Search

Abstract: The effects of S 24795, a newly developed partial agonist at α7 nAChRs, were tested on synaptic transmission and plasticity using extracellular field excitatory postsynaptic potentials (fEPSPs) evoked in the CA1 region by Schaffer collateral stimulation in hippocampal slices obtained from adult mice. S 24795 reduced the amplitude of the fEPSPs in a concentration-dependent manner with an IC50 of 127μM and a Hill coefficient of 1.1. The reduction in amplitude of the fEPSPs started at S 24795 concentrations higher than 3μM and reached 71% of controls at 300μM. This effect was mediated by α7 nAChRs since it was blocked by nAChR antagonists and was not observed in α7 −/− mice. This effect was probably due to a reduction in glutamate release from presynaptic terminals since it was associated with a significant increase in the paired pulse ratio. In addition, S 24795 (100μM) significantly reduced the frequency, but not the amplitude of spontaneous excitatory postsynaptic currents, recorded in the whole cell configuration of the patch clamp technique (in voltage clamp mode), further supporting a presynaptic site of action of S 24795. In addition, S 24795 at 3μM, a concentration that did not affect basic synaptic transmission, potentiated LTP. This effect was mediated by α7 nAChRs since it was prevented by MLA (10nM) and was absent in α7 −/− mice. Galantamine an allosteric modulator of nAChRs, at the concentrations of 0.3–3μM, failed to potentiate LTP. In view of its powerful effect on LTP and on cognitive function, S 24795 can be considered a novel useful tool for the treatment of AD patients and other senile forms of dementia. [Copyright &y& Elsevier]

Abstract: Acetylcholinesterase (AChE) is shown to promote deposition of β-amyloid (Aβ) peptides and to enhance Aβ toxicity. Tg2576 (transgenic mice carrying the Swedish mutation of amyloid precursor protein, APPswe) mice and mice overexpressing human synaptic acetylcholinesterase (AChE-S) were crossed (hAChE-Tg//APPswe), to study the effects of brain Aβ, from 1 to 10 months of age, under the constant influence of AChE-S. The effect of nicotine treatment was also evaluated in these mice since we have previously shown that nicotine dramatically decreases Aβ levels in single transgenic APPswe mice. Already at 1 and 3 months, hAChE-Tg//APPswe mice showed increased levels of cortical insoluble Aβ1–40 and Aβ1–42 compared with APPswe mice, whereas APPswe mice displayed increased soluble Aβ1–40. Aβ plaques were detected at 7 months, thus before onset of plaque formation in APPswe mice. No differences were found in [125I]α-bungarotoxin binding sites or hippocampal glial fibrillary acidic protein (GFAP) immunoreactivity between hAChE-Tg//APPswe, and APPswe mice at either 1 or 10 months of age. l(−)-Nicotine (final dose 0.45 mg/kg) treatment twice daily for 10 days to 14-month-old hAChE-Tg//APPswe mice increased cortical insoluble Aβ1–40 levels, while both l(−)- and d(+)-nicotine (final dose 0.45 mg/kg) increased soluble Aβ1–42. l(−)-Nicotine reduced hippocampal GFAP immunoreactivity both in hAChE-Tg//APPswe mice and non-transgenic controls, while d(+)-nicotine caused a decrease only in hAChE-Tg//APPswe mice. Moreover, d(+)-nicotine increased the [125I]α-bungarotoxin binding sites in the hippocampus, and cortex of the hAChE-Tg//APPswe mice. In conclusion, already at a very young age, hAChE-Tg//APPswe mice exhibit increased levels of aggregated Aβ compared with APPswe mice, due to the possible interaction between Aβ and AChE-S, whereas APPswe mice exhibit increased soluble Aβ. The interaction between Aβ and AChE-S may also explain the different effect of nicotine on Aβ pathology in the hAChE-Tg//APPswe mice. The results in this study emphasize the importance of using different transgenic mouse models for evaluating the effect of new drug candidates for the treatment of Alzheimer’s disease. [Copyright &y& Elsevier]

Among the diverse sets of nicotinic acetylcholine receptors (nAChRs), the α7 subtype is highly expressed in the hippocampus and cortex and is thought to play important roles in a variety of cognitive processes. In this review, we describe the properties of a novel biaryl diamine α7 nAChR agonist, A-582941. A-582941 was found to exhibit high-affinity binding and partial agonism at α7 nAChRs, with acceptable pharmacokinetic properties and excellent distribution to the central nervous system (CNS). In vitro and in vivo studies indicated that A-582941 activates signaling pathways known to be involved in cognitive function such as ERK1/2 and CREB phosphorylation. A-582941 enhanced cognitive performance in behavioral models that capture domains of working memory, short-term recognition memory, memory consolidation, and sensory gating deficit. A-582941 exhibited a benign secondary pharmacodynamic and tolerability profile as assessed in a battery of assays of cardiovascular, gastrointestinal, and CNS function. The studies summarized in this review collectively provide preclinical validation that α7 nAChR agonism offers a mechanism with potential to improve cognitive deficits associated with various neurodegenerative and psychiatric disorders. [ABSTRACT FROM AUTHOR]

Nicotine is known to enhance learning and memory in hippocampus-dependent tasks such as contextual fear conditioning. The present study was designed to directly examine whether the hippocampus plays a role in mediating this enhancement and which nicotinic acetylcholine receptor (nAChR) subtypes localized to the hippocampus are critical for enhanced learning. Contextual fear conditioning consisted of two white noise conditioned stimuli presentations, each coterminating with a 2 s, 0.57 mA footshock separated by a 120 s intertrial interval. Nicotine (0.09, 0.18, and 0.35 µg per side) was bilaterally infused into the dorsal hippocampus before training and testing. Infusions of nicotine into the dorsal hippocampus produced a dose-dependent enhancement of contextual fear conditioning. To determine which nAChRs are critical to the enhancing effect of nicotine, the preferential α4β2 nAChR antagonist, dihydro-β-erythroidine (DHβE) (6.00 and 18.00 µg per side), or the preferential α7 nAChR antagonist, methyllycaconitine (MLA) (13.50 and 27.00 µg per side), was bilaterally infused into the dorsal hippocampus before systemic injections of nicotine (0.09 mg/kg). DHβE infusions dose-dependently blocked the enhancement of contextual fear conditioning by nicotine, where as MLA infusions yielded an intermediate effect. In addition, neither DHβE nor MLA had an effect on contextual fear conditioning in the absence of systemic nicotine. The present results suggest a critical role for α4β2 nAChRs in the dorsal hippocampus for mediating the enhancing effect of nicotine on contextual fear conditioning. [ABSTRACT FROM AUTHOR]

Abstract: Extensive 3D-QSAR studies were performed on 158 diverse analogues of 3-pyridyl ethers, which are excellent ligands of α4β2 neuronal nicotinic acetylcholine receptor (NnAChR). Comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) techniques were used to relate the binding affinities with the ligand structures. Two QSAR models were obtained using CoMFA and CoMSIA techniques. The two QSAR models were proved to be statistically significant and have high predictive power. The best CoMFA model yielded the cross-validated q 2 =0.605 and the non-cross-validated r 2 =0.862. The derived model indicated the importance of steric (85.9%) as well as electrostatic (14.1%) contributions. The CoMFA model demonstrated the steric field as the major descriptor of the ligand binding. The best CoMSIA model gave q 2 =0.723 and r 2 =0.685. This model showed that steric (30.3%) and H-bond interaction (61.8%) properties played major roles in ligand binding process. The squares of correlation coefficient for external test set of 28 molecules were 0.723 and 0.685 for the CoMFA model and the CoMSIA model, respectively. The two models were further graphically interpreted in terms of field contribution maps. SAR studies were also performed on different series of compounds in order to get a more reasonable understanding of the interactions between the ligands and the receptor. With the results, we have also presumed some assistant elements as supplements to the traditional pharmacophoric elements. A crude vision of ligand localization in the ligand-binding pocket of the receptor was also obtained, which would favor for the docking study of this kind of ligands. [Copyright &y& Elsevier]

Abstract: The Ca2+ microdomains generated around the mouth of open ion channels represent the basic building blocks from which cytosolic Ca2+ signals are constructed. Recent improvements in optical imaging techniques now allow these microdomains to be visualized as single channel calcium fluorescence transients (SCCaFTs), providing information about channel properties that was previously accessible only by electrophysiological patch-clamp recordings. We review recent advances in single channel Ca2+ imaging methodologies, with emphasis on total internal reflection fluorescence microscopy (TIRFM) as the technique of choice for recording SCCaFTs from voltage- and ligand-gated plasmalemmal ion channels. This technique of ‘optical patch-clamp recording’ is massively parallel, permitting simultaneous imaging of hundreds of channels; provides millisecond resolution of gating kinetics together with sub-micron spatial resolution of channel locations; and is applicable to diverse families of membrane channels that display partial permeability to Ca2+ ions. [Copyright &y& Elsevier]

Activation of neuronal nicotinic acetylcholine receptors (nAChRs) modulates the induction of long-term potentiation (LTP): a possible cellular mechanism of learning. To investigate the effect of nicotine on synaptic plasticity in chronically lead-exposed rats, field excitatory postsynaptic potentials and paired-pulse facilitation (PPF) were recorded in the CA1 area of hippocampal slices from chronically lead-exposed 23–30-day-old rats. The results showed the following. (1) Nicotine (1 µm) facilitated the induction of LTP in CA1 by a weak tetanic stimulation (100 Hz, 20 pulses), which does not by itself produce LTP in lead-exposed rats. This effect was significantly suppressed by mecamylamine, a nicotinic antagonist, suggesting that the facilitation of LTP was through nAChRs. (2) The nicotine-facilitated LTP was blocked by dihydro-β-erythroidine (DHβE), a non-α7 nAChR antagonist, whereas long-term depression (LTD) was produced by the combination of nicotine and methyllycaconitine, a α7-nAChR antagonist. This type of LTD was blocked by DHβE. This suggested that several nAChR subtypes were involved in the nicotine-facilitated synaptic plasticity. (3) Nicotine enhanced PPF in the hippocampal CA1 region, and the nicotine-facilitated LTP in lead-exposed rats was blocked by eitherd-(–)-2-amino-5-phosphonopentanoic acid, the N-methyl-d-aspartate (NMDA) receptor antagonist, or picrotoxin, an antagonist of γ-aminobutyric acidA receptors. We suggest that nicotine-facilitated synaptic plasticity was due to the activation of NMDARs by disinhibition of pyramidal cells through presynaptic nAChRs. This may represent the cellular basis of nicotine-facilitated cognitive enhancement observed in chronically lead-exposed rats. [ABSTRACT FROM AUTHOR]

Behavioral and genetic studies in Drosophila have contributed to our understanding of molecular mechanisms that underlie the complex processes of learning and memory. Use of this model organism for exploration of the cellular mechanisms of memory formation requires the ability to monitor synaptic activity in the underlying neural networks, a challenging task in the tiny adult fly. Here, we describe an isolated whole-brain preparation in which it is possible to obtain in situ whole-cell recordings from adult Kenyon cells, key members of a neural circuit essential for olfactory associative learning in Drosophila. The presence of sodium action potential (AP)-dependent synaptic potentials and synaptic currents in >50% of the Kenyon cells shows that these neurons are members of a spontaneously active neural circuit in the isolated brain. The majority of sodium AP-dependent synaptic transmission is blocked by curare and by α-bungarotoxin (α-BTX). This demonstrates that nicotinic acetylcholine receptors (nAChRs) are responsible for most of the spontaneous excitatory drive in this circuit in the absence of normal sensory input. Furthermore, analysis of sodium AP-independent synaptic currents provides the first direct demonstration that α-BTX-sensitive nAChRs mediate fast excitatory synaptic transmission in Kenyon cells in the adult Drosophila brain. This new preparation, in which whole-cell recordings and pharmacology can be combined with genetic approaches, will be critical in understanding the contribution of nAChR-mediated fast synaptic transmission to cellular plasticity in the neural circuits underlying olfactory associative learning. [ABSTRACT FROM AUTHOR]

Abstract: Ligand-gated ion channels (LGICs) are cell surface proteins that play an important role in fast synaptic transmission and in the modulation of cellular activity. Due to their intrinsic properties, LGICs respond to neurotransmitters and other effectors (e.g. pH) and transduce the binding of a ligand into an electrical current on a microsecond timescale. Following activation, LGICs open allowing an ion flux across the cell membrane. Depending upon the charge and concentration of ions, the flux can cause a depolarization or hyperpolarization, thus modulating excitability of the cell. While our understanding of LGICs has significantly progressed during the past decade, many properties of these proteins are still poorly understood, in particular their modulation by allosteric effectors. LGICs are often thought as a simple on–off switches. However, a closer look at these receptors reveals a complex behavior and a wide repertoire of subtle modulation by intrinsic and extrinsic factors. From a physiological point of view, this modulation can be seen as an additional level of complexity in the cell signaling process. Here we review the allosteric modulation of LGICs in light of the latest findings and discuss the suitability of this approach to the design of new therapeutic molecules. [Copyright &y& Elsevier]

Abstract: This paper investigates the role of cholinergic mechanisms in auditory gating by assessing the acute effects of nicotine, an acetylcholinomimetic drug, on behavioral and electrophysiological measures of consonant–vowel (CV) discrimination in quiet and in broadband noise (BBN). In a single-blind procedure, categorical boundaries and mismatch negativity (MMN) in two conditions (quiet, BBN) were obtained from 10 non-smokers and 4 smokers with normal hearing under two drug conditions (nicotine, placebo). After the nicotine sessions, plasma tests revealed a subject’s nicotine concentration and subjects reported any symptoms. Larger MMN areas and steeper slopes at the boundary were interpreted as reflecting better electrophysiological and behavioral CV discrimination, respectively. Results indicate that, in non-smokers, the effects of nicotine on electrophysiological CV discrimination in quiet increase with an increase in severity of symptoms. Specifically, asymptomatic non-smokers (N=5) demonstrate little improvement (and sometimes decrements) in performance while symptomatic non-smokers (N=5) exhibit nicotine-enhanced discrimination, as do smokers. In noise, all subjects demonstrate nicotine-enhanced behavioral and electrophysiological discrimination. Additionally, in noise, smokers exhibit a larger number of measurable categorical boundaries as well as larger MMN areas than non-smokers in both placebo and nicotine sessions. Results are consistent with the hypothesis that nicotinic cholinergic mechanisms play a role in the gating of auditory stimuli. [Copyright &y& Elsevier]

Abstract: Both normal aging and age-related disease, such as Alzheimer''s disease, have diverse effects on forebrain-dependent cognitive tasks as well as the underlying neurobiological substrates. The purpose of the current study was to investigate if age-related alterations in the function of the cholinergic system are associated with memory impairments in auditory-cued and contextual fear conditioning. Young (2–3 months) and aged (19–20 months) C57BL/6 mice were administered scopolamine (0.1, 0.3, 0.5, or 1.0 mg/kg), a muscarinic cholinergic receptor antagonist, mecamylamine (1.0 and 2.0 mg/kg), a nicotinic cholinergic receptor antagonist, both scopolamine and mecamylamine (0.1 and 1.0 mg/kg, respectively), or saline prior to training. Training consisted of two white-noise CS (85 dB, 30 s)-footshock US (0.57 mA, 2 s) presentations. Testing occurred 48 h post-training. Scopolamine administration impaired contextual and cued fear conditioning in young and aged mice, although the aged mice were less sensitive to disruption by scopolamine. Mecamylamine did not disrupt conditioned fear in the young or aged mice. Scopolamine and mecamylamine co-administration, at doses sub-threshold for disrupting fear conditioning with separate administration, disrupted contextual and auditory-cued fear conditioning in the young mice, indicating that in the young mice the muscarinic and nicotinic cholinergic processes interact in the formation and maintenance of long-term memories for conditioned fear. Co-administration of both antagonists did not disrupt fear conditioning in the aged mice, indicating that age-related alterations in the cholinergic receptor subtypes may occur. [Copyright &y& Elsevier]

Abstract: In the present study, immunohistochemistry combined with retrograde labeling techniques were used to determine if hypoglossal motoneurons (HMNs), retrogradely labeled after cholera toxin B subunit (CTB) injection to the genioglossus muscle in rats, show immunoreactivity for alpha-7 and alpha-4 subunits of nicotinic acetylcholine receptors (nAChRs). CTB-positive HMNs projecting to the genioglossus muscle were consistently labeled throughout the rostrocaudal extent of the hypoglossal nuclei with the greatest labeling at and caudal to area postrema. Alpha-7 subunit immunoreactivity was found in 39.44±5.10% of 870 CTB-labeled motoneurons and the alpha-4 subunit in 51.01±3.71% of 983 CTB-positive neurons. Rostrally, the number of genioglossal motoneurons demonstrating immunoreactivity for the alpha-7 subunit was 45.85±10.04% compared to 34.96±5.11% at and caudal to area postrema (P>0.1). The number of genioglossal motoneurons that showed immunoreactivity for the alpha-4 subunit was 55.03±4.83% at and caudal to area postrema compared to 42.98±3.90% in rostral areas (P=0.074). These results demonstrate that nAChR immunoreactivity is present in genioglossal motoneurons and suggest a role for alpha-7 and alpha-4 subunits containing nAChRs in the regulation of upper airway patency. [Copyright &y& Elsevier]

Epibatidine is a potent but nonselective nAChR agonist. Its biological effects appear to be mediated largely by α4β2 nAChRs. Surprisingly, only a limited number of epibatidine analogues have been synthesized and evaluated in in vitro assays. Even fewer analogues have received in vivo pharmacological evaluation. In this paper, SAR studies directed toward epibatidine analogues will be reviewed. [Copyright &y& Elsevier]

: ObjectivesIn the current study, we used a model of limb ischemia to determine whether nicotine could enhance arteriogenesis, to compare the magnitude of this effect to the angiogenic factor basic fibroblast growth factor (bFGF), and to investigate the mechanisms of the effect.: BackgroundWe have shown previously that nicotine stimulates angiogenesis via stimulation of endothelial nicotinic cholinergic receptors. Stimulation of endothelial nicotinic cholinergic receptors causes endothelial cell proliferation, migration, and formation of capillary networks in vitro and angiogenesis in vivo in conditions of ischemia and inflammation.: MethodsNew Zealand White rabbits (n = 85) underwent unilateral femoral artery occlusion and were randomized to nicotine (0.05 to 5.0 μg/kg/day), bFGF (10 μg/kg/day), or vehicle delivered intra-arterially via osmotic minipumps. At day 21, morphologic changes were assessed by immunohistochemistry and angiography. Blood flow in the ischemic limb was determined by intra-arterial Doppler flow measurements and microsphere distribution.: ResultsNicotine enhanced capillary density in the ischemic hind-limb to a similar extent as bFGF. Nicotine also increased angiographic score, calf blood pressure ratio, intra-arterial Doppler flow, and microsphere distribution. In vitro, nicotine stimulated monocyte adhesion and transmigration. Nicotine increased by two- to three-fold the expression of monocyte adhesion molecules CD11b and CD11a; the expression of the endothelial adhesion molecule intercellular adhesion molecule-1; and the endothelial release of monocyte chemoattractant protein-1.: ConclusionsIn the short term, nicotine promotes angiogenesis and arteriogenesis in the setting of ischemia. The effect of nicotine may be mediated in part by activation of endothelial-monocyte interactions involved in arteriogenesis. [Copyright &y& Elsevier]

Current concepts concerning nicotine's CNS mechanism(s) of action suggest that this drug produces its effects via an interaction at nicotinic-cholinergic receptors (nAChRs) sensitive to acetylcholine. In vitro research further suggests that, following its initial agonist effect, this cholinergic drug may also induce a rapid desensitization of the nAChR similar to that of acetylcholine, resulting in termination of its pharmacological effect. Research described in this paper provides evidence of this secondary desensitization process in vivo by demonstrating nicotine's ability to induce acute tolerance in a Discriminative Stimulus (DS) paradigm. The ability of nicotine (400 µg/kg, SC) to elicit DS control of behavior in a two-lever operant procedure was significantly reduced via a challenge dose (800 µg/kg, SC) of nicotine administered 15-180 min before the training dose. Twenty-three of 52 rats demonstrated this phenomenon. The time to develop acute tolerance varied, providing additional evidence that these effects may be contingent upon individual rat variability. In addition, physostigmine was also observed to induce a similar desensitization in a random population of desensitizing rats. Lastly, there were no differences between desensitizers and non-desensitizers in relation to the ability of mecamylamine (1000 µg/kg, SC) to antagonize the DS, while in both populations of rats scopolamine (100 µg/kg, SC) failed to antagonize the DS. [ABSTRACT FROM AUTHOR]

The nicotinic acetylcholine receptors (nAChR) are made of subunits evolved from a common ancestor. Despite the similarity in their sequences and structures, the properties of these subunits vary significantly. Thus, identifying the evolution features and function-related sites specific to each subunit is essential for understanding the characteristics of the subunits and the receptors assembled by them. In this study, we examined the sequence features of the nine neuronal nAChRs subunits from representative vertebrate species. Analysis revealed that all the subunits were subject to strong purifying selection in evolution, and each was under a unique pattern of selection pressures. At the same time, the functional constraints were not uniform within each subunit, with different domains in the molecule being subject to different selection pressures. We also detected potential positive selection events in the subunits or subunit clusters, and identified the sites might be associated with the function specificity of each subunit. Furthermore, positive selection at some domains might contribute to the diversity of subunit function; for example, the β9 strand might be related to the agonist specificity of α subunit in heteromeric receptor and β4-β5 linker could be involved in Ca 2+ permeability. Subunits α7, α4 and β2 subunits possess a strong adaptability in vertebrates. Our results highlighted the importance of tracking functional differentiation in protein sequence underlying functional properties of nAChRs. In summary, our work may provide clues on understanding the diversity and the function specificity of the nAChR subunits, as well as the receptors co-assembled by them.Communicated by Ramaswamy H. Sarma.

[Display omitted] • α-Conotoxins with high potency on nAChR attract much interest in drug development. • Fmoc-based method is an efficient method for synthesizing cyclic α- [S9A]TxID. • Cyclization of c[S9A]TxID-6 maintains native-like structure and activity. • c[S9A]TxID-6 increases resistance to proteinase K digestion relative to [S9A]TxID. Head-to-tail cyclization is an effective strategy to improve the biological stability of peptides. The α-conotoxin [S9A]TxID is a peptide that inhibits α3β4 nAChR with high activity and selectivity. Herein, we established a method for cyclizing and oxidative folding of [S9A]TxID, and six cyclic analogues of [S9A]TxID were chemically synthesized with various linker lengths. We used the electrophysiology assay to measure activity values of these cyclic analogues, and obtained the most potent analogue c[S9A]TxID-6, which was more stable than native [S9A]TxID against proteinase K. [ABSTRACT FROM AUTHOR]

The fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL) enzymes are the predominant catabolic regulators of the major endocannabinoids (eCBs) anadamide (AEA) and 2-arachidonoylglycerol (2-AG), respectively. The expression and roles of eCBs during early embryogenesis remain to be fully investigated. Here, we inhibited FAAH and MAGL in zebrafish embryos during the first 24 h of life and examined motor neuron and locomotor development at 2 and 5 days post fertilization (dpf). Application of the dual FAAH/MAGL inhibitor, JZL195 (2 µmol l-1), resulted in a reduction in primary and secondary motor neuron axonal branching. JZL195 also reduced nicotinic acetylcholine receptor (nAChR) expression at neuromuscular junctions. Application of URB597 (5 µmol l-1), a specific inhibitor of the FAAH enzyme, also decreased primary motor neuron branching but did not affect secondary motor neuron branching and nAChR expression. Interestingly, JZL184 (5 µmol l-1), a specific inhibitor of MAGL, showed no effects on motor neuron branching or nAChR expression. Co-treatment of the enzyme inhibitors with the CB1R inhibitor AM251 confirmed the involvement of CB1R in motor neuron branching. Disruption of FAAH or MAGL reduced larval swimming activity, and AM251 attenuated the JZL195- and URB597-induced locomotor changes, but not the effects of JZL184. Together, these findings indicate that inhibition of FAAH, or augmentation of AEA acting through CB1R during early development, may be responsible for locomotor deficiencies., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2021. Published by The Company of Biologists Ltd.)

Smoking is the leading preventable cause of death worldwide and tobacco addiction has become a serious public health problem. Nicotine is the main addictive component of tobacco, and the majority of people that smoke regularly develop nicotine dependence. Nicotine addiction is deemed to be a chronic mental disorder. Although it is well known that nicotine binds to the nicotinic acetylcholine receptors (nAChRs) and activates the mesolimbic dopaminergic system (MDS) to generate the pleasant and rewarding effects, the molecular mechanisms of nicotine addiction are not fully understood. Brain-derived neurotrophic factor (BDNF) is the most prevalent growth factor in the brain, which regulates neuron survival, differentiation, and synaptic plasticity, mainly through binding to the high affinity receptor tyrosine kinase receptor B (TrkB). BDNF gene polymorphisms are associated with nicotine dependence and blood BDNF levels are altered in smokers. In this review, we discussed the effects of nicotine on BDNF expression in the brain and summarized the underlying signaling pathways, which further indicated BDNF as a key regulator in nicotine dependence. Further studies that aim to understand the neurobiological mechanism of BDNF in nicotine addcition would provide a valuable reference for quitting smoking and developing the treatment of other addictive substances.

Nicotine improves endotoxic manifestations of hypotension and cardiac autonomic dysfunction in rats. Here, we test the hypothesis that brainstem antiinflammatory pathways of α7/α4β2 nicotinic acetylcholine receptors (nAChRs) modulate endotoxic cardiovascular derangements. Pharmacologic and molecular studies were performed to determine the influence of nicotine or selective α7/α4β2-nAChR ligands on cardiovascular derangements and brainstem neuroinflammation caused by endotoxemia in conscious rats. The i.v. administration of nicotine (50 μg/kg) abolished the lipopolysaccharide (LPS, 10 mg/kg i.v.)-evoked: (i) falls in blood pressure and spectral measure of cardiac sympathovagal balance (ratio of the low-frequency to high-frequency power, LF/HF), (ii) elevations in immunohistochemical protein expressions of NFκB and α4β2-nAChR in medullary neurons of the nucleus tractus solitarius (NTS) and rostral ventrolateral medulla (RVLM), and (iii) decreases in medullary α7-nAChR protein expression. These favorable nicotine influences were replicated in rats treated intracisternally (i.c.) with PHA-543613 (selective α7-nAChR agonist) or 5-iodo-A-85380 (5IA, selective α4β2-nAChRs agonist). Measurement of arterial baroreflex activity by the vasoactive method revealed that nicotine, PHA, or 5IA reversed the LPS depression of reflex bradycardic, but not tachycardic, activity. Moreover, the counteraction by nicotine of LPS hypotension was mostly inhibited after treatment with i.c. methyllycaconitine (MLA, α7-nAChR antagonist) in contrast to a smaller effect for dihydro-β-erythroidine (DHβE, α4β2-nAChR antagonist), whereas the associated increases in LF/HF ratio remained unaltered. The data signifies the importance of brainstem α7, and to a lesser extent α4β2, receptors in the nicotine counteraction of detrimental cardiovascular and neuroinflammatory consequences of endotoxemia. • Nicotine blunts LPS-evoked hypotension and cardiac autonomic dysfunction. • Nicotine normalized NFκB and α7-nAChR expression in brainstem of endotoxic rats. • Nicotine effects are replicated after activation of brainstem α7 or α4β2 receptors. • Blockade of central α7 or α4β2 receptors attenuated the favorable nicotine effects. [ABSTRACT FROM AUTHOR]

α-Conotoxin TxIB is a specific antagonist of α6/α3β2β3(α6β2*) nicotinic acetylcholine receptor (nAChR) with an IC50 of 28 nM. Previous studies have shown that α6β2* nAChRs are abundantly expressed in midbrain dopaminergic neurons and play an important role in mediating the mechanism of nicotine and other drugs reward effect. It provided important targets for the development of anti-addiction drugs. The present study evaluated the pharmacological activity of TxIB in vivo with conditioned place preference (CPP) model, which were induced by subcutaneous injection (s.c.) of nicotine (NIC, 0.5 mg/kg). α-Conotoxin TxIB inhibited the expression and reinstatement of CPP in mice dose-dependently, but had no significant effect on locomotor activity. The concentrations of dopamine (DA), γ-aminobutyric acid (GABA) and noradrenaline (NE) in different brain regions were measured by enzyme-linked immunosorbent assay (ELISA). We found that TxIB could inhibit the concentrations of DA, GABA and NE in different brain regions (such as nucleus accumbens (NAc), hippocampus (HIP) and prefrontal cortex (PFC)) in NIC-induced mice. The concentrations of DA and NE were decreased in ventral tegmental area (VTA), while GABA had little change. The current work described the inhibition activity of TxIB in NIC-induced CPP, suggesting that α6β2* nAChR-targeted compound may be a promising drug for nicotine addiction treatment. [ABSTRACT FROM AUTHOR]

The naturally occurring indole alkaloid des-formylflustrabromine (dFBr; 1) is one of the first agents shown to act as a selective positive allosteric modulator (PAM) at α4β2 nicotinic acetylcholine receptors (nAChRs). We previously deconstructed this agent to determine which of its structural features contribute to its actions and have identified an agent that might serve as the basis for a " working pharmacophore". Here, we elaborate the dFBr (1; EC 50 = 0.2 μM) structure to identify how various structural modifications impact its actions. Electrophysiological studies with Xenopus laevis oocytes identified several compounds with dFBr-like potency and one, the 5-bromo analogue of 1 (i.e., 5-bromo dFBr; 25; EC 50 = 0.4 μM), with more than twice the efficacy of 1 as a PAM at α4β2 nAChRs.

Background: Nicotinic acetylcholine receptors (nAChRs) belong to the Cys-loop ligandgated ion-channel (LGIC) superfamily, which also includes the GABA, glycine, and serotonin receptors. Many nAChR subunits have been identified and shown to be involved in signal transduction on binding to them of either the neurotransmitter acetylcholine or exogenous ligands such as nicotine. The nAChRs are pentameric assemblies of homologous subunits surrounding a central pore that gates cation flux, and they are expressed at neuromuscular junctions throughout the nervous system., Methods and Results: Because different nAChR subunits assemble into a variety of pharmacologically distinct receptor subtypes, and different nAChRs are implicated in various physiological functions and pathophysiological conditions, nAChRs represent potential molecular targets for drug addiction and medical therapeutic research. This review intends to provide insights into recent advances in nAChR signaling, considering the subtypes and subunits of nAChRs and their roles in nicotinic cholinergic systems, including structure, diversity, functional allosteric modulation, targeted knockout mutations, and rare variations of specific subunits, and the potency and functional effects of mutations by focusing on their effects on nicotine addiction (NA) and smoking cessation (SC). Furthermore, we review the possible mechanisms of action of nAChRs in NA and SC based on our current knowledge., Conclusion: Understanding these cellular and molecular mechanisms will lead to better translational and therapeutic operations and outcomes for the prevention and treatment of NA and other drug addictions, as well as chronic diseases, such as Alzheimer's and Parkinson's. Finally, we put forward some suggestions and recommendations for therapy and treatment of NA and other chronic diseases., (Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.)

Introduction: Polypharmacology, which refers to the ability of a molecule to simultaneously interact with multiple target proteins, is shifting the drug discovery process from a 'one-drug-one-target' paradigm to a conceptual framework in which the multitarget profile of small molecules is proactively pursued. Nicotinic acetylcholine receptors (nAChRs) appear as attractive targets for the design of polypharmacological agents. These proteins participate in the regulation of multiple physiological processes and impressive progress has been made regarding their structure and function. Moreover, they contain several ligand binding sites, and a number of compounds including orthosteric and allosteric ligands, have been described., Areas Covered: The authors provide an overview of some of these topics and briefly discuss the mechanisms of action of some known promiscuous drugs that act at nAChRs, with the idea that this analysis will serve to guide the development of novel polypharmacological agents with a wide spectrum of actions., Expert Opinion: The authors anticipate that many innovative drugs will be compounds intentionally designed to have polypharmacological properties. Furthermore, the authors suggest that although the search for multitarget drugs acting at the orthosteric site of nAChRs will remain an interesting option, allosteric sites of these receptors exhibit a much greater polypharmacological potential.

In this study, we report the synthesis, nAChR in vitro and in vivo pharmacological properties of 2'-fluoro-(carbamoylpyridinyl)deschloroepibatidine analogues (5, 6a,b, and 7a,b), which are analogues of our lead structure epibatidine. All of the analogues had subnanomolar binding affinity for α4β2*-nAChRs, and all were potent antagonists of α4β2-nAChRs in an in vitro functional assay. Analogues 6a,b were also highly selective for α4β2- relative to α3β4- and α7-nAChRs. Surprisingly, all of the analogues were exceptionally potent antagonists of nicotine-induced antinociception in the mouse tail-flick test, relative to standard nAChR antagonists such as DHβE. 2'-Fluoro-(4-carbamoyl-3-pyridinyl)deschloroepitabidine (6a) displayed an attractive combination of properties, including subnanomolar binding affinity (Ki = 0.07 nM), submicromolar inhibition of α4β2-nAChRs in the functional assay (IC50 = 0.46 μM) with a high degree of selectivity for α4β2- relative to the α3β4/α7-nAChRs (54-/348-fold, respectively), potent inhibition of [(3)H]dopamine release mediated by α4β2*- and α6β2*-nAChRs in a synaptosomal preparation (IC50 = 21 and 32 nM, respectively), and an AD50 of 0.007 μg/kg as an antagonist of nicotine induced antinociception in the mouse tail-flick test which is 64 250 times more potent than DHβE. These data suggest that compound 6a will be highly useful as a pharmacological tool for studying nAChRs and merits further development.

α-Conotoxin LvIA is derived from Conus lividus, native to Hainan, and is the most selective inhibitor of α3β2 nicotinic acetylcholine receptors (nAChRs) known to date. In this study, an efficient approach for the production of recombinant α-Conotoxin LvIA is described. Tandem repeats of a LvIA gene fragment were constructed and fused with a KSI gene and a His₆ tag in a Escherichia coli (E. coli) expression vector pET-31b(+). The recombinant plasmids were transformed into E. coli and were found to express well. The KSI-(LvIA)n-His₆ fusion protein was purified by metal affinity chromatography and then cleaved with CNBr to release recombinant LvIA (rLvIA). High yields of fusion protein ranging from 100 to 500 mg/L culture were obtained. The pharmacological profile of rLvIA was determined by two-electrode voltage-clamp electrophysiology in Xenopus laevis oocytes expressing rat nAChR subtypes. The rLvIA antagonized the α3β2 nAChR subtype selectively with a nano-molar IC50. The rLvIA was analgesic in a mouse hot-plate test model of pain. Overall, this study provides an effective method to synthesize α-conotoxin LvIA in an E. coli recombinant expression system, and this approach could be useful to obtain active conopeptides in large quantity and at low cost.

Prenatal nicotinic exposure (PNE) prolongs bronchopulmonary C-fiber (PCF)-mediated apneic response to intra-atrial bolus injection of capsaicin in rat pups. The relevant mechanisms remain unclear. Pulmonary substance P and adenosine and their receptors (neurokinin-A receptor, NK1R and ADA1 receptor, ADA1R) and transient receptor potential cation channel subfamily V member 1 (TRPV1) expressed on PCFs are critical for PCF sensitization and/or activation. Here, we compared substance P and adenosine in BALF and NK1R, ADA1R, and TRPV1 expression in the nodose/jugular (N/J) ganglia (vagal pulmonary C-neurons retrogradely labeled) between Ctrl and PNE pups. We found that PNE failed to change BALF substance P and adenosine content, but significantly upregulated both mRNA and protein TRPV1 and NK1R in the N/J ganglia and only NK1R mRNA in pulmonary C-neurons. To define the role of NK1R in the PNE-induced PCF sensitization, the apneic response to capsaicin (i.v.) without or with pretreatment of SR140333 (a peripheral and selective NK1R antagonist) was compared and the prolonged apnea by PNE significantly shortened by SR140333. To clarify if the PNE-evoked responses depended on action of nicotinic acetylcholine receptors (nAChRs), particularly α7nAChR, mecamylamine or methyllycaconitine (a general nAChR or a selective α7nAChR antagonist) was administrated via another mini-pump over the PNE period. Mecamylamine or methyllycaconitine eliminated the PNE-evoked mRNA and protein responses. Our data suggest that PNE is able to elevate PCF NK1R expression via activation of nAChRs, especially α7nAChR, which likely contributes to sensitize PCFs and prolong the PCF-mediated apneic response to capsaicin., (Copyright © 2015 Elsevier Inc. All rights reserved.)

For several years Amyloid-beta peptide (Aβ) has been considered the main pathogenetic factor of Alzheimer's disease (AD). According to the so called Amyloid Cascade Hypothesis the increase of Aβ triggers a series of events leading to synaptic dysfunction and memory loss as well as to the structural brain damage in the later stage of the disease. However, several evidences suggest that this hypothesis is not sufficient to explain AD pathogenesis, especially considering that most of the clinical trials aimed to decrease Aβ levels have been unsuccessful. Moreover, Aβ is physiologically produced in the healthy brain during neuronal activity and it is needed for synaptic plasticity and memory. Here we propose a model interpreting AD pathogenesis as an alteration of the negative feedback loop between Aβ and its physiological receptors, focusing on alpha7 nicotinic acetylcholine receptors (α7-nAchRs). According to this vision, when Aβ cannot exert its physiological function a negative feedback mechanism would induce a compensatory increase of its production leading to an abnormal accumulation that reduces α7-nAchR function, leading to synaptic dysfunction and memory loss. In this perspective, the indiscriminate Aβ removal might worsen neuronal homeostasis, causing a further impoverishment of learning and memory. Even if further studies are needed to better understand and validate these mechanisms, we believe that to deepen the role of Aβ in physiological conditions might represent the keystone to elucidate important aspects of AD pathogenesis., (Copyright © 2015 IBRO. Published by Elsevier Ltd. All rights reserved.)

Conformational restriction of the pyrrolidine nitrogen in nicotine by the introduction of an ethylene bridge provided a potent and selective antagonist of the α4β2-subtype of the nicotinic acetylcholine receptors. Resolution by chiral SFC, pharmacological characterization of the two enantiomers, and determination of absolute configuration via enantioselective synthesis showed that the pharmacological activity resided almost exclusively in the (R)-enantiomer.

In Drosophila associative olfactory learning, an odor, the conditioned stimulus (CS), is paired to an unconditioned stimulus (US). The CS and US information arrive at the Mushroom Bodies (MB), a Drosophila brain region that processes the information to generate new memories. It has been shown that olfactory information is conveyed through cholinergic inputs that activate nicotinic acetylcholine receptors (nAChRs) in the MB, while the US is coded by biogenic amine (BA) systems that innervate the MB. In this regard, the MB acts as a coincidence detector. A better understanding of the properties of the responses gated by nicotinic and BA receptors is required to get insights on the cellular and molecular mechanisms responsible for memory formation. In recent years, information has become available on the properties of the responses induced by nAChR activation in Kenyon Cells (KCs), the main neuronal MB population. However, very little information exists on the responses induced by aminergic systems in fly MB. Here we have evaluated some of the properties of the calcium responses gated by Dopamine (DA) and Octopamine (Oct) in identified KCs in culture. We report that exposure to BAs induces a fast but rather modest increase in intracellular calcium levels in cultured KCs. The responses to Oct and DA are fully blocked by a VGCC blocker, while they are differentially modulated by cAMP. Moreover, co-application of BAs and nicotine has different effects on intracellular calcium levels: while DA and nicotine effects are additive, Oct and nicotine induce a synergistic increase in calcium levels. These results suggest that a differential modulation of nicotine-induced calcium increase by DA and Oct could contribute to the events leading to learning and memory in flies., (Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.)

In order to select which action should be taken, an animal must weigh the costs and benefits of possible outcomes associate with each action. Such decisions, called cost-benefit decisions, likely involve several cognitive processes (including memory) and a vast neural circuitry. Rodent models have allowed research to begin to probe the neural basis of three forms of cost-benefit decision making: effort-, delay-, and risk-based decision making. In this review, we detail the current understanding of the functional circuits that subserve each form of decision making. We highlight the extensive literature by detailing the ability of dopamine to influence decisions by modulating structures within these circuits. Since acetylcholine projects to all of the same important structures, we propose several ways in which the cholinergic system may play a local modulatory role that will allow it to shape these behaviors. A greater understanding of the contribution of the cholinergic system to cost-benefit decisions will permit us to better link the decision and memory processes, and this will help us to better understand and/or treat individuals with deficits in a number of higher cognitive functions including decision making, learning, memory, and language., (© 2014 Elsevier Inc. All rights reserved.)

The sweet potato whitefly, Bemisia tabaci (Gennadius) (Hemiptera:Aleyrodidae), is an invasive and damaging pest of field crops worldwide. The neonicotinoid insecticide imidacloprid has been widely used to control this pest. We assessed the species composition (B vs. Q), imidacloprid resistance, and association between imidacloprid resistance and the expression of five P450 genes for 14-17 B. tabaci populations in 12 provinces in China. Fifteen of 17 populations contained only B. tabaci Q, and two populations contained both B and Q. Seven of 17 populations exhibited moderate to high resistance to imidacloprid, and eight populations exhibited low resistance to imidacloprid, compared with the most susceptible field WHHB population. In a study of 14 of the populations, resistance level was correlated with the expression of the P450 genes CYP6CM1 and CYP4C64 but not with the expression of CYP6CX1, CYP6CX4, or CYP6DZ7. This study indicates that B. tabaci Q has a wider distribution in China than previously reported. Resistance to imidacloprid in field populations of B. tabaci is associated with the increased expression of two cytochrome P450 genes (CYP6CM1 and CYP4C64)., (Crown Copyright © 2013. Published by Elsevier Inc. All rights reserved.)

Nicotinic acetylcholine receptors (nAChRs) are ligand-gated cation-conducting transmembrane channels from the cys-loop receptor superfamily. The neuronal subtypes of these receptors (e.g. the α7 and α4β2 subtypes) are involved in neurobehavioral processes such as anxiety, the central processing of pain, food intake, nicotine seeking behavior, and a number of cognitive functions like learning and memory. Neuronal nAChR dysfunction is involved in the pathophysiology of many neurological disorders, and behavioral studies in animals are useful models to assess the effects of compounds that act on these receptors. Allosteric modulators are ligands that bind to the receptors at sites other than the orthosteric site where acetylcholine, the endogenous agonist for the nAChRs, binds. While conventional ligands for the neuronal nAChRs have been studied for their behavioral effects in animals, allosteric modulators for these receptors have only recently gained attention, and research on their behavioral effects is growing rapidly. Here we will discuss the behavioral effects of allosteric modulators of the neuronal nAChRs., (Published by Elsevier Inc.)