Nicotinic Acetylcholine Receptor Antagonist Research Articles

Cerebral Cortical Vasodilation via Nicotinic Receptors by Heated Tobacco Product Aerosol Extract in Rats

Introduction: Smoking increases the risk of lung cancer due to a number of components of smoke. The use of novel heated tobacco products (HTPs), alternative to conventional combustion cigarettes, has increased in recent years. However, the in vivo biological effects of HTPs are poorly understood. This study aimed to clarify the acute effects of injecting aerosol extract prepared from an HTP on regional cerebral blood flow (rCBF) in rat cortex by comparing them to the effects of injecting smoke extract prepared from conventional combustible cigarettes. Methods: In urethane anesthetized rats, rCBF was measured using laser speckle contrast imaging simultaneously with arterial pressure. Results: Both cigarette smoke extract and HTP aerosol extract, at a dose equivalent to 30 μg nicotine/kg, injected intravenously, increased cortical rCBF without changing arterial pressure. The magnitude and time course of the increased rCBF response to both extracts were similar throughout the cortical area, and the rCBF increases were all abolished by dihydro-β-erythroidine, an α4β2-preferring nicotinic acetylcholine receptor (nAChR) antagonist. Conclusion: In conclusion, our study demonstrated that the effect of injecting aerosol extract prepared from an HTP, an acute increase in cortical rCBF, is mediated via activation of α4β2-like neuronal nAChRs in the brain.

The Role of Glucocorticoid and Nicotinic Acetylcholine Receptors in the Reward-Enhancing Effects of Nicotine in the ICSS Procedure in Male and Female Rats.

Tobacco use disorder is a chronic disorder that affects more than one billion people worldwide and causes the death of millions each year. The rewarding properties of nicotine are critical for the initiation of smoking. Previous research has shown that the activation of glucocorticoid receptors (GRs) plays a role in nicotine self-administration in rats. However, the role of GRs in the acute rewarding effects of nicotine are unknown. In this study, we investigated the effects of the GR antagonist mifepristone and the nicotinic acetylcholine receptor (nAChR) antagonist mecamylamine on the reward-enhancing effects of nicotine using the intracranial self-stimulation (ICSS) procedure in adult male and female rats. The rats were prepared with ICSS electrodes in the medial forebrain bundle and then trained on the ICSS procedure. Nicotine lowered the brain reward thresholds and decreased response latencies similarly in male and female rats. These findings suggest that nicotine enhances the rewarding effects of ICSS and has stimulant properties. Treatment with the GR antagonist mifepristone did not affect the reward-enhancing effects of nicotine but increased response latencies, suggesting a sedative effect. Mecamylamine did not affect the brain reward thresholds or response latencies of the control rats, but prevented the nicotine-induced decrease in brain reward thresholds and reward latencies. These findings indicate that the rewarding effects of nicotine are mediated via the activation of nAChRs, and that the activation of GRs does not contribute to the acute rewarding effects of nicotine. These studies enhance our understanding of the neurobiological mechanisms underlying tobacco use disorder.

Gelatin nanoparticles loaded with 3-alkylpyridinium salt APS7, an analog of marine toxin, are a promising support in human lung cancer therapy

This study demonstrates the potential of gelatin nanoparticles as a nanodelivery system for antagonists of nicotinic acetylcholine receptors (nAChRs) to improve chemotherapy efficacy and reduce off-target effects. Too often, chemotherapy for lung cancer does not lead to satisfactory results. Therefore, new approaches directed at multiple pharmacological targets in cancer therapy are being developed. Following the activation of nAChRs (e.g. by nicotine), cancer cells begin to proliferate and become more resistant to chemotherapy-induced apoptosis. This work shows that the 3-alkylpyridinium salt, APS7, a synthetic analog of a toxin from the marine sponge Haliclona (Rhizoneira) sarai, acts as an nAChR antagonist that inhibits the pro-proliferative and anti-apoptotic effects of nicotine on A549 human lung adenocarcinoma cells. In this study, gelatin-based nanoparticles filled with APS7 (APS7-GNPs) were prepared and their effects on A549 cells were compared with that of free APS7. Both APS7 and APS7-GNPs inhibited Ca2+ influx and increased the efficacy of cisplatin chemotherapy in nicotine-stimulated A549 cells. However, significant benefits from APS7-GNPs were observed – a stronger reduction in the proliferation of A549 lung cancer cells and a much higher selectivity in cytotoxicity towards cancer cells compared with non-tumorigenic lung epithelial BEAS-2B cells.

αO-Conotoxin GeXIVA[1,2] Suppresses In Vivo Tumor Growth of Triple-Negative Breast Cancer by Inhibiting AKT-mTOR, STAT3 and NF-κB Signaling Mediated Proliferation and Inducing Apoptosis.

Breast cancer is one of the leading causes of cancer mortality worldwide, and triple-negative breast cancer (TNBC) is the most problematic subtype. There is an urgent need to develop novel drug candidates for TNBC. Marine toxins are a valuable source for drug discovery. We previously identified αO-conotoxin GeXIVA[1,2] from Conus generalis, which is a selective antagonist of α9 nicotinic acetylcholine receptors (nAChRs). Recent studies indicated that α9 nAChR expression is positively correlated with breast cancer development; thus, α9 nAChR could serve as a therapeutic target for breast cancer. In this study, we aimed to investigate the in vivo antitumor effects of GeXIVA[1,2] on TNBC and to elucidate its underlying anticancer mechanism. Our data showed that GeXIVA[1,2] effectively suppressed 4T1 tumor growth in vivo at a very low dose of 0.1 nmol per mouse. Our results uncovered that the antitumor mechanism of GeXIVA[1,2] simultaneously induced apoptosis and blocked proliferation. Further investigations revealed that GeXIVA[1,2]-induced Caspase-3-dependent apoptosis was achieved through regulating Bax/Bcl-2 balance, and GeXIVA[1,2]-inhibited proliferation was mediated by the downregulation of the AKT-mTOR, STAT3 and NF-κB signaling pathways. Our study provides valuable arguments to demonstrate the potential of GeXIVA[1,2] as a novel marine-derived anticancer drug candidate for the treatment of TNBC.

Activation of the nonneuronal cholinergic cardiac system by hypoxic preconditioning protects isolated adult cardiomyocytes from hypoxia/reoxygenation injury.

Activation of the vagus nerve mediates cardioprotection and attenuates myocardial ischemia/reperfusion (I/R) injury. In response to vagal activation, acetylcholine (ACh) is released from the intracardiac nervous system (ICNS) and activates intracellular cardioprotective signaling cascades. Recently, however, a nonneuronal cholinergic cardiac system (NNCCS) in cardiomyocytes has been described as an additional source of ACh. To investigate whether the NNCCS mediates cardioprotection in the absence of vagal and ICNS activation, we used a reductionist approach of isolated adult rat ventricular cardiomyocytes without neuronal cells, using hypoxic preconditioning (HPC) as a protective stimulus. Adult rat ventricular cardiomyocytes were isolated, the absence of neuronal cells was confirmed, and HPC was induced by 10/20 min hypoxia/reoxygenation (H/R) before subjection to 30/5 min H/R to simulate I/R injury. Cardiomyocyte viability was assessed by trypan blue staining at baseline and after HPC+H/R or H/R. Intra- and extracellular ACh was quantified using liquid chromatography-coupled mass spectrometry at baseline, after HPC, after hypoxia, and after reoxygenation, respectively. In a subset of experiments, muscarinic and nicotinic ACh receptor (m- and nAChR) antagonists were added during HPC or during H/R. Cardiomyocyte viability at baseline (69 ± 4%) was reduced by H/R (10 ± 3%). With HPC, cardiomyocyte viability was preserved after H/R (25 ± 6%). Intra- and extracellular ACh increased during hypoxia; HPC further increased both intra- and extracellular ACh (from 0.9 ± 0.7 to 1.5 ± 1.0 nmol/mg; from 0.7 ± 0.6 to 1.1 ± 0.7 nmol/mg, respectively). The addition of mAChR and nAChR antagonists during HPC had no impact on HPC's protection; however, protection was abrogated when antagonists were added during H/R (cardiomyocyte viability after H/R: 23 ± 5%; 13 ± 4%). In conclusion, activation of the NNCCS is involved in cardiomyocyte protection; HPC increases intra- and extracellular ACh during H/R, and m- and nAChRs are causally involved in HPC's cardiomyocyte protection during H/R. The interplay between upstream ICNS activation and NNCCS activation in myocardial cholinergic metabolism and cardioprotection needs to be investigated in future studies.NEW & NOTEWORTHY The intracardiac nervous system is considered to be involved in ischemic conditioning's cardioprotection through the release of acetylcholine (ACh). However, we demonstrate that hypoxic preconditioning (HPC) protects from hypoxia/reoxygenation injury and increases intra- and extracellular ACh during hypoxia in isolated adult ventricular rat cardiomyocytes. HPC's protection involves cardiomyocyte muscarinic and nicotinic ACh receptor activation. Thus, besides the intracardiac nervous system, a nonneuronal cholinergic cardiac system may also be causally involved in cardiomyocyte protection by ischemic conditioning.

Mifepristone decreases nicotine intake in dependent and non-dependent adult rats.

Addiction to tobacco and nicotine products has adverse health effects and afflicts more than a billion people worldwide. Therefore, there is an urgent need for new treatments to reduce tobacco and nicotine use. Glucocorticoid receptor blockade shows promise as a novel treatment for drug abuse and stress-related disorders. These studies aim to investigate whether glucocorticoid receptor blockade with mifepristone diminishes the reinforcing properties of nicotine in rats with intermittent or daily long access to nicotine. The rats self-administered 0.06 mg/kg/inf of nicotine for 6 h per day, with either intermittent or daily access for 4 weeks before treatment with mifepristone. Daily nicotine self-administration models regular smoking, while intermittent nicotine self-administration models occasional smoking. To determine whether the rats were dependent, they were treated with the nicotinic acetylcholine receptor antagonist mecamylamine, and somatic signs were recorded. The rats with intermittent access to nicotine had a higher level of nicotine intake per session than those with daily access but only the rats with daily access to nicotine showed signs of physical dependence. Furthermore, mecamylamine increased nicotine intake during the first hour of access in rats with daily access but not in those with intermittent access. Mifepristone decreased total nicotine intake in rats with intermittent and daily access to nicotine. Moreover, mifepristone decreased the distance traveled and rearing in the open field test and operant responding for food pellets. These findings indicate that mifepristone decreases nicotine intake but this effect may be partially attributed to the sedative effects of mifepristone.

Hydroxynorketamine, but not ketamine, acts via α7 nicotinic acetylcholine receptor to control presynaptic function and gene expression

Ketamine is clinically used fast-acting antidepressant. Its metabolite hydroxynorketamine (HNK) shows a robust antidepressant effect in animal studies. It is unclear, how these chemically distinct compounds converge on similar neuronal effects. While KET acts mostly as N-methyl-d-aspartate receptor (NMDAR) antagonist, the molecular target of HNK remains enigmatic. Here, we show that KET and HNK converge on rapid inhibition of glutamate release by reducing the release competence of synaptic vesicles and induce nuclear translocation of pCREB that controls expression of neuroplasticity genes connected to KET- and HNK-mediated antidepressant action. Ro25-6981, a selective antagonist of GluN2B, mimics effect of KET indicating that GluN2B-containing NMDAR might mediate the presynaptic effect of KET. Selective antagonist of α7 nicotinic acetylcholine receptors (α7nAChRs) or genetic deletion of Chrna7, its pore-forming subunit, fully abolishes HNK-induced synaptic and nuclear regulations, but leaves KET-dependent cellular effects unaffected. Thus, KET or HNK-induced modulation of synaptic transmission and nuclear translocation of pCREB can be mediated by selective signaling via NMDAR or α7nAChRs, respectively. Due to the rapid metabolism of KET to HNK, it is conceivable that subsequent modulation of glutamatergic and cholinergic neurotransmission affects circuits in a cell-type-specific manner and contributes to the therapeutic potency of KET. This finding promotes further exploration of new combined medications for mood disorders.

Corneal acetylcholine regulates sensory nerve activity via nicotinic receptors

PurposeSensory nerve terminals are highly distributed in the cornea, and regulate ocular surface sensation and homeostasis in response to various endogenous and exogenous stimuli. However, little is known about mediators regulating the physiological and pathophysiological activities of corneal sensory nerves. The aim of this study was to investigate the presence of cholinergic regulation in sensory nerves in the cornea. MethodsLocalization of choline acetyltransferase (ChAT) and vesicular acetylcholine transporter (vAChT) was evaluated using western blotting and immunohistochemical analysis. The synthesis and liberation of acetylcholine from the cornea were assessed using corneal segments pre-incubated with [3H]choline. The responsiveness of corneal neurons and nerves to cholinergic drugs was explored using calcium imaging with primary cultures of trigeminal ganglion neurons and extracellular recording from corneal preparations in guinea pigs. ResultsChAT, but not vAChT, was highly distributed in the corneal epithelium. In corneal segments, [3H] acetylcholine was synthesized from [3H]choline, and was also released in response to electrical stimuli. In cultured corneal neurons, the population sensitive to a transient receptor potential melastatin 8 (TRPM8) agonist exhibited high probability of responding to nicotine in a calcium imaging experiment. The firing frequency of cold-sensitive corneal nerves was increased by the application of nicotine, but diminished by an α4 nicotinic acetylcholine receptor antagonist. ConclusionsThe corneal epithelium can synthesize and release acetylcholine. Corneal acetylcholine can excite sensory nerves via nicotinic receptors containing the α4 subunit. Therefore, corneal acetylcholine may be one of the important regulators of corneal nerve activity arranging ocular surface condition and sensation.

Sex differences in nicotine intake and relapse behavior in nicotine-dependent adult wistar rats.

Tobacco use is highly addictive and the leading cause of premature mortality in the world. Long-access nicotine self-administration procedures in rats closely model human smoking behavior. However, significant gaps remain in our understanding of sex differences in the development of dependence and relapse in adult rats. In the present study, we investigated operant responding for both nicotine and saline and the development of dependence in adult rats of both sexes. The rats had daily access to nicotine or saline for 6h per day, 7days per week. Dependence was assessed by evaluating precipitated and spontaneous somatic withdrawal signs, measuring locomotor activity in the small open field test, and assessing anxiety-like behavior in the large open field and elevated plus maze test. The sucrose preference test was used to determine if cessation of nicotine intake leads to anhedonia. It was also investigated if a period of forced abstinence affects nicotine-seeking behavior. This study showed that nicotine intake is higher in females than in males when given daily long access to nicotine. Daily nicotine self-administration led to more precipitated and spontaneous somatic withdrawal signs compared to saline self-administration, with no sex differences observed. In addition, cessation of nicotine intake led to a similar increase in activity in both males and females in the small open field test. However, cessation of nicotine intake did not increase anxiety-like behavior or cause anhedonia in either males or females. A time course analysis revealed that the nicotinic acetylcholine receptor antagonist mecamylamine affected nicotine intake differently in males and females, increasing intake in males and decreasing intake in females. Three weeks of forced abstinence led to an increase in nicotine and saline-seeking behavior. The rats exhibited more nicotine than saline seeking, and the females displayed more nicotine seeking than the males. The present findings demonstrate that females self-administer more nicotine and display more nicotine-seeking behavior than males. Furthermore, there were no sex differences in somatic withdrawal signs or activity during abstinence from nicotine. This work underscores the importance of considering sex differences across various aspects of addiction, including intake and relapse, when developing novel treatments for tobacco use disorder.

Coniin, in Five Little Pigs

In this manuscript, I provide some insights into the novel Five Little Pigs (US title: Murder in Retrospect) by Agatha Christie, and overview the neurotoxin coniine that plays an essential role in that story. Coniine is a nicotinic acetylcholine receptor antagonist, and induces a slowly spreading effect of paralysis by acting directly on the peripheral nervous system. This agent has been used as a poison for thousands of years; indeed, the philosophical text Phaedo describes that coniine was used to put Socrates to death. Based on this background, Christie's views on human nature and her creative powers are also discussed.

α-Conotoxin recombinant protein ImI-AFP3 efficiently inhibits the growth and migration of lung cancer cells

α-Conotoxin ImI is a selective antagonist of alpha7 nicotinic acetylcholine receptor (α7 nAChR) that is involved in cancer development. Human alpha fetoprotein domain 3 (AFP3) is a prototype of anticancer agents. In an effort to design drugs for anticancer treatments, we fused the ImI peptide to AFP3 as a fusion protein for testing. The fusion protein (ImI-AFP3) was highly expressed in the insect Bac-to-Bac system. The purified fusion protein was found to have improved anticancer activity and synergized with the drug gefitinib to inhibit the growth and migration of A549 and NCI-H1299 lung cancer cells. Our data have demonstrated that the recombinant protein ImI-AFP3 is a promising candidate for drug development to suppress lung cancer cell growth, especially to suppress hepatoid adenocarcinoma of the lung (HAL) cell growth.

Nicotine plays a protective role in rats with induced viral pneumonia with polyinosinic-polycytidylic acid through α7nAChR

ObjectiveTo study the effect of nicotine in rat model of pneumonia induced by polyinosinic-polycytidylic acid [Poly (I:C)] and explore the underlying mechanism. MethodsTwenty-four healthy adult male Sprague-Dawley (SD) rats (200–250 g) were randomly divided into normal saline control group (NS group); Poly (I:C) group; nicotine group (NIC group); and α7 nicotinic acetylcholine receptor (α7nAChR) antagonist group (α-BGT group) (n = 6 each). Rats in the Poly (I: C), NIC, and α-BGT groups were administered 1.5 mg/mL 100 μL Poly (I:C) intranasally to establish pneumonia model. In α-BGT group, 1 μg/kg α-bungarotoxin (α-BGT) was intraperitoneally injected 45 min before intranasal Poly (I:C), and 400 μg/kg nicotine was intraperitoneally injected 15 min after α-BGT injection. The NIC group received an equal volume of NS in place of α-BGT while the other treatments were same. The Poly (I:C) group received equal volume of NS in place of nicotine while the other treatments were same as in NIC group. In the NS group, only NS was administered at all three time points. PaCO2, PaO2, and PaO2/FiO2 levels were determined 24 h after administration of Poly (I:C). After euthanization, rat lung tissues were extracted for pathological examination, and wet weight/dry weight (W/D ratio) was determined. Expression of tumor necrosis factor-α (TNF-α), interleukin (IL)-6, IL-1β, and interferon (IFN)-γ in lung tissue was determined by ELISA. q-PCR was used to detect nuclear factor kappa-B P65 (NF-κBP65). ResultsCompared with NS group, Poly (I:C) and α-BGT groups showed significantly increased W/D ratio, PaCO2, TNF-α, IL-6, IL-1β, and IFN-γ content, NF-κB P65 expression, and reduced PaO2 and PaO2/FiO2 (p < 0.05), along with obvious signs of pathological injury. Nicotine pre-treatment reduced W/D ratio, PaCO2, proinflammatory cytokines, NF-κBP65 expression, and increased PaO2 and PaO2/FiO2 levels. The above effects were negated in α-BGT group. ConclusionPre-administration of nicotine improved Poly (I:C)-induced pneumonia by activating the cholinergic anti-inflammatory pathway.

Vagus Nerve Stimulation Relives Irritable Bowel Syndrome and the Associated Depression via α7nAChR-mediated Anti-inflammatory Pathway.

The present study is designed to investigate the role of vagus nerve in the treatments of irritable bowel syndrome (IBS) and the associated central nervous system disorders. An IBS animal model was established by giving acetic acid and chronic-acute stress (AA-CAS) treatment in adult male Wistar rats. Subdiaphragmatic vagotomy (SDV) and vagus nerve stimulation (VNS) were performed to intervene the excitability of vagus nerve. Permeability of blood brain barrier (BBB) was measured and agonist and antagonist of α7 nicotinic acetylcholine receptor (α7nAChR) were used to explore the relevant mechanisms. AA-CAS treatment resulted in abnormal fecal output, increased visceral sensitivity, depressive-like behaviors, and overexpression of inflammatory mediators, all of which were reversed by VNS treatment. The effects of VNS could also be observed when α7nAChR agonist was applied. Whereas α7nAChR antagonist (methyllycaconitine, MLA) reversed VNS's effects. Interestingly, VNS also reduced the increased permeability of blood brain barrier (BBB) following AA-CAS treatment in IBS rats. SDV treatment only show temporary efficacy on AA-CAS-induced symptoms and had no effect on the permeability of BBB. The intestinal abnormalities and depressive symptoms in IBS rats can be improved by VNS treatment. This positive effect of VNS was achieved through α7nAChR-mediated inflammatory pathway and may also be associated with the decreased of BBB permeability.

Ghrelin Amplifies the Nicotine-Induced Release of Dopamine in the Bed Nucleus of Stria Terminalis (BNST).

Ghrelin is an orexigenic neuropeptide that is known for stimulating the release of growth hormone (GH) and appetite. In addition, ghrelin has been implicated in addiction to drugs such as nicotine. Nicotine is the principal psychoactive component in tobacco and is responsible for the reward sensation produced by smoking. In our previous in vitro superfusion studies, it was demonstrated that ghrelin and nicotine stimulate equally the dopamine release in the rat amygdala, and ghrelin amplifies the nicotine-induced dopamine release in the rat striatum. However, less attention was paid to the actions of ghrelin and nicotine in the bed nucleus of the stria terminalis (BNST). Therefore, in the present study, nicotine and ghrelin were superfused to the BNST of male Wistar rats, and the dopamine release from the BNST was measured in vitro. In order to determine which receptors mediate these effects, mecamylamine, a non-selective nicotinic acetylcholine receptor (nAchR) antagonist, and GHRP-6, a selective growth hormone secretagogue receptor (GHS-R1A) antagonist, were also superfused to the rat BNST. Nicotine significantly increased the release of dopamine, and this effect was significantly inhibited by mecamylamine. Ghrelin increased dopamine release even more significantly than nicotine did, and this effect was significantly inhibited by GHRP-6. Moreover, when administered together, ghrelin significantly amplified the nicotine-induced release of dopamine in the BNST, and this additive effect was reversed partly by mecamylamine and partly by GHRP-6. Therefore, the present study provides a new base of evidence for the involvement of ghrelin in dopamine signaling implicated in nicotine addiction.

Domain loss enabled evolution of novel functions in the snake three-finger toxin gene superfamily

Three-finger toxins (3FTXs) are a functionally diverse family of toxins, apparently unique to venoms of caenophidian snakes. Although the ancestral function of 3FTXs is antagonism of nicotinic acetylcholine receptors, redundancy conferred by the accumulation of duplicate genes has facilitated extensive neofunctionalization, such that derived members of the family interact with a range of targets. 3FTXs are members of the LY6/UPAR family, but their non-toxin ancestor remains unknown. Combining traditional phylogenetic approaches, manual synteny analysis, and machine learning techniques (including AlphaFold2 and ProtT5), we have reconstructed a detailed evolutionary history of 3FTXs. We identify their immediate ancestor as a non-secretory LY6, unique to squamate reptiles, and propose that changes in molecular ecology resulting from loss of a membrane-anchoring domain and changes in gene expression, paved the way for the evolution of one of the most important families of snake toxins.

0027 Ravaged Rat Rhythms: Circadian Rhythm Influence on Mecamylamine-Induced Nicotine Withdrawal

Abstract Introduction Mecamylamine (Mec) is a nicotinic acetylcholine receptor (nAChR) antagonist, serving as an important piece of nicotine addiction cessation therapies. When co-administered with nicotine, Mec blocks the positive reinforcing effects of the substance of abuse and may promote a lessened desire to perpetuate an addictive cycle. On the other hand, the magnitude of the withdrawal symptoms caused by this co-administration may reinforce addiction as users can choose to terminate the process of quitting. Methods The present study uses Sprague-Dawley rats to examine if the time of withdrawal onset in relation to circadian rhythms impacts the magnitude of the relevant aversive symptoms. We hypothesized that Mec injected during the rat’s dark period show significantly less aversive symptoms when compared to when it’s done during their light period. For this, we injected rats (n=3 per group) twice a day for thirteen days subcutaneously, with either saline or nicotine, a validated protocol to induce addiction. To measure aversive symptoms of nicotine precipitated withdrawal in light vs dark periods, we used a conditioned place aversion (CPA) behavioral assay in which the rats were either tested mid-light or mid-dark periods. In CPA, the rats were first introduced to the two distinct chambers and allowed to freely move in between them (day 10, for 15 minutes), while time spent in each one was analyzed. Then, they were conditioned to associate one chamber with saline and the other with Mec (days 11-12, for 30 minutes each). Finally, they were placed again in freedom, and the time spent in the mecamylamine-paired chamber was detracted from pre-conditioning to give us the results of aversion (day 13, for 15 minutes). Results We predicted that in the aftermath, the light-period rats on nicotine addiction schedule would show the shortest change in time in Mec-paired chamber, while saline-scheduled rats across both periods would show a change of zero—or no impact of Mec. Results indicated no significant differences between group averages for time spent in the Mec-paired chamber, but they showed saline-scheduled rats to be similarly aversive to it. Conclusion This result indicates the potential need for a study with a more selective nicotine blocker. Support (if any)

Nicotine activates HIF-1α and regulates acid extruders through the nicotinic acetylcholine receptor to promote the Warburg effect in non-small cell lung cancer cells

Cigarette smoking is the greatest risk factor for lung cancer, accounting for approximately 90% of all lung cancer-related deaths. Moreover, nicotine is associated with lung cancer onset and progression. Hypoxia-inducible factor 1α (HIF-1α) is involved in the metabolic reprogramming of cancer cells and accelerates cancer progression via regulation of pH and acid–base homeostasis. Previous studies have reported that nicotine upregulates HIF-1α expression. Therefore, we hypothesized that nicotine-mediated activation of HIF-1α regulates metabolic reprogramming and pH homeostasis in non-small cell lung cancer A549 cells and could potentially play a role in the progression of lung cancer. We examined the effects of nicotine on metabolic reprogramming and intracellular pH (pHi) homeostasis, which are critical for cancer progression. A549 cells were exposed to nicotine in the absence and presence of the nicotinic acetylcholine receptor antagonist, mecamylamine (MEC). We then analyzed glycolytic stress and the activity and expression of acid-extruder proteins, including the Na+–H+ exchanger 1 (NHE1) and monocarboxylate cotransporters 1 & 4 (MCT1 and MCT4, respectively). Nicotine promoted the Warburg effect, which is associated with accelerated migration of A549 cells through the activation of nicotinic acetylcholine receptors. Furthermore, nicotine upregulated the activities and expression of acid-extruder proteins, namely NHE1 and MCT4, and facilitated glycolysis. To the best of our knowledge, this is the first study to demonstrate that nicotine plays a pivotal regulatory role in metabolic reprogramming as well as regulation of pHi homeostasis in A549 cells via activation of nicotinic acetylcholine receptors and can therefore aggravate lung cancer progression.

Diagnoses and new therapeutic strategy focused on physiological alteration of tryptophan metabolism

The monoamine hypothesis has been common hypotheses for the pathophysiology of major depressive disorder (MDD). Since mainstream antidepressants are selective serotonin (5-HT) reuptake inhibitors, hypo-serotonergic function has been implicated in the MDD. However, one-third of patients are refractory to the treatment with antidepressants. Tryptophan (TRP) is metabolized via the kynurenine (KYN) and 5-HT pathways. Indoleamine 2,3-dioxygenase 1 (IDO1) is the first metabolizing enzyme in the TRP-KYN pathway which is inducible by pro-inflammatory cytokines, involved depression-like behavior via 5-HT depletion due to decreased level of TRP in the 5-HT pathway. Kynurenine 3-monooxygenase (KMO) is the enzyme in the metabolism of KYN to 3-hydroxykynurenine. KMO deficiency increases level of kynurenic acid (KA), a KYN metabolite by kynurenine aminotransferases (KATs) and induces depression-like behavior. Interestingly, Chronic unpredictable mild stress (CUMS) is associated with a disruption of the hypothalamus-pituitary-adrenocortical (HPA) system and increases KA level with decreased KMO expression in the prefrontal cortex. The decrease of KMO may be related to the reduction in expression of microglia, since KMO is mainly found in microglia in the nervous system. CUMS increases KA level via alternation of enzymes from KMO to KAT. KA is α7 nicotinic acetylcholine receptor (α7nAChR) antagonist. Activation of α7nAChR by nicotine or galantamine attenuates CUMS-induced depression-like behaviors. Taken together, depletion of 5-HT by induction of IDO1 and α7nAChR antagonism by KA via decreased KMO expression cause depression-like behavior, suggesting that metabolic alterations in TRP-KYN pathway are highly involved in the pathophysiology of MDD. Therefore, TRP-KYN pathway is expected to be an attractive target for the development of novel diagnosis of MDD and antidepressants.

Acetylcholine potentiates glutamate transmission from the habenula to the interpeduncular nucleus in losers of social conflict

Switching behaviors from aggression to submission in losers at the end of conspecific social fighting is essential to avoid serious injury or death. We have previously shown that the experience of defeat induces a loser-specific potentiation in the habenula (Hb)-interpeduncular nucleus (IPN) and show here that this is induced by acetylcholine. Calcium imaging and electrophysiological recording using acute brain slices from winners and losers of fighting behavior in zebrafish revealed that the ventral IPN (vIPN) dominates over the dorsal IPN in the neural response to Hb stimulation in losers. We also show that GluA1 α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor subunits on the postsynaptic membrane increased in the vIPN of losers. Furthermore, these loser-specific neural properties disappeared in the presence of an α7 nicotinic acetylcholine receptor (nAChR) antagonist and, conversely, were induced in brain slices of winners treated with α7 nAChR agonists. These data suggest that acetylcholine released from Hb terminals in the vIPN induces activation of α7 nAChR followed by an increase in postsynaptic membrane GluA1. This results in an increase in active synapses on postsynaptic neurons, resulting in the potentiation of neurotransmissions to the vIPN. This acetylcholine-induced neuromodulation could be the neural foundation for behavioral switching in losers. Our results could increase our understanding of the mechanisms of various mood disorders such as social anxiety disorder and social withdrawal.

The Acute Effects and Mechanism of Ketamine on Nicotine-Induced Neurogenic Relaxation of the Corpus Cavernosum in Mice.

The present study aimed to investigate the acute effects and the mechanism of ketamine on nicotine-induced relaxation of the corpus cavernosum (CC) in mice. This study measured the intra-cavernosal pressure (ICP) of male C57BL/6 mice and the CC muscle activities using an organ bath wire myograph. Various drugs were used to investigate the mechanism of ketamine on nicotine-induced relaxation. Direct ketamine injection into the major pelvic ganglion (MPG) inhibited MPG-induced increases in ICP. D-serine/L-glutamate-induced relaxation of the CC was inhibited by MK-801 (N-methyl-D-aspartate (NMDA) receptor inhibitor), and nicotine-induced relaxation was enhanced by D-serine/L-glutamate. NMDA had no effect on CC relaxation. Nicotine-induced relaxation of the CC was suppressed by mecamylamine (a non-selective nicotinic acetylcholine receptor antagonist), lidocaine, guanethidine (an adrenergic neuronal blocker), Nw-nitro-L-arginine (a non-selective nitric oxide synthase inhibitor), MK-801, and ketamine. This relaxation was almost completely inhibited in CC strips pretreated with 6-hydroxydopamine (a neurotoxic synthetic organic compound). Ketamine inhibited cavernosal nerve neurotransmission via direct action on the ganglion and impaired nicotine-induced CC relaxation. The relaxation of the CC was dependent on the interaction of the sympathetic and parasympathetic nerves, which may be mediated by the NMDA receptor.