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  • 1
    Electronic Resource
    Electronic Resource
    α-Bungarotoxin Binds to Low-Affinity Nicotine Binding Sites in Rat Brain (1986)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 47 (1986), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Reported differences in the pharmacology and distribution of [3H]nicotine and [125I]α-bungarotoxin binding sites in mammalian brain suggest that these ligands label separate receptor sites. Affinity purification of an α-bungar-otoxin binding protein from rat brain failed to copurify the high-affinity nicotine binding site, which remained in the nonbound soluble fraction after the affinity chromatogra-phy step. This confirms the independence of these putative receptor sites. Nevertheless, the binding of [125I]α-bungaro-toxin to P2 membranes was inhibited by (-)-nicotine (Ai= 9 × 10-6 M), and this sensitivity was preserved after affinity purification. It is proposed that α-bungarotoxin binds to a population of low-affinity nicotine binding sites. Comparison of the enantiomers of nicotine in competition studies at both radioligand binding sites revealed an 80-fold preference for the (-) form at the high-affinity [3H]nicotine binding site, whereas the site labelled by [125I]α-bungarotoxin displayed little stereoselectivity. In this respect, the brain α-bungarotoxin binding site resembles the nicotinic acetyl-choline receptor from Torpedo electric organ.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1986.tb13078.x
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  • 2
    Electronic Resource
    Electronic Resource
    Evidence for Functional Activity of Up-Regulated Nicotine Binding Sites in Rat Striatal Synaptosomes (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 55 (1990), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: A number of studies have found that the chronic administration of nicotine causes an increase in the density of nicotinic binding sites in the brain, but it is not known whether these additional binding sites are functionally active receptors. In this study, the effects of 1-week administration of the potent nicotinic agonist, (+)-anatoxin-a (96 nmol/day via osmotic minipumps), was assessed on [3H]nicotine binding and [3H]dopamine uptake and release in rat striatal synaptosomes. Chronic (+)-anatoxin-a treatment resulted in a 32% increase in the Bmax of [3H]nicotine binding in anatoxin-treated animals compared to control. There was a 43% increase in the activity of 3 μM nicotine to release [3H]dopamine from synaptosomes of anatoxin-treated animals, but the release induced by 20 mM K+ depolarization was unaffected. There was no effect of chronic (+)-anatoxin-a treatment on the uptake of [3H]dopamine. A strong positive correlation (r= 0.64) was found between the density of [3H]nicotine binding sites and the nicotine-induced stimulation of [3H]dopamine release in individual animals. These results indicate that (+)-anatoxin-a, like nicotine, produces an up-regulation of nicotine binding sites following chronic administration, and that these additional sites are functional receptors capable of mediating the release of dopamine from striatal synaptosomes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1990.tb05802.x
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  • 3
    Electronic Resource
    Electronic Resource
    Nicotinic Modulation of [3H]Dopamine Release from Striatal Synaptosomes: Pharmacological Characterisation (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 54 (1990), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Presynaptic nicotinic acetylcholine receptors on striatal nerve terminals modulate the release of dopamine. We have compared the effects of a number of nicotinic agonists and antagonists on a perfused synaptosome preparation preloaded with [3H]dopamine. (–)-Nicotine, acetylcholine, and the nicotinic agonists cytisine and 1,1-dimethyl-4-phenylpiperazinium iodide (DMPP), at micromolar concentrations, stimulated the release of [3H]dopamine from striatal nerve terminals. Carbamylcholine was a much weaker agonist. The actions of (–)-nicotine, cytisine, and DMPP were inhibited by low concentrations of the nicotinic antagonists dihydro-β-erythroidine, mecamylamine, pempidine, and neosurugatoxin; α-bungarotoxin was without effect, and extending the time of exposure to this toxin resulted in only very modest inhibition. This pharmacology points to a specific nicotinic receptor mechanism that is clearly distinct from that at the neuromuscular junction. Atropine failed to antagonise the effects of acetylcholine and carbamylcholine, suggesting that no muscarinic component is involved. The nicotinic receptor ligands (–)-[3H]nicotine and 125I-α-bungarotoxin bound to specific sites enriched in the synaptosome preparation. Drugs tested on the perfused synaptosomes were examined for their ability to interact with these two ligand binding sites in brain membranes. The differential sensitivity to the neurotoxins α-bungarotoxin and neosurugatoxin of the 125I-α-bungarotoxin and (–)-[3H]nicotine binding sites, respectively, leads to a tentative correlation of the (–)-[3H]nicotine site with the presynaptic nicotinic receptor on striatal nerve terminals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1990.tb02341.x
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  • 4
    Electronic Resource
    Electronic Resource
    Stereoselective Nicotine-Induced Release of Dopamine from Striatal Synaptosomes: Concentration Dependence and Repetitive Stimulation (1988)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 50 (1988), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Using a sensitive perfusion system we have studied the nicotine-induced release of [3H]dopamine ([3H]DA) from striatal synaptosomes. Nicotine-evoked release was concentration dependent with an EC50 of 3.8 μM. The response to 1 μM nicotine was comparable to that to 16 mM K+ 10 μM veratridine evoked a larger response. All three samuli were Ca2+ dependent but only the response to veratridine was blocked by tetrodotoxin. Repetitive stimulations by 1 μM (–)-nicotine (100 μl) at 30-min intervals resulted in similar levels of [3H]DA release; higher concentrations of (–)-nicotine resulted in an attenuation of the response particularly following the third stimulation. This may reflect desensitisation or tachyphylaxis of the presynaptic nicotinic receptor. The action of nicotine was markedly stereoselective: a 100-fold higher concentration of (+)-nicotine was necessary to evoke the same level of response as 1 μM (–)-nicotine. It is proposed that these presynaptic nicotinic receptors on striatal terminals are equivalent to high-affinity nicotine binding sites described in mammalian brain.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1988.tb10582.x
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  • 5
    Electronic Resource
    Electronic Resource
    Characterization of Nicotinic Receptor-Mediated [3H]Dopamine Release from Synaptosomes Prepared from Mouse Striatum (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 59 (1992), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: This study establishes that presynaptic nicotinic receptors modulate dopamine release in the mouse striatum. Nicotinic agonists elicit a dose-dependent increase in the release of [3H]dopamine from synaptosomes prepared from mouse striatum. At low concentrations, this release is Ca2+ dependent, whereas at higher concentrations Ca2+-independent, mecamylamine-insensitive release was also observed. The Ca2+-dependent nicotine-evoked release was not blocked by α-bungarotoxin but was effectively blocked by neuronal bungarotoxin as well as several other nicotinic receptor antagonists. The relationship between potency for stimulation of release for agonists and potency for inhibition of release for antagonists was compared to the affinity of these compounds for the [3H]nicotine binding site. The overall correlation between release and binding potency was not high, but the drugs may be classified into separate groups, each of which has a high correlation with binding. This finding suggests either that more than one nicotinic receptor regulates dopamine release or that not all agonists interact with the same receptor in an identical fashion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1992.tb08322.x
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  • 6
    Electronic Resource
    Electronic Resource
    Presynaptic Nicotinic Modulation of Dopamine Release in the Three Ascending Pathways Studied by In Vivo Microdialysis: Comparison of Naive and Chronic Nicotine-Treated Rats (1997)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 68 (1997), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The modulation of dopamine release by presynaptic nicotinic receptors in vitro is well established, but the significance of this effect in vivo is unclear. We have characterised the effect of nicotine, locally applied via a microdialysis probe, on dopamine release from the terminal regions of three ascending dopaminergic pathways in conscious, freely moving rats. Nicotine caused a dose-dependent increase in dopamine release in the striatum, the nucleus accumbens, and, to a lesser extent, the frontal cortex. Metabolite levels were unaltered by any concentration of nicotine. Prior administration of mecamylamine via the probe abolished the nicotine-evoked increase in dopamine release, confirming the mediation of nicotinic receptors. The dose dependence of mecamylamine-sensitive, nicotine-evoked dopamine release was similar in all three brain regions. However, 10−5M tetrodotoxin totally blocked nicotine-stimulated dopamine release in the striatum and the accumbens but not the cortex. Daily subcutaneous injections of nicotine (0.4 mg kg−1 for 7 days) increased the response to a subsequent local application of nicotine in the striatum, and a similar trend was found in the other brain areas. The same daily dose of nicotine given as a continuous infusion had no effect, whereas infusion of 4 mg kg−1 day−1 increased the response to a subsequent nicotine challenge. The localisation and regulation of nicotinic receptors in the terminal fields of dopaminergic pathways are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.1997.68041511.x
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  • 7
    Electronic Resource
    Electronic Resource
    An autoradiographic study of the distribution of binding sites for the novel α7-selective nicotinic radioligand [3H]-methyllycaconitine in the mouse brain (1999)
    Oxford, UK : Blackwell Science Ltd
    European journal of neuroscience 11 (1999), S. 0 
    Details
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: [3H]-Methyllycaconitine ([3H]-MLA) is a new radioligand with selectivity for α7-type neuronal nicotinic acetylcholine receptors (nAChRs). In our previous study [Davies, A.R.L., Hardick, D.J., Blagbrough, I.S., Potter, B.V.L., Wolstenholme, A.J. & Wonnacott, S. (1999) Neuropharmacology, 38, 679–690], this radioligand labelled a single class of site in rat brain membranes; its pharmacology and distribution in crudely dissected brain regions closely paralleled that of the well-established α7-ligand [125I]-α-bungarotoxin. However, a small population of [3H]-MLA binding sites was apparently insensitive to α-bungarotoxin. Here we have extended the study to mouse brain, using autoradiography to examine the distribution of [3H]-MLA and [125I]-α-bungarotoxin binding sites. [3H]-MLA labelled a single class of site in mouse brain membranes with a KD of 2.2 n m and a Bmax of 45.6 fmol/mg protein. Specific binding, defined by unlabelled MLA (Ki = 0.69 n m), was completely inhibited by (–)-nicotine (Ki = 1.62 μm), whereas α-bungarotoxin inhibited only 85% of specific binding (Ki = 3.5 n m). The distributions of [125I]-α-bungarotoxin and [3H]-MLA binding sites were compared by autoradiography, and binding was quantitated in 72 brain regions. Binding of both radioligands was highly correlated, with highest densities in the dorsal tegmental nucleus of the pons, colliculi and hippocampus. Serial sections labelled with [3H]-MLA in the absence or presence of unlabelled MLA or α-bungarotoxin provided no evidence for any α-bungarotoxin-resistant binding. The results are discussed in terms of binding sites that are inaccessible to α-bungarotoxin in membrane preparations. This study demonstrates the utility of [3H]-MLA for characterization of α7-type nicotinic receptors in mammalian brain, and suggests that it labels a population identical to that defined by [125I]-α-bungarotoxin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1460-9568.1999.00685.x
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  • 8
    Electronic Resource
    Electronic Resource
    Characterization of a nicotinic acetylcholine receptor from the insect Manduca sexta (1998)
    Oxford, UK : Blackwell Science Ltd
    European journal of neuroscience 10 (1998), S. 0 
    Details
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Manduca sexta is a nicotine-insensitive insect, the larval form of which feeds on tobacco. It has been postulated that its nicotine insensitivity may reflect the presence of a modified nicotinic acetylcholine receptor whose α subunits lack the amino acid residues necessary for binding nicotine: we have performed ligand binding assays and molecular cloning to examine this hypothesis. [125I]α-Bungarotoxin bound specifically to both larval and adult membranes, with Kd values of 7.6 and 6.5 nm and Bmax values of 119 and 815 fmol/mg protein, respectively. The pharmacological profile of [125I]α-bungarotoxin binding was similar in both tissues. In particular, nicotine (Ki values: 1.6 μm and 2 μm for larvae and adults, respectively) competed with an affinity similar to that found for nicotine-sensitive insects. No α-bungarotoxin-insensitive binding sites labelled by [3H]epibatidine could be detected. Using the α-like subunit from the locust Schistocerca gregaria to probe two cDNA libraries, and by inverse PCR on circularized genomic DNA from Manduca sexta, we have obtained overlapping cDNA clones that contain the complete coding sequence of a putative nicotinic subunit from Manduca sexta (MARA1). No other α-subunit cDNAs were isolated using this probe, although it hybridized to multiple bands on Southern blots. The sequence of MARA1 is consistent with an α-like subunit capable of binding α-bungarotoxin, and it retains all those amino acids implicated in nicotine binding to vertebrate nicotinic receptors. Taken together, these findings provide no support for the hypothesis that the nicotine insensitivity of Manduca sexta is the result of a nicotinic receptor with diminished nicotine binding.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1460-9568.1998.00095.x
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  • 9
    Electronic Resource
    Electronic Resource
    Intracellular Ca2+ signals evoked by stimulation of nicotinic acetylcholine receptors in SH-SY5Y cells: contribution of voltage-operated Ca2+ channels and Ca2+ stores (2002)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 81 (2002), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Neuronal nicotinic acetylcholine receptors (nAChR) can regulate several neuronal processes through Ca2+-dependent mechanisms. The versatility of nAChR-mediated responses presumably reflects the spatial and temporal characteristics of local changes in intracellular Ca2+ arising from a variety of sources. The aim of this study was to analyse the components of nicotine-evoked Ca2+ signals in SH-SY5Y cells, by monitoring fluorescence changes in cells loaded with fluo-3 AM. Nicotine (30 µm) generated a rapid elevation in cytoplasmic Ca2+ that was partially and additively inhibited (40%) by α7 and α3β2* nAChR subtype selective antagonists; α3β4* nAChR probably account for the remaining response (60%). A substantial blockade (80%) by CdCl2 (100 µm) indicates that voltage-operated Ca2+ channels (VOCC) mediate most of the nicotine-evoked response, although the α7 selective antagonist α-bungarotoxin (40 nm) further decreased the CdCl2- resistant component. The elevation of intracellular Ca2+ levels provoked by nicotine was sustained for at least 10 min and required the persistent activation of nAChR throughout the response. Intracellular Ca2+ stores were implicated in both the initial and sustained nicotine-evoked Ca2+ responses, by the blockade observed after ryanodine (30 µm) and the inositoltriphosphate (IP3)-receptor antagonist, xestospongin-c (10 µm). Thus, nAChR subtypes are differentially coupled to specific sources of Ca2+: activation of nAChR induces a sustained elevation of intracellular Ca2+ levels which is highly dependent on the activation of VOCC, and also involves Ca2+ release from ryanodine and IP3-dependent intracellular stores. Moreover, the α7, but not α3β2* nAChR, are responsible for a fraction of the VOCC-independent nicotine-evoked Ca2+ increase that appears to be functionally coupled to ryanodine sensitive Ca2+ stores.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.2002.00846.x
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  • 10
    Electronic Resource
    Electronic Resource
    Subcellular fractionation and distribution of cholinergic binding sites in fetal human brain (1986)
    Springer
    Neurochemical research 11 (1986), S. 1011-1023 
    Details
    ISSN: 1573-6903
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Conventional subcellular fractionation techniques have been applied to human fetal brain (13–15 weeks gestation) and the fractions have been characterized by assaying for marker enzymes, cholinergic binding sites and electron microscopy. Fractionation of the homogenate resulted in a nuclear pellet (P1), a crude mitochrondrial pellet (P2) and a supernatant (S2). Further resolution of the P2 fraction by density gradient centrifugation resulted in two bands at the gradient interfaces and a pellet. The P2 and subsequently the P2B fraction contained intact plasma membrane profiles as judged by the predominance of adenylate cyclase activity and the presence of occluded lactate dehydrogenase which constituted over 70% of the total activity in these fractions. Morphological examination of the gradient fractions revealed that the P2B fraction contains membrane bound structures which resembie synaptosomes prepared from neonatal rat brain. These structures have a granular matrix in which mitochondria and frequently, neurofilaments were observed. Very few synaptic vesicles were present and there was no evidence for post synaptic attachments. The cholinergic markers choline acetyltransferase, acetylcholinesterase and receptor sites defined by quinuclidinyl benzilate and α-bungarotoxin binding were enriched in fractions P2 and P2B which contained the bulk of nerve ending particles. This enriched preparation of fetal synaptosomes may be valuable for functional studies on pre-synaptic terminals in developing brain.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00965590
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