Controversies regarding the association between COVID-19 hospitalizations and smoking suggest that nAChRs may contribute to SARS-CoV-2 respiratory syndrome. We recently detailed the expression and localization of all nAChR subunits in the human lung. Since virus association with nAChRs has been shown in the past, we hypothesize that nAChR subunits act as SARS-CoV-2 Spike co-receptors. Based on sequence alignment analysis, we report domains of high molecular similarities in nAChRs with the binding domain of hACE2 for SARS-CoV-2 Spike protein. This hypothesis supported by in silico pilot data provides a rational for the modelling and the in vitro experimental validation of the interaction between SARS-CoV-2 and the nAChRs.

Sevoflurane is an effective adjuvant to propofol-based total intravenous anesthesia for attenuating cough reflex in nonintubated video-assisted thoracoscopic surgery

BACKGROUND

Nonintubated video-assisted thoracic surgery (VATS) has been widely developed during the recent years. Cough reflex is an inevitably encountered problem while approaching lung lesions, and it may induce major bleeding. Sevoflurane anesthesia may attenuate cough reflex by inhibiting the pulmonary irritant receptors. However, the incidence of postoperative nausea and vomiting (PONV) in inhalational anesthesia is higher than in the propofol-based total intravenous anesthesia (TIVA). We investigated the effect of sevoflurane combination with propofol-based TIVA on cough reflex and PONV in nonintubated VATS.

METHODS

Ninety patients undergoing nonintubated VATS with laryngeal mask airway (LMA) and spontaneous breathing were randomly assigned for TIVA or propofol/sevoflurane anesthesia. In the TIVA group (n = 45), anesthesia was induced and maintained with propofol and fentanyl; in the propofol/sevoflurane (P/S) group (n = 45), 1% sevoflurane anesthesia was added to propofol and fentanyl anesthesia. The primary outcome measurements were cough reflex. In addition, the incidence of PONV and extubation time were investigated.

RESULTS

Patients with cough reflex were significantly fewer in the P/S group than in the TIVA group (10/45 vs 34/45; P < .001). The cough severity (35/5/5/0 vs 11/17/17/0; P < .001) and limb movement (40/5/0/0 vs 28/17/0/0; P < .001) were lower in the P/S group than in the TIVA group. Besides, incremental fentanyl bolus for cough reflex was 5 (0 [0-1]) in the P/S group and 17 (0 [0-3]) in the TIVA group (P < .05). And there was no conversion to general anesthesia, postoperative hemorrhage, aspiration pneumonia, or PONV in the 2 groups. Besides, there was no significant difference in extubation time (TIVA: 5.04 ± 2.88 vs P/S: 4.44 ± 2.98 minutes; P = .33).

CONCLUSION

Sevoflurane attenuated cough reflex under propofol-based TIVA and did not increase the incidence of PONV and extubation time in nonintubated VATS.

α-Conotoxins active at α3-containing nicotinic acetylcholine receptors and their molecular determinants for selective inhibition

Neuronal α3-containing nicotinic acetylcholine receptors (nAChRs) in the peripheral nervous system (PNS) and non-neuronal tissues are implicated in a number of severe disease conditions ranging from cancer to cardiovascular diseases and chronic pain. However, despite the physiological characterization of mouse models and cell lines, the precise pathophysiology of nAChRs outside the CNS remains not well understood, in part because there is a lack of subtype-selective antagonists. α-Conotoxins isolated from cone snail venom exhibit characteristic individual selectivity profiles for nAChRs and, therefore, are excellent tools to study the determinants for nAChR-antagonist interactions. Given that human α3β4 subtype selective α-conotoxins are scarce and this is a major nAChR subtype in the PNS, the design of new peptides targeting this nAChR subtype is desirable. Recent studies using α-conotoxins RegIIA and AuIB, in combination with nAChR site-directed mutagenesis and computational modelling, have shed light onto specific nAChR residues, which determine the selectivity of the α-conotoxins for the human α3β2 and α3β4 subtypes. Publications describing the selectivity profile and binding sites of other α-conotoxins confirm that subtype-selective nAChR antagonists often work through common mechanisms by interacting with the same structural components and sites on the receptor.

LINKED ARTICLES

This article is part of a themed section on Nicotinic Acetylcholine Receptors. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.11/issuetoc.

Targets of polyamine dysregulation in major depression and suicide: Activity-dependent feedback, excitability, and neurotransmission

Major depressive disorder (MDD) is a leading cause of disability worldwide characterized by altered neuronal activity in brain regions involved in the control of stress and emotion. Although multiple lines of evidence suggest that altered stress-coping mechanisms underlie the etiology of MDD, the homeostatic control of neuronal excitability in MDD at the molecular level is not well established. In this review, we examine past and current evidence implicating dysregulation of the polyamine system as a central factor in the homeostatic response to stress and the etiology of MDD. We discuss the cellular effects of abnormal metabolism of polyamines in the context of their role in sensing and modulation of neuronal, electrical, and synaptic activity. Finally, we discuss evidence supporting an allostatic model of depression based on a chronic elevation in polyamine levels resulting in self-sustained stress response mechanisms maintained by maladaptive homeostatic mechanisms.

Anacardium occidentale Linn. (Anacardiaceae) stem bark extract induces hypotensive and cardio-inhibitory effects in experimental animal models

Anacardium occidentale Linn. (Anacardiaceae) is a plant largely used in Africa for the treatment of different diseases. In Côte d'Ivoire it's commonly used for the treatment of hypertension. The present study was carried out in order to assess the effects of Anacardium occidentale extract (ANOE) on cardiovascular parameters in animal models. A mercury manometer kymograph of Ludwig was used to measure the blood pressure of normotensive rabbits in control conditions (normal physiological solution) and under the influence of ANOE. The contractile activity of an isolated rat heart was also measured in control conditions and under the influence of ANOE in different physiological media using a modified Langendhorff (1895) apparatus. The aqueous Anacardium occidentale (ANOE) bark extract applied intravenously in different doses (12, 40, 90, and 167 mg/kg b.w.), produced a significant dose-dependent decrease in blood pressure of previously normotensive rabbits (up to 89% vs control). Atropine (1 mg/ml) pre-treatment failed to reverse the hypotensive effects elicited by the extract. ANOE applied to isolated rat heart preparations in different concentrations (0.01, 0.1, 1.0, and 10 µg/ml) induced negative inotropic and chronotropic effects. Atropine pre-treatment of heart preparations (0.1 µg/ml) failed to reverse the negative effects induced by ANOE. The extract's action on heart contractile activity studied in modified culture media further confirmed its cardio-inhibitory effects. ANOE induced strong hypotensive and cardio-inhibitory effects in animal models.

Chemosensitivity of unmyelinated axons in isolated human gastric vagus nerve

Vagal afferent neurons from the stomach may be activated not only by chemical stimuli in the mucosa but also by circulating factors. In the present study, we have used electrophysiological techniques to characterize functional activity of several receptors for chemical mediators on unmyelinated axons in isolated fascicles of human gastric vagus nerve. Application of agonists at the nicotinic acetylcholine receptor (nAChR), 5-HT(3) subtype of serotonin receptor, and the transient receptor potential vanilloid receptor-1 (TRPV1) resulted in a change in the height and/or threshold of the C-fiber compound action potential. These effects were blocked by specific antagonists of nAChR (mecamylamine), 5-HT(3) (Y-25130), and TRPV1 (capsazepine). We conclude that the chemosensitivity of unmyelinated vagal axons can be studied using isolated segments of human gastric vagus nerve. The presence of receptors indicates that circulating factors may modify vagal afferent neurons also by effects on the axonal membrane.

Hidden function of neuronal nicotinic acetylcholine receptor β2 subunits in ganglionic transmission: comparison to α5 and β4 subunits

Neuronal nicotinic acetylcholine receptors (nAChR), which modulate fast excitatory postsynaptic potentials (f-EPSP), are located on both pre- and postganglionic sites in the autonomic nervous system (ANS). The receptor subunits alpha3, alpha5, alpha7, beta2 and beta4 are present in autonomic ganglia in various combinations and modulate acetylcholine (ACh) transmission. In the present study, autonomic functions were systemically examined in mice lacking beta2 subunits (beta2-/-) to further understand the functional role of beta2 subunits in modulating ganglionic transmission. The results show normal autonomic functions, both under physiological conditions and in perturbed conditions, on thermoregulation, pupillary size, heart rate responses and ileal contractile reactions. This suggests that the function of beta2-containing receptors in ganglionic transmission is hidden by the predominant beta4 containing receptors and confirms previous studies which suggest that alpha3alpha5beta4 nAChRs are sufficient for autonomic transmission. On the other hand, beta2-containing receptors have only a minor function on postsynaptic responses to ACh, but may modulate ACh release presynaptically, although there is no evidence for this.

Weak neurotoxin from Naja kaouthia cobra venom affects haemodynamic regulation by acting on acetylcholine receptors

Recent in vitro studies of weak neurotoxins from snake venoms have demonstrated their ability to interact with both muscle-type and neuronal alpha7 nicotinic acetylcholine receptors (nAChR). However, the biological activity in vivo of weak neurotoxins remains largely unknown. We have studied the influence of weak neurotoxin (WTX) from the venom of cobra Naja kaouthia on arterial blood pressure (BP) and heart rate (HR) in rats and mice. It was found that intravenous injection of WTX induced a dose-dependent decrease in BP and an increase in HR in both species, the rats being more sensitive to WTX. Application of WTX following blockade of nAChRs or muscarinic acetylcholine receptors (mAChR) by hexamethonium or atropine, respectively, showed that both nAChRs and mAChRs are involved in the haemodynamic effects of WTX. Blockade of either nAChRs or mAChRs affected WTX action differently in rats and mice, thus reflecting interspecies differences in haemodynamic regulation.

Expression of functional nicotinic acetylcholine receptors in neuroepithelial bodies of neonatal hamster lung

Pulmonary neuroepithelial bodies (NEB) are presumed airway chemoreceptors involved in respiratory control, especially in the neonate. Nicotine is known to affect both lung development and control of breathing. We report expression of functional nicotinic acetylcholine receptors (nAChR) in NEB cells of neonatal hamster lung using a combination of morphological and electrophysiological techniques. Nonisotopic in situ hybridization method was used to localize mRNA for the beta 2-subunit of nAChR in NEB cells. Double-label immunofluorescence confirmed expression of alpha 4-, alpha 7-, and beta 2-subunits of nAChR in NEB cells. The electrophysiological characteristics of nAChR in NEB cells were studied using the whole cell patch-clamp technique on fresh lung slices. Application of nicotine ( approximately 0.1-100 microM) evoked inward currents that were concentration dependent (EC50 = 3.8 microM; Hill coefficient = 1.1). ACh (100 microM) and nicotine (50 microM) produced two types of currents. In most NEB cells, nicotine-induced currents had a single desensitizing component that was blocked by mecamylamine (50 microM) and dihydro-beta-erythroidine (50 microM). In some NEB cells, nicotine-induced current had two components, with fast- and slow-desensitizing kinetics. The fast component was selectively blocked by methyllcaconitine (MLA, 10 nM), whereas both components were inhibited by mecamylamine. Choline (0.5 mM) also induced an inward current that was abolished by 10 nM MLA. These studies suggest that NEB cells in neonatal hamster lung express functional heteromeric alpha 3 beta 2, alpha 4 beta 2, and alpha 7 nAChR and that cholinergic mechanisms could modulate NEB chemoreceptor function under normal and pathological conditions.

In vitro effect of sanguinarine alkaloid on binding of [3H]candesartan to the human angiotensin AT1 receptor

The type of interaction of 5-methyl-2,3,7,8-bis(methylenedioxy)benzo[c]phenanthridinium (sanguinarine), an alkaloid isolated from the root of Bocconia frutescens L., with the human angiotensin AT(1) receptor was evaluated in both intact cells and membrane binding of [3H](2-ethoxy-1-[(2'-(1H-tetrazol-5-yl)biphenyl-4-yl)methyl]-1H-benzimidazoline-7-carboxylic acid) ([3H]candesartan). The results indicate that the inhibition of [3H]candesartan binding by sanguinarine is independent of cell viability, since the alkaloid inhibited at a similar extent radioligand binding on both intact Chinese hamster ovary (CHO) cells transfected with the human angiotensin AT(1) receptor (hAT(1)) and their cell membranes (K(i)=0.14 and 1.10 microM, respectively). The unsuccessful recovery of [3H]candesartan binding after washing sanguinarine off the cells suggested a nearly irreversible or slow reversible interaction. Saturation binding studies showed a substantial reduction of the B(max) without affecting the K(d). In addition, the presence of 2-n-butyl-4chloro-5-hydroxymethyl-1-[(2'-(1H-tetrazol-5-yl)biphenyl-4-yl)methyl]imidazole (losartan) could not prevent sanguinarine inhibition of [3H]candesartan binding neither. The present findings indicate that sanguinarine interacts with the receptor in a slow, nearly irreversible and noncompetitive manner.

Nicotinic receptor-mediated effects on appetite and food intake

It is well known, although not well understood, that smoking and eating just do not go together. Smoking is associated with decreased food intake and lower body weight. Nicotine, administered either by smoking or by smokeless routes, is considered the major appetite-suppressing component of tobacco. Perhaps the most renowned example of nicotine's influence on appetite and feeding behavior is the significant weight gain associated with smoking cessation. This article presents an overview of the literature at, or near, the interface of nicotinic receptors and appetite regulation. We first consider some of the possible sites of nicotine's action along the complex network of neural and non-neural regulators of feeding. We then present the hypothesis that the lateral hypothalamus is a particularly important locus of the anorectic effects of nicotine. Finally, we discuss the potential role of endogenous cholinergic systems in motivational feeding, focusing on cholinergic pathways in the lateral hypothalamus.