Presence of alpha7 nicotinic acetylcholine receptors on dorsal root ganglion neurons proved using knockout mice and selective alpha-neurotoxins in histochemistry

Marine Origin Ligands of Nicotinic Receptors: Low Molecular Compounds, Peptides and Proteins for Fundamental Research and Practical Applications

The purpose of our review is to briefly show what different compounds of marine origin, from low molecular weight ones to peptides and proteins, offer for understanding the structure and mechanism of action of nicotinic acetylcholine receptors (nAChRs) and for finding novel drugs to combat the diseases where nAChRs may be involved. The importance of the mentioned classes of ligands has changed with time; a protein from the marine snake venom was the first excellent tool to characterize the muscle-type nAChRs from the electric ray, while at present, muscle and α7 receptors are labeled with the radioactive or fluorescent derivatives prepared from α-bungarotoxin isolated from the many-banded krait. The most sophisticated instruments to distinguish muscle from neuronal nAChRs, and especially distinct subtypes within the latter, are α-conotoxins. Such information is crucial for fundamental studies on the nAChR revealing the properties of their orthosteric and allosteric binding sites and mechanisms of the channel opening and closure. Similar data are provided by low-molecular weight compounds of marine origin, but here the main purpose is drug design. In our review we tried to show what has been obtained in the last decade when the listed classes of compounds were used in the nAChR research, applying computer modeling, synthetic analogues and receptor mutants, X-ray and electron-microscopy analyses of complexes with the nAChRs, and their models which are acetylcholine-binding proteins and heterologously-expressed ligand-binding domains.

Snake Toxins Labeled by Green Fluorescent Protein or Its Synthetic Chromophore are New Probes for Nicotinic acetylcholine Receptors

Fluorescence can be exploited to monitor intermolecular interactions in real time and at a resolution up to a single molecule. It is a method of choice to study ligand-receptor interactions. However, at least one of the interacting molecules should possess good fluorescence characteristics, which can be achieved by the introduction of a fluorescent label. Gene constructs with green fluorescent protein (GFP) are widely used to follow the expression of the respective fusion proteins and monitor their function. Recently, a small synthetic analogue of GFP chromophore (p-HOBDI-BF₂) was successfully used for tagging DNA molecules, so we decided to test its applicability as a potential fluorescent label for proteins and peptides. This was done on α-cobratoxin (α-CbTx), a three-finger protein used as a molecular marker of muscle-type, neuronal α7 and α9/α10 nicotinic acetylcholine receptors (nAChRs), as well as on azemiopsin, a linear peptide neurotoxin selectively inhibiting muscle-type nAChRs. An activated N-hydroxysuccinimide ester of p-HOBDI-BF₂ was prepared and utilized for toxin labeling. For comparison we used a recombinant α-CbTx fused with a full-length GFP prepared by expression of a chimeric gene. The structure of modified toxins was confirmed by mass spectrometry and their activity was characterized by competition with iodinated α-bungarotoxin in radioligand assay with respective receptor preparations, as well as by thermophoresis. With the tested protein and peptide neurotoxins, introduction of the synthetic GFP chromophore induced considerably lower decrease in their affinity for the receptors as compared with full-length GFP attachment. The obtained fluorescent derivatives were used for nAChR visualization in tissue slices and cell cultures.

Nicotinic Acetylcholine Receptor Partial Antagonist Polyamides from Tunicates and Their Predatory Sea Slugs

In our efforts to discover new drugs to treat pain, we identified molleamines A-E (1-5) as major neuroactive components of the sea slug, Pleurobranchus forskalii, and their prey, Didemnum molle, tunicates. The chemical structures of molleamines were elucidated by spectroscopy and confirmed by the total synthesis of molleamines A (1) and C (3). Synthetic 3 completely blocked acetylcholine-induced calcium flux in peptidergic nociceptors (PNs) in the somatosensory nervous system. Compound 3 affected neither the α7 nAChR nor the muscarinic acetylcholine receptors in calcium flux assays. In addition to nociceptors, 3 partially blocked the acetylcholine-induced calcium flux in the sympathetic nervous system, including neurons from the superior cervical ganglion. Electrophysiology revealed a block of α3β4 (mouse) and α6/α3β4 (rat) nicotinic acetylcholine receptors (nAChRs), with IC₅₀ values of 1.4 and 3.1 μM, respectively. Molleamine C (3) is a partial antagonist, reaching a maximum block of 76-82% of the acetylcholine signal and showing no partial agonist response. Molleamine C (3) may thus provide a lead compound for the development of neuroactive compounds with unique biological properties.

Balanced cholinergic modulation of spinal locomotor circuits via M2 and M3 muscarinic receptors

Neuromodulation ensures that neural circuits produce output that is flexible whilst remaining within an optimal operational range. The neuromodulator acetylcholine is released during locomotion to regulate spinal motor circuits. However, the range of receptors and downstream mechanisms by which acetylcholine acts have yet to be fully elucidated. We therefore investigated metabotropic acetylcholine receptor-mediated modulation by using isolated spinal cord preparations from neonatal mice in which locomotor-related output can be induced pharmacologically. We report that M2 receptor blockade decreases the frequency and amplitude of locomotor-related activity, whilst reducing its variability. In contrast, M3 receptor blockade destabilizes locomotor-related bursting. Motoneuron recordings from spinal cord slices revealed that activation of M2 receptors induces an outward current, decreases rheobase, reduces the medium afterhyperpolarization, shortens spike duration and decreases synaptic inputs. In contrast, M3 receptor activation elicits an inward current, increases rheobase, extends action potential duration and increases synaptic inputs. Analysis of miniature postsynaptic currents support that M2 and M3 receptors modulate synaptic transmission via different mechanisms. In summary, we demonstrate that M2 and M3 receptors have opposing modulatory actions on locomotor circuit output, likely reflecting contrasting cellular mechanisms of action. Thus, intraspinal cholinergic systems mediate balanced, multimodal control of spinal motor output.

Detection of human neuronal α7 nicotinic acetylcholine receptors by conjugates of snake α-neurotoxin with quantum dots

Fluorescent derivatives are widely used to study the structure and functions of proteins. Quantum dots (QDs), fluorescent semiconductor nanocrystals, have a high quantum yield and are much more resistant to bleaching compared to organic dyes. Conjugates of α-neurotoxins with QDs were used for visualization of human α7 acetylcholine receptors heterologously expressed in GH4C1 pituitary adenoma cells. Specific staining of cells by the conjugated toxins was observed.

Calcium imaging with genetically encoded sensor Case12: Facile analysis of α7/α9 nAChR mutants

Elucidation of the structural basis of pharmacological differences for highly homologous α7 and α9 nicotinic acetylcholine receptors (nAChRs) may shed light on their involvement in different physiological functions and diseases. Combination of site-directed mutagenesis and electrophysiology is a powerful tool to pinpoint the key amino-acid residues in the receptor ligand-binding site, but for α7 and α9 nAChRs it is complicated by their poor expression and fast desensitization. Here, we probed the ligand-binding properties of α7/α9 nAChR mutants by a proposed simple and fast calcium imaging method. The method is based on transient co-expression of α7/α9 nAChR mutants in neuroblastoma cells together with Ric-3 or NACHO chaperones and Case12 fluorescent calcium ion sensor followed by analysis of their pharmacology using a fluorescence microscope or a fluorometric imaging plate reader (FLIPR) with a GFP filter set. The results obtained were confirmed by electrophysiology and by calcium imaging with the conventional calcium indicator Fluo-4. The affinities for acetylcholine and epibatidine were determined for human and rat α7 nAChRs, and for their mutants with homologous residues of α9 nAChR incorporated at positions 117-119, 184, 185, 187, and 189, which are anticipated to be involved in ligand binding. The strongest decrease in the affinity was observed for mutations at positions 187 and 119. The L119D mutation of α7 nAChR, showing a larger effect for epibatidine than for acetylcholine, may implicate this position in pharmacological differences between α7 and α9 nAChRs.

Activation of α7nAChR Promotes Diabetic Wound Healing by Suppressing AGE-Induced TNF-α Production

Diabetes frequently presents accumulation of advanced glycation end products (AGEs), which might induce excessive TNF-α production from macrophages to cause impaired wound healing. Recent studies have shown that activation of α7 nicotinic acetylcholine receptor (α7nAChR) on macrophages efficiently suppressed TNF-α synthesis. The aim of this study was to investigate the accumulation of AGEs in the wounds and determine whether PNU282987, an α7nAChR agonist, can improve wound repair by inhibiting AGE-mediated TNF-α production in a streptozotocin (STZ)-induced diabetic mouse model. Animals were assigned into four groups: wounded control group, wounded diabetic group, wounded diabetic group treated intraperitoneally with PNU282987, or wounded diabetic group treated intraperitoneally with vehicle. Compared with the non-diabetic control mice, the diabetic mice exhibited delayed wound healing that was characterized by elevated accumulation of AGEs, increased TNF-α level and macrophage infiltration, and decreased fibroblast number and collagen deposition at the late stage of repair. Besides, macrophages of diabetic wounds showed expression of α7nAChR. During late repair, PNU282987 treatment of diabetic mice significantly reduced the level of TNF-α, accelerated wound healing, and elevated fibroblast number and collagen deposition. To investigate the cellular mechanism of these observations, RAW 264.7 cells, a macrophage cell line, were incubated with AGEs in the presence or absence of PNU282987. TNF-α production from AGE-stimulated macrophages was significantly decreased by PNU282987 in a dose-dependent manner. Furthermore, PNU282987 significantly inhibited AGE-induced nuclear factor-κB (NF-κB) activation and receptor for AGE (RAGE) expression. These results strongly suggest that activating α7nAChR can promote diabetic wound healing by suppressing AGE-induced TNF-α production, which may be closely associated with the blockage of NF-κB activation in macrophages.

Neurotoxins from snake venoms and α-conotoxin ImI inhibit functionally active ionotropic γ-aminobutyric acid (GABA) receptors

Ionotropic receptors of γ-aminobutyric acid (GABAAR) regulate neuronal inhibition and are targeted by benzodiazepines and general anesthetics. We show that a fluorescent derivative of α-cobratoxin (α-Ctx), belonging to the family of three-finger toxins from snake venoms, specifically stained the α1β3γ2 receptor; and at 10 μm α-Ctx completely blocked GABA-induced currents in this receptor expressed in Xenopus oocytes (IC50 = 236 nm) and less potently inhibited α1β2γ2 ≈ α2β2γ2 > α5β2γ2 > α2β3γ2 and α1β3δ GABAARs. The α1β3γ2 receptor was also inhibited by some other three-finger toxins, long α-neurotoxin Ls III and nonconventional toxin WTX. α-Conotoxin ImI displayed inhibitory activity as well. Electrophysiology experiments showed mixed competitive and noncompetitive α-Ctx action. Fluorescent α-Ctx, however, could be displaced by muscimol indicating that most of the α-Ctx-binding sites overlap with the orthosteric sites at the β/α subunit interface. Modeling and molecular dynamic studies indicated that α-Ctx or α-bungarotoxin seem to interact with GABAAR in a way similar to their interaction with the acetylcholine-binding protein or the ligand-binding domain of nicotinic receptors. This was supported by mutagenesis studies and experiments with α-conotoxin ImI and a chimeric Naja oxiana α-neurotoxin indicating that the major role in α-Ctx binding to GABAAR is played by the tip of its central loop II accommodating under loop C of the receptors.

Natural compounds interacting with nicotinic acetylcholine receptors: from low-molecular weight ones to peptides and proteins

Nicotinic acetylcholine receptors (nAChRs) fulfill a variety of functions making identification and analysis of nAChR subtypes a challenging task. Traditional instruments for nAChR research are d-tubocurarine, snake venom protein α-bungarotoxin (α-Bgt), and α-conotoxins, neurotoxic peptides from Conus snails. Various new compounds of different structural classes also interacting with nAChRs have been recently identified. Among the low-molecular weight compounds are alkaloids pibocin, varacin and makaluvamines C and G. 6-Bromohypaphorine from the mollusk Hermissenda crassicornis does not bind to Torpedo nAChR but behaves as an agonist on human α7 nAChR. To get more selective α-conotoxins, computer modeling of their complexes with acetylcholine-binding proteins and distinct nAChRs was used. Several novel three-finger neurotoxins targeting nAChRs were described and α-Bgt inhibition of GABA-A receptors was discovered. Information on the mechanisms of nAChR interactions with the three-finger proteins of the Ly6 family was found. Snake venom phospholipases A₂ were recently found to inhibit different nAChR subtypes. Blocking of nAChRs in Lymnaea stagnalis neurons was shown for venom C-type lectin-like proteins, appearing to be the largest molecules capable to interact with the receptor. A huge nAChR molecule sensible to conformational rearrangements accommodates diverse binding sites recognizable by structurally very different compounds.

Small changes in bone structure of female α7 nicotinic acetylcholine receptor knockout mice

Background

Recently, analysis of bone from knockout mice identified muscarinic acetylcholine receptor subtype M3 (mAChR M3) and nicotinic acetylcholine receptor (nAChR) subunit α2 as positive regulator of bone mass accrual whereas of male mice deficient for α7-nAChR (α7KO) did not reveal impact in regulation of bone remodeling. Since female sex hormones are involved in fair coordination of osteoblast bone formation and osteoclast bone degradation we assigned the current study to analyze bone strength, composition and microarchitecture of female α7KO compared to their corresponding wild-type mice (α7WT).

Methods

Vertebrae and long bones of female 16-week-old α7KO (n = 10) and α7WT (n = 8) were extracted and analyzed by means of histological, radiological, biomechanical, cell- and molecular methods as well as time of flight secondary ion mass spectrometry (ToF-SIMS) and transmission electron microscopy (TEM).

Results

Bone of female α7KO revealed a significant increase in bending stiffness (p < 0.05) and cortical thickness (p < 0.05) compared to α7WT, whereas gene expression of osteoclast marker cathepsin K was declined. ToF-SIMS analysis detected a decrease in trabecular calcium content and an increase in C₄H₆N⁺ (p < 0.05) and C₄H₈N⁺ (p < 0.001) collagen fragments whereas a loss of osteoid was found by means of TEM.

Conclusions

Our results on female α7KO bone identified differences in bone strength and composition. In addition, we could demonstrate that α7-nAChRs are involved in regulation of bone remodelling. In contrast to mAChR M3 and nAChR subunit α2 the α7-nAChR favours reduction of bone strength thereby showing similar effects as α7β2-nAChR in male mice. nAChR are able to form heteropentameric receptors containing α- and β-subunits as well as the subunits α7 can be arranged as homopentameric cation channel. The different effects of homopentameric and heteropentameric α7-nAChR on bone need to be analysed in future studies as well as gender effects of cholinergic receptors on bone homeostasis.

Functional alpha7 nicotinic receptors are expressed on immature granule cells of the postnatal dentate gyrus

Neurogenesis occurs throughout life in the subgranular zone of the dentate gyrus, and postnatal-born granule cells migrate into the granule cell layer and extend axons to their target areas. The α7*nicotinic receptor has been implicated in neuronal maturation during development of the brain and is abundant in interneurons of the hippocampal formation of the adult brain. Signalling through these same receptors is believed also to promote maturation and integration of adult-born granule cells in the hippocampal formation. We therefore aimed to determine whether functional α7*nicotinic receptors are expressed in developing granule cells of the postnatal dentate gyrus. For these experiments we used 2-3 week-old Wistar rats, and 2-9 week old transgenic mice in which GABAergic interneurons were marked by expression of green fluorescent protein. Immunohistochemistry indicated the presence of α7*nicotinic receptor subunits around granule cells close around the subgranular zone which correlated with the distribution of developmental markers for immature granule cells. Whole-cell patch clamp recording showed that a proportion of granule cells responded to puffed ACh in the presence of atropine, and that these cells possessed electrophysiological properties found in immature granule cells. The nicotinic responses were potentiated by an allosteric α7*nicotinic receptor modulator, which were blocked by a specific α7*nicotinic receptor antagonist and were not affected by ionotropic glutamate or GABA receptor antagonists. These results suggest the presence of functional somato-dendritic α7*nicotinic receptors on immature granule cells of the postnatal dentate gyrus, consistent with studies implicating α7*nicotinic receptors in dendritic maturation of dentate gyrus neurons in adult brain.

Expression of acetylcholine receptors by experimental rat renal allografts

Chronic allograft injury (CAI) is a major cause for renal allograft dysfunction and characterized by vasculopathies, tubular atrophy, and fibrosis. We demonstrated that numerous leukocytes interact with vascular endothelial cells of allografts and produce acetylcholine, which contributes to vascular remodeling. The cholinergic system might be a promising target for the development of novel therapies. However, neither the cellular mechanisms nor the acetylcholine receptors involved in CAI are known. Kidney transplantation was performed in the Lewis to Lewis and in the Fischer-334 to Lewis rat strain combination, which is an established experimental model for CAI. Expression of nicotinic and muscarinic acetylcholine receptors mRNA was quantified in renal tissue by real-time RT-PCR on days 9 and 42 after surgery. We detected CHRNA2-7, CHRNA10, CHRNB2, CHRNB4, and CHRM1-3 mRNA in normal kidneys and in renal transplants. In contrast, CHRNA9, CHRM4, and CHRM5 mRNA remained below the threshold of detection. In renal allografts, CHRNA3 and CHRNB4 mRNA expression were dramatically reduced compared to isografts. In conclusion, we demonstrated that most acetylcholine receptor subtypes are expressed by normal and transplanted kidneys. Allograft rejection downmodulates CHRNA3 and CHRNB4 mRNA. The role of different acetylcholine receptor subtypes in the development of CAI remains to be established.

Functional expression and axonal transport of α7 nAChRs by peptidergic nociceptors of rat dorsal root ganglion

In recent pain studies on animal models, α7 nicotinic acetylcholine receptor (nAChR) agonists demonstrated analgesic, anti-hyperalgesic and anti-inflammatory effects, apparently acting through some peripheral receptors. Assuming possible involvement of α7 nAChRs on nociceptive sensory neurons, we investigated the morphological and neurochemical features of the α7 nAChR-expressing subpopulation of dorsal root ganglion (DRG) neurons and their ability to transport α7 nAChR axonally. In addition, α7 receptor activity and its putative role in pain signal neurotransmitter release were studied. Medium-sized α7 nAChR-expressing neurons prevailed, although the range covered all cell sizes. These cells accounted for one-fifth of total medium and large DRG neurons and <5% of small ones. 83.2% of α7 nAChR-expressing DRG neurons were peptidergic nociceptors (CGRP-immunopositive), one half of which had non-myelinated C-fibers and the other half had myelinated Aδ- and likely Aα/β-fibers, whereas 15.2% were non-peptidergic C-fiber nociceptors binding isolectin B4. All non-peptidergic and a third of peptidergic α7 nAChR-bearing nociceptors expressed TRPV1, a capsaicin-sensitive noxious stimulus transducer. Nerve crush experiments demonstrated that CGRPergic DRG nociceptors axonally transported α7 nAChRs both to the spinal cord and periphery. α7 nAChRs in DRG neurons were functional as their specific agonist PNU282987 evoked calcium rise enhanced by α7-selective positive allosteric modulator PNU120596. However, α7 nAChRs do not modulate neurotransmitter CGRP and glutamate release from DRG neurons since nicotinic ligands affected neither their basal nor provoked levels, showing the necessity of further studies to elucidate the true role of α7 nAChRs in those neurons.

Systemic administration of an alpha-7 nicotinic acetylcholine agonist reverses neuropathic pain in male Sprague Dawley rats

Alpha-7 nicotinic acetylcholine receptor (α7 nAChR) agonists attenuate pain and inflammation in preclinical models. This study tested whether systemic delivery of an α7 nAChR agonist attenuates neuropathic pain and associated immune-mediated pro-inflammation. Hind paw response thresholds to mechanical stimuli in male Sprague Dawley rats were assessed before and after sciatic chronic constriction injury (CCI) or sham surgery. Osmotic mini-pumps containing TC-7020, an α7 nAChR selective agonist, were implanted 10 to 14 days after surgery. TC-7020 (1, 3, and 10 mg/kg/d; s.c.) significantly attenuated CCI-induced allodynia, which lasted through 2 weeks of test compound administration. Spinal cords were collected after 2 weeks and processed for microglial and astrocyte activation markers within the ipsilateral L4-L6 dorsal horn. In addition, ipsilateral L4-5 dorsal root ganglia (DRGs) were processed for neuronal injury and satellite cell activation markers. CCI-induced central glial cell activation markers were not suppressed by TC-7020, even though TC-7020 is mildly blood-brain barrier permeable. However, TC-7020 downregulated the integrated density of activation transcription factor 3 (ATF3) but not the number of ATF positive cells. TC-7020 also downregulated phosphorylated extracellular signal kinase (p-ERK) and satellite cell activation in the CCI-affected DRGs. Therefore, systemic α7 nAChR agonist may be effective in treating neuropathic pain via reducing neuronal injury and immune cells activation occurring in the periphery.

PERSPECTIVE

These studies demonstrated that TC-7020, an alpha7 nicotinic acetylcholine receptor agonist with partial blood-brain barrier permeability, reversed neuropathic pain in rats, likely via attenuation of inflammation in the DRG and/or the site of sciatic injury.

Azemiopsin from Azemiops feae viper venom, a novel polypeptide ligand of nicotinic acetylcholine receptor

Azemiopsin, a novel polypeptide, was isolated from the Azemiops feae viper venom by combination of gel filtration and reverse-phase HPLC. Its amino acid sequence (DNWWPKPPHQGPRPPRPRPKP) was determined by means of Edman degradation and mass spectrometry. It consists of 21 residues and, unlike similar venom isolates, does not contain cysteine residues. According to circular dichroism measurements, this peptide adopts a β-structure. Peptide synthesis was used to verify the determined sequence and to prepare peptide in sufficient amounts to study its biological activity. Azemiopsin efficiently competed with α-bungarotoxin for binding to Torpedo nicotinic acetylcholine receptor (nAChR) (IC₅₀ 0.18 ± 0.03 μm) and with lower efficiency to human α7 nAChR (IC₅₀ 22 ± 2 μm). It dose-dependently blocked acetylcholine-induced currents in Xenopus oocytes heterologously expressing human muscle-type nAChR and was more potent against the adult form (α1β1ϵδ) than the fetal form (α1β1γδ), EC₅₀ being 0.44 ± 0.1 μm and 1.56 ± 0.37 μm, respectively. The peptide had no effect on GABA_A (α1β3γ2 or α2β3γ2) receptors at a concentration up to 100 μm or on 5-HT₃ receptors at a concentration up to 10 μm. Ala scanning showed that amino acid residues at positions 3–6, 8–11, and 13–14 are essential for binding to Torpedo nAChR. In biological activity azemiopsin resembles waglerin, a disulfide-containing peptide from the Tropidechis wagleri venom, shares with it a homologous C-terminal hexapeptide, but is the first natural toxin that blocks nAChRs and does not possess disulfide bridges.

Mitochondria express α7 nicotinic acetylcholine receptors to regulate Ca2+ accumulation and cytochrome c release: study on isolated mitochondria

Nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels that mediate synaptic transmission in the muscle and autonomic ganglia and regulate transmitter release in the brain. The nAChRs composed of α7 subunits are also expressed in non-excitable cells to regulate cell survival and proliferation. Up to now, functional α7 nAChRs were found exclusively on the cell plasma membrane. Here we show that they are expressed in mitochondria and regulate early pro-apoptotic events like cytochrome c release. The binding of α7-specific antibody with mouse liver mitochondria was revealed by electron microscopy. Outer membranes of mitochondria from the wild-type and β2−/− but not α7−/− mice bound α7 nAChR-specific antibody and toxins: FITC-labeled α-cobratoxin or Alexa 555-labeled α-bungarotoxin. α7 nAChR agonists (1 µM acetylcholine, 10 µM choline or 30 nM PNU-282987) impaired intramitochondrial Ca²⁺ accumulation and significantly decreased cytochrome c release stimulated with either 90 µM CaCl₂ or 0.5 mM H₂O₂. α7-specific antagonist methyllicaconitine (50 nM) did not affect Ca²⁺ accumulation in mitochondria but attenuated the effects of agonists on cytochrome c release. Inhibitor of voltage-dependent anion channel (VDAC) 4,4′-diisothio-cyano-2,2′-stilbene disulfonic acid (0.5 µM) decreased cytochrome c release stimulated with apoptogens similarly to α7 nAChR agonists, and VDAC was co-captured with the α7 nAChR from mitochondria outer membrane preparation in both direct and reverse sandwich ELISA. It is concluded that α7 nAChRs are expressed in mitochondria outer membrane to regulate the VDAC-mediated Ca²⁺ transport and mitochondrial permeability transition.

{alpha}7-nAChR-mediated suppression of hyperexcitability of colonic dorsal root ganglia neurons in experimental colitis

Controlled clinical trials of nicotine transdermal patch for treatment of ulcerative colitis have been shown to improve histological and global clinical scores of colitis. Here we report that nicotine (1 microM) suppresses in vitro hyperexcitability of colonic dorsal root ganglia (DRG) (L(1)-L(2)) neurons in the dextran sodium sulfate (DSS)-induced mouse model of acute colonic inflammation. Nicotine gradually reduced regenerative multiple-spike action potentials in colitis mice to a single action potential. Nicotine's effect on hyperexcitability of inflamed neurons was blocked in the presence of an alpha(7)-nicotinic acetylcholine receptor (nAChR) antagonist, methyllicaconitine, while choline, the alpha(7)-nAChR agonist, induced a similar effect to that of nicotine. Consistent with these findings, nicotine failed to suppress hyperexcitability in colonic DRG neurons from DSS-treated alpha(7) knockout mice. Furthermore, colonic DRG neurons from DSS-treated alpha(7) knockout mice were characterized by lower rheobase (10 +/- 5 vs. 77 +/- 13 pA, respectively) and current threshold (28 +/- 4 vs. 103 +/- 8 pA, respectively) levels than DSS-treated C57BL/J6 mice. An interesting observation of this study is that 8 of 12 colonic DRG (L(1)-L(2)) neurons from control alpha(7) knockout mice exhibited multiple-spike action potential firing while no wild-type neurons did. Overall, our findings suggest that nicotine at low 1 microM concentration suppresses in vitro hyperexcitability of inflamed colonic DRG neurons in a mouse model of acute colonic inflammation via activation of alpha(7)-nAChRs.