Acetylcholine Receptor Blocker Research Articles

That’s Pretty Hard to Swallow: A Rare Case of Dysphagia Due to Myasthenia Gravis

Introduction: An 89-year-old woman with GERD and hypothyroidism presented with a 7-month history of dysphagia and odynophagia to both solids and liquids. She was admitted 1 month prior to this admission for similar symptoms and underwent an EGD, which revealed a hiatal hernia. Despite compliance with omeprazole 40 mg daily, she returned to the emergency room with worsening symptoms. She denied abdominal pain, nausea, vomiting, diarrhea, constipation, dark stools, blood per rectum, or jaundice. Physical exam revealed an elongated face with bitemporal wasting, bilateral partial ptosis, and dysarthria. Motor strength was 4/5 in both upper and lower extremities. The abdominal exam was benign. Evaluation for gastrointestinal causes of dysphagia included a video esophagram showing decreased peristalsis and a repeat EGD revealing no resistance to a balloon dilator nor evidence of stricture, rings, or masses. Due to negative GI imaging, evaluation for neurological causes of dysphagia was completed. This included MRI brain and MRA of the head & neck which were negative for infarction or stenosis of vessels. CT scan of the neck was negative for right recurrent laryngeal nerve paralysis. By hospital admission day 4, she was intubated for inability to swallow her secretions and given an NG tube for feeds. Labs revealed elevated aldolase level of 7.9. Due to suspicion for neuromuscular causes of dysphagia, electromyography was completed, revealing a neuromuscular junction abnormality. Voltage-gated Ca-channel antigen and anti-MuSK antibody were negative while acetylcholine receptor-binding antibody level was 5.63 (high), acetylcholine receptor-modulating antibody level was 30 (high), and acetylcholine receptor-blocking antibody was 83 (high), thus confirming the diagnosis of myasthenia gravis as the cause of dysphagia. Repetitive nerve stimulation showed a decremental response further solidifying the diagnosis. CT scan of the chest did not reveal presence of a thymoma. She was started on IV immunoglobulins for 5 days, prednisone 50 mg daily, and pyridostigmine 60 mg three times a day with improvement in her muscle weakness, ptosis, and dysphagia. Dysphagia as the primary presenting symptom of myasthenia gravis is very rare and has only been reported in 6-15% of cases of myasthenia gravis. Myasthenia gravis is more commonly reported as a paraneoplastic phenomenon associated with a thymoma/thymic tumor, which was absent in our case. Late-onset myasthenia gravis is more common in men and is often acetylcholine-receptor antibody negative. The age of onset along with the gender and antibody profile of our patient makes this case very unique. Our case truly increases awareness of nongastrointestinal causes of dysphagia. Disclosure - 1. Dr. Kumkum Patel--no financial relationships. 2. Dr. Jacqueline Forman--no financial relationships. 3. Dr. Bhawna Halwan--no financial relationships. 3. Dr. James Grendell-Consultant: NPS Pharmaceuticals Advisory Board.

Rapid and slow chemical synaptic interactions of cholinergic projection neurons and GABAergic local interneurons in the insect antennal lobe.

The antennal lobe (AL) of insects constitutes the first synaptic relay and processing center of olfactory information, received from olfactory sensory neurons located on the antennae. Complex synaptic connectivity between olfactory neurons of the AL ultimately determines the spatial and temporal tuning profile of (output) projection neurons to odors. Here we used paired whole-cell patch-clamp recordings in the cockroach Periplaneta americana to characterize synaptic interactions between cholinergic uniglomerular projection neurons (uPNs) and GABAergic local interneurons (LNs), both of which are key components of the insect olfactory system. We found rapid, strong excitatory synaptic connections between uPNs and LNs. This rapid excitatory transmission was blocked by the nicotinic acetylcholine receptor blocker mecamylamine. IPSPs, elicited by synaptic input from a presynaptic LN, were recorded in both uPNs and LNs. IPSPs were composed of both slow, sustained components and fast, transient components which were coincident with presynaptic action potentials. The fast IPSPs were blocked by the GABAA receptor chloride channel blocker picrotoxin, whereas the slow sustained IPSPs were blocked by the GABAB receptor blocker CGP-54626. This is the first study to directly show the predicted dual fast- and slow-inhibitory action of LNs, which was predicted to be key in shaping complex odor responses in the AL of insects. We also provide the first direct characterization of rapid postsynaptic potentials coincident with presynaptic spikes between olfactory processing neurons in the AL.

Fluoxetine prevents acetylcholine-induced excitotoxicity blocking human endplate acetylcholine receptor

Fluoxetine is an open channel blocker of fetal muscle acetylcholine (ACh) receptor (AChR) and slow-channel mutant AChRs. It is used commonly to treat patients with slow-channel congenital myasthenic syndromes. Fluoxetine effects on adult wild-type endplate AChR are less characterized, although muscle AChR isoforms are differentially modulated by some drugs. Excitotoxicity assays and patch clamp recordings were performed in human embryonic kidney 293 (HEK) cells expressing wild-type or slow-channel mutant human AChRs. Fluoxetine (2-10 μM) abolished ACh-induced death and decreased ACh-activated whole-cell currents in cells expressing all AChR types. In outside-out patches, fluoxetine rapidly curtailed ACh evoked unitary activity and macroscopic currents. The effect was increased if fluoxetine was applied before ACh. Fluoxetine is an open channel blocker, but it also affects AChR in the closed state. AChR blockade likely underlies the rescue of HEK cells from ACh-induced death.

Electroacupuncture Acutely Improves Cerebral Blood Flow and Attenuates Moderate Ischemic Injury via an Endothelial Mechanism in Mice

Electroacupuncture (EA) is a novel therapy based on traditional acupuncture combined with modern eletrotherapy that is currently being investigated as a treatment for acute ischemic stroke. Here, we studied whether acute EA stimulation improves tissue and functional outcome following experimentally induced cerebral ischemia in mice. We hypothesized that endothelial nitric oxide synthase (eNOS)-mediated perfusion augmentation was related to the beneficial effects of EA by interventions in acute ischemic injury. EA stimulation at Baihui (GV20) and Dazhui (GV14) increased cerebral perfusion in the cerebral cortex, which was suppressed in eNOS KO, but there was no mean arterial blood pressure (MABP) response. The increased perfusion elicited by EA were completely abolished by a muscarinic acetylcholine receptor (mAChR) blocker (atropine), but not a β-adrenergic receptor blocker (propranolol), an α-adrenergic receptor blocker (phentolamine), or a nicotinic acetylcholine receptor (nAChR) blocker (mecamylamine). In addition, EA increased acetylcholine (ACh) release and mAChR M3 expression in the cerebral cortex. Acute EA stimulation after occlusion significantly reduced infarct volume by 34.5% when compared to a control group of mice at 24 h after 60 min-middle cerebral artery occlusion (MCAO) (moderate ischemic injury), but not 90-min MCAO (severe ischemic injury). Furthermore, the impact of EA on moderate ischemic injury was totally abolished in eNOS KO. Consistent with a smaller infarct size, acute EA stimulation led to prominent improvement of neurological function and vestibule-motor function. Our results suggest that acute EA stimulation after moderate focal cerebral ischemia, but not severe ischemia improves tissue and functional recovery and ACh/eNOS-mediated perfusion augmentation might be related to these beneficial effects of EA by interventions in acute ischemic injury.

Iptakalim Preferentially Decreases Nicotine-induced Hyperlocomotion in Phencyclidine-sensitized Rats: A Potential Dual Action against Nicotine Addiction and Psychosis

ObjectiveIptakalim is a putative ATP-sensitive potassium (KATP) channel opener. It is also a novel nicotinic acetylcholine receptor (nAChR) blocker and can antagonize nicotine-induced increase in dopamine release in the nucleus accumbens. Our recent work also shows that iptakalim exhibits a clozapine-like atypical antipsychotic profile, indicating that iptakalim may possess a dual action against nicotine addiction and schizophrenia.MethodsThe present study examined the potential therapeutic effects of iptakalim on nicotine use in schizophrenia. We created an animal model of comorbidity of nicotine addiction and schizophrenia by injecting male Sprague-Dawley rats with nicotine (0.40 mg/kg, subcutaneously[sc]) or saline, in combination with phencyclidine (PCP, 3.0 mg/kg, sc) or saline daily for 14 consecutive days.ResultsDuring the PCP/nicotine sensitization phase, PCP and nicotine independently increased motor activity over time. PCP also disrupted prepulse inhibition (PPI) of acoustic startle response. Acute nicotine treatment attenuated the PCP-induced hyperlocomotion and PCP-induced disruption of PPI, whereas repeated nicotine treatment potentiated these effects. Importantly, pretreatment with iptakalim (10-20 mg/kg, intraperitoneally) reduced nicotine-induced hyperlocomotion in a dose-dependent fashion. This reduction effect was highly selective: it was more effective in rats previously sensitized to the combination of PCP and nicotine, but less effective in rats sensitized to saline, nicotine alone or PCP alone.ConclusionTo the extent that the combined nicotine and PCP sensitization mimics comorbid nicotine addiction in schizophrenia, the preferential inhibitory effect of iptakalim on nicotine-induced hyperlocomotion suggests that iptakalim may be a potential useful drug for the treatment nicotine abuse in schizophrenia.

Nicotine induces the expression of C-reactive protein via MAPK-dependent signal pathway in U937 macrophages.

Atherosclerosis is an inflammatory disease in the vessel wall. Nicotine, a major component of cigarette smoke, is an independent risk factor for cardiovascular diseases including atherosclerosis. As an inflammatory molecule, C- reactive protein (CRP) participates in atherogenesis. Although it has been confirmed that CRP level in smoking patient is significantly higher than non-smokers and cigarette withdrawal, it is unknown whether nicotine induces CRP expression in macrophages. The present study was to observe effect of nicotine on CRP production and the related signal pathway in U937 macrophages. The results showed that nicotine significantly increased mRNA and protein expression of CRP in U937 macrophages in time- and concentration-dependent ways. Nicotinic acetylcholine receptor (nAChR) blocker hexamethonium, MEK1/2 inhibitor PD98059, p38 MAPK inhibitor SB203580 and NF-κB inhibitor PDTC almost completely abolished nicotineinduced CRP expression in mRNA and protein levels in U937 macrophages. The further study indicated that hexamethonium, PD98059, and SB203580 significantly inhibited ERK1/2 and p38 MAPK phosphorylation. These demonstrate that nicotine has ability to induce CRP expression in macrophages through nAChR-ERK1/2/p38 MAPK-NF-κB signal pathway, which contributes to better understanding of the pro-inflammatory and pro-atherosclerotic effects of nicotine in cigarette smokers.

Rituximab in Severe Seronegative Juvenile Myasthenia Gravis: Review of the Literature

Myasthenia gravis is an autoimmune neuromuscular disorder caused by circulating antibodies that block acetylcholine receptors at the postsynaptic neuromuscular junction. Awide range of symptomatic therapy with acetylcholinesterase inhibitors and immunotherapy such as corticosteroids, azathioprine, cyclosporine, mycophenolate mofetil, plasmapheresis, and intravenous immunoglobulin has been used in the treatment of myasthenia gravis, with variable responses. However, most modalities of treatment involve delayed onset of action. We describe a child with severe, life-threatening seronegative myasthenia gravis who repeatedly failed extubation and responded dramatically to rituximab. She achieved complete and sustained remission for more than 9 months, with gradual reduction in steroid dose without any side effects. Advances in the treatment of myasthenia gravis have reduced mortality and morbidity and improved the quality of life in these patients.

Neural regulation of esophageal striated muscle in the house musk shrew (Suncus murinus)

In the present study, we characterized the neural regulation of esophageal striated muscle in Suncus murinus (a house musk shrew; "suncus" used as a laboratory name), which was compared with that in the rat. The tunica muscularis consists of striated muscle in the suncus esophagus. An isolated segment of the suncus esophagus was placed in an organ bath and the contractile responses were recorded using a force transducer. Electrical stimulations to vagus nerves induced contractile responses in the esophageal segment. Treatment with α-bungarotoxin, a blocker of nicotinic acetylcholine receptors, blocked the vagally mediated contractions of the suncus esophagus. D-tubocurarine and succinylcholine, typical antagonists of nicotinic acetylcholine receptors, also inhibited the suncus esophageal contractions, while higher concentrations of the agents were required rather than concentrations for producing an equivalent block in the rat. We used capsaicin, a stimulator of small-caliber afferent neurons, for activating the peripheral neural network. The reagent inhibited the vagally mediated twitch contractions of striated muscle in the suncus esophagus, which was reversed by pretreatment with a nitric oxide synthase inhibitor, N(G)-nitro-L-arginine methyl ester. Application of a nitric oxide donor, diethylamine NONOate diethylammonium salt, mimicked capsaicin-induced inhibition. The results suggest that motility of the suncus esophagus, which consists of striated muscles, is regulated by vagal cholinergic neurons. The local neural network including capsaicin-sensitive neurons and intrinsic nitrergic neurons can modify the vagally mediated motility in the suncus esophagus. In addition, nicotinic acetylcholine receptors of the suncus esophagus might be pharmacologically distinct from those of rodent esophagi.

Interneuronal synapses formed by motor neurons appear to be glutamatergic

Acetylcholine release at motor neuron synapses has been long established; however, recent discoveries indicate that synaptic transmission by motor neurons is more complex than previously thought. Using whole-cell patch clamp, we show that spontaneous excitatory postsynaptic currents of rat motor neurons in primary ventral horn cultures are entirely glutamatergic, although the cells respond to exogenous acetylcholine. Motor neurons in cultures express the vesicular glutamate transporter VGlut2, and culturing motor neurons for weeks with glutamate receptors blocked upregulates glutamate signaling without increasing cholinergic signaling. In spinal cord slices, motor neurons showed no decrease in spontaneous excitatory synaptic potentials after blocking acetylcholine receptors. Our results suggest that motor neuron synapses formed on other neurons are largely glutamatergic in culture and the spinal cord.

The Method of In-Vivo Electrical Field Stimulation to Study Neurogenic Control of Skin Blood Flow

Skin blood flow (SkBF) plays a vital role in regulating body temperature but the mechanisms regulating it remain poorly understood. Current methods used to study these mechanisms may activate both local and systemic factors which may limit our ability to differentiate the role of various neurochemicals involved in the regulation of SkBF. PURPOSE: To characterize a novel method of in-vivo electrical field stimulation (I-EFS) to study neurogenic control of cutaneous vasodilation in the absence of the sympathetic adrenergic nervous system. METHODS: Three intradermal microdialysis probes were placed in the skin of the dorsal side of the forearm of 6 men and 3 women. The adrenergic nervous system was eliminated by delivery of a cocktail of phentolamine (0.01 mg/ml), propranolol (1 mM), and BIBP-3226 (10 μM). At one skin site, atropine (0.1 mg/ml) was added to also block acetylcholine receptors (RACh). At a second site L-NAME (10 mM) and atropine (0.1 mg/ml) blocked nitric oxide synthase (NOS) and RACh. Finally at a third site, RACh, NOS, and vasoactive intestinal peptide receptors (RVIP, 0.47 mg/ml VIP10-28) were blocked. The SkBF response to 1 minute stages of graded increases in frequency (0.2, 1, 2, 4, 8, and 32 Hz) at a current of 1.0 ± 0.1 mA was used to generate a stimulus-response curve before and after drug delivery. RESULTS: I-EFS in the presence of adrenergic blockade produced a frequency dependent increase in SkBF with area under the SkBF-time curve (AUC) averaging 614 ± 279% SkBFmax·min. RACh blockade had minimal impact on AUC which averaged 591 ± 331% SkBFmax·min (p>0.05). Combined NOS and RACh blockade appeared to lower the vasodilator response to I-EFS by 23% (1036 ± 457 to 801 ± 448% SkBFmax·min, p>0.05). Combined NOS, RACh, and RVIP blockade reduced the vasodilator response by 48% from 802 ± 412 to 418 ± 268% SkBFmax·min (p=0.07). CONCLUSION: RACh blockade had no effect on the vasodilation induced by I-EFS in the presence of adrenergic blockade, while NOS and RVIP blockade appeared to attenuate the vasodilator response to I-EFS. I-EFS may be an effective method to determine the role of various local neurochemicals on skin blood flow.

Depolarization-induced Ca2+ entry preferentially evokes release of large quanta in the developing Xenopus neuromuscular junction.

The amplitude histogram of spontaneously occurring miniature synaptic currents (mSCs) is skewed positively at developing Xenopus neuromuscular synapses formed in culture. To test whether the quantal size of nerve-evoked quanta (eSCs) distributes similarly, we compared the amplitude histogram of single quantum eSCs in low external Ca(2+) with that of mSCs and found that nerve stimulation preferentially released large quanta. Depolarization of presynaptic terminals by elevating [K(+)] in the external solution or by direct injection of current through a patch pipette increased the mSC frequency and preferentially, but not exclusively, evoked the release of large quanta, resulting in a second broad peak in the amplitude histogram. Formation of the second peak under these conditions was blocked by the N-type Ca(2+) channel blocker, ω-conotoxin GVIA. In contrast, when the mSC frequency was elevated by thapsigargin- or caffeine-induced mobilization of internal Ca(2+), formation of the second peak did not occur. We conclude that the second peak in the amplitude histogram is generated by Ca(2+) influx through N-type Ca(2+) channels, causing a local elevation of internal Ca(2+). The mSC amplitude in the positively skewed portion of the histogram varied over a wide range. A competitive blocker of acetylcholine (ACh) receptors, d-tubocurarine, reduced the amplitude of smaller mSCs in this range relatively more than that of larger mSCs, suggesting that this variation in the mSC amplitude is due to variable amounts of ACh released from synaptic vesicles. We suggest that Ca(2+) influx through N-type Ca(2+) channels preferentially induces release of vesicles with large ACh content.

Comparison of human and guinea pig acetylcholinesterase sequences and rates of oxime-assisted reactivation

Poisoning via organophosphorus (OP) nerve agents occurs when the OP binds and inhibits the enzyme acetylcholinesterase (AChE). This enzyme is responsible for the metabolism of the neurotransmitter acetylcholine (ACh) which transmits signals between nerves and several key somatic regions. When AChE is inhibited, the signal initiated by ACh is not properly terminated. Excessive levels of ACh result in a cholinergic crisis, and in severe cases can lead to death. Current treatments for OP poisoning involve the administration of atropine, which blocks ACh receptors, and oximes, which reactivate AChE after inhibition. Efforts to improve the safety, efficacy, and broad spectrum utility of these treatments are ongoing and usually require the use of appropriate animal model systems. For OP poisoning, the guinea pig ( Cavia porcellus) is a commonly used animal model because guinea pigs more closely mirror primate susceptibility to OP poisoning than do other animals such as rats and mice. This is most likely because among rodents and other small mammals, guinea pigs have a very low relative concentration of serum carboxylesterase, an enzyme known to bind OPs in vitro and to act as an endogenous bioscavenger in vivo. Although guinea pigs historically have been used to test OP poisoning therapies, it has been found recently that guinea pig AChE is substantially more resistant to oxime-mediated reactivation than human AChE. To examine the molecular basis for this difference, we reverse transcribed mRNA encoding guinea pig AChE, amplified the resulting cDNA, and sequenced this product. The nucleotide and deduced amino acid sequences of guinea pig AChE were then compared to the human version. Several amino acid differences were noted, and the predicted locations of these differences were mapped onto a structural model of human AChE. To examine directly how these differences affect oxime-mediated reactivation of AChE after inhibition by OPs, human and guinea pig red blood cell ghosts were prepared and used as sources of AChE, and the relative capacity of several different oximes to reactivate each OP-inhibited AChE were determined. The differences we report between human and guinea pig AChE raise additional concerns about the suitability of the guinea pig as an appropriate small animal model to approximate human responses to OP poisoning and therapies.

First-principles determination of molecular conformations of indolizidine (−)-235B′ in solution

Indolizidine (-)-235B' is a particularly interesting natural product, as it is the currently known, most potent and subtype-selective open-channel blocker of the alpha4beta2 nicotinic acetylcholine receptor (nAChR). In the current study, extensive first-principles electronic structure calculations have been carried out in order to determine the stable molecular conformations and their relative free energies of the protonated and deprotonated states of (-)-235B' in the gas phase, in chloroform, and in aqueous solution. The (1)H and (13)C NMR chemical shifts calculated using the computationally determined dominant molecular conformation of the deprotonated state are all consistent with available experimental NMR spectra of (-)-235B' in chloroform, which suggests that the computationally determined molecular conformations are reasonable. Our computational results reveal for the first time that two geminal H atoms on carbon-3 (C3) of (-)-235B' have remarkably different chemical shifts (i.e. 3.24 and 2.03 ppm). The computational results help one to better understand and analyze the experimental (1)H NMR spectra of (-)-235B'. The finding of remarkably different chemical shifts of two C3 geminal H atoms in a certain molecular conformation of (-)-235B' may also be valuable in analysis of NMR spectra of other related ring-containing compounds. In addition, the pK(a) of (-)-235B' in aqueous solution is predicted to be ~9.7. All of the computational results provide a solid basis for future studies of the microscopic and phenomenological binding of various receptor proteins with the protonated and deprotonated structures of this unique open-channel blocker of alpha4beta2 nAChRs. This computational study also demonstrates how one can appropriately use computational modeling and spectroscopic analysis to address the structural and spectroscopic problems that cannot be addressed by experiments alone.

Synthesis of (+)-Lepadin B

Lepadin B was isolated from the tunicate Clavelina lepadiformis. It is a potent blocker of neuronal nicotinic acetylcholine receptors which are involved in disorders such as Alzheimer’s and Parkinson’s diseases and nicotine addiction. The Barbe-Charette synthesis hinges on a ring-closing/ring-opening metathesis sequence to form the cis-fused decahydro­quinoline core.

Neuroprotective effects of donepezil through inhibition of GSK‐3 activity in amyloid‐β‐induced neuronal cell death

Acetylcholinesterase inhibitors (AChE-inhibitors) are used for the treatment of Alzheimer's disease. Recently, the AChE-inhibitor donepezil was found to have neuroprotective effects. However, the protective mechanisms of donepezil have not yet been clearly identified. We investigated the neuroprotective effects of donepezil and other AChE-inhibitors against amyloid-beta1-42 (Abeta42)-induced neurotoxicity in rat cortical neurons. To evaluate the neuroprotective effects of AChE-inhibitors, primary cultured cortical neurons were pre-treated with several concentrations of AChE-inhibitors for 24 h and then treated with 20 microM Abeta42 for 6 h. In addition to donepezil, other AChE-inhibitors (galantamine and huperizine A) also showed increased neuronal cell viability against Abeta42 toxicity in a concentration-dependent manner. However, we demonstrated that donepezil has a more potent effect in inhibiting glycogen synthase kinase-3 (GSK-3) activity compared with other AChE-inhibitors. The neuroprotective effects of donepezil were blocked by LY294002 (10 microM), a phosphoinositide 3 kinase inhibitor, but only partially by mecamylamine (10 microM), a blocker of nicotinic acetylcholine receptors. Additionally, donepezil's neuroprotective mechanism was related to the enhanced phosphorylation of Akt and GSK-3beta and reduced phosphorylation of tau and glycogen synthase. These results suggest that donepezil prevents Abeta42-induced neurotoxicity through the activation of phosphoinositide 3 kinase/Akt and inhibition of GSK-3, as well as through the activation of nicotinic acetylcholine receptors.

Partial neuromuscular blockade in humans enhances muscle blood flow during exercise independently of muscle oxygen uptake and acetylcholine receptor blockade

This study examined the role of acetylcholine for skeletal muscle blood flow during exercise by use of the competitive neuromuscular blocking agent cisatracurium in combination with the acetylcholine receptor blocker glycopyrrone. Nine healthy male subjects performed a 10-min bout of one-legged knee-extensor exercise (18 W) during control conditions and with cisatracurium blockade, as well as with cisatracurium blockade with prior glycopyrrone infusion. Thigh blood flow and vascular conductance in control and with cisatracurium infusion were similar at rest and during passive movement of the leg, but higher (P < 0.05) during exercise with cisatracurium than in control (3.83 +/- 0.42 vs. 2.78 +/- 0.21 l/min and 26.9 +/- 3.4 vs. 21.8 +/- 2.0 ml.min(-1).mmHg(-1) at the end of exercise). Thigh oxygen uptake was similar in control and with cisatracurium infusion both at rest and during exercise, being 354 +/- 33 and 406 +/- 34 ml/min, at the end of exercise. Combined infusion of cisatracurium and glycopyrrone caused a similar increase in blood flow as cisatracurium infusion alone. The current results demonstrate that neuromuscular blockade leads to enhanced thigh blood flow and vascular conductance during exercise, events that are not associated with either acetylcholine or an increased oxygen demand. The results do not support an essential role for acetylcholine, released form the neuromuscular junction, in exercise hyperemia or for the enhanced blood flow during neuromuscular blockade. The enhanced exercise hyperemia during partial neuromuscular blockade may be related to a greater recruitment of fast-twitch muscle fibers.

Abolishment of Serotonergic Neurotransmission to Cardiac Vagal Neurons During and After Hypoxia and Hypercapnia With Prenatal Nicotine Exposure

Cardioinhibitory cardiac vagal neurons (CVNs) do not receive inspiratory-related excitatory inputs under normal conditions. However, excitatory purinergic and serotonergic pathways are recruited during inspiratory activity after episodes of hypoxia and hypercapnia (H/H). Prenatal nicotine (PNN) exposure is known to dramatically change cardiorespiratory responses and decrease the ability to resuscitate from H/H. This study tested whether PNN exposure alters excitatory neurotransmission to CVNs in the nucleus ambiguus during and after H/H. Spontaneous and inspiratory evoked excitatory postsynaptic currents were recorded in CVNs from rats that were exposed to nicotine (6 mg x kg(-1) x d(-1)) throughout the prenatal period. In contrast to unexposed animals, in PNN animals H/H recruited excitatory neurotransmission to CVNs during inspiratory-related activity that was blocked by the alpha3beta4 nicotinic acetylcholine receptor (nAChR) blocker alpha-conotoxin AuIB (alpha-CTX AuIB, 100 microM) and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 50 microM) and d(-)-2-amino-5-phosphonopentanoic acid (AP5, 50 microM), selective AMPA/kainate and N-methyl-d-aspartate receptor blockers, respectively. Following H/H, there was a significant increase in inspiratory-related excitatory postsynaptic currents that were unaltered by alpha-CTX AuIB or ondansetron, a 5-HT3 receptor blocker, but were subsequently inhibited by pyridoxalphosphate-6-azophenyl-2', 4'-disulphonic acid (100 microM), a purinergic receptor blocker and CNQX and AP5. The results from this study demonstrate that with PNN exposure, an excitatory neurotransmission to CVNs is recruited during H/H that is glutamatergic and dependent on activation of alpha3beta4-containing nAChRs. Furthermore, exposure to PNN abolishes a serotonergic long-lasting inspiratory-related excitation of CVNs that is replaced by recruitment of a glutamatergic pathway to CVNs post H/H.

Donepezil, an acetylcholinesterase inhibitor, enhances adult hippocampal neurogenesis

Donepezil hydrochloride is a potent and selective acetylcholinesterase inhibitor and has been treated for Alzheimer's disease, in which the cholinergic dysfunction is observed. Recently, the degeneration of medial septal cholinergic nuclei in adult rat suppressed the neurogenesis in hippocampal dentate gyrus (DG) was reported. Then, we determined whether donepezil which activated the brain cholinergic system could modulate hippocampal neurogenesis in normal rats. After the injection of 5′-bromo-2′-deoxyuridine (BrdU) to label dividing cells, we orally treated with donepezil (0.5 or 2 mg/kg) once a day for 4 weeks. In the other group, we performed 4-week subcutaneous infusion of scopolamine (0.75 or 3 mg/day), a muscarinic acetylcholine receptor blocker. The doses of donepezil and scopolamine we used in this study were reported to activate and inhibit cholinergic activity in rats, respectively. One day after the completion of drug treatment, the animals were sacrificed, and immunohistochemical analysis was performed. Donepezil increased, but scopolamine decreased, the number of BrdU-positive cells in the DG as compared with the vehicle-treated control. Neither drug had any effects on the percentage of BrdU-positive cells that were also positive for a neuronal marker NeuN, nor the number of proliferating cell nuclear antigen-positive cells in the DG. These results indicate that donepezil enhances and scopolamine suppresses the survival of newborn neurons in the DG without affecting the proliferation of neural progenitor cell and the neuronal differentiation. We also found that chronic treatment of donepezil enhanced, and scopolamine suppressed phosphorylation of cAMP response element binding protein (CREB), which was involved in cell survival, in the DG. These results suggest that donepezil activates the central cholinergic transmission and enhances the survival of newborn neurons in the DG via CREB signaling.

Chronic nicotinein uteroselectively suppresses hypoxic sensitivity in neonatal rat adrenal chromaffin cells

Nicotine in cigarette smoke has been linked to several deleterious side effects on the offspring of smoking mothers, including impaired development of the sympathoadrenal system, abnormal arousal reflexes, and sudden infant death syndrome. Catecholamine (CA) release from adrenomedullary chromaffin cells (AMCs) in response to asphyxial stressors, e.g., low O(2) (hypoxia) and elevated CO(2) (hypercapnia), is critical for adaptation to extrauterine life and occurs before splanchnic innervation. Here, we investigated the effects of prenatal nicotine bitartrate exposure on the ability of neonatal (P0) rat AMCs to respond appropriately to asphyxial stressors. Control AMCs isolated from pups born to saline-treated dams displayed typical responses to hypoxia and hypercapnia, including inhibition of outward K(+) current, membrane depolarization, increased cytosolic calcium, and CA secretion. In contrast, P0 AMCs from pups born to nicotine-treated dams showed a marked suppression or loss of hypoxic sensitivity, although hypercapnic sensitivity and the expression of CO(2) markers (i.e., carbonic anhydrase I and II) appeared normal. Moreover, isolated saline-treated P0 AMCs lost their hypoxic sensitivity when grown in culture for approximately 1 wk in the presence of a subsaturating concentration of nicotine base (50 microM), and this effect was abolished by the nicotinic acetylcholine receptor (nAChR) blocker mecamylamine (100 microM). Taken together, these data suggest that the adverse effects of maternal smoking on sympathoadrenal function in the offspring are due in part to a loss or suppression of acute hypoxic sensitivity in adrenal chromaffin cells, triggered by the direct action of nicotine on endogenous nicotinic acetylcholine receptors.

Synthesis of poison-frog alkaloids 233A, 235U, and 251AA and their inhibitory effects on neuronal nicotinic acetylcholine receptors

We previously reported that the synthetic quinolizidine 1-epi- 207I is a relatively selective blocker of α7 nicotinic acetylcholine receptors. We now synthesized the analogous poison frog alkaloids 233A, 235U, and 251AA, and investigated the biological activities at two major types of neuronal nicotinic receptors. Electrophysiological study showed that the alkaloid 233A blocked α7 and α4β2 currents with similar potencies. Alkaloids 235U and 251AA also showed similar potencies for blockade of α7 and α4β2 currents. Thus, based on these studies, it would appear that C4 substituents greater in length than the allyl of 1-epi- 207I reduce α7-potency without affecting α4β2-potency.